Abstract
There have been many potential explanations put forward as to why polyandry often persists despite the multiple costs it can inflict on females. One such explanation is avoidance of costs associated with mating with genetically incompatible males. Genetic incompatibility can be thought of as a spectrum from individuals that are genetically too similar (inbreeding) to those that are too dissimilar (outbreeding or hybridization). Here we look for evidence that the level of outbreeding influences the benefits of polyandry in the seed bug Lygaeus equestris. Our system allows us to test for benefits of polyandry at levels of genetic similarity ranging from full siblings to heterospecifics, both in terms of egg production and hatching success. We found that while outbreeding level appeared to have no effect on fitness for intraspecific matings, and polyandry did not appear to result in any increase in fertility or fecundity, hybridization with a closely related species, Lygaeus simulans, carried considerable fitness costs. However, these costs could be rescued with a single mating to a conspecific. Thus, polyandry may be beneficial in populations that co-occur with closely related species and where there is reproductive interference. However, within-species genetic incompatibility is unlikely to be the driving force behind polyandry in this species. Furthermore, the mechanism underlying this rescue of fertility remains unclear as manipulation of male cuticular hydrocarbon profile, a possible mechanism by which females can assess male identity, had no effect on female offspring production.
Highlights
Mating is known to carry nontrivial costs for females, yet female polyandry is widespread in insects (Arnqvist and Nilsson 2000; Hosken and Stockley 2003; Pizzari and Wedell 2013; Simmons 2005)
We focused on the cost of hybridization when female L. equestris are paired with male L. simulans versus conspecific males
Mate number did not significantly affect the number of nymphs (F1, 305 = 2.24, P = 0.14) or eggs (F1, 305 = 0.89, P = 0.35) a female produced. Both measures were affected by outbreeding level (F3, 303 = 22.27, P < 0.0001 and F3, 303 = 11.21, P < 0.0001 for nymph and egg number, respectively), and this seems to be a result of lowered egg and nymph production in females mated to L. simulans males (Figures 1 and 2)
Summary
Mating is known to carry nontrivial costs for females, yet female polyandry is widespread in insects (Arnqvist and Nilsson 2000; Hosken and Stockley 2003; Pizzari and Wedell 2013; Simmons 2005). Female mating rate may be the result of conflict between the sexes over mating, shifting mating rate away from the (presumably low) female optima (Chapman et al 2003). One outcome of this is convenience polyandry, where females mate to mitigate the costs of harassment by males (good examples include water striders: Rowe et al 1994 and seaweed flies: Shuker and Day 2001; Thornhill and Alcock 1983). Females may receive benefits from mating more than once, which can be classified as either direct or indirect benefits
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