VARIATION, SEXUAL DIMORPHISM, AND MATURITY IN A QUEBEC POPULATION OF THE COMMON SNAPPING TURTLE, CHELYDRA SERPENTINA

Abstract

An analysis was made of a sample of 55 snapping turtles, Chelydra serpentina, from a single locality in southern Quebec. The variation studied is regarded as being representative of that of a single population of the species. Analysis of covariance was used in studying dimorphism in various measurements. Conclusions reached are: (a) the sex ratio is one; (b) males grow to a larger size than females; (c) males and females become mature at a carapace length of about 200 millimeters; (d) the ratio precloacal distance over posterior lobe of the plastron gives a practical index for sex determination in adults; (e) there is a set of small but interrelated changes correlated with a greater precloacal distance in the male: These are that males have the plastron shifted forward slightly, have the bridge slightly longer relative to plastron length, and have the posterior lobe of the plastron slightly shorter relative to plastron length; (f) the precloacal length of the male (which area accommodates the penis) grows relatively faster than carapace length; the precloacal length of the female grows at the same relative rate as carapace length; (g) there is virtually no dimorphism in shell dimensions nor in head width.