Date of Award

Winter 11-30-2020

Semester of Degree

December

Document Type

Restricted Access Dissertation

Degree Name

Ph.D. in Environmental and Forest Biology

Department

Environmental and Forest Biology

Major Professor

Rebecca Rundell

Steering Committee Member

Warren Allmon

Steering Committee Member

Alex Weir

Abstract

Many aspects of the evolution and biogeography of land snails remain unexplored for all but the most well studied families in select few areas of the world. The evolutionary history of land snails is further complicated by their poor fossil record especially in extant centers of their diversity (e.g. Southeast Asia, Pacific Islands). The objectives of this dissertation were to investigate: 1) the land snail fauna of mid-Cretaceous Burmese amber, and 2) the evolution and biogeography of the threatened punctoid land snail fauna of Belau (Republic of Palau, Oceania).

Twelve specimens were described from Burmese amber representing 5 new genera, and 6 new species from 4 families (Diplommatinidae, Cyclophoridae, Pupinidae, and Assimineidae). These specimens include some of the earliest fossil representatives of these families and reveal the faunal stability of this land snail community since the late Mesozoic. After nearly a century of taxonomic confusion, the position of superfamily Punctoidea is confirmed as basal within the stylommatophoran suborder Helicina. Superfamily Punctoidea and Endodontidae are estimated to have originated on Gondwana in the Late Jurassic and Early Cretaceous respectively, based on divergence time estimation and the fossil and extant biogeography of Punctoidea. The Pacific endemic distribution of the Endodontidae is thus likely due to long distance dispersal events from the fragmenting supercontinent and source continental extinction. The phylogenetic relationships of the Belau punctoid fauna were also resolved revealing a lack of geographic signal characterisitic of more well studied island land snail faunas. In addition, shell morphologies traditionally interpreted as being adaptive (e.g. shell shape and apertural barriers) have arisen and have been lost without ecological divergence suggesting non-adaptive trait shifts. In addition, six new Belau punctoid taxa are reported from living individuals for the first time in over 50 years. Finally, molecular species delimitation methods conducted for the three described Semperdon species reveal 3 additional cryptic lineages. The phylogeographic structure of Semperdon ITS2 haplotypes reveal high genetic distance between island groups within the archipelago despite short geographic distances. This isolation between island groups is likely maintained through the extremely low-vagility of these snails and fine-scale vicariance events associated with sea-level change.

Share

COinS