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Evolutionary history of relict Congeria (Bivalvia: Dreissenidae): unearthing the subterranean biodiversity of the Dinaric Karst

Helena Bilandžija12, Brian Morton3, Martina Podnar4 and Helena Ćetković1*

Author Affiliations

1 Division of Molecular Biology, Rudjer Boskovic Institute, Bijenička 54, 10 000 Zagreb, Croatia

2 Croatian Biospeleological Society, Demetrova 1, 10 000 Zagreb, Croatia

3 Department of Zoology, The Natural History Museum, Cromwell Road, London SW7 5BD, UK

4 Croatian Natural History Museum, Demetrova 1, 10 000 Zagreb, Croatia

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Frontiers in Zoology 2013, 10:5  doi:10.1186/1742-9994-10-5

Published: 6 February 2013

Abstract

Background

Patterns of biodiversity in the subterranean realm are typically different from those encountered on the Earth’s surface. The Dinaric karst of Croatia, Slovenia and Bosnia and Herzegovina is a global hotspot of subterranean biodiversity. How this was achieved and why this is so remain largely unresolved despite a long tradition of research. To obtain insights into the colonisation of the Dinaric Karst and the effects of the subterranean realm on its inhabitants, we studied the tertiary relict Congeria, a unique cave-dwelling bivalve (Dreissenidae), using a combination of biogeographical, molecular, morphological, and paleontological information.

Results

Phylogenetic and molecular clock analyses using both nuclear and mitochondrial markers have shown that the surviving Congeria lineage has actually split into three distinct species, i.e., C. kusceri, C. jalzici sp. nov. and C. mulaomerovici sp. nov., by vicariant processes in the late Miocene and Pliocene. Despite millions of years of independent evolution, analyses have demonstrated a great deal of shell similarity between modern Congeria species, although slight differences in hinge plate structure have enabled the description of the two new species. Ancestral plesiomorphic shell forms seem to have been conserved during the processes of cave colonisation and subsequent lineage isolation. In contrast, shell morphology is divergent within one of the lineages, probably due to microhabitat differences.

Conclusions

Following the turbulent evolution of the Dreissenidae during the Tertiary and major radiations in Lake Pannon, species of Congeria went extinct. One lineage survived, however, by adopting a unique life history strategy that suited it to the underground environment. In light of our new data, an alternative scenario for its colonisation of the karst is proposed. The extant Congeria comprises three sister species that, to date, have only been found to live in 15 caves in the Dinaric karst. Inter-specific morphological stasis and intra-specific ecophenotypic plasticity of the congerid shell demonstrate the contrasting ways in which evolution in the underground environments shapes its inhabitants.

Keywords:
Dinaric Karst; Subterranean habitats; Cave bivalve; Congeria; Dreissenidae; New species; Ecophenotypic plasticity