- Environmental and evolutionary physiology
- Toxicity of metals and ions
- Temperature and hypoxia
- Trophic transfer/food web dynamics
- Aquatic insect osmoregulation and respiration
- Ecological indicators
The major themes that we explore in our lab are comparative invertebrate ecophysiology and trace metal bioaccumulation and detoxification. A major goal of our work is to better understand how and why species are differentially responsive to environmental stressors such as trace metals and other ions. We primarily work with field collected populations from both reference and contaminated ecosystems, though we are developing a mayfly (Centroptilum triangulifer) as a model organism. We are particularly interested in the use of phylogenetic frameworks as a means of predicting a taxon’s physiological performance.
1) Comparative aquatic insect ecophysiology
How do species vary in physiological processes critical to their success in aquatic environments? Aquatic insects provide ideal models to study these basic questions because of their fascinating evolutionary histories. Aquatic insects are believed to be derived from terrestrial ancestors who invaded aquatic habitats several times over evolutionary history. As a result, they have developed a variety of solutions to the three major challenges associated with aquatic life: locomotion, respiration and osmoregulation. We are particularly interested in respiratory and osmoregulatory physiology as it relates to the accumulation of contaminants and responses to thermal stress. Current projects include the use radiotracers to measure fluxes of ions into and out of organisms (see below). We are also beginning to explore insect strategies (enzymatic and non-enzymatic) for dealing with oxidative stress. How much physiological variation exists within and among various insect lineages? Can phylogenetic position be a useful predictor of physiological performance?
2) Trace metal bioaccumulation and detoxification
All invertebrates accumulate trace metals in their tissues, but different species accumulate metals differently, even when they are in the same water. Differences in accumulation patterns can arise from different physiological traits including the propensity to accumulate metals directly from water, the assimilation of metals from their diets, and/or the ability to efflux metals from their tissues. We use radiotracers to examine these ecophysiological traits in different species to help understand why some species are so exquisitely sensitive to trace metal toxicity, while others are able to thrive in metal-polluted environments. A major challenge is to better understand the consequences of accumulated metals in different species, because species vary in their abilities to protect cells from oxidative damage via the sequestration of metals by metallothionein-like proteins, glutathione and other proteins. Furthermore, species vary in their abilities to evade oxidative damage resulting from metal exposures, by differential expression of antioxidative enzymes and non-enzymatic antioxidants.
3) Temperature and dissolved oxygen
Temperature and dissolved oxygen profoundly determine where species can live. We are currently exploring the extent to which oxygen limitation explains aquatic insect responses to thermal stress. Specifically, we are examining genes in the mayfly Centroptilum triangulifer that are responsive to hypoxia (HIF 1a, EGL-9, lactate dehydrogenase) and thermal challenge (HSPs, oxidative stess genes). These studies are complimented by respirometry experiments that examine oxygen consumption as a function of temperature and dissolved oxygen.
4) The use of insects as ecological indicators
The use of insects as indicators of ecological condition has a long and rich history. While biologists and ecologists can use insect communities to infer whether or not systems are ecologically impaired, the ability to use resident biota to determine the causes of this putative impairment remains elusive. Generalizations hinder the utility of many current bioassessment protocols. The use of a single tolerance value to describe a taxon’s susceptibility to all stressors is a major problem in bioassessment today. Generalizations are also problematic with the lumping of broad taxonomic groups (e.g. “chironomids are tolerant” or “mayflies are sensitive”). These generalizations are pervasive in bioassessment today and need to be replaced by a more fundamental understanding of how and why certain species are responsive to environmental stressors. Work in our lab explores physiological traits in a phylogenetic context to better understand the mechanisms underlying sensitivity differences among taxa.
5). Development of a mayfly model for ecotoxicology and toxicogenetic studies
With collaborators at the Stroud Water Research Center, we are working to develop the mayfly Centroptilum triangulifer as a new model organism. This parthenogenic species is amenable to lab culture and is a promising test organism for life cycle assays. We have recently completed a large cDNA sequencing effort, resulting in a ‘transcriptome” of >22,000 genes. To date, we have cloned and confirmed several genes and are performing qPCR experiments related to thermal challenge and hypoxia.
6). Mercury dynamics in the environment
Mercury is a ubiquitous and highly toxic environmental pollutant. We are interested in indentifying factors, both biotic and abiotic, that are responsible for mercury accumulation in different environments and species. We use a Cold Vapor Atomic Fluorescence Spectrophotometer to measure Hg concentrations in various media including tissue samples. We have performed Hg analyses for collaborators on a diversity of samples, including song bird feathers, black bear tissues, fish tissues, insects and sediments.