Hey, it’s Friday night so let’s do a snake frite with some useful takehome info:
Here’s the abstract of a new closed-access paper:
Abstract: Theory predicts that threatened species living in small populations will experience high levels of inbreeding that will increase their genetic load, but recent work suggests that the impact of load may be minimized by purging resulting from long-term population bottlenecks. Empirical studies that examine this idea using genome-wide estimates of inbreeding and genetic load in threatened species are limited. Here we use individual genome resequencing data to compare levels of inbreeding, levels of genetic load (estimated as mutation load) and population history in threatened Eastern massasauga rattlesnakes (Sistrurus catenatus), which exist in small isolated populations, and closely related yet outbred Western massasauga rattlesnakes (Sistrurus tergeminus). In terms of inbreeding, S. catenatus genomes had a greater number of runs of homozygosity of varying sizes, indicating sustained inbreeding through repeated bottlenecks when compared to S. tergeminus. At the species level, outbred S. tergeminus had higher genome-wide levels of mutation load in the form of greater numbers of derived deleterious mutations compared to S. catenatus, presumably due to long-term purging of deleterious mutations in S. catenatus. In contrast, mutations that escaped species-level drift effects within S. catenatus populations were in general more frequent and more often found in homozygous genotypes than in S. tergeminus, suggesting a reduced efficiency of purifying selection in smaller S. catenatus populations for most mutations. Our results support an emerging idea that the historical demography of a threatened species has a significant impact on the type of genetic load present, which impacts implementation of conservation actions such as genetic rescue.
A friend who knows the scene writes: First, their findings run counter to classic theory with respect to depression caused by inbreeding. Second, no beneficial mutations are discussed, only benign ones, and then deleterious mutations of varying degrees. Much as in Michael Behe’s Darwin Devolves.
Incidentally, New Scientist tells us that snakes started eating birds and mammals mostly after dinosaurs went extinct. That implies that a number of dinos must have been very small (for dinos). Ars Technica calls it a “snakesplosion of biodiversity”: “To study this evolutionary change, a team of researchers examined the diets of existing snake species to get a glimpse into the past. ‘After the K–Pg extinction, [snakes] just underwent this massive ecological explosion,’ Michael Grundler, one of the paper’s authors and a post-doc researcher at the University of California Los Angeles, told Ars.”