Contemplating host race formation
R. pomonella ovipositing in an apple
B. treatae in search of an oviposition site
Imature and mature leaf galls on live
oaks (Q. fusiformis) in centarl TX.
Live oak after an outbreak of defoliators
I am a graduate student at the University of Notre Dame in the lab of Dr. Jeffrey Feder. I was born and raised outside of Houston, Texas and received both my B.Sc. in Biology and M.Sc. in Population and Conservation Biology from Texas State University-San Marcos (in the lab of Dr. James R. Ott). Even after several years up North, I am still adjusting to average winter temperatures below 60°F and am learning that scarfs are not used only as winter accessories. To the dismay of my mother I rarely cut my hair (see picture on left) which is proving useful in the northern winters.
I have broad research interests in insect ecology and evolution. Specifically I am interested in (1) the evolution and maintenance of new species (speciation), (2) the coevolution of parasitic insects and their hosts, (3) the evolution of life cycle events and complex life histories and (4) the natural history, ecology, behavior, and evolution of gall forming insects.
Current Research Projects
The aim of my dissertation research is to better understand the mechanisms that induce and maintain speciation events in nature. Specifically, I am investigating speciation via host shifting of an entire community of parasitoids species (Hymenoptera: Braconidae) that attack fruit flies of the genus Rhagoletis (Diptera: Tephritidae). Outlined below are several ongoing projects.
1. Sequential Speciation: Flies in the Rhagoletis pomonella species complex (the apple maggot fly and closely related host races and species) are a model system for sympatric speciation via host plant shifting (hawthorn flies have shifted onto domesticated apples after being introduced from Europe ~ 200 ya). Forbes et al. (Science, 2009) showed that a Rhagoletis-attacking parasitoid, Diachasma alloeum, was diverging in parallel with its fly host (termed sequential sympatric speciation). The sequential speciation hypothesis has been proposed as a mechanisms to help explain astonishing levels of insect biodiversity (estimations as high as 30 million speices 20% of which are thought to be parasitoids) My dissertation research focuses on the asking similar questions using several other species of Rhagoletis attacking parasitoids (Utetes canaliculatus and Diachasmimorpha mellea). I am addressing these questions by:
(a) Fruit odor preference testing: Do parasitoid show prefer natal fruit odors and avoid non-natal fruit odors generating prezygotic reproductive isolation?
(b) Characterizing the length of overwinter dipause: Do parasitoids emerge to match the fruiting phenology and their host plant and adult emergence phenology of their fly host creating a barrier to gene flow during host race formation?
(c) Using next generation sequencing techniques to test for genome wide patterns of host race formation and incipient speciation events.
2. The role of interspecific competition in speciation: Parasitoids are excellent systems to study how competition effects evoutionary ecology (Hood et al. 2012). Do parasitoid species co-occur, and if so, how and why? Does interspecific competition between competing parasitoids induce or preclude speciation in Rhagoletis-attacking parasitoids? In collaboration with Dr. Jason McLaughlin at the University of Notre Dame, we are working on a Baysian model incorportaing measures of parasitoid co-occurrence and interspecific competition on various levels (within a single developing fly, fruit, tree, site as well as locally and and regionally) to estimate how interspecific competition affects parasitoid species.
Recently funded by NSF (link). Proposal title: Does Sequential Speciation Amplify Biodiveristy Across Trophic Levels?
Watch this video (link) via NSF of Jeff Feder discussing sequential speciation in Rhagoletis-attacking parasitoids.
3. Evolutionary ecology of gall-forming insects: My master's thesis addressed the consequences that host plant defoliation by outbreaks of caterpillars have on various aspects of gall former ecology, including the timing of oviposition and adult emergence, the number of galls produced/female, final gall size and survivorship protected from and exposed to parasitoid natural enemies. I found that defoliation, and subsequent refoliation created a 6–8 week delayed in the timing of oviposition. However, temporal variation in the timing of oviposition conserved emergence times, did not affect the number of galls produced/female or final gall size. When protected from natural enemies, variation in the timing of oviposition did not affect gall former survivorship but when exposed to natural enemies later oviposition increased gall former survivorship over an order of magnitude. I hypothesize that defoliation creating temporally variability in the timing of oviposition allows those gall formers that are ovipositing later to escape attack from a subset of the natural enemy community. Details of more gall related research can be found below.
4. The evolution of complex life histories: The gall former, Belonocnema treatae, is a hetergonic cynipid (i.e. cyclic parthenogenesis) where an asexual (agamic) generation alternates with a sexual generation. About 80 species of described cynipids have a hetergonic life cycle and although it has likely evolved independently multiple times within the cynipidae lineage, I am interested in determining which generation (asexual or sexual) is the ancestral state. Using measurement of body size and potential fecundity (egg load) differences between the generations, Dr. James Ott and I are working on developing a hypothesis for predicting the direction of evolution of heterogony.
5. Ecological specialization and speciation in gall former communities: Live oaks in the southern U.S. can be home to as many as 15 species of gall forming wasps. Dr.'s Scott Egan, James Ott and myself are examining if and how divergent host plant use among entire communities of gall forming wasps inhabiting different species of live oaks along the southern coast of the U.S. drives parallel patterns of speciation. We have documented ecological divergence associated with host plant use in two species thus far (B. treatae and Disholcaspis quercusvirens) and are currently investigating the pattern in several other species.
* Photos of Rhagoletis flies and their associated parasitoids curtesy of A.A. Forbes.