AGE ESTIMATION IN DESMOGNATHINE SALAMANDERS ASSESSED BY SKELETOCHRONOLOGY

Abstract

We analyzed lines of arrested growth (LAGs), presumably annual, in cross sections of the femoral diaphysis of three species of desmognathine salamanders from the southern Appa- lachian Mountains (Wolf Creek, Cowee Mountains, North Carolina). For 100 of 101 Desmognathus quadramaculatus of all size groups, including larvae, LAGs were clearly defined. In our sample, the largest larva showed three LAGs, confirming that in this population larvae may spend at least 3 yr before metamorphosis. There is no clear LAG linked to this event, but in adults some of the first LAGs may be resorbed, requiring a back calculation for the final age estimation. Growth reached a plateau at about 9 or 10 yr. The largest individual was at least 13 yr old. Taking into account the pattern of deposition of LAGs, we concluded that sexual maturity is not reached before 6 yr for males and 7-8 yr for females. In D. monticola, but especially in D. ochrophaeus, LAGs are more difficult to read. In both species, larvae spend one winter before metamorphosis, corre- sponding to one LAG in most of the smallest juveniles examined. No metamorphic LAG could be identified and no more than two LAGs had been resorbed in adults. Of 90 individuals of D. monticola, 83 were accurately aged. Growth reached a plateau at 7 or 8 yr and the oldest, a male, was 11 yr old. Although age of sexual maturity was not obvious from growth mark patterns, it was estimated to be at least 5 yr in males and 5-7 yr in females. For 76 of 87 individuals of D. ochrophaeus that could be aged reliably in our sample, the maximum age observed was 10 yr. Sexual maturity was estimated at 3-4 yr in males and 4-5 yr in females. Skeletochronology is more difficult to apply in Plethodontidae than in Salamandridae. Never- theless, in desmognathines, analysis of bone growth marks can be used to separate age groups; it is especially valuable for age mixtures of adults that overlap in body size, and it provides estimates of longevity in natural populations.