FEMALE RESISTANCE AND DURATION OF MATE-GUARDING IN 3 AQUATIC PERACARIDS (CRUSTACEA)

Both theoretical and empirical studies have treated mate-guarding in a quatic Crustacea purely as a male decision problem. However, male and female interests are rarely identical, as implied by observations of f emale resistance against guarding attempts. We tested experimentally t he occurrence of sexual conflict over guarding duration in three crust acean species: Idotea baltica, Asellus aquaticus (Isopoda), and Gammar us zaddachi (Amphipoda). Specifically, we manipulated, by osmotic stre ss or a neuromuscular blocking agent, the female's ability to resist g uarding attempts. Female manipulation, by both methods, roughly double d precopula duration in I. baltica (Figs. 1 and 2) showing that female resistance effectively diminishes guarding duration. However, in A. a quaticus and G. zaddachi female manipulation had no effect on guarding duration, which also was longer than in I. baltica (Fig. 2). This imp lies either that male and female interests are equal or that the confl ict is resolved according to the male interest in these species. The l ack of female resistance in such species allows long precopulatory gua rding. In I. baltica we also manipulated, by osmotic stress and by cli pping nails, male ability to hold the female. These treatments had no effect on guarding duration (Figs. 1 and 2). Male size tended to corre late positively with guarding duration in control groups, but not in f emale manipulation groups (Fig. 3). Thus, conflict is mainly resolved according to the female interest in I. baltica. Results in this specie s also suggest that female resistance selects for large male size. Con sequently, mechanisms of sexual selection may differ considerably betw een species with otherwise comparable mating patterns.