Abstract
Whereas some authors have proposed that sexual dimorphism in the immune response is fixed, others pose that it is dynamic and depends on diet. The aim of the present study was to explore the second hypothesis. Immunocompetence differences between females and males can be linked to resource availability. We tested this idea by providing a low or high quality diet to two groups of Gryllodes sigilatus during their developmental period. Then, at the adult phase half of each group was challenged with LPS from Serratia marcescens. The size, phenol oxidase (PO), and lytic activity were compared between groups according to diet, sex, and immune challenge. Results show that diet quality favor size in both sexes. However, the overall immune response did not seem to be significantly different based on diet, but instead on sex. Females showed greater phenol oxidase levels than males, but the opposite was found with lytic activity. Perhaps in G. sigillatus the differences in the pathogens commonly confronted by each sex in the distinct habitat of each could explain the differences on PO and lytic activity.
Highlights
The understanding of sexual dimorphism (SD) is one of the central challenges in evolutionary biology
Females showed greater phenol oxidase levels than males, but the opposite was found with lytic activity
Regarding sexual dimorphism (SD), some authors suggest that it is fixed, males being less immunocompetent than females [1, 5, 6], while others pose that it is dynamic and depends upon diet [10, 12]
Summary
The understanding of sexual dimorphism (SD) is one of the central challenges in evolutionary biology. The underlying physiological mechanism of this dimorphic resistance could be that females are more immunocompetent than males, implying SD in the immune response. To understand why females are more immunocompetent than males can be explained by two hypotheses: sexual selection [2, 5] and the immunocompetence handicap hypothesis [6]. The second hypothesis known as the immunocompetence handicap hypothesis considers that females invest in the immune response to favor longevity, which is positively correlated with fecundity [8]. The problem with the sexual selection and the immunocompetence handicap hypotheses is that there are some cases in which males are more immunocompetent than females and others in which no differences have been found between sexes [8]. In invertebrates, females seem not to be more immunocompetent or resistant
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