Interview with the author: Dynamics of genomic change during evolutionary rescue in the seed beetle Callosobruchus maculatus

We interviewed graduate student Alexandre Rêgo and Professor Zach Gompert from Utah State University about their work on evolutionary rescue in seed beetles where they explore how demographic history affects parallel evolution at the genetic level. Their results have important implications for or understanding of repeatability and predictability of evolution. Read the full text below:

Alexandre Rêgo, Frank J. Messina, and Zachariah Gompert. (2019) Dynamics of genomic change during evolutionary rescue in the seed beetle Callosobruchus maculatus.

Drawing of C. maculatus (by Amy Springer)
Drawing of Callosobruchus maculatus (by Amy Springer)

What led to your interest in this topic / what was the motivation for this study?

(AR and ZG) We were interested in evolutionary rescue, that is in cases where population decline and extinction in a marginal or stressful environment is halted and reversed by adaptive evolution. We were especially interested in what patterns of change and natural selection look like across the genome during rescue. How many genes are involved? How much do gene/allele frequencies change? And how fast? We turned to an evolve-and-resequence experiment with Callosobruchus maculatus seed beetles for this. Past work has shown that these beetles can barely survive on lentils (survival rates are ~1%), but that they sometimes can rapidly adapt and persist on this novel host (survival rates can climb to 80 or 90% in fewer than 20 generations).

What difficulties did you run into along the way?

(AR and ZG) Extinction. We were drawn to this system because of the potential for adaptation or extinction, and because of the related extraordinary pace and degree of adaptation when it occurs. We wanted to measure selection and genome-wide evolutionary change during evolutionary rescue, but (for better and worse) only one of 10 replicate lines was rescued. This limited our ability to assess parallelism during rescue, but also highlighted how real the possibility of extinction (in the absence of rapid adaptation) is in this system.

What is the biggest or most surprising finding from this study?

(AR and ZG) We were most shocked by just how rapid evolutionary changes were at the molecular level. We saw numerous cases where allele frequencies at multiple (albeit not always independent) genetic loci shifted by 20-40% or more in a single generation. This is really much more extreme than rates of change often considered.

Moving forward, what are the next steps for this research?

(AR and ZG) We are taking our work on C. maculatus in two directions. First, we have finished creating and sequencing crosses between the lentil adapted and source populations to identify genetic variants associated with specific fitness components (e.g., development time and adult size) on lentil. This will make a nice comparison with the selection scans. Second, we are now working with additional populations, some of which do a bit better on lentil, to examine consistency in genomic change across lines in lentil adaptation and to figure out whether hybridization facilitates adaptation to this marginal host.

Adult C. maculatus on their ancestral host, mung bean.

What would your message be for students about to start their first research projects in this topic?

(AR) Attention to detail is critical. Be as careful as possible in how you plan and organize your data on analyses. Population genomic analyses, especially with approximate Bayesian computation, generate an inordinate amount of output. And you will almost certainly want to re-run things with slightly different parameters, etc., so carefully documenting everything is critical.

What have you learned about science over the course of this project?

(AR) There are many things that must be done in order to complete a study, each requiring a different set of skills. As a graduate student, it can be daunting to acquire and become proficient at so many things. However, at the end of this study, I can look back and see that I have made progress as a scientists on many fronts. What I’ve learned from this project has provided me a solid foundation for my current studies on which I can further improve.

Describe the significance of this research for the general scientific community in one sentence.

(AR and ZG) Very rapid adaptation is possible when species or populations find themselves in harsh environments, sometimes this is enough to prevent extinction, and sometimes it isn’t.

Describe the significance of this research for your scientific community in one sentence.

(AR and ZG) Population genomic patterns associated with evolutionary rescue differ in subtle and not so subtle ways from patterns observed in other situations involving less extreme or softer selection, and thus warrant more study and consideration.

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