Determinants of Natural Mating Success in the Cannibalistic Orb-Web Spider Argiope bruennichi

Stefanie M Zimmer,Klaas W Welke,Jutta M Schneider,Stephen R Proulx

doi:10.1371/journal.pone.0031389

Stefanie M Zimmer, Klaas W Welke + Show 2 more

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https://doi.org/10.1371/journal.pone.0031389

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Journal: PloS one	Publication Date: Feb 3, 2012
Citations: 68	License type: CC BY 4.0

Affiliation: Universität Hamburg, Museum am Rothenbaum

Abstract

Monogynous mating systems (low male mating rates) occur in various taxa and have evolved several times independently in spiders. Monogyny is associated with remarkable male mating strategies and predicted to evolve under a male-biased sex ratio. While male reproductive strategies are well documented and male mating rates are easy to quantify, especially in sexually cannibalistic species, female reproductive strategies, the optimal female mating rate, and the factors that affect the evolution of female mating rates are still unclear. In this study, we examined natural female mating rates and tested the assumption of a male-biased sex ratio and female polyandry in a natural population of Argiope bruennichi in which we controlled female mating status prior to observations. We predicted variation in female mating frequencies as a result of spatial and temporal heterogeneity in the distribution of mature females and males. Females had a low average mating rate of 1.3 and the majority copulated only once. Polyandry did not entirely result from a male-biased sex-ratio but closely matched the rate of male bigamy. Male activity and the probability of polyandry correlated with factors affecting pheromone presence such as virgin females' density. We conclude that a strong sex ratio bias and high female mating rates are not necessary components of monogynous mating systems as long as males protect their paternity effectively and certain frequencies of bigyny stabilise the mating system.

Highlights

Polyandry is a common phenomenon and requires an explanation as females in many species accept diverse costs of mating to gain more and/or more diverse sperm than required to fertilise their eggs [1]
Optimal female mating rates should not be seen as fixed optima but as varying with different contexts e.g. defined by the degree of sexual conflict [2]
Because A. bruennichi males may use either one or both of their pedipalps with the same female, we distinguish a female’s mating rate from her copulation rate

Summary

Introduction

Polyandry is a common phenomenon and requires an explanation as females in many species accept diverse costs of mating to gain more and/or more diverse sperm than required to fertilise their eggs [1]. It is assumed that benefits and costs of mating vary in magnitude, depending on how often a female mates [2]. Optimal female mating rates are likely to balance various costs and benefits of mating but natural mating rates will reflect trade-offs between the degrees of competition, conflict, and cooperation within and between the sexes [2]. Optimal female mating rates should not be seen as fixed optima but as varying with different contexts e.g. defined by the degree of sexual conflict [2]. Females will be under selection to develop adaptations that reduce the costs of mating and shift the female mating rate back towards its optimum [10]

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Conclusion