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Ancient Endemism Among Freshwater Isopods (Crustacea^ Phreatoicidea)

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Ancient Endemism Among Freshwater Isopods (Crustacea^ Phreatoicidea) Ancient endemism among freshwater isopods (Crustacea^ Phreatoicidea) George D. F. Wilson1 and Richard T. Johnson1 Centre for Evolutionary Research, The Australian Museum, 6 College Street, Sydney, New South Wales 2000 Ancient clades with restricted geographic distributions have been found in the isopod crustacean suborder Phreatoicidea. These isopods colonized fresh water in Gondwana by the Triassic Era and today are restricted to permanent groundwaters. A phylogenetic analysis of 21 exemplar species showed that major cladogenic events took place prior to the fragmentation of Gondwana. Nichollsia, a genus restricted to India, was deeply nested within a Western Australian and Victorian clade. The Phreatoicidae branched off early in all cladograms, with Australian and New Zealand sister clades. Some clades may be closely associated with Gondwanan landmasses that were subdivided by shallow Cretaceous seas. INTRODUCTION distinct genetic forms known from the South Australian artesian springs of the Lake Eyre The Phreatoicidea are the earliest derived supergroup (M. Adams, Environmental Report, isopod Crustacea (Brusca and Wilson 1991), Kinhill Engineers Pty Ltd); Hypsimetopus sp. appearing in the marine fossil record during from near Zeehan, Tasmania, possibly the Carboniferous (~325 mybp: Hessler conspecific with H. intrusor Sayce 1902 but 1969; Schram 1970, 1974). Phreatoicideans variation has not been fully evaluated; cf. invaded fresh waters of the Gondwanan Hyperoedesipus sp. from the Pilbara region supercontinent by the Triassic (Protamphisopus of Western Australia, a new genus with wianamattensis (Chilton 1918), see Nicholls presumed affinities to H. plumosus Nicholls 1943) and subsequently became extinct in the and Milner 1923. The Tasmanian genera oceans. Today, phreatoicideans are restricted are poorly defined but are labelled in Figure to permanent fresh waters and occur in 1 to indicate the possible phreatoicidean Australia as well as on a few other continental diversity of this area. fragments derived from Gondwana (Banarescu 1990; Wilson and Keable, in press). The A taxonomic database in the DELTA format distribution of phreatoicideans within Australia (Dallwitz 1980; Dallwitz et al. 1993) was used shows much endemism at the level of genus to generate the phylogenetic data (as in and higher (Fig. 1). This paper examines Wilson and Keable, in press). As of October phreatoicidean phylogeny and biogeography 1997, the« database contained 21 species, in Australia in relation to taxa that occur in including representatives of non-Australian other Gondwanan localities. The distributions genera and several undescribed species. Data evident today may reflect the biogeography of on some taxa were derived from the literature clades derived during the Mesozoic. (e.g., Nichollsia Chopra and Tiwari 1950 and Neophreatoicus Nicholls 1944) or were not fully dissected because specimens were type MATERIALS AND METHODS material (e.g., adult Hyperoedesipus plumosus). Distributional data in this paper comes Because congeners typically formed single from localities where we have inspected clades (e.g., the Victorian and New South specimens, either in the collections of the Wales genus Crenoicus Nicholls 1944), only Australian Museum or from other sources. one species from each genus was used to Some records from the literature were not simplify the resulting cladograms. The data, included because the specimens have not therefore, comprised only 17 taxa. The been examined. Figure 1 shows this phylogenetic data (135 unordered morpho­ distribution of phreatoicidean taxa within logical characters, 98 of which were Australia, based on the taxonomy of Nicholls informative) were analysed using the computer (1943, 1944) but including several new program PAUP version 3.1.1 (Swofford genera. Undescribed species included in this 1993; parsimony analysis settings TBR, analysis are: Eophreatoicus sp., one of >5 new Mulpars, addseq = random, 10 iterations). species from Kakadu, Northern Territory and Space constraints preclude the presentation distinct from E. kershawi Nicholls 1926; of our primary data in this paper, but they Phreatomerus sp., possibly conspecific with may be obtained on request from the first P. latipes (Chilton 1922) but one of several author. Although the current analysis yielded Pp. 264-68 in The Other 99%. The Conservation and Biodiversity of Invertebrates ed by Winston Ponder and Daniel Lunney, 1999. Transactions of the Royal Zoological Society of New South Wales, Mosman 2088. Eophreatoicus New Genus New Genus 1 cf}J-lyperoedesipus I Paramphisopus t^Hyperoedesipus Ky ^ *J—rNew Genus -\ ' New Genus 4 Metaphreatoicus Amphisopus