Research

Marine systems are highly connected systems characterized by the lack of physical barriers and the high dispersal potential of marine organisms. Unlike terrestrial systems, most marine organisms have larvae dispersal, which shapes their ecological and evolutionary processes. However, tagging larvae is a nearly impossible task using common tracking methods (e.g., satellite or acoustic tags), and we therefore rely on using genetics to understand how connected populations are. 

The amount of gene flow (i.e., genetic connectivity) among populations is an important driver of the genetic pool of the meta-population. Isolated populations with restricted gene flow are expected to have lower genetic diversity, which may hinder their adaptive potential. Thus, understanding the degree of gene flow is a long-standing problem, particularly in marine systems, due to the lack of biogeographic barriers, and it has crucial conservation implications. Past research efforts in the lab have focused on understanding genetic connectivity in a wide range of organisms, including sea anemones, zoanthids, angelfishes, and damselfishes.

Species range expansions are occurring across the globe at unprecedented rates as global warming continues to accelerate, and even more so in marine species. Evolutionary theory predicts the rapid accumulation of deleterious mutations in edge populations during range expansions (i.e., expansion load) (Fig. 1), leading to a loss in fitness. Fishing triggers similar evolutionary dynamics of population declines and lower genetic diversity, similarly increasing expansion loads. Marine species experience faster range expansions than terrestrial species due to their high dispersal ability and are heavily impacted by fishing pressure. The interaction between these processes threatens populations on the expanding range margins and could alter one of the most common ways species respond to climate change. I recently obtained a two-year NSF Ocean Sciences postdoctoral fellowship to test the evolutionary theory of the accumulation of deleterious mutations in a rapid climate-driven range expansion and harvested marine fish, Black sea bass (Centropristis striata). This work is being done in collaboration with Dr. Katie Lotterhos and Dr. Jonathan Grabowski in Northeastern University’s Marine and Environmental Science Department.

Genetic variation shared between closely related species can result from two different processes. The first process is the transfer of genetic information from one species to another by hybridization and backcrossing (i.e., introgression). The second process is the retention of ancestral variation in a sister species from an ancestral species. Both processes produce similar genetic signatures making them hard to differentiate, yet understanding how these processes drive genetic variation is a fundamental area of research for evolutionary genetics and conservation. Evolutionary theory predicts that the retention of ancestral variation is primarily seen in species with large population sizes and in species that have recently diverged where selection and recombination have not completely sorted these ancestral alleles (i.e., the removal of shared genetic variation). We are using Holacanthus angelfishes from the TEP (Fig. 2) that have recently diverged (~3MyA) and are known to hybridize, to test whether their genetic variation was the result of introgression or the presence of ancestral variation. Our results show that the shared genetic variation was driven by the retention of ancestral alleles of the King angelfish in the Clarion angelfish largely due to the large population size of the Clarion angelfish compared to the Clipperton angelfish. This is one of the few empirical studies demonstrating the vital role population size plays in the retention of ancestral variation, as smaller effective population sizes lead to faster sorting of alleles (Gatins et al. in prep). Future research will consider where the ancestral variation is located along the genome (coding vs. non-coding regions) to understand its effect on selection.