Ethan Linck

Postdoc @ U. Tennessee

My research uses population genetics to understand how geography and ecology interact to shape dispersal and range limits, speciation, and the organization of biological diversity. I collect empirical data from wild populations of birds and insects and validate models using evolutionary simulations and theory. I’m passionate about tropical mountains, natural history museums, and trying to understand how your tools work.

What is speciation with gene flow and when does it happen?

After decades of imprecise verbal models and a general sense that Darwin misnamed his famous book, a resurgence of theory and the onset of high throughput DNA sequencing has reinvigorated the study of speciation. We’re now faced with reconciling biological intuition and evidence from species distributions (that suggest geographic isolation is crucial to most speciation events) with new theory and genomic evidence (which suggest that gene flow and selection are rampant throughout the evolutionary history of diverging lineages). The central chapter of my dissertation used young sister species segregating across a tropical mountainside to understand the the relative importance of these forces using phenotypic data and whole genome sequencing. Based partly on these results, my collaborator CJ Battey and I are working to understand how quickly speciation can occur when brief periods of isolation are interspersed with gene flow, and whether this process leaves a detectable signature.

The genomic landscape of divergence in Syma kingfishers

How do landscapes shape dispersal, gene flow, and range limits?

The movement of individual organisms across landscapes affects most processes I can think of in ecology and evolutionary biology. Unfortunately, dispersal is difficult to observe and difficult to predict, and we have to get creative. To infer connectivity between wintering and breeding populations of an iconic iconic songbird (and thus describe migratory routes), I have used both DNA sequence data and natural history museum collection metadeta. To understand the environments where dispersal is and isn’t likely to be adaptive, I have investigated drift / migration balance in highly vagile “supertramp” species living on disturbance-prone coral atolls, and am currently testing predictions of Dan Janzen’s classic paper on why mountain passes are “higher” in the tropics (an ongoing collaboration with my current postdoc advisor Kimberly Sheldon). Early next year I’ll get the chance to combine many of these interests as I begin a two year NSF postdoctoral fellowship aimed at understanding the population genetics of species range limits in Andean birds.

The effect of maladaptive alleles on effective population size at a range limit

How do we know what we know?

Biology is messy. Massive DNA sequence datasets require computational analyses and interpretation at the limits of our current knowledge, adding another layer of noise to the signals of biological processes. Because it’s useful to understand what can be contributing to uncertainty in your conclusions, I’m interested in methods for generating and analyzing genomic data. I’ve worked to validate laboratory methods for collecting population genomic data from degraded DNA sources, and to understand how coalescent theory can explain why bioinformatic filtering steps can alter inferred patterns of population genetic structure. I have also used a classic taxonomic conundrum in ornithology to demonstrate why incomplete geographic sampling can mislead us when we try to understand phylogenetic relationships and species limits.

Mutational age and minor allele frequencies across a coalescent tree

Tropical natural history

Natural history provides the raw material for biological hypotheses. The overwhelming grandeur of tropical montane biodiversity has played a significant role in determining my interests as a biologist, but for many species (the vast majority?) we lack detailed information on distributions, abundances, life history, behavior, reproduction, and other basic biological parameters. I am committed to the slow but invaluable work of contributing these fundamental data, and have written notes on high alpine bird communities, nesting biology in a widespread swallow, and the surviving bird communities of the Mariana Islands (In press, Wilson Journal of Ornithology). I am particularly interested in natural history of the rainforests of New Guinea and Solomon Islands, where I have spent significant time and reported on community conservation initiatives as a photojournalist.

A high elevation Wattled Brushturkey (megapode) egg from 1800m on Mt. Wilhelm, Papua New Guinea