The effects of elevated temperature on the sexual traits, immunology and survivorship of a tropical ectotherm.

In 2007, the Intergovernmental Panel on Climate Change projected an average global air temperature increase of 1.1-6.4°C by the end of the 21st century. Although the tropics are predicted to experience less extreme temperature increases than regions of higher latitude, tropical ectotherms live close to their thermal limits, and are thus particularly vulnerable to increases in temperature. In this study, we examined how predicted patterns of global warming will affect survival and sexual traits in the Trinidadian guppy (Poecilia reticulata). Guppies were exposed from birth to one of four temperature treatments: 23, 25 (control), 28 or 30°C. We measured brood survival and, at sexual maturity, male ornamentation, sperm traits and immune response. Our results show that increases in temperature result in guppies that have shorter, slower sperm but that there is an optimum temperature for ornamental hue at 28°C. Given the importance of sperm quality for reproduction, these results suggest population viability could be affected by warming. However, we found no difference in brood survival or immune response to a novel antigen across the treatments, indicating that survival may not be as vulnerable as previously thought. Overall, our data suggest that male sexual traits, and in particular sperm performance, are more sensitive than survival to a warming environment.

The metabolic, locomotor and sex-dependent effects of elevated temperature on Trinidadian guppies: limited capacity for acclimation.

Global warming poses a threat to many ectothermic organisms because of the harmful effects that elevated temperatures can have on resting metabolic rate (RMR) and body size. This study evaluated the thermal sensitivity of Trinidadian guppies (Poecilia reticulata) by describing the effects of developmental temperature on mass, burst speed and RMR, and investigated whether these tropical fish can developmentally acclimate to their thermal conditions. These traits were measured following exposure to one of three treatments: 70 days at 23, 25, 28 or 30°C (acclimated groups); 6 h at 23, 28 or 30°C following 70 days at 25°C (unacclimated groups); or 6 h at 25°C following 70 days in another 25°C tank (control group). Body mass was lower in warmer temperatures, particularly amongst females and individuals reared at 30°C. The burst speed of fish acclimated to each temperature did not differ and was marginally higher than that of unacclimated fish, indicative of complete compensation. Conversely, acclimated and unacclimated fish did not differ in their RMR at each temperature. Amongst the acclimated groups, RMR was significantly higher at 30°C, indicating that guppies may become thermally limited at this temperature as a result of less energy being available for growth, reproduction and locomotion. Like other tropical ectotherms, guppies appear to be unable to adjust their RMR through physiological acclimation and may consequently be susceptible to rising temperatures. Also, because larger females have higher fecundity, our data suggest that fecundity will be reduced in a warmer climate, potentially decreasing the viability of guppy populations.

Pollution-induced behavioural effects in the brown bullhead (Ameiurus nebulosus).

Aquatic ecosystems are major sinks for pollutants which can have adverse effects on biodiversity. Thus, it is important to understand the nature of pollution-induced change in aquatic ecosystems. We show that brown bullheads (Ameiurus nebulosus) may have evolved in response to chronic pollution exposure. We collected adults from the Detroit River (polluted site) and Belle River (control site). Both adults and common-garden raised juveniles were tested for aggression, locomotion, and escape response using consecutive unchallenged (clean) and challenged (polluted) trials. Detroit River fish were more aggressive than Belle River fish when challenged. Furthermore, Belle River fish showed increased locomotion when exposed to pollutants, whereas Detroit River fish were unaffected. The consistent difference in adult and juvenile behaviour across trials suggests a genetic response to pollution. Escape response on the other hand, showed inter-population differences, but no consistency between adults and juveniles, indicating that this behaviour is influenced by non-genetic factors. We discuss our data with respect to the potential adaptation of populations to pollution and the implications for prioritizing remediation efforts.