Monday, November 1, 2021

What is a pair bond? Review of pair bonding in invertebrates, fishes, birds, ...

What is a pair bond? Karen L. Bales et al. Hormones and Behavior, Volume 136, November 2021, 105062. https://doi.org/10.1016/j.yhbeh.2021.105062

Highlights

• Pair bonding has been defined differently across animal taxa.

• We review these definitions as well as the occurrence of probable pair bonding behavior.

• We revise the definition of pair bonding, with an emphasis on affective components.

Abstract: Pair bonding is a psychological construct that we attempt to operationalize via behavioral and physiological measurements. Yet, pair bonding has been both defined differently in various taxonomic groups as well as used loosely to describe not just a psychological and affective phenomenon, but also a social structure or mating system (either social monogamy or just pair living). In this review, we ask the questions: What has been the historical definition of a pair bond? Has this definition differed across taxonomic groups? What behavioral evidence do we see of pair bonding in these groups? Does this observed evidence alter the definition of pair bonding? Does the observed neurobiology underlying these behaviors affect this definition as well? And finally, what are the upcoming directions in which the study of pair bonding needs to head?

2. What is a pair bond?

When examining existing definitions of pair bonds across taxa, it is vital to identify the key recurring elements. Most definitions agree that a pair bond is a selective association that exists between two adult individuals of the same species (Black, 1996aKleiman, 1977Nowicki et al., 2020Whiting and While, 2017). Definitions in most taxa specify that a pair bond is formed between a single adult male and a single adult female, although it is generally unclear whether the exclusion of same-sex pairings is intentional. For example, many avian researchers apply the term to same-sex dyads that meet the other components of the definition (Tomaszycki and Zatirka, 2014). Another important element in most existing definitions of pair bonds is time, and many definitions require or assume that pairs sustain their relationship beyond the duration of a single reproductive cycle or mating season (Tecot et al., 2016Whiting and While, 2017).

Some definitions specify that a pair bond includes mating behavior, sometimes even as far as specifying sexual exclusivity. The majority of definitions conclude that certain behaviors (or at least their frequency) are exclusive to the pair (Kleiman, 1977Tecot et al., 2016). These behaviors appear to be broken into four main categories: shared territory, proximity, certain types of affiliation like allogrooming or allopreening, and joint displays. Even the most simple and flexible definitions of pair-bonded species build on the idea of a territory shared by members of a pair. A high degree of proximity maintenance accompanies a pair bond in several definitions and some even argue that the amount of time a pair spends in proximity is indicative of the pair bond's strength (Kleiman, 1981). Some definitions of pair bonds also include joint displays such as duetting, aggression towards strangers, or defending territory. Coordinated care of offspring is also included within some definitions (Caldwell, 1997). These behavioral attributes are sometimes but not always included in definitions of pair bonds. However, they provide context to the relationship between pair partners and specify how bonded partners interact.

Finally, some researchers use definitions for a pair bond that are based on human relationships or attachment theory (Hazan and Shaver, 1987). In this case, the definition is expanded to include an affective or emotional component, defined as preference for the familiar partner, distress upon separation, and the ability of the partner to buffer the individual against other stressors (Hazan and Shaver, 1987Mason and Mendoza, 1998). In the following section, we review the occurrence and definitions of pair bonding across animals, returning afterward to address the key components of these definitions.

3. Pair bonding across the animal kingdom

3.1. Invertebrates

Invertebrates account for 94% of identified animal species (Peterson, 2001). Due to the diversity of invertebrate species and said species' wide ranging sensory systems, defining a pair bond (or even pair living) in invertebrates can be challenging, and thus far few studies have tried. However, some observational work suggests that a few groups of invertebrate animals display behaviors potentially consistent with pair bonding. In many invertebrates, the relationship between mates involves some degree of proximal living or joint territoriality either to defend mates or to protect resources. In addition to proximal living, in some invertebrate species individuals preferentially live with another individual even outside of the reproductive period. Some invertebrates also display territorial behavior (Hultgren et al., 2017Osaki and Kasuya, 2021), cooperative duty sharing (Hultgren et al., 2017), or biparental care (Osaki and Kasuya, 2021). These observations may potentially indicate that pair bonding exists in some invertebrate species.

A few key examples highlight the diversity of pair behavior shown in invertebrate taxa. Crustaceans show wide variation in social structure, but a large portion of species are pair living. Although pair-living snapping shrimp (Synalpheus spp.) do not exhibit parenting, they do perform sponge-cleaning duties cooperatively and participate in joint territorial sponge defense (Hultgren et al., 2017). Notably, Synalpheus species that are polygamous do participate in parental care. Another unique example of pair living arises in limpets (Schaefer et al., 2020). Limpets (Siphonaria gigas) are flexible in their living condition: even in the absence of territoriality, parental care, or mate-guarding, 75% of S. gigas live in pairs as opposed to living alone. Though S. gigas participate in extra-pair copulations, paired individuals primarily mate with each other and produce twice as many egg masses as single individuals, suggesting fitness benefits to pair living that are likely tied to limpets' reciprocally hermaphroditic mating (Schaefer et al., 2020).

At least one invertebrate species does show evidence of enduring preferential living encompassing more than a single reproduction. Wood-feeding cockroaches (Salganea taiwanensis) mate and live as pairs; quite notably, after choosing a mate, paired cockroaches chew off each other's wings (Osaki and Kasuya, 2021). After cannibalizing their pair mate's non-fleshy wings, paired individuals mate and produce multiple cycles of offspring that are cared for by both parents. Paired wood-feeding cockroaches mate with each other exclusively and for life (Osaki and Kasuya, 2021). The pairs appear to be more or less continuously reproducing (Maekawa et al., 2008), and thus it is not possible to study a post-pairing non-reproductive period in this species.

The majority of termite species display pair behavior in which one male (the king) and one female (the queen) are the sole breeders of their colony. Pair formation occurs when sexually mature individuals disperse from their natal colonies and participate in mass swarming events, during which male and female individuals form pairs, then set off in search of a suitable nest site (Hartke and Baer, 2011). Once the colony is formed, the male and female can remain together for years; termite kings are able to provide viable sperm to the queen for decades (Hartke and Baer, 2011). Often, colonies do not survive the death of their king and queen. Termites show biparental care in which both the king and queen care for young. In some species, queens provide more care for offspring than kings (Brossette et al., 2019), but in other species the division of labor is fairly equal and not sex-specific (Rosengaus and Traniello, 1991). Termites are aggressive to non-colony members (Nel, 1968), particularly reproductive individuals who could usurp the king or queen (Hartke and Baer, 2011). Termites and wood-feeding cockroaches therefore both represent species which are potentially pair bonding, but for which little data exists on affective components of the bond.

