To harass or to respect: the economy of male persistence despite female refusal in a damselfly with scramble mate competition

Abstract

In sexual conflict, males are often thought to gain fitness benefits from harassing females over mating. Yet when harassment itself incurs costs to males and if alternative, receptive females are available in a local population, theory predicts that when confronted with a female refusal, a male’s choice of persisting or retreating is determined in part by the likelihood of achieving a mating. We tested that prediction in the damselfly Enallagma hageni, whose males compete by intense scramble competition, resulting in widespread mating harassment toward females, which have a high level of control over mating. Using captive individuals of E. hageni in outdoor insectaries, we quantified male persistence in mating after refusals by pre- and post-oviposition focal females whose egg content we quantified after observations. We documented a novel, context-dependent head-turning refusal signal of sexual non-receptivity, most often displayed in tandem pairs by post-oviposition females that typically carried few mature eggs for males to fertilize. Male persistence was less likely to result in mating with post-oviposition females compared with pre-oviposition females carrying a clutch of mature eggs. Accordingly, males were less likely to persist following refusal signals given by post-oviposition females, supporting the theoretical prediction. Compared with a refusal signal known as wing spread, head-turning was significantly more effective in deterring harassing males. Our results suggest that despite on-going sexual conflict over mating, cooperation benefits both sexes when females use the honest signal of non-receptivity because they carry few mature eggs that males could fertilize.

Sexual conflict and the evolution of monandry: The case of the damselfly Ischnura hastata (Odonata: Coenagrionidae) in the Galápagos Islands

“…This contrast with other odonates whose females accept to mate because the insistence of males is too costly for them, in a case of convenience polyandry (Cordero Rivera & Andrés, 2002). In another coenagrionid it has been recently shown that females use a head turn display to indicate non‐receptivity, and males were less likely to persist when females used this display (Xu & Fincke, 2022). In I. hastata female monogamy produces a scenario of extreme sexual conflict over mating rate, where males are very insistent, perhaps because their motivation to mate is very high once they have grasped a female, which is clearly a very unusual event in their life.…”