Diversification of epizoic freshwater limpets in ancient lakes on Sulawesi, Indonesia: Coincidence or coevolution?

Abstract

The set of ancient lakes on Sulawesi, Indonesia, represents a unique global hotspot of aquatic biodiversity. These lakes have been recognized widely because of their high number of endemic species with specialized and distinctive morphological characters, life history and ecological adaptations. An interesting case of unusual life history involving brood care exists in the planorbid limpets of the genus Protancylus, which live exclusively as epizoans on the endemic pachychilid gastropod Tylomelania. We aimed to unravel the evolutionary and phylogeographical patterns of Protancylus from the Malili lakes and Lake Poso using two mitochondrial markers in an integrated framework that includes morphological, life-history and ecological data. At least three species of Protancylus evolved allopatrically, with a newly recognized species occurring in lakes Matano and Mahalona. All species are characterized by low morphological variation, shared life-history traits including a unique reproduction strategy. Our genetic data indicates that a drift-based geographic speciation mode correlates with the present distribution pattern. The initial diversification significantly predates the ages of the respective lakes and the lineages of Protancylus are significantly older than their corresponding Tylomelania ‘hosts’. The deep split between P. pileolus of Lake Poso and the populations in the Malili lakes is remarkable and hints to a very early separation in a time frame when Sulawesi reached its current composition. As colonization and onset of diversification is strikingly different in Tylomelania and the epizoic Protancylus, co-evolutionary components in this association can be excluded and both evolved largely independently. We discuss and compare our findings to other invertebrate assemblages in the ancient lakes of Sulawesi.