Very few studies have examined the underlying neurobiology and endocrinology of explicitly pair living and pair-bonded invertebrates. However, a few promising directions suggest conserved neuroendocrine systems may promote invertebrate pair bonds. The serotonergic (5-HT) system plays a critical role in sociality and evidence exists for the importance of 5-HT in many non-pair-bonding invertebrate species. Elevated levels of endogenous 5-HT predict the formation of larger leech groups (Bisson et al., 2012). Beyond 5-HT, oxytocin (OT)––along with its homologs––facilitates sociality across the animal kingdom (Lockard et al., 2017). For instance, nematodes (Garrison et al., 2012), leeches (Wagenaar et al., 2010), and snails (van Kesteren et al., 1995) all show OT-mediated mating behaviors; OT-homologs facilitate cuttlefish reproduction (Bardou et al., 2010) and oviposition in leeches (Fujino et al., 1999) and earthworms (Oumi et al., 1996). Thus, OT homologs could conceivably play a role in the pair behavior seen in the invertebrate species identified above. Future studies should aim to explore 5-HT and OT homologs as mediators of pair bonding and pair living in invertebrates.

3.2. Reptiles and amphibians

Reptiles and amphibians are socially diverse; however, there is limited work on pair bonds, which are uncommon in reptiles outside of the Egernia group of lizards (Whiting and While, 2017). As such, there is no clear definition of a pair bond in these classes of animals. Smith and Schuett (2015) propose that for a “pair association” to be identified, the association must persist for a quarter of the breeding season (Smith and Schuett, 2015). Time spent together outside of reproduction (i.e., spending “quality time” together) is a common feature in the definition of reptilian and amphibian “associations” (Botterill-James et al., 2017Gillette et al., 2000Martín et al., 2020). Some definitions require the presence of biparental care (Caldwell, 1997). In general, the study of these “associations” focuses on mating strategy rather than behavior, affect, or physiology of pairs. Nonetheless, there is some evidence that certain reptile and amphibian species may be considered pair bonding.

An example of a reptile that likely forms pair bonds is the Australian sleepy lizard (Tiliqua rugosa). Bonded pairs spend considerable time together before (and for some time after) mating, and pairs will search for one another if separated (Bull and Lindle, 2002How and Bull, 2002Leu et al., 2010). This cycle of reunion and pair living repeats each breeding cycle, and re-pairing with a different partner is rare (Bull, 1988), therefore the association is long lasting. The sleepy lizard's behavior matches that of other pair-bonding animals (e.g., prairie voles, zebra finches).

In amphibians there is very limited available evidence of a bonded relationship forming between partners, and when pair bonding is discussed it tends to be in the context of its relationship to biparental care (Brown et al., 2010Caldwell and de Oliveira, 1999Roland and O’Connell, 2015). The red-backed salamander (Plethodon cinereus) may be one of the few known cases. During the mating season, red-backed salamanders engage in mate guarding and prefer their partner over unfamiliar conspecifics (Gillette et al., 2000). These associations between pairs dampen outside of the mating season but do not entirely disappear, and associations lasting as long as three years have been observed (Gillette et al., 2000).

Poison frogs represent a group which includes both non-pair-bonding and potentially pair-bonding species (Roland and O’Connell, 2015). Behavioral and ecological differences were found between Dendrobates (later Ranitomeyavariabilis and D. imitatorImitator was identified as engaging in biparental care and genetic monogamy (Brown et al., 2010); however, reproductive pairs only remained together for a single field season, with little or no interactions outside of mating and offspring care (Brown et al., 2008). These and other poison dart frog species (Caldwell, 1997) therefore may or may not meet a broader definition of pair bonding.

The neurobiology underlying the formation and maintenance of pair bonds has not been studied as extensively in reptiles and amphibians as it has in other classes of animals. However, one line of research has focused on chemosensory communication (e.g., sense of smell), a process that is not only vital for survival in reptiles and amphibians, but also for relationships. In social species of reptiles and amphibians, the chemosensory pathways that regulate self-recognition and recognition of friendly conspecifics (for example, a bonded partner) have been identified (Jaeger and Forester, 1993Martín et al., 2020). Interestingly, male White's skinks (Liopholis whitii) will punish their female partners for extra-pair copulations, evidence of which can be detected through olfactory cues (Botterill-James et al., 2017). Despite extra-pair copulations, males will remain with their unfaithful partner and tolerate unrelated offspring on their territory. It is unknown if neural and hormonal systems underlying pair-bond formation and maintenance are similar between reptiles, amphibians, and other animals, but this is an area ripe for further research.

3.3. Fish

Pair bonding within the fish literature is defined as a selective, prosocial, and enduring affiliation between two conspecifics (Leese, 2012Nowicki et al., 2020), with some definitions designating that affiliation must be maintained beyond reproduction (Fischer et al., 2019Nowicki et al., 2018b). Other definitions indicate that pair bonding is simply the preferential interaction of individuals to the exclusion of other potential partners (Cardoso et al., 2015O'Connor et al., 2016). Definitions vary concerning the length of the pair bond. Some pairs are considered pair-bonded if they remain together for a single reproductive period and do not include explicit considerations of subsequent breeding seasons, whereas in others, a pair bond persists across several breeding seasons, with or without parental care (Whiteman and Côté, 2004).

Shared parental care is also often included in definitions of pair bonding in fish (de Waal and Gavrilets, 2013), yet others assert that this phenomenon is not a requirement (Fischer et al., 2019). In fact, pair bonding has evolved in several coral reef fishes without biparental care (Nowicki, 2017Reavis and Barlow, 1998), although some species do display shared parental care such as bass, some types of cichlids, and Murray cod (Avise et al., 2002Couch et al., 2020DeWoody et al., 2000Garcia, 2019Little, 2014Reddon et al., 2015).

Pair bonds can be found in a variety of fish, including the convict cichlid (Amatitlania nigrofasciata), daffodil cichlid (Neolamprologus pulcher), Texas cichlid (Herichthys cyanoguttatus), Indo-Pacific cleaner wrasse (Labroides dimidiatus), Caribbean cleaning goby (Gobiosoma evelynae), pipefish (Syngnathinae), butterflyfishes (Chaetodontidae), and Murray cod (Maccullochella peelii) (Cardoso et al., 2015Couch et al., 2020Harding et al., 2003Itzkowitz and Draud, 1992Leese, 2012Nowicki et al., 2018b). Moreover, within all vertebrate lineages, teleost (i.e., ray-finned) fishes display the second highest frequency of pair bonding, second only to birds (Nowicki, 2017).

