Body Size and Multiple Copulations in a Neotropical Grasshopper with an Extraordinary Mate-Guarding Duration

Abstract

After copulation, male grasshoppers of Sphenarium purpurascens (Orthoptera: Pyrgomorphidae) remain in a postinsemination association with their mate. A male can spend as many as 17 days mounted on a female. Guarding duration is related to both male and female body size and the female's mating history. Longest guarding durations were recorded at the middle of the reproductive season, when the probability of encounter between the sexes (sex ratio and population density) was decreasing, at the beginning of the associated dry season. These guardings were associated with large individuals of both sexes and with females that had more previous partners. Moreover, a positive association was found among guarding duration, female and male body size and age, and number of copulations performed by the males. Maybe males invest time and sperm in females as a function of the probability of sperm competition. Nevertheless, guarding may provide benefits to both sexes. Males may reduce the possibility of sperm competition, and females may obtain nutritional benefit for themselves or their offspring as a result of multiple copulations. Changes in male investment in guarding duration and number of copulations may be the result of physiological constraints related to seminal and/or sperm production. Moreover, guarding duration could be constrained by ecological factors such as a reduction of food availability associated with the beginning of the dry season.