Searching for mates may shape parental investment and immune response

A wide variety of strategies have emerged in different animal species for attracting mates. These strategies, such as chemical signals and calling songs, fuel competition for mates and can lead to the evolution of distinct courtship behaviours within a species. These behaviours often involve males and females taking on different roles in attracting mates. For example, limitations in signal production or perception can make one of the sexes sedentary. Regarding Poecilimon bushcrickets specifically, in 2012 McCartney et al. proposed a theory to explain sex role differentiation within the mate-searching system in certain species. According to this model, sex roles in mate-searching systems propose that in species where females search for males, females should receive a larger spermatophore gift. This study tests this theory for two Poecilimon species with differing strategies in terms of females’ response to male calling songs regarding spermatophore investment (P. sureyanus-female searching and P. inflatus-male searching). Given that reproductive effort and physiological activities are both costly for the organism, there is a trade-off due to limited energy resources. To investigate the specific trade-off in allocating resources between reproductive functions and immune defence in these species, the presents study compared two immune parameters (phenoloxidase and lytic activities). In nature, immune activities are much more plastic than the differentiation of reproductive traits between the sexes. The results showed that spermatophore investment may critically depend on differences in mate-searching strategies, particularly in terms of females’ response to male calling songs within the species. The findings also indicated that there may be trade-offs between the costs related to reproduction and the immune system.