Safran’s work involve swallows, as pictured above. Her experiments often manipulate the streamers, or tail, and ventral feathers of these birds. Source: Wikipedia
On April 19, Rebecca Safran, a professor and researcher at University of Colorado at Boulder, presented in the Life Sciences Center at Dartmouth College on her research involving sexual selection and speciation.
As a behavioral and evolutionary ecologist, Safran works to better understand how individual behavior and population patterns might help to reveal the underlying mechanism of variation. Her research focuses on answering what generates and maintains phenotypic variation in closely related populations.
Safran described her comparative and integrative approach to research by organizing her methods into parts: the quantitative analysis of trait variation, understanding the role of history, and revealing the mechanisms underlying patterns in the role of sexual selection and in the dynamics between physiology-morphology.
Safran’s analysis of 1,600 empirical studies indicated that there was incomplete evidence in favor of any role of sexual selection in speciation. She found that the ecological context and interactions between different forms of selection made it difficult to accurately single out the role of sexual selection in these studies. As such, Safran began to work with scientific theoreticians to create testable models to see the effects of sexual selection.
These models made use of non-migratory populations of Hirundo rustica, or the barn swallow songbird. There are six subspecies around the world: rustica in Europe, savignii in Egypt, transitiva in the Eastern Mediterranean, gutturalis in Asia, tytleri in Russia, and erythrogaster in North America. Safran’s studies tested on the erythrogaster subspecies in Colorado, USA, and a population of transitiva in Israel.
Swallows possess several phenotypic characteristics that are sexual signals developed before mating season. The two characteristics focused on by Safran are the varying lengths of tail streamers and the different shades of ventral plumage on male swallows.
Through field methods involving taking blood samples of particular birds, it was discovered that, though the birds are socially monogamous, often partners would sire children with swallows of a different pair. It was found that, on average, a male swallow would care for a nest in which he sired only two fifths of the nestlings.
Safran used this information to compare the affects of tail streamers and ventral color on certain birds. Through altering specific male’s streamer lengths and plumage, she could compare paternity after this phenotypic manipulation and could then note if the individual had more success relative to his initial and final number of young he cared for that he had sired.
Interestingly enough, the results varied by subspecies. While the Colorado population showed marked increased success for birds with darkened plumage or shortened streamers, swallows in England and Israel longer streamers proved more beneficial.
Safran has made great strides in her research, and her organization and creativity in the field has allowed her to create testable methods to gather information about an extremely difficult, enigmatic topic. However, Safran sees many more experiments in the future before she can make any definitive conclusions regarding the role of sexual selection in speciation.