Dalhousie Springs hydrobiids : 
T 
hu ee of an endemic hydrobiid genus at Dalhousie Springs with a sister group in the Lake 
concrete SC SS questions about the origin and age of these taxa. Unfortunately there are few 
Dalhousie S on the age of any of the springs associated with the Great Artesian Basin. The age of 
Pleistocene eg has been discussed by Krieg (1989) who concludes that they are probably 
Eyre mede age, being no older than 1-2 million years. Ponder (1986) has suggested that the Lake 
Dalhousie S oup springs contain such a differentiated fauna that they may well be Tertiary in age. If 
to the sprin Penes are indeed Pleistocene in age, it 1s highly probable that Dalhousia is an immigrant 
at D. TE rom some other, now extinct, artesian spring group. It is possible (although unlikely), 
Scenario, the 5 ane D. harrisi had become specifically distinct before this immigration. Thus, in this 
Presence a P а housia fauna of Dalhousie Springs would represent two colonization events. The 
cannot be dis . centralia indicates that multiple invasions of hydrobiids are possible and, indeed, 
other sample КИНЕ from our genetic data. The genetic differentiation of the D24 population from 
Rn Ee Н globosa has probably developed in situ, although, again, the possibility of a third 
to that GES? be discounted. The genetic distance between D24 and D. globosa is comparable 
residence of 5 7 globosa and D. harrisi, supporting the idea that there has been sufficiently long 
кна а ee at Dalhousie Springs for speciation to have occurred in situ. 
Species ma Y iS Fluvidona, on the other hand, is probably not tied to artesian springs and this 
Bees m» e an immigrant from some, probably now extinct habitat, or, possibly, the Flinders 
Separated ATE to us, however, that recent dispersal of such faunas between these two widely 
abitats, pos E is less likely than immigration of the hydrobiids from nearby, previously suitable 
s Ge sibly іп the early Pleistocene. 1 
the EE amphipod at Dalhousie (Zeidler, 1991) is related to another surface species living in 
Sp.) is simi E may have evolved in situ. On the other hand, the surface amphipod (Austrochiltonia 
abitats in т to a species living in the Lake Eyre Supergroup springs and in many other aquatic 
Australia E Australia (Zeidler, 1989), although it is not known elsewhere in central 
he SE Edgbaston Springs in western Queensland (Ponder, 1986). ; 
elsewhere Tee of the hydrobiids within Dalhousie Springs will be discussed in more detail 
genetic dix Jet great morphological plasticity may in part be coupled with their considerable 
| versity. The interplay of factors in the physical and biological environment may also have a 
Signifi i 
nificant influence on shell morphology. There is a considerable range of physical factors such as 
Spring si 
8 size, water depth and temperature and biological factors are also probably important. Ponder 
datory catfish (Neosilurus sp.) in some of 
(198 
the зге ted, for example, that the presence of the pre 
actors, e AER may result in the selection of larger, heavier-shelled individuals. Other biological 
Dalhousia p parasitism, can be significant in some springs. 
Spring m globosa and D. harrisi maintain their genetic in 
Species anb clearly indicating that they are distinct species. Each may yet be found to represent a 
тау be not Set with the Cala (D24) sample of "D. globosa" being the most likely candidate. It 
Pooled gr however, that gene flow in both D. globosa and D. harrisi is apparently high when 
individuals аге considered, with spring groups exchanging migrants at rates of the order of 20 
generally ere ing group per generation (Colgan & Ponder, 1994). This level of gene flow would 
Wit SOEUR sufficient to prevent fragmentation of Dalhousia into isolated, non-interbreeding species 
estricted ranges. 
tegrity over their range within the 
Acknowledgements 
Our f; 
Was nga UK was assisted by J. Waterhouse, D. McIntosh and Н. and J . Renay. Previous field work 
GI. А; y D. Winn and greatly facilitated and supported by W. Zeidler and the South Australian 
natomical e also thank the South Australian Dept. of Conservation for facilitating the work. 
1893086] and shell drawings were rendered by A. Murray. This work was supported by ARC grant 
A 
