Intellectual Merit

Climate change is impacting the distributions of organisms on Earth in both terrestrial and marine environments.  In marine systems, planktonic species are among the most sensitive indicators of environmental change.  While plankton are known to exhibit dramatic range shifts as an important ecological response to ocean change, very little is known about their potential for evolutionary response. Given the key roles that metazoan plankton play in marine food webs and in biogeochemical cycling, obtaining deeper understanding of the genetics and adaption of plankton populations is critically important in the context of climate change. The goal of this research was to determine how the pelagic environment controls genetic variation within plankton species, and the extent to which plankton populations in distinct ocean habitats are locally adapted to their environment. This award supported rapid response research in collaboration with the Atlantic Meridional Transect Programme, and these investigators obtained an exceptionally valuable set of samples and oceanographic data across a basin-scale ocean transect that transited all major pelagic biomes in the Atlantic Ocean.

Our results support the overarching inference that metazoan plankton populations are locally adapted to particular oceanographic environments. Population genomic studies in both planktonic copepods and pteropods identified genetically distinct populations that were endemic to particular ocean ecosystems (e.g, equatorial Atlantic; Figs. 1 & 2), suggesting long-term isolation from populations in other ocean biomes. For example, using a RADSeq approach to assay single-nucleotide (SNP) variation across the genome in 322 animals of the large-bodied migratory copepod Pleuromamma xiphias (49 °N – 45 °S, 12 sites; Fig. 2), we documented three genetically distinct populations across the distribution of this species in the Atlantic Ocean, with sites in the equatorial biome exhibiting highest levels of differentiation in Bayesian clustering, principal component, and pairwise F_STanalyses. A suite of 57 loci were identified that were putatively under directional selection, with allele frequencies at these loci strongly linked to ocean habitat. Ecological studies in P. xiphias also found significant shifts in animal condition across ocean biomes, with particularly high variance in condition in the equatorial province (Fig. 3). There appear to be two, co-occurring P. xiphias populations in the equatorial Atlantic that may correspond to populations identified in population genomic studies, one of which has high animal condition and one of which has low condition (residents, migrants). Relatively few prior population genetic studies have been conducted in oceanic zooplankton, and these observations provide important insight into the presence and geographic distribution of genetically distinct metazoan plankton populations. 

In addition, we completed several related studies on the biogeography of zooplankton communities across the Atlantic Ocean (copepods, pteropods, amphipods; Fig. 4), characterizing abundance, biomass, and latitudinal gradients in diversity for these groups, as well as identifying biogeographic boundaries and regions of community transition. Results for pteropods and heteropods are particularly timely and important given the sensitivity of these animals to changing ocean chemistry.  This award also supported modeling studies in plankton dispersal among ocean biomes in the Atlantic (Chang MS thesis), with results suggesting that both ontogenetic and diel vertical migration significantly impact plankton dispersal.

Collectively, our work provides novel insight into the large-scale distribution of genetically distinct populations of metazoan plankton, and some of the mechanisms that drive these patterns at ocean basin scales. Our results also suggest that metazoan plankton are locally adapted to distinct ocean provinces across their distributional range, and they likely do have substantial capacity to adapt in response to ocean change.

Broader Impacts

All data generated under this award have been submitted for public release, and are available through the project webpage at BCO-DMO (http://www.bco-dmo.org/project/537991).  Citable archival copies of several datasets are linked through the project webpage (e.g., doi10.1575/1912/bco-dmo.704664, doi 10.1575/1912/bco-dmo.682247).

This award supported significant student training, with four students involved in the research completing BSc, MSc or PhD theses/dissertations in the last year of the award.  The students trained also diversify the workforce in Geoscience fields, with the women scientists trained continuing on to postdoctoral or doctoral training, or into STEM teaching positions following completion of their degrees.

Our research results were broadly distributed to the scientific community through peer-reviewed journal articles (12), and presentations to scientific audiences at national and international meetings (20). Results were communicated to the public through online blogs while we were at sea (https://atlanticplankton.wordpress.com, http://earthscigradblog.wordpress.com), and through a science outreach event at our School that educates > 5,000 children bi-annually about the ocean that surrounds their Island home (SOEST Open House). Our images of metazoan plankton were published and disseminated in National Geographic magazine (Dutch language edition; July 2015), annual reports for scientific non-profit organizations, and an introductory biology textbook, as well as other outlets.

Last Modified: 10/03/2018
Modified by: Erica Goetze