Local climatic adaptation in a widespread microorganism

Exploring the ability of organisms to locally adapt is critical for determining the outcome of rapid climate changes, yet few studies have addressed this question in microorganisms. We investigated the role of a heterogeneous climate on adaptation of North American populations of the wild yeast Saccharomyces paradoxus. We found abundant among-strain variation for fitness components across a range of temperatures, but this variation was only partially explained by climatic variation in the distribution area. Most of fitness variation was explained by the divergence of genetically distinct groups, distributed along a north–south cline, suggesting that these groups have adapted to distinct climatic conditions. Within-group fitness components were correlated with climatic conditions, illustrating that even ubiquitous microorganisms locally adapt and harbour standing genetic variation for climate-related traits. Our results suggest that global climatic changes could lead to adaptation to new conditions within groups, or changes in their geographical distributions.     

云杉幼苗对气候变暖和UV-B辐射增强的光合响应

采用开顶式有机玻璃罩(OTCs)及紫外灯分别模拟气候变暖和紫外辐射B(UV-B)增强,对位于气候变暖和UV-B增强突出的青藏高原东缘、高山峡谷地云杉(Picea asperata)幼苗的光合气体交换和叶绿素荧光参数进行测定分析,探讨云杉幼苗对气候变暖和UV-B增强的光合响应特性。结果显示:(1)UV-B辐射增强显著抑制了云杉幼苗茎和根的伸长生长以及生物量的累积,显著降低了云杉幼苗的净光合速率(Pn)、最大光合速率(Pmax)和表观量子产量(Φ),但是提高了光补偿点(LCP);UV-B辐射增强导致了云杉幼苗光合系统Ⅱ(PSⅡ)的光抑制,使PSⅡ有效量子产量(ΦPSⅡ)显著降低。(2)单纯OTC模拟增温显著提高了云杉幼苗的Pn和Pmax,而对气孔导度(Gs)、蒸腾速率(Tr)和Φ无显著影响。(3)模拟增温缓解了UV-B增强对云杉幼苗光合作用的抑制作用,显著提高了UV-B胁迫下幼苗的Pn、Pmax、PSⅡ的潜在量子效率(Fv/Fm)和有效量子产量(ΦPSⅡ),并且提高了UV-B胁迫下幼苗茎、根的生长以及生物量的累积。研究表明,在未来气候变暖和UV-B辐射增强同时存在时,气候变暖能够在一定程度上缓解UV-B增强对云杉林光合作用的抑制作用。     

Atlantic wolf‐fish Anarhichas lupus population diversity: growth and maturation

Biological data from 1125 female Atlantic wolf‐fish Anarhichas lupus were collected during 2002–2006 at their main spawning and fishing grounds in Iceland. The results demonstrated substantial annual variation in growth and maturity of female A. lupus. The fast growing females mature earlier than the slow growing ones. In addition, females mature at a larger size and greater age in warmer temperatures than colder ones. There was a strong negative relationship between temperature and growth, which may indicate that the sea temperature west of Iceland has risen above the optimum for growth of female A. lupus and thereby reduced the reproductive potential of the species.     

Coldwater fish in a warm water world: Implications for predation of salmon smolts during estuary transit

1. Predator–prey systems face intensifying pressure from human exploitation and a warming climate with implications for where and how natural resource management can successfully intervene. We hypothesized young salmon migrating to the Pacific Ocean face a seasonally intensifying predator gauntlet when warming water temperature intensifies a multiple predator effect (MPE) from Striped Bass Morone saxatilis and Largemouth Bass Micropterus salmoides. We evaluated this hypothesis using data synthesis and simulation modeling.
2. Contemporary studies based on acoustically tagged fish reaffirmed older observations that Chinook Salmon smolts must transit the Delta before water temperature reaches 20°C or mortality will be nearly 100%. Striped Bass attack rates on tethered smolts were insensitive to distance from shore and water temperature, whereas Largemouth Bass attack rates were highest near shorelines in warm water, supporting the temporal aspect of the hypothesis. Whether the combined effects of the two predators produce an MPE remains unconfirmed due to limitations on quantifying salmon behavior.
3. We used multiple simulation models to try to reconstruct the empirical relationship between smolt survival and water temperature. Simulations reinforced attack rate results, but could not recreate the temperature dependence in smolt survival except at higher than observed temperatures. We propose three hypotheses for why and recommend discerning among them should be a focus of research.
4. We found significant linear relationships between monthly mean inflow to the Delta from each of its two largest tributaries and monthly mean water temperatures along associated salmon migration routes, but these relationships can be nonlinear, with most of the correlation occurring at low inflows when water temperature is largely controlled by air temperature and day length. As the global climate warms, changed circumstances in predator–prey relationships may present important challenges when managing species vulnerable to extinction in addition to presently more abundant species.

