Literaturdatenbank
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Fritz, U. , Conflicts between genetics and morphology: A recurrent pattern in tortoises (testudinidae). Unpublished paper presented at XII Congresso Luso Espanhol de Herpetologia.
Added by: Admin (06 Jan 2014 18:22:48 UTC) |
| Resource type: Conference Paper BibTeX citation key: anon2012n View all bibliographic details  |
Categories: General Keywords: Chelonoidis chilensis, Chelonoidis nigra, Genetik - genetics, Schildkröten - turtles + tortoises, Stigmochelys pardalis, Systematik - taxonomy, Testudinidae, Testudo graeca, Testudo marginata Creators: Fritz Collection: XII Congresso Luso Espanhol de Herpetologia |
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| Abstract |
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Testudinidae Tortoises (Testudinidae) occur on all continents except Australia and Antarctica and embrace species displaying considerable morphological variation. Besides ‘mediumsized species’, there are dwarfed taxa (Homopus spp., maximum shell lengths of approximately 10 cm and body masses below 100 g) and giant species, exceeding 1 m shell length and 120 kg body mass (Galápagos and Aldabra tortoises, Chelonoidis nigra complex and Aldabrachelys gigantea). However, even within the same species a striking degree of morphological variability may occur. In the present talk, I will review several recent investigations, mostly of my own research group. These studies suggest that environmental factors strongly affect body size, coloration and shell shape. Consequently, morphological variability sometimes clearly conflicts with phylogeographic differentiation patterns (mitochondrial DNA sequences, microsatellites and AFLPs). In the case of the widespread Mediterranean spur-thighed tortoise (Testudo graeca) we showed that small-bodied, very light-coloured animals and substantially larger and darker specimens may occur in close proximity. Such tortoises are genetically not clearly differentiated. In this case the substrate coloration (lighter or darker background) and the humidity of the habitat (food availability!) seem to be responsible for the morphological differences. The marginated tortoise (Testudo marginata) from the southern Balkan peninsula presents another example: Marginated tortoises from the hottest and driest part of the distribution area are genetically virtually indistinguishable from considerably larger specimens from other regions; the smaller individuals in this case were originally even considered to be a separate species. A similar case occurs in the South American Chaco tortoises (Chelonoidis chilensis complex). Some authors recognized from north to south three distinct species, mainly differing in size, with the northernmost species reaching 17 cm shell length being the smallest and the southernmost species with more than 43 cm shell length being the largest. However, when we analysed Chaco tortoises from throughout Argentina, it turned out the differentiation pattern does not match the ‘three species hypothesis’, and we detected only limited geographical divergence in genetic markers. However, the northern populations comprise genetically diverse tortoises, while the southern populations harbour tortoises with reduced genetic variation, inversing the wellknown pattern of ‘southern genetic richness and northern purity’ of the northern hemisphere. In the sub-Saharan leopard tortoise (Stigmochelys pardalis), again, there are considerable size differences that are not correlated with phylogeographic differentiation, so that it can be inferred that external morphology of land tortoises is subject to very strong selective pressure, leading to a high degree of phenotypic plasticity.
Added by: Admin |