Compensating for Small Body Size: The Reproductive Ecology of Southern Spotted Turtle (Clemmys guttata) Populations
Gradients in environmental conditions across a species' geographic distribution can drive variability in a variety of life history traits. In North American freshwater turtles, both body and clutch size have commonly been shown to vary latitudinally, and these two traits are often directly related, with larger individuals producing larger clutches. We studied the reproductive ecology in two Georgia populations of Spotted Turtles (Clemmys guttata) from 2016–2020 by attaching radio transmitters to female turtles during the breeding season. We x-rayed turtles to determine clutch sizes and used thread bobbins to locate nesting locations, allowing us to determine nest fates. Across all Spotted Turtle clutches (n = 41), mean clutch size was 2.1 (range: 1–4) eggs per clutch. Approximately 92% of individuals that we monitored produced at least one clutch during the breeding season, and we identified 16 instances of individuals producing more than one clutch in a single year, including six turtles triple clutching during 2018. We located 24 Spotted Turtle nests during the study, nine (37.5%) of which either hatched or partially hatched. The other nests were either depredated (41.7%), did not hatch due to infertility or environmental reasons (8.3%), or had an undetermined fate (12.5%). Our results indicate that annual reproductive output in southern Spotted Turtle populations can exceed that of northern populations where individuals produce a single larger clutch per reproductive season. Finally, opportunistic observations in Florida from 2014–2021 indicated that the reproductive season can begin over a month earlier than in southern Georgia, highlighting the variability in reproductive ecology even across a relatively short latitudinal distance.
Reproductive ecology was monitored in four Spotted Turtle (Clemmys guttata) populations spread across southeastern Georgia and northern Florida from 2014–2021 (A). In Georgia, female Spotted Turtles were tracked to nesting locations using a combination of radio telemetry and thread bobbins (B). Nests were laid in a variety of substrates, including loose soils and leaf litter, sphagnum moss clumps, and rotten logs, and female turtles failed to completely cover eggs on multiple occasions (C).
Clutch size by annual clutch number observed in two Spotted Turtle (Clemmys guttata) populations in southeastern Georgia from 2016–2020. White dots represent the mean clutch size, and gray dots indicate the actual clutch size measurements. Bars represent the 67th and 95th percentile of clutch sizes.
Timing of Spotted Turtle (Clemmys guttata) nesting events at two sites in Georgia during 2018 (above black line) and 2020 (below black line). The first time turtles were identified as gravid (determined by a combination of x-rays and palpation) is indicated by black circles.
Spotted Turtle (Clemmys guttata) nesting locations and approximate distance from normal activity areas to nesting locations from a population in southeastern Georgia. Nesting movements were defined by movements out of a turtle's normal activity area followed by nesting and immediate return to the normal activity area.
Contributor Notes
Associate Editor: D. S. Siegel.