Relatedness and genetic structure in a socially polymorphic population of the spiderAnelosimus studiosus

Abstract

The evolution of sociality remains a challenge in evolutionary biology and a central question is whether association between kin is a critical factor favouring the evolution of cooperation. This study examines genetic structure of Anelosimus studiosus, a spider exhibiting polymorphic social behaviour. Two phenotypes have been identified: an 'asocial' phenotype with solitary female nests and a 'social' phenotype with multi-female/communal nests. To address the questions of whether these phenotypes are differentiated populations and whether cooperative individuals are closely related, we used microsatellites to analyse individuals from both communal and solitary nests. We found no evidence of differentiation between social and solitary samples, implying high rates of interbreeding. This is consistent with the hypothesis that these phenotypes coexist as a behavioural polymorphism within populations. Pairwise relatedness coefficients were used to test whether cooperating individuals are more closely related than expected by chance. Pairwise relatedness of females sharing communal webs averaged 0.25, the level expected for half-siblings and significantly more closely related than random pairs from the population. Solitary females collected at similar distances to the communal spider pairs were also more closely related than expected by chance (mean relatedness = 0.18), but less related than social pairs. These results imply that low dispersal contributes to increase likelihood of interaction between kin, but relatedness between social pairs is not explained by spatial structure alone. We propose that these phenotypes represent stages in the evolution of sociality, where viscous population structure creates opportunities for kin selection and cooperation is favoured under certain environmental conditions.

Similar patterns of frequency‐dependent selection on animal personalities emerge in three species of social spiders

“…policing behaviour, phenotype‐biased dispersal and selective cessation of reproduction) should be favoured for most or all colony constituents, regardless of their phenotypes. Moreover, the heritability of aggressiveness in these three species seems more dubious than in A. studiosus , given that within‐group relatedness is much lower in A. studiosus than other species of social spiders (Avilés, ; Smith et al ., ; Duncan et al ., ).…”

“…Within colonies, females vary in their aggressiveness where females exhibit one of two relatively discrete, temporally stable behaviour phenotypes: either a ‘docile’ or ‘aggressive’ type (Riechert & Jones, ; Pruitt et al ., ). These distinctions are highly heritable in at least some species, despite colonies being composed of related individuals (average relatedness = 0.25) (Duncan et al ., , ; Pruitt & Goodnight, ). Aggressive females are more aggressive in foraging, antipredator behaviour and mating and are more active than their docile counterparts (Pruitt et al ., , ).…”

Within-group behavioral variation promotes biased task performance and the emergence of a defensive caste in a social spider

“…Characteristically, social spider colonies cooperate in prey capture, web repair, and alloparental care, and colony members are highly related (e.g., r  ≈ 0.30 Anelosimus studiosus ) (Avilés 1997; Lubin and Bilde 2007; Duncan et al 2010). Despite the finding that colonies are commonly encumbered by a rich community of kleptoparasites and colony-level predators (typically heterospecific spiders, hereafter termed “foreign spiders”), few investigations have considered the role of colony defense for individual and colony-level fitness (but see Cangialosi 1990, 1991).…”

Maternal care and subsocial behaviour in spiders

“…Some degree of inbreeding is probably the norm in these species, and the effects of inbreeding are relatively minor (Bilde et al, 2005;Avilés & Bukowski, 2006) and may be entirely masked by the positive effects of cooperation (Avilés & Bukowski, 2006). studiosus (Furey, 1998;Duncan et al, 2010), Theridion grallator (Gillespie, 1990), Scytodes pallida (Li & Kuan, 2006), and St. tentoriicola (Ruch et al, 2009b). studiosus (Furey, 1998;Duncan et al, 2010), Theridion grallator (Gillespie, 1990), Scytodes pallida (Li & Kuan, 2006), and St. tentoriicola (Ruch et al, 2009b).…”