An examination of competitive gametic isolation mechanisms between the damselflies Ischnura graellsii and I. elegans

Abstract

Recent findings suggest that postmating prezygotic isolation (i.e. gametic barriers) could be an important factor preventing hybrid formation. Competitive gametic barriers emerge when a female is inseminated by a conspecific and a heterospecific male. We examined whether sperm proportions after double matings and copulation duration impede hybrid formation. For this, we used females of Ischnura graellsii that mated with one conspecific and one heterospecific (I. elegans) male and vice versa, and calculated paternity of the second male by using RFLPs. Values of paternity (although preliminary because of a small sample size) suggest no bias in paternity towards conspecific males. However, proportion of sperm stored in the bursa and spermatheca of the female was biased towards the conspecific male when the heterospecific male was the first male, while copulation duration did not differ between conspecific and heterospecific males. Our results suggest that the relative sperm volumes may play a role as a gametic barrier in this species. However, cryptic female choice mediated by the preferential use of the conspecific sperm, although not detected, could not be discarded owing to small sample sizes in some cases.

Keywords: prezygotic barriers, competitive gametic mechanisms, paternity, RFLPs, copulation duration, sperm volumes, ischnurines

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