Mating rates and their adaptive value in spiders of the genus Argiope

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A mating system is characterised by the number of mating partners per sex whereas the sex specific mating rates determine the degree of competition, conflict and cooperation within and between the sexes. Sexually cannibalistic spider species diverge from common systems because males are monogamous even through there is no paternal care. A theoretical model produced in my group showed that such a mating strategy can evolve under very specific conditions, including a male biased sex-ratio and polyandry. Polyandry is difficult to explain because females will generally not increase their reproductive output through accepting multiple partners and costly copulations. Models that explain the evolution of polyandry postulate direct, material benefits or indirect benefits e.g. through the possibility for females to cryptically select better or more compatible males. Aim of this proposal is to quantify the distribution of female mating rates in natural populations and determine the costs and benefits of multiple mating in the sexually cannibalistic spider Ar$iope bruennichi in field and laboratory experiments. We will measure and control for direct benefits but will focus on the indirect benefit via the possibility of post - copula to ry (cryptic) female choice of genetically superior or more compatible males. Cryptic mate choice has only rarely been demonstrated and its existence is frequently questioned. Argiope spiders are ideal model systems because of the males paired sperm-transfer organs that are used one at a time and the females paired sperm storage organs that, as a result of sexual cannibalism, are most often filled by different males. We are able to capitalise on our extensive knowledge of the reproductive biology of several Argiope species and preliminary results are very encouraging. Our research will further our understanding of the evolution of female mating rates and will be a valuable addition to the limited number of studies of post-copulatory mate choice.