Spatial roost networks and resource selection of female wild turkeys

Wildlife demography is influenced by behavioural decisions, with sleep being a crucial avian behaviour. Avian species use roost sites to minimize thermoregulation costs, predation risk and enhance foraging efficiency. Sleep locations are often reused, forming networks within the home range. Our study, focusing on female eastern wild turkeys (Meleagris gallopavo silvestris) during the reproductive season, used social network analysis to quantify both roost site selection and network structure. We identified roost networks which were composed of a small percentage of hub roost sites connecting satellite roosts. Hub roosts were characterized by greater values of betweenness (β = 0.62, s.e. = 0.02), closeness (β = 0.59, s.e. = 0.03) and eigenvalue centrality (β = 1.15, s.e. = 0.05), indicating their importance as connectors and proximity to the network's functional centre. The probability of a roost being a hub increased significantly with greater eigenvalue centrality. Female wild turkeys consistently chose roost sites at lower elevations and with greater topographical ruggedness. Hub roost probability was higher near secondary roads and further from water. Our research highlights well-organized roost site networks around hub roosts, emphasizing the importance of further investigations into how these networks influence conspecific interactions, reproduction and resource utilization in wild turkeys.

Neurogenomic landscape associated with status-dependent cooperative behaviour

The neurogenomic mechanisms mediating male-male reproductive cooperative behaviours remain unknown. We leveraged extensive transcriptomic and behavioural data on a neotropical bird species (Pipra filicauda) that performs cooperative courtship displays to understand these mechanisms. In this species, the cooperative display is modulated by testosterone, which promotes cooperation in non-territorial birds, but suppresses cooperation in territory holders. We sought to understand the neurogenomic underpinnings of three related traits: social status, cooperative display behaviour and testosterone phenotype. To do this, we profiled gene expression in 10 brain nuclei spanning the social decision-making network (SDMN), and two key endocrine tissues that regulate social behaviour. We associated gene expression with each bird's behavioural and endocrine profile derived from 3 years of repeated measures taken from free-living birds in the Ecuadorian Amazon. We found distinct landscapes of constitutive gene expression were associated with social status, testosterone phenotype and cooperation, reflecting the modular organization and engagement of neuroendocrine tissues. Sex-steroid and neuropeptide signalling appeared to be important in mediating status-specific relationships between testosterone and cooperation, suggesting shared regulatory mechanisms with male aggressive and sexual behaviours. We also identified differentially regulated genes involved in cellular activity and synaptic potentiation, suggesting multiple mechanisms underpin these genomic states. Finally, we identified SDMN-wide gene expression differences between territorial and floater males that could form the basis of 'status-specific' neurophysiological phenotypes, potentially mediated by testosterone and growth hormone. Overall, our findings provide new, systems-level insights into the mechanisms of cooperative behaviour and suggest that differences in neurogenomic state are the basis for individual differences in social behaviour.

Benefits of living closer to kin vary by genealogical relationship in a territorial mammal

While cooperative interactions among kin are a key building block in the societies of group-living species, their importance for species with more variable social environments is unclear. North American red squirrels (Tamiasciurus hudsonicus) defend individual territories in dynamic neighbourhoods and are known to benefit from living among familiar conspecifics, but not relatives. However, kin-directed behaviours may be restricted to specific genealogical relationships or strongly mediated by geographical distance, masking their influence at broader scales. Using distance between territories as a proxy for the ability of individuals to interact, we estimated the influence of primary kin (parents, offspring, siblings) on the annual survival and reproductive success of red squirrels. This approach revealed associations between fitness and access to kin, but only for certain genealogical relationships and fitness components. For example, females had enhanced annual survival when living closer to their daughters, though the reverse was not true. Most surprising was the finding that males had higher annual reproductive success when living closer to their father, suggesting possible recognition and cooperation among fathers and sons. Together, these findings point to unexpected nuance in the fitness consequences of kinship dynamics for a species that is territorial and largely solitary.

