Contributions to Zoology, 77 (2) - 2008Frederick R. Schram: Does biogeography have a future in a globalized world with globalized faunas?

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Anaspidacea

The order Anaspidacea has long fascinated carcinologists. The group was known from the fossil record, with the description of Uronectes fimbriatus (Jordan, 1847) from the Permian of Bohemia, a long time before the first living form, Anaspides tasmaniae Thomson, 1892, was recognized. Calman (1917) was the first to suggest a link between that fossil and the at-that-time newly redescribed Bathynella natans as well as the Tasmanian mountain shrimp, A. tasmaniae. Indeed, Uronectes fimbriatus was the first described species of what came to be acknowledged as a diverse radiation of ‘palaeocaridaceans’ in the Paleozoic. However, cladistic analyses (currently underway) reveal that the so-called ‘order’ Palaeocaridacea constitutes a paraphyletic series of stem families that lead to the crown group Anaspidacea. One Triassic fossil from New South Wales, Anaspidites antiquus (Chilton, 1929), is in fact assigned to the anaspidines and another fossil from the Cretaceous of Victoria, Koonaspides indistinctus Jell and Duncan, 1986, appears to also lie within the anaspidines.

However, what the distribution of the modern representatives of the family Anaspididae tells us leads us to question whether everything about Anaspidacea can be related to the status as a so-called ‘living fossil’ (Schram and Hessler, 1984). Anaspididae occurs only on Tasmania, extending from the central plateau down into the south and southwestern sections of the state. Four species have been recognized: Anaspides tasmaniae (originally described from Mt. Wellington but thought to be widespread across the island), Paranaspides lacustris Smith, 1909 (restricted to certain lakes on the central plateau), and Allanaspides hickmani Swain, Wilson and Ong, 1970 and A. helonomus Swain, Wilson, Hickman and Ong, 1970 (restricted to the region around Lakes Pedder and Gordon in the southwest). A fifth species Anaspides spinulae Williams, 1965 (from Lake St. Claire) has generally found little acceptance, most authorities considering it a morphological variant of A. tasmaniae.

Jarman and Elliott (2000) examined 16S rDNA sequences and uncovered a diverse radiation within the genus Anaspides, with at least three ‘species’ clades indicated: their ‘species 1’ clade containing the type locality of A. tasmaniae and the controversial A. spinulae, and the clades of ‘species 2 + 3’ being quite distinct (see Jarman and Elliot, 2000, fig. 4) from species.

Subsequently, Andrew (2004) conducted electrophoretic studies of an array of populations from across the island of all the species of anaspidids and uncovered similar, though slightly different, results to those of Jarman and Elliott: a set of southern populations that accorded well with ‘species 1’, southwestern populations that accorded with ‘species 2’, an array of central plateau populations that include the type locality for A. spinulae, and finally the separate Mt. Wellington type locality for A. tasmaniae.

The number of new species necessary to accommodate this molecular diversity remains to be determined (Ahyong, personal communication). Of special interest, however, are the molecular clock estimates for times of divergence (Tables 1 & 2). While the limited fossil material indicates Mesozoic origins for the anaspidines, the clock estimates place the radiation of known Anaspididae well within the Tertiary.

FIG2

Table 1. Molecular clock estimates of times of divergence of species of Anaspididae on Tasmania, modified from Jarman and Elliott (2000).

FIG2

Table 2. Molecular clock estimates of times of divergence of species of Anaspididae on Tasmania, modified from Andrew (2004).

At face value, it would appear that the Tasmanian anaspidids might not be ‘living fossils’ at all. A careful examination of the phylogeography of the living anaspidids reveals that in this supposedly ancient group, the speciation actively going on is a rather young event – of an order of 10s of millions of years rather hundreds of millions of years.