Juvenile Experience with Male Cues Triggers Cryptic Choice Mechanisms in Adult Female Redback Spiders

Female choice may be linked to population density if the expected encounter rates with potential mates affects choosiness (the energy and risk engaged to express mate preferences). Choosiness should covary with male availability, which could be assessed using the social cues available during development. We tested whether the exposure of juvenile females to cues of male density affected the mechanisms of choosiness of adult Latrodectus hasselti spiders in two experiments simulating natural contexts. The juvenile females were exposed to (1) volatile chemicals from two densities of adult males (airborne cues), and (2) tactile, vibrational and chemical cues from adult males or other females (cohabitation cues). As adults, the females mated readily, regardless of the treatment, but there was strong evidence for post-copulatory mechanisms of choosiness in females exposed to cues of high male availability. These included abbreviated matings (in both experiments), cannibalism of the males before the mating was complete (cohabitation), and, remarkably, a reduction in the successful placement of internal sperm plugs (cohabitation). These shifts decrease the likelihood that the first mate would monopolize paternity if the female chose to mate again. We conclude that female choosiness may impose a strong selection on males despite the high mating rates, and these effects can hinge on the cues of male availability detected by juveniles.

Costly mate preferences can promote reproductive isolation along ecological gradients

Species often replace each-other spatially along ecological or environmental gradients. In models of parapatric speciation driven by assortative mating, delayed mating when females are too choosy about mates has so far been ignored. Yet, this generates a cost of choosiness, which should cause direct sexual selection against female choosiness. In our spatially-explicit individual-based model, disruptive viability selection leads to divergence of an ecological trait in a population distributed along an ecological gradient. Additionally, female choosiness (following a ‘matching mating rule’ based on the same ecological trait) can evolve at the risk of delaying mating, and can limit gene flow between diverging populations. We show that, along ecological gradients, a cost of choosiness associated with delayed mating modifies the genotypic frequencies on which viability selection acts. This cost can even remove much of the viability selection acting indirectly against choosiness at the ends of the gradient, thereby favouring the evolution of strong choosiness. A cost of choosiness can therefore promote reproductive isolation in parapatry, depending on the characteristics of the ecological gradient.

Female choosiness and mating opportunities in the blood-sucking bug Rhodnius prolixus

We investigated the relationship between female choosiness and mating opportunities in the blood sucking bug Rhodnius prolixus. Rhodnius prolixus females exhibit active discrimination behaviour to male mating attempts which delays or prevents copulation. Female rejection behaviours can be beneficial if mating opportunities are readily available and the pool of males varies in their quality. Thus, the benefits of finding a better quality male may override the cost of rejecting a mating opportunity. Since the availability of mating opportunities is affected by the ratio of sexually active males to females, we randomly assigned focal pairs to arenas with a sex ratio biased toward males, females or without other individuals. More females exhibited rejection behaviour when conspecifics were present, however, no differences were found when the sex ratio was biased toward either males or females. We discuss possible explanations for these results and hypothesize about the adaptive function of female rejection behaviour.

Predator experience overrides learned aversion to heterospecifics in stickleback species pairs

Predation risk can alter female mating decisions because the costs of mate searching and selecting attractive mates increase when predators are present. In response to predators, females have been found to plastically adjust mate preference within species, but little is known about how predators alter sexual isolation and hybridization among species. We tested the effects of predator exposure on sexual isolation between benthic and limnetic threespine sticklebacks ( Gasterosteus spp.). Female discrimination against heterospecific mates was measured before and after females experienced a simulated attack by a trout predator or a control exposure to a harmless object. In the absence of predators, females showed increased aversion to heterospecifics over time. We found that predator exposure made females less discriminating and precluded this learned aversion to heterospecifics. Benthic and limnetic males differ in coloration, and predator exposure also affected sexual isolation by weakening female preferences for colourful males. Predator effects on sexual selection were also tested but predators had few effects on female choosiness among conspecific mates. Our results suggest that predation risk may disrupt the cognitive processes associated with mate choice and lead to fluctuations in the strength of sexual isolation between species.