Genetic markers substantiate long-term storage and utilization of sperm by female painted turtles

Most studies of genetic parentage in natural populations have been limited to a single breeding season or reproductive episode and, thus, provide only a snapshot of individuals' mating behaviours. Female turtles can store viable sperm in their reproductive tracts for as long as several years, but the extent to which this capacity is utilized in nature has remained unknown. Here, we employ microsatellite markers to assess genetic paternity in successive clutches of individually marked, free-ranging female painted turtles (Chrysemys picta) over a four year period. The genetic data from 113 clutches from this natural population demonstrate that most females (80.5%) remated each year and that each female generally used a single male's sperm to fertilize all clutches laid within a year. However, sperm usage among females varied considerably, and some females apparently used sperm that had been stored for up to three years to fertilize some or all eggs laid in consecutive nesting seasons. Thus, remating by females is not necessary for continued offspring production from a given sire. Furthermore, 13.2% of all clutches examined showed evidence of multiple paternity, and the genetic paternity patterns across years suggest a 'last in, first out' operation of the females' sperm storage tubules.