My Research


Current Projects

Background

The fodder of adaptation in animals has been classically attributed to variation that already exists in the genome, or mutation. However, recently it has become increasingly clear that there's another common mechanism that introduces new adaptive variation into populations: hybridization!

Hybridization is mating between species. You probably learned that a species is distinct because it specifically CAN'T mate with other species (that's the "Biological Species Concept"). But it turns out that more than 25% of all plant species can mate with at least one other species, and more recently we learned that over 10% of animal species can too (Mallet 2005)! So what even is a species? This is a spicy question with spicy debate that I won't dip into here, but here's a summary of the ongoing dilemma.

I'm exploring how hybridization fascilitates adaptation to environmental stress - in particular, thermal stress. A population's tolerance of its thermal environment is critically important to its survival. As temperatures rise globally, many populations are being forced to physically move to suitable thermal habitat, rapidly adapt, or collapse. For many populations, including those of riverine fishes like swordtails, relocating to thermally-suitable habitat isn't always possible. Selection on standing variation in the genome and mutations can take a long time to yield adaptions, perhaps longer than it would take for climate change to extirpate a population. But hybridization offers a fast-track option. If hybrid offspring are able to mate with individuals from one of their parent species, they can move genes from one species into the gene pool of the other, thereby introducing novel adaptive variation into that species' genome. Hybridization may provide the opportunity for thermal adaptations to move from resilient populations into more sensitive populations.

Swordtail fishes are the perfect model system for studying adaptation via hybridization, both in the lab and the field. Adored by hobbyists and scientists alike, swordtails are live-bearing freshwater fishes that exhibit a wide range of vibrant physical traits, which can be mix-n-matched between some hybridizing species. Sometimes hybrids express phenotypes that are similar to those of one of their parents, and sometimes they exhibit phenotypes that are intermediate (in between) or extreme. For example, crosses between swordless and sworded species (like X. birchmanni and X. malinche, respectively) result in hybrids with intermediate sword lengths (we partially described the genetic basis of the sword trait here).

Thermal tolerance, or the ability to withstand high temperatures, is another trait that is intermediately expressed in swordtail hybrids. X. birchmanni, which lives in the warmer lowlands, has a significantly higher thermal tolerance than X. malinche, the cooler highland species, even when controlling for plasticity. This suggests that there is a genetic basis for this trait, and therefore that thermal adaptations could be passed from one species to the other, via hybridization.

Uncovering the genetic basis of thermal tolerance

Using a combination of genetics and biochemical approaches, such as QTL mapping, expression analysis, and functional assays, I am teasing apart the genes and molecular pathways that explain variation in the thermal tolerance trait between X. birchmanni and X. malinche.

Tracking introgression of thermal adaptations along thermal clines

X. birchmanni and X. malinche form hybrid zones along rivers that have thermal clines. As river temperatures warm, I predict that adaptive thermal tolerance genes from the more thermally-resilient X. birchmanni populations may move into the more sensitive X. malinche populations. By looking for shifts in ancestry proportions at tolerance genes in natural populations along ancestry clines, I can pinpoint the X. birchmanni adaptations that are likely to help wild populations survive climate change and that are compatible against an X. malinche genomic background.

Investigating the role of mitochondria in thermal adaptation

It is clear that mitochondria play a non-trivial role in thermal tolerance in many systems. There are notable coding and expression differences between X. birchmanni and X. malinche mitochondrial genomes, as well as nuclear-encoded mitochondrial genes, that could explain differences in thermal tolerance between these species. Using in vitro functional and enzymatic assays, I am measuring differential mitochondrial activity and efficiency under variable thermal conditions.

Parallel X. malinche-X. birchmanni hybrid zones. Images adapted from Google Earth.

Past Projects


Some A. hyacinthus reef-building coral populations are more resilient to heat stress than others. Using population genetic and comparative genomics approaches, I worked on identifying genetic markers that distinguish "strong", or heat resilient, corals. This work may inform reef restoration and management efforts by helping predict which populations will be best-equipped to survive rising ocean temperatures.

Visit the project page and repo for more info.

Several Queen Conch populations in the Caribbean are CITES-listed, meaning they are (or recommended to be) protected against over-exploitation by an international trade agreement. A central conservation problem is identifying where conch in the trade were poached from, so that the fishery can be managed accordingly. I worked on developing a new tool using multiplex-PCR to quickly and cheaply mass genotype informative markers, which can be used to predict a conch's population origin.

Visit the project repo.

A new species of deep-sea, wood-eating asteroid of the genus Xyloplax was found from the Juan de Fuca Ridge hydrothermal vent system, off the coast of Oregon, US.

Visit my Marine Invertebrates Lab bio.

I used assays and purification techniques to describe the properties of and reaction(s) responsible for light emission from a new species of octocoral with a seemingly novel bioluminescence system.

I characterized the bioluminescence of shallow water radiolarian species and deep water phaeodarian species in the Monterey Bay.

Visit the CIPRES-notebooks repo.