     

Effect of the rate of temperature increase of the dynamic method on the heat tolerance of fishes

Heat tolerance is commonly determined by exposing organisms to increasing temperatures until they show symptoms of thermal stress or death. Here we carried out an experiment on a blenny species (Acantemblemaria hancocki; Pisces: Chaenopsidae) and reviewed the literature to evaluate the extent to which variations in the rate at which temperature is increased in experimental trials affects thermal tolerance of fishes. For the blenny species, we found that thermal tolerance decreases significantly from an intermediate heating rate of ∼1 °C/h towards quicker and slower heating rates. In the literature we found very few comparisons of thermal tolerance among heating rates (i.e. eight fish species) and although such comparisons were done over narrow ranges of heating rates, overall they appear to follow the pattern described for the blenny species. We discuss a variety of factors including variations in the levels of acclimation, energy use and body quality among heating rates as the causes for this pattern. However, available data are still limited and further research will be necessary to determine the generality and causes of the pattern we found here. Nevertheless, our results indicate the need for caution in the extrapolation of thermal tolerance data when assessing the tolerance of organisms to environmental phenomena that vary in their rates of warming.     

Climatic and intertrophic effects detected in 10-year population dynamics of biological control of the arrowhead scale by two parasitoids in southwestern Japan

Relative effects of weather and three-trophic interactions were studied for a classical biological control system consisting of the arrowhead scale Unaspis yanonensis, known formerly as a serious pest of the Satsuma mandarin orange Citrus unshiu, and its two introduced parasitoids, Coccobius fulvus and Aphytis yanonensis. Yearly population responses of the three insect species on a per-tree basis for up to 10 years at two orange groves were analyzed by general linear models, with a backward stepwise procedure, to select among abiotic (summer/winter temperature and rainfall) and biotic (densities of the three insect species and orange bearing in the previous years) independent variables. Temperature positively affected the arrowhead scale and the two parasitoids. A negative correlation of rainfall was detected for all three insect species. Mandarin fruiting showed negative delayed density dependence, thereby supporting the observed alternate bearing phenomenon in mandarins, presumably due to physiological imbalance triggered by climatic factors. The arrowhead scale was negatively correlated with fruit production in the preceding years, possibly due to reduced resistance in subsequent years of mast fruiting. We found a negative correlation of the arrowhead scale with Coccobius only in a single grove and none with Aphytis. Thus, it appears that bottom-up forces may be more important than top-down control by the parasitoids in the post-transient phase of this system.     

Invasive behaviour of Lactuca serriola (Asteraceae) in the Netherlands: Spatial distribution and ecological amplitude

Species invasions have been a central theme in ecology over the past decades, with a focus on invasions of non-indigenous European species in the New World. However, within Europe, native species may also become invasive. Such species rapidly increase their geographic range and may at the same time broaden their ecological amplitude. We report on Lactuca serriola L., which has shown a rapid range expansion in many parts of Europe. We reconstructed its geographical spread through The Netherlands; furthermore, we tested for changes in its ecological amplitude.

Before 1950, L. serriola was rare in The Netherlands, recorded from only 80 grid-cells (of 5×5 km²). Subsequently, its distribution increased from 219 grid-cells (1980), to 546 cells (990) and 998 grid cells (2000). It currently occupies at least 60% of The Netherlands. Analyses of relevées demonstrate, using detrended correspondence analysis (DCA), that the variance in the assemblage of species co-occurring with L. serriola increased significantly since 1940, indicating that the species currently occurs in a broader range of vegetation types. Correlating averages of Ellenberg's indicator values per vegetation relevée with time, we found correlations for continentality (+), acidity (−) and (soil) humidity (+). Moreover, the proportion of phanerophytes in the relevées increased over time. These findings suggest that in addition to its original ruderal habitat, L. serriola also currently occurs in more closed vegetation types. Based on analyses of two other co-occurring Asteraceae species, we showed that these patterns were specific for L. serriola only. We conclude that L. serriola has broadened its ecological amplitude and discuss four mutually non-exclusive explanations for the recent invasiveness of L. serriola: (i) Effects of a changed environment: global warming and ruderalisation; (ii) metapopulation dynamics and increased diaspore pressure; (iii) microevolution; (iv) genetic reinforcement due to hybridisation with conspecific (crop) species.     

