Date of Award

8-1-2003

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biology

Abstract

The geographical and geneological limits of species are firmly rooted in historical and current processes. Phylogenetic studies focus on the historical aspect and examine character states to estimate ancestor-descendent relationships. The number of described species in the world has been estimated at 1.4 to 1.8 million and other estimates suggest that as many as 30 million species may exist (May, 1990; Wilson, 1992). Phylogenetic studies provide the information needed to delimit and classify these species based on their historical relationships. Studies on species population structure focus on the current and historical processes acting on a species. These studies use a variety of methods and estimate gene flow and allele frequencies across the species range.

This thesis is composed of three chapters that examine the phylogeny and population structure of the prairie skink, Eumeces septentrionalis. Chapter 1 reviews some of the current methods available for examining population structure and justifies the m ethods used in this study. Chapter 2 examines the phylogenetic relationships within Eumeces septentrionalis using DMA sequence data from two portions of the mitochondrial genome. Specifically, populations from the northern subspecies, E. s. septentrionalis, are compared with the southern subspecies, E. s. obtusirostris. These data along with the phylogenetic species concept are then used to examine the placement of E. s. septentrionalis and E. s. obtusirostris as one or two distinct species. Chapter 3 focuses on the population structure of E. septentrionalis specifically with respect to the northern populations to examine the recolonization pattern following Pleistocene glaciation events.

Two field seasons in the spring and summer of 2001 and 2002 were conducted for this study during which sixty-four tissue samples were collected from individuals in Canada, North Dakota, South Dakota, Minnesota, Wisconsin, and Kansas. ND4 (807 bp) and d-loop (~747 bp) regions of the mitochondrial genome (ND4 and d-loop) were sequenced from the collected samples, and these data were used in both phylogenetic and population structure analyses.

Phylogenetic analyses demonstrated a substantial sequence divergence and reciprocal monophyly between the northern and southern subspecies of E. septentrionalis. Uncorrected pairwise distance values between the northern and southern subspecies ranged from 6.7 - 7.0%, and the monophyly of the northern and southern subspecies, E. s. septentrionalis and E. s. obtusirostris, were strongly supported by both maximum parsimony (bootstrap = 100) and maximum likelihood analyses. These results support the morphological differences found in previous studies and suggest that these two subspecies may be on separate evolutionary trajectories.

The population structure of the prairie skink, E. septentrionalis, was examined using nested clade analyses, which revealed isolation by distance with restricted gene flow as the inferred geographical pattern for northern populations (E. s. septentrionalis). This pattern reflects the lack of overlapping haplotypes in distant populations and was found at both the hapiotype and upper clade levels. These results indicate that E. septentrionalis was likely subject to one or more vicariant events, and subsequently several localities probably acted as refugia and source populations during times of glacial advance and retreat.

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