Date of Award

6-2011

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology/Environmental Biology

First Advisor

Ron Etter

Second Advisor

Michael Rex

Third Advisor

Richard Kesseli

Abstract

The evolution of deep-sea fauna is poorly known. We know little about the scales of population differentiation, radiation and colonization of the deep sea. This dissertation explores evolution in the deep sea at the level of population differentiation on ocean-wide scales in a gastropod species Benthonella tenella and phylogeny of a deep-sea subfamily of protobranch bivalves, Ledellinae. While working on the phylogeny of the Ledellinae the presence of mitochondrial heteroplasmy was discovered.

Genetic variation was quantified within and among populations of deep-sea gastropod Benthonella tenella to identify the extent of population differentiation and potential mechanisms that might isolate gene pools. Benthonella tenella shows significant population differentiation among basins, especially between eastern and western corridors of the Atlantic. Genetic divergence among samples was correlated with depth on numerous scales - ocean-wide, within the western Atlantic, and within some basins. Isolation by distance was not detected within the western Atlantic. Genetic population structure in this species is related to a complex array of evolutionary processes including depth-related environmental changes, historical events, topographic barriers and ocean currents.

Most metazoan species have strict maternal inheritance of the mitochondrial genome. A unique inheritance pattern called, Double Uniparental Inheritance (DUI) occurs in at least seven bivalve families. In this system, males inherit and carry mtDNA from both parents, while females only carry mtDNA from the mother. Evidence of DUI was detected in two species of protobranch bivalves from the family Nuculanidae. Divergent 16S rRNA sequences were obtained within individuals for both Ledella ultima and Ledella sublevis. Ratios of homoplasmic to heteroplasmic individuals were approximately 1:1, in agreement with sex ratios in protobranchs.

The subfamily Ledellinae was used to test hypotheses about colonization and speciation patterns within the Atlantic. Phylogenies based on the mitochondrial 16S, and the nuclear 18S, 28S and H3 genes were developed. A monophyletic grouping of the Ledellinae was supported and consisted of Ledella ultima, Spinula species and other Ledella species. There is a bathymetric pattern of abyssal species Ledella ultima and the Spinula sp. forming a deep branch basal to the other confamilial species with a more recent radiation at bathyal depths.

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