CORRELATES OF REPRODUCTIVE SUCCESS WITHIN ALTERNATIVE MATING TACTICS OF THE COMMON SHREW

Male common shrews (Sorer araneus) adopt two discrete mating tactics. The most successful males, in terms of number of offspring fathered, a re those that establish large overlapping home ranges in areas of high female density early in the breeding season. An alternative, less suc cessful mating tactic is to travel long distances in search of mating opportunities. This study is an investigation of correlates of reprodu ctive success for males adopting these different mating tactics. Repro ductive success under natural conditions was assessed using DNA finger printing, and survival of offspring was monitored in the field. The nu mber of offspring fathered by males with overlapping home ranges was p ositively correlated with the number of female ranges overlapped durin g the breeding season and with testes mass. The number of offspring fa thered by males that made long-distance movements was positively corre lated with their epididymal sperm counts. It is argued that competitiv ely superior (overlapping) males achieve high reproductive success by competing to maximize the number of females inseminated, whereas those adopting an alternative mating tactic instead compete largely via spe rm competition, aiming to maximize insemination success with any parti cular female. There was no significant difference in the fluctuating a symmetry (FA) of males adopting different mating tactics (FA was measu red as the difference in length of the paired lateral scent glands). F luctuating asymmetry was not related to the number of offspring father ed by males adopting either mating tactic, but was significantly corre lated with the proportion of male offspring fathered that survived to sexual maturity. Although apparently not correlated with mating succes s in this species, EA may reflect some aspect of genetic quality that affects offspring survival.