Influence of female cuticular hydrocarbon (CHC) profile on male courtship behavior in two hybridizing field crickets Gryllus firmus and Gryllus pennsylvanicus

Background The hybridizing field crickets, Gryllus firmus and Gryllus pennsylvanicus have several barriers that prevent gene flow between species. The behavioral pre-zygotic mating barrier, where males court conspecifics more intensely than heterospecifics, is important because by acting earlier in the life cycle it has the potential to prevent a larger fraction of hybridization. The mechanism behind such male mate preference is unknown. Here we investigate if the female cuticular hydrocarbon (CHC) profile could be the signal behind male courtship. Results While males of the two species display nearly identical CHC profiles, females have different, albeit overlapping profiles and some females (between 15 and 45%) of both species display a male-like profile distinct from profiles of typical females. We classified CHC females profile into three categories: G. firmus-like (F; including mainly G. firmus females), G. pennsylvanicus-like (P; including mainly G. pennsylvanicus females), and male-like (ML; including females of both species). Gryllus firmus males courted ML and F females more often and faster than they courted P females (p < 0.05). Gryllus pennsylvanicus males were slower to court than G. firmus males, but courted ML females more often (p < 0.05) than their own conspecific P females (no difference between P and F). Both males courted heterospecific ML females more often than other heterospecific females (p < 0.05, significant only for G. firmus males). Conclusions Our results suggest that male mate preference is at least partially informed by female CHC profile and that ML females elicit high courtship behavior in both species. Since ML females exist in both species and are preferred over other heterospecific females, it is likely that this female type is responsible for most hybrid offspring production.

Immunity, Sex and Parasites: Does Sex of Sand-Field Cricket (Gryllus firmus) Affect Immune Response to Eugregarine Parasites?

There is controversy about the effects gut-dwelling eugregarine parasites have on their invertebrate hosts. If crickets (Gryllus firmus) apportion resources to reproduction differently in males vs. females, then resources used to mount immune responses to parasites may also differ – especially if the parasites are pathogenic. I investigated the possible differences in immune response between male and female crickets and attempted to determine whether these differences are related to intensity of parasitic infection. To do this, pieces of nylon filament were implanted into the hemocoel of crickets which tested the immune response where hemocytes surround the filament (encapsulation). These responses were compared to intensity of parasitic infection. No statistically significant relationship between sex and melanisation, or sex and parasite load were found. I found that the duration of melanization was negatively correlated to parasite abundance and that there was a positive correlation between body size and parasite number. This result suggests the existence of a relationship between the parasite and host that could be conflicting with sexual selection theory, such as host manipulation by the parasite.