An overview of our research

The goal of our lab is to bring together several biological disciplines (ecology, evolution, animal behavior, toxicology, conservation, and genetics) to understand how species interact in aquatic systems. We examine numerous behavioral, morphological, and life historical traits of a diverse array of organisms and employ a variety of techniques including field surveys, laboratory experiments, mesocosm experiments, and field experiments.

We are currently focused on six areas:

1. The effects of pesticides on aquatic communities
2. The plasticity of animal behavior, morphology, and life history
3. How this phenotypic plasticity evolves
4. The ecological consequences of phenotypic plasticity
5. The evolution and ecology of population differences
6. Long-term monitoring of aquatic communities

 

1. The effects of pesticides on aquatic communities

Most pesticide studies suggest that current pesticide application rates are below lethal limits for nontarget species such as amphibians. These conclusions are based upon 2-4 day toxicity tests in the laboratory which exclude most of the factors that occur in natural ponds. We have found that very low concentrations (1% of four-day LC50 concentrations) of pesticides can be quite lethal if the exposure times are simply increased by a few days (not unrealistic in natural ponds) or if pesticides are combined with the stress of chemical cues that are emitted by aquatic predators. The combined stress of pesticides and predator cues can make pesticides up to 46 times more lethal. We have now completed tests on six different species of tadpoles with two insecticides and one herbicide and found that the smell of predators in the water can make all three pesticides much more deadly.

Because animals in nature experience more than one pesticide at a time, we have also examined how combinations of pesticides impact tadpoles. We found that although combinations of pesticides can be more lethal (and reduce growth) more than each pesticide alone, the impact of adding two pesticides together is very similar to the impact of simply doubling the concentration of either pesticide alone.

It is important that we test pesticides not only under laboratory conditions, but also under more natural outdoor mesocosm conditions (i.e. artificial ponds). With this mind, we have completed a large number of experiments in which we have examined the impacts of different pesticides on whole aquatic food webs and identified a wide range of direct and indirect effects that were previously unknown. Our current research is pursuing many more questions that have derived from this early round of mesocosm experiments.

2. The plasticity of animal behavior, morphology, and life history...(check out our tadpole movie)

Predator-induced plasticity in tadpoles

A number of studies have examined responses of prey to predators (primarily behavioral responses), but most have focused on how a single prey species responds to a single predator species by changing a single trait. We have taken a much more extensive approach, examining how several species of tadpoles alter their behavior, morphology, and life history when exposed to several different predators. We found that phenotypic plasticity is widespread in larval anurans, that the responses are predator- and prey-specific, and that predator-induced phenotypes are more resistant to predation at the cost decreased competitive ability. We have also shown how tadpoles respond to combinations of predators and that that anti-predator defenses change over ontogeny. Moreover, prey defenses can be induced throughout much of a tadpole's lifetime and, contrary to conventional wisdom, predator-induced behavior and morphology are both highly reversible in a short period of time.

Competitor-induced plasticity in tadpoles

While most studies of phenotypic plasticity in animals have focused on predator induction, we discovered that competitors induce all of the same behavioral and morphological traits in tadpoles as predators, but in the opposite direction. Competitor-induced tadpoles are more competitive but less resistant to predators.

The interaction of predator- and competitor-induced plasticity in tadpoles

Given that predators and competitors induce the same suite of tadpole traits but in opposite directions, we can ask how tadpoles respond to a large number of predator-competitor combinations. It turns out that tadpoles are amazingly adept at knowing how many predators and competitors are in their environment and they can fine-tune their behavioral and morphological responses to balance these two conflicting challenges.

Because predation in nature causes induction, selection (i.e. nonrandom killing), and reduced competition (i.e. thinning) in prey populations, all three processes should contribute to the phenotype that we see in nature. In an experiment that examined these three processes alone and in combination, we found that the impact of lethal predators on growth was mediated primarily through thinning, the impact on morphology was primarily through induction, and the impact on behavior was affected similarly by thinning and induction. Surprisingly, while we knew from numerous studies that the dragonflies kill tadpoles nonrandomly, selection did not have a significant impact on the final phenotypes of the tadpoles.

Predator-induced plasticity in freshwater snails

The lasting effects of plasticity

Because larval predator and competitor environments can alter larval traits, they also have the potential to alter post-metamorphic (juvenile) traits. In two studies, we have shown that larval predators and competitors alter size and relative shape of juvenile frogs. Further, these morphological changes in the juveniles can have dramatic impacts on subsequent fitness.

These types of experiments are conducted using laboratory aquaria and outdoor pond mesocosms (i.e. wading pools)

3. The evolution of phenotypic plasticity

Theory predicts that plasticity should evolve when: 1) a population experiences alternative environments, 2) these alternative environments favor alternative phenotypes, 3) there is additive genetic variation for traits and trait plasticities, and 4) there are relatively low costs of carrying the ability to be phenotypically plastic. Nearly all organisms experience heterogeneous environments, but our work has shown that predator and no-predator environments do select for different traits in tadpoles. This divergent selection likely differs among populations, leading to population-specific responses to environmental change. We have also conducted heritability studies to quantify the additive genetic variation and covariation of the behavioral and morphological traits. Finally, we have documented costs of simply carrying the ability to be plastic.

4. Ecological consequences of phenotypic plasticity

When individuals alter their phenotype, it should in turn affect expect how the individual interacts with other species in the community. In a series of experiments, we have shown that changes in behavior and morphology can alter the growth of larval anurans and the competitive outcome between larval anurans. Further, because these trait-mediated changes in growth are acting concomitantly with density-mediated changes, we have examined the separate and combined effects of these two processes. We found that if we understand both the pairwise density effects and the pairwise trait changes, we can correctly predict the nature of the interactions when the community is reassembled.

When we want to understand how plastic responses affect species interactions, we typically conduct the experiments under more natural conditions, using large pond mesocosms (left)...   ...or screened pens placed into natural ponds (right).

5. Long-term monitoring of aquatic communities

Michigan (USA)

One of the keys to asking important ecological and evolutionary questions is to spend time in the field and observe the natural patterns that drive experimental questions. For the past 6 years, we have worked in a collaborative effort to assess the long-term population dynamics of fauna in 37 ponds on the E. S. George Reserve in southeast Michigan (USA). The earliest data on these ponds goes back 30 years to the graduate school days of Henry Wilbur and Jim Collins! Thus, this research represents one of the most extensive long-term data sets available and has provided us with many answers about the factors that determine aquatic species assemblages.

 The Patagonia (Chile)

We have recently begun monitoring aquatic communities in the beautiful Chilean Patagonia as part of a multidisciplinary team of scientists at the University of Connecticut. Our work began in January 1999 and currently consists of annual expeditions to sample the aquatic fauna in the area. Our expeditions to Chile include a number of Americans and Chileans. The volunteers pay their own way and get to work with a variety of scientists (working with mammals, birds, insects, and amphibians) and enjoy the spectacular natural world that is the Patagonia!