Abstract
In many species of insects, larvae are distributed in an aggregated fashion. As they may differ in size and size matters to predation risk, small larvae may be less likely to fall prey to predators when near large and therefore better-defended larvae. We hypothesize that the small larvae may profit even more when these large larvae are siblings. We tested this hypothesis on kinship-dependent survival in groups of larvae of the Western flower thrips (Frankliniella occidentalis) exposed to a predatory mite (Iphiseius degenerans). Our experiments showed that small larvae in sibling groups survive significantly better than in non-sibling groups, but only when such groups consisted of a mixture of small and large larvae. To test whether the survival effect we found is due to familiarity of thrips larvae growing up together (i.e. on one leaf), we also measured survival in sibling groups of larvae grown up on different leaves and in non-sibling groups of larvae grown up on the same leaf. These experiments showed an increased survival of small thrips larvae only in groups of sibling larvae from the same leaf. Non-sibling larvae did not show an increased survival when they come from the same leaf. Our results indicated that the increased survival in sibling groups was only partly due to the familiarity effect we tested. Growing up together did not return the same survival effect for non-siblings as it did for siblings. We conclude that growing up together is a necessary but not sufficient condition for discrimination in thrips larvae.
Highlights
Kin discrimination and its effects on fitness have been well studied in mammals (Silk 2002), birds (Komdeur and Hatchwell 1999), amphibians (Blaustein and Waldman 1992) and social insects (e.g. Queller and Strassmann 1998, but see Keller 1997)
Fellowes (1998) identified six behavioural elements in non-social arthropods that could be biased by relatedness: (1) resource exploitation, (2) sex allocation under local mate competition, (3) inbreeding, (4) cannibalism, (5) superparasitism and (6) aggregation when exposed to predation risk, which is the element of interest in this study
When first- and second-instar larvae were put together on a leaf disc with a predatory mite, the difference in survival of larvae between sibling and non-sibling groups was significant after 8 h (Fig. 1a, left panel; GLM deviance=4.2, df=1, p
Summary
Kin discrimination and its effects on fitness have been well studied in mammals (Silk 2002), birds (Komdeur and Hatchwell 1999), amphibians (Blaustein and Waldman 1992) and social insects (e.g. Queller and Strassmann 1998, but see Keller 1997). When presented with a predator model (stuffed badger), black-tailed prairie dogs call alarm more frequently when they are in groups with close genetic relatives than when they are in groups without (Hoogland 1983). In this way, kin discrimination serves to direct potentially beneficial behaviour towards relatives, rather than towards unrelated individuals. Some predators attack only the smallest individuals (Lima and Dill 1990) or individuals from a certain size range (Tonn et al 1992; Chase 1999). In the former case, smaller prey individuals can experience decreased predation risk in the vicinity of larger individuals because larger prey individuals may actively or
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