STUDENT RESEaRch SympoSiUm 2010 - Graduate and Research ...

AbstrActs
#249 3:15
Shape Analysis of the Mandibles of Odontocetes (Toothed
Whales)
Celia Barroso, Biology (M)
Annalisa Berta, Biology
Odontocete mandibles serve multiple functions, including feeding
and hearing. Sound is thought to enter the hearing apparatus
through the pan bone of the posterior mandibles (Norris, 1968).
Recently, computer models suggest that sound also follows a
“gular” pathway below the mandibles (Cranford et al. 2008).
The unambiguous link between form and function has catalyzed
our study of mandibular shape. Previous studies have described
odontocete mandibles using linear morphometrics and focused
on multiple populations within a single genus (Westgate, 2007).
We use Geometric Morphometrics (GM) to avoid some limitations
of linear morphometric studies, using relative 3-D landmark positions
instead of lengths. The objective of this study is to use GM
to quantify mandibular shape variation across all major lineages
of odontocetes (36 specimens, 22 species). This superimposition
technique measures shape only, excluding any scaling, rotational,
and positional effects. Preliminary results indicate that the
majority of shape variation occurs within portions of the mandible
that are associated with feeding – the length of the symphysis
(43%), the connection between left and right mandibles, and
splay, or width, of the mandiblar condyles (35%). Portions of
the mandibles associated with sound reception exhibit the next
largest amount of shape variation (7%). Furthermore, comparative
phylogenetic analyses suggest that ecological factors, such
as feeding behavior, may play a role in shaping jaws, in addition to
phylogenetic relationships.
#250 3:30
The Comparative Anatomy of Baleen and its Role in
Mysticete Feeding Ecology
Samantha Young, Evolutionary Biology (M)
Annalisa Berta, Biology
The four extant families of mysticete (baleen) whales employ
a variety of filter-feeding methods: continuous ram feeding, or
skimming (Balaenidae, right whales, and Neobalaenidae, pygmy
right whale), intermittent suction feeding (Eschrichtiidae, gray
whale), and intermittent ram feeding, or engulfment/lunge feeding
(Balaenopteridae, rorquals). Mysticetes are specialized in
their strategies of filtering prey and exhibit unique morphological
features, which contribute to effective consumption of large
quantities of invertebrates and small fish. They utilize a novel
filter feeding apparatus known as baleen, an epidermal tissue
composed of keratin which occupies the place of teeth in the
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mysticete jaw. The primary objective of this study is to describe
the anatomy of baleen, focusing on the morphological and structural
variation between and within mysticete families. Furthermore,
selective pressures (e.g. phylogenetic relationships/inertia,
feeding ecology, inherent property of baleen morphology) that
may be acting upon and driving this variation will be investigated.
Finally, the evolution of baleen and filter feeding in mysticetes will
be examined. Previous work has provided ecologically significant
broad scale measurements of baleen, including four variables
highlighted in this study: baleen plate length and width, bristle
density and bristle diameter. Data collected from 23 balaenopterids,
eight balaenids and three eschrichtiids were employed in
statistical analyses and ancestral character state reconstructions.
The preliminary results indicate differences in baleen plate length
and width between balaenids and balaenopteroids (balaenopterids
+ eschrichtiids) and quantify the coarse bristles found in
eschrichtiids. Bristle density shows no familial groupings and is
likely correlated with feeding ecology. Balaenids and eschrichtiids
are significantly different for all three variables analyzed.
Ancestral character state reconstructions show consistency in
phylogenetic relationships for plate length and width; however,
feeding strategies/diets show phylogenetic convergence between
eschrichtiids and balaenids, and Megaptera novaeangliae (humpback)
and Balaenoptera acutorostrata (minke).
#251 3:45
Testing Phylogenetic and Phylogeographic Hypotheses
in Acuclavella (Opiliones, Ischyropsalidoidea) from the
Western Hemlock Zone of the Pacific Northwest
Casey Richart, Evolutionary Biology (M)
Marshal Hedin, Biology
Phylogenetics and phylogeography have played a pivotal role in
the study of evolutionary processes, such as population divergence
and speciation. The role of geographic barriers or climatic
fluctuations in evolutionary diversification can now be explored
via testable hypotheses. Since the study of vicariance of disparate
populations or speciation via allopatry could potentially
be explored at the intraspecific or interspecific (often sister)
levels, methodological tools ranging the phylogeographic-tophylogenetic
spectrum must be employed (Carstens et al. 2004).
These tools are employed in the context of thorough geographic
sampling, morphometrics, and multiple loci. Here, the non-vagile
opilionid genus Acuclavella is explored using an integrated approach
to test species limits in the genus, and to test regional
hypotheses pertaining to Pleistocene refugia, riverine barriers,
and ancient vicariance.
STUDENT RESEARCH SYMPOSIUM 2010