Did European waterlice (Asellidae) originate from Lake Baikal?
Bert Hidding, University of Amsterdam
Lake Baikal, the deepest and oldest lake in the world, is known for its huge biodiversity and high level of endemism. Some taxa show extraordinary degrees of radiation (Martens 1997; Sherbakov 1999). Asellids however, (Crustacea, Isopoda) commonly known as waterlice, do not. They have five described representatives in the lake, all of which endemic. Their morphology resembles that of European asellids, and more importantly, strikingly similar karyologies between the European species Asellus aquaticus and the Baikalian Baicalasellus angarensis have been observed (Natyaganova et al, 1996). This does suggest that these species are phylogenetically closely connected. It is our idea that European asselid species may have originated from Lake Baikal. Aim of this study will be to elucidate the role of Lake Baikal as a 'cradle', using molecular phylogeny as a tool. The analysis will include Baikalian and non-Baikalian asellids.
Baikalian asellids can be subdivided into the subgenera Mesoasellus and Baicalasellus. Mesoasellus, which is also known from Japan and California, is represented by one described species. Another Mesoasellus species does live in Baikal, but is yet undescribed. The subgenus Baicalasellus, comprising four species, is endemic to Lake Baikal. Morphological studies suggest that Baicalasellus is a relatively young taxon. Mesoasellus is believed to be a tertiary 'relict' (Birstein 1951,Vekhoff 1994), and may be the ancestor of Baicalasellus.
It is suggested that Milankovitch climate oscillations cause extinctions at high latitudes, leaving deep and stable reservoirs mostly unharmed (Dynesius & Jansson 2000), and are therefore, a source of colonization after glacial periods. According to palaeorecords, a river system connecting Yenisej river and western European river systems existed in the Pleistocene. The close kinship between B. angarensis and A. aquaticus does suggest that A. aquaticus originates from Baikal, and thus exemplifies the role of Baikal as a cradle. Both the morphology and ecological characteristics of another asellid species from Western Siberia, Asellus latifrons resembles that of Asellus aquaticus. (Vekhoff 1994) To include these non-Baikalian species in a phylogenetic analysis may shed light on the biogeography and evolutionary history of asellids.
Fig 1 & 2: Two simplified alternative hypotheses for the phylogeny of Baikalian asellids. Fig1: Ancestral species of A. aquaticus was probably non-Baikalian. Fig 2: Ancestral species of A. aquaticus was Baikalian.
Sampling of isopods will be performed in July in the Netherlands (A. aquaticus), in Western Siberia in the end of August, (A. latifrons), in Lake Baikal (Baicalasellus, Mesoasellus) and Lake Bount (A. epimeralis), east of Baikal, thus creating a biogeographical transect from west to east. For deep sampling in Lake Baikal, an expedition is scheduled for September. I will sequence mitochondrial 16s RNA and COI for phylogenetic reconstruction of asselid isopods. The results of this study will help to better understand the role of ancient lakes as a source of biodiversity.
Research will be done in cooperation with the Limnological Institute (Russian Academy of Sciences, Siberian Division) in Irkutsk. Sequencing of asellid DNA will be done partially in Amsterdam and partially in Irkutsk. I will cooperate with Tonya Natyaganova and Tanya Pudovkina under supervision of Dr. D. Yu. Sherbakov. In the Netherlands this project will be supervised by Dr. E. Michel and Prof. dr. S.B.J. Menken at IBED-ZMA, University of Amsterdam. Dr. J.A.J. Breeuwer, also at IBED, will supervise practical molecular work in the Netherlands.
ReferencesBirstein, Y. A. (1951) Freshwater asellid isopods (Asellotta) Fauna SSSR Rakoobraznye. Moscow- Leningrad, AN SSSR Publ. T.7. No.5. 142 pp. (In Russian)
Dynesius, M and Jansson, R. (2000) Evolutionary consequences of changes in species' geographical distributions driven by Milankovitch climate oscillations. PNAS, August 1, vol. 97, no. 16, 9115-9120
Martens, K. (1997) Speciation in ancient lakes. TREE, vol. 12. No. 5, May, 177-182
Natyaganova, A.V. , Kamaltynov, R.M , Sherbakov, D.Yu. (1996) The chromosomes of Baicalasellus angarensis (Isopoda, Asellidae) Crustaceana 69 (6), 696-702
Sherbakov, D. Yu. (1999) Molecular phylogenetic studies on the origin of biodiversity in Lake Baikal. TREE, vol. 14. No. 3, March, 92-95
Vekhoff, N. V. (1994)Waterlice from the extra-tundra areas of Siberia and the Far East of Russia, with notes on systematics and zoogeography. (Crustacea Isopoda Asselidae) Arthropoda selecta 3 (3-4): 21-31
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