Searching for mates may shape the immune response and parental investments

In the sexual reproduction model, a wide variety of strategies have emerged in different animal species for individuals to pursue the opposite sex for mating purposes. Many ways (such as chemical signals and calling songs) are utilized to stimulate or invite the other sex. This may lead to differential evolution of sexes in a species. For example, the limitations in signal production or perception of one of the sexes can make this sex sedentary, therefore strategies in pursuing mates evolve diversely among sexes. In this context, McCartney et al. (2012) proposed a theory to explain the differentiation of the mate-searching system in some species of Poecilimon bushcrickets and the reasons for the change in the sexual roles in the search. The aim of the present study was the testing of this theory proposed by McCartney et al. (2012) for Poecilimon species on spermatophore investment, with two species ( P. sureyanus -female searching and P. inflatus - male searching), which have different strategies in terms of females’ response to male calling songs. Reproductive effort and physiological activities are both costly for the organism, and these traits belie a trade-off due to the limited energetic resources. Therefore, some immune parameters (Phenoloxidase and lytic activities) of these two species were compared within the context of the allocation of resources resulting from the trade-off between reproductive functions and immune defence. Immune activities are much more plastic in nature than the differentiation of reproductive traits among sexes. The results of this study showed that a mate searching strategy difference, based on the female’s ability to respond to male call sounds -which must acoustically communicate for reproduction-may play a decisive role in both spermatophore and immune activities. On the other hand, the findings also indicated that there may be trade-offs between the costs related to reproduction and the immune system. In addition, it has been revealed that there may be a trade-off between the immune activities and the differences between sexes. On the other hand, our data indicated that the duration of morphogenesis did not have a decisive role on spermatophore and sperm allocation in bushcrickets.