Behavioral Ecology

Seasonal variation strongly influences honey bee colony dynamics, leading to time-dependent changes in behavioral and physiological phenotypes. However, the extent to which seasonal fluctuations affect the susceptibility and tolerance of honey bees to viral infection remains largely unexplored. To address this, we conducted a longitudinal study in which adult honey bee workers were collected monthly from research colonies and experimentally infected with Israeli acute paralysis virus (IAPV) over the course of a year. Our results showed significant seasonal variation in the mortality and IAPV load of inoculated bees, with bees challenged during the pre-overwintering period (i.e., fall) exhibiting the highest susceptibility and lowest tolerance to IAPV infection compared to bees challenged in spring, summer, or winter. To investigate factors underlying these seasonal differences, we conducted nutrition-based studies that determined: 1) the variation in lipid content of colonies throughout the year and its potential link to our observed trends in IAPV tolerance, and 2) the impact of seasonally collected pollen on the survivorship of IAPV-challenged bees. Our findings support that seasonal changes in honey bee physiology and nutritional status play key roles in influencing honey bee viral tolerance. We conclude that honey bee colonies are particularly vulnerable to viral infection during the pre-overwintering period, most likely as a result of reduced tolerance to pathogen stress when transitioning from a summer to winter worker population. We further hypothesize that this period of increased vulnerability to viral infection, in correlation with other disease factors such as Varroa mite abundance and available forage, likely contributes to the relatively high overwintering losses experienced by beekeepers. Given the recent reports of severe colony losses attributed to honey bee viruses, understanding the relationship between seasonality and viral tolerance in honey bees is crucial for better informing management strategies and improving overwintering success. AUTHOR SUMMARYWe explored how seasonal changes affect the ability of honey bees to withstand viral infections. Previous research has shown that there are physical and behavioral differences between summer and winter bees, but its unclear how these seasonal differences affect a honey bees ability to withstand viral infection. To investigate this, we collected honey bee workers monthly and infected them with Israeli acute paralysis virus (IAPV) over the course of a year. Our results showed that honey bees were most vulnerable to IAPV in the fall (i.e., prior to overwintering), as they showed the highest mortality rates and lowest viral tolerance, based on their IAPV loads, during this time. By following up with nutrition-based studies, we found that seasonal changes in bee nutrition in part explained the seasonal differences we observed in honey bee virus tolerance. Overall, our findings suggest that bees are less tolerant to viral infection during the pre-overwintering period when colonies transition from a summer to a winter worker population. This vulnerable period may help explain the high rates of colony losses experienced by beekeepers nationwide and demonstrates the importance of developing seasonally-dependent disease management strategies.

Cross-Fostering, i.e., the exchange of eggs or hatchlings, is a widely used technique, to disentangle genetic from environmental effects or to manipulate the clutch size. In most bird species, this manipulation is easily accepted by the social parents, leading to the conclusion that fostering has no detrimental effect. Using a dataset of four cohorts (N=298) of zebra finches (Taeniopygia castanotis), in which we fostered routinely a single egg into another nest of zebra finches, we explored potential short- and long-time effects of fostering. Noteworthy, these experiments were not designed to test this hypothesis. The objective of the egg fostering experiments was to test for parental recognition (Caspers et al. 2017) and mate choice decisions (Goluke 2018). Consequently, the aim of the present study is purely explorative. Our study confirmed previous findings that fostering has no short-term effects on the morphology and growth rates of the chicks, neither in males nor in females. However, we found that fostering has a sex-specific long-term effect. Females originating from fostered eggs had a significantly reduced lifespan compared to those from non-fostered eggs. Conversely, the lifespan of fostered males was similar to that of non-fostered males. All birds were housed in large groups, experiencing the same conditions after nutritional independence (day 35). Therefore, we can only speculate that fostering might result in early developmental stress, which may affect the individual fitness of females later in life, ultimately leading to shorter lifespans.

