Inbreeding avoidance mechanisms: dispersal dynamics in cooperatively breeding southern pied babblers

Abstract

Summary1. Breeding with kin can reduce individual fitness through the deleterious effects of inbreeding depression. Inbreeding avoidance mechanisms are expected to have developed in most species, and especially in cooperatively breeding species where individuals may delay dispersal until long after sexual maturity. Such potential mechanisms include sex-biased dispersal and avoidance of kin known through associative learning. 2. The investigation of inbreeding avoidance through dispersal dynamics can be enhanced by combining fine-scale population genetic structure data with detailed behavioural observations of wild populations. 3. We investigate possible inbreeding avoidance in a wild population of cooperatively breeding southern pied babblers (Turdoides bicolor). A combination of genetic, geographic and observational data is used to examine fine-scale genetic structure, dispersal (including sex-biased dispersal) and inheritance of dominance in cooperatively breeding groups. 4. Unusually, sex-bias in dispersal distance does not occur. Rather, individuals appear to avoid inbreeding through two routes. First, through dispersal itself: although both males and females disperse locally, they move outside the range within which genetically similar individuals are usually found, going twice as far from natal groups as from non-natal groups. Second, through avoidance of familiar group members as mates: individuals inherit a dominant position in the natal group only when an unrelated breeding partner is present. 5. This study uses spatial genetic analyses to investigate inbreeding avoidance mechanisms in a cooperative breeder and shows that individuals of both sexes can avoid inbreeding through a dispersal distance mechanism. While it appears that dispersal allows most individuals to move beyond the range of closely related kin, matings may still occur between distant kin. Nevertheless, any costs of breeding with a distant relative may be outweighed by the benefits of local dispersal and the immense fitness gains available from attaining a breeding position.

Nepotism and subordinate tenure in a cooperative breeder

“…We suggest that dominant males gain indirect fitness benefits when their own relatives (sons and/or brothers) are nepotistically prioritized in the queue of males waiting in the 'safe haven' of the group for local dominance opportunities [16]. Nepotistic tolerance also allows related subordinate males to inherit the dominant position in the event that the dominant male dies, provided the dominant female is unrelated and the subordinate male is the oldest such male [8]. Tolerant dominant males may also improve their direct fitness because there is significantly greater territory overlap when neighbouring dominants are close kin [17].…”

“…Florida scrub jays, Aphelocoma coerulescens), subordinates lose nepotistic tolerance and are more likely to disperse [4,6,7]. On the other hand, when unrelated dominants provide adult subordinates with within-group breeding opportunities, sexual competition may result [1,8,9], increasing the likelihood of delayed dispersal (e.g. Seychelles warbler (Acrocephalus sechellensis) subordinate females [10]).…”

Natal Dispersal, Mating Patterns, and Inbreeding in the AntFormica exsecta

“…Increased dispersal distances per se are expected to counteract inbreeding as individuals are by chance less likely to encounter relatives further away from their natal site (Nelson-Flower et al 2012). We found no support for this in our study population, as neither an increase in distance between the natal colonies of parents, nor an increase in the natal dispersal distance of males or females resulted in less homozygous offspring.…”

Costly reproductive competition between females in a monogamous cooperatively breeding bird

“…A subordinate female could gain dominance in a non-natal group by aggressively overthrowing the dominant female [16]. Immigration of a new dominant male or female occurred when a breeding vacancy could not be inherited by a natal subordinate owing to inbreeding avoidance [15]. Potential breeding partners for adult subordinate females were determined through known group life histories (only unrelated males were considered to be potential partners [14,15]).…”

“…Immigration of a new dominant male or female occurred when a breeding vacancy could not be inherited by a natal subordinate owing to inbreeding avoidance [15]. Potential breeding partners for adult subordinate females were determined through known group life histories (only unrelated males were considered to be potential partners [14,15]). Rarely, young males or females immigrated into non-natal groups as subordinate helpers [14,16]; if adults, these subordinate females were included in the analyses as potential competitors.…”