Pair-bonded fish exhibit several affiliative behaviors. In cichlids, pair-bonded individuals display parallel swimming, tail beating, circling, greeting, and affiliative bites (Garcia, 2019Reddon et al., 2015). Notably, in convict cichlids, color changes indicate pairing status. Females' abdomens change color from black or very dark gray to yellow/orange with some blue when they are courting or engaged in affiliative behaviors with males (Garcia, 2019). Studies with butterflyfishes also demonstrate the importance of visual signals for recognition, identification and location of mates, territorial defense, and as indicators of behavioral state (Hamilton and Peterman, 1971Nowicki et al., 2018bTricas, 1989Zumpe, 1965). Other behavioral manifestations of partner affiliation occur in the Australian seahorse (Hippocampus whitei) including coordinated motor displays and daily greetings—with these behaviors perhaps supporting pair-bond maintenance outside of the breeding season (Vincent and Sadler, 1995).

Despite some definitions that require pair-bonded individuals to be adult or opposite-sex, studies with coral reef butterflyfishes have suggested that pair bonding may occur within both sexually immature and same-sex partners (Gore, 1983Nowicki et al., 2018b). However, in these studies, pair bonding or “pair formation” was defined by a fairly low level of association—for instance, in butterflyfishes, merely by remaining within 1 m for 10 min (Pratchett et al., 2006). Preliminary evidence also suggests that there are non-reproductive adaptive benefits of pair bonding like social assistance. For example, cooperative defense of high-value resources (e.g., food, shelter, or nesting sites) by one or both partners may be one such process (Nowicki et al., 2018b), but thus far the role of assisted resource defense in promoting pair bonding has received less attention relative to more common behaviors (i.e., mate guarding or biparental care).

Recent work by Nowicki et al. (2018b) comparing two species of butterflyfishes (C. baronessa and C. lunulatus) that exhibit alternative modes of assisted resource defense (male-prioritized vs. mutual defense, respectively) revealed that while assisted resource defense may drive pairing, males and females contribute equally to and benefit from resource defense. In both species, partner assistance appeared to confer gains in both feeding and energy reserves for pairs compared to solitary fish. Results from this study suggest that pair-bonded partners use territorial defense assistance to increase food and energy reserves. Furthermore, partner fidelity promotes territorial defense assistance between partners, which confers an ecological advantage to pair formation and fidelity in these species. However, the consequences of this advantage are unclear and future studies should seek to discern whether long-term pair bonding improves survivorship and lifetime fitness.

Similar to what has been observed in other pair-bonding vertebrates, elevated levels of species-specific homologs of arginine vasopressin (AVP) and OT are associated with pair bonding in fish (Cardoso et al., 2015Cunha-Saraiva et al., 2019O'Connor et al., 2016Oldfield et al., 2015Reddon et al., 2015Shumway, 2010). OT levels have been demonstrated to rise in response to separation from partners in fish (Garcia, 2019). Studies examining the effects of manipulations of the OT and AVP systems have further demonstrated the role of these two neuropeptides in pair bonding, as blocking OT and AVP receptors prevents pair-bond formation in fish (Fischer et al., 2019Nowicki, 2017Oldfield and Hofmann, 2011). In addition to OT and AVP, dopamine (DA) receptors within the mesolimbic reward system appear to be important for pair bonding in fish (Fischer et al., 2019Nowicki, 2017Nowicki et al., 2020). Interestingly, it appears that neuromodulatory systems within the ventral striatal reward/reinforcement circuits such as AVP, OT, and DA have repeatedly contributed to the convergence of monogamy among vertebrates (Johnson and Young, 2018). In fish, AVP receptors within the lateral septum homologue (Nowicki et al., 2020) as well as OT receptors within the ventral telencephalon and amygdala/bed nucleus of the stria terminalis homologue (Nowicki et al., 2020) play an important role in pair bonding. It is also thought that the preoptic area, lateral septum, amygdalahypothalamus, and periaqueductal gray are important for pair bonding in fish (Dewan and Tricas, 2011Nowicki, 2017Nowicki et al., 2020O'Connell and Hofmann, 2011Oldfield et al., 2015). Given the similarity in brain regions associated with pair bonding in fish and other pair-bonding vertebrates, it is possible that pair bonding may have partially converged between taxa through repeated co-option of molecular and anatomical homologies.

3.4. Birds

Monogamy is well studied as a social system in birds (Black, 1996a), and is represented in a large proportion of species, usually cited as 90% (Lack, 1968). However, distinctions exist in the literature between continuous partnerships, as opposed to “part-time” partnerships which do not continue during the non-breeding season (Black, 1996b). Therefore, some bird species which are classified as socially monogamous may not exhibit what we would define as a pair bond, based on these seasonal patterns of association. A number of other bird species do exhibit well-studied, continuous partnerships that include maintenance of association outside of the reproductive season and, while they may not have been experimentally studied in terms of pair bond behaviors, are likely to be pair bonding. Examples include blue ducks, Hymenolaimus malacorhynchos (Williams and McKinney, 1996); barnacle geeseBranta leucopus (Black et al., 1996); swans, genus Cygnus (Rees et al., 1996); jackdawsCorvus monedula (Kubitza et al., 2015); and Pinyon and Florida scrub jays, Gymnorhinus cyanocephalus and Aphelocoma coerulescens (Marzluff et al., 1996). An interesting study of captive Caribbean flamingos (Phoenicopterus ruber ruber) found that some of the flamingos formed putative pair bonds, characterized mostly by continuous proximity, shared breeding and lack of courtship behaviors towards other animals (Shannon, 2000). Experimental evidence has also shown that greylag geese (Anser anser) show both a separation response and stress buffering (Wascher et al., 2012), although whether the separation response would be specific to the mate is unclear.

In avian species, a pair bond is often defined via behaviors such as higher proximity, allopreening, mate guarding, vocalizations, cohabitation, and courtship, all with a specific partner and over a long duration of time (Adkins-Regan, 1999Kenny et al., 2017Tomaszycki and Adkins-Regan, 2005). Compared to other organisms, birds are highly dependent on auditory communication and have physiological reactions to vocalizations, a process that plays major roles in pair bonds (Eriksson and Wallin, 1986Mello et al., 1992Tomaszycki and Adkins-Regan, 2005). Though multiple avian species have been identified as pair bonding, the model organism used by most researchers is the zebra finch (Taeniopygia guttata). Zebra finches have been studied in a wide range of paradigms that have both observationally and experimentally determined that they demonstrate strongly coordinated pair behavior and mate-guarding (Adkins-Regan, 2009), preference for the familiar partner (Smiley et al., 2012), and distress upon separation from the partner (Remage-Healey et al., 2003).

