BiologicalJournal of the Linnean Society (1995), 56: 553-596. With 20 figures Genetic differentiation of aquatic snails (Gastropoda: Hydrobiidae) from artesian springs in arid Australia WINSTON F. PONDER, PETER EGGLER AND DONALD J. COLGAN Australian Museum, 6 College Street, Sydney, NSW; 2000, Australia Received 78 August 1994; acceptedforpublication 19 January 1995 Electrophoretic surveys of 10 species of hydrobiid snails in two indigenous genera (Fomcochlca and Trochidrobia) living in arid-zone artesian ‘mound’ springs are reported. The study is baaed on 96 populations of hydrobiid snails living in 32 different springs representing 18 spring groups in the Lake Eyre Supergroup, northern South Australia. The species-level taxonomy of these snails, previously based on morphological differences alone, was tested and modified. The snails were examined within five clear-cut morphological groups: the two largest, fully. aquatic species (Fonscochlea accepa and F. aquatica) were treated independently, as was the amphibious F. .&ikri The morphologically similar three smaller aquatic species were investigated as a group. Within this group one new species is described and, on the basis of the genetic evidence, two others (F. variabilir and F. conica) are considered conspeciiic. The four species of Trochidrobia are investigated together and T. punicea separately in more detail. Sympatry between Trochidrobia smithi and T. punicea is recorded for the first time. The springs are arranged in an essentially linear pattern and genetic differentiation largely follows an isolation by distance model, although there is a significant genetic discontinuity between two nearby spring groups, BeresfordWarburton Springs and Strangways Spring, which is presumably the result of differential historical continuity of spring habitat. The size of the spring iniluences the degree of genetic difference between springs within spring groups, with small springs attaining greater levels of differentiation than large springs. The findings suggest that if genetic diversity is to be conserved, current management strategies protecting only single springs within a group are inadequate. Despite the considerable number of indigenous species found in these springs, currently all remain on pastoral leases and some are threatened by the continuing expansion of water extraction from the Great Artesian Basin. 0 The Linnean Society of London ADDITIONAL KEY WOBDS-electrophoresis - allozyme - conservation - endangered species - gene llow - new species. CONTENTS Introduction . . . . . . MaterialandMethods : : . . . . . . 554 . . . 555 Results . . . . . . . . . . . . . . 558 Validation and clarification ofspecies . . . . . . . 558 The large aquatic species of Fonscochlea . . . . . . 559 The small aquatic species of Fomcochka . . . . . 565 The amphibious species of Fonscochlea . . . . . . . . 569 Genus Trochidrobia . . . . . . . . . . . . 571 Relationship of geographic distance to genetic differentiation . . 572 Geneticdifferentiationandthe type ofmound . . . . . . 577 553 0024-4066/95/012553+44 $12.0010 Q 1995 The Lirmean Society of London