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Aim: Forest understory microclimates are often buffered against extreme heat or cold, with important implications for the organisms living in these environments. We quantified seasonal effects of understory microclimate predictors describing canopy structure, canopy composition and topography (i.e. local factors), as well as forest patch size and distance to coast (i.e. landscape factors). Location: Temperate forests in Europe Time period: 2017-2018 Major taxa studied: Woody plants Methods: We combined data from a microclimate sensor network with weather station records to calculate the difference – or offset – between temperatures measured inside and outside forests. We used regression analysis to study the effects of local and landscape factors on the seasonal offset of minimum, mean and maximum temperatures. Results: Maximum temperature during summer was on average cooler by 2.1 °C and minimum temperature during winter and spring were 0.4 °C and 0.9 °C warmer inside than outside forests. The local canopy cover was a strong non-linear driver of the maximum temperature offset during summer, and we found increased cooling beneath tree species that cast the deepest shade. Seasonal offsets of minimum temperature were mainly regulated by landscape and topographic features, such as the distance to coast and topographic position. Main conclusions: Forest organisms experience less severe temperature extremes than suggested by currently available macroclimate data, so climate-species relationships and species’ responses to anthropogenic global warming cannot be modelled accurately in forests using macroclimate data alone. Changes in canopy cover and composition will strongly modulate warming of maximum temperatures in forest understories, with important implications for understanding responses of forest biodiversity and functioning to the combined threats of land-use change and climate change. Our predictive models are generally applicable across lowland temperate deciduous forests, providing ecologically important microclimate data for forest understories.
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Closely related populations often display similar patterns of genomic differentiation, yet it remains an open question which ecological and evolutionary forces generate these patterns. The leading hypothesis is that this similarity in divergence is driven by parallel natural selection. However, several recent studies have suggested that these patterns may instead be a product of the depletion of genetic variation that occurs as result of background selection (i.e. linked negative selection). To date, there have been few direct tests of these competing hypotheses. To determine the relative contributions of background selection and parallel selection to patterns of repeated differentiation, we examined 24 independently derived populations of freshwater stickleback occupying a variety of niches and estimated genomic patterns of differentiation in each relative to their common marine ancestor. Patterns of genetic differentiation were strongly correlated across pairs of freshwater populations adapting to the same ecological niche, supporting a role for parallel natural selection. In contrast to other recent work, by examining populations adapting to the same niche we did not find evidence that similar patterns of genomic differentiation are generated by background selection. We also found that overall patterns of genetic differentiation were considerably more similar for populations found in closer geographic proximity. In fact, the effect of geography on the repeatability of differentiation was greater than that of parallel selection. Our results suggest that shared selective landscapes and ancestral variation are the key drivers of repeated patterns of differentiation in systems that have recently colonized novel environments.
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Anthropogenic activities are placing increasing pressure on many species, particularly those that rely on more than one ecosystem. River herring (alewife, Alosa pseudoharengus and blueback herring, A. aestivalis collectively) are anadromous fishes that reproduce in rivers and streams of eastern North America and migrate to the western Atlantic Ocean. Here, we use data from single nucleotide polymorphisms (SNPs) to provide a comprehensive analysis of population structure for both species of river herring throughout their native ranges. We sampled river herring spawning runs in rivers from Newfoundland to Florida, examining a total of 108 locations, and genotyping over 8000 fish. We identified geographic population groupings (regional genetic groups) in each species, as well as significant genetic differentiation between most populations and rivers. Strong correlations between geographic and genetic distances (i.e., isolation by distance) were found range-wide for both species, although the patterns were less consistent at smaller spatial scales. River herring are caught as bycatch in fisheries and estimating stock proportions in mixed fishery samples is important for management. We assessed the utility of the SNP datasets as reference baselines for genetic stock identification. Results indicated high accuracy of individual assignment (76–95%) to designated regional genetic groups, and some individual populations, as well as highly accurate estimates of mixing proportions for both species. This study is the first to evaluate genetic structure across the entire geographic range of these species and provides an important foundation for conservation and management planning. The SNP reference datasets will facilitate continued multi-lateral monitoring of bycatch, as well as ecological investigation to provide information about ocean dispersal patterns of these species.