Some avian species demonstrate considerable behavioral flexibility in the pair bond. In bearded vultures (Gypaetus barbatus), it was found that in a more competitive environment for resources, the vultures engaged in less monogamous behaviors, instead forming a trio relationship (Carrete et al., 2006). There are also multiple avian species that engage in same-sex pair bonding. A four-year field study of Laysan albatross (Phoebastria immutabilis) in Hawaii demonstrated that 31% of nests identified were home to two pair-bonded females. The characterization of the pair bond was based upon a high frequency of mutual allopreening and mate guarding, and nearly half of the same-sex pair-bonded females remained together for the entire length of the study (Young et al., 2008). In addition, an experiment examining same-sex pair bonds in zebra finch found that same-sex pair-bonded males did not separate from their pair mate even when presented with a female (Tomaszycki and Zatirka, 2014).

Compared to most other groups, birds are highly dependent on auditory cues and communicate vocally. A complex network of taxon-dependent versions of DA, OT, and AVP seem to be involved in the formation and maintenance of pair bonds in avian species. OT receptor antagonists injected into the lateral ventricle of zebra finch disrupted pair-bonded behaviors in a sex-specific manner in both males and females (Klatt and Goodson, 2013). Disruption of AVP production in the paraventricular nucleus also disrupted social group interaction and affected aggression towards the opposite sex in a sex-specific manner (Kelly and Goodson, 2014). When monitoring DA levels in the brain using PET in zebra finches, researchers found that males experience an uptick of DA in response to female mating calls and demonstrate high motivation to work to hear the calls (Tokarev et al., 2017). In addition, injection of a D2 receptor antagonist decreased motivation to work to hear female mating calls (Tokarev et al., 2017). When looking for neurobiological maintenance mechanisms of pair bonding in zebra finches, researchers found increased levels of glucocorticoids (CORT) in pair-bonded mates upon separation from their mate and levels did not return to baseline until reunion (Remage-Healey et al., 2003). In a study investigating ZENK (a gene that is expressed with cell activation) and pair-mate reunion, researchers found an increase in ZENK expression of the nucleus taeniae in females once mates were reunited, indicating a potential neurobiological mechanism in maintenance of a pair bond (Svec et al., 2009).

3.5. Mammals

In class Mammalia, researchers have defined a pair bond in a variety of ways from simply “pair living” to more expansive and specific criteria. Beyond simply living together, a pair bond among mammals has been defined as an element of social structure in which an adult male and adult female form a close and long-lasting association (Kappeler and Van Schaik, 2002). In order Artiodactyla (even-toed ungulates), researchers have defined a pair bond as stable groupings of a single breeding male and female spanning more than one reproductive cycle (Norton, 1980Tilson, 1980). Researchers of order Primates have considered the definition of a pair bond extensively. Fuentes (1998) defines a pair bond as “a special and exclusive relationship between an adult male and an adult female” (page 890). Anzenberger (1992) defines the pair bond even more explicitly, requiring that there are “indications of a strong mutual attraction, a close spatial relationship, partner specific behaviors and signs of distress during separation from the pair mate.” Fuentes (2002) theorizes that there are two essential components of the pair bond: the social and the sexual. The social component consists of a long-term relationship between opposite-sex, non-kin adults in which partners engage in affiliative and/or energy depleting behaviors that are unique to the pair—or at frequencies of affiliation that are unique to the pair—and maintain greater proximity to the pair mate relative to strangers or other members of the social group (Fuentes, 2002). The sexual component of the pair bond consists of a long-term relationship in which pair mates prefer to copulate with each other to the point of exclusivity, such that the pair demonstrates a monogamous mating pattern (Fuentes, 2002Fuentes, 1998).

Newer definitions have built on these principles and added additional criteria such as endocrine responses to separation from and reunion with the pair mate in order to differentiate “dispersed pairs”—those pair-living primates with looser association and relationships—from “associated pairs”—those pair-living primates that demonstrate emotional attachments unique to their pair mate (Huck et al., 2020). There are several components that help characterize the emotional attachment an animal forms with their pair mate that have been adapted from research on mother-infant attachment, mainly: a strong and unique desire for proximity, distress upon separation, preference for the attachment figure, and ability of the attachment figure to alleviate or buffer stress (Ainsworth, 1978Bowlby, 1982Hazan and Shaver, 1987).

Behavioral components within mammalian pair bonds include affiliation, proximity maintenance, duration, and synchrony. Kleiman (1981) proposed that the strength of mammalian pair bonds could be quantified by several factors: 1) the amount of affiliation in which a pair engages, 2) the duration of pair-bond formation, 3) the degree of synchrony in daily activities between pair mates, and 4) the duration of the relationship. First, the ratio of affiliative behaviors to agonistic and avoidant behaviors––with higher rates of affiliation relative to aggression signaling stronger bonds and affiliative behaviors defined as behaviors that promote proximity between pair mates––can be used to capture variation in affiliation within a given species. These behaviors vary by species, but can include courtship and mating displays, vocal communication while engaging in independent activities, co-sleeping, huddling, and allogrooming. Second, weaker bonds are formed more quickly, are accompanied by more courtship, and are more easily disturbed than bonds that take relatively more time to form. Third, pairs that spend more of their day engaging in the same activities at the same time tend to be more strongly bonded than those who are more independent from their partner. And finally, pairs that associate for a longer duration (relative to species longevity and reproductive frequency), tend to form stronger bonds than pairs that associate for shorter durations.

Several mammalian species assumed to be socially monogamous and capable of forming pair bonds have later been shown to display sexual promiscuity or polygyny under different conditions (Adams et al., 2020Cavallini, 1996Pauw, 2000). As such, it can be difficult to decipher from the literature when animals labeled as socially monogamous exhibit intrapair interactions indicative of a pair bond. For example, the aardwolf hyena (Proteles cristata) was found to exhibit either polygynous or socially monogamous mating strategies depending on the study (Kotze et al., 2012Marneweck et al., 2015). Other species appear fluid in their mating strategy, appearing promiscuous in some wild circumstances but monogamous in captivity (Cavallini, 1996Kotze et al., 2012Tardif et al., 2003). Among the wide range of mating strategies there remains a distinct question about the relationships between breeding pairs: can a species with flexible mating systems form pair bonds? And is it possible that some strictly monogamous species do not form pair bonds at all?