Interindividual differences in nest defense towards a single predator type have been shown to be repeatable in multiple species, supporting the presence of personality. Here, we assessed if the nest defense of female northern house wrens (Troglodytes aedon) was repeatable across different types of predators, which is predicted by personality and largely untested. Over three years, we placed a decoy of a common nest predator, the eastern rat snake (Pantherophis alleghaniensis), on top of nest boxes and measured female behavior. Each season, we also presented a second stimulus of varying threat level, including an eastern chipmunk decoy (Tamias striatus), a taxidermied Coopers hawk (Accipiter cooperii), and a novel object of unknown threat. We measured repeatability between each pair of threats and compared the population-level response to the snake across years. Nest defense was significantly repeatable between the snake and chipmunk, which presented similar risks. It was also repeatable between the snake and novel object despite the population-level response to the object being significantly weaker. In contrast, nest defense was not repeatable between the snake and the hawk, which posed a significant threat to adult survival that may have disrupted the consistency of the female response. Finally, the average, population-level response to the snake did not detectably differ among years, indicating stability in this behavior despite high turnover in breeding adults. These results suggest the presence of personality in nest defense, but more research is needed to evaluate the effect of high-risk predators on the repeatability of this behavior. Significance StatementDifferences among individuals in the strength of nest defense are often repeatable towards a specific predator, indicating the presence of personality. However, few studies have tested the repeatability of nest defense across different predators of varying threat levels. Personality predicts that weak/strong responders to one predator should also be weak/strong to another. We tested this prediction in female northern house wrens by placing decoys of different predators and a novel object on top of their nest boxes to measure nest defense. Nest defense was repeatable between two predators of similar risk and between a predator and a novel object of unknown risk. However, nest defense was not repeatable between a low and high-risk predator. The results suggest the presence of personality, but research is needed on the effects of high-risk predators that appear to disrupt behavioral consistency.

Oscine songbirds are an ideal system for investigating how early experience affects behavior. Young songbirds face a challenging task: how to recognize and selectively learn only their own species song, often during a time-limited window. Because birds are capable of hearing birdsong very early in life, early exposure to song could plausibly affect recognition of appropriate models; however, this idea conflicts with the traditional view that song learning occurs only after a bird leaves the nest. Thus, it remains unknown whether natural variation in acoustic exposure prior to song learning affects the template for recognition. In a population where sister species, golden-crowned and white-crowned sparrows, breed syntopically, we found that nestlings discriminate between heterospecific and conspecific song playbacks prior to the onset of song memorization. We then asked whether natural exposure to more frequent or louder heterospecific song explained any variation in golden-crowned nestling response to heterospecific song playbacks. We characterized the amount of each species song audible in golden-crowned sparrow nests and showed that even in a relatively small area, the ratio of heterospecific to conspecific song exposure varies widely. However, although many songbirds hear and respond to acoustic signals before fledging, golden-crowned sparrow nestlings that heard different amounts of heterospecific song did not behave differently in response to heterospecific playbacks. This study provides the first evidence that song discrimination at the onset of song learning is robust to the presence of closely related heterospecifics in nature, which may be an important adaptation in sympatry between potentially interbreeding taxa.

While the function of bird song has been well studied in male songbirds, the function of female song is less well understood. This is partly due to a historical view of females occupying a passive role compared with males, which led to ignoring female song even in some well-studied species. We report one such case in yellow warblers (Setophaga petechia), as no other study investigated female song in 35 years after the first documentation of solo female songs. We interrogate the seasonal patterns and functions of female song in Galapagos yellow warblers (Setophaga petechia aureola), in which females perform solo song and produce duets with their male social partners. We carried out simulated territory intrusions by broadcasting male, female, or duet songs during breeding and non-breeding seasons, and conducted a territory retention survey for over a year. We measured the association between aggressive response and singing behaviour, sex-specific patterns of response, and territory retention across years. Females sang mostly during the non-breeding season and predominantly in male-led duets. Although females were strongly aggressive towards female song playback, they gave the weakest singing response towards them. There was no association between female aggressive behaviour and song output in response to a simulated intruder. Moreover, the probability of territory retention across years was not explained by song output or aggression in response to intruders, though evidence for this was weak due to the small sample size. We suggest that female song in this year-round resident island system does not function for territory defense or intrasexual competition, but may have other functions. HighlightsO_LIGalapagos Yellow Warbler females produce solo songs and duets with their male partners. C_LIO_LIFemale song and aggression were mainly restricted to the non-breeding season. C_LIO_LIWhile females were equally aggressive to all intruders, they had the lowest song rate in response to females. C_LIO_LIIn contrast to males, aggressive behaviour didnt predict song output in females. C_LIO_LIFemale singing behaviour did not increase the probability of territory retention. C_LI

