How do sexual differences in growth and maturation interact to determine size in northern and southern painted turtles?
Widely distributed animals often show considerable differences in growth and maturation both between sexes and among populations. We compared growth and maturation between the sexes in the painted turtle (Chrysemys picta) at the northern limit of its range and related these differences to patterns observed in southern populations. In British Columbia, females grow faster and mature later than males, and as a consequence, are both larger and older than males at maturity. Northern individuals of both sexes show greater annual growth than populations farther south, despite a shorter growing season. Northern males may mature at a similar age to those in the south but northern females mature later than those in the south and this, coupled with faster growth, results in larger size at maturity. Because of constraints on the number of clutches that may be successfully incubated per year at a higher latitude, northern females reproduce at most once per year, whereas southern females can produce several clutches over a summer. Therefore, delayed maturity and faster growth may be favoured in northern females so that they may produce larger clutches at a necessarily lower annual frequency.