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Christopher Martin


Assistant Professor

Contact Information

Office: 2256 Genome Sciences Building
Email: chmartin[at]unc.edu
Office Phone: (919) 962-4841

Martin Lab Website

Education

Ph.D., University of California, Davis

Research Description

I am broadly interested in the origins of biodiversity. My research centers on the rapid evolution of new fish species with novel ecology in relatively simple tropical ecosystems (salt lakes, volcanic craters) in order to capture the early stages of this process in tractable field environments. These studies integrate a variety of approaches including large-scale field experiments, population genomics, quantitative genetic mapping, phylogenetic comparative methods, natural history observations, functional morphology, and behavioral ecology. By mapping the complex relationships between fitness, phenotype, genotype, and environment, I hope to gain a predictive understanding of the processes driving the origins of biodiversity.

I am currently developing two tropical field systems for these investigations. First, Caribbean pupfishes present a fascinating problem: novel dietary specialists – such as a scale-eating species – have evolved from a generalist common ancestor in only two places in the entire Caribbean: salt lakes on one tiny Bahamian island and one Yucatan lake, despite thousands of similar lakes containing generalist pupfish. By directly measuring evolutionary fitness in the wild from the growth and survival of laboratory-reared F2 hybrids placed in field enclosures, I previously demonstrated that multiple fitness peaks on a fitness landscape are driving adaptive diversification in this system (Fig. 1). This provides a starting point for experimental investigation of a fundamental question: what ecological and genetic factors ignited the rapid evolution of specialists, despite an abundance of comparable environments?

Figure 1. Empirical fitness landscape for pupfishes on the tiny island of San Salvador, Bahamas: Heat map in a) three dimensions and b) two dimensions depicting the probability of F2 hybrid survival in one field enclosure (●survivor, ○death). Hybrid phenotypes resembling the widespread generalist species are stranded on a local fitness peak, separated by a fitness valley from a higher fitness peak corresponding to hybrid phenotypes resembling the molluscivore specialist. This observation may explain the rare evolution of new specialist species across the Caribbean if this local fitness peak for generalists provides a barrier to adaptive divergence due to strong stabilizing selection limiting trait diversification.

Figure 1. Empirical fitness landscape for pupfishes on the tiny island of San Salvador, Bahamas: Heat map in a) three dimensions and b) two dimensions depicting the probability of F2 hybrid survival in one field enclosure (●survivor, ○death). Hybrid phenotypes resembling the widespread generalist species are stranded on a local fitness peak, separated by a fitness valley from a higher fitness peak corresponding to hybrid phenotypes resembling the molluscivore specialist. This observation may explain the rare evolution of new specialist species across the Caribbean if this local fitness peak for generalists provides a barrier to adaptive divergence due to strong stabilizing selection limiting trait diversification.

Second, I am studying the origins of new species confined to small volcanic crater lakes in Cameroon, originally made famous due to their possible in situ evolution in these simple environments (Fig. 2). This is known as “sympatric speciation”, one of the most controversial ideas in evolutionary biology. My subsequent investigations of these lakes suggest that additional gene flow has occurred and that speciation may be stalled in some cases, but additional work is needed to pinpoint which species were affected and to build models of speciation for this system.

Figure 2. Three crater lakes in northwestern Cameroon with endemic radiations of rapidly evolving cichlid species. For example, Lake Ejagham is only 900 meters in diameter, but contains five fish species found nowhere else in the world. In comparison, North Carolina contains only six fish species found nowhere else.

Figure 2. Three crater lakes in northwestern Cameroon with endemic radiations of rapidly evolving cichlid species. For example, Lake Ejagham is only 900 meters in diameter, but contains five fish species found nowhere else in the world. In comparison, North Carolina contains only six fish species found nowhere else.

Common themes in my work include 1) the origins of adaptive radiation, 2) mechanisms driving this process in the context of the adaptive landscape, and 3) the evolution of novelty. I encourage lab members to pursue both field and laboratory studies of tropical fish systems because they present such a vast, diverse, and poorly studied amount of overall vertebrate biodiversity.