Integrative Studies of Sexual Selection in Manakins, a Clade of Charismatic Tropical Birds

The neotropical manakins (family Pipridae) provide a great opportunity for integrative studies of sexual selection as nearly all of the 51 species are lek-breeding, an extreme form of polygyny, and highly sexually dimorphic both in appearance and behavior. Male courtship displays are often elaborate and include auditory cues, both vocal and mechanical, as well as visual elements. In addition, the displays are often extremely rapid, highly acrobatic, and, in some species, multiple males perform coordinated displays that form the basis of long-term coalitions. Male manakins also exhibit unique neuroendocrine, physiological, and anatomical adaptations to support the performance of these complex displays and the maintenance of their intricate social systems. The Manakin Genomics Research Coordination Network (Manakin RCN, https://www.manakinsrcn.org) has brought together researchers (many in this symposium and this issue) from across disciplines to address the implications of sexual selection on evolution, ecology, behavior, and physiology in manakins. The objective of this paper is to present some of the most pertinent and integrative manakin research as well as introducing the papers presented in this issue. The results discussed at the manakin symposium, part of the 2021 Society for Integrative and Comparative Biology Conference, highlight the remarkable genomic, behavioral, and physiological adaptations as well as the evolutionary causes and consequences of strong sexual selection pressures that are evident in manakins.

hiphop: Improved paternity assignment among close relatives using a simple exclusion method for biallelic markers

Assignment of parentage with molecular markers is most difficult when the true parents have close relatives in the adult population. Here, we present an efficient solution to that problem by extending simple exclusion approaches to parentage analysis with single nucleotide polymorphic markers (SNPs). We augmented the previously published homozygote opposite test (hot), which counts mismatches due to the offspring and candidate parent having different homozygous genotypes, with an additional test. In this case, parents homozygous for the same SNP are incompatible with heterozygous offspring (i.e., "Homozygous Identical Parents, Heterozygous Offspring are Precluded": hiphop). We tested this approach in a cooperatively breeding bird, the superb fairy-wren, Malurus cyaneus, where rates of extra-pair paternity are exceptionally high, and where paternity assignment is challenging because breeding males typically have first-order adult relatives in their neighbourhood. Combining the tests and conditioning on the maternal genotype with a set of 1376 autosomal SNPs always allowed us to distinguish a single most likely sire from his relatives, and also to identify cases where the true sire must have been unsampled. In contrast, if just the hot test was used, we failed to identify a single most-likely sire in 2.5% of cases. Resampling enabled us to create guidelines for the number of SNPs required when first-order relatives coexist in the mating pool. Our method, implemented in the R package hiphop, therefore provides unambiguous parentage assignments even in systems with complex social organisation. We also identified a suite of Z- and W-linked SNPs that always identified sex correctly.

Testosterone-mediated behaviour shapes the emergent properties of social networks

Social networks can vary in their organization and dynamics, with implications for ecological and evolutionary processes. Understanding the mechanisms that drive social network dynamics requires integrating individual-level biology with comparisons across multiple social networks. Testosterone is a key mediator of vertebrate social behaviour and can influence how individuals interact with social partners. Although the effects of testosterone on individual behaviour are well established, no study has examined whether hormone-mediated behaviour can scale up to shape the emergent properties of social networks. We investigated the relationship between testosterone and social network dynamics in the wire-tailed manakin, a lekking bird species in which male-male social interactions form complex social networks. We used an automated proximity system to longitudinally monitor several leks and we quantified the social network structure at each lek. Our analysis examines three emergent properties of the networks-social specialization (the extent to which a network is partitioned into exclusive partnerships), network stability (the overall persistence of partnerships through time) and behavioural assortment (the tendency for like to associate with like). All three properties are expected to promote the evolution of cooperation. As the predictor, we analysed the collective testosterone of males within each social network. Social networks that were composed of high-testosterone dominant males were less specialized, less stable and had more negative behavioural assortment, after accounting for other factors. These results support our main hypothesis that individual-level hormone physiology can predict group-level network dynamics. We also observed that larger leks with more interacting individuals had more positive behavioural assortment, suggesting that small groups may constrain the processes of homophily and behaviour-matching. Overall, these results provide evidence that hormone-mediated behaviour can shape the broader architecture of social groups. Groups with high average testosterone exhibit social network properties that are predicted to impede the evolution of cooperation.

