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Potential Hybridization Between Three Species Of Colorado Cottontail Rabbits

Humans are modifying the environment and altering the habitable ranges of species, bringing together species that were previously geographically separated and providing new opportunities for hybridization. Determining how range expansion and urbanization have impacted species interactions will allow us to better understand the influence humans are having on speciation and hybridization. We focused on three cottontail rabbit species (eastern, desert, and mountain; genus Sylvilagus) with human-disrupted ranges that currently converge along the Front Range Urban Corridor. It is currently unknown what impact human disturbance has had on these species and whether it has led to possible hybridization. Using museum specimens, we developed a method to genetically identify the species of each cottontail rabbit by sequencing the cytb mitochondrial gene. To assess if the three species are hybridizing, we then compared the species identity determined by mitochondrial genetics to the species identity indicated by morphology, with disagreement between the two indicating possible hybridization. We found three individuals that show signatures consistent with hybridization, but additional sequencing is needed for confirmation. Hybridization could lead to a breakdown in mating barriers and may redefine our definitions of these three cottontail species. If the species aren’t hybridizing, further research should be done to understand how mating barriers are being maintained.

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