Evaluation of spot patterns and carapace abnormalities of an Endangered freshwater turtle, Clemmys guttata, as a potential tool for population assignment

Lj Brown,Cm Davy

doi:10.3354/esr01120

Abstract

Many of the world’s contemporary species of turtle are extinct or threatened with extinction due to habitat loss, increases in anthropogenic sources of mortality, and poaching (illegal collection). The slow life-history strategy of most turtle species magnifies the effects of poaching because the loss of even a few mature individuals can impact population growth. Returning poached turtles to their population of origin, where possible, can mitigate these effects, but identifying the origin of these individuals can be challenging. We hypothesized that spot patterns might allow assignment of Endangered spotted turtlesClemmys guttatato their population of origin. We characterized and compared spot patterns from carapace photographs of 126 individuals from 10 sites. To explore other types of information these photographs might provide, we also documented carapacial scute abnormalities and quantified their association with genetic diversity and latitude. Spot pattern similarity was not higher within populations than among populations and did not accurately differentiate populations. Carapacial scute abnormalities occurred in 82% of turtles and were not correlated with estimates of neutral genetic diversity. Abnormalities were positively correlated with latitude, implicating thermal stress during the early stages of development in the generation of some scute deformities. However, this relationship became non-significant when line (scute seam) abnormalities were excluded from the data, suggesting a different primary cause for the more severe scute deformities. Further research should continue to investigate the drivers of these deformities, as monitoring shifts in the frequency of scute deformities may provide relevant information for conservation and recovery of endangered turtles.

Highlights

Effective management and conservation of wildlife populations require a sound knowledge of population demographics, which involves unique marking or identification of individuals within a population
We quantified the frequency of carapacial scute abnormalities at these sites. These abnormalities are partially determined by genetic factors but may provide a proxy for physiological stress experienced during egg development, so we explored their association with genetic diversity and latitude
Pairwise I3S Spot similarity scores based on spot patterns overlapped substantially between within-site and among-site comparisons (Fig. 3), indicating that spot pattern similarity assessed with the methods we applied cannot be used to reliably assign a spotted turtle to its site of origin

Summary

Introduction

Effective management and conservation of wildlife populations require a sound knowledge of population demographics, which involves unique marking or identification of individuals within a population. Occurring spot patterns have been used to successfully identify individuals of many taxa, including leopards Panthera pardus kotiya Facial or cranial scale patterns can be used to identify individual sea turtles If markings are either heritable or are driven by environmental variation, some may be population- or site-specific. Heritability and environmental effects of natural markings vary among taxa. Some aspects of spot patterns in giraffes Giraffa camelopardalis are partially heritable (Lee et al 2018), while natural markings of Andean bears Tremarctos ornatus are not related to kinship (i.e. not heritable; Van Horn et al 2015). If markings are reliably population- or site-specific (suggesting either heritability or environmental drivers of natural markings), they could be used to assign confiscated, illegally collected individuals to their populations of origin. Reinforcement of populations might improve the longterm conservation potential (IUCN 2000); if it can be determined that the preservation and welfare of existing wild populations of the species will not be harmed, the addition/return of individuals to an existing population of the same taxon could be a powerful conservation tool for these species

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Conclusion