Phylogeny, biogeography and systematics of the Philippine Helicostylinae (Gastropoda: Stylommatophora: Camaenidae)
Authors:   , Batomalaque Gizelle Akiate , Rosenberg Gary 
Published: March 2022

Land snails on oceanic islands have captured the fascination of biologists for years, including Charles Darwin who wrote in a letter to the botanist Joseph Hooker, "I have for [the] last 15 months been tormented & haunted by land Mollusca, which occur on every oceanic island; & I thought that the double creationists or continental extensionists had here a complete victory" (Darwin Correspondence Project, 2019). Darwin then conducted experiments by immersing hibernating land snails in sea water for twenty days and found that one species, Helix pomatia, recovered (Darwin, 1859). Several workers have followed suite in trying to understand the means of dispersal and diversification of land snails in oceanic islands, such as those in the Hawaiian Islands (Rundell et al., 2004), the Galapagos Islands (Parent & Crespi, 2006), and the Ogasawara Islands (Chiba & Davison, 2007). The Philippine archipelago is known for its high diversity and endemism of terrestrial fauna (Posa et al., 2008). Owing to its dynamic geological history, several biogeographical studies of Philippine taxa have been conducted, although these heavily focused on vertebrates (Evans et al., 2003; Esselstyn & Oliveros, 2010; Brown & Siler, 2014) and no biogeographic studies have been conducted on land snails. The land snail subfamily Helicostylinae are among the most speciose and morphologically diverse groups of land snails in the Philippines, yet their diversification across the islands is not well understood (Parkinson et al., 1987). This thesis seeks to shed light on the evolution of this hyper diverse group of land snails in the Philippines. Chapter 2 provides an overview of the diversity and distribution of helicostyline land snails. Literature and various museum specimens-including type materials-were examined to produce a comprehensive species list. Furthermore, distribution maps of each genus were generated to visualize malacofaunal regions and possible areas of endemism within the archipelago. Chapter 3 elucidates the phylogenetic relationship of subfamily Helicostylinae with respect to other land snails in Asia and Australia that belong to families Bradybaenidae and Camaenidae. This was done through high throughput sequencing of the exome. A time-calibrated phylogeny was also generated using fossils. This chapter also answers the age-old question of whether the Bradybaenidae and Camaenidae should be treated as a single family or separate families. In Chapter 3, the species currently classified under subfamily Helicostylinae are rendered non-monophyletic. Chapter 4 focuses on the evolutionary relationships within the crown helicostylines as well as their biogeographical history in the Philippine archipelago. A time-calibrated phylogeny was generated using a secondary calibration from the previous chapter. Likelihood-based character evolution was estimated for several conchological and anatomical characters. A likelihood-based approach was also implemented to estimate the biogeographical events (i.e. long-distance dispersal, range-expansion) that occurred in the crown helicostyline history. Finally, Chapter 5 is a genus-level taxonomic revision of the Philippine helicostylines, wherein the phylogenetic relationships are reflected. Shell morphology and reproductive anatomy were examined and are described and illustrated here for the first time.