Population connectivity is central to marine ecosystem resilience. Unlike terrestrial ecosystems in which the subfield of landscape genetics is more advanced, there are severe knowledge gaps in the understanding of marine genetic structure. In the past few years, seascape genetics (the marine equivalent to landscape genetics) has made great strides in describing gene flow in the sea hitherto considered to be stochastic due to non-linear relationships between geographic distances and genetic differentiation. Comparatively little research has focused on the seascape genetics of organisms with more complex life cycles in which there are two free-living stages differing in ploidy levels. One of the major hallmarks of the Krueger-Hadfield lab is the study of haploid-diploid algal population structure and gene flow. Marine algae are fundamental components of the global ecosystem through diverse processes, such as primary production, carbon transport and the formation of three-dimensional structure and complexity in near-shore marine communities. We investigate how marine populations are connected in terms of micro-scale, such as within a single intertidal zone, to macro-scale patterns of natural and anthropogenic dispersal.
Maintenance of haploid-diploidy
Our research provides evidence of metapopulation dynamics within the intertidal shorescape with core and marginal population dynamics, highlighting the role of marginal, high shore populations in the adaptive potential of these species to increasing environmental stress scenarios. For example, though sexual reproduction connects the haploid and diploid phases regardless of tidal height in the red seaweed Chondrus crispus, the pathogenic, endophytic alga Ulvella operculata may underlie the maintenance of haploid-diploidy. Our work was the first to demonstrate increased infection rates in male versus female gametophytes (with potential implications for the reproductive mode and mating system) as well as the correlation of infection rates with haploid-diploid ratios. Recently, we have been investigating the impacts of the invasion of novel habitats on the haploid-diploid life cycle was completely uncoupled during the invasion of novel habitats in the ubiquitous marine invader Gracilaria vermiculophylla. During the invasion of the Northern Hemisphere, this seaweed was primarily introduced to soft-bottomed habitats in which hard substratum is rare. Therefore, spores cannot easily recruit to the population. As a consequence, introduced populations have lost the free-living haploid stage. We are currently addressing the mechanisms underlying the maintenance or breakdown of these complex life cycle.
Responses to global climate change
Over the course of the 20th century, sea levels rose in elevation, became warmer, more acidic and biological invasions increased. These physical changes will continue to accelerate, significantly altering both near-shore and open-ocean ecosystems. It is difficult to ascertain whether marine populations will decline, experience range changes (e.g., shift poleward) or adapt in response to changing environmental conditions. I explore the impacts of environmental perturbations on marine populations using several approaches: (i) microevolutionary responses to climate change, (ii) macroecology and (iii) biological invasions. We use models ranging from single-celled microalgae to ascidians (or sea squirts) to macroalgae to explore how global change will impact population dynamics in the marine environment.