Body Size and Age in Amphibians and Reptiles

Abstract

We question the widespread assumption that body size and age are strongly correlated in adult amphibians and reptiles. Data for the smooth newt (Triturus vulgaris) suggest that growth rate prior to the age of first breeding is a much more significant source of variance in body size than age. A review of the data available for amphibians and reptiles suggests that this is true for the majority of species. Four methods for determining age are discussed and we conclude that only two of them, skeletochronology and mark-recapture, are reliable. We argue that female choice in anurans that favours larger males may not, as has frequently been suggested, mean that females mate with older males, but with males that have shown rapid juvenile growth. It is widely assumed that amphibians and reptiles show indeterminate growth and that body size and age are therefore posi- tively correlated (Duellman and Trueb, 1985). This assumption has formed the ba- sis of various evolutionary hypotheses, for example, that, if female anurans show a mating preference for larger males, they will mate with older males whose ability to survive a long time may have some her- itable basis (Howard, 1978; Halliday, 1983a, b; Duellman and Trueb, 1985). In this pa- per, we review the evidence that body size and age are correlated in adult amphibians and reptiles, critically evaluate four meth- ods that have been used to estimate age, and discuss the extent to which hypotheses that assume a size-age correlation are ten- able.