Mammalian groups that contain potentially pair-bonding species include ArtiodactylaCarnivoraMacroscelideaPrimates, and Rodentia. Within the order CarnivoraLukas and Clutton-Brock (2013) classified 16% of species as monogamous, but among that 16%, very few species actually appear to form pair bonds (Lukas and Clutton-Brock, 2013). Among monogamous canids, breeding pairs appear to be capable of forming strong, long-term bonds. Several species of foxes have been observed living in bonded pairs sharing parenting duties, co-sleeping, foraging together, and maintaining proximity, even outside of mating season (Deuel et al., 2017Macdonald and Courtenay, 1996Wright et al., 2010). Similarly, bush dogs, raccoon dogs, and coyotes exhibit biparental care and territorial defense as well as scent marking behaviors to advertise their pair bond and ward off strangers (Drygala et al., 2008Gese and Ruff, 1997Porton, 1983Schell, 2015). Pair-bonding behavior in pack-living canids is complicated by the hierarchical structure of the pack. Gray wolves live in packs with multiple adult males and females, but only the alpha animals form a pair bond, rear offspring, maintain proximity, and lead hunts (Ausband, 2019Bernal-Stoopen and Packard, 1997Peterson et al., 2002). Despite thorough documentation of canid behavior, very little is understood specifically about intrapair interactions and the neural mechanisms involved in canid pair bonding. Although data collection on many of these species is difficult due to their ecology, it remains valuable for future research to investigate the way sociality and pair bonding in canids, both behaviorally and neurobiologically, compares to other species.

Due to its clear expression of pair-bonding behaviors and suitability for laboratory research, the prairie vole (Microtus ochrogaster) has become the primary animal model for studying pair bonding. Prairie voles engage in a variety of affiliative and maintenance behaviors including huddling, grooming, mate preference, and mate guarding (DeVries et al., 1997). Research has also pinpointed specific biological and behavioral responses apparent in the prairie vole that resemble human pair bonds enough to stand out as a translational research model (Aragona and Wang, 2004). In addition to prairie voles there are many other rodent species that appear capable of forming pair bonds. For example, California mice (Peromyscus californicus) are biparental, live in pairs with their offspring, and express a variety of pair-maintenance behaviors. Paired male California mice will suppress ultrasonic vocalizations (typically emitted during mating behavior) in the presence of a strange female following administration of testosterone, while there was no such effect in unpaired males (Pultorak et al., 2015). Female California mice also form a clear preference for one mate over others and maintain this mate preference outside of estrous (Gubernick and Addington, 1994). Captive Cape porcupines (Hystrix africaeaustralis) engage in several pair-bonding behaviors such as allogrooming, scent marking, proximity maintenance, and copulation outside of the mating season (Morris and van Aarde, 1985Sever and Mendelssohn, 1988). With the use of telemetry collars, Matsukawa and colleagues found evidence of pair bonding in wild long-tailed porcupines (Trichys fasciculata)––a biparental species that live in small social groups consisting of a single adult pair with their offspring––where the adult pair maintained their bond across multiple breeding seasons (Matsukawa et al., 2019). Behavioral and ecological factors have made it difficult to study many of the other monogamous rodent species.

Among order Artiodactyla, pair bonds are characterized by a single breeding pair of adults sharing and defending a mutual territory. Klipspringers (Oreotragus oreotragus) are defined as pair bonding on the basis that they hold a mutual territory, engage in pair maintenance through mutual scent marking (Burger, 1997Dunbar and Dunbar, 1974), territorial defense (Dunbar and Dunbar, 1980), and joint vocal displays (Tilson and Norton, 2012). Additionally, klipspringers demonstrate behavioral synchrony and a high degree of proximity maintenance with their pair mates, as well as an intolerance of opposite-sex strangers (Dunbar and Dunbar, 1980Norton, 1980). Dik-diks (Madoqua kirki) are often referred to as pair-bonded due to the fact that they are typically found in pairs and maintain close proximity in their daily life (Brotherton and Manser, 1997Kranz, 1991). Male dik-diks are more territorial than their female counterparts: they engage in the majority of territorial scent marking (Kranz, 1991) and aggressively guard their mates during estrus (Brotherton et al., 1997). This is likely due to male mating strategy flexibility demonstrated by a willingness to engage in extra-pair copulations and even polygyny (Brotherton and Manser, 1997). Finally, reedbucks (Redunca arundinum) are sometimes referred to as pair-bonding because they live in single-male single-female pairs accompanied only by their sub-adult offspring (Junguis, 1970).

Within order Primates, researchers have proposed that behaviors that accompany a pair bond would include bond-reinforcing species-specific behavior like duetting, mutual displays, and partner contact behaviors (Anzenberger, 1988French and Schaffner, 1999Palombit, 1999) as well as behaviors that carry energetic costs like food sharing, grooming, and assistance in aggressive encounters (Fuentes, 2002). According to the strict definition of a primate pair bond by Fuentes (1998), only a few species of primates truly demonstrate pair bonds: genuses Callicebus and Plecturocebus (titi monkeys), genus Aotus (owl monkeys), Avahi laniger (the eastern woolly lemur), and Indri indri (indris). Titi monkeys (genus Callicebus and genus Plecturocebus) demonstrate behaviors consistent with pair bonding like mate guarding, vocal duets, joint territorial displays, affiliation rates unique to the pair mate, unique attachment to the pair mate, distress upon separation from the pair mate, and amelioration of distress upon reunion with the pair mate (Anzenberger, 1988Fernandez-Duque et al., 1997Mason, 1966Mason and Mendoza, 1998). Gibbons (family: Hylobates) have been referred to as pair living and pair bonding and many species of gibbons do indeed demonstrate preferential pair-living and pair behavior (Cheyne, 2010Choudhury, 1990), as well as territoriality enforced by vocal displays (Raemaekers and Raemaekers, 1984). However, there are documented cases of fluid sociosexual structure among adult gibbons, which tend to be influenced by resource availability (Savini et al., 2009), and a minority of gibbon species do not engage in coordinated vocalizations (Geissmann, 2002). By some definitions, these observations exclude those species from being considered truly pair bonding (Fuentes, 1998). There is also mixed information on whether sakis (genus: Pithecia) form pair bonds. While some studies found that sakis form preferential close relationships with their mating partners (Porter et al., 2015Thompson, 2016), others debate whether sakis exhibit enough of the essential pair-bonding behaviors (e.g. mate guarding and maintained interaction beyond one interbirth interval), to be considered a pair-bonding species (Porter et al., 2015Thompson, 2016Thompson and Norconk, 2011). Some species of lemurs have also been proposed as pair bonding. Red-bellied lemurs (Eulemur rubriventer) exhibit several intrapair behaviors that indicate the possibility of a pair bond: territorial defense, pair-specific vocalizations, and pair-specific behaviors (Grebe et al., 2021Tecot et al., 2016).

