Jennifer Britt
brittje@bcc.orst.edu
Oregon
State University
Zoology Department
5084 Cordley Hall
Corvallis, OR 97331 USA
Former Advisors:
Dr.
Michael Lynch, currently at IU
Dr.
John H. Postlethwait, Institute of Neuroscience
IGERT Trainee from 1999-2001
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Research Interests
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Jennifer earned her Ph.D. in 2001 and is currently working in the Menge/Lubchenko Lab at Oregon State University as the PISCO Program Manager
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Evolutionary theory predicts that organisms will diverge phenotypically under the pressure of natural selection as they adapt to new niches and different ways of life, yet we see similar traits evolving repeatedly in separate lineages as they evolve and diverge. This type of resemblance among taxa is often due to the recurrent evolution of phenotypic traits, termed homoplasy, rather than common ancestry. The study of homoplastic evolution can provide unique insights into the nature of adaptive evolution. It may help us to understand the influence that internal design mechanisms can have on the development of the phenotypic patterns we see today.
A broad phylogenetic analysis of the genus Daphnia reveals a melanized cuticle has arisen on at least five separate occasions, via homoplastic evolution, in an apparent response to increased levels of ultra violet radiation (figure 1) (Colbourne 2000 in prep). The addition of the genus Scapholeberis to the phylogeny suggests a sixth gain of cuticular melanization in the Cladocerans. It also appears that melanin biosynthesis in Daphnia is developmentally controlled. The melanin is shed with the carapace at each molt and is synthesized new during ecdysis as the carapace forms.
In order to understand how the same trait can evolve over and over in distinct lineages and how underlying developmental mechanisms are involved in that evolution, I am interested in investigating the recurrent evolution of cuticular melanization in the Daphnia. Given the highly conserved process of melanin synthesis, how is such a seemingly complex spatially and temporally controlled pathway altered to produce a melanic phenotype? I will examine this by addressing two main questions:
- Are genes involved in melanin biosynthesis expressed in the same of different spatial and temporal patterns in each branch of melanic Daphnia?
- Is the same regulatory gene responsible for the induction of cuticular melanization in all the melanic Daphnia?
To resolve these questions I am taking two different approaches in the study of cuticular melanization in Daphnia. To determine the spatial and temporal expression patterns of the genes involved in melanin synthesis, I will carry out in situ hybridizations on known genes in the melanin pathway throughout ecdysis in melanic and non-melanic Daphnia morphotypes. Comparative in situ's will allow me to determine if the expression of the melanin pathway genes expression are the same or different in separate Daphnia lineages. Gene expression patterns during ecdysis will also demonstrate how the genes are regulated during juvenile and adult development. Taking advantage the Daphnia genome linkage map being created in the Mike Lynch's lab, I will be able to map and define the regulatory gene, or genes, responsible for the induction of cuticular melanization in Daphnia. Once I have located this gene in one melanic lineage, I can look for the same gene, or changes in the gene, in other melanic and non-melanic lineages. The results of these experiments should provide strong clues as to how cuticular melanism evolved in the genus Daphnia and how genetic, genomic, and developmental factors interact to produce a novel phenotype.
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Publications
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