My research
adaptive dynamics of genetic assimilation (postdoc at UBC)
Current projects include an investigation into the molecular basis of convergence in Escherichia coli bacteria. By sequencing the genomes of evolved strains of E. coli, we hope to determine the degree to which phenotypic convergence observed across replicate populations was due to similar genetic changes. Another project explores the relationship between the heritabilities of individual- and collective-level traits.
In order to explore the role of phenotypic plasticity in sympatric diversification, we modeled the ecological and evolutionary dynamics of E. coli in batch cultures. Our results describe an evolutionary pathway leading to metabolic diversification in a sympatric environment without spatial structure. In an environment that fluctuates widely and predictably, evolutionary branching leads to diversification and stable coexistence of generalist and specialist ecotypes for some combinations of parameters.
volvocine algae (PhD research at University of Arizona)
The transition from unicellular to differentiated multicellular organisms constitutes an increase in the level complexity, because previously existing individuals are combined to form a new, higher-level individual. The volvocine algae represent a unique opportunity to study this transition because extant species display a range of intermediate grades between unicellular and multicellular, with functional specialization of cells.
Following the approach Darwin used to understand “organs of extreme perfection” such as the vertebrate eye, evolution of multicellularity can be understood as a series of small steps that cumulatively describe a transition between the two levels. I used phylogenetic reconstructions of ancestral character states to trace the evolution of steps involved in this transition. The history of these characters includes several well-supported instances of multiple origins and reversals.
In contrast to the previously accepted date of 50-75 million years ago, we have shown that the multicellular volvocine algae diverged from unicellular ancestors at least 200 million years ago. Developmental changes over this span have been sporadic, with a number of important changes occurring within a relatively short time after the divergence from unicellular ancestors. In contrast to this relatively rapid period of change, some lineages have undergone relatively little change over long time spans, and some extant species are living fossils whose basic body plans have changed little in the last 200 million years.
The
evolution of mortal somatic cells was a critical step in the evolution
of complex body plans and the major radiations of multicellular life.
To test hypotheses about the origin of somatic cells, we subjected the
volvocine alga Pleodorina starrii to selection on colony size in two different environments.
squirrel phylogeny and phylogeography (Master’s research at UCF)
Using mitochondrial DNA sequences, I explored evolutionary relationships at various taxonomic levels within they rodent family Sciuridae,
one of the largest and most widely dispersed families of mammals. The
broad-scale analysis (114 species in 21 genera) revealed substantial
conflicts with taxonomic assignments at the subfamily, tribe, genus and
species levels. The fine-scale analysis focused on African ground squirrels of the genus Xerus.
Relationships among Xerus species suggest that the genus originated in
northern Africa, dispersed to southern Africa through an ‘arid
corridor’ running from the Horn of Africa to the Cape region, and
subsequently diverged into the two southern African species (X. inauris and X. princeps). Xerus inauris includes three major clades, which probably diverged because of climate-driven allopatric fragmentation.