Recent work and publications.
Inter-individual variation in mussel physiological performance
In the Dowd Lab, we are interested in how variation shapes population-level responses to warming. The intertidal zone experiences a wide range of environmental conditions that vary on a temporal and spatial scale, resulting in extremes within its microclimates. Intertidal mussels may deal with these conditions in many different ways on the cellular level, but arrive at similarly successful phenotypes. How do we assess the impacts of inter-individual variation on fitness to better predict population-level responses to warming and increases in extreme temperatures with climate change?
Currently we are working with transcriptomic and proteomic data to look for signatures of differential variation and expression in certain gene pathways to understand the interplay between how the organism mounts a response (RNA expression) and what happens in actuality (protein expression).
Tanner, R.L. & Dowd W.W. (2019). Inter-individual physiological variation in responses to environmental variation and environmental change: integrating across traits and time. Invited submission at Comparative Biochemistry and Physiology: Part A (special issue: Mechanisms of sensitivity and resilience in a rapidly changing ocean).
Visit my WSU lab page from my postdoctoral position at https://labs.wsu.edu/dowd/
Thermal tolerance plasticity in mollusks
During my PhD, I focused on how increases in warming impacted the acclimation capacity of mollusks in dealing with increases in both average temperature and extreme events. My dissertation focused on the eelgrass sea hare, Phyllaplysia taylori, but I also have projects in a variety of eastern Pacific nudibranchs and Lottia limatula with collaborators.
The eelgrass sea hare has many unique life history characteristics that make it an ideal system for studying the evolution of plasticity: it plays an ecologically important role as an epiphyte grazer, it has direct development, cannot disperse actively, has two generations per year in thermally disparate seasons, and withstands wide environmental variation within estuarine eelgrass beds. We found a wide range of populations expressing different reversible acclimation capacities and overall thermal tolerance. We were able to correlate this with underlying genetic profiles and look forward to using this knowledge to build physical models of sea hare passive dispersal to inform existing population structure and make recommendations for future restoration introductions. We also looked at developmental and transgenerational thermal tolerance plasticity, finding that future climate scenarios (both warming and extremes) decrease offspring success. We were also able to determine that persistence through thermally disparate seasons is due to plasticity in maternal provisioning, and future climate scenarios disrupt this "alternation of generations" in thermal tolerance due to a stress on energy budgets.
Experimental approaches for these projects include measurements of metabolic rate, heart rate, foot muscle function, reproductive success, and survival.
Armstrong, E. J., Tanner, R. L., & Stillman, J. H. (2019). High heat tolerance is negatively correlated with heat tolerance plasticity in nudibranch mollusks. Physiological and Biochemical Zoology 92:4, 430-444. doi:10.1086/704519.
Wang T., Tanner R. L., Armstrong E. J., Lindberg D. R., & Stillman J. H. (2019). Thermal plasticity in file limpet, Lottia limatula, across oceanic to estuarine gradients in habitat temperature. Aquatic Biology 28: 113-125. doi:10.3354/ab00714.
Stay tuned for all of these publications in review!
Salinity effects on the eelgrass sea hare and eelgrass beds
In the 2017 winter season, San Francisco Bay experienced heavy rains that resulted in a complete shift to freshwater conditions for multiple months. Consequently, we saw local extirpation of the eelgrass sea hare during this time. This extreme freshwater event did not similarly affect the populations surveyed for previous projects, so we were able to assess any potential reductions in genetic diversity due to this extreme event in other populations, while also looking at the ecological implications of losing this key grazer species in San Francisco Bay.
I also worked on a project with a Stillman Lab masters student, Lindsay Faye, where we looked at the potential synergistic effects of salinity and temperature changes with future climate scenarios. We look forward to using these data to inform restoration efforts in San Francisco Bay to aid in eelgrass bed recovery.
Tanner, R. L., Faye, L. E. & Stillman, J. H. (2019). Temperature and salinity sensitivity of respiration, grazing, and defecation rates in the estuarine eelgrass sea hare, Phyllaplysia taylori. Marine Biology 166(8): 109. doi:10.1007/s00227-019-3559-4.
Restoration ecology of seagrasses and associated fauna
Using ecology and physiology to inform management efforts has been a theme in my research since my undergraduate work at USC.
In Southern California eelgrass beds, we used estimates of secondary productivity to assess the fishery value of eelgrass as nursery ground for Paralabrax clanthratus, the kelp bass. We found variation in young of the year fish populations dependent on season, and made recommendations for the timing of management assessment of these eelgrass beds. We were also able to add eelgrass canopy height to the currently surveyed metrics (shoot density and areal coverage) as an important indicator of kelp bass biomass.
In eastern Pacific eelgrass beds, I found that land use, not abiotic indicators, best predicted eelgrass sea hare presence in existing eelgrass beds. However when assessed over time, the same indicators as above (with secondary productivity of fishes) were important in predicting sea hare abundance. I used this information to create a model of sea hare presence/absence for use in restoration schemes, and was able to apply it successfully to currently designated San Francisco Bay planned restoration sites. I found that only ~50% of currently planned eelgrass restoration areas are predicted to support healthy populations of sea hares, giving more opportunity for us to investigate the role of grazer community success in eelgrass restoration efforts.
Tanner R. L. (2018). Predicting Phyllaplysia taylori (Anaspidea: Aplysiidae) presence in Northeastern Pacific estuaries to facilitate grazer community inclusion in eelgrass restoration. Estuarine, Coastal and Shelf Science 214: 110-119. doi:10.1016/j.ecss.2018.09.011