Jennifer Brisson
Campus Box 1137
Department of Biology
Washington University
St. Louis, MO 63130
brisson@biology.wustl.edu

publications and support

Evolution and Development of Abdominal Pigmentation Pattern in Natural Populations of Drosophila polymorpha
My primary interest, how changes in the temporal or spatial deployment of genes during development result in morphological differences between individuals or species, falls within the realm of evolutionary developmental biology. This field has traditionally focused primarily on comparative gene expression studies over large phylogenetic distances, and has yielded significant insights into the basic processes underlying the development of metazoans. However, since evolutionary forces act on morphological variation at the level of individuals within a reproducing population, an intraspecific study is especially appropriate for addressing the link between genotype, phenotype and the environment.
I am thus performing a microevolutionary developmental study on a trait that exhibits a high level of variation at the intraspecific level in natural populations: abdominal pigmentation pattern in the South American species Drosophila polymorpha (see picture). Collections from Brazil have yielded an interesting pattern: darker phenotypes are commonly associated with open, dry conditions, whereas lighter phenotypes are associated with forested, more humid environments. This pattern is reflected in other species of the group as well: D. neocardini, a fly with a light abdomen, is restricted to forests whereas D. cardini, a fly with a dark abdomen, is primarily found in more open environments. I am currently testing whether this trait is in some way associated with water balance in D. polymorpha.
a) light male b) light female c) intermed. male d) intermed. female e) dark male f) dark femalephoto courtesy of Daniela De Toni

My thesis project is based on three primary objectives, and is being done in collaboration with Dr. Alan Templeton of the population genetics and evolutionary biology program and Dr. Ian Duncan of the development program at Washington University:
Objective 1. Compare the expression of genes suspected to play a role in the development of the abdominal pigmentation phenotype in developing pupae of both light and dark morphs of D. polymorpha;
Objective 2. Correlation of genotype with phenotype: sequence haplotypes at candidate loci and look for correlations with the abdominal pigmentation phenotype;
Objective 3. Phylogeographic study to examine microevolutionary forces acting on the species, and their correlation with the distribtion of the abdominal phenotypes.

The effects of fire management on populations of collared lizards in the Missouri Ozarks
Each summer, in collaboration with Jared Strasburg and Alan Templeton, I study the effects of fire management on collared lizard (Crotaphytus collaris collaris) populations at Taum Sauk Mountain State Park in the Ozarks of southeastern Missouri using mark-recapture data. Collared lizards are desert-adapted, relictual species in the Ozarks, the most northeastern part of their range. As such, they are restricted to the dry arid conditions found on glades, rocky outcrops that are habitat "islands" in the midst of the oak-hickory forests typical of the Ozarks. Without periodic fires, junipers begin to overtake the glade habitats, which subsequently opens them for further plant succession. Thus, without fires, glade habitat degenerates.
male collared
female collared with gravid coloration

Further, without fires, the forest understory becomes dense, and effectively impedes any dispersal of collared lizards between glades separated by as little as 50 meters. Collared lizard populations are typically small, and isolation of these small populations leads to predictable results: inbreeding, susceptibility to stochastic processes, and local extinction.

Areas of Taum Sauk have been burnt periodically since December of 1992. With our mark-recapture study, we have been monitoring movement between glade habitats, growth rates and sizes of lizards, and local population sizes. Since we initiated the study in 1998, we have seen a significant increase in population size, as well as colonization of previously uninhabited glades, probably due to fire management improving the health of the glade habitat and opening up new glades.
typical glade habitat in the Missouri Ozarks
This study complements a larger ongoing study being conducted at Peck Ranch by Robert Robertson and others. The Peck Ranch study in combination with the Taum Sauk study are demonstrating that fire management can have positive effects on the general health of collared lizards in the Missouri Ozarks. Monitoring of this species is especially important because it is listed as a species of special concern by the Missouri Department of Conservation.
Templeton, Robertson, Brisson and Strasburg. 2001. Disrupting evolutionary processes: the effect of habitat fragmentation on collared lizards of the Missouri Ozarks. PNAS 98:5426-5432.
Some images from Taum Sauk:
gravid female
lefty
 lizard catching crew
male Sceloporus
yearling female
basking male