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  • Molecular Ecology (2006)

    15

    , 2969–2984 doi: 10.1111/j.1365-294X.2006.03018.x

    © 2006 The Authors Journal compilation © 2006 Blackwell Publishing Ltd

    Blackwell Publishing Ltd

    Comparative phylogeography of Ponto-Caspian mysid crustaceans: isolation and exchange among dynamic inland sea basins

    ASTA AUDZIJONYTE,

    *†

    MIKHAIL E . DANELIYA

    *‡

    and RISTO VÄINÖLÄ

    *

    *

    Finnish Museum of Natural History, POB 26, FI-00014 University of Helsinki, Finland,

    Department of Biological and Environmental Sciences, FI-00014 University of Helsinki, Finland,

    Department of Zoology, Rostov State University, B. Sadovaya 105, Rostov-on-Don, 344006, Russia

    Abstract

    The distributions of many endemic Ponto-Caspian brackish-water taxa are subdivided among the Black, Azov and Caspian Sea basins and further among river estuaries. Of the two alternative views to explain the distributions, the relict school has claimed Tertiary fragmentation of the once contiguous range by emerging geographical and salinity barriers, whereas the immigration view has suggested recolonization of the westerly populations from the Caspian Sea after extirpation during Late Pleistocene environmental perturba- tions. A study of mitochondrial (COI) phylogeography of seven mysid crustacean taxa from the genera

    Limnomysis

    and

    Paramysis

    showed that both scenarios can be valid for different species. Four taxa had distinct lineages related to the major basin subdivision, but the lineage distributions and depths of divergence were not concordant. The data do not support a hypothesis of Late Miocene (10–5 Myr) vicariance; rather, range subdivisions and dispersal from and to the Caspian Sea seem to have occurred at different times throughout the Pleistocene. For example, in

    Paramysis lacustris

    each basin had an endemic clade 2–5% diverged from the others, whereas

    Paramysis kessleri

    from the southern Caspian and the western Black Sea were nearly identical. Species-specific ecological characteristics such as vagility and salinity tolerance seem to have played important roles in shaping the phylogeographic patterns. The mitochondrial data also suggested recent, human-mediated cryptic invasions of

    P. lacustris

    and

    Limnomysis benedeni

    from the Caspian to the Sea of Azov basin via the Volga-Don canal. Cryptic species-level subdivisions were recorded in populations attributed to

    Paramysis baeri

    , and possibly in

    P

    .

    lacustris

    .

    Keywords

    : Caspian Sea, cytochrome oxidase I (COI),

    Limnomysis

    , Mysida,

    Paramysis

    , zoogeography

    Received 26 January 2006; revision received 29 April 2006; accepted 9 May 2006

    Introduction

    The history and diversity of aquatic biota in the Ponto- Caspian basin, which encompasses the Caspian, Azov and Black seas, is attracting scientific interest at least for two reasons. The Caspian Sea is one of the ancient lakes of the world; it has been effectively separated from oceans for

    c

    . 7 million years (Myr) and is currently characterized by 50–80% endemism of the fauna (Martens 1997; Dumont 2000). The geography and mechanisms of speciation in

    ancient lakes has been a topic of much discussion (Rossiter & Kawanabe 2000). For the Ponto-Caspian, potential factors promoting species divergence involve its wide environ- mental fluctuations and the intermittent interbasin subdivi- sions and connections (Dumont 1998). More recently, the Ponto-Caspian brackish-water fauna has come into focus as a major source of aquatic invading species in Europe and North America (Ricciardi & MacIsaac 2000; Leppäkoski

    et al

    . 2002; Jazdzewski

    et al

    . 2004). Molecular tools have been invoked to trace the sources and pathways of inva- sions (Cristescu

    et al

    . 2001, 2004), but their successful application is contingent on proper taxonomy and genetic characterization of the populations in the native ranges.

    Correspondence: Asta Audzijonyte, Fax: +358-9-19144430; E-mail: asta.audzijonyte@helsinki.fi

  • 2970

    A . A U D Z I J O N Y T E , M . E . D A N E L I Y A and R . V Ä I N Ö L Ä

    © 2006 The Authors Journal compilation © 2006 Blackwell Publishing Ltd

    Recent invasions also threaten the Ponto-Caspian region itself, particularly the Caspian Sea, which since the opening of the Volga-Don canal in the 1950s has received a wave of nonindigenous species (Grigorovich

    et al

    . 2003; Orlova

    et al

    . 2004; Therriault

    et al

    . 2005). The southern and central parts of the Black and Caspian

    seas have markedly different faunas — the Black Sea (18‰ S) is inhabited by typical marine (Mediterranean) taxa, whereas the Caspian Sea (13‰) has many endemic groups (Zenkevitch 1963; B

