Sevan Suni

Dept. of Ecology and Evolutionary Biology

sssuni@email.arizona.edu
Mailing address: P.O. Box 210088, University of Arizona, Tucson, Arizona 85721-0088

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Research Interests

I use population genetic techniques to investigate and predict responses of organisms to environmental change. My current work focuses on orchid bees (tribe Euglossini), which are one of the most important groups of pollinators in the tropics. Their iridescent colors and extraordinary behavior have fascinated biologists for decades. Males can often be seen collecting fragrances from orchids and storing them on their legs, for later use in courtship behavior. Orchid bees comprise up to 25% of the bee species richness in Central and South America and are the sole pollinators of close to 700 orchid species. As much as 10% of these orchids may be pollinated by only one species of bee, and females often pollinate different plants than males, such as the Brazil nut tree. The ability of orchid bees to fly long distances makes them effective pollinators of tropical plants, which are often dispersed far from one another. The response of orchid bee populations to environmental change is important to understand because of their role in the maintenance of tropical plant diversity and because of their status as important models for insect behavior and chemical ecology.

Our knowledge of the status of orchid bee populations is constrained by the limited number and conflicting results of studies on bee responses to habitat. Most studies that have examined the responses of bee populations to habitat fragmentation have used measures of abundance to characterize population health. Genetic information may more accurately reflect the status of bee populations. Even when large, populations with low genetic diversity are less resilient and more vulnerable to extinction for two reasons. First, genetic diversity allows populations to adapt to a changing environment. Second, low genetic diversity increases the number of sterile individuals in bee populations because of their unique system of sex-determination.

In bees, females develop from fertilized eggs and are diploid. Males develop from unfertilized eggs and are usually haploid. Sex is determined by genotype at one locus in the genome. Individuals with two different alleles develop into females and individuals with one allele develop into males. When genetic diversity is low, some diploids develop into males instead of females because both sex-determining alleles are the same. These diploid males are sterile. The percentage of diploid males in bee populations has been proposed as an indicator of pollinator decline.

Estimates of diploid male frequencies vary dramatically throughout Central and South America. It is likely that frequencies do vary somewhat because of the high environmental heterogeneity throughout the region, however, discrepancies probably also reflect differences in species sampled in each study and the genetic methods used. Studies have used allozymes to detect diploid males. Because the number of alleles at allozyme loci is generally small, little information about population genetic diversity has been garnered. Empirical support for the theorized link between low genetic diversity in wild bee populations and diploid male load is lacking, and virtually nothing is known about how landscape factors affect genetic diversity in orchid bee populations. My research will clarify the link between abundance, genetic diversity, and diploid male load, and elucidate how environmental change may affect levels of diploid males and genetic diversity in populations.