Christina Riehl

Fine‐scale genetic structure in animal populations can create opportunities for both kin‐directed co‐operation and kin competition. Knowledge of kinship is therefore key to understanding the selective pressures shaping sociality as well as the effects of social behaviour on local genetic structure. Here we investigate patterns of relatedness in compound nests of Palmchats Dulus dominicus , a co‐operatively breeding bird endemic to Hispaniola. Compound nests are large stick structures that contain separate nesting chambers attended by different breeding pairs and putative family groups (breeding pairs and non‐breeding helpers); nests are occupied and maintained year‐round. We captured and genetically sampled 102 Palmchats from 10 compound nests (range = 6–17 birds captured per nest) and genotyped them with 779 single‐nucleotide polymorphisms (SNPs). Both relatives and non‐relatives were associated with compound nests: the majority of dyads were unrelated, but some dyads were consistent with first‐ or second‐order kin relationships. Average genetic relatedness, although low, was higher within nests than between nests for all types of dyads (female–female, female–male and male–male). Patterns of spatial autocorrelation revealed no association between relatedness and distance between compound nests for either males or females. The population exhibited weak (though significant) overall genetic structuring as measured by F _ST , indicating that low levels of genetic variance within the population existed between compound nesting groups. However, we detected no significant patterns of isolation‐by‐distance nor significant differences between the sexes. Groups of Palmchats using compound nests appear to be composed of kin and non‐kin, suggesting that social nesting involves both direct and indirect fitness benefits.

Cooperatively breeding vertebrates typically live in family groups in which some offspring delay breeding and remain on the natal territory to help rear younger siblings. However, field studies find that helpers can have a neutral or even negative effect on the survival of their relatives. Why, then, do helpers remain, and why do parents tolerate them? Here, we use a kin selection approach to model the conditions under which tolerating helpers is adaptive to parents. Unlike previous models, we consider scenarios in which relatives compete for breeding opportunities in a saturated habitat. We show that kin competition is sufficient to favour tolerance of helpers, even when helpers decrease parental survival or fecundity. Helping is additionally favoured when delaying dispersal benefits the helper (either by decreasing the costs of dispersal or by increasing the chance of territory inheritance). This suggests that the division of reproduction in cooperative family groups can emerge for reasons unrelated to the effects of help itself, but the resulting society sets the stage for more elaborate forms of division of labour. Kin-based helping may therefore be adaptive not only because helpers are related to the brood whom they help, but also because delayed breeding reduces reproductive conflict among siblings. This article is part of the theme issue ‘Division of labour as a key driver of social evolution’.

Nest predation rates critically influence avian biodiversity and evolution. In the north temperate zone, increased nest failure along edges of forest fragments is hypothesized to play a major role in the disappearance of bird species from disturbed landscapes. However, we lack comprehensive syntheses from tropical latitudes, where biodiversity is highest and increasingly threatened by habitat fragmentation and disturbance. We assembled data from five decades of field studies across the global tropics (1,112 populations of 661 species) and used phylogenetic models to evaluate proposed predictors of nest success. We found significant effects of several traits, including adult body mass and nest architecture. Contrary to results from many temperate locations, anthropogenic habitat disruption did not consistently reduce nest success; in fact, raw nest success rates were lower in large tracts of primary forest than in disturbed or fragmented landscapes. Follow-up analyses within species, using a subset of 76 species for which we had estimates of nest survival in habitats with different levels of disruption, confirmed that neither disturbance nor fragmentation significantly influenced nest success. These results suggest that nest predation alone cannot explain observed declines in avian biodiversity in tropical forest fragments, raising new questions about the demographic processes that drive extinction in the tropics.

Referential signaling, a complex form of communication in which specific signals are associated with external referents, was once thought to be limited to primates. Recent research has documented referential signaling in several other cooperative taxa, predominantly in kin-based societies. Here, we show that greater anis, communally nesting birds that breed in nonkin groups, give one type of alarm call in response to aerial threats (flying raptors) and another to more general threats (nonaerial predators). Observational data show that anis give these calls in response to different classes of threats, and playback experiments in the field confirmed that the alarm calls alone are sufficient to elicit appropriate behavioral responses even in the absence of an actual threat. Genetic data on a subset of groups confirmed that breeding groups are composed of nonkin, suggesting that referential alarm calls are often given in situations when no genetic relatives are present. These results suggest that complex referential communication can occur in social groups composed of nonrelatives, despite the absence of kin-selected fitness benefits.

The frequency of extra‐pair paternity (EPP) varies widely across socially monogamous birds, but the proximate mechanisms driving this variation remain unclear. In this study, we tested two major factors hypothesized to influence extra‐pair mating – breeding density and genetic diversity – by comparing genetic mating patterns in two populations of black catbirds Melanoptila glabrirostris . This Neotropical songbird is endemic to the Yucatán Peninsula, including eastern Mexico, and its offshore islands. We sampled one mainland (Sian Ka'an Biosphere Reserve) and one island (Isla Cozumel) population and used single‐nucleotide polymorphisms (SNPs) to quantify heterozygosity and genetic parentage over two breeding seasons. Moderate levels of EPP occurred in both populations (9.5–35% of offspring and 17–45% of nests). Contrary to predictions, breeding density did not affect EPP: although breeding densities were much higher on the mainland than on the island, EPP rates did not differ between populations, and local breeding density was not correlated with EPP at individual nests. In contrast, partial support emerged for the hypothesis that genetic diversity influences EPP: extra‐pair offspring were more heterozygous than within‐pair offspring. However, the two populations did not differ in genetic diversity, and neither the heterozygosity of social fathers nor within‐pair relatedness predicted EPP. These results are consistent with recent comparative studies suggesting that breeding density is not a critical driver of EPP rates, and that not all tropical songbirds exhibit low rates of EPP.