To a scientist 30 years ago, the term “natural history” might have conjured up images of a field biologist studying minutia with a magnifying glass, or of a systematist measuring specimens in a dusty museum. Today, wildlife biologists often use the latest molecular techniques for purposes of monitoring, conservation, and/or to study natural history and evolution. A few examples from the DeWoody lab in the Purdue’s Department of Forestry & Natural Resources are highlighted below.
Shed reptile skins, eggshells, poop samples, or hair caught in barbed wire: all contain DNA that can be used to “fingerprint” the donor. Similarly, shed feathers can be used to determine donor sex and identity. This is particularly informative with species that are difficult to capture and monitor using conventional methods such as mist nets. Some of these species, like eagles, also utilize the same nest (eyrie) year after year. By collecting many shed feathers from nests year after year and fingerprinting the associated DNA, we can determine nest occupancy, turnover, mating preferences, and reproductive success—all factors that influence the “health” of a population. In the past, we’ve worked with Imperial eagles from central Asia, and are just beginning a similar project on golden eagles in California.
Zoos are important conservation agencies, but animal sex can be a challenge when the animal’s natural breeding behavior is incompatible with captivity. One such organism that needs a more vigorous sex life is the koala! Koalas paired for breeding purposes either love each other (vigorously!) or ignore each other entirely. Unfortunately, zoo breeders cannot predict which pairs will ignore each other, and these failed matings are a considerable waste of resources. One factor that has not yet been incorporated into zookeeper calculus is the genotypic compatibility at Major Histocompatibility Complex (MHC) genes. The MHC is a group of linked immune genes that help detect foreign proteins (e.g., from bacteria or viruses) and produce an appropriate immune response. Mice, lizards, salamanders, salmon, and even humans (!) are known to mate nonrandomly with respect to MHC genotype. The suspected reason? MHC-diverse offspring can better detect and clear infections, thus living longer and producing more offspring. This means that females should select males with MHC genotypes that are dissimilar to their own to produce offspring with the most diverse MHC genotype possible. We are characterizing koala MHC genes in a collaboration with the San Diego Zoo to determine if these genes influence koala mating success. If so, we hope to develop a simple DNA assay whereby zookeepers can determine if koalas will hit it off before matings are arranged.
Natural history (kangaroo rats)
Some of our projects focus on using genetics to study adaptations to the environment. One famous example of an environmental adaptation is found in the banner-tailed kangaroo rat (Dipodomys spectabilis). These rodents live in the deserts of the southwestern U.S./northern Mexico, and are known for their ability to get all of their water from the seeds they eat. They don’t even need to drink surface water! The reason for this is their kidneys are incredibly efficient at retaining water during waste production. We are studying the genes expressed in kangaroo rat kidney to understand which genes are integral to water retention. Some of the genes we’ve identified so far have also been linked to kidney disease in humans. As a result, our evolutionary studies of these genes may have implications for human health.
Evolution (salamanders and passerine birds)
We’ve all heard that climate change may be in our future, but one thing is for sure—we know that climate change is part of the earth’s recent past! Our studies of salamanders have revealed that their historic population sizes expanded with the retreat of the Wisconsonian glaciers roughly 15,000 years ago. Did other species respond similarly? To address this question, we are studying 16 different bird species from the island of Hispaniola (i.e., Dominican Republic and Haiti). Some of these species are migratory birds that breed in North America and winter in the Caribbean, whereas others live and breed in the Caribbean year-around. We hypothesize that because the migratory birds would have experienced a range expansion in their breeding area after the retreat of North American glaciers (similar to tiger salamanders and other N. American species), they should exhibit a more pronounced population expansion than the sedentary species. Indeed, our results to date suggest this is the case. By understanding how populations responded to historic climate change, we can better predict how they might respond to future climate change.