Ph.D. Candidate, Oklahoma State University Center for Health Sciences
Most modern species are identified using evolutionary trees developed from mitochondrial and nuclear DNA. Fossil vertebrate taxa, on the other hand, are identified as a species based on skeletal traits. This is because DNA from these specimens is often too degraded for molecular analysis. Recent studies have shown, however, that DNA and skeletal morphology do not always support the same evolutionary relationships. Instead effects of habitat and climate on the skeleton can swamp out genetic signal. How congruent, therefore, are fossil and biological species? I am testing this question using the North American pine marten, Martes, as a model. This taxon is represented by two modern subspecies and an extinct species, all of which are exposed to a wide variety of habitat and climatic factors. I am collecting 3D geometric morphometric data from the limb bones of modern, historic, and ancient specimens to: 1) quantify the variation present in limb morphology of pine martens; and 2) determine whether this variation correlates with habitat or climate. From these same specimens, I am collecting sequences from four mitochondrial genes to: 1) report the genetic variation present in genes that have never been sequenced; 2) determine the molecular taxonomic status of the extinct noble marten; and 3) test for congruence between the molecular and morphological datasets to determine whether molecularly and morphologically defined species are in fact equivalent. The results of the data I collect in my research will shed light on the reliability of morphology in diagnosing species in the fossil record. If species diagnoses from morphological and molecular data are not congruent, it has considerable implications for how extinct taxa are incorporated into phylogenetic analyses, paleoecological studies, and behavioral/life history interpretations. My research will be the first to study multiple mitochondrial genes in the noble marten and will add to the few genes sequenced in extinct taxa. In addition, my research will provide a >12,000 year record of morphological and mitochondrial variation for North American Martes. This data can then be used to study how the taxon has responded to past changes in habitat and climate and to better project how modern populations may respond to the current habitat shrinking and climatic warming they face.
Abstract: Convergence in morphology can result from evolutionary adaptations in species living in environments with similar selective pressures. Here, we investigate whether the shape of the forelimb long bones has converged in environments imposing similar functional constraints, using musteloid carnivores as a model. The limbs of quadrupeds are subjected to many factors that may influence their shape. They need to support body mass without collapsing or breaking, yet at the same time resist the stresses and strains induced by locomotion. This likely imposes strong constraints on their morphology. Our geometric morphometric analyses show that locomotion, body mass and phylogeny all influence the shape of the forelimb. Furthermore, we find a remarkable convergence between: (i) aquatic and semi-fossorial species, both displaying a robust forelimb, with a shape that improves stability and load transfer in response to the physical resistance imposed by the locomotor environment; and (ii) aquatic and arboreal/semi-arboreal species, with both groups displaying a broad capitulum. This augments the degree of pronation/supination, an important feature for climbing as well as grasping and manipulation ability, behaviors common to aquatic and arboreal species. In summary, our results highlight how musteloids with different locomotor ecologies show differences in the anatomy of their forelimb bones. Yet, functional demands for limb movement through dense media also result in convergence in forelimb long-bone shape between diverse groups, for example, otters and badgers.
Pub.: 23 May '15, Pinned: 17 Jun '17
Abstract: The arrival of bison in North America marks one of the most successful large-mammal dispersals from Asia within the last million years, yet the timing and nature of this event remain poorly determined. Here, we used a combined paleontological and paleogenomic approach to provide a robust timeline for the entry and subsequent evolution of bison within North America. We characterized two fossil-rich localities in Canada’s Yukon and identified the oldest well-constrained bison fossil in North America, a 130,000-y-old steppe bison, Bison cf. priscus. We extracted and sequenced mitochondrial genomes from both this bison and from the remains of a recently discovered, ∼120,000-y-old giant long-horned bison, Bison latifrons, from Snowmass, Colorado. We analyzed these and 44 other bison mitogenomes with ages that span the Late Pleistocene, and identified two waves of bison dispersal into North America from Asia, the earliest of which occurred ∼195–135 thousand y ago and preceded the morphological diversification of North American bison, and the second of which occurred during the Late Pleistocene, ∼45–21 thousand y ago. This chronological arc establishes that bison first entered North America during the sea level lowstand accompanying marine isotope stage 6, rejecting earlier records of bison in North America. After their invasion, bison rapidly colonized North America during the last interglaciation, spreading from Alaska through continental North America; they have been continuously resident since then.
Pub.: 13 Mar '17, Pinned: 17 Jun '17
Abstract: The straight-tusked elephants Palaeoloxodon spp. were widespread across Eurasia during the Pleistocene. Phylogenetic reconstructions using morphological traits have grouped them with Asian elephants (Elephas maximus), and many paleontologists place Palaeoloxodon within Elephas. Here, we report the recovery of full mitochondrial genomes from four and partial nuclear genomes from two P. antiquus fossils. These fossils were collected at two sites in Germany, Neumark-Nord and Weimar-Ehringsdorf, and likely date to interglacial periods ~120 and ~244 thousand years ago, respectively. Unexpectedly, nuclear and mitochondrial DNA analyses suggest that P. antiquus was a close relative of extant African forest elephants (Loxodonta cyclotis). Species previously referred to Palaeoloxodon are thus most parsimoniously explained as having diverged from the lineage of Loxodonta, indicating that Loxodonta has not been constrained to Africa. Our results demonstrate that the current picture of elephant evolution is in need of substantial revision.
Pub.: 07 Jun '17, Pinned: 17 Jun '17
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