Abstract
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.
Highlights
The female reproductive tract of many species is physiologically capable of storing viable sperm for varying periods of time following a copulation event (Howarth, 1974; Smith, 1984): typically a matter of days in mammals, weeks in many insects and birds, months in some salamanders, and, incredibly, several years in some snakes and turtles (Birkhead & Mùller, 1993; Galbraith, 1993; Palmer et al, 1998)
The suspicion of long-term sperm storage by female turtles originally came from observations that captive individuals maintained in isolation may continue to produce ospring long after contact with a male (Coker, 1920; Ewing, 1943), by hard criteria such outcomes alone cannot eliminate the possibility of parthenogenetic reproduction
One potential caveat to the latter conclusion is that consecutive clutches sired by the same male might register remating by the female with that individual, rather than the storage of his sperm for long periods in her reproductive tract
Summary
The female reproductive tract of many species is physiologically capable of storing viable sperm for varying periods of time following a copulation event (Howarth, 1974; Smith, 1984): typically a matter of days in mammals, weeks in many insects and birds, months in some salamanders, and, incredibly, several years in some snakes and turtles (Birkhead & Mùller, 1993; Galbraith, 1993; Palmer et al, 1998). The deduction that females are capable of utilizing long-stored sperm later was bolstered by the physical ®nding of sperm sequestered in oviduct tissue (Gist & Jones, 1989). Such observations do not reveal whether females in nature utilize long-stored sperm to fertilize their eggs, and if so, how often or under what circumstances. We employ microsatellite markers in conjunction with long-term ®eld observations to assess patterns of sperm utilization within and across four breeding seasons in a natural population of the painted turtle (Chrysemys picta), a species in which females have the potential to store sperm for long periods of time (Gist & Jones, 1989)
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