Reverse sex‐biased philopatry in a cooperative bird: genetic consequences and a social cause

Abstract

The genetic structure of a group or population of organisms can profoundly influence the potential for inbreeding and, through this, can affect both dispersal strategies and mating systems. We used estimates of genetic relatedness as well as likelihood-based methods to reconstruct social group composition and examine sex biases in dispersal in a Costa Rican population of white-throated magpie-jays (Calocitta formosa, Swainson 1827), one of the few birds suggested to have female-biased natal philopatry. We found that females within groups were more closely related than males, which is consistent with observational data indicating that males disperse upon maturity, whereas females tend to remain in their natal territories and act as helpers. In addition, males were generally unrelated to one another within groups, suggesting that males do not disperse with or towards relatives. Finally, within social groups, female helpers were less related to male than female breeders, suggesting greater male turnover within groups. This last result indicates that within the natal group, female offspring have more opportunities than males to mate with nonrelatives, which might help to explain the unusual pattern of female-biased philopatry and male-biased dispersal in this system. We suggest that the novel approach adopted here is likely to be particularly useful for short-term studies or those conducted on rare or difficult-to-observe species, as it allows one to establish general patterns of philopatry and genetic structure without the need for long-term monitoring of identifiable individuals.

The absence of sex-biased dispersal in the cooperatively breeding grey-crowned babbler

“…It is difficult to explain the absence of sex‐biased dispersal in grey‐crowned babblers when the phenomenon is so widespread among otherwise similar cooperatively breeding birds. The forces driving sex‐biased dispersal in cooperative birds and mammals are poorly understood (Berg et al. 2009).…”

The evolution of group dispersal with leaders and followers

“…We do not view the assumption that individuals in leader-follower relationships are related as restrictive because genetic relatedness has been shown to help facilitate the emergence of many types of social interactions and social organisations (McElreath and Boyd, 2007;Lukas et al, 2005). Consequently, while leader-follower relationships can occur among non-relatives, many (van Vugt, 2008;Schoof et al, 2009;Wikberg, 2012;Nichols et al, 2012;Yano, 2008;Berg et al, 2009;Mumme et al, 1988;Lewis et al, 2011;Andersson and Wallander, 2004;Hoppitt et al, 2008) (if not most) observed leader-follower behaviour has occurred between relatives. Therefore the general conclusions drawn from our model should still be applicable to a wide variety of animal species.…”

“…Despite this, little is known theoretically about the evolution of dispersal involving leader-follower relationships. It is standard in mathematical models to assume that dispersal occurs independently, but in many species dispersal occurs in groups of individuals that are often but not always related, and group dispersal is frequently initiated by a subset of individuals (Schoof et al, 2009;Wikberg, 2012;Nichols et al, 2012;Yano, 2008;Berg et al, 2009;Mumme et al, 1988;Lewis et al, 2011;Andersson and Wallander, 2004). The few models that incorporate the concept of group dispersal do not examine the emergence or maintenance of this biological phenomenon, nor do they assume the presence of leader-follower relationships (Gardner and West, 2006;Gardner et al, 2009;Nakamaru et al, 2014).…”

Multilocus phylogeography (mitochondrial, autosomal and Z-chromosomal loci) and genetic consequence of long-distance male dispersal in Black-throated tits (Aegithalos concinnus)

“…According to the breeding system hypothesis (Greenwood, 1980), cooperatively breeding birds with biparental care, a socially monogamous and a resource defense mating system should have female-biased dispersal pattern. Several cooperatively breeding birds are yet known to have the malebiased dispersal patterns, such as Brown jays (Cyanocorax morio) (Williams, 2000;Williams and Rabenold, 2005), Seychelles warblers (Acrocephalus sechellensis) (Richardson et al, 2002) and White-throated magpie-jays (Calocitta formosa) (Berg et al, 2009). Interestingly, a close relative to the Black-throated tits, the cooperatively breeding longtailed tits (Aegithalos caudatus) exhibit female dispersal (Sharp et al, 2011).…”