Life Sciences Commons^™

Hearing On The Fly: The Effects Of Wing Position On Noctuid Moth Hearing, Shira D. Gordon, Elizabeth Klenschi, James F. C. Windmill

Dartmouth Scholarship

The ear of the noctuid moth has only two auditory neurons, A1 and A2, which function in detecting predatory bats. However, the noctuid's ears are located on the thorax behind the wings. Therefore, as these moths need to hear during flight, it was hypothesized that wing position may affect their hearing. The wing was fixed in three different positions: up, flat and down. An additional subset of animals was measured with freely moving wings. In order to negate any possible acoustic shadowing or diffractive effects, all wings were snipped, leaving the proximal-most portion and the wing hinge intact. Results revealed …

Natural Selection On Thermal Performance In A Novel Thermal Environment, Michael L. Logan, Robert M. Cox, Ryan Calsbeek

Dartmouth Scholarship

Tropical ectotherms are thought to be especially vulnerable to climate change because they are adapted to relatively stable temperature regimes, such that even small increases in environmental temperature may lead to large decreases in physiological performance. One way in which tropical organisms may mitigate the detrimental effects of warming is through evolutionary change in thermal physiology. The speed and magnitude of this response depend, in part, on the strength of climate-driven selection. However, many ectotherms use behavioral adjustments to maintain preferred body temperatures in the face of environmental variation. These behaviors may shelter individuals from natural selection, preventing evolutionary adaptation …

Variation In Arabidopsis Flowering Time Associated With Cis-Regulatory Variation In Constans, Ulises Rosas, Yu Mei, Qiguang Xie, Joshua A. Banta, Royce W. Zhou, Gabriela Seufferheld, Silvia Gerard, Lucy Chou, Naeha Bhambhra, Jennifer Deane Parks, Jonathan M. Flowers, C. Robertson Mcclung, Yoshie Hanzawa, Michael D. Purugganan

Dartmouth Scholarship

The onset of flowering, the change from vegetative to reproductive development, is a major life history transition in flowering plants. Recent work suggests that mutations in cis-regulatory mutations should play critical roles in the evolution of this (as well as other) important adaptive traits, but thus far there has been little evidence that directly links regulatory mutations to evolutionary change at the species level. While several genes have previously been shown to affect natural variation in flowering time in Arabidopsis thaliana, most either show protein-coding changes and/or are found at low frequency (<5%). Here we identify and characterize natural variation in the cis-regulatory sequence in the …

Reconstruction Of Family-Level Phylogenetic Relationships Within Demospongiae (Porifera) Using Nuclear Encoded Housekeeping Genes, Malcolm S. Hill, April Hill, Jose Lopez, Kevin J. Peterson

Dartmouth Scholarship

Background: Demosponges are challenging for phylogenetic systematics because of their plastic and relatively simple morphologies and many deep divergences between major clades. To improve understanding of the phylogenetic relationships within Demospongiae, we sequenced and analyzed seven nuclear housekeeping genes involved in a variety of cellular functions from a diverse group of sponges.

Methodology/Principal Findings: We generated data from each of the four sponge classes (i.e., Calcarea, Demospongiae, Hexactinellida, and Homoscleromorpha), but focused on family-level relationships within demosponges. With data for 21 newly sampled families, our Maximum Likelihood and Bayesian-based approaches recovered previously phylogenetically defined taxa: Keratosap, Myxospongiaep, Spongillidap, Haploscleromorphap (the …

Evolution Of Plant Sucrose Uptake Transporters, Anke Reinders, Alicia B. Sivitz, John M. Ward

Dartmouth Scholarship

In angiosperms, sucrose uptake transporters (SUTs) have important functions especially in vascular tissue. Here we explore the evolutionary origins of SUTs by analysis of angiosperm SUTs and homologous transporters in a vascular early land plant, Selaginella moellendorffii, and a non-vascular plant, the bryophyte Physcomitrella patens, the charophyte algae Chlorokybus atmosphyticus, several red algae and fission yeast, Schizosaccharomyces pombe. Plant SUTs cluster into three types by phylogenetic analysis. Previous studies using angiosperms had shown that types I and II are localized to the plasma membrane while type III SUTs are associated with vacuolar membrane. SUT homologs were …

Evolution Acts On Enhancer Organization To Fine-Tune Gradient Threshold Readouts, Justin Crocker, Yoichiro Tamori, Albert Erives

Dartmouth Scholarship

The elucidation of principles governing evolution of gene regulatory sequence is critical to the study of metazoan diversification. We are therefore exploring the structure and organizational constraints of regulatory sequences by studying functionally equivalent cis-regulatory modules (CRMs) that have been evolving in parallel across several loci. Such an independent dataset allows a multi-locus study that is not hampered by nonfunctional or constrained homology. The neurogenic ectoderm enhancers (NEEs) of Drosophila melanogaster are one such class of coordinately regulated CRMs. The NEEs share a common organization of binding sites and as a set would be useful to study the relationship …

Integration Without Unification: An Argument For Pluralism In The Biological Sciences, Sandra D. Mitchell, Michael R. Dietrich

Dartmouth Scholarship

In this article, we consider the tension between unification and pluralism in biological theory. We begin with a consideration of historical efforts to establish a unified understanding of evolution in the neo‐Darwinian synthesis. The fragmentation of the evolutionary synthesis by molecular evolution suggests the limitations of the general unificationist ideal for biology but not necessarily for integrating explanations. In the second half of this article, we defend a specific variety of pluralism that allows for the integration required for explanations of complex phenomena without unification on a large scale.

Linking Direct And Indirect Data On Dispersal: Isolation By Slope In A Headwater Stream Salamander, Winsor H. Lowe, Gene E. Likens, Mark A. Mcpeek, Don C. Buso

Dartmouth Scholarship

There is growing recognition of the need to incorporate information on movement behavior in landscape-scale studies of dispersal. One way to do this is by using indirect indices of dispersal (e.g., genetic differentiation) to test predictions derived from direct data on movement behavior. Mark–recapture studies documented upstream-biased movement in the salamander Gyrinophilus porphyriticus (Plethodontidae). Based on this information, we hypothesized that gene flow in G. porphyriticus is affected by the slope of the stream. Specifically, because the energy required for upstream dispersal is positively related to slope, we predicted gene flow to be negatively related to change in elevation between …

Origin Of The Eumetazoa: Testing Ecological Predictions Of Molecular Clocks Against The Proterozoic Fossil Record, Kevin J. Peterson, Nicholas J. Butterfield

Dartmouth Scholarship

Molecular clocks have the potential to shed light on the timing of early metazoan divergences, but differing algorithms and calibration points yield conspicuously discordant results. We argue here that competing molecular clock hypotheses should be testable in the fossil record, on the principle that fundamentally new grades of animal organization will have ecosystem-wide impacts. Using a set of seven nuclear-encoded protein sequences, we demonstrate the paraphyly of Porifera and calculate sponge/eumetazoan and cnidarian/bilaterian divergence times by using both distance [minimum evolution (ME)] and maximum likelihood (ML) molecular clocks; ME brackets the appearance of Eumetazoa between 634 and 604 Ma, whereas …