Abstract
BackgroundPhenotypic similarities among cave-dwelling animals displaying troglomorphic characters (e.g. reduced eyes and lack of pigmentation) have induced a long-term discussion about the forces driving convergent evolution. Here we introduce Garra barreimiae Fowler & Steinitz, 1956, as an interesting system to study the evolution of troglomorphic characters. The only hitherto known troglomorphic population of this species lives in Al Hoota Cave (Sultanate of Oman) close to a surface population. As a first approach, we assessed the genetic differentiation between the two morphotypes of G. barreimiae to determine whether gene flow still occurs.ResultsWe analysed the mitochondrial control region (CR). In G. barreimiae the CR starts immediately downstream of the tRNA-Thr gene, while the tRNA-Pro gene is missing at this genomic location. Interestingly, a putative tRNA-Pro sequence is found within the CR. The phylogenetic analyses of the CR sequences yielded a tree divided into three clades: Clade 1 has a high genetic distance to the other clades and contains the individuals of three populations which are separated by a watershed from all the others. Clade 2 comprises the individuals from Wadi Bani Khalid, the geographically most remote population. Clade 3 comprises all other populations investigated including that of Al Hoota Cave. The latter forms a haplogroup which also includes individuals from the adjacent surface population.ConclusionsOur data indicates that the troglomorphic cave population is of quite recent origin supporting the hypothesis that selection drives the fast evolution of troglomorphic traits. In this context pleiotropic effects might play an important role as it has been shown for Astyanax. There seems to be some gene flow from the cave population into the adjacent surface populations. One blind individual, found at a surface locality geographically distinct from Al Hoota Cave, is genetically differentiated from the other blind specimens indicating the probable existence of another cave population of G. barreimiae. The phylogeographic analyses show that while some of the surface populations are either still in contact or have been until recently, the population Wadi Bani Khalid is genetically separated. One group consisting of three populations is genetically highly differentiated questioning the conspecifity with G. barreimiae.
Highlights
Phenotypic similarities among cave-dwelling animals displaying troglomorphic characters have induced a long-term discussion about the forces driving convergent evolution
In G. barreimiae, the control region (CR) starts immediately after the tRNA-Thr, while tRNA-Pro is missing at this genomic location
The putative tRNA-Pro gene has an antiparallel orientation as has been described for other vertebrates and the sequence identity to the tRNA-Pro gene of Cyprinus carpio [20] is about 80%
Summary
Phenotypic similarities among cave-dwelling animals displaying troglomorphic characters (e.g. reduced eyes and lack of pigmentation) have induced a long-term discussion about the forces driving convergent evolution. We introduce Garra barreimiae Fowler & Steinitz, 1956, as an interesting system to study the evolution of troglomorphic characters. The discussion about the forces driving convergent evolution of reduced eyes and loss of development and in the formation of other constructive traits (e.g., taste bud and forebrain development [7,8,9,10]). There are, some cave-living fishes without troglomorphic phenotype [11]. Most studies conducted on cave fishes were carried out on species of the genus Astyanax, which became model organisms for investigating many different aspects of the development of troglomorphic characters (for a review see [5]). Convergent evolution of various troglomorphic species might be driven by different evolutionary mechanisms.
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