Confucius tells us to study the past in order to know the future. This wisdom applies not only to acts of love and war, but also to the conservation of nature in our changing world. As a marine scientist, I study how changes in ocean climate over recent geological time have shaped the evolutionary and population histories of marine animals, and I use this information to predict the future of our oceans. In the absence of fossil data, my work relies on genetics and ecological modeling to reveal the historical processes that have shaped spatiotemporal patterns of biodiversity, phenotypic variation, and population connectivity in coastal marine ecosystems.
Within this framework, my research program is organized around the following primary themes:
1) Climatic niche evolution over space
2) Climatic niche evolution on geological and ecological time scales
3) Seascape genetics
4) Developing GIS infrastructure for marine spatial ecology
Climatic niche evolution over space
Case Study: Local adaptation despite high gene flow in the Atlantic silverside
The Atlantic silverside, Menidia menidia (Image courtesy of FishBase)
We are testing the balance between neutral and selective determinants of phenotypic variation in Menidia menidia, a silverside fish common to estuaries and coastal areas along the east coast of North America. Like many other marine fishes, the Atlantic silverside follows Jordan’s Rule by exhibiting a latitudinal cline in vertebral number. This trait is highly heritable and yet, clinal variation persists across a climatic gradient despite high gene flow across its range. This dichotomy suggests a strong role for local adaptation in maintaining the observed spatial patterns of phenotypic variation. We are combining ocean climate data and estimates of gene flow from hyper-variable genetic markers to quantify the contributions of genetic and environmental influences on vertebral number. Our findings have implications for phenotypic evolution under warmer ocean conditions in our study system and in other fishes that conform to Jordan’s Rule. Future work will focus on identifying genomic targets of selection and in utilizing museum resources to test the validity of space-for-time substitutions in this study system.
Climatic niche evolution on geological time scales
Case Study: Indo-Pacific Coral Reefs
Thermal niche of Indo-Pacific corals (purple) compared to modern and paleo-climate
Resilience in the face of environmental change is determined, in part, by a species’ ability to adapt to novel climatic combinations, but also in its ability to track its preferred niche across the landscape via dispersal. Examining the response of species and communities to climatic changes from paleontological to modern times may provide insight into their long-term persistence in the future. Within this context I am examining biodiversity patterns on Indo-Pacific coral reefs as a function of modern climate and also the velocity of climate change since the peak of the last ice age (21,000 years ago). My findings indicate that Indo-Pacific corals possess the capacity for climatic niche evolution over tens of thousands of years, but are vulnerable to rapid warming. This historical approach will aid in conservation prioritization across the region by allowing for the identification of reefs at risk as well as potential climate refugia.
Climatic niche evolution on ecological time scales
Case Study: The Caribbean lionfish invasion
Biological invasions are accidental experiments that offer excellent insight into species responses to novel climatic combinations and their ability to evolve on ecological time scales. A notorious example of marine biological invasions is that of the red lionfish, Pterois volitans, a western Pacific native that has established breeding populations in the southeastern United States and entire Gulf of Mexico and Caribbean over the last two decades. The rapid proliferation of an invasive apex predator in an ecosystem already stressed by over-fishing, pollution, and climate change has made the lionfish invasion one of the most significant marine conservation concerns in recent history. Our work in this area aims to quantify differences between the climatic niche of native and invasive lionfish populations. We are using a spatially explicit methods to test hypotheses of climatic niche conservatism or expansion during the Caribbean lionfish invasion. Our findings underscore the need for future studies of lionfish physiology, particularly with respect to salinity tolerance, and suggest that ecological niche models may underestimate the capacity of marine species to persist through the next century of climate change. Future work will include comparative transcriptomics of native and invasive populations to identify genes related to stress tolerance and geographic variation in “invasibility” across the lionfish native range.
Seascape genetics
Least cost path over stable climate (pink) versus shortest distance over water (black) between Bali and Brunei.
In collaboration with the Diversity of the Indo-Pacific Network (DIPnet), I am investigating the relative importance of historical environmental stability, habitat suitability, and oceanographic circulation on stepping-stone connectivity across the Coral Triangle and broader Indo-Pacific. Our “seascape genetics” framework builds on isolation by distance theory that states that genetic differentiation among populations should increase as a function of distance. For benthic marine organisms, however, the geographic distance relevant to population connectivity may not be the shortest path over water. Rather, distance may be better measured along “seascape” features, such as meandering ocean currents, relict connectivity pathways established during times of lowered sea-level, or pathways formed by past or present environmental filters. To investigate this problem, we are using spatially explicit models and multivariate statistical tools to weigh the relative effects of these features on spatial patterns of connectivity among tropical marine species from the Indo-Pacific.
Developing GIS infrastructure for marine spatial ecology
Multivariate analysis of MARSPEC variables in the Indo-West Pacific
Species distribution models can be useful for predicting the responses of animals to future climate change, as well as to establish working hypotheses about the evolutionary and demographic histories of species. Until recently, however, this tool has has been under-utilized in marine systems, partially due to the difficulty in obtaining marine climate data in formats compatible with ArcGIS or R. This has hampered the modeling efforts of marine ecologists and evolutionary biologists who are not necessarily savvy in the handling of raw oceanographic or satellite data. Part of my work as a graduate student and postdoctoral fellow has been to develop the MARSPEC and paleo-MARSPEC databases: high resolution climatic and geophysical GIS data layers for the global ocean. Data layers are freely available for both modern and paleo (the last glacial maximum and mid-Holocene) time periods from the MARSPEC website. Future plans include the development of climate layers for various future time slices and Representative Concentration Pathways, development of additional paleoclimate layers from the Last Interglacial and Pliocene time periods, an improved web interface that allows for the selection and download of smaller spatial subsets of the data, and the inclusion of biogeochemical data layers in the database.
Elizabeth J. Sbrocco, Ph.D. 