I study the interaction between microevolutionary, population, community, and ecosystem processes. Virtually all of my research has been on inland-water organisms, especially zooplankton and fish.

Graduate students in my lab work on ecological and evolutionary processes in aquatic (usually freshwater) organisms, but the topics range broadly. Recent Ph.D. students have investigated (1) the microevolutionary response of Daphnia to rapid environmental change in a polluted lake, (2) the factors affecting food chain length in lakes of differing size and productivity, (3) the developmental and genetic mechanisms underlying a trophic polymorphism (jaw morphology) in pupfish, (4) the role of dispersal in spatial genetic variation in water mites and fairy shrimp, (5) the role of prolonged diapause in the coexistence of competing species of Daphnia, (6) genetic variation in the ability of Daphnia to consume and grow on cyanobacteria, and (7) the effect of body size and shape of different zooplanktivorous fish in the efficacy of piscivory and its ultimate impact on zooplankton and phytoplankton.

Undergraduate students work in my lab either on my research projects, or carry out their own studies. Independent investigations have involved the effect of chemicals exuded by predators on the morphology of their invertebrate prey, the patterns of Daphnia abundance in Austrian Alpine lakes with very long histories of fish introduction, the identification of past invasions by exotic species in using molecular analysis of dormant eggs from lake sediments, molecular genetic analysis of genetic variation in copepod species with and without prolonged diapause, and genetic changes in algal prey during predator-prey cycles. When appropriate, undergraduate students participate as co-authors on publications (e.g., Hairston & Van Brunt 1994; Dowell 1997 Am Mdl.Nat. 137:362-8; Hairston, Perry et al. 1999; Duffy, Perry et al. 2000; Hairston... Perry et al. 2005; Meyer et al. in press; Bohonak, Holland et al. in press - all names except mine and Bohonak's were undergrads in my lab when the published work was carried out).

Current and Past Research

Microevolutionary processes-- In evolutionary biology, I am interested in ways that organisms deal with variable environments and the way that rapid adaptive evolutionary response to environmental change (whether natural or anthropogenic) influences ecological dynamics. My colleagues and I have devised a method for assessing the rates of evolutionary and ecological change on a single time scale (Hairston et al. 2005). We estimate the way that both and evolving character and a changing environment impact a third variable such as the rate of change of an ecological process.

Dispersal between habitat patches can be of central importance for evolution in a spatially varying environment. Similarly, dispersal through time can be critical for evolution in an environment where selection fluctuates temporally (Ellner and Hairston, 1994; Hairston et al. 1996). This temporal dispersal is created in the crustacean zooplankton that I study through long-lived dormant eggs. These eggs routinely survive for decades in lake sediments (Hairston 1996), and in extreme instances, for centuries (Fig. A; Hairston et al. 1995). In the case of Diaptomus sanguineus (Fig. B) living in small lakes in Rhode Island, an important fitness character is the seasonal timing of the production of dormant eggs (Fig. C). In summer, the animals would normally be subjected to intense predation by fish, but the copepods avoid this by producing dormant eggs that rest on the lake bottom where the fish do not find them. The optimal time in spring to begin dormant-egg production varies from year to year depending upon fish density and activity. There is genetic variation for the timing of dormancy (Hairston and Dillon 1990), and the populations respond to changes between years in selection pressure (Hairston and De Stasio 1988; Hairston and Dillon 1990). Theory suggests that this fluctuating selection, combined with the overlap in generations created by the dormant "egg bank," creates conditions for the maintenance of genetic variation for the seasonal timing of dormancy. It is this genetic variation that permits response to changes in natural selection. Interestingly, the variation maintained is not continuous. Rather, two distinct phenotypes coexist (Fig. D; and Hairston et al. 1996; Ellner et al. 1998). One deals with year-to-year variations in fish predation by switching to dormancy early in the season (thus avoiding even the earliest onset of predation). Copepods with an early switch also have a high probability of hatching from the egg bank. The other phenotype suffers low fitness in most years, but in years of late onset of predation can have very high fitness. These late-switching copepods have a relatively low probability of hatching from dormancy in the sediments. The exact diapause timing by the copepod population in any given year is the result of past natural selection combined with the influence of proportions of two phenotypes hatching from the lake sediments (Ellner et al. 1999). Based on the method in Hairston et al. (1005), the rate of adaptive evolution in this system is on the order of 20% of the rate of ecological change.

In a separate study of the Daphnia galeata in Lake Constance (Europe), colleagues at the Max-Planck-Institute for Limnology, Plön, Germany, and from my lab at Cornell, used diapausing eggs extracted from the lake sediments to show how the population evolved resistance to dietary cyanobacteria during the course of lake eutrophication (Fig E; Hairston et al. 1999). Using reaction norms, we have gone on to show that the degree of phenotypic plasticity evolved in this population as cyanobacteria became more prevalent in the plankton during the period 1960 - 1980. The Daphnia genotypes taken from sediments deposited during the 1960s show a significantly larger average change in performance (specific juvenile growth rate) than do genotypes obtained from sediments dated from the late 1970s.

Another thrust of my research is to capitalize on the fact that lakes and ponds represent isolated bits of aquatic habitat well suited for investigations in evolutionary ecology. Seemingly similar bodies of water may be deep or shallow, temporary or permanent, differ in nutrient content, and have different predators. As a result, members of a single species may live in lakes and ponds quite near to each other and yet be subjected to widely differing environments. In this context, I have studied how and why populations differ in pigmentation (Hairston 1979), in vertical distribution in the water column (Hairston 1980), and in population dynamics (Hairston et al. 1983).