Behavioural variation is a hallmark of animal societies, which commonly contain breeders and nonbreeders, and helpers and nonhelpers. In some cases labour is divided with nonbreeders \"helping\" - gaining indirectly, via genetic benefits, or directly, e.g. by augmenting group size. Conversely, they may benefit by not helping, conserving energy for breeding later. However, subordinate behaviour after inheriting a breeding position is rarely evaluated.\n\nIn the Australian interior, Acacia thrips Dunatothrips aneurae (Thysanoptera) glue Acacia phyllodes together into \"domiciles\". Foundresses, usually sisters, build domiciles singly or communally. Some co-foundresses are nonreproductive, and their role is currently unknown. I experimentally rejected the idea that they substantially \"help\" by contributing to domicile repair. Nonreproductives were less likely to repair damage than reproductives. Alternatively, they may be waiting to inherit the domicile, or simply of too poor quality to reproduce or help. To test these alternatives, in the field, I allowed repairer or nonrepairer females to \"inherit\" a domicile by removing their nestmate(s). Thus isolated, \"nonrepairer\" females took much longer to repair domiciles than \"repairers\", control singletons or pairs. Although ovarian condition was equivalent across groups, after 21 days nonrepairers actually laid fewer eggs compared to other groups.\n\nThus, labour was not divided: instead reproduction and helping covaried, probably depending on female quality and the outcome of intra-domicile competition. Nonreproductive nonhelpers were not waiting to breed. Their role, and their net effect on colony productivity, remains to be shown. They are likely subfertile, and may make the \"best of a bad job\" by gaining indirect benefits to the best of their limited ability.

Songs play an important role in mate choice for many bird species. Females of some species prefer mates with song characteristics such as complexity, or with specific temporal or note features. In some species, females also prefer familiar songs, or songs that are acoustically similar to those of their fathers. These different aspects of songs may provide distinct information about the birds that produced those songs. For example, perceived familiarity may be a signal of local adaptation, locally relevant information or learned behaviours, or genetic compatibility, while song complexity may be a signal of overall genetic quality or ability to provide parental care. As a result, multiple axes of variation could influence female song preferences. We examined female preference for song familiarity and complexity using the Java sparrow (Lonchura oryzivora) as a model species. Females were presented with two pairs of song stimuli. In one pair one song was from the females father or from a social relative with an acoustically similar song and the other was unfamiliar. In the other pair the songs differed in two aspects of complexity: note repertoire and linearity. Females preferred their fathers songs over unfamiliar songs, but we did not find strong evidence that females generalized this preference to other socially related individuals. Females also preferred complex songs, specifically those with larger note repertoires and lower linearity. Our results suggest that female song preference in Java sparrows is multi-faceted, and females may obtain multiple kinds of information from male song.

Inter-individual recognition is crucial for stable social relationships and it is frequently mediated through vocal signatures. In socially complex species, recognition may additionally require additional levels corresponding to other layers of social organisation such as the pair, family, social group or colony. Additional vocal signatures may encode these different levels of social organisations for recognition. We investigated this hypothesis in the calls of the rook (Corvus frugilegus), a highly social corvid. Rooks form large breeding colonies where multiple pairs nest in clusters. We recorded the calls of five colonies located in France and in Great Britain, including both wild and captive colonies. To exclude variations due to different call types, we focused on the loud nest call produced exclusively by nesting females during the breeding season. We compared the acoustic distance of calls from each individual and between individuals at various levels of nest proximity, i.e. from the same nest cluster, from different nest clusters, from colonies within the same country, and from colonies in different countries. The only vocal signatures we found were at the individual level, but not at the nest cluster or colony level. This suggests a lack of vocal convergence in this species, at least for the nest call, which may be important for pair recognition in large colonies. Further studies should now evaluate if types of calls other than the nest call better carry vocal signatures as markers of different layers of sociality in this species, or if vocal divergence is a more general vocal phenomenon. In that case, applying new methods of monitoring vocal signatures in wild individuals should help understand the cognitive, social and environmental mechanisms underlying this vocal singularisation. 1. Significance statementInter-individual recognition is crucial for social relationships in animals, and is often mediated by individual-specific acoustic characteristics in vocalisations, called a vocal signature. High levels of social organisations, such as a social group of familiar conspecifics or a breeding colony, may likewise be signalled by vocal signatures shared by multiple individuals. We used machine-learning techniques to investigate vocal signatures at multiple social levels in the nest call of brooding female rooks, a corvid species that breeds colonially but lives year-round in social groups. We find evidence of a strong individual vocal signature, but no common vocal signature even in females that nest close together, or in the same colony. A strong individual vocal signature may be a potent tool to monitor populations in this species with minimal disturbance and minimal material, especially as corvids are frequently targeted by human-fauna conflicts in continental Europe.

