| Gene flow is the evolutionary force concerned with the movement of individuals from one population to another. More accurately, it is the movement of genetic material from one population to another. When it comes to evolution, I view gene flow as a “homogenizing force”. In isolation of other forces, higher rates of gene flow cause populations to become more similar due to the swapping of genetic material. After all, sufficient levels of gene flow may warrant treating previously multiple populations as one. However, the absence of gene flow has consequences as well. In last week’s newsletter, we covered genetic drift. In it, I briefly mentioned founder effects, those situations where a small subset of the population establishes itself as a separate entity. A classic example may be the cases of anoles arriving on isolated islands, however, human history shows repeated founder effects following our species dispersal around the world. These founder populations are greatly influenced by drift, particularly when they stay isolated. However, you may be surprised to learn that only a single migrant per generation into a subpopulation can be enough to minimize the loss of diversity and inhibit speciation. |
| Gene Flow and Conservation |
| Of course with real populations, the answer to “how much migration is needed?” is “it depends”. For todays newsletter I want to share 2 examples of gene flow’s importance to conservation. The Florida Panther and the Sierra Nevada Red Fox. |
| Its no secret that conservationists create gene flow by relocating organisms between populations. We call this genetic rescue, or the process of bolstering a population’s fitness by introducing new genetic material. |
| I first heard of genetic rescue during my undergraduate at A&M from a peer doing research with Florida Panthers (Puma concolor coryi) – the only known breeding population of mountain lions East of the Mississippi. Unfortunately, decades of extirpation shot the population down to only a few dozen individuals in the 80’s. Naturally, they were suffering the effects of inbreeding. |
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| Photo Credit: USFWS |
| In 1995, 8 young-adult female panthers from Texas were released into the Florida Panther population to introduce new genetic material. And it worked. The population increased to around 120 individuals, and Texas x Florida Panther hybrids were healthier, more genetically diverse, and showed significant decreases in inbred traits. |
| There are some nuances here that likely deserves a deeper break down. Mainly, are these even Florida panthers anymore? However, the point stands that conservation managers use genetic rescue as an effective tool for conserving populations. However, what about in wild populations? |
| The Sierra Nevada Red Fox |
| Back in 2019, I was keyed into this fascinating paper detailing an instance of natural genetic rescue with Sierra Nevada Red Foxes (Vulpes vulpes necator). |
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| Photo Credit: California Department of Fish and Wildlife |
| This subspecies of Red Fox (Vulpes vulpes necator) is split between 2 distinct population segments (abbreviated here as DPS). The Southern Cascades DPS in California and Oregon, which does not receive any federal protections (however the Center for Biological Diversity is petitioning to change that). However, the Sierra Nevada Red Fox DPS, found only in Montane California was listed as federally endangered in 2021 (after this paper was published). Less than 40 individuals remain in the wild today. |
| From 2010-2017, these foxes were genetically monitored through environmental DNA (scat, fur, urine etc). The silver lining of having such a small population, is that the entire population can be monitored. When compared to other populations of Red Fox (Vulpes vulpes), early results showed evidence of inbreeding depression, low allelic diversity, and reduced heterozygosity within the Sierra Nevada population. From 2010-2012, the authors did not find evidence of reproduction; consistent with the effects of inbreeding depression. It was likely this population had already fallen into anextinction vortex. A positive feedback loop of negative effects, that can quickly cause a population to go extinct. But then, something unexpected happened… |
| In 2012, 2 individuals from the Great Basin subspecies (Vulpes vulpes macroura) of North East Nevada happened to come in contact with our introgressed population. Followed by another Great Basin individual in 2014. Incredibly, they ended up mating with the Sierra Nevada DPS 2 years into the study period. To quote the study: “the first 3 immigrants (2 in 2012, 1 in 2014) introduced 63 novel alleles to the pre-immigration population, nearly doubling the allelic diversity in the 2 years immediately following immigration”. Additionally, heterozygosity peaked immediately in the hybrid offspring, they detected a marked increase in reproductive success followed by a subsequent increase in genetic diversity. All thanks to the serendipitous migration of 3 individuals. |
| Their story is still going… |
| Naturally, the conservation story of these foxes is not over. In fact, just a few months ago this paper was published discussing genetic rescue strategies in Sierra Nevada Red Foxes by looking at the whole genome. At some point, I may want to do a deeper dive into the whole story, but for now, I’m focusing on a few other things: First, enrollment just opened for my R for Biologists Workshop happening in February. Space is limited and all the information can be found at this link: https://learnadv.com/product/r-for-biologists-workshop/ Over on YouTube, ive actually been posting a series on the very basics of phylogenetics. My long term goal there is to have an entire playlist filled with focused videos on phylogenetic concepts that students of any level can watch! But with that, i’m coming to you next week with a nice cap on our evolutionary forces series with Natural Selection! See you then! -D |