Variation at small spatial and temporal scales
Increasingly, biologists are acknowledging the relevance of the tremendous amount of spatial and temporal variation that exists for organisms within the same population. Understanding the impacts of environmental variation at these relatively small scales is both conceptually and technologically challenging. We are attempting to tackle this variation head on, and we are constantly searching for new ways to address the causes and consequences of environmental variation.
How do individuals experience environmental variation?
One important hurdle to overcome is gaining a better understanding of the ways in which individual animals experience environmental variation. In collaboration with Dr. Luke Miller of San Jose State University, we have deployed a custom MusselTracker system to monitor body temperatures (mantle cavity temperatures every second) of up to 36 individual mussels through time in their natural rocky intertidal zone habitat. In addition to recording temperature, these sensors also record the valve gaping behavior and postural position of the animals. In two summer field seasons, we have generated roughly 30 Gigabytes worth of observations. Adjacent mussels can differ in their body temperature by up to 14°C at the same intertidal site during the same low-tide period, an extraordinary amount of inter-individual variation over a very small spatial scale. The mussels modulate gaping patterns based on both where they grew up and their recent experience, but, unlike sunflowers and lizards, do little to change their postural orientation to the sun, which is the primary source of heat.
- Miller. L. P., and W. W. Dowd. 2017. Multimodal in situ datalogging quantifies inter-individual variation in thermal experience and persistent origin effects on gaping behavior among intertidal mussels (Mytilus californianus). J. Exp. Biol. 220: 4305-4319
Is individual experience correlated with physiological status?
The unique individual monitoring data from the MusselTracker system have enabled us to pursue links between individuals’ varying experiences in the wild and their corresponding physiological profiles. For example, mussels that experienced more frequent and intense episodes of heat stress during a month-long monitoring period exhibited higher levels of oxidative damage within their gill tissue, as well as higher gill concentrations of the small organic molecule (a.k.a. osmolyte) taurine. Taurine has both thermoprotective and antioxidant properties in other systems, suggesting an intriguing link between changes in cellular amino acid metabolism (taurine is a derivative of the amino acid cysteine) and environmental stress in this mussel in nature.
- Gleason, L. U., Miller, L. P., Winnikoff, J., Somero, G. N., Yancey, P. H., and W. W. Dowd. 2017. Thermal history and gape of individual Mytilus californianus correlate with oxidative damage and thermoprotective osmolytes. J. Exp. Biol. 220: 4292-4304
In what environmental contexts is physiological variation among neighbors maximized?
We have also manipulated the presence/absence of inter-individual variation, as well as its magnitude, using reciprocal transplant and common-garden experiments. As predicted, removing environmental variation from one individual to the next (in this case in body temperature) abolishes a significant degree of the physiological variation among individuals. This inter-individual physiological variation was restored only when mussels were outplanted to high, thermally stressful intertidal habitats at which the environment varied around an elevated mean temperature. Mussels transplanted to a benign, low-intertidal site were still more similar to one another in their physiological profiles. We have now turned our attention to inter-individual variation in global patterns of gene and protein expression in mussels subjected to these manipulations.
- Jimenez, A. G., Jayawardene, S., Dallmer, J., Alves, S., and W. W. Dowd. 2015. Micro-scale environmental variation amplifies physiological variation among individual mussels. Proc. R. Soc. B. 20152273.