Years of neurobiological research in prairie voles have revealed a critical role of OT and AVP systems in the formation and maintenance of mammalian pair bonds (see Walum and Young, 2018 for a detailed review). The specific distribution of OT and AVP receptors significantly differ between closely related vole species depending on whether or not they are socially monogamous. Further pharmacological manipulations of OT and AVP, as well as DA and opioids, revealed detailed neural circuits dedicated to the social process of pair bonding (Chappell et al., 2016Lim et al., 2004Liu et al., 2001Liu and Wang, 2003Resendez et al., 2012). Research in nonhuman primates has expanded our understanding of these neural circuits. Relationship formation in titi monkeys is supported by the dopaminergic reward system, specifically D1 receptors in the lateral septum (Hostetler et al., 2017) and increased activity (measured by glucose uptake) in the nucleus accumbens and ventral pallidum (Bales et al., 2007Maninger et al., 2017a). Relationship maintenance in titi monkeys is supported by brain areas involved in motivation like the nucleus accumbens, ventral pallidum, caudate, and putamen as well as by areas involved in emotion, reproduction, and social memory like the medial preoptic area, amygdala, lateral septum, and posterior cingulate cortex (Bales et al., 2017Bales et al., 2007Maninger et al., 2017b). D1 receptors also play a role in pair-bond maintenance as regulators of mate guarding behaviors, suggesting that the dopaminergic reward system plays an important role in the agonistic components of pair-bond maintenance (Rothwell et al., 2019).

Despite the evidence for some commonalities in the neurobiology of pair bonding across mammal species, primate studies suggest that we still do not fully understand neural mechanisms for pair bonding. A recent study in monogamous and non-monogamous Eulemur species (Grebe et al., 2021) examined the distribution of AVP and OT receptors in the brains of two monogamous and five non-monogamous lemur species. Surprisingly, the differences between OT and AVP receptor distributions in monogamous and non-monogamous lemurs were minimal, even in dopaminergic areas. This finding was unexpected, given the striking differences found between monogamous and non-monogamous voles (Insel and Shapiro, 1992) and between monogamous titi monkeys vs. non-monogamous rhesus monkeys (Freeman and Young, 2016). These findings suggest that there could be distinctive mechanisms underlying pair bonding in lemurs, or that lemurs might not really form pair bonds.

The lemur study and its deviation from expected patterns suggests that it is likely that the presence of some combination of molecular mechanisms out of a larger suite may better predict whether a species will form an emotional pair bond or not. This idea of a “redundant systems model” was previously proposed to explain how all behavioral aspects of pair bonding are not reliably expressed by all pair-bonding species (Mendoza et al., 2002). It is possible that a combination of the activity of certain molecular mechanisms, such as OT, AVP, DA, and CORT, play some role in the expression of pair bonding; however, these mechanisms and their sites of action may differ based on how pair bonding evolved in that species. In our quest to understand the evolution of pair bonding, we must also continually return to our behavioral definitions to understand whether we are all talking about the same phenomenon.

3.6. Humans

Definitions of human pair bonding typically include proximity or cohabitation, relative stability over time, and a strong affective attachment to the partner (Fernandez-Duque et al., 2020Fletcher et al., 2015Quinlan, 2008). The behavioral expression of pair bonding in humans has many common elements with the behaviors observed in other pair-bonding species, as well as many unique elements. As in other species, human pair bonds typically follow a normative developmental course, including initiation, maintenance, and occasionally dissolution (Clark et al., 2018Eastwick et al., 2019Rusbult et al., 2004). Human pair bonds are also studied in the context of romantic love, a construct characterized by compassion, intimacy, and caregiving (for a discussion of the robustness of this three-factor structure, see Fletcher et al., 2015). However, the term “romantic love” has been used somewhat inconsistently across the fields of social and evolutionary psychology, with some using the term “romantic love” as an equivalent to “pair bonding” (Carter and Perkeybile, 2018), and others describing “romantic love” as a separate process that is related to human pair bonding and has potential parallels in other animal species (Diamond, 2003). In this article, we consider romantic love and pair bonding as related and largely overlapping constructs.

Given the human capacity for language, human pair mates sometimes express romantic affection verbally, sometimes through song, poetry, or music. Humans also show cognitive bias, and in committed pair bonds, pair mates tend to hold positive illusions about their partner (Clark et al., 2018Lemay and Clark, 2015). There is also large variation between (and within) cultural groups in how humans form and express pair bonds (Eastwick, 2013Quinlan, 2008). Moreover, humans are the only species in which monogamous pair bonding is imbedded within complex, multi-level male/female groups (Chapais, 2013). Although it could be argued that some of these elements of human pair bonding exist to some degree in other animal species, in most cases it is impossible to know, given that animal pair bonding can only be assessed through behavior and physiology.

There has been much debate on the evolutionary origins and timing of human pair bonding and social structure. There are two primary competing hypotheses: either (1) human pair bonding evolved to support the large investment needed to rear offspring, or (2) human pair bonding evolved because it was too costly for males to have multiple mates (Chapais, 2013Fletcher et al., 2015Quinlan, 2008Stanyon and Bigoni, 2014). Many pressures may have selected for human pair bonding, including sex ratios, the spatial distribution of females, innovation of hunting and cooking technologies, alloparenting, life history (i.e., slow maturation of offspring), male-female division of labor (i.e., paternal provisioning), and shortened inter-birth intervals (although note, in some cases, pair bonding may have evolved first or concurrently) (Quinlan, 2008Quinlan and Quinlan, 2008). Regardless of how pair bonding evolved, it is generally agreed that, in humans, it evolved after maternal care (common to all mammals), but before paternal (i.e., biparental) care (Chapais, 2013Diamond, 2004). This could potentially explain why the neural processes that support mother-infant bonding (particularly those involving DA and OT) overlap with those that support romantic-partner bonding (Diamond, 2004Feldman, 2017Ortigue et al., 2010). Further, Chapais (2013) argued that human pair bonding first evolved in a polygamous context, and that monogamy evolved after pair bonding. If this is true, it raises important questions about whether exclusivity should be included in the definition of “pair bonding” in humans (and other species), or whether multiple pair bonds can be maintained at a time (Fletcher et al., 2015).