Competitive interactions among conspecifics are often resolved by assessing signals that honestly indicate individual fighting ability or dominance. In territorial species, signals of competitive ability are thought to function primarily during the early stages of territory establishment, but recent evidence suggests that these signals continue to influence interactions with floaters and neighbors well after territory establishment. Here, we examine the influence of the extent of chest spotting displayed by an intruding male on the response of territorial male song sparrows. We exposed males to 3-D printed models with large or small spotting area coupled with conspecific playback and recorded their behavior. We also assessed the response of a subset of males to both the 3-D printed models and a traditional, taxidermic mount to ensure the 3-D models were a realistic stimulus. We found no differences in the number of attacks or proximity to the model due to spotting area. However, territorial males produced more soft songs and tended to sing fewer loud songs, both of which predict attack in our population, in response to the model with less chest spotting. One possibility is that males with less chest spotting elicit a stronger response because they are seen as a greater threat. Based on our previous findings in this system, we think it is more likely that models with less chest spotting are perceived as subordinate and therefore easier to defeat, leading to a stronger response by territory holders. We found males were equally likely to attack 3-D printed models and a taxidermic mount but signaled more aggressively during trials with the taxidermic mount than the 3-D printed models. This suggests that birds recognized the 3-D models as meaningful stimuli but that the use of 3-D printed models should be validated through comparison to a traditional taxidermic mount when possible.

Avian incubation is a highly complex, adjustable behavior essential to embryo development and survival. When incubating, parents face a tradeoff between investing in incubation to maintain optimal temperatures for egg development or in self-maintenance behaviors to ensure their own survival and future reproduction. Because nest ectoparasites are costly and can reduce nestling quality and survival, infections could shift parental investment in current vs. future offspring. However, it is not well understood whether birds change investment in incubation in response to nest ectoparasitism, particularly in the context of other factors that are known to influence incubation behavior, such as ambient temperature, clutch size, and embryo development. We hypothesized that parents could respond to nest parasites by 1) investing more in incubation to promote the development of high-quality offspring to help offset the cost of parasites, 2) investing less in incubation or even abandoning their nest during incubation to save resources for future reproduction, or 3) being unresponsive to parasite infections, as incubation is more constrained by other factors. We tested these hypotheses by experimentally removing and adding mites in barn swallow nests at the start of incubation and deploying thermocouple eggs to measure egg temperatures at one-minute intervals until hatching. We found that while ambient temperature, clutch initiation date, embryo age, and clutch size were the main factors driving variation in egg conditions and parental incubation behavior, parasitized nests had higher mean egg temperatures, which could aid in nestling immune development. However, despite more optimal developmental temperatures, eggs in parasitized nests also had lower hatching success. Our results indicate that incubation is a dynamic behavior that is largely driven by the constraints of maintaining appropriate egg temperatures for development. Although quite costly upon hatching, ectoparasites appear to play a relatively minor role in driving variation in parental incubation investment. LAY SUMMARYO_LIIncubation is a complex behavior shaped by both internal and external factors. C_LIO_LIEctoparasites often decrease quality and survival of nestlings and could influence investment in incubation because of tradeoffs in how parents spend energy. C_LIO_LIWe manipulated parasites in barn swallow nests and used fake eggs with temperature sensors to collect data on egg temperatures and parental behavior throughout incubation. C_LIO_LIWe found that other factors were the main drivers of variation in incubation behavior, but that eggs in parasite nests were warmer on average, which could help nestlings better cope with parasites upon hatching. C_LIO_LIDespite more optimal developmental temperatures, eggs in parasitized nests had lower hatching success. C_LIO_LIAlthough quite costly to nestlings, ectoparasites played a minor role in shaping parental incubation behavior. C_LI