Testosterone as a mediator of the tradeoff between cooperation and competition in the context of cooperative reproductive behaviors

Behavioral tradeoffs occur when the expression of one behavior detracts from the expression of another. Understanding the proximate mediators of behavioral tradeoffs is important as these tradeoffs can act as potential constraints on evolutionary responses to selection. Here, we describe the tradeoff between cooperation and competition faced by species that exhibit cooperative reproductive behaviors and propose that testosterone is a key hormonal mediator of the tradeoff. Cooperative reproductive behaviors occur when multiple individuals coordinate their efforts to gain a reproductive advantage over other individuals and/or those individuals attempting to reproduce in absence of cooperation. We propose that testosterone, a sex steroid known to mediate a number of physiological and behavioral actions associated with reproductive competition, is involved in mediating the tradeoff between cooperation and competition. To support this proposition, we first describe the importance of individual variation in behavior to the evolution of cooperative behaviors. We then describe how proximate mechanisms represent a prominent source of individual variation in social behaviors and highlight evidence suggesting testosterone mediates variation in cooperative behaviors. Two case studies in which the relationship between testosterone and cooperative behaviors have been investigated in detail are then summarized. Throughout we highlight the importance of studying individual variation to understand the mechanistic basis of behaviors, behavioral tradeoffs, and the evolution of cooperative reproductive behaviors more broadly.

Reciprocity and behavioral heterogeneity govern the stability of social networks

The dynamics of social networks can determine the transmission of information, the spread of diseases, and the evolution of behavior. Despite this broad importance, a general framework for predicting social network stability has not been proposed. Here we present longitudinal data on the social dynamics of a cooperative bird species, the wire-tailed manakin, to evaluate the potential causes of temporal network stability. We find that when partners interact less frequently and when social connectedness increases, the network is subsequently less stable. Social connectivity was also negatively associated with the temporal persistence of coalition partnerships on an annual timescale. This negative association between connectivity and stability was surprising, especially given that individual manakins who were more connected also had more stable partnerships. This apparent paradox arises from a within-individual behavioral trade-off between partnership quantity and quality. Crucially, this trade-off is easily masked by behavioral variation among individuals. Using a simulation, we show that these results are explained by a simple model that combines among-individual behavioral heterogeneity and reciprocity within the network. As social networks become more connected, individuals face a trade-off between partnership quantity and maintenance. This model also demonstrates how among-individual behavioral heterogeneity, a ubiquitous feature of natural societies, can improve social stability. Together, these findings provide unifying principles that are expected to govern diverse social systems.

Reduced cooperative behavior as a cost of high testosterone in a lekking passerine bird

Many studies have identified the reproductive benefits of cooperative behaviors, yet few have identified the mechanisms that underlie these behaviors. Mechanistic studies can inform our understanding of why some individuals are more or less cooperative, as well as identify the physiological constraints imposed upon the evolution of reproductive traits. Male wire-tailed manakins (Pipra filicauda) exhibit cooperative courtship behaviors and more cooperative territory holders have been shown to exhibit higher reproductive success. To begin to understand the proximate basis of cooperative display behaviors, we conducted both an observational study and an experimental study. Because coordinated courtship displays underlie this form of cooperation, our study also examined both the hormonal and social drivers of individual variation in courtship behavior more broadly (e.g., courtship display rates). Our observational study revealed that males with higher testosterone levels performed fewer cooperative display bouts. In addition, our experimental study demonstrated that the proportion of a male’s courtship displays that were cooperative decreased after being administered a testosterone-filled hormone implant. We found no relationship between an individual’s courtship display effort (i.e., display rate and time spent performing courtship displays) and circulating testosterone in either study. However, more cooperative males spent a greater proportion of time performing courtship displays than did less cooperative males, suggesting that testosterone may indirectly mediate courtship display behaviors by influencing a territory holder’s cooperative behavior. Overall, both our observational and experimental results suggest that reduced cooperative behavior is a cost of maintaining high levels of testosterone for territory-holding males.

