RESEARCH IN THE KOOP LAB
Invasive species pose a major threat to global biodiversity. Aside from direct effects on ecosystems, such as competition with native species, invasive species can themselves be or introduce invasive parasites and pathogens. Transmission of parasites to novel hosts can lead to epidemics that devastate local host populations. Despite a major effort by researchers, our understanding of the parameters that enable successful parasite invasions is still relatively limited. Broadly, my research uses field and lab tools in a multidisciplinary approach of evolutionary biology, invasion biology, and conservation biology to investigate the evolutionary ecology of invasive parasites.
Evolutionary genetics of invasions
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One of the most pressing questions in invasion biology aims to understand if and how certain species overcome genetic bottlenecks during their initial invasion. Most invasions are assumed to be the result of a few individuals founding a new population in a previously uninhabited space. As a consequence of this small founding population, invasive species should suffer from population bottlenecks that reduce genetic diversity and thus, limit their ability to adapt to new environments. However, despite this restriction, biological invasions are common. Processes such as hybridization, multiple founding events, and rapid evolution of adaptive traits are hypothesized to help invading species overcome initial losses in genetic diversity. Alternatively, the success of invading species may be attributed to unique levels of phenotypic plasticity. For invasive parasites, the process is further complicated since the genetic diversity of the parasite, possible vectors, and the hosts they infect can all limit the success of an invasion.
In the Galapagos, the recent invasion of Philornis downsi is considered to be a serious threat to the avian hosts it infects, including Darwin’s finches. P. downsi is a muscid fly that, in its larval stages, resides in the nest material of finches and feeds on the blood of nestling and adult birds. My earlier work showed that P. downsi can cause 60-100% mortality of infested nestlings. Recent work by colleagues found that P. downsi collected and genotyped from Ecuador were nearly identical to those from the Galapagos, consistent with the idea that shipping and air trade routes from Ecuador to the Galapagos present the most likely route of introduction. A preliminary study of the population genetic structure of P. downsi found evidence of a recent bottleneck in the founding population, but already some degree of genetic differentiation among island populations. Together, these intriguing results suggest that P. downsi is likely a recent invader and that the success of its invasion may be tied to the biotic and abiotic conditions encountered on each island. We aim to reconstruct the invasion history of P. downsi in the Galapagos and to explore the ecological and evolutionary processes contributing to its successful invasion. Currently, this system offers students the opportunity to gain experience using lab techniques such as DNA extraction, sequencing, and population genetics analysis. |
Evolution of virulence
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Transmission-virulence dynamics are often described in the context of a tradeoff. The more transmissible a parasite or pathogen, the more virulent it can be toward its host. Deviants risk driving their hosts or themselves locally extinct. However, an additional layer of complexity is applied when trying to understand the dynamics of this tradeoff within the context of a species invasion. In some systems, invasive parasites are most virulent at the forefront of an invasion while in other systems, virulence increases only after the initial wave of invasion passes. My lab is studying the ecological processes underpinning the evolution of virulence within just such a spatial context.
We use the invasive aquatic faucet snail (Bithynia tentaculata) and the non-native trematode parasites (Cyathocotyle bushiensis, Sphaeridiotrema globulus, and Leyogonimus polyoon) that it vectors to address questions related to the evolution of virulence. This snail was introduced to the Great Lakes region in the late 1800s and has since slowly progressed westward and southward. The forefront of the invasion now lies in the upper Mississippi River region, where large-scale waterfowl die-offs are being attributed to these trematodes. The trematodes use the faucet snail as their first and second intermediate hosts and waterfowl as their definitive hosts. We are currently collecting snails (and trematodes) from throughout the Great Lakes and Mississippi regions to begin addressing fundamental questions about the evolution of virulence and impacts on transmission dynamics. This project currently provides opportunities for students to gain experience working in the field, performing animal husbandry, molecular techniques, experimental design and analysis. |