American Crows (Corvus brachyrhynchos brachyrhynchos) are long-lived birds with pair bonds that may last many years. Pairs in Stillwater, OK, nested singly or in groups with up to 10 auxiliaries (Caffrey and Peterson 2015). Breeders did most of the nest building. Pair members contributed at approximately equal rates, although the sexes differed slightly in details: males tended to carry sticks and hand off materials more often, and females spent more time at and in nests. Both sexes worked faster on second and third attempts than on first attempts of the season. We found no evidence that pair members were (sexually) signaling to each other via their contributions. Incubation periods were characterized by low levels of activity at nests, where females spent most of their time and were fed once every 3-4 hours, mostly by their mates. Contributions to both stages of nesting by auxiliaries varied widely and exhibited no patterns with respect to any measured phenotypic characteristics.

Differential reproduction is a key driver of evolution that is determined by individual characteristics and mating opportunities, including mate choice. Social interactions between conspecifics are hypothesized to be important in facilitating mate choice and reproductive success but are difficult to measure. Using data from 52 adult barn swallows (Hirundo rustica erythrogaster), whose social interactions were measured via proximity tags, we tested the hypothesis that social interactions mediate the relationship between age (a proxy for experience) and condition-dependent plumage traits, and their associations with reproductive success. We found that older female barn swallows had higher fecundity and that older males have higher paternity. Older males achieved higher paternity through extra pair copulations, not by greater paternity with their social mate. Longer tail streamers were associated with greater fecundity/paternity in both sexes, but this effect was independent of age only among females. Darker ventral plumage coloration was not associated with higher reproductive success in either sex. We also observed that older birds appear to be less social with conspecifics, as indicated by fewer numbers of social interactions, though these associations were only marginally significant in males. Interestingly, females with fewer social interactions had higher fecundity. Finally, we found no evidence of mediation by the number of social interactions. Taken together, our results suggest that older, more experienced birds can produce more offspring while being less social.

In social species, maternal social relationships, in addition to direct care, impact offspring survival but much of what we know about these effects comes from studies of obligately social and cooperatively breeding species. Yellow-bellied marmots (Marmota flaviventer) are a facultatively social species whose social groups vary in composition, size, and cohesiveness. This natural variation in sociality and cooperative breeding behavior makes yellow-bellied marmots an ideal species within which to study the effects of maternal affiliative and agonistic social behavior on offspring. We used social network analysis to investigate the relationship between maternal social connectivity and integration on offspring summer and yearly survival, with the hypothesis that offspring with more affiliative mothers are more likely to survive than the offspring of more agonistic mothers. However, we found the inverse to be true: pups born to mothers who received more affiliative interactions were less likely to survive while the offspring of mothers who were more highly integrated into agonistic networks had enhanced survival. Overall, maternal social network measures were positively and negatively correlated with offspring survival, indicating that pups are influenced by their mothers social world, often in contradictory ways. Relative predation risk and colony location also mediated the effects of social relationships on pup survival. This study contributes to a small but growing body of work that demonstrates that specific attributes of sociality have specific consequences and that by adopting an attribute-focused view of sociality we are better able to understand how environmental conditions mediate the costs and benefits of sociality. Lay SummaryMaternal social relationships can impact offspring survival but much of what we know about these effects comes from studies of obligately social species. In faculatively social yellow-bellied marmots we found that pups born to mothers who received more affiliative interactions were less likely to survive while the offspring of mothers who were more highly integrated into agonistic networks had enhanced survival. Overall, pups are influenced by their mothers social world, often in contradictory ways.

