| Apple snails (Ampullariidae) are freshwater, operculate snails globally distributed in humid tropical and subtropical habitats. Nine genera are recognized: Afropomus, Saulea and Lanistes are African; Pila is African and Asian; Asolene, Felipponea, Marisa and Pomella are South American; Pomacea ranges from Argentina to the southeastern USA. Ampullariid taxonomy and evolutionary relationships have historically been poorly understood, especially regarding Pomacea , which has implications for research on many aspects of ampullariid evolutionary biology. In this dissertation I present the most comprehensive assessment of ampullariid phylogenetic systematics to date and explore some central themes in evolutionary biology that are pertinent to apple snails and their evolution in the Neotropics. In reconstructing the phylogenetic relationships of the ampullariids I used two mitochondrial and three nuclear genes. Analyses of these genes independently and in combination support the reciprocal monophyly of the New and Old World taxa and confirm the need for a taxonomic revision of the New World genera. The phylogeny also reveals a trend of increasingly amphibious habits among some of the more derived ampullariids. Such changes in habits appear to have evolved in parallel with increases in siphon length and expansion of the lung, efficacy of atmospheric oxygen uptake, diversification and enlargement of the copulatory apparatus, desiccation resistance, oviposition behavior and egg morphology. All these changes, in concert with the changing freshwater systems of the Neotropics during the last 90 myr, have probably played a significant role in the evolution of ampullariids. Understanding such processes combined with the well resolved phylogeny have allowed me to better characterize apple snail invasiveness and accurately identify those species introduced outside their native ranges. Finally, since the Ampullariidae are probably the sister group to all Caenogastropoda, this phylogeny establishes the basis for future studies that will provide insights into gastropod evolution in general. |
