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Intraspecific variation in digit reduction in Testudo: the case of the Hermann’s tortoise

  • Àngel H. LujánEmail author
  • Mariona Ferrandiz-RoviraEmail author
  • Cristina Torres
  • Albert Bertolero
Original Article

Abstract

Phalangeal reduction is a common and widespread phenomenon among tortoises that has been associated with the adaptation to terrestrial life. While reduced manual digit 1 appears characteristic in almost all Testudo species, it is uncertain why the metacarpal I and distal carpal of the same digit are completely missing in some individuals of Hermann’s tortoise (Testudo hermanni hermanni). To clarify this issue, we investigated the number of manual claws in six populations of Hermann’s tortoise (one from the Ebro Delta in the Iberian Peninsula and five from Minorca Island), their age, sex, genetic lineage, and the substrate type that they inhabit. The number of claws was ascertained based on direct counts (n > 1500 individuals) and by X-rays (n = 32 individuals), obtaining three different phalangeal formulae: (1-2-2-2-1, D-2-2-2-1, 0-2-2-2-1). Thus, claw counts through both methodologies (direct count and X-ray) further confirm that the observed claws serve as a good proxy to assess the actual number of digits. Our results show no loss of phalanges, metacarpal and carpal bones in digit 1 associated with age, sex, or substrate, contrary to some previous authors who hypothesized a relationship between this loss and sexual dimorphism. Therefore, variations in the number of manual digits and the loss of metacarpal I and distal carpal in digit 1 in Hermann’s tortoise are related to population and genetic lineage. More detailed comparisons with other Testudo hermanni populations from elsewhere in Europe would be required to understand the evolutionary significance concerning the intrapopulation variability in the number of digits remaining.

Keywords

Testudo hermanni Phalange reduction Ebro Delta Minorca Island Phalangeal formula 

Notes

Acknowledgments

AB thanks especially Delta de l’Ebre Natural Park staff, Joan Pretus and Marta Massana, for their valuable assistance over several years. We thank Pierre Dupont and Vérane Berger for helpful comments and discussion of statistical analyses. We further acknowledge the Editor (A. Wanninger) and two reviewers (W. Joyce and G. Ferreira) for helpful and constructive comments and suggestions that helped us to improve a previous version of this paper.

Author contributions

MFR and CT performed the statistical analyses; AB and AHL coordinated the data collection; AB, AHL, and MFR conceived and designed the experiment; AB, AHL, MFR, and CT analyzed the data; AB, AHL, and MFR wrote the paper.

Funding information

The research reported in this work was funded by the Spanish Agencia Estatal de Investigación – European Regional Development Fund of the European Union (CGL2016-76431-P and CGL2017-82654-P, AEI/FEDER EU to À.H.L) and the Generalitat de Catalunya (CERCA Programme to À.H.L and 2017 SGR 1006 to M.F.R). À.H.L. is financially supported through postdoctoral grant by the European Union at Masaryk University, Czech Republic (CZ.02.2.69/0.0/0.0/16_027/0008360) during the elaboration of this paper and a research visit to the University of Comenius in Bratislava, Slovakia (National Scholarship Programme of the Slovak Republic for the support of mobility of researchers, Autumn Call 2017). AB is supported by the Delta de l’Ebre Natural Park (Generalitat de Catalunya), l’Institut Menorquí d’Estudis, and the Conselleria de Medi Ambient (Direcció General de Biodiversitat) de les Illes Balears.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

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Copyright information

© Gesellschaft für Biologische Systematik 2019

Authors and Affiliations

  1. 1.Department of Geological Sciences, Faculty of SciencesMasaryk UniversityBrnoCzechia
  2. 2.Department of Ecology, Faculty of Natural SciencesComenius University in BratislavaBratislavaSlovakia
  3. 3.Institut Català de Paleontologia Miquel CrusafontUniversitat Autònoma de BarcelonaCerdanyola del VallèsSpain
  4. 4.CREAF, Campus de Bellaterra (UAB) Edifici CCerdanyola del VallèsSpain
  5. 5.BABVE, Edifici C Facultat de BiociènciesUniversitat Autònoma de BarcelonaCerdanyola del VallèsSpain
  6. 6.Departament de Biologia Evolutiva, Ecologia i Ciències AmbientalsUniversitat de BarcelonaBarcelonaSpain
  7. 7.Associació Ornitològica Picampall de les Terres de l’EbreDeltebreSpain

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