Pair‐bonded primates have uniquely enduring relationships and partners engage in a suite of behaviors to maintain these close bonds. In titi monkeys, pair bond formation has been extensively studied, but changes across relationship tenure remain unstudied. We evaluated differences in behavioral indicators of pair bonding in newly formed (~6 months paired,
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Behavior is often linked to gonadal sex; however, ecological or social environments can induce plasticity in sex-biased behaviors. In biparental species, pairs may divide offspring care into two parental roles, in which one parent specializes in territory defense and the other in nest care. The African cichlid fish Julidochromis marlieri displays plasticity in sex-biased behaviors. In Lake Tanganyika, J. marlieri form female-larger pairs in which the female is more aggressive than the male who performs more nest care, but under laboratory conditions, male-larger pairs can be formed in which these sex-biased behaviors are reversed. We investigated the influence of social environment on behavior by observing how individuals in both pair-types respond to conspecific intruders of either sex. We examined behavioral responses to three factors: sex of the subject, relative size of the subject, and the sex of the intruder. We confirm that relative size is a factor in behavior. The larger fish in the pair is more aggressive than the smaller fish is towards an intruder. While neither fish in the female-larger pairs varied their behaviors in response to the sex of the intruder, both members of the male-larger pairs were sensitive to intruder sex. Both individuals in the male-larger pairs engaged in more biting behaviors towards the intruder. Intruder biting behaviors strongly correlated with the biting behavior of the larger individual in the pair and occurred more frequently when encountering pairs with same sex as the larger fish when compared to pairs with the same sex as the smaller fish. Our results support the role of the social environment as a contributor in the expression of sex-biased behavior.
more » « less- PAR ID:
- 10549950
- Publisher / Repository:
- bioRxiv
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- Medium: X
- Institution:
- bioRxiv
- Sponsoring Org:
- National Science Foundation
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Abstract n = 9) compared to well‐established pairs (average 3 years paired,n = 8) of titi monkeys (Callicebus cupreus ) as well as sex differences within the pairs. We hypothesized that overall males would contribute more to maintenance than females, but that the pattern of maintenance behaviors would differ between newly formed and well‐established pairs. Each titi monkey (N = 34) participated in a partner preference test (PPT), where the subject was placed in a middle test cage with grated windows separating the subject from the partner on one side and an opposite‐sex stranger on the other side. During this 150‐min behavioral test, we quantified four key behaviors: time in proximity to the partner or stranger as well as aggressive displays toward the partner or stranger. Overall, we found different behavioral profiles representing newly formed and well‐established pair‐bond relationships in titi monkeys and male‐biased relationship maintenance. Males spent ∼40% of their time in the PPT maintaining proximity to the female partner, regardless of relationship tenure. Males from well‐established bonds spent less time (14%) near the female stranger compared to males from newly formed bonds (21%) at the trend level. In contrast, females from well‐established bonds spent less (23%) time near the male partner in the PPT compared to females from newly formed bonds (47%). Aggressive displays were more frequent in newly formed bonds compared to well‐established bonds, especially for females. Scan sampling for homecage affiliation showed that newly formed pairs were more likely to be found tail twining than well‐established pairs. -
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SUMMARY Both individual sex and population sex ratio can affect lifetime reproductive success. As a result, multiple mechanisms have evolved to regulate sexual phenotype, including adult sex change in fishes. While adult sex change is typically socially regulated, few studies focus on the non‐chromosomal mechanisms regulating primary sex allocation. We investigated primary sex determination in the bluebanded goby (
Lythrypnus dalli ), a bidirectionally sex‐changing fish. Of the studies investigating primary sex determination in species with adult sex change, this is the first to incorporate the roles of social status and size, key factors for determining adult sex allocation. ForL. dalli , adult sex is regulated by social status: dominants are male; subordinates are female. In social groups of laboratory‐reared juveniles, we demonstrate that status also predicts primary sex. Dominant juveniles developed male‐typical genitalia, and their gonads contained significantly less ovarian tissue than subordinates, which developed female‐typical genitalia. To better understand natural development, we quantified the distribution of juveniles and adults on the reef and analyzed genital papilla and gonad morphology in a sample of wild‐caught juveniles. Juveniles were observed in various social environments, and most grouped with other juveniles and/or adults. The majority of field‐caught juveniles had female‐typical genitalia and bisexual, female‐biased gonads. These data are consistent with a single mechanism that regulates sexual phenotype throughout life. Social status could first cause and then maintain through adulthood a female‐biased population, allowing individuals to regulate sex based on local conditions, which is important for optimizing lifetime reproductive success. -