When an organism explores a new environment or stimulus it varies its behavior to ensure proper sampling. As contingencies are learned, variance can give-way to routines and stereotypies. This phenomenon is common across species but has not been well studied in the social domain, in which the stimulus an animal investigates, another individual, may react negatively to unexpected behaviors. Here we investigate the effects of social familiarity on interaction variability in degus, female members of which are predisposed to form relationships with new, same-sex individuals. Degus were presented with a series of 20 minute, dyadic "reunion" sessions across days, interleaving exposures to familiar and unfamiliar same-sex conspecifics. We found that session-to-session variability in males was higher between strangers compared with cagemates, suggesting males may establish relationships by testing different social roles. In contrast, following an initial exposure, female strangers showed lower session-to-session change compared with cagemates, potentially establishing new relationships by maintaining behavioral norms. Social novelty did not appear to affect variability of interaction timing within a session. Given ecological pressures on female degus to form large, stable social networks, the data are consistent with the notion that higher behavioral variability across encounters is maladaptive for establishing cooperative peer relationships.

Females are traditionally presented as the choosier sex, selecting males based on the quality of their traits. Yet, there is increasing evidence that male mate choice is also important, even in species without male parental care. Social environment and learning are key factors in determining mate preference, and animals are able to use the information they gather from previous experience to potentially increase their odds of obtaining a high-quality mate. We examined how the social environment affects male mate choice in the guppy (Poecilia reticulata). We evaluated whether male guppies with previous social experience of female receptivity cues learn to prefer and adapt their behavioural repertoire towards females with higher receptiveness levels, as this represents an optimal use of time and energy and is more likely to result in insemination. For this, we measured sexual preference and behaviour for receptive females in no-choice and dichotomous choice tests using guppy males experienced or naive to female receptivity cues. Experience with receptivity cues did not change the strength of preference towards receptive females. However, male guppies that had previous experience with female receptivity cues adapted their mating tactic compared to naive males. The change in mating tactics but lack of preference towards receptive females shows that the influence of social learning is present but might be weaker than predicted in this species. Furthermore, these results provide further support to studies of female mate choice suggesting mating status is not a key factor driving the strength of sexual preferences in natural populations.

Natural disturbances like drought and wildfires are expected to increase in prevalence, so understanding how organisms are affected is a key goal for conservationists and biologists alike. While many studies have illustrated long-term effects of perturbations on survival and reproduction, little is known of short-term effects to physiology and sexual signal expression. Ornamental traits have been proposed as reliable indicators of environmental health, yet studies are lacking in the context of natural disturbances. Here we present short-term responses of male Red-backed Fairywrens (Malurus melanocephalus) to wildfire near the onset of the typical breeding season. Males of this species are characterized by plastic expression of sexual plumage phenotypes in their first breeding season. Using two populations with Fairywren captures before and after separate wildfires we illustrate that wildfire suppressed molt into ornamented plumage, including in third year males that typically show little plasticity in ornamentation. Baseline plasma corticosterone was elevated in males sampled after fire, but condition (furcular fat stores) was unaffected. Although testosterone levels did not decrease following fire, we found a positive correlation between testosterone and plumage ornamentation. In addition, males molting in ornamental plumage had higher circulating levels of testosterone than males molting in unornamented plumage following fire. Collectively, these findings suggest that wildfires inhibit or greatly delay acquisition of ornamentation in young males without exerting obvious effects on condition, but rather through subtle effects on testosterone and corticosterone circulation. This natural experiment also reveals that expression of alternative male reproductive phenotypes in this species is sensitive to environmental conditions and more plastic than previously assumed.

A key explanation for phenotypic plasticity is that changing behaviour to match conditions increases fitness. Affiliative social associations with conspecifics can be important for coping with challenging conditions, and therefore plasticity in social behaviour in response to environment variation may bring fitness benefits. Here we test the adaptive benefit of social plasticity by quantifying female bottlenose dolphins (Tursiops truncatus) plastic responses to salmon (Salmo salar) abundance and determine if either this plasticity or mean social behaviour is associated with calving success. We found that more gregarious females and those better connected to all parts of the entire social network had higher calving success, but plasticity in social behaviour in response to salmon abundance was not associated with this component of fitness. This lack of relationship may have arisen as salmon abundance in either current or previous years was not associated with the probability of producing a calf. We therefore demonstrate that being more social is positively associated with females calving success in our study population, but social plasticity itself is not associated with fitness benefits, questioning whether this is likely to be a mechanism for this population of dolphins to cope with challenging environmental conditions.

