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Cryptic ostracod species in an Ancient Lake: the Cytherissa flock from Baikal

Final Report Summary - CRYSTAL (Cryptic ostracod species in an Ancient Lake: the Cytherissa flock from Baikal)

Introduction

Biodiversity is a fundamental part of the Earth's life. It provides basic natural services for humans, such as fresh water, fertile soil and clean air. Biodiversity is also relevant for pollinating flowers and crops, cleaning up waste and providing food. Without it, humanity would not be able to survive (Cardinale et al. 2012). Biodiversity also matters for ethical, emotional, environmental and economic reasons. The current global extinction rate of species has been estimated to be 1 000 to 10 000 times higher than the natural background extinction rate (see http://ec.europa.eu/environment/nature/biodiversity/intro/index_en.htm online for further details). This makes knowledge on the patterns and processes on natural formation of new species essential to develop suitable management plans for protecting natural biodiversity.

Ancient lakes are freshwater habitats that have long been recognised as natural evolutionary laboratories and hot spots of endemic biodiversity; speciation processes that have led to the formation of many endemic ancient lake taxa have received much attention in evolutionary research (Martens 1994, 1997). Ancient lakes thus act as engines generating novel diversity inside and outside of the lake. For non-marine ostracods (Crustacea), ancient lakes are especially important as they hold at least one quarter of the currently known 2000 morpho-species worldwide (Martens et al. 2008) The discovery of so-called cryptic diversity, being defined by two or more genetic species that cannot be distinguished morphologically, has been of great importance for providing real (and much higher) levels of biodiversity and for adapting future conservation management. Genetic studies have detected cryptic diversity in many animal taxa including ostracods (Crustacea) (e.g. Bode et al. 2010; Schön et al. 2012), with the general implication that there are many more species than were previously recognised (Scheffers et al. 2012).

Summary objectives: Our project assessed the importance of cryptic ostracod species for biodiversity estimates and conservation of ancient lakes and investigated the underlying evolutionary and ecological processes that may have led to the high diversity in explosive lacustrine radiations. The Cytherissa-radiation from Lake Baikal was used as model system because it is one of the most species-rich ostracod flocks and contains 47 morphological (sub-) species.

Work performed and main results

The examined material was sampled from 90 sites during six expeditions on Lake Baikal in different years, whereby the fellow participated in the last two.

Morphology and identification: The fellow investigated the morphology of more than 100 Baikalian ostracods in detail by scanning electronic microscopy (SEM) of the carapace, hemipenis and chaetotaxy, thus greatly advancing reliable species identification of Baikalian Cytherissa, which was so far limited to a single scientific publication (Mazepova 1990) based on valve characters only. The novel morphological descriptions will be published soon in the European Journal of Taxonomy with open access to ensure world-wide access to this important information.

Molecular phylogeny and cryptic species: deoxyribonucleic acid (DNA) was extracted from 125 Baikalian specimens. The fellow successfully modified and optimised existing genetic protocols on polymerase chain reaction (PCR) amplification and automatic sequencing of two mitochondrial and one nuclear marker, thus significantly increasing the available genetic information on these endemic species from Lake Baikal. DNA sequence data were used to construct phylogenies and tested for cryptic species. Depending on the marker and statistical method used, the fellow found twice as many cryptic as morpho-species, hereby doubling existing estimates of Cytherissa diversity from Lake Baikal.

Speciation: Geographic analyses revealed that cryptic species coincide with geographic separation or bathymetric separation indicating that allo- and parapatric speciation might have been the most important speciaton modes for Cytherissa species. This has important consequences for conservation as cryptic Cytherissa species have to be protected at a local scale.

Besides allopatric speciation, also sexual selection must have contributed to the formation of new Cytherissa species as is indicated by the morphological variation of certain hemipenis characters in for example C. sernovi and C. cytheriformis and the position of these species in the phylogenetic tree. Plotting the occurrence of species through time showed additional evidence that all speciation processes have happened in an explosive manner in the more recent evolutionary history of Baikalian Cytherissa.

Conclusion: the novel results of CRYSTAL clearly show that diversity of ostracods from ancient lakes is much higher than previously assumed because of the presence of cryptic species making that these lakes even more important as reservoirs and engines for generating freshwater diversity.

Outreach: All novel results are currently prepared for scientific publication in high-level journals where they will surely attract the attention of the scientific community. They will also be presented at next International Symposium on Ostracoda in Rome in 2013.

Contact information: Prof. Dr Koen Martens (Coordinator)
Head of Department
Royal Belgian Institute of Natural Sciences
Freshwater Biology
Vautierstraat 29
1000 Brussels, Belgium
tel: +32-262-74315, fax : +32-264-64433
email: martens@naturalsciences.be darwinula@gmail.com

Fellow: Dr Valentina Pieri
Royal Belgian Institute of Natural Sciences
Freshwater Biology
Vautierstraat 29
1000 Brussels, Belgium
tel: +32-262-74336, fax: +32-264-64433
email: valentina.pieri@gmail.com