Multiple mating in a lizard increases fecundity but provides no evidence for genetic benefits

Multiple paternity is taxonomically widespread, yet the relative role of direct and indirect (genetic) fitness benefits in explaining the evolution of multiple mating is a topic of intense debate. We test whether female Eastern Water Skinks (Eulamprus quoyii) gain direct (fecundity) and/or indirect genetic (increased offspring fitness) benefits through multiple mating. We maintained 216 (108 males and 108 females) E. quoyii in 6 large outdoor enclosures for a single breeding season before bringing gravid females into the lab to give birth. We classified female clutches as being singly or multiply sired using 6 polymorphic microsatellite DNA loci. To test whether females gain genetic benefits, we measured 5 fitness traits on offspring over their first active season and compared these traits between single paternity and multiple paternity clutches. Contrary to predictions from genetic benefits models, offspring from multiple paternity and single paternity clutches did not differ significantly in snout–vent length, mass, growth rate, sprint speed, or endurance. Although multiple paternity and single paternity females did not differ significantly in body size, condition, or mass, multiple paternity females invested more heavily in reproduction when body size, mass, and condition were controlled, producing significantly more offspring compared with single paternity females. We suggest that polyandry in E. quoyii possibly evolved as a mechanism to ensure fertilization of ova, similar to what has been reported in some other taxa.