Allozyme variation in the troglobitic millipede Stygiochiropus communis (Diplopoda: Paradoxosomatidae) from arid tropical Cape Range, northwestern Australia: population structure and implications for the management of the region

WA Museum Records and Supplements | Updated 8 years ago

ABSTRACT – The millipede genus Stygiochiropus is endemic to Cape Range in the arid tropics of northwestern Australia. The genus is restricted to caves throughout the range and is highly troglomorphic. Millipedes collected from 36 caves were examined for genetic variation at up to 27 allozyme loci. The allozyme data reveal the existence of three genetic provinces within Stygiochiropus communis. Between provinces there is an average of 25% fixed differences, indicating that no short-term gene flow occurs between any of the three. The provinces are loosely concordant with the geomorphological structure of Cape Range, namely with the gorges which cut through the cavernous limestone into a non-cavernous limestone below. The three genetic provinces have different characteristics; the southern province is genetically much more homogeneous that the northern or central provinces. There are also a large number of statistically significant differences in allele frequency, involving 10 loci, between caves within each province, with the number increasing from south to north. The loci involved in any province differ entirely from those exhibiting differences in the other provinces. Within provinces, distant caves may exhibit no significant differences in allele frequency from one another whereas caves spatially much closer may show substantial allozymic differences. This result suggests that the genetic structuring within provinces is associated with surface drainage basins as well as with deep gorges within the provinces and mdicates that the discrete sub-population model should be applied to the population structure in this species between and, in some cases, within genetic provinces. The general concordance of the major provinces with those found in other terrestrial and aquatic troglobitic taxa suggests that the overall management of the Cape Range karst should take cognisance of these genetic patterns. It suggests also that the northern part of the range, which is a more immature karst development, is likely to contain a diversity of distinct species across many taxa. The clear differentiation of the three genetic provinces, plus the northern area outside the range of S. communis where several additional species of Stygiochiropus occur, suggest that each area is likely to contain a suite of troglobitic species restricted to these areas. In addition, the absent or severely restricted gene flow between many caves within the karst provinces is likely to be reflected in other members of the rich troglobitic fauna of Cape Range. Comprehensive conservation of the troglobitic fauna requires that populations are maintained throughout the extent of Cape Range.