Validation and Application of Skeletochronology for Age Determination of the Ryukyu Ground Gecko,Goniurosaurus kuroiwae (Squamata: Eublepharidae)

Abstract

Skeletochronology is a method commonly used for estimating the age of amphibians and reptiles in the wild.However,the number of lines of arrested growth(LAGs)does not necessarily reflect age in some species.We validated the applicability of this method to an endangered eublepharid gecko,Goniurosaurus kuroiwae,then inferred its longevity and age structures in wild populations.We classified young geckos into three groups using previously published data for early growth:Group 1 contained hatchlings before the first winter,Group 2 contained hatchlings after the first winter,and Group 3 included yearlings after the second winter.LAG numbers in these groups were then compared.All individuals in Group 1 possessed a single LAG,which was considered as a hatching line.Most individuals in Groups 2and 3 possessed one and two additional LAGs,respectively(LAG1 and LAG2),corroborating the notion that LAGs are formed annually.A few geckos exhibited fewer LAGs than expected.Analysis of variations in LAG and marrow cavity diameter demonstrated that in animals with fewer LAGs,endosteal resorption or fusion of hatching line and LAG1had occurred.LAG2 was never lost by endosteal resorption and was identifiable by its diameter.Thus,the age of adult geckos could be determined by counting LAGs outward from LAG2.Application of this method to wild populations revealed that the longevity of this species is not less than 83 months,but that almost all individuals in fragmented habitats die before 50 months,suggesting lower population sustainability in such habitats.