Human pair bonding is supported by various brain regions and neurotransmitters, many of which are implicated across other pair bonding species. For examples, a large body of comparative research suggests that across humans (Feldman, 2017), non-human primates (Bales et al., 2017), and many other species (Fischer et al., 2019) pair bonding is supported by systems including DA,OT, and AVP in the hypothalamus, ventral tegmental area, nucleus accumbens, and the globus pallidum, as well as other limbic and cortical regions (Feldman, 2017Fischer et al., 2019). However, in humans there may be an increased role for the cortex (see Feldman, 2017), a brain region that is greatly expanded in humans compared to other species and that likely enables many human-specific cognitive and emotional processes (Teffer and Semendeferi, 2012). For example, in humans, many regions in the prefrontal cortex, cingulate cortex, and insula project to the mid-brain pair-bonding circuitry (Bartels and Zeki, 2000Feldman, 2017Marsh, 2018). These neural processes likely enable a vast suite of cognitive abilities that allow partners to evaluate and interpret each other's thoughts, feelings, intentions, goals, emotions, and character (Fletcher et al., 2015), manifest in both behavior and language.

Daily & weekly data on Google searches for 107 countries: The COVID-19 crisis resulted in a massive rise in the intensity of prayer on all continents, at all levels of income, inequality, and insecurity, and for all types of religion, except Buddhism

In Crisis, We Pray: Religiosity and the COVID-19 Pandemic. Jeanet Sinding Bentzen. Journal of Economic Behavior & Organization, Nov 1 2021. https://doi.org/10.1016/j.jebo.2021.10.014

Abstract: In times of crisis, humans have a tendency to turn to religion for comfort and explanation. The 2020 COVID-19 pandemic is no exception. Using daily and weekly data on Google searches for 107 countries, this research demonstrates that the COVID-19 crisis resulted in a massive rise in the intensity of prayer. During the early months of the pandemic, Google searches for prayer relative to all Google searches rose by 30%, reaching the highest level ever recorded. A back-of-the-envelope calculation shows that by April 1 2020, more than half of the world population had prayed to end the coronavirus. Prayer searches remained 10% higher than previously throughout 2020, particularly so in Europe and the Americas. Prayer searches rose more among the more religious, rose on all continents, at all levels of income, inequality, and insecurity, and for all types of religion, except Buddhism. The increase is not merely a substitute for services in the physical churches that closed down to limit the spread of the virus. Instead, the rise is due to an intensified demand for religion: People pray to cope with adversity. The results thus reveal that religiosity has risen globally due to the pandemic with potential direct long-term consequences for various socio-economic outcomes.

Keywords: COVID-19 pandemicdisasterpsychological copingreligiosityempirical analysisGoogle search data


Sunday, October 31, 2021

Reminder from 2010... Genetically, hunter-gatherer peoples of southern Africa, the oldest known lineage of modern human, seem to be, on average, more different from each other than a European and an Asian

Complete Khoisan and Bantu genomes from southern Africa. Stephan C. Schuster et al. Nature volume 463, pages943–947. Feb 18 2010. https://www.nature.com/articles/nature08795

Abstract: The genetic structure of the indigenous hunter-gatherer peoples of southern Africa, the oldest known lineage of modern human, is important for understanding human diversity. Studies based on mitochondrial1 and small sets of nuclear markers2 have shown that these hunter-gatherers, known as Khoisan, San, or Bushmen, are genetically divergent from other humans1,3. However, until now, fully sequenced human genomes have been limited to recently diverged populations4,5,6,7,8. Here we present the complete genome sequences of an indigenous hunter-gatherer from the Kalahari Desert and a Bantu from southern Africa, as well as protein-coding regions from an additional three hunter-gatherers from disparate regions of the Kalahari. We characterize the extent of whole-genome and exome diversity among the five men, reporting 1.3 million novel DNA differences genome-wide, including 13,146 novel amino acid variants. In terms of nucleotide substitutions, the Bushmen seem to be, on average, more different from each other than, for example, a European and an Asian. Observed genomic differences between the hunter-gatherers and others may help to pinpoint genetic adaptations to an agricultural lifestyle. Adding the described variants to current databases will facilitate inclusion of southern Africans in medical research efforts, particularly when family and medical histories can be correlated with genome-wide data.


Our review of recent studies finds a small-but-consistent gap in men & women's beliefs about their health risks related to the present pandemic; these risk beliefs are crucial determinants of whether individuals take protective measures

Gender differences in perceived risk of COVID-19. Andrew Lewis, Raymond Duch. Social Science Quarterly, October 29 2021. https://doi.org/10.1111/ssqu.13079

Abstract

Objective: We examine gender-based differences in perceived risks related to COVID-19.

Methods: We analyze published findings from COVID-related research on beliefs and attitudes about the health risks posed by the pandemic. We also design and administer a pair of online survey experiments (n = 502) to test if and how responsive men's attitudes are to information about male-specific risks.

Results: Across 16 studies, men consistently express lower perceived risk of contracting COVID-19 and less concern about the potential health consequences if they were to catch it. Our experimental results are mixed: Results for one information treatment indicate that men report greater relative risk of adverse outcomes. Men in one of the risk information treatments express less concern for their health if they were to contract the disease. Risk perceptions are positively correlated with self-reported propensity toward protective behaviors.

Conclusion: Our review of recent studies finds a small-but-consistent gap in men and women's beliefs about their health risks related to the present pandemic. These risk beliefs are crucial determinants of whether individuals take protective measures. Our experimental results suggest that informing men of male-specific risks associated with COVID-19 can reduce their risk perceptions 

DISCUSSION AND CONCLUSION

A central concern of public health officials world-wide has been to communicate to the general public the risks associated with the COVID-19 virus. It is widely accepted, and our evidence confirms, that risk beliefs are correlated with behavior.

In order to effectively convince the general public about the risks associated with the COVID-19, public health authorities require a sound understanding of current beliefs about the virus and of the effective communication strategies they should adopt. This research note provides two important insights in this regard. First, we address the notion that there is a gender gap in COVID-19 risk perceptions. We conduct an extensive meta-analysis of recent research on COVID—19 risk perceptions. This analysis indicates that men generally have lower estimates, than women, of their COVID-related risks; and men tend to be more tolerant than women of those risks.

