Molluscan Research 26(1):
8-18; published 22 May 2006
Copyright © The
Malacological Society of Australasia
Mitochondrial DNA variation in an
endemic aquatic snail genus, Caldicochlea (Hydrobiidae;
Caenogastropoda) in Dalhousie Springs, an
Australian arid-zone spring complex
D. J. COLGAN, W. F. PONDER
AND P. DA COSTA
Evolutionary Biology Unit and
Malacology Section, The Australian Museum, 6 College Street, Sydney,
NSW 2010, Australia
Email: Don.colgan@austmus.gov.au
Abstract
The gastropod genus Caldicochlea,
with two recognized species C. harrisi and C. globosa,
is endemic to Dalhousie Springs, an artesian spring system in arid
northern South Australia. A previous study using allozymes showed that
C. harrisi is found in most of the active outflows but C.
globosa is confined to the larger, hotter springs in the northern
third of the complex where the species are sympatric and that
hybridization may be frequent in only two springs. The evolutionary
relationships within Caldicochlea were investigated using 16S
ribosomal RNA (16S: 75 sequences) and cytochrome c oxidase I
(COI: 27 sequences). Clades corresponding to the two species are seen
in both the 16S and COI analyses, the average Kimura 2-parameter
distance between the clades being 0.028 ± 0.007 for 16S rRNA and
0.040 ± 0.016 for COI with no evidence that the recognized taxa
represent species complexes. Only four of 22 16S haplotypes in C.
harrisi were found in more than one spring and only two of 12 in C.
globosa. No COI haplotype was found in more than one spring. In
one spring where earlier research suggested that interbreeding may
occur, all scored DNA sequences belonged to the C. harrisi
clade and in the other such spring all scored sequences belonged to
the C. globosa clade. The data do not clarify whether the time
of primary divergence between the species occurred in situ at
Dalhousie Springs. The absence of suitable habitat refugia since the
onset of Pleistocene aridity suggests that the species have been
sympatric or parapatric over tens of thousands of years, raising
questions as to how an incomplete reproductive isolation can be
maintained and how both species could persist in such a geographically
restricted area.
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