O_LIAnimal personality differences, i.e. consistent among-individual behavioural differences within populations, are prevalent across the animal kingdom. However, we are just beginning to understand the adaptive significance of the observed behavioural variation. We are particularly in need of empirical studies testing hypotheses of proposed theoretical frameworks aiming to understand the existence animal personality differences. In this study, we investigated a hypothesis derived from a framework suggesting that sexual selection may generate and maintain personality variation. The authors of this framework propose parental care as a mechanism linking animal personality and reproductive fitness. C_LIO_LIWe repeatedly measured individual boldness in male and female rainbow kribs, Pelvicachromis pulcher, a West African cichlid known for territorial cave breeding and shared parental care. We then formed 54 breeding pairs with varying behavioural contrasts in boldness. For pairs that produced offspring (N = 20), we repeatedly recorded parental care behaviour (parental boldness and brood guarding) of both parents over one month. Reproductive success was measured as the likelihood to reproduce, the number of offspring, and offspring size at the end of breeding. C_LIO_LIIn both sexes, we found consistent among-individual differences in boldness before breeding and in parental care behaviours. Bolder males were less likely to reproduce but, when breeding was successful, produced bigger broods compared to less bold males. Female parental boldness positively correlated with the number of offspring produced. However, individual boldness before breeding did not predict parental care behaviour in either sex and we found no effects of the pairs contrast in prebreeding boldness on parental care coordination or reproductive success. C_LIO_LIThe outcomes of our study may suggest that among-individual variation in male boldness is maintained by males with different behavioural types playing different reproductive strategies of equal average fitness. Future research should delve into understanding the intricate link between male boldness and reproductive success, exploring for instance underlying genetic mechanisms and interactions with environmental conditions. C_LI

In species where multiple breeding females co-reside in a social group, female-female competition may be particularly acute when many females have dependent young at the same time, with potential negative consequences for offspring survival. Here, we used more than four decades of data on wild baboons (Papio sp.) in Amboseli, Kenya, to examine the effects of early lactational synchrony (the proportion of females in a group with an infant <90 days old) on female-female agonistic interactions and infant survival. Because early lactation is energetically demanding for mothers and high-risk for infants, we expected both female-female aggression and protection by males to intensify during this period. In support, when early lactational synchrony was high, rates of female-female agonism increased. High-ranking females increased their time associating with adult males, while the time that low-ranking females associated with adult males decreased. Furthermore, high early lactational synchrony strongly predicted infant mortality, even though periods of high synchrony tended to be brief in duration in this nonseasonally breeding population. This association may result from both aggression among adult females and infanticidal behavior by peripubertal females. These findings provide novel evidence that synchronous reproduction alters competitive regimes and compromises reproductive outcomes even in nonseasonal breeders.

Major Histocompatibility Complex (MHC) polymorphism is maintained by balancing selection through host-pathogen interactions and mate choice. MHC-based mate choice has been proposed across a wide range of vertebrates. However, the likelihood of its existence in songbirds has been questioned because of their poorly developed olfactory sense, which is a trait considered crucial in pre-copulatory mate choice to determine both own MHC and the MHC of putative partners. In this study, we show that female reed warblers, Acrocephalus scirpaceus, with extra-pair young in their nests have a lower MHC class I (MHC-I) dissimilarity with their social mate than females without extra-pair young in their nests. We also show that the MHC-I dissimilarity of successfully siring extra-pair males is not different from that of either the other males with territories surrounding the social nest (i.e. putative extra-pair males) or the pairs without extra-pair young in their nests. Taken together with the observation that extra-pair mating in reed warblers is common, we argue that these results support a scenario where extra-pair mating is more likely to lead to successful fertilisation when there is a high similarity in MHC-I between the female and her social male. Furthermore, as our data suggest that extra-pair mating at random can result in a higher MHC-I dissimilarity this scenario does not require any active female mate choice for MHC-I dissimilar males to drive this pattern.