Female Reproductive Cycle and Sexual Con~ict over Precopulatory Mate!guarding in Thermosphaeroma "Crustacea\ Isopoda#

In species with time!limited opportunities for insemination\ precopulatory mate!guarding is expected to coevolve with the duration of female reproductive cycles[ Despite this adaptation to female characteristics\ it may also be advan! tageous for males to adjust the duration of guarding with respect to sex ratio because the bene_ts of guarding are dependent on the availability of females[ If female _tness is reduced because of guarding\ male guarding behavior leads to intersexual con~ict[ We studied these aspects of male mate!guarding behavior in two closely related\ thermal!spring isopods "Thermosphaeroma#[ First\ guarding duration showed species speci_city which was related to the duration of repro! ductive cycle^ cycle length for females and duration of guarding by males in T[ milleri were twice as long as in T[ thermophilum[ Second\ males in both species adjusted their guarding duration with sex ratio\ guarding longer when a competing male was present[ Third\ in T[ thermophilum\ ovarian development began immedi! ately after the birth of the previous brood and continued through guarding\ sexual molt and post!molt periods until oviposition\ whereas in T[ milleri\ ovarian devel! opment was largely postponed until the post!molt period[ Because guarding during ovary provisioning periods may be costly for females\ we tested the existence of intersexual con~ict over guarding duration in T[ thermophilum[ We compared the duration of guarding of control pairs with those of pairs in which either male guarding ability or female ability to resist guarding was reduced experimentally[ Guarding durations for manipulated and control males were equal\ but manipu! lated females were guarded longer\ suggesting that con~ict exists and that females can e}ectively shorten guarding duration by their behavior[ Moreover\ we suggest that selection in the context of intersexual con~ict may play an important role in the evolution of delayed oviposition and sperm!storage organs in mate!guarding