Investigating the cause of same-sex sexual behaviour in Jamaican field crickets using mixed sex-pheromones

Sammanfattning

Same-sex sexual behaviours (SSB) are widespread in the animal kingdom, but their proximate and ultimate causes are still debated. A recent explanation, called the mating filter hypothesis, proposes that SSB results from having a broad mating filter, which means being permissive with what one regards as a potential mate. The hypothesis has been supported by a study showing SSB is condition-dependent male Pacific field crickets (Teleogryllus oceanicus). However, this hypothesis assumes that the proximate cause for SSB is inaccurate sex recognition, which is not yet known. Here I attempted to examine this assumption by investigating whether male Jamaican field crickets (Gryllus assimilis) in poor condition are less likely to court females when sex recognition cues are obscured. Male condition was manipulated through diet, and sex recognition cues were altered by extracting and reapplying male and female pheromones onto dead female crickets. Males were then exposed to live females and pheromone-manipulated females in behavioural trials. The sample size I achieved was limited, causing large uncertainties, and therefore estimates should be interpreted cautiously. In line with inaccurate sex recognition as a proximate cause for SSB, I found no evidence that mixed sex-pheromones affected either the likelihood or amount of male courtship. I also found no evidence for an interaction between diet and pheromone treatment, which does not support the prediction that males in poor condition become more selective when sex-recognition cues are unreliable. However, I found weak evidence that a low-quality diet made males less likely to court dead females despite not affecting courtship towards live females, which is in line with the mating filter hypothesis. Additionally, only males that courted a live female subsequently courted a mixed-pheromone female, suggesting that this behaviour is linked to normal mating motivation and providing some support for inaccurate sex-recognition as a proximate cause.