Impacts of Zika emergence in Latin America on endemic dengue transmission.

In 2015 and 2016, Zika virus (ZIKV) swept through dengue virus (DENV) endemic areas of Latin America. These viruses are of the same family, share a vector and may interact competitively or synergistically through human immune responses. We examine dengue incidence from Brazil and Colombia before, during, and after the Zika epidemic. We find evidence that dengue incidence was atypically low in 2017 in both countries. We investigate whether subnational Zika incidence is associated with changes in dengue incidence and find mixed results. Using simulations with multiple assumptions of interactions between DENV and ZIKV, we find cross-protection suppresses incidence of dengue following Zika outbreaks and low periods of dengue incidence are followed by resurgence. Our simulations suggest correlations in DENV and ZIKV reproduction numbers could complicate associations between ZIKV incidence and post-ZIKV DENV incidence and that periods of low dengue incidence are followed by large increases in dengue incidence.

Watershed-Scale Land Use Activities Influence the Physiological Condition of Stream Fish.

Land use changes within watersheds can have large effects on stream ecosystems, but the mechanistic basis of those effects remains poorly understood. While changes to population size presumably reflect underlying variation in organismal health and condition, such individual-level metrics are rarely evaluated in the context of ecosystem disturbance. To address this deficiency, we combined physiological sampling with geographic information systems to quantify the effects of land use on physiological indicators of health in largemouth bass. More specifically, we first quantified blood metrics relating to nutrition, oxidative stress, and the glucocorticoid stress response from largemouth bass residing in eight watersheds. We then used Akaike's information criterion to define relationships between these blood metrics and land cover, including forests, agricultural areas, urban areas, and wetlands. The proportion of forest cover in a watershed was the best predictor of blood metrics representing recent feeding and resistance to oxidative stress, whereas the proportion of wetlands was the best predictor of glucocorticoid function; however, further investigation is needed, as the explanatory power of the models was relatively low. Patterns in energy reserves were not influenced by any land use practices. Interestingly, anthropogenic land use categories, such as urban and agricultural areas, were not the best predictor for any blood metrics. Together, our results indicate that fish health is most related to natural features of a landscape rather than anthropogenic land uses. Furthermore, these findings suggest that physiological methods could supplement traditional population and community assessments to develop a more comprehensive understanding of ecosystem interactions and improve stream management.

Stress in the neighborhood: Tissue glucocorticoids relative to stream quality for five species of fish.

Anthropogenic alterations to terrestrial habitat (e.g., urbanization, deforestation, agriculture) can have a variety of negative effects on watercourses that flow through disturbed landscapes. Currently, the relationship between stream habitat quality and fish condition remains poorly understood. The use of physiological metrics such as glucocorticoids (GCs) provides a useful tool for quantifying these effects by relating the health of resident fishes to stream quality. To date, however, most studies that measure GC levels tend to focus on a single, large-bodied species, rather than evaluating how GCs may be influenced differently between species in a community. In this study, we measured cortisol, the glucocorticoid found in fishes, from fish tissues to quantify effects of habitat degradation on the glucocorticoid function of five species of juvenile and small-bodied stream fish which differ ecologically and phylogenetically. Largemouth bass Micropterus salmoides, brown bullhead Ameiurus nebulosus, white sucker Catostomus commersonii, pumpkinseed Lepomis gibbosus, and logperch Percina caprodes were sampled from a reference and a degraded stream. Upon capture, fish were either euthanized immediately, to quantify baseline stress parameters, or following a standardized stressor, to quantify GC responsiveness. As a result of stream degradation largemouth bass possessed altered baseline GC concentrations and brown bullhead and logperch had altered GC responses to a stressor. White sucker and pumpkinseed did not demonstrate any alteration in baseline or post-stress GC concentrations. Together, our results show that different species residing in identical habitats can demonstrate a variety of responses to environmental stress, highlighting the variation in physiological ability to cope under poor environmental conditions, as well as the difficulty of predicting GC dynamics in wild animals. Understanding the relationships between GC function, habitat quality, and population-level processes will increase the ability of researchers and managers to predict how fish communities and aquatic ecosystems will be shaped by anthropogenic environmental change.