engleski

The molecular evolution of the cave animals

One of the most notable adaptations of cave animals is albinism, the loss of melanin pigment, which has evolved in most animals that are adapted to life in caves. The results of a melanogenic substrate assay showed that all cave animals thus far tested have lost their pigment due to a change in the first step of melanin synthesis pathway, the conversion of L-tyrosine to L-DOPA. Therefore, the evolution of albinism is convergent at both the phenotypic and metabolic levels. L-tyrosine is a precursor of another biosynthetic pathway, the synthesis of catecholamines (dopamine, noradrenaline, and adrenaline), which suggests a possible pleiotrophic effect of the loss of melanin pigment: excess of L-tyrosine substrate could be used advantageously in the alternative pathway. The attempts to explain the evolution of regressive traits have caused many controversies since the beginning of cave biology research, and our data suggest that the natural selection may be a driver for the evolution of albinism. Strong selection operating during the colonization of caves by various taxa results in the same set of adaptations and often similar morphologies which obstruct the recognition of true phylogenetic positions and relationships. For example, the closest surface relative of cave sponge Eunapius subterraneus, Sket & Velikonja, 1984, according to molecular data, belongs to the genus Ephydatia. In addition, phylogenetic analysis revealed many inconsistencies in taxonomy of freshwater sponges, even at the level of families. The lack of robust morphological characters coupled with the fact that many of the traits show plasticity (body shape, spicules, gemmules) makes the classification of sponges in general very challenging. Another frequent outcome of using molecular analysis in cave fauna studies is overlooked biodiversity and this is the result of cave bivalve Congeria kusceri Bole 1962 research. The phylogenetic data revealed that cave bivalves have separated into three distinct species, the already recognized C. kusceri and two newly described species: C. mulaomerovici Morton & Bilandžija, 2013. and C. jalzici, Morton & Bilandžija, 2013. Each species is confined to its own hydrological region except C. jalzici which exhibits a specific pattern. It encompasses isolated populations living in basins of different sea catchments. Further, functional adaptation to a distinct hydrological regime in Lukina Jama-Trojama Cave System resulted in very different shell morphology of bivalve population living there, making C. jalzici an extraordinary example of phenotypic plasticity. The rich fossil record of dreissenids enabled the use of recently developed and more reliable molecular clock tools. The epicentre of evolution of the whole family Dreisssenidae was the Paratetys and the genus Congeria appeared and radiated in Lake Pannon. From there, it is hypothesized, the ancestor of extant cave Congeria colonized the Dinarides and caves. The last common ancestor of all three species evolved 5, 4 Mya, which fits the timeframe when all other Congeria species vanished from the fossil record. Subsequent divergence occurred during the Pliocene Epoch, about 2, 6 Mya. It is not known exactly when during their evolution these lineages have colonized the caves. Comparative phylogeography together with molecular dating can provide valuable insights and contribute to the formation of an integrated picture of the Dinaric karst and its underground fauna evolution. Very rich subterranean biodiversity of the Dinaric karst was shaped by a combination of events and circumstances that took place mostly during geological history: the high biodiversity and therefore the productivity of surface habitats both in the past and today, the complex and turbulent geological evolution of both Dinaric and adjacent regions, and the excessive karstification of limestone bedrock that created a vast and diverse underground network of habitats but also frequently changed hydrological relationships causing further subdivision of lineages are some of the factors that influenced the biodiversity seen today. This research added further information to this story but, perhaps more importantly, provided valuable information that can help address conservation issues of these rare and endangered animals.

cave fauna; albinism; melanin biosynthesis; phylogeny; Dinarides

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