Natalie Sopinka

Manipulating glucocorticoids in wild animals: basic and applied perspectives

Experimental elevations of glucocorticoids are used to understand how chronic exposure to stressors affects vertebrate performance. A variety of methods exist to exogenously manipulate glucocorticoids. Animal responses to glucocorticoid manipulations are variable within and among species. Incorporating glucocorticoid measures into conservation physiology should involve consideration of factors driving this variation.

Mother knows best, even when stressed? Effects of maternal exposure to a stressor on offspring performance at different life stages in a wild semelparous fish.

The environment mothers are exposed to has resonating effects on offspring performance. In iteroparous species, maternal exposure to stressors generally results in offspring ill-equipped for survival. Still, opportunities for future fecundity can offset low quality offspring. Little is known, however, as to how intergenerational effects of stress manifest in semelparous species with only a single breeding episode. Such mothers would suffer a total loss of fitness if offspring cannot survive past multiple life stages. We evaluated whether chronic exposure of female sockeye salmon (Oncorhynchus nerka) to a chase stressor impaired offspring performance traits. Egg size and early offspring survival were not influenced by maternal exposure to the repeated acute stressor. Later in development, fry reared from stressed mothers swam for shorter periods of time but possessed a superior capacity to re-initiate bouts of burst swimming. In contrast to iteroparous species, the mechanisms driving the observed effects do not appear to be related to cortisol, as egg hormone concentrations did not vary between stressed and undisturbed mothers. Sockeye salmon appear to possess buffering strategies that protect offspring from deleterious effects of maternal stress that would otherwise compromise progeny during highly vulnerable stages of development. Whether stressed sockeye salmon mothers endow offspring with traits that are matched or mismatched for survival in the unpredictable environment they encountered is discussed. This study highlights the importance of examining intergenerational effects among species-specific reproductive strategies, and across offspring life history to fully determine the scope of impact of maternal stress.

Bycatch mortality of endangered coho salmon: impacts, solutions, and aboriginal perspectives

We used biotelemetry and human dimensions surveys to explore potential solutions to migration mortality of an endangered population of coho salmon caught as bycatch in an aboriginal beach seine fishery. From 2009 to 2011, 182 wild coho salmon caught as bycatch in the lower Fraser River (Canada) were radio-tagged and tracked as they attempted to complete their migrations to natal spawning areas over 300 km upstream. Failure to survive to reach terminal radio receiving stations averaged 39% over three years. This mortality estimate is low compared to those obtained from telemetry studies on other salmon fisheries in the Fraser River. However, this value is markedly higher than the mortality estimate currently used to manage the fisherys impact. It is also in contrast to the perceptions of the majority of aboriginal fishers, who did not think survival of coho salmon is affected by capture and release from their fishery. Increased probability of survival was associated with lower reflex impairment, which is consistent with previous findings. Reflex impairment was positively correlated with entanglement time, suggesting that greater efforts by the fishers to release bycatch from their nets quickly would minimize post-release mortality. Survey responses by aboriginal fishers also suggested that they are receptive to employing new bycatch handling methods if they are shown to increase post-release survival. However, attempts to facilitate revival of a subset of captured fish using cylindrical in-river recovery bags did not improve migration success. Fisheries managers could use the new information from this study to better quantify impacts and evaluate different harvest options. Since aboriginal fishers were receptive to using alternate handling methods, efforts to improve knowledge on minimizing reflex impairment through reductions in handling time could help increase bycatch survival. Such a direct integration of social science and applied ecology is a novel approach to understanding conservation issues that can better inform meaningful actions to promote species recovery.

Stress Indicators in Fish

1. Why Do We Measure Stress? 2. Quantifying Stress 3. Specific Measures of Fish Stress 3.1. Cellular and Molecular Indicators 3.2. Primary and Secondary Physiological Indicators 3.3. Whole-Organism Indicators 4. Considerations for Measuring and Interpreting Stress 4.1. Interspecific Differences 4.2. Intraspecific Differences 4.3. Context-Specific Differences 4.4. Stressor Severity 4.5. Field Versus Laboratory 4.6. Temporal Aspects 5. From Individual Indicators to Ecosystem Health 6. Stress Indicators of the Future 7. Conclusion A fish is chased with a net in an aquarium before being captured, scooped out of the water, and placed in a nearby testing arena. Is it stressed? How can we tell? Are our indicators reliable? Quantification of stress in fish has evolved from the initial development of radioimmunoassays to measure cortisol in plasma to the rapidly expanding suite of genome-based assays. Indicators range from the intracellular to whole-animal level. Expression of heat shock proteins (HSPs) and activity of metabolic enzymes can be paired with straightforward observations of reflexes and survival. Both traditional and emerging indicators have advantages and disadvantages, and their use is tissue- and context-specific. Ecological, biological, and methodological factors must be considered when selecting, measuring, and interpreting stress indicators. Inter- and intraspecific, sex, life stage, and temporal differences in physiological responses to stressors can confound confirmation of a stressed state. Despite numerous types of indicators, our understanding of how absolute levels of indicators relate to stressor severity and recovery to date remains limited. How accurately indicators characterize stress in wild populations naturally exposed to stressors is still an evolving discussion. The integration of research disciplines and involvement of stakeholders and user groups will aid in filling these knowledge gaps, as well as the translation of individual-level indicators to population- and ecosystem-level processes.

