Climate change induced hybridization in flying squirrels

There is now unequivocal evidence for global climate change; however, its potential impacts on evolutionary processes remain unclear. Many species have responded to contemporary climate change through shifts in their geographic range. This could lead to increased sympatry between recently diverged species; likely increasing the potential for hybridization. Recently, following a series of warm winters, southern flying squirrels ( Glaucomys volans ) in Ontario, Canada rapidly expanded their northern range limit resulting in increased sympatry with the closely related northern flying squirrel ( Glaucomys sabrinus ). This provided the opportunity to test the prediction that contemporary climate change can act as a catalyst creating conditions for the formation of hybrid zones. Following extensive sampling and molecular analyses (nuclear and mitochondrial DNA), we identified the occurrence of hybridization between sympatric G. sabrinus and G. volans . There was evidence of backcrossing but not of extensive introgession, consistent with the hypothesis of recent rather than historic hybridization. To our knowledge, this is the first report of hybrid zone formation following a range expansion induced by contemporary climate change. This is also the first report of hybridization between North American flying squirrel species.     

Increased seawater temperature and decreased dissolved oxygen triggers fish kill at the Cocos (Keeling) Islands, Indian Ocean

At the Cocos (Keeling) Islands in the north‐eastern Indian Ocean >592 fishes from at least 11 species died in a series of events in December 2007, January and February 2008 and April 2009. The dead fishes were from a wide range of taxonomic families, indicating that conditions exceeded the tolerances of a broad array of species. The 2007–2008 die‐off events occurred on the warmest and calmest days of a significantly warmer and calmer summer. Fishes died in the southern inshore areas of the coral atoll lagoon at survey sites where seawater temperature was highest (33–35° C) and dissolved oxygen was lowest (1·4–1·8 mg l^?1). The water temperature at these fish‐kill survey sites (33–35° C) was significantly warmer than previous years (1997 to 2005, mean ±s.e. = 28·7 ± 0·1° C). Fishes probably died because they were unable to obtain the additional oxygen required for metabolism at higher temperatures. Repeated die‐off events over the last 130 years indicate that some fishes have not yet adapted to rises in seawater temperature. This study provides empirical evidence to support suggestions that differences in physiological tolerances to increasing sea temperatures may be important in determining the structure of future coral‐reef fish communities with respect to climate change.     

Global Documentation of Fish Introductions: the Growing Crisis and Recommendations for Action

Fish provides 15% of the total animal protein in human diets. It is also the primary source of livelihood for 35 million people (30 M in Asia and 2.6 M in Africa). The increase in global population and demand for fish protein cannot be met by capture fisheries alone. Governments are turning towards aquaculture as the source of fish protein. However, it has also led to the introduction and establishment of non-native species in local ecosystems through their escapement from aquaculture facilities to the wild. In freshwater ecosystems with relatively high endemism, this has become a significant problem. Documenting the international movement of fish is one way of providing a general view of the magnitude of these movements and the existing and potential threat faced by ecosystems due to species invasiveness. Information, however, is limited and scattered in different journals and agency/project reports. Several agencies, both local and international, have databases that provide information on invasive species (terrestrial and aquatic, local, regional or international in scope). The critical challenge is for consolidation, common access through data sharing and development of risk assessment and management tools. This is proposed through the use of Internet technology, sharing of databases or having a gateway or portal to which all introduced and invasive fish species related databases link. The fusion of these information sources will allow access to updated and reliable information. The experience of the WorldFish Center in documenting these phenomena through developing the FishBase information system and global partnerships is presented with recommendations for harmonizing approaches. An erratum to this article is available at .     

Interactive Effects of Fire, Elevated Carbon Dioxide, Nitrogen Deposition, and precipitation on a California Annual Grassland

Although it is widely accepted that elevated atmospheric carbon dioxide (CO₂), nitrogen (N) deposition, and climate change will alter ecosystem productivity and function in the coming decades, the combined effects of these environmental changes may be nonadditive, and their interactions may be altered by disturbances, such as fire. We examined the influence of a summer wildfire on the interactive effects of elevated CO₂, N deposition, and increased precipitation in a full-factorial experiment conducted in a California annual grassland. In unburned plots, primary production was suppressed under elevated CO₂. Burning alone did not significantly affect production, but it increased total production in combination with nitrate additions and removed the suppressive effect of elevated CO₂. Increased production in response to nitrate in burned plots occurred as a result of the enhanced aboveground production of annual grasses and forbs, whereas the removal of the suppressive effect of elevated CO₂ occurred as a result of increased aboveground forb production in burned, CO₂-treated plots and decreased root production in burned plots under ambient CO₂.The tissue nitrogen–phosphorus ratio, which was assessed for annual grass shoots, decreased with burning and increased with nitrate addition. Burning removed surface litter from plots, resulting in an increase in maximum daily soil temperatures and a decrease in soil moisture both early and late in the growing season. Measures of vegetation greenness, based on canopy spectral reflectance, showed that plants in burned plots grew rapidly early in the season but senesced early. Overall, these results indicate that fire can alter the effects of elevated CO₂ and N addition on productivity in the short term, possibly by promoting increased phosphorus availability.     

