Seasonality, body size, and maturation time in the neotropical grasshopper Sphenarium histrio across an altitudinal gradient

Abstract

AbstractIn insects, male mating success and female fecundity usually increase with body size. However, natural selection favors faster maturation, reducing the risk of pre‐reproductive death, when the reproductive season is short in habitats located at high altitudes or far from the equator. Also, if males that mature earlier than females under these conditions increase their mating opportunities, protandry may evolve in their populations. Nonetheless, as body size is strongly correlated with maturation time in insects, faster sexual maturation is reached at the expense of having a small body size. We analyzed the differences in adult body size of males and females of the grasshopper Sphenarium histrio Gerstaecker (Orthoptera: Pyrgomorphidae) in three sites across an altitudinal gradient in southern Mexico. We also evaluated the possibility of protandry in these sampling sites using a common garden experiment. Male and female grasshoppers collected from low altitude sites in the field and reared in the laboratory were larger than those from a high altitude, suggesting genetic differentiation. Grasshoppers from a high altitude hatched earlier, had a shorter development time, presented fewer instars, and were smaller than grasshoppers from the other sampling sites. Moreover, development time in the three sampling sites was shorter in males than in females, suggesting protandry. Interestingly, the males from the three sites showed similar growth rates, but the females from low and high altitudes, respectively, had the fastest and slowest growth rates. In general, the adaptive value of the evolution of protandry has been focused on males. However, it may be that the growth rates of females in these sites could modify the degree of protandry as a response to their risk of pre‐reproductive death and the potential benefits associated with multiple matings.