Brooding crustaceans in a highly fragmented habitat: the genetic structure of Mediterranean marine cave-dwelling mysid populations

Habitat fragmentation and climate change are two major threats on biodiversity. Fragmentation limits the number of patches and their decreased connectivity cannot always maintain populations at dynamic equilibrium. The natural extreme fragmentation of marine cave habitats represents an opportunity to understand how these processes interact. The hypothesis of a low gene flow among populations due to a high level of fragmentation was tested by analysing sequence variation in a fragment of the mitochondrial gene of the cytochrome oxidase subunit I in 170 individuals (23 localities across the NW Mediterranean) of two marine cave-dwelling mysids of the genus Hemimysis. The species Hemimysis margalefi recently replaced its congener Hemimysis speluncola, a species shift that could be related to the warming of the Mediterranean Sea and to differences in their thermal tolerances. There were too few H. speluncola samples to further discuss their genetic structuring, but for H. margalefi, the present study revealed high levels of genetic diversity and genetic structuring, as shown by the eight genetically distinct groups identified. The Croatian group might constitute a sibling species due to a strong divergence (15%). Nevertheless, these groups present reduced but orientated gene flow according to the general circulation in the Mediterranean, and fit a stepping-stone model. At local scale (Marseille area, France), gene flow among caves is dependent on unexpected local hydrodynamic barriers, that determine metapopulation sizes. Through the example of mysid species inhabiting marine caves, the present work confirms the strong influence of habitat disjunction (natural fragmentation) on population structure, and stresses the importance of coastal geomorphological features in inducing complex interactions between the circulation of water masses and the circulation of genes.     

Disturbance facilitates rapid range expansion of aspen into higher elevations of the Rocky Mountains under a warming climate

Aim Trembling aspen (Populus tremuloides Michx.) is absent in the upper foothills region of west‐central Alberta because of the cold conditions and short growing season at this high elevation. However, in recent years it appears that aspen has been establishing from seed in this zone and that it has been doing so mainly as a result of forest harvesting. The objectives of this study were to determine the frequency of and types of microsite required for the successful establishment of aspen seedlings at these higher elevations. Location Rocky Mountains Upper Foothills Natural Subregion of west‐central Alberta, Canada. Methods The current distribution of mature aspen and the presence and absence of aspen seedlings in harvested areas were determined in an area c. 300 km² in size, using ground and aerial surveys. In an intensive study, 12 belt transects (180 m long and 5 m wide) were established in areas disturbed by forest harvesting at high elevations where no aspen was present prior to harvesting. Transects were surveyed seven growing seasons after disturbance and the microsites occupied by aspen seedlings were characterized according to their substrate and microtopography. Similarly, the availability of different substrates and microtopographic positions were assessed by systematic point sampling on these sites. Results On level surfaces, aspen seedling regeneration was found up to 200 m higher in elevation than the mature aspen in the original undisturbed forests. Overall, there were 428 seedlings ha^?1 established on these transects, and the age distribution indicates that aspen seedlings had established in each of the seven growing seasons since the disturbance. Nearly all of the seedlings (93%) were established on mineral soil microsites and virtually no seedlings were established on undisturbed forest floor layers. Significantly more seedlings were found in concave microtopographic positions. Main conclusions This study indicates that aspen establishment from seed is currently not a stochastic event and demonstrates that aspen is rapidly expanding its range upslope in the Canadian Rocky Mountain region as a result of forest management practices that expose mineral soil substrates in conjunction with a warming climate. The change in canopy composition from conifer to deciduous forests at these higher elevations will have far‐reaching implications for ecosystem processes and functions.