Conservation Genetics of Rare Tree Snails from the Hawaiian and Mariana Islands: Distribution of Genetic Diversity at Varying Scales of Population Fragmentation and Isolation

Sischo, David

Conservation Genetics of Rare Tree Snails from the Hawaiian and Mariana Islands: Distribution of Genetic Diversity at Varying Scales of Population Fragmentation and Isolation

Files

2015-08-phd-sischo_r.pdf (10.82 MB)

2015-08-phd-sischo_uh.pdf (10.86 MB)

Date

2015-08

Authors

Sischo, David

Publisher

[Honolulu] : [University of Hawaii at Manoa], [August 2015]

Abstract

Island archipelagos across the Pacific have hosted spectacular land-snail radiations. Unfortunately, due primarily to habitat fragmentation and loss and the introduction of invasive snail predators, these spectacular island radiations are now facing rapid extinctions. Although much effort is focused on tree-snail conservation, little is understood regarding how fragmentation and isolation impact the dynamics and distribution of genetic diversity in remaining populations. This dissertation consists of three separate studies using conservation genetics to broadly investigate how fragmentation and isolation of populations, at varying scales, impacts populations of tree snails, and what can be done to better manage genetic diversity to prevent extinction. First, a phylogenetic approach was used to assess the distribution of extant tree snails in the family Partulidae of the Mariana Islands. This study focused on Partula gibba, a species that has an unusually large and fragmented distribution across nine islands. A cryptic species endemic to the island of Rota was found, as well as two distinct clades of P. gibba distributed across islands. Intra-island genetic diversity was low providing further evidence that P. gibba self-fertilizes and highlights the need to conserve populations across the range of P. gibba to prevent drastic losses of genetic diversity. Next, I assessed the population structure of Partulina redfieldi, a tree snail once widespread on the Hawaiian island of Moloka‘i, that now exits only in a small fragmented portion of its former range. The distribution of genetic diversity across habitat patches was assessed using 11 microsatellite loci. Evidence of reduced gene flow and significant isolation-by-distance effects between habitat patches over very short distances (>20 meters) was observed. Lastly, demographic and genetic methods were used to assess a drastic population decline occurring over 20 years and four generations in an ex situ population of Achatinella fuscobasis, a tree snail endemic to the Hawaiian Island of O‘ahu. While there is evidence that the founding individuals came from an already bottlenecked population, there was no additional change in genetic diversity measures such as allelic richness, gene diversity, and observed heterozygosity among all generations. Due to the signal of a selection event in the F3 generation, we now suspect the population decline may be stochastic in nature, with bottleneck effects that occurred before the founding of the ex situ population, acting synergistically with other factors.

Description

Ph.D. University of Hawaii at Manoa 2015.
Includes bibliographical references.

Keywords

Conservation Genetics, Tree Snail, Phylogeography, Habitat Fragmentation

URI

http://hdl.handle.net/10125/51128

Related To

Theses for the degree of Doctor of Philosophy (University of Hawaii at Manoa). Zoology

Collections

Ph.D. - Zoology

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