Few studies have considered the reproductive biology and behaviour of turtles from the perspective of mating systems.  A few studies have demonstrated variation among males in home range structure, agonistic behaviours, and sexual size dimorphism, but have not determined the adaptive value of these traits.  During the last five years, considerable progress in paternity analysis among vertebrates has been made possible by the discovery of hypervariable minisatellite "fingerprint" loci.

In this study, samples of genomic DNA from 19 turtle species from seven families, probed with the Jeffreys 33.6 and 33.15 DNA probes, produced hypervariable patterns of the fingerprint type.  Segregation analysis of the fingerprint bands in clutches of snapping turtles (Chelydra serpentina) and wood turtles (Clemmys insculpta) confirmed that most fingerprint bands were independently segregating, but that a few bands were allelic or were parts of multi-fragment alleles.  Analysis of the sources of error in estimates of molecular weights of DNA fingerprint and RFLP bands indicated that the comparison of large numbers of offspring and males to detect fathers was possible.

Analysis of paternity by DNA fingerprinting was carried out among offspring from 10 clutches from a population of wood turtles.  Previous studies had found a linear dominance hierarchy among adult males in this population, in which rank is positively correlated with frequency of mating attempts and body size.  Of the 18 males known in the study area, seven fathered hatchlings in the 1989 nests.  A significant association was found between the dominance rank of the males and the number of offspring each had fathered, and almost all hatchlings were fathered by males in the upper half of the dominance hierarchy.  Multiple paternity was detected in several clutches of both snapping turtles and wood turtles.  The most dominant individuals may be attaining the majority of the successful reproductive attempts by being better able to complete copulation without being dislodged by rival males.

Multiple paternity was also detected within two of three clutches of snapping turtles sampled from known females in Algonquin Park, Ontario.  Long-term sperm storage and the potential for multiple matings in turtles indicates that sperm competition may be present, and that observation of copulatory behaviour is not sufficient to study male reproductive success.  Determination of paternity by use of genetic markers is necessary in such studies.

© David A. Galbraith  1991