Are there intergenerational and population-specific effects of oxidative stress in sockeye salmon (Oncorhynchus nerka)?

Intergenerational effects of stress have been reported in a wide range of taxa; however, few researchers have examined the intergenerational consequences of oxidative stress. Oxidative stress occurs in living organisms when reactive oxygen species remain unquenched by antioxidant defense systems and become detrimental to cells. In fish, it is unknown how maternal oxidative stress and antioxidant capacity influence offspring quality. The semelparous, migratory life history of Pacific salmon (Oncorhynchus spp.) provides a unique opportunity to explore intergenerational effects of oxidative stress. This study examined the effects of population origin on maternal and developing offspring oxidative stress and antioxidant capacity, and elucidated intergenerational relationships among populations of sockeye salmon (Oncorhynchus nerka) with varying migration effort. For three geographically distinct populations of Fraser River sockeye salmon (British Columbia, Canada), antioxidant capacity and oxidative stress were measured in adult female plasma, heart, brain, and liver, as well as in developing offspring until time of emergence. Maternal and offspring oxidative stress and antioxidant capacity varied among populations but patterns were not consistent across tissue/developmental stage. Furthermore, maternal oxidative stress and antioxidant capacity did not affect offspring oxidative stress and antioxidant capacity across any of the developmental stages or populations sampled. Our results revealed that offspring develop their endogenous antioxidant systems at varying rates across populations; however, this variability is overcome by the time of emergence. While offspring may be relying on maternally derived antioxidants in the initial stages of development, they rapidly develop their own antioxidant systems (mainly glutathione) during later stages of development.

Does among-population variation in burst swimming performance of sockeye salmon Oncorhynchus nerka fry reflect early life migrations?

Using a fixed-speed test, burst swimming performance was found to vary among nine populations of emergent sockeye salmon Oncorhynchus nerka fry reared in a common-garden environment. No consistent relationship was, however, detected between difficulty of fry migration (upstream v. downstream) to rearing areas and total burst swimming duration or bursting rate.

Examining the relationships between egg cortisol and oxidative stress in developing wild sockeye salmon (Oncorhynchus nerka)

Maternally-derived hormones in oocytes, such as glucocorticoids (GCs), play a crucial role in embryo development in oviparous taxa. In fishes, maternal stressor exposure increases circulating and egg cortisol levels, the primary GC in fishes, as well as induces oxidative stress. Elevated egg cortisol levels modify offspring traits but whether maternal oxidative stress correlates with circulating and egg cortisol levels, and whether maternal/egg cortisol levels correlate with offspring oxidative stress have yet to be determined. The objective of this study was to examine the relationships among maternal and egg cortisol, and maternal and offspring oxidative stress to provide insight into the potential intergenerational effects of stressor exposure in sockeye salmon (Oncorhynchus nerka). Antioxidant concentration and oxidative stress were measured in maternal tissues (plasma, brain, heart and liver) as well as offspring developmental stages (pre-fertilization, 24h post-fertilization, eyed, and hatch), and were compared to both naturally-occurring and experimentally-elevated (via cortisol egg bath) levels of cortisol in eggs. Oxygen radical absorptive capacity of tissues from maternal sockeye salmon was measured spectrophotometrically and was not correlated with maternal or egg cortisol concentrations. Also, naturally-occurring and experimentally-elevated cortisol levels in eggs (to mimic maternal stress) did not affect oxidative stress or antioxidant capacity of the offspring. We conclude that the metrics of maternal stress examined in sockeye salmon (i.e., maternal/egg cortisol, maternal oxidative stress) are independent of each other, and that egg cortisol content does not influence offspring oxidative stress.

Water fleas stand the heat and stay in the city

One of the most dramatic visuals of the 21st century is the sprawling skyline of a city. Glass-paned buildings as you look up, endless pavement as you look down. Cars honk. Tailpipes leak out pollutants. Lightbulbs buzz as a metropolis works into the night. What you do not necessarily see or hear... but might feel... is the heat. Because of human activities, there is an increase in air temperatures as you move into a city from its rural edges. This urban-rural temperature gradient is called the ‘urban heat island’ effect.

Back Page Photo Series: Intertidal After Dark

How did you find yourself studying intertidal zones? I find myself as an intertidal ecologist due to a surprising combination of happenstance and interest. Growing up in coastal Connecticut, I always felt an affinity for marine ecology. But when I decided to attend the University of Chicago, I figured I would have few chances to study ocean ecosystems while based in the Midwest. Luckily, in my third year, I took a course taught by Catherine Pfister, who I soon discovered worked in the rocky intertidal ecosystem of Washington’s Olympic Peninsula. When I approached Catherine about working in her lab, she happened to have a languishing project perfect for an undergraduate. We worked together for two years, eventually publishing the project (Barner et al. 2011). After I graduated, I knew that I wasn’t done with the intertidal, or with the Pacific Northwest. I was offered the opportunity to pursue a Ph.D. in ecology at Oregon State University, and I have spent five very happy field seasons in Oregon’s rocky intertidal.