Communication under sexual selection hypotheses: challenging prospects for future studies under extreme sexual conflict

Diffuse resistance courtship in the scorpion Rhopalurus rochai (Scorpiones: Buthidae)

Male-female courtship signals are frequently subject to arms races, with patterns of behaviour evolving reciprocally to manipulate the reproductive output. Female resistance should be particularly effective when asymmetrical offspring care occurs under low and unpredictable resource distribution, because this would increase maternal costs. Our hypothesis is that under these conditions females will evolve diffuse mating strategies to avoid predictable exploitation by male optimal counter tactics. Mating in scorpions is a complex process, and female resistance occurs through specific behaviours. Here we focus on the scorpion Rhopalurus rochai that inhabits strongly unpredictable arid habitats. We find that courtship success does not rely on typical resistance and stimulatory patterns of behaviours. The screening for prospective partners occurs in the pre-dance phase. Network statistics reveal that unsuccessful courtships are characterised by reduced complexity of interactions, a result typical of non-additive interactions that introduce unpredictability in the network. Unpredictable female resistance reduces male control over female reproduction more effectively than resistance through specific behavioural tactics; it could be selected in cases of extreme parental investment asymmetry, particularly in the context of resource fluctuation, as in the scorpion R. rochai, that inhabits environments with characteristic climatic unpredictability. Female resistance through a diffuse process would function as an extremely efficient screening device. The establishment of diffuse female resistance courtship would preclude the evolution of simple/single male optimal behavioural patterns, and thus the male-female arms races would reach a more complex state, whereby varied and contextually dependent male strategies would be required to settle the reproductive game.

Communication during copulation in the sex-role reversed wolf spider Allocosa brasiliensis: Female shakes for soliciting new ejaculations?

Traditional studies on sexual communication have focused on the exchange of signals during courtship. However, communication between the sexes can also occur during or after copulation. Allocosa brasiliensis is a wolf spider that shows a reversal in typical sex roles and of the usual sexual size dimorphism expected for spiders. Females are smaller than males and they are the roving sex that initiates courtship. Occasional previous observations suggested that females performed body shaking behaviors during copulation. Our objective was to analyze if female body shaking is associated with male copulatory behavior in A. brasiliensis, and determine if this female behavior has a communicatory function in this species. For that purpose, we performed fine-scaled analysis of fifteen copulations under laboratory conditions. We video-recorded all the trials and looked for associations between female and male copulatory behaviors. The significant difference between the time before and after female shaking, in favor of the subsequent ejaculation is analyzed. We discuss if shaking could be acting as a signal to accelerate and motivate palpal insertion and ejaculation, and/or inhibiting male cannibalistic tendencies in this species.