Evolution of the scale and manner of brother competition in pollinating fig wasps

Abstract

Contest competition and male dispersal have evolved a number of times in pollinating fig wasps. Given their highly female-biased sex ratios and high relatedness between competing males, this phenomenon is surprising. Using a comparative approach, we found a significant association between high adult sex ratios (male:female), fighting and dispersal. We conclude that a relatively high proportion of males could have led to the evolution of fighting and to excess males that avoid kin conflict through dispersal. These wasps respond to increased competition between relatives by altering the scale at which they compete, but also by competing more intensely. In support of the new generation of kin selection models, we found that relatedness of competing males has no effect on the likelihood of fighting. Even so, selection at a higher hierarchical level has selected for dispersal and hence a larger scale at which competition occurs. We found that although the sex ratio gives a rough indication of the mating system it fails to be accurate at a finer scale. Ó

Sex ratio dependent dispersal when sex ratios vary between patches

“…On the other hand, in species where there is male dispersal, the fitness penalty of sex ratio variation will be reduced and sex ratios may become less precise (Greeff, 2002). This suggestion is supported by observations that pollinating fig wasps with dispersal have higher variance in their sex ratios (Greeff, 2002;Nelson and Greeff, 2009).…”

“…Therefore, dispersal by sons will not be sufficient to reduce LMC to a level that is optimal for the mother and she will still keep the number of sons produced low (Nelson and Greeff, 2009). Hamilton (1967) pointed out that for single mother patches his model predicts a sex ratio of zero, but in reality the mother should produce just enough sons to fertilize all her daughters.…”

“…One possible resolution to this excess of males could be that the surplus males disperse to other patches to avoid competition with their brothers (Van Valen, 1971;Hamilton and May, 1977; for reviews see Clobert et al, 2001;Ronce, 2007). Male dispersal has indeed been observed in species with local mate competition (Wrensch and Ebbert, 1993;Greeff et al, 2003;Peer and Taborsky, 2005;Nelson and Greeff, 2009). Here we ask if males will evolve to be more likely to disperse away from patches with higher sex ratios?…”

Reproductive strategies of two forms of flightless males in a non‐pollinating fig wasp under partial local mate competition

“…males fight using their mandibles and can kill each other. Their greater willingness to emerge from figs means that they are more likely to find themselves in situations where they will be fighting with unrelated males (Hamilton, 1979;Greeff, 1997;West et al, 2001), but evidence from pollinator fig wasps suggests that this is not linked to a greater likelihood of fighting (Nelson & Greeff, 2009). Dark males were produced in figs where other males were likely to be present, which may favour a willingness to fight over females, despite the lack of any relationship between combined brood sizes and overall sex ratios in the figs (Nelson & Greeff, 2009).…”

“…Reflecting this, the sex ratios of pollinators and internally ovipositing NPFW are typically female-biased and vary according to foundress number Raja et al, 2008;Song et al, 2008). Consequently, their sex ratios are typically much less femalebiased, a characteristic that may favour the development of fighting (Nelson & Greeff, 2009). Consequently, their sex ratios are typically much less femalebiased, a characteristic that may favour the development of fighting (Nelson & Greeff, 2009).…”