Collaborative Research: Comparative genomics and physiology to discover integrated mechanisms that support phenotypic plasticity

Most species are adapted to live in relatively stable environments. Rare are those species that tolerate environments that fluctuate rapidly and severely. Little is known about what drives the physiological flexibility needed for species to survive and thrive in highly variable environments.

This research will use genetic and physiological tools and approaches developed for North American killifish to gain an integrative understanding of how extreme physiological flexibility is assembled and how it works. Within the Fundulus genus, some species of fish are highly flexible and can adjust to huge extremes in environmental salinity, but others are much less flexible.

High-flexibility species are compared to closely-related low-flexibility species, for multiple pairs of species. This comparative approach is powerful for distinguishing what makes high-flexibility species unique. Results should provide new insights into how features of the genome (variation in gene sequences, variation in genetic control elements, variation in gene content) may enable or disable physiological adjustments to extreme environmental change.

One hallmark of global climate change is an increase in the frequency and severity of environmental variability, and this variability is posing yet another threat to the global biodiversity crisis. This research should provide insights into what makes some species more or less likely to do well in the face of environmental variability. This project is jointly funded by Integrative Ecological Physiology and the Established Program to Stimulate Competitive Research (EPSCoR).

The genomic infrastructure that supports physiological flexibility, an important form of phenotypic plasticity, is likely complex and multigenic but is poorly understood. Most aquatic species live in osmotically stable fresh or salty (marine) waters which vary little in salinity, where residents exhibit narrow limits for accommodating salinity changes and are considered “stenohaline”.

In contrast, euryhaline species can adjust their physiology to accommodate large changes in salinity; they survive and thrive in osmotically dynamic environments such as estuaries. Euryhalinity is an extraordinary and important form of phenotypic plasticity. Comparative experiments that integrate physiological, transcriptomic, and structural genomic information, will be used to reveal the mechanistic infrastructure that supports euryhalinity.

The Fundulus genus of killifish includes many species of euryhaline estuarine specialists. Multiple independent radiations into fresh water have also resulted in repeated losses of euryhalinity. Physiological challenge experiments will be used, within a phylogenetic-comparative framework where independently evolved losses of plasticity in three clades provide replicated opportunities to infer the mechanisms that support plasticity that is ancestrally retained.

Experiments will test the hypothesis that euryhalinity is underpinned by gene regulatory flexibility maintained and constrained by natural selection. This work will illuminate the mechanistic basis of a trait that is both physiologically important, and important in the history of vertebrate diversification. Since euryhalinity is also a compelling example of phenotypic plasticity, findings will contribute to the elaboration of a growing general theory of the mechanistic and molecular-genetic basis of phenotypic plasticity.

This project is jointly funded by Integrative Ecological Physiology and the Established Program to Stimulate Competitive Research (EPSCoR).

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.