Current Research Projects

 

Predator-induced selection on insect flight and dispersal across landscapes

Unraveling the mechanisms that govern the movement of individuals is key to understanding a major determinant of the fates of individuals, the structure and dynamics of populations, communities, ecosystems, and the evolution and diversity of life. Insects exhibit remarkable variation in flight and dispersal that are important to investigate because many insects are ecologically and economically important. In addition, studying the genetic to ecological factors that explain variation in flight and dispersal is fundamental because the evolution of flight presaged the most extensive animal radiation in evolutionary history. Selection by predators for enhanced flight performance to escape being eaten by their prey was intense during the evolution of winged animals, such as insects.

Yet, a mechanistic understanding by which even contemporary predator-induced selection affects insect flight traits and subsequent dispersal ability, propensity, and the fate of dispersers is lacking. This research project will address this important knowledge gap by investigating how predatory fish affect flight traits and dispersal of insects, such as stoneflies, that live in rivers during one life stage and on land as winged insects during their final life stage.

Using four linked objectives, this research will use observations, experiments, and a model to provide one of the first integrative studies of predator effects on flight traits at the biochemical, physiological, and morphological levels, how these traits are ecologically linked to dispersal distance and directionality, and their interaction with landscape-scale habitat configuration in river networks. In so doing, this study will transform our understanding of contemporary selective agents on insect flight and dispersal. Results from this research will benefit society by providing information on factors affecting landscape-scale movements of adult aquatic insects, some of which are human pests or disease vectors, and will have implications for understanding the impacts of introduced predators on traits of prey species.

This project is funded by the National Science Foundation.

Food web consequences of Didymosphenia geminata (rock snot) blooms

Recent blooms of the stalk-producing diatom, Didymosphenia geminata, in rivers worldwide have generated concern because of the possible impacts on pristine rivers and their salmonid fisheries. Although studies have shown that invertebrate communities differ between rivers with and without D. geminata blooms, no studies have tested whether these changes in the invertebrate community are caused by D. geminata and whether they propagate through the river food web to affect top predators, such as fish.

Understanding how D. geminata propagates through the food web to affect fish is important because fish, as top predators, structure river food webs and because recreational fishing is a multibillion dollar industry. Moreover, the increase in frequency and occurrence of D. geminata blooms and the possible links to climate change suggest that blooms could be more common in the future.

I am investigating the bottom-up effects of D. geminata on river food webs. I have discovered several novel pathways whereby D. geminata has indirect negative effects on top predators (fish) by reducing growth and promoting disease. D. geminata shifts the composition of the invertebrate prey of trout to smaller-sized individuals that are lower in nutritional quality on a per mass basis, and less readily available for trout to eat because they take refuge in D. geminata filaments. D. geminata also promotes the abundance of tubificid worms, which are the only host of the pathogen, Myxobolus cerebralis, that causes whirling disease in trout. As a result, disease prevalence is higher and trout growth rate is lower in rivers with the stalked growth form of D. geminata.

Environmental and genetic causes of Didymosphenia geminata (rock snot) blooms

Recent blooms of the stalk-forming diatom Didymosphenia geminata are an important environmental and societal problem because they are primarily occurring in unpolluted rivers that support ecologically and economically important salmonid fisheries and other ecosystem services. The blooms are an enigma because they primarily occur in low-nutrient ecosystems; yet, conventional wisdom is that algal blooms are associated with high nutrients. The amount of extracellular biomass produced by D. geminata is unprecedented for river algae (e.g., 3 kg/m2 dry mass)!

The recent temporal synchrony of blooms at disparate locations around the world suggests a common causal mechanism. The idea that blooms are caused by the spread of D. geminata cells on the boots of fishermen has been widely publicized, but our new evidence suggest that blooms are not caused by new introductions or the emergence of a novel genotype. Multiple labs are independently studying the causes of D. geminata blooms; however, international collaborations have been limited and researchers have focused on system-specific causes of the blooms with limited success, rather than taking a global perspective that enables both system-specific and common causes to be tested.

One hypothesis for the cause of recent blooms that may apply globally is a decline in dissolved inorganic phosphorus (DIP) to extremely low concentrations. Some hurdles to addressing this potential global cause of blooms is a lack of a collaborative research network, and that the DIP threshold that appears to trigger excessive extracellular stalk production, or the bloom state, is below the detection limits of commonly used analytical methods. This project will overcome these hurdles by catalyzing a new international collaborative team who will develop consistent, state-of-the-art methods to obtain comparative preliminary data from a global subset of rivers with and without blooms to investigate the hypothesis that recent occurrences of D. geminata blooms are caused by a common mechanism, such as low DIP, operating at regional-to-global scales.

At a more local scale (Colorado Rockies), Max Bothwell and I have recently (summer 2017) combined observational and experimental field-based approaches with Next Generation Sequencing to explore differences in gene expression of D. geminata experimentally exposed to just high and low DIP as well as stream water from rivers that support D. geminata but never develop macroscopic blooms.  We have successfully cllected nearly pure samples of D. geminata from natural streams and successfully extracted sufficient amounts as well as high quality RNA for libraries and sequencing.  We are excited that this approach will yield important discoveries about the causes of D. geminata blooms.

Consequences of Climate-Induced Range Shifts on Multiple Ecosystem Functions

The healthy functioning of natural ecosystems depends on the interactive roles of the various species that coexist in nature. Different but closely related species that contribute to ecosystem processes replace each other along environmental gradients (e.g., from dry to moist soils). In some cases species are functionally similar, but in other cases the replacement of one by another can have profound effects on how an ecosystem functions and the goods and services they provide societies. Species distributions around the planet are shifting in response to a changing climate, yet little is known about how those shifts will affect ecosystem processes.

Continuous study over the past 25 years of the distribution and abundance of aquatic animals in high-elevation ponds in the Rocky Mountains of Colorado reveals that species are shifting towards higher elevations. Also, within elevations, animals are shifting across different types of ponds (permanent vs. temporary) as drying regimes change. The central goal of this research is to determine how shifts in species distributions affect rates of key ecosystem processes including 1) the incorporation of nutrients and energy in dead plant material (detritus) into the animals that eat this material (detritivores), 2) the degree to which changes in the consumption of dead plant material by detritivores releases nutrients that in turn stimulate the other primary food source (algae) at the base of pond food chains, and 3) how new combinations of species affect overall productivity of pond ecosystems.

The research will compare these three ecosystem outcomes between the combinations of species observed before and after climate-change induced shifts in distribution. Species combinations will be first manipulated in experimental ponds, and the results of those experiments will be used subsequently to design similar experiments in complex environment of natural ponds. This National Science Foundation project is a collaboration with Scott Wissinger at Allegheny College, Hamish Greig at the University of Maine, and postdoctoral research scholar Amanda DelVecchia.