Body Size, Growth, and Longevity in Northern Map Turtles (Graptemys geographica) in Indiana
Body size, growth, and longevity in Northern Map Turtles (Graptemys geographica) from Dewart Lake in northern Indiana were studied from 1979 to 2016. Based on captures of 214 males (72 recaptures) and 99 females (40 recaptures), we generated von Bertalanffy growth equations which corroborated our growth curves based on counts of plastral growth rings and recaptured turtles. Females diverge from males in their faster growth by the end of their second season. Our oldest females were only 18–20 seasons old, and the oldest males were only 13–15 seasons old, suggesting a short generation time and a possible sexual difference in longevity. For the species, we detected no latitudinal pattern of size or age at maturity but found some support for a latitudinal increase in body size in accordance with Bergmann's Rule.Abstract
Relationships of carapacial growth rate (GR; mm/yr) to mean carapace length (CL in mm) at first and last capture for Graptemys geographica in Dewart Lake, Indiana. Solid dots for carapace lengths <65 mm are unsexed 2-yr-old juveniles included in both regression calculations; some solid dots represent male and female turtles with identical data. For 63 males and 77 2-yr-old juveniles, GR = 48.065–0.447CL (n = 140; r = 0.88; P < 0.0001; 95% confidence intervals for slope = −0.41 to −0.49). For 34 females and 77 2-yr-old juveniles, GR = 33.707–0.130 CL (n = 111; r = 0.82; P < 0.0001; 95% confidence intervals for slope = −0.11 to −0.15).
Estimated growth curves for Graptemys geographica at Dewart Lake, Indiana based on von Bertalanffy growth model analyses and records based on recaptures of turtles first captured and aged as juveniles or subadults. Age (t) is plotted in seasons of growth after emergence from the nest. The von Bertalanffy curve (dotted lines) for males and unsexed juveniles (lower curve) was CL (in mm) = 107.5(1–0.724e−0.447t) and for females and unsexed juveniles (upper curve) it was CL (in mm) = 259.3(1–0.885e−0.130t). Unsexed aged turtles are not plotted.
Latitudinal variation in mean maximum carapace length (filled circles, in mm) and mean maximum plastron length (open circles, in mm) for adult females across populations of Graptemys geographica (see Table 1). Excluding the Maryland data, least squares regression lines are plotted and both are significant at P < 0.05 (see Table 2 and Results).
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