Beyond that, the basic population genetics and evolutionary history of elements such as Medea represent a fascinating yet understudied dimension in evolutionary biology (Burt & Trivers, 2006).īeyond the importance of understanding natural SGEs for advancing basic science, knowledge of natural SGEs is relevant to the newly emerging technology of “gene drives” that aims at using synthetic SGEs to drive genes into pest populations that will act to suppress the populations or decrease vectorial capacity of the populations (e.g., Godfray, North, & Burt, 2017 Rode, Estoup, Bourguet, Courtier‐Orgogozo, & Debarre, 2019 Sinkins & Gould, 2006). The influence of selfish genetic elements on populations and species can be substantial, from providing additional genetic variation that enables adaptation (e.g., Li, Schuler, & Berenbaum, 2007) to the lowering of population fitness (e.g., Carroll, Meagher, Morrision, Penn, & Potts, 2004). Because only non‐ Medea (i.e., “wild‐type”) offspring produced by mothers that are heterozygous for the Medea element die, the Medea allele frequency is expected to increase within a population over time, provided that Medea introduction frequency is not extremely low, and the element does not carry a substantial fitness cost (Wade & Beeman, 1994). Currently, the most parsimonious model suggests Medea's action involves two tightly linked loci-one encoding a lethal, maternally expressed toxin in all eggs, and the other encoding a zygotic antidote that rescues only those progeny inheriting at least one Medea allele (Beeman & Friesen, 1999 Beeman et al., 1992). Medea elements are genomic sequences which cause death of the non‐ Medea offspring of Medea‐bearing mothers (Beeman, Friesen, & Denell, 1992). Many populations of red flour beetle ( Tribolium castaneum) harbor naturally occurring selfish Medea elements (Beeman & Friesen, 1999). Selfish genetic elements (SGEs) have been found to occur naturally in a huge variety of taxa, but despite decades of study by evolutionary biologists, the origins, mechanisms, and population‐level impacts of these elements are still largely unknown (Burt & Trivers, 2006). The finding of patchy distributions of Medea elements suggests that released synthetic SGEs cannot always be expected to spread uniformly, especially in target species with limited dispersal. There is great interest in using synthetic SGEs, including synthetic Medea, to alter or suppress pest populations, but there is concern about unpredicted spread of these SGEs and potential for populations to become resistant to them. Our results indicate the absence of rigid barriers to Medea spread in the United States, so assessment of what factors have limited its current distribution requires further investigation. By using a genetic marker of Medea‐1 (M 1), we found five unique geographic clusters with high and low M 1 frequencies in a pattern not predicted by microsatellite‐based analysis of population structure. We sampled beetles in 2011–2014 and show that the distribution of M 4 in the United States is dynamic and has shifted southward. distributions of Medea‐4 (M 4) had been mapped based on samples from 1993 to 1995. Medea SGEs occur naturally in some populations of red flour beetle ( Tribolium castaneum) and are expected to increase in frequency within populations and spread among populations. Selfish genetic elements (SGEs) are DNA sequences that are transmitted to viable offspring in greater than Mendelian frequencies.
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