CONFLICT BETWEEN SEXES IN THE WATER STRIDER GERRIS-LACUSTRIS - A TESTOF 2 HYPOTHESES FOR MALE GUARDING BEHAVIOR

We studied the effect of operational sex ratio on female reluctance an d male persistence to mate as well as on the length of copulation and postcopulatory guarding in Gen's lacustris by adding five surplus male s or females to the basin with a pair in tandem. In the control treatm ent, a pair alone was tested. According to the copulatory guarding hyp othesis (CGH), males should prolong mating and guard females in the pr esence of surplus males. According to the convenience polyandry hypoth esis (CPH), females should show lower levels of resistance to prolonge d mating in the presence of surplus males because the mating male prot ects the female against harassment from other males. As expected on th e basis of both the CGH and CPH, mating (copulation + guarding) averag ed longer in the male-biased treatment. The behavior of males and fema les during mating suggested that both hypotheses hold true: females sh owed less resistance to prolonged mating (as predicted from CPH), and male behavior suggested stronger efforts to stay on the female when su rplus males were present (as predicted from CGH). Comparisons of the t reatment with surplus females with the results from the mating pair wi thout surplus individuals suggested that the capabilities of water str iders in tandem to assess the sex of nearby nonmating striders are lim ited.