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Transposable elements (TEs)—selfish DNA sequences that can move within the genome—comprise a large proportion of the genomes of many organisms. Although low-coverage whole genome sequencing can be used to survey TE composition, it is non-economical for species with large quantities of DNA. Here, we utilize restriction site associated DNA sequencing (RADSeq) as an alternative method to survey TE composition. First, we demonstrate in silico that double digest restriction-site associated DNA sequencing (ddRADseq) markers contain the same TE compositions as whole genome assemblies across arthropods. Next, we show empirically using eight Synalpheus snapping shrimp species with large genomes that TE compositions from ddRADseq and low-coverage whole genome sequencing are comparable within and across species. Finally, we develop a new bioinformatic pipeline, TERAD, to extract TE compositions from RADseq data. Our study expands the utility of RADseq to study the repeatome, making comparative studies of genome structure for species with large genomes more tractable and affordable.
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1) The construction of dams on large rivers has negative impacts on native species. Environmental flows have been proposed as a tool to mitigate these impacts, but in order for these strategies to be effective they must account for disparate temperature and flow needs of different species. 2) We applied a multi-objective approach to identify tradeoffs in dam release discharge and temperature for imperiled warm- and cold-water fishes while simultaneously meeting the needs of human water users. 3) Using the Sacramento River (California, USA) as a case study, our model suggests that current management aimed at conserving an endangered cold-water species (winter-run Chinook salmon; Oncorhynchus tshawytscha) and providing high discharge for downstream water users has detrimental impacts on a threatened warm-water species (green sturgeon; Acipenser medirostris). 4) We developed an optimal dam release scenario that can be used to meet the needs of salmon, sturgeon, and human water users. Our results show that dam releases can be managed to successfully achieve these multiple objectives in all but the most severe drought years. Synthesis and applications This study shows that managing dam releases to meet the needs of a single species can have detrimental effects on other native species with different flow and temperature requirements. We applied a multi-objective approach to balance environmental requirements of multiple species with the needs of human water users. Our findings can be used to guide management of Shasta Dam and our approach can be applied to achieve multi-object management goals in other impounded rivers beyond California’s Sacramento River.
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1. Effects of climate change on plant community functional diversity are of interest since experiments have found functional diversity to predict ecosystem function. Functional diversity has been hypothesized to confer resilience to plant communities (as a “driver” of community change), but in unmanipulated natural communities, it might alternatively (or additionally) act as a “passenger” by responding to changes in plant diversity caused by extrinsic factors such as climate. 2. We examined trends in plant functional diversity in annual grasslands in Northern California over a 19-year period, during which a trend toward drier winters had previously been associated with the losses of drought-intolerant species. We tested whether functional diversity decreased over the period of the study (acting as a passenger), and also whether initial site functional diversity influenced the degree of community change over the study period (acting as a driver). 3. Initial community functional diversity was not related to species richness loss or community variability. We found that functional diversity declined as plant species richness and community mean specific leaf area declined over the course of the study, and all of these trends were associated with declining precipitation, indicating that functional diversity acted as a passenger of community change. 4. Synthesis. This study is among the first to demonstrate that recent climatic trends may drive loss of functional diversity. Our findings highlight that functional diversity does not necessarily confer community resilience when its variation is shaped by the environment rather than by experimental treatments.
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Body size correlates with most structural and functional components of an organism’s phenotype – brain size being a prime example of allometric scaling with animal size. Therefore, comparative studies of brain evolution in vertebrates rely on controlling for the scaling effects of body size variation on brain size variation by calculating brain weight/body weight ratios. Differences in the brain size-body size relationship between taxa are usually interpreted as differences in selection acting on the brain or its components, while selection pressures acting on body size, which are among the most prevalent in nature, are rarely acknowledged, leading to conflicting and confusing conclusions. We address these problems by comparing brain-body relationships from across >1,000 species of birds and non-avian reptiles. Relative brain size in birds is often assumed to be 10 times larger than in reptiles of similar body size. We examine how differences in the specific gravity of body tissues and in body design (e.g., presence/absence of a tail or a dense shell) between these two groups can affect estimates of relative brain size. Using phylogenetic comparative analyses, we show that the gap in relative brain size between birds and reptiles has been grossly exaggerated. Our results highlight the need to take into account differences between taxa arising from selection pressures affecting body size and design, and call into question the widespread misconception that reptile brains are small and incapable of supporting sophisticated behavior and cognition.
