Global Diversity of Ostracods in Freshwater

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Hydrobiologia (2008) 595:185–193 DOI 10.1007/s10750-007-9245-4

FRESHWATER ANIMAL DIVERSITY ASSESSMENT

Global diversity of ostracods (Ostracoda, Crustacea) in freshwater ¨ Koen Martens Æ Isa Schon Æ Claude Meisch Æ David J. Horne

Ó Springer Science+Business Media B.V. 2007

Abstract There are close to 2,000 subjective species and about 200 genera of Recent non-marine Ostracoda. Together, Cyprididae (1,000 spp.) and Candonidae (c. 550 spp.) represent more than 75% of the extant specific diversity; the remaining 11 families comprise the other 25% of the species. The Palaearctic region has the highest absolute nonmarine ostracod diversity, followed by the Afrotropical. The Australian region has the highest relative endemicity. About 90% of the species and 60% of the genera occur in one zoogeographical region only. This means that all the biological mechanisms which lead up to efficient dispersal and which are present in at least part of the non-marine Ostracoda (e.g. ´ ˆ Guest editors: E. V. Balian, C. Leveque, H. Segers & K. Martens Freshwater Animal Diversity Assessment ¨ K. Martens (&) Á I. Schon Freshwater Biology, Royal Belgian Institute of Natural Sciences, Vautierstraat 29, 1000 Brussels, Belgium e-mail: martens@naturalsciences.be K. Martens University of Ghent, Ghent, Belgium C. Meisch ´ Musee national d’Histoire Naturelle, Luxembourg, Luxembourg D. J. Horne Department of Geography, Queen Mary, University of London, London, UK

brooding, drought-resistant eggs, parthenogenesis) have not induced common cosmopolitan distributions in ostracods. Several habitats are hotspots for ostracod diversity and endemicity. For example, it appears that the ancient lakes hold up to 25% of the total ostracod diversity. Other speciation-prone habitats are groundwater, temporary pools and Australian salt lakes; in the latter two instances, cladogenesis has often been paralleled by gigantism. The present ostracod diversity results from 9 to 12 separate invasions of the non-marine habitat, starting about 400 Myr ago. Genetic diversity can be very different in different species, mostly, but not always, related to reproductive mode. Keywords Ostracoda Á Freshwater Á Species Á Genera Á Ancient lakes

Introduction Mussel-shrimps, or Ostracoda, are small, bivalved Crustacea. Their calcified carapaces have an average length of c. 1 mm and completely envelop the reduced body (Fig. 1). Ostracods are very common in most inland waters, where they abound in the benthic and periphytic animal communities, but they also occur in marine, interstitial and even (semi-) terrestrial environments. Ostracoda are of great interest as a model group in various ecological and evolutionary studies. This is mainly so because the

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Fig. 1 External views of carapaces of main extant non-marine ostracod groups. A, Ilyocypris (Ilyocyprididae, Cypridoidea); B, Centrocypris (Notodromadidae, Cypridoidea); C, Potamocypris (Cyprididae, Cypridoidea); D, Cyprinotus (Cyprididae, Cypridoidea); E, Candona (Candonidae, Cypridoidea);

F, Cyprideis (Cytherideidae, Cytheroidea); G, Limnocythere (Limnocytheridae, Cytheroidea); H, Metacypris (Limnocytheridae, Cytheroidea); I, Darwinula (Darwinulidae, Darwinuloidea). Scale bar = 0.5 mm

calcified valves of non-marine ostracods can be very common in lake sediments and this adds a real-time frame to the evolution of ostracod lineages as well as of their biological traits. At present, ostracods are popular model organisms for research on the evolution of reproductive modes (Martens, 1998a) and as proxies for climate and ecosystem changes (Holmes & Chivas, 2002). There are three main lineages of recent non-marine ostracods (Fig. 2), all belonging to the Podocopida. All three originated in the Palaeozoic and are between 450 and 360 million years old. The Cytheroidea are mostly marine, but have several nonmarine incursions of which the Limnocytheridae are the most common. The...
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