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Boston University Arts & Sciences
CAS News October 4, 2013
What Is It About the Tropics?
Sean Mullen leads effort to understand why species adapt more quickly in warm climes

In recent decades, scientists have discovered that the vast majority of organisms exhibit greater genetic variation in tropical regions than they do in temperate regions. Many types of animals, from rodents to birds to butterflies, appear to adapt and form new traits and new species more quickly in the tropics. Biologists have offered various theories to explain this phenomenon, but so far its causes remain in dispute.

BU Assistant Professor of Biology Sean Mullen is leading a team of researchers into the mountains and lowlands of Ecuador, the forests of Costa Rica, and the eastern and western United States to try to find answers, thanks to nearly $2 million in funding from the National Science Foundation (NSF). His team’s research subjects? Butterflies. One of the most-studied organisms, butterflies make ideal research subjects because of their great morphological diversity (think of all those different wing colors and patterns).

As principal investigator, Mullen, along with his collegues, will look at butterfly species within the Adelpha genus, comparing their rates of genetic variations and the nature of their environmental interactions in both temperate and tropical regions. Mullen’s team includes scientists from the University of Chicago, UC Irvine, University of the Pacific, and the Florida Museum of Natural History.

The team will examine rates of molecular evolution for genes underlying key adaptive traits, such as color, vision, and taste. To do this, they will need to sequence and assemble a genome for a closely related species (Limentis arthemis) that they will use as a reference for their analysis of the Adelpha genus. The team will also be generating a massive, species-level phylogeny (or family tree) of the Adelpha genus; the genus includes such species as Adelpha californica (California Sister) and Adelpha eulalia (Arizona Sister). Finally, they will conduct field experiments to measure predation rates, territoriality, niche breadth, and host plant breadth for multiple species in both temperate and tropical field sites.

Their results will not only illuminate the genetic mechanisms behind butterfly adaptation rates, but could help explain why a broad range of species adapts more quickly in the tropics. “Understanding the ecological and evolutionary processes that shape temporal and spatial patterns of biodiversity is a central goal of biology, and an increasingly important facet of the endangered species management, particularly in a time of rapid global climate change,” notes Mullen.

Besides Mullen, researchers on the project include:

Dr. Marcus Kronforst (University of Chicago)

Dr. Adriana Briscoe (UC Irvine)

Dr. Ryan Hill (University of the Pacific)

Dr. Keith Willmott (Florida Museum of Natural History at the University of Florida)

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