We are interested in how organisms respond to novel and changing environments. In much of our research we approach this question by trying to understand why organisms vary in learning and phenotypic plasticity, and using this understanding to predict adaptive developmental adjustments to new environments. In a range of other projects, we explicetely consider a variety of anthropogenic environments, from large agricultural monocultures, to roadsides and cities. In much of this research, we seek to apply basic knowledge and also develop conservation and management reccommendations. Here we give an overview of some of the ongoing research questions in the lab.
THE EVOLUTION OF DEVELOPMENTAL PLASTICITY
Developmental mechanism matters in the evolution of plasticity – developmental selection forms of plasticity are particularly costly. Not all plasticity is created equal. Some of the most impressive forms of plasticity result from evolved, developmental switches, such as horned-hornless polyphenisms in beetles. These forms of plasticity are not particularly costly to an individual – instead, models suggest they should be limited at the evolutionary level by weakened selection on genes specific to alternate developmental pathways (some data). In contrast, developmental selection forms of plasticity are incredibly costly to an individual – sampling different traits over time, for instance during motor learning or the development of antibodies, is a powerful mechanism to match a phenotype to the environment, but costs time and energy (see review here). Relative to a specialist, investing in developmental selection mechanisms of plasticity should result in delays in reproduction, and increased investment in offspring to survive the delay in trait function.
Costs of learning and behavioral plasticity. Costs associated with developmental selection have been best studied in the context of behavioral plasticity (see review here), for instance in studies of costs of learning or in life history tradeoffs with brain size across species. We are continuing these studies in several areas using butterflies as a system because of their experimental tractability and the ease with which we can measure plasticity in host use, for instance investigating reproductive tradeoffs associated with information use – does taking the time to pay attention to more cues trade-off with fecundity? (see recent work by Sarah Jaumann here)
Variability of gene expression as a case study of costs of plasticity. In theory, costs of developmental selection should be seen across any developmental process that involves variation and environmental feedback. It has been suggested that stochasticity in gene expression, in some cases coupled with epigenetic feedbacks within individuals, may function as a mechanism of developmental plasticity. We are testing whether such a mechanism comes with similar life history tradeoffs as analogous processes at the level of learning. In particular, we are focusing on digestive gene expression in specialist and generalist-populations of butterflies, predicting that generalist populations will show signatures of developmental selection (high gene expression variation early in development) and life history tradeoffs (increased investment in each egg and thus fewer eggs). In this work, we are taking advantage of a specialist population of cabbage white butterflies that feeds on canola in Northern North Dakota.
Resource availability constrains the evolution of life histories and plasticity. Life history theory has long recognized that resources shape the expression of life history traits and tradeoffs: underlying tradeoffs may be obscured by variation in resource availability or acquisition. We are investigating this idea across longer evolutionary time scales – to what extent do limited resources constrain life history evolution over millions of years, or are constraints relaxed as organisms adapt to their diet? Are tradeoffs between plasticity (e.g., brain size) and reproduction more pronounced for species with poorer diets? We are using butterflies as a system because they feed on a wide variety of plant families that vary in nutrient content, in particular in nitrogen levels. To date, our results suggest that nutrition can indeed be a long term constraint for both life history traits (see work here by Eli Swanson) and brain size.
Niche construction and the evolution of plasticity. Theory suggests plasticity should evolve in variable environments. However, organisms construct their experience of environmental variation, thus setting up complex feedbacks between traits that influence movement and the evolution of plasticity (see review here). Recent work in the lab has considered how sensory biases and movement may shape behavioral plasticity (for instance work by Meredith Steck).
PLASTICITY IN THE ANTHROPOCENE
Humans can have direct influences on the development of plasticity. This is particularly pronounced through our effects on nutrients that were once limited in availability but are now available in large quantities in certain environments (e.g., nitrogen and phosphorus, see review here). In a 2014 study, we tested how road salt runoff can influence sodium availability of roadside plants, which, in turn, affects neural and muscle development of roadside herbivores such as Monarch caterpillars. While very high levels of sodium result in a high mortality rate, moderate increases on sodium can result in an increase in brain and eye size. Studies such as this suggest that in some cases, nutritional changes could have somewhat positive effects on the expression of plasticity in human environments, at least until the point where the nutrient increase becomes stressful. In other instances, humans may be having negative impacts on the development of plasticity.
Anthropogenic environments can result in evolutionary changes in plasticity and life history within species. In a 2013 study, we made use of the Bell Museum mammal collection to test changes in relative cranial capacity – a very rough proxy for behavioral flexibility across species – over time and space in association with humans. City populations of two rodent species showed greater cranial capacity than rural populations, and cranial capacity of all insectivores (shrews and bats) showed significant increases over time. These results suggest that in some cases, organisms may be adapting to rapid environmental change through an increase in plasticity. In more recent work, we have considered how human-induced changes in nitrogen availability have shifted sexual selection dynamics in agricultural environments (Espeset et al., in press).
Understanding interactions between nutrition, plasticity and behavior can improve conservation strategies. In much of our current work, we are asking whether roadsides may be acting as an ecological trap for pollinators -- are butterflies and bees drawn to high sodium and nitrogen content of roadside plants, only to be harmed by toxic levels of sodium and heavy metals from road runoff? In a series of lab and field experiments, we are describing patterns of roadside nutrients in plants used by butterflies and bees, and then testing at which point these nutrients and metals become toxic to pollinators of conservation concern (see recent work by Megan Kobiela on heavy metal tolerance). These data will be used to make management recommendations with respect to which roadsides should be prioritized for restoration for pollinators.