We conjecture that some of this gender gap difference can be narrowed by exposing men to information regarding the health dangers of COVID-19. The survey experiment is designed to test this proposition. A second contribution implements survey experiments designed to identify the effect of information treatments on men's beliefs about the risks of the COVID-19 virus. First, presentation matters; we observer stronger treatment effects for Experiment 2 that presents the risk information in a graphic format. In fact, none of the treatment effects are significant in Experiment 1 when we have subjects read a short discussion of the risks of COVID-19. Second, how messages are framed and communicated matters—in fact, information frames can have perverse outcomes. Our Experiment 2 treatment simply highlights men's increased risks of adverse outcomes from COVID-19—but the framing has the perverse effect of reducing self-reported concern about the disease.

There is no evidence in our two experiments to suggest that providing information about the risks associated with the COVID-19 will cause men to increase their risk assessments associated with the disease—in fact they might have the opposite effect. This highlights the importance of carefully crafting information campaigns designed to change risk perceptions. Future work could focus, for example, on framing this risk information in ways that are amenable to “identity-protective cognition,” such that men are less likely to view the treatment as a threat to their own self-perception. As Kahan (2007) writes, “it is not enough that the information be true; it must be framed in a manner that bears an acceptable social meaning.”

Newly self-employed people are overly optimistic about their future life satisfaction; this overoptimism also holds for successful entrepreneurs who remain in business

Are Newly Self-Employed Overly Optimistic About Their Future Well-Being? Reto Odermatt, Nattavudh Powdthavee, Alois Stutzer. Journal of Behavioral and Experimental Economics, October 31 2021, 101779. https://doi.org/10.1016/j.socec.2021.101779

Highlights

• We study if newly self-employed people accurately predict their future well-being

• We use individual panel data to compare expected and the realized life satisfaction

• Newly self-employed people are too optimistic about their future life satisfaction

• The overoptimism also holds for successful entrepreneurs who remain in business

• We discuss reasons for the misprediction such as underestimating heavy workload

Abstract: The formation of expectations is considered a fundamental aspect of the decision process when people reason about entering self-employment. We evaluate the accuracy of newly self-employed individuals’ predictions of their overall future well-being. Based on individual panel data for Germany, we find that they, on average, are overly optimistic when we compare their predictions right after the status change with their actual life satisfaction five years later. This finding is robust to controlling for any time invariant personality traits like individual optimism. And it also holds for those self-employed individuals who successfully remain in business for at least five years. A possible reason for the biased prediction might be that they underestimate the heavy workload reflected in higher working hours than desired, as well as the decline in leisure satisfaction after the status change.

Keywords: Self-employmentoveroptimismlife satisfactionprojection biaspredicted well-being

JEL D83 D91 J20 I31

6. Concluding remarks

The formation of expectations is a fundamental part of the process when people decide about becoming self-employed. Our evaluation of the expectations and experiences of people who become self-employed in Germany allowed us to examine empirically some of the popular beliefs about the (well-being) consequences of self-employment. We made use of the large German Socio-Economic Panel including information about people's work environment, work conditions as well as their evaluation of their satisfaction with various aspects of their work and private life. Importantly, we studied people's predictions of how satisfied they expect to be five years in the future and compare these predictions with the actual realizations five years later.

We showed that, irrespective of their stable optimistic personality traits, people who enter self-employment tend to be overly optimistic about how satisfied they will be with their lives in the future. This overoptimism is prevalent even for the successful self-employed who manage to remain self-employed for at least five years, which suggests that overoptimism is not caused entirely by people mispredicting their own probability of success in the business.9 Rather, it is more likely to be caused by people putting too much weight on the positive work engagement and too little weight on the amount of workload when making a forecast about what their life would be like as a self-employed, which is consistent with findings in the affective forecasting literature (Wilson and Gilbert, 20032013). This is reflected in the evidence that self-employed people report lower leisure satisfaction and an increase in the number of hours worked that go beyond the desired level of working hours in the years after the transition. However, one promise of becoming self-employed seems to come true, namely that these people, on average, report an increase in autonomy in their occupational actions.

There are several limitations to drawing general welfare implications from our findings. First, although our results suggest that some people might only have entered self-employment due to overoptimism, the current empirical framework simply does not allow us to test such a hypothesis directly. Second, even if unrealistic expectations tend to be observed generally with the decision to become self-employed, people who take that leap but do not succeed may still gain valuable experiences from doing so. For example, first time failure might lead to a higher success rate when they run a self-employed activity for a second time. They may also become more satisfied when they return to paid employment as they might value a secure income and regular working hours more after the experience. Third, the observed overoptimism might reflect motivated beliefs (Bénabou and Tirole 2016) for which accuracy might not be the only objective as beliefs also serve an important purpose of motivating people so that they persevere with putting in effort to achieve goals. This instrumental aspect emphasizing the enhancement of self-efficacy is complemented by other motives as people might want to share beliefs in accordance with their peer group or their self-image. Fourth, the individual perspective also neglects welfare effects at the societal level. Successful as well as failed self-employment might contribute to the development of new products and services creating positive spillovers in society.

In future research, we need to better understand how the beliefs about the value of self-employed activities are formed and to what degree they influence people's decision to enter self-employment. In particular, it would be interesting to understand how the beliefs are related to the treatment of “successful” and “failed” business owners in society. This is an issue of entrepreneurial and self-employment culture but also the choice of legal institutions. A more complete understanding of how different institutional environments relate to actual as well as expected outcomes of latent and actual self-employed individuals will contribute productively to the policy discourse on self-employment and entrepreneurship.

Our findings challenge the notion that merely thinking about a romantic partner's success or failure has a substantial impact on implicit self-esteem; 78pct effect is smaller than in Ratliff and Oishi (2013)

Implicit self-esteem following a romantic partner's success: Three replications and a meta-analysis. Heather-Christina C. Hawkins, Tara L. Lesick, Ethan Zell. Personal Relationships, October 24 2021. https://doi.org/10.1111/pere.12408

Abstract: Few studies have examined how social comparisons with one's romantic partner influence self-esteem. Ratliff and Oishi (2013) found that writing about a romantic partner's success versus failure lowered men's implicit self-esteem (i.e., automatic associations between the concepts self/other and good/bad). We conducted three replications of this research (two preregistered). In each replication, the effect of writing about a romantic partner's success was not statistically significant. Furthermore, a meta-analysis of our three replication studies yielded a small overall effect (d = 0.13) that was 78% smaller than the overall effect obtained by Ratliff and Oishi (2013). Our findings challenge the notion that merely thinking about a romantic partner's success or failure has a substantial impact on implicit self-esteem. Exploratory analyses, however, suggest that this effect may occur for men who are low in relationship satisfaction.