Resident Parasites Influence Appearance, Mate Selection, & Evolution of Barn Swallows

Barn swallows live almost everywhere on the planet, recognizable by their forked tail and agility in the air. Yet, while they share these characteristics, these little birds often look slightly different in each place they live--with some so distinct they're splitting off to become new species. Researchers at Colorado University at Boulder (CU-Boulder) think that local parasites are influencing why barn swallows in Europe, the Middle East, and Colorado are choosing their mates differently. The new research, published online on May 8, 2020 in Evolution, finds that these parasites could be playing an important role in changing the traits displayed to attract mates early in the process of the creation of new species. The Evolution article is titled “Divergent Sexual Signals Reflect Costs of Local Parasites.” "It's possible we haven't appreciated just how important parasites might be in shaping the evolution of their hosts," said lead author Amanda Hund, PhD, who conducted the research when sh was a doctoral candidate in the Ecology and Evolutionary Biology Department at CU-Boulder. Dr. Hund is now a postdoctoral fellow at the University of Minnesota. Every organism, including humans, has co-evolved with a unique community of parasites, that by definition live at the expense of their host. While they are not beneficial to us as many other microbes are, parasites have shaped our own immune system, pheromones, and even our mate selection, previous research has shown. Hund set out to characterize as many parasite communities as she could in barn swallows, to find out if the parasites could be influencing the barn swallows’ mate selection, and therefore, the male birds' physical traits and the creation of new species. Dr. Hund and her colleagues studied barn swallows at sites in Colorado, the Czech Republic, and Israel over four years.
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