Sexual Selection in a Water Strider: The Function, Mechanism of Selection and Heritability of a Male Grasping Apparatus

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Abstract
Males of the water strider Gerris odontogaster have two abdominal ventral processes (MAPs) that provide a posterior attachment to females during mating. Females were reluctant to mate, and the MAPs were important for males to succeed in copulations. Low male mating success and absence of second male take-over attempts during mating, suggested the functional significance of the processes to be intersexual rather than intrasexual. The length of MAPs varied considerably in the studied population (range 0.08-0.22 mm, CV = 15.4%). Laboratory experiments showed that males with longer MAPs had a greater ability to endure females'' rejection behaviour than males with shorter MAPs. The mating and non-mating fractions of a natural population significantly differed in length of MAPs, thus indicating sexual selection in the field. The heritability of process length was high, contrary to what is predicted by classic quantitative genetic theory for important fitness traits.