Sampling baseline androgens in free-living passerines: Methodological considerations and solutions

Obtaining baseline hormone samples can be challenging because circulating hormone levels often change rapidly due to the acute stress of capture. Although field protocols are established for accurately sampling baseline glucocorticoid concentrations, fewer studies have examined how common sampling techniques affect androgens levels. Indeed, many studies focused on understanding the functional significance of baseline androgen levels use sampling methods known to activate the endocrine responses to stress. To understand how different field sampling protocols affect plasma androgen levels, we measured the androgen response to two types of capture stressors in a free-living tropical bird, the wire-tailed manakin (Pipra filicauda). First, we subjected males to a standardized capture and restraint protocol lasting either 15 or 30 min. Second, males were passively captured in nets that were filmed (to establish exact duration of time between capture and blood sampling) and checked every 30 min. The first study showed that circulating plasma androgen levels decreased significantly following both 15 and 30 min of restraint in a cloth bag, with a trend for the 30 min samples to be lower than the 15 min samples. Further, the change in androgen levels was dependent on an individual's initial androgen levels, with the individuals with the highest initial levels registering the largest declines. The results of the second study suggest that hanging in a mist net for extended periods of time also leads to a decrease in circulating androgen levels, but this effect was weaker than that of capture and restraint in a cloth bag. Our findings demonstrate that, overall, circulating androgen levels decrease in response to common sampling techniques; a finding that has important implications for studies measuring baseline androgen levels in free-living birds. Future studies should prioritize sampling individuals immediately upon removal from the mist net, as handling and restraint have a strong negative effect on circulating androgen levels. When constant monitoring of the mist net is not possible, investigators should use video cameras to record the amount of time an individual spends in the net prior to blood sampling and then statistically control for the effect of this variable in analyses.

Tales of testosterone: Advancing our understanding of environmental endocrinology through studies of neotropical birds

Studies of birds have greatly advanced our understanding of how testosterone modulates complex phenotypes, specifically its role in mediating male reproductive and associated behaviors. Yet most of the foundational studies have been limited to northern latitude breeding species despite the fact that they represent only a small fraction of worldwide avian diversity. In contrast, phylogenetic, life-history, and mating system diversity all reach their apex in neotropical avifauna and yet these birds, along with more southern latitude species, remain very poorly understood from an endocrine perspective. Despite the relatively limited previous work on taxa breeding in Central and South America, empirical findings have had a disproportionately large impact on our understanding of testosterone's role in everything from geographic variation to behavioral roles and neuroplasticity. Here, we synthesize how studies of neotropical breeding avifauna have advanced our understanding of how testosterone's actions can and are associated with the broad patterns of phenotypic diversity that we see in birds. In addition, we outline how these studies can be used individually or in a comparative context to address fundamental questions about the environmental endocrinology of testosterone and to understand the diversity of roles that testosterone plays in mediating behavioral variation, reproductive strategies, and associated life-history trade-offs.

Dynamic network partnerships and social contagion drive cooperation

Both reciprocity and positive assortment (like with like) are predicted to promote the evolution of cooperation, yet how partners influence each other's behaviour within dynamic networks is not well understood. One way to test this question is to partition phenotypic variation into differences among individuals in the expression of cooperative behaviour (the 'direct effect'), and plasticity within individuals in response to the social environment (the 'indirect effect'). A positive correlation between these two sources of variation, such that more cooperative individuals elicit others to cooperate, is predicted to facilitate social contagion and selection on cooperative behaviour. Testing this hypothesis is challenging, however, because it requires repeated measures of behaviour across a dynamic social landscape. Here, we use an automated data-logging system to quantify the behaviour of 179 wire-tailed manakins, birds that form cooperative male-male coalitions, and we use multiple-membership models to test the hypothesis that dynamic network partnerships shape within-individual variation in cooperative behaviour. Our results show strong positive correlations between a bird's own sociality and his estimated effect on his partners, consistent with the hypothesis that cooperation begets cooperation. These findings support the hypothesis that social contagion can facilitate selection for cooperative behaviour within social networks.

