Ristiyanti M. Marwoto

A Snail Perspective on the Biogeography of Sulawesi, Indonesia: Origin and Intra-Island Dispersal of the Viviparous Freshwater Gastropod Tylomelania

The complex geological history of the Indonesian island Sulawesi has shaped the origin and subsequent diversification of its taxa. For the endemic freshwater snail Tylomelania a vicariant origin from the Australian margin has been hypothesized. Divergence time estimates from a mtDNA phylogeny based on a comprehensive island-wide sampling of Tylomelania fit regional tectonic constraints and support the ‘out-of-Australia’ vicariance hypothesis. The Banggai-Sula region of the Sula Spur, the Australian promontory colliding with West Sulawesi during the Miocene, is identified as a possible source area for the colonization of Sulawesi by the ancestor of Tylomelania. The molecular phylogeny also shows a rapid diversification of Tylomelania into eight major lineages with very little overlap in their distribution on the island. Haplotype networks provide further evidence for a strong spatial structure of genetic diversity in Tylomelania. Distribution boundaries of the major lineages do at best partially coincide with previously identified contact zones for other endemic species groups on Sulawesi. This pattern has likely been influenced by the poor dispersal capabilities and altitudinal distribution limits of this strict freshwater inhabitant. We suggest that late Miocene and Pliocene orogeny in large parts of Sulawesi has been the vicariant event driving primary diversification in Tylomelania.

Preface: Speciation research in ancient lakes – classic concepts and new approaches

Ancient lakes harbor some of the most formidable aquatic ecosystems on earth. Most of the long-term stable lakes are large and extraordinarily deep, and their biotas have evolved under more or less pronounced isolation. This isolation, and the often restricted number of lineages of organisms that successfully invaded their waters, have set the stage for some of the most impressive cases of adaptive radiation, local endemism, and highly adapted organismal communities. It has for long been recognized that the biotas of ancient lakes offer outstanding opportunities for testing hypotheses in evolutionary biology, ecology, climatic history, and geology (Brooks, 1950). In the continuously expanding field of speciation research, much of the knowledge available to date rests upon studies performed in radiations restricted to isolated lakes of varying ages (Martens, 1997; Rossiter & Kawanabe, 2000). This present Special Issue of Hydrobiologia is devoted to recent progresses in the field of speciation in ancient lakes, arising from the 6th SIAL Conference (‘‘Speciation in Ancient Lakes: Classic concepts and new approaches’’), held in Cibinong, Indonesia, in August 2012. Beyond its extraordinarily rich riverine freshwater faunas, distributed over thousands of islands, Indonesia harbors on Sulawesi two ancient water bodies, namely Lake Poso and the Malili Lakes system. It is hence little surprising that several contributions at SIAL 6 were devoted to Indonesia’s native lakes and to the evolution of their endemic species flocks. The range of research presented was however much broader, highlighting the patterns of speciation, and its temporal as well as abiotic context, in ancient lakes from Baikal and Ohrid to Tanganyika. It is in the nature of the topic that the need for definitions stipulated some discussion on the question of the age of so-called ‘‘ancient lakes’’. Electronic supplementary material The online version of this article (doi:10.1007/s10750-014-2028-9) contains supplementary material, which is available to authorized users.

Lack of signal for the impact of venom gene diversity on speciation rates in cone snails

Understanding why some groups of organisms are more diverse than others is a central goal in macroevolution. Evolvability, or lineages’ intrinsic capacity for evolutionary change, is thought to influence disparities in species diversity across taxa. Over macroevolutionary time scales, clades that exhibit high evolvability are expected to have higher speciation rates. Cone snails (family: Conidae, >900 spp.) provide a unique opportunity to test this prediction because their venom genes can be used to characterize differences in evolvability between clades. Cone snails are carnivorous, use prey-specific venom (conotoxins) to capture prey, and the genes that encode venom are known and diversify through gene duplication. Theory predicts that higher gene diversity confers a greater potential to generate novel phenotypes for specialization and adaptation. Therefore, if conotoxin gene diversity gives rise to varying levels of evolvability, conotoxin gene diversity should be coupled with macroevolutionary speciation rates. We applied exon capture techniques to recover phylogenetic markers and conotoxin loci across 314 species, the largest venom discovery effort in a single study. We paired a reconstructed timetree using 12 fossil calibrations with species-specific estimates of conotoxin gene diversity and used trait-dependent diversification methods to test the impact of evolvability on diversification patterns. Surprisingly, did not detect any signal for the relationship between conotoxin gene diversity and speciation rates, suggesting that venom evolution may not be the rate-limiting factor controlling diversification dynamics in Conidae. Comparative analyses showed some signal for the impact of diet and larval dispersal strategy on diversification patterns, though whether or not we detected a signal depended on the dataset and the method. If our results remain true with increased sampling in future studies, they suggest that the rapid evolution of Conidae venom may cause other factors to become more critical to diversification, such as ecological opportunity or traits that promote isolation among lineages.