Evolution of thermal performance curves: A meta-analysis of selection experiments

Temperatures are increasing due to global changes, putting biodiversity at risk. Organisms are faced with a limited set of options to cope with this situation: adapt, disperse or die. We here focus on the first possibility, more specifically, on evolutionary adaptations to temperature. Ectotherms are usually characterized by a hump-shaped relationship between fitness and temperature, a non-linear reaction norm that is referred to as thermal performance curve (TPC). To understand and predict impacts of global change, we need to know whether and how such TPCs evolve. Therefore, we performed a systematic literature search and a statistical meta-analysis focusing on experimental evolution and artificial selection studies. This focus allows us to directly quantify relative fitness responses to temperature selection by calculating fitness differences between TPCs from ancestral and derived populations after thermal selection. Out of 7561 publications screened, we found 47 studies corresponding to our search criteria representing taxa across the tree of life, from bacteria, to plants and vertebrates. We show that, independently of species identity, the studies we found report a positive response to temperature selection. Considering entire TPC shapes, adaptation to higher temperatures traded off with fitness at lower temperatures, leading to niche shifts. Effects were generally stronger in unicellular organisms. By contrast, we do not find statistical support for the often discussed “Hotter is better” hypothesis. While our meta-analysis provides evidence for adaptive potential of TPCs across organisms, it also highlights that more experimental work is needed, especially for under-represented taxa, such as plants and non-model systems.     

Cell wall organic matrix composition and biomineralization across reef-building coralline algae under global change

Crustose coralline algae (CCA) are one of the most important benthic substrate consolidators on coral reefs through their ability to deposit calcium carbonate on an organic matrix in their cell walls. Discrete polysaccharides have been recognized for their role in biomineralization, yet little is known about the carbohydrate composition of organic matrices across CCA taxa and whether they have the capacity to modulate their organic matrix constituents amidst environmental change, particularly the threats of ocean acidification (OA) and warming. We simulated elevated pCO₂ and temperature (IPCC RCP 8.5) and subjected four mid-shelf Great Barrier Reef species of CCA to 2 months of experimentation. To assess the variability in surficial monosaccharide composition and biomineralization across species and treatments, we determined the monosaccharide composition of the polysaccharides present in the cell walls of surficial algal tissue and quantified calcification. Our results revealed dissimilarity among species' monosaccharide constituents, which suggests that organic matrices are composed of different polysaccharides across CCA taxa. We also observed that species differentially modulate composition in response to ocean acidification and warming. Our findings suggest that both variability in composition and ability to modulate monosaccharide abundance may play a crucial role in surficial biomineralization dynamics under the stress of OA and global warming.     

Observed forest trait velocities have not kept pace with hydraulic stress from climate change

The extent to which future climate change will increase forest stress and the amount to which species and forest ecosystems can acclimate or adapt to increased stress is a major unknown. We used high-resolution maps of hydraulic traits representing the diversity in tree drought tolerance across the United States, a hydraulically enabled tree model, and forest inventory observations of demographic shifts to quantify the ability for within-species acclimation and between-species range shifts to mediate climate stress. We found that forests are likely to experience increases in both acute and chronic hydraulic stress with climate change. Based on current species distributions, regional hydraulic trait diversity was sufficient to buffer against increased stress in 88% of forested areas. However, observed trait velocities in 81% of forested areas are not keeping up with the rate required to ameliorate projected future stress without leaf area acclimation.     

The carbon-quality temperature hypothesis: Fact or artefact?

Climate warming can reduce global soil carbon stocks by enhancing microbial decomposition. However, the magnitude of this loss remains uncertain because the temperature sensitivity of the decomposition of the major fraction of soil carbon, namely resistant carbon, is not fully known. It is now believed that the resistance of soil carbon mostly depends on microbial accessibility of soil carbon with physical protection being the primary control of the decomposition of protected carbon, which is insensitive to temperature changes. However, it is still unclear whether the temperature sensitivity of the decomposition of unprotected carbon, for example, carbon that is not protected by the soil mineral matrix, may depend on the chemical recalcitrance of carbon compounds. In particular, the carbon-quality temperature (CQT) hypothesis asserts that recalcitrant low-quality carbon is more temperature-sensitive to decomposition than labile high-quality carbon. If the hypothesis is correct, climate warming could amplify the loss of unprotected, but chemically recalcitrant, carbon and the resultant CO₂ release from soils to the atmosphere. Previous research has supported this hypothesis based on reported negative relationships between temperature sensitivity and carbon quality, defined as the decomposition rate at a reference temperature. Here we show that negative relationships can arise simply from the arbitrary choice of reference temperature, inherently invalidating those tests. To avoid this artefact, we defined the carbon quality of different compounds as their uncatalysed reaction rates in the absence of enzymes. Taking the uncatalysed rate as the carbon quality index, we found that the CQT hypothesis is not supported for enzyme-catalysed reactions, which showed no relationship between carbon quality and temperature sensitivity. The lack of correlation in enzyme-catalysed reactions implies similar temperature sensitivity for microbial decomposition of soil carbon, regardless of its quality, thereby allaying concerns of acceleration of warming-induced decomposition of recalcitrant carbon.