Phreatoicopsis & Colubotelson Synamphisopus Mesacanthotelson & Phreatoicopsis & Onchotelson Phreatoicoides cf. Colubotelson, Hypsimetopus & Uramphisopus & Phreatoicoides other genera Figure 1. Isopoda Phreatoicidea: distribution of genus-level taxa in Australia, based on material that we have examined (filled circles) and using the taxonomy of Nicholls (1943, 1944). Several new genera but not all nominal genera are shown. "New Genus 1" is described in Wilson and Keable (in press) and "cf. Hyperoedesipus" is under description. Other new genera are not yet described, and therefore do not appear in the cladistic analysis. unrooted trees, we orientated the resulting Nicholls 1944 from Victoria to Tasmania may topologies by placing the South African be a taxonomic artifact. All other genera species Mesamphisopus capensis (Barnard 1914) appear to be localized to relatively small as the "outgroup" because this genus may regions. For example, Eophreatoicus species are be derived basally (Wilson and Keable, in found only on and around the Arnhem press). These cladistic estimates should be Plateau of the Northern Territory, and considered preliminary because some clades Paramphisopus Nicholls 1944 species, despite may change position after the addition of being good swimmers and presumably new taxa. The data are not complete, because capable of active dispersal, is found only several undescribed genera (noted in Fig. 1) in the coastal ponds of the Perth region, and many taxa from Tasmania, New Zealand Western Australia. and other areas are not included. Relation­ Are these distributions recent, being ships between areas of endemism were established during the times when Australia evaluated by replacing phreatoicidean names became arid, or are they older? If older, with their areas on the strict consensus of the how old? The phylogenetic analysis (Fig. 2) trees obtained in the parsimony analysis. allows this issue to be addressed as well as to test the effectiveness of the existing RESULTS AND DISCUSSION classification. The family Amphisopodidae is Figure 1 demonstrates that most super- paraphyletic, with the Phreatoicidae and the specific taxa consist of geographically restricted Nichollsiidae nested within it. In Nicholls' clades. Crenoicus is an exception to this (1943) conception, the Amphisopodidae was pattern, with a distribution that spans the based on what he regarded as primitive Great Dividing Range through New South characters, so the paraphyly of this family Wales and Victoria (Wilson and Ho 1996). is no surprise. The monophyly of the The apparent distribution of Colubotelson Phreatoicidae is supported (Wilson and Keable, June 1999 The Other 99%. The Conservation and Biodiversity of Invertebrates 265 AMPHISOPODIDAE the modern distribution of phreatoicideans. PHREATOICIDAE w NICHOLSIIDAE .S3 05 3 Because phreatoicidean isopods were present co '•=••5* & C in Gondwanan fresh waters by the Triassic 0 CO .52 ri. E g w a <o co CD 0 .3 CO CO (Chilton 1918), many of the cladogenic events ri. .& «° to must have pre-dated the supercontinent's 3 H> "-" ^3 CO to .8 Ss co CO breakup. 0 O .<2 .CO P .11 0 Some phreatoicidean clades within Australia I g a I may also reflect the association of CO CO 5CO 8 <2> J I II I Gondwanan landmasses that were subdivided ^ O ^ £ by shallow Mesozoic seas. Figure 4 overlays u the approximate distribution of dry land- w\y v masses during the mid-Cretaceous (BMR Palaeogeographic Group 1990) and the current distribution of phreatoicidean localities in Australia. During this period, shallow seas largely divided Australia into a western and an elongate southeast to Figure 2. Strict consensus of 3 trees (length 416, consistency index 0.44) resulting from a parsimony northwest part. Two distal clades in the analysis of data derived from the DELTA database. taxon-area consensus show a vicariant pattern Extent of the families in the current classification of the that may be influenced by this inundation Phreatoicidea (Nicholls 1943; Chopra and Tiwari 1950) event, the Paramphisopus — Phreatomerus are indicated by horizontal lines for the Phreatoicidae (beneath) and the Amphisopodidae (extending laterally, clade and the Amphisopus Nicholls 1926 — dashed), and by an arrow for the Nichollsiidae. Synamphisopus Nicholls 1943 clade, both suggesting relationships between Victoria and Western Australia. in press), although this clade has proven to be unstable with the addition of more taxa. CO Although the existing classification does not Ito i= CO =3 J "CO I adequately describe these preliminary phylo- "co < to to C to i_ < genetic estimates, named clades (genera) ^ < 0 < < c show clear relationships with geography. The <-sr Q £ =3 1 C B B 2 § B to major cladogenic events in the phreato- 8 O Ho CD to 0 icideans appear to have taken place prior to 5J «< * CO 5 I N CD CO eg .co 5 CO the fragmentation
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