Reproductive Ecology of an Endangered Turtle in a Fragmented Landscape
Reproductive success is often difficult to ascertain in reptiles because of inconspicuous reproductive behaviors such as courtship that occurs in aquatic habitats and cryptic breeding outcomes such as multiple paternity and sperm storage. We corroborated field observations of mating behavior with genetic parentage analysis to assess the mating system and reproductive success in the rare Blanding's Turtle (Emydoidea blandingii) within a fragmented landscape in Will County, Illinois. During four consecutive years of radio-telemetry monitoring, we observed promiscuous mating behavior among males and females. Parentage was strongly skewed (one male sired 38% of 272 offspring) and multiple paternity was rare (11% of 28 clutches). Both males and females produced offspring with multiple individuals over the course of the study, but parentage did not always correspond with observed mating attempts; only 41% of male mating attempts observed in the field corresponded with sired offspring. For males, number of female mates inferred from paternity analysis was positively correlated with total number of offspring sired. No correlation was found between relatedness of observed mating pairs and hatching success. Repeat paternities in clutches were detected among years, with one confirmed instance of across-season sperm storage. High variation in reproductive success and low levels of multiple paternity in Blanding's Turtle in Will County compared to other areas may be attributed to habitat modification, small population size, and disruption of the mating system.
Map of northeastern Illinois and study area bordering the west side of Des Plaines River in Will County, Illinois. Inset shows the urban matrix surrounding the study area (sites Will 1 and Will 2). Map was created using ArcMap 10.1 (ESRI 2012. ArcGIS Desktop. Environmental Systems Research Institute, Redlands, CA).
Total number of unique mounting behavior (i.e., potential mating) observations of male–female pairs among eight male and 15 female E. blandingii during radio-telemetry surveys from 2006–2009 in Will County, Illinois. Mating attempts were considered successful (yes) if the observed pair parented a clutch during the nesting season following the observation. Observations are denoted by a “?” when mating success could not be determined because nests could not be located, transmitter failure, or clutches had 100% hatch failure. Mating success is denoted by “n/a” when females did not produce a clutch during the nesting season following a documented mating attempt that occurred in the preceding fall or spring.
Paternity assignment of 272 hatchling and 35 clutches produced by 16 female E. blandingii from 2007–2010 in Will County, Illinois. All offspring and clutches were assigned to eight telemetered and one unsampled male. Open bars represent clutches having single paternity (n = 28) and shaded bars represent clutches having multiple paternity (n = 3, among three males). Complete failure of embryo development precluded paternity assignment in four clutches.
Contributor Notes
Associate Editor: D. S. Siegel.