Community dynamics-- At the community level, long-term dormancy may provide a mechanism for maintaining species diversity in a changing environment. At Onondaga Lake, New York State, industrial development has created a lake environment that has changed dramatically over the past century. I and others in my lab are studying the ability of the zooplankton community to respond to these changes through reintroduction from the egg bank, and the possible effects of pollution in the sediments on reducing the viability of dormant eggs (and hence reducing community response). One interesting result is the replacement of native species of Daphnia by exotic species during the period of peak pollution (by salt waste, heavy metal inputs, and nutrient pollution). The exotic species (D. exilis and D. curvirostris) are themselves native to saline environments in the southwestern U.S. and Europe (Hairston et al. 1999, Duffy et al. 2000).

A group of people from my lab have initiated the use of molecular markers to explore the genetic changes in populations over time through the analysis of dormant eggs. One application will be in studying rates of microevolutionary change. We used allozymes on animals hatched from the sediments to show that Onondaga Lake was invaded by D. exilis through the hatching of a single egg (genotype). Analysis of the 12S region of mtDNA extracted directly from diapausing eggs was used to identify the invasion of Onondaga Lake during the 1950s by D. curvirostris when the eggs could not be hatched (Duffy et al. 2000). Another use of molecular techniques will be in understanding the frequency of reestablishment of populations from the egg bank, in comparison to reestablishment via dispersal from outside the lake. Together with colleagues at the Max-Planck-Institute, Matthew Holland from my lab is using the COI region of mtDNA in copepods to evaluate the role of prolonged diapause in the nature of genetic variation in two species of diaptomid copepods.

Internally-driven temporal variation-- Stephen Ellner and Laura Jones (Cornell University), Gregor Fussmann (now on the faculty at McGill University), Takehito Yoshida (soon to be on the faculty at Tokyo University), and I, as well as a codre of dedicated undergraduate students (most notably Justin Meyer) use highly controlled culture conditions (chemostats) to create predator-prey oscillations between algae and rotifers. We have been able to predict the dynamics in our culture system with mechanistic mathematical models (Fussmann et al. 2000) and then to use these models to predict unexpected behaviors. One very intersting result has been the observation that when the prey (algae) can evolve in response to temporally varying selection imposed by predation (rotifer grazing) and competition for limiting nutrients (nitrogen), the pattern of the predor-prey osciallations is radically altered (Yoshida et al. 2003). Thus contemporary evolution can dramatically alter what has traditionally been viewed as a purely ecological process. In this system, the rate of evolution is about double the rate of ecological change (Hairston et al. 2005). We are now exploring in collaboration with Edward Mills whether dynamics of this kind occur in natural populations in real lakes using Daphnia-phytoplankton interactions Oneida Lake.

Fluctuating environments can be created by external forces, such as climatic variations between years, or they may be caused by processes internal to the organisms that reside within them. My colleagues and I (and especially a graduate student, Becky Doyle-Morin) are using embayments with different levels of connectivity to Lake Ontario, and hence differing levels of external forcing, to study this process in nature. In some circumstances, mathematical models predict chaotic dynamics. Whether such complex dynamics, or "chaos," are important in natural populations is unclear. Methods for detecting chaos in population data require testing against data that are known to exhibit complex dynamics. We plan to explore whether chaos can be produced in our rotifer-algal chemostat system and how these dynamics are influenced by the rapid evolutionary change we have documented.

Visual ability and diet choice by fish-- Another interest of mine is the way that zooplanktivorous fish locate their prey and how they make dietary decisions. William Walton (University of California at Riverside), Stephen Easter (University of Michigan), and I have studied how the ability of bluegill sunfish (Lepomis machrochirus) to detect prey visually increases during ontogeny and the effect that this has on diet choice (Hairston et al. 1982, Walton et al. 1992). As fish grow, sensory cells are added to the retina causing visual resolution to increase. At the same time, the eye grows larger and the retina recedes from the lens, with the result that visual resolution declines. The net effect is a non-linear increase in visual resolution as fish grow. Behavioral studies show that the feeding reaction (orientation and capture) of fish to their zooplankton prey follow this non-linear pattern closely. The ability of fish to find their prey increases with age (and size), and this in concert with changing ability to handle prey after they are captured results is a diet choice that closely matches predictions of optimal foraging theory.

Interactions between community composition and nutrient cycling-- With Robert Howarth (Ecology and Systematics, Cornell University), I have studied the role that zooplankton community structure has on the cosystem-level processes of nutrient cycling. Using the Cornell Experimental Ponds Facility, we manipulated zooplankton community structure by having fish present (produces a copepod-dominated community) or absent (produces a Daphnia-dominated community). We also manipulated nutrient additions with all ponds having high phosphorous inputs, but some having low nitrogen additions and others having high nitrogen additions. Based on research by others, we would have expected high rates of nitrogen fixation in ponds with low N:P ratios. However, we found this result only in the presence of fish (where grazing by zooplankton is relatively low). When fish are absent, the Daphnia graze down the cyanobacteria to low levels and N-fixation is greatly reduced. Although cyanobacteria are generally considered poor food for Daphnia, these grazers appear early in the year and prevent any cyanobacterial bloom from starting (Schaffner et al. 1994). Much of this research is not yet published.

Effects of grazing on rooted aquatic plants-- Research carried out in my laboratory by Robert Johnson (manager of the Cornell Experimental Ponds ) has focused on the factors determining the abundance of the exotic, nuisance, rooted aquatic plant Eurasian Water milfoil (Myriophyllum spicatum). Many lakes in North America have become dominated by this invading plant during the past few decades. We have found that the larva of an aquatic moth, Acentria ephermerella , may serve as an effective biocontrol agent. The larva not only eats the leaves and stems of the plant, but also makes a refuge out of the meristem of the plant. These activities substantially reduce the growth and survival of the milfoil (Johnson et al. 1998).