Monogamous, pair-bonded animals coordinate intra-pair behavior for spatially separated challenges including territorial defense and nest attendance. Paired California mice, a monogamous, territorial and biparental species, approach intruders together or separately, but often express behavioral convergence across intruder challenges. To gain a more systems-wide perspective of potential mechanisms contributing to behavioral convergence across two conspecific intruder challenges, we conducted an exploratory study correlating behavior and receptor mRNA (Days 10 and 17 post-pairing). We examined associations between convergence variability in pair time for intruder-oriented behaviors with a pair mRNA index for oxytocin (OXTR), androgen (AR), and estrogen alpha (ERα) receptors within the medial amygdala (MeA) and the anterior olfactory nucleus (AON), brain regions associated with social behavior. An intruder behavior index revealed a bimodal distribution of intruder-related behaviors in Challenge 1 and a unimodal distribution in Challenge 2, suggesting population behavioral convergence, but no significant correlations with neuroendocrine measures. However, OXTR, AR, and ERα mRNA in the MeA were positively associated with convergence in individual intruder-related behaviors, suggesting multiple mechanisms may influence convergence. Mice could also occupy the nest during intruder challenges and convergence in nest attendance was positively correlated with MeA OXTR. At an individual level, nest attendance was positively associated with MeA ERα. Vocalizations were positively associated with AR and ERα mRNA. No positive associations were found in the AON. Overall, neuroendocrine receptors were implicated in convergence of a monogamous pair’s defense behavior, highlighting the potential importance of the MeA as part of a circuit underlying convergence.more » « less
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Rosenfeld, Cheryl S. (Ed.)Pair-bonding allows for division of labor across behavioral tasks such as protecting a territory, caring for pups or foraging for food. However, how these labor divisions are determined, whether they are simply intrinsic differences in the individual’s behavior or a coordinated behavioral response by the pair, remains unknown. We used the monogamous, biparental and territorial California mouse ( Peromyscus californicus ) to study how behavioral approach to an aggressive vocal stimulus in a novel environment was affected by pair-bonding. Using a three-chambered vocal playback paradigm, we first measured the amount of time individuals spent in close proximity to aggressive bark vocalizations. We found that animals could be categorized as either approachers or avoiders. We then paired individuals based on their initial approach behavior to an opposite sex individual who displayed either similar or different approach behaviors. These pairs were then retested for approach behavior as a dyad 10–11 days post-pairing. This test found that pairs showed convergence in their behavioral responses, such that pairs who were mismatched in their approach behaviors became more similar, and pairs that were matched remained so. Finally, we analyzed the ultrasonic vocalizations (USV) produced and found that pairs produced significantly more USVs than individuals. Importantly, increased USV production correlated with increasing behavioral convergence of pairs. Taken together, this study shows that pair-bonded animals alter their approach behaviors to coordinate their response with their partner and that vocal communication may play a role in coordinating these behavioral responses. Overall, our findings indicate that pair-bonding generates an emergent property in pairs, adjusting their combined approach behavior towards a new aggressive stimulus representing a potential challenge to the bonded pair. Such findings may be broadly important for social bonding in other social systems.more » « less
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Tworzydlo, W and (Ed.)Sex determination and sexual development are highly diverse and controlled by mechanisms that are extremely labile. While dioecy (separate male and female functions) is the norm for most animals, hermaphroditism (both male and female functions within a single body) is phylogenetically widespread. Much of our current understanding of sexual development comes from a small number of model systems, limiting our ability to make broader conclusions about the evolution of sexual diversity. We present the calyptraeid gastropods as a model for the study of the evolution of sex determination in a sequentially hermaphroditic system. Calyptraeid gastropods, a group of sedentary, filter-feeding marine snails, are sequential hermaphrodites that change sex from male to female during their life span (protandry). This transition includes resorption of the penis and the elaboration of female genitalia, in addition to shifting from production of spermatocytes to oocytes. This transition is typically under environmental control and frequently mediated by social interactions. Males in contact with females delay sex change to transition at larger sizes, while isolated males transition more rapidly and at smaller sizes. This phenomenon has been known for over a century; however, the mechanisms that control the switch from male to female are poorly understood. We review here our current understanding of sexual development and sex determination in the calyptraeid gastropods and other molluscs, highlighting our current understanding of factors implicated in the timing of sex change and the potential mechanisms. We also consider the embryonic origins and earliest expression of the germ line and the effects of environmental contaminants on sexual development.more » « less
