'Failure to launch': Is there a reproductive cost to males living at home?

Abstract

Differential reproductive success commonly reflects variations in reproductive physiology, behavior, and morphology. In some species, competition among males results in the evolution of alternative reproductive tactics that confer a fitness advantage relating to social status, density, or myriad other factors. In the Cape ground squirrel (Xerus inauris), a species that is highly competitive but lacks typical mammalian aspects of intrasexual competition (e.g., territoriality and aggression), 2 alternative reproductive tactics occur relating to dispersal. While physiological and behavioral differences have been demonstrated between dispersed males and males that delay dispersal, we used microsatellite markers to quantify variations in reproductive success between tactics. We found dispersed males are in better body condition with larger home ranges likely allowing greater encounter frequencies with estrous females. However, we found no difference in copulation frequency between tactics and the decision to delay dispersal does not preclude reproduction. Over 70% of males did not sire any offspring yet the average number of offspring sired was equal between tactics. Thus, all males are equally likely of copulating but paternity is strongly skewed towards a few males regardless of tactic. Natal philopatry may be a condition-dependent tactic that does not reduce reproductive success.