Climate, demography and lek stability in an Amazonian bird

Lekking is a rare, but iconic mating system where polygynous males aggregate and perform group displays to attract females. Existing theory postulates that demographic and environmental stability are required for lekking to be an evolutionarily viable reproductive strategy. However, we lack empirical tests for the hypotheses that lek stability is facilitated by age-specific variation in demographic rates, and by predictable, abundant resources. To address this knowledge gap, we use multistate models to examine how two demographic elements of lek stability-male survival and recruitment-vary with age, social status and phase of the El Niño Southern Oscillation (ENSO) in a Neotropical frugivorous bird, the wire-tailed manakin (Pipra filicauda). Our results show that demographic and environmental conditions were related to lek stability in the Ecuadorean Amazon. Apparent annual survival probability of territorial males was higher than that of non-territorial floaters, and recruitment probability increased as males progressed in an age-graded queue. Moreover, annual survival of territorial males and body condition of both floaters and territory holders were higher following years with El Niño conditions, associated with reduced rainfall and probably higher fruit production in the northern Neotropics, and lower after years with wet, La Niña conditions that predominated our study. Recruitment probabilities varied annually, independent of ENSO phase, and increased over our study period, but the annual mean number of territorial males per lek declined. Our results provide empirical support for hypothesized demographic and environmental drivers of lek dynamics. This study also suggests that climate-mediated changes in resource availability can affect demography and subsequent lek stability in a relatively buffered, lowland rainforest.

Inclusive fitness and sexual conflict: how population structure can modulate the battle of the sexes

Competition over reproductive opportunities among members of one sex often harms the opposite sex, creating a conflict of interest between individual males and females. Recently, this battle of the sexes has become a paradigm in the study of intersexual coevolution. Here, we review recent theoretical and empirical advances suggesting that - as in any scenario of intraspecific competition - selfishness (competitiveness) can be influenced by the genetic relatedness of competitors. When competitors are positively related (e.g. siblings), an individual may refrain from harming its competitor(s) and their mate(s) because this can improve the focal individual's inclusive fitness. These findings reveal that population genetic structure might be of paramount importance when studying the battle of the sexes. We conclude by identifying some new lines of research at the interface of sexual selection and social evolution.

Proximity data-loggers increase the quantity and quality of social network data

Social network analysis is an ideal quantitative tool for advancing our understanding of complex social behaviour. However, this approach is often limited by the challenges of accurately characterizing social structure and measuring network heterogeneity. Technological advances have facilitated the study of social networks, but to date, all such work has focused on large vertebrates. Here, we provide proof of concept for using proximity data-logging to quantify the frequency of social interactions, construct weighted networks and characterize variation in the social behaviour of a lek-breeding bird, the wire-tailed manakin, Pipra filicauda. Our results highlight how this approach can ameliorate the challenges of social network data collection and analysis by concurrently improving data quality and quantity.

Understanding testosterone variation in a tropical lek-breeding bird

Male reproductive coalitions, in which males cooperate to attract females, are a rare strategy among vertebrates. While some studies have investigated ultimate aspects of these relationships, little is known about the mechanistic role that hormones play in modulating cooperative behaviours. Here, we examined male testosterone variation in a tropical lekking bird, the wire-tailed manakin (Pipra filicauda), which exhibits cooperative male-male display coalitions. We found that testosterone levels in territorial males were comparable to those of temperate breeding birds, a surprising result given their environmental, social and reproductive dynamics. In addition, social status rather than plumage was a strong predictor of testosterone variation. Territorial males had significantly higher testosterone levels than did two other plumage classes of floater males, who do not hold territories. We hypothesize that testosterone variation plays an important role in the establishment of male dominance hierarchies (competition), while concurrently facilitating stable display partnerships (cooperation).