    Å

    n

    Å

    rescu 1991). In contrast, the diluted northern areas of the seas and the lower reaches of their rivers contain a largley shared brackish-water fauna, comprising, among others, numerous species of crusta- ceans (in the Mysida, Amphipoda, Cumacea, Cladocera) and molluscs (in Dreissenidae, Cardiidae, Pyrgulidae). These taxa typically occur in salinities lower than 6‰ and show relatively little taxonomic differentiation among the three basins (Fig. 1a, Table 1) (Mordukhai-Boltovskoi 1979; Komarova 1991; Daneliya 2003). The history of their disjunct distributions has been an issue of debate in Ponto-

    Caspian zoogeography between proponents of the immigra- tion and relict views.

    The immigration view emphasizes the role of drastic Pleistocene environmental perturbations that must have caused repeated local extirpation in the western basins but also facilitated faunal exchange (Birshtein 1935; Mordukhai- Boltovskoi 1960, 1979; Dedyu 1967). For example, during the last 1 Myr the Black Sea salinity has fluctuated from nearly oceanic during contacts with the Mediterranean, to almost freshwater during glaciation maxima and these events were coupled with

    c

    . 150 m changes in the water level; the shallow Sea of Azov was nearly dry during the low stands (Fig. 1b) (Alekseev

    et al

    . 1986; Svitoch

    et al

    . 2000). During the cold climatic phases of the Middle and Late Pleistocene the Caspian Sea experienced extensive transgressions, which caused overflow of water to the Azov basin via the Manych depression; the latest event was

    c

    . 15 000 years ago (Mangerud

    et al

    . 2004; Bahr

    et al

    . 2005). Repeated colonizations from the Caspian basin during the Pleistocene were believed to be the prime source of the

    Fig. 1 (a) Map of the Ponto-Caspian region indicating sampling sites and their cor- responding codes as listed in Table 2. (b) Schematic presentation of Late Pleisto- cene history of the Black, Azov and Caspian seas (according to Mamedov 1997; Ryan et al. 2003; Mangerud et al. 2004). Dashed lines depict limits of the lakes and rivers during the latest regression stages. Limits of the last extensive Caspian tran- sgression are also shown together with the direction of the outflow to the Azov basin along the Manych Strait. Saline water intru- sions into the Black Sea occurred from the Marmara Sea in the course of a repeatedly established connection through the Bosporus Strait. The Volga-Don canal, opened in 1952, is recognized as a current route of faunal exchange and an invasion corridor.

  • P O N T O - C A S P I A N M Y S I D S

    2971

    © 2006 The Authors Journal compilation © 2006 Blackwell Publishing Ltd

    current brackish-water fauna of the Black Sea and Sea of Azov basins, thus referred to as the Caspian fauna (e.g. Mordukhai-Boltovskoi 1979; Reid & Orlova 2002). Throughout the Holocene, until recently, the basins were again hydrographically isolated, the Caspian being an inland lake with no outlet (now 28 m below world sea level). The Sea of Azov represents a common estuary of the Don and Kuban rivers, and geographically actually makes a part of the Black Sea basin. As regards the zoogeographical ques- tions in this study, the sea is however, hydrographically isolated from the estuaries of the large western Black Sea rivers (Danube, Dnestr, Dnepr), has a special position in its past and current contacts with the neighbouring Caspian basin, and also has its own biogeographical characteristics, which justify its treatment here as a distinct zoogeographical unit.

    The relict zoogeographical view claims that the current distributions of the brackish-water fauna mark the extent of the ancient Sarmatian (

    c

    . 10 Myr) or Pontian (

    c

    . 6 Myr) inland seas, which later were fragmented into the distinct basins. Accordingly, the faunal element has been coined as Sarmatian or Pontian relicts (Sars 1907; Martynov 1924; Ekman 1953; Weish & Türkay 1975). River deltas and lagoons are seen as long-term refugia, and deep evolutionary subdivisions among the populations in different basins are anticipated (Starobogatov 1970; Grigoriev & Gozhik 1976). The different schools of zooge- ography are also reflected in the current taxonomy and in an uneven degree of endemism recognized in various animal groups. Thus a number of endemic Azov and Black Sea species have been described in gastropod and bivalve molluscs (Golikov & Starobogatov 1966; Grigoriev & Gozhik

    1976), whereas in mysid crustaceans