Mating duration and prolonged post-copulatory associations in Arrenurus water mites (Actinotrichida: Parasitengonina: Hydrachnidiae)

Abstract

Conflicts of interest between the sexes over control of mating can be reflected in various aspects of morphology and behaviour, including structure of genitalia and copulation duration. In Arrenurus water mites (Hydrachnidia: Arrenuridae) there are two main patterns of sperm transfer that differ in degree of potential male control of sperm uptake by females. In some species, males are equipped with an intromittent organ (the ‘petiole’) that is used to forcefully insert sperm into the female reproductive tract. In others, males lack an intromittent organ and females appear to push sperm into their reproductive opening themselves. Theory suggests that the amount of time spent in courtship after sperm transfer should differ between males with and without an intromittent structure. We predicted that male Arrenurus able to push sperm into the female’s reproductive tract (petiolate males) should spend less time courting females after transferring sperm than apetiolate males, which may have to ‘convince’ females to take up their sperm. Here, we examined durations of mating for 10 species of Arrenurus with males that differ in genital morphology: six species with males equipped with a well developed petiole (= ‘petiolate’ species) and four species with males that either completely lack a petiole or have a minute peg-like petiole that does not appear to function as an intromittent organ (= ‘apetiolate’ species). We tested whether males of petiolate species spend less time in the stage of courtship that takes place after sperm transfer (= ‘post-transfer courtship’) than apetiolate males. In contrast to our prediction, we found that species with well developed petioles spent significantly more time in post-transfer behaviours than species lacking petioles. The possible function of protracted post-transfer courtship in the genus Arrenurus is discussed.