Ph.D. Candidate in Zoology
Michigan State University
After obtaining my Bachelor degrees in Computer Science and Mathematics, I decided to apply my skills to solving problems in science. I wrote a computer identification system for identifying individual polar bears using photographs of their whisker spots. That project became my thesis for a Master's degree in Biology (University of Central Florida). I then wanted to study speciation computationally, and found the Avida group at Michigan State University, where I'm pursuing a Ph.D. in Zoology (expected graduation in Spring 2013). I'm interested in the generality of evolution. If we were to discover alien life (or it discover us), would our theories of evolution still apply? One of the ways to answer this question is to remove the specifics of 'biology' from the study of evolution and be left with the 'essence' of an evolving system.
I'm using artificial life, specifically the software Avida, to research questions in evolutionary biology. In Avida, a population of 'digital organisms' can evolve via natural selection and drift. Each digital organism contains a 'genome,' a sequence of instructions that code for the organism's ability to replicate and perform computational functions. Variation among digital organisms arises through random mutations and recombination (for sexual organisms). Because digital organisms reproduce at different rates—depending on the functions they can perform—they adapt naturally, without a user's 'directing hand.' Remarkably, many genetic properties of digital organisms, like the distribution of mutational effects and the types of epistasis, are similar to that of biological organisms. Avida has been used by researchers for over a decade to answer some of the most fundamental problems in evolutionary biology, such as the complexity of adaptive traits, the evolution of sex, and evolvability.
Deleterious mutations may accumulate in a population by various processes, such as population bottlenecks, hitchhiking with a beneficial mutation, or transient environmental changes. Secondary mutations that compensate for the effects of deleterious mutations can then arise and spread through the population, causing rapid genetic evolution without any phenotypic change. Because compensatory mutations are likely specific to the deleterious mutations for which they compensate, recently diverged populations that acquire different deleterious mutations and therefore different compensatory mutations may be genetically incompatible, even though they may be phenotypically similar. As a result of this genetic incompatibility, populations can become reproductively isolated (e.g., hybrid inviability), leading to speciation. Using Avida, I'm looking into whether compensatory adaptation can result in hybrid unfitness, and so far my experiments show that it can, that it happens rapidly, and that both deleterious and compensatory mutations are involved in hybrid incompatibilities.
When a population becomes geographically divided into two, each population evolves independently of the other—each population can acquire unique mutations and follow a unique evolutionary path. Because the mutations that arise in one population cannot be shared with the other, each substitution that occurs in one population may create an incompatibility with the genetic background of the other. Genetic incompatibilties may cause hybrids to be sterile or inviable, which is a form of reproductive isolation (i.e., speciation). One theoretical prediction of the process described posits that the number of pairwise genetic incompatibilities should increase quadratically through time (the so-called 'snowball effect'). This prediction is very difficult to test with biological organisms because a lot of genetic manipulations would have to be performed. Using Avida, I've tested the snowball effect and found that pairwise incompatibilities do increase quadratically through time. However, I also found the presence of 'buffer' alleles in hybrids that can lessen the fitness impact of these incompatibilities, showing that pairwise interactions are not sufficient to explain hybrid unfitness.
Reproductive isolation between two populations is known to be facilitated when the populations adapt to different environments ('ecological speciation'). But whether reproductive isolation can also occur when populations independently adapt to the same environment ('mutation-order speciation') is less well-understood. I've found in Avida that ecological speciation forms stronger reproductive isolation than mutation-order speciation, possibly because parallel evolution in mutation-order speciation often involves similar loci, such that divergence is weaker. In addition, I've tested the effect of gene flow in both of these processes, and I've found that mutation-order speciation is much more sensitive to gene flow than ecological speciation, as has been proposed theoretically.