Tuesday, April 4, 2017

[Ichthyology • 2017] The First European Cave Fish: Barbatula Cave Loach from southern Germany


Figure 1: Cave loaches [Barbatula sp.adapted to life in constant darkness are of recent origin but genetically divergent from surface populations residing in the same drainage.
 
 (A) Two cave loaches in their natural habitat. (B) Adult male loach with typical adaptations to living in caves: reduced eyes, enlarged barbels and pale body coloration. (C) Typical epigean loach from the surface population in the Danube.


Summary
Subterranean biodiversity in Europe is spectacularly rich, with the Western Balkans being home to about 400 cave species, representing the highest number of species per area worldwide. Nonetheless, cave fishes, which are the most commonly found vertebrates in underground habitats, have not been described from Europe so far. Here, we report the first European record of a cave fish population, a loach of the genus Barbatula, found in the Danube–Aach system, an underground karst water system in Southern Germany. The fish exhibit traits typically observed in organisms adapted to subterranean life including reduced eyes and pale body coloration. The newly discovered population also represents globally the northernmost cave fish found so far. The geological history of the region implies that the Danube–Aach system was colonized post-glacially. A recent origin of the cave fish is supported by genetic analyses, because the subterranean population shares COI gene haplotypes with adjacent surface stone loach (Barbatula barbatula) populations. Nonetheless, population genetic analyses based on microsatellites indicated that cave fish are genetically isolated from populations in surface habitats and exhibit reduced genetic variability. Hence, the newly discovered European cave loaches do not represent individuals displaced from surface populations, but they follow a unique evolutionary trajectory towards cave life.



Figure 1: Cave loaches [Barbatula sp.adapted to life in constant darkness are of recent origin but genetically divergent from surface populations residing in the same drainage.  
 (A) Two cave loaches in their natural habitat. (B) Adult male loach with typical adaptations to living in caves: reduced eyes, enlarged barbels and pale body coloration. (C) Typical epigean loach from the surface population in the Danube.  

Figure 1 Cave loaches adapted to life in constant darkness are of recent origin but genetically divergent from surface populations residing in the same drainage.
(A) Two cave loaches in their natural habitat. (B) Adult male loach with typical adaptations to living in caves: reduced eyes, enlarged barbels and pale body coloration. (C) Typical epigean loach from the surface population in the Danube. (D) Neighbour-joining tree of Cytochrome oxidase subunit1 (COI) sequences for European stone loaches. European loaches form three clusters comprising sequences from Rhine, Danube and Elbe drainages. Loaches from the Danube–Aach cave system (AC, highlighted in orange) share haplotypes with individuals from the southern lineage sampled in the upper Rhine and Danube drainage, individuals from GenBank identified by their accession numbers. Numbers at major nodes indicate bootstrap values (>50%, 1000 replicates). (E) Graphical representation of an analysis of genetic population structure. Inferred genomic ancestry in three genetic clusters (y-axis) is depicted by red, green and blue colors for all individuals (x-axis). With prior information on the sample location of individuals, three clearly distinct genetic clusters separate cave loaches from both surface populations upstream (Danube) and downstream (Radolfzeller Aach) in the same drainage. Without prior information on the sample location of individuals, cave fish are grouped with the upstream but clearly separated from the downstream loach population.


  Jasminca Behrmann-Godel, Arne W. Nolte, Joachim Kreiselmaier, Roland Berka and Jörg Freyhof. 2017. The First European Cave Fish. Current Biology. 27(7); R257–R258. DOI: 10.1016/j.cub.2017.02.048



   

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