We often think of species as separate and distinct, but sometimes they can interbreed and create hybrids. When this happens consistently in a specific area, it forms what's known as a hybrid zone. These zones can be highly dynamic or remarkably stable, and studying them can reveal key insights into how species boundaries evolve -- or sometimes blur. In a new study published in Evolution, researchers at the University of Illinois Urbana-Champaign describe a hybrid zone between two manakin species in Panama that has overall remained relatively stable over the past 30 years.
Hybrids resulting from mixed-species breeding are not uncommon; consider, for example, the mule (horse-donkey) or the liger (lion-tiger). However, many of these classic examples of hybrids are typically infertile and exist only as first-generation crosses. In contrast, along the western edge of Panama, against the Caribbean Sea, a long-term hybrid zone exists between two species of birds, the golden-collared manakin and the white-collared manakin.
Previous research conducted nearly 30 years ago on this hybrid zone found that the genomic center -- where the population's genome is nearly 50% white-collared DNA and 50% golden-collared DNA -- did not overlap with the phenotypic transition zone, the area where the population visually transitions from more golden-collared plumage to more white-collared. The previous study found these two areas were about 60 km apart, and until recently, it was unclear whether there had been any changes over the years.
Kira Long, a former graduate student in Jeff Brawn's lab, now a postdoctoral researcher at the University of Idaho, and her team decided to compare the current population of manakins in the hybrid zone to those from the previous study ~30 years ago. Doing so would allow the researchers to see whether the genomic center or the phenotypic transition zone has moved over time, and how stable the genomic and phenotypic traits are across the population.
"Currently, hybrids at the genomic center look phenotypically almost identical to the golden-collared manakins," explained Long. "They have the golden yellow collar and dark green belly of golden-collared manakins. What's crazy is that these hybrids are the most genetically mixed between white and golden-collared manakins, yet they look almost identical to the golden-collared parents. Whereas the birds that visually look the most mixed have genetically a majority of white-collared DNA."
Long's team includes Illinois researchers Jeff Brawn, a professor emeritus of natural resources and environmental sciences, Julian Catchen (CIS/GNDP), an associate professor of integrative biology, and his former graduate student Angel Rivera-Colón, as well as collaborators from the University of Maryland College Park and the Smithsonian Institution.
Over four years, the team captured and took blood samples from over 600 manakins across different areas of the hybrid zone. The blood samples were sequenced using RADseq to examine thousands of genomic markers across the genome. These were then compared to samples taken from museum specimens housed at the Smithsonian Institution that were used in the original, older study. The team also measured phenotypic traits of the wild-caught and historical birds, known to differ between golden-collared and white-collared manakins, including feather coloration and length.
sources-science daily
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