The utility of plastron shape for uncovering cryptic diversity in Hermann's tortoise

Abstract

Although a significant unexploited potential of the geometric morphometrics in taxonomy and systematics has been documented, only a few studies so far have focused on the utility of this method in the detection of population genetic structure in turtles. For the first time, we employed geometric morphometrics to explicitly analyse whether populations possessing divergent haplotypes evolved different patterns of plastral shape in any Testudo species using the Greek populations of Hermann's tortoise as a case study. To molecularly characterize the Greek populations of Testudo hermanni boettgeri used for plastron shape analyses, 12s rRNA gene of tortoises sampled from seven localities in Greece was sequenced. Three divergent haplotypes were observed, regionally corresponding to the north‐western (HI), south‐western (HII) and Peloponnese (HIII) areas of Greece. In both females and males, haplotypes HI and HII showed the lack of plastral shape divergence, but were both statistically significantly different relative to HIII found in Peloponnese. The Peloponnesian populations (HIII) had longer bridges and the wider and shorter anterior part of the plastron, relative to populations from the mainland Greece (HI and HII). Hence, both morphological and molecular markers suggested Peloponnese as a distinct lineage in relation to mainland populations. Finally, we consider geometric morphometrics as an efficient method to detect and characterize subtle interpopulation differences. Findings in this study have conservation applications as well, implying the presence of cryptic genetic and taxonomic diversity, and, thus, filling the crucial gap in the assessment of the conservation status of T. hermanni.

Morphological Divergence of Hermann’s Tortoise (Testudo hermanni boettgeri Mojsisovits, 1889) in Albania

“…The presence of allometric growth can affect growth rate and mortality or survival rates, which may affect their morphology. The allometric growth has been previously reported for different populations of Hermanni tortoises [ 26 , 39 , 53 ]. However, its effect on population divergence is limited based on both carapace and plastron shape analysis [ 26 , 53 ].…”

“…The allometric growth has been previously reported for different populations of Hermanni tortoises [ 26 , 39 , 53 ]. However, its effect on population divergence is limited based on both carapace and plastron shape analysis [ 26 , 53 ]. We did not examine the allometry of Hermanni tortoises of Albania in the present study.…”

The shell measurements that best describe sexual dimorphism in the spur-thighed tortoise <em>Testudo graeca</em> from Algeria

“…Although size-correction is not advisable in such cases (McCoy et al, 2006), the interaction "size:sex" has been seldom tested in tortoise literature (e.g. Carretero et al 2005;Djordjević et al 2011; although see Djurakic & Milankov, 2019). We, therefore, recommend the standardization of morphometric recording protocols and analytical procedures to generate comparable data and results among research groups.…”

A practical, step-by-step, guide to taxonomic comparisons using Procrustes geometric morphometrics and user-friendly software (part B): group comparisons

“…Fishes, for instance, can be captured, anesthetized, carefully positioned and photographed, and rapidly released (Herler et al 2007). Photographs of live individuals have also been used, in combination with genetics, to uncover cryptic diversity in Hermann's tortoises (Djurakic & Milankov 2020). Similar approaches have a clear potential in other organisms with complete or partial exoskeletons, including arthropods, which represent the majority of living animal species (Zhang 2013).…”