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Most organisms are constantly adapting to pathogens and parasites that exploit their host for their own benefit. Less studied, but perhaps more ubiquitous, are intragenomic parasites or selfish genetic elements. These include transposable elements, selfish B chromosomes and meiotic drivers that promote their own replication without regard to fitness effects on hosts. Therefore, intragenomic parasites are also a constant evolutionary pressure on hosts. Gamete-killing meiotic drive elements are often associated with large chromosomal inversions that reduce recombination between the drive and wildtype chromosomes. This reduced recombination is thought to reduce the efficacy of selection on the drive chromosome and allow for the accumulation of deleterious mutations. We tested whether gamete-killing meiotic drive chromosomes were associated with reduced immune defense against two bacterial pathogens in three species of Drosophila. We found little evidence of reduced immune defense in lines with meiotic drive. One line carrying the Drosophila melanogaster autosomal Segregation Distorter did show reduced defense, but we were unable to attribute that reduced defense to either genotype or immune gene expression differences. Our results suggest that though gamete-killing meiotic drive chromosomes likely accumulate deleterious mutations, those mutations do not result in reduced capacity for immune defense.
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In Drosophila, long sperm are favoured in sperm competition based on the length of the female’s primary sperm storage organ, the seminal receptacle (SR). This sperm-SR interaction, together with a genetic correlation between the traits, suggests that the coevolution of exaggerated sperm and SR lengths may be driven by Fisherian runaway selection. Here, we explore the costs and benefits of long sperm and SR genotypes, both in the sex that carries them and in the sex that does not. We measured male and female fitness in inbred lines of D. melanogaster derived from four populations previously selected for long sperm, short sperm, long SRs, or short SRs. We specifically asked: what are the costs and benefits of long sperm in males and long SRs in females? Furthermore, do genotypes that generate long sperm in males or long SRs in females impose a fitness cost on the opposite sex? Answers to these questions will address whether long sperm are an honest indicator of male fitness, if male post-copulatory success is associated with male pre-copulatory success, if female choice benefits females or is costly, and whether intra-genomic conflict could influence evolution of these traits. We found that both sexes have increased longevity in long sperm and long SR genotypes. Males, but not females, from long SR lines had higher fecundity. Our results suggest that sperm-SR coevolution is facilitated by both increased viability and indirect benefits of long sperm and SRs in both sexes.
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1. Rapid adaptation in response to novel environments can facilitate species invasions and range expansions. Understanding how invasive disease vectors rapidly evolve to novel conditions—particularly at the edge of its non-native range—has important implications for mitigating the prevalence and spread of disease. 2. Here, we evaluate the role of local adaptation in overwintering capability of the Asian tiger mosquito, Aedes albopictus. This species invaded the Southern US in the 1980s and rapidly spread northward into novel climate compared to its native range. Photoperiodically induced egg diapause is a key trait contributing to the establishment and spread of Ae. albopictus in temperate latitudes, and diapause incidence rapidly developed a cline along a latitudinal gradient in the US shortly after its initial invasion. However, variation in overwintering survival of diapause-induced eggs along this gradient is not known, but is critical to the fitness-related role of diapause evolution in the establishment and spread of Ae. albopictus in its northern US range. 3. Using reciprocal transplants, we detected local adaptation in overwinter survival of diapausing Aedes albopictus eggs. In northern range-edge winters, eggs produced by range-edge individuals survived better than those produced by range-core individuals. Diapause eggs from range-edge and range-core locations survived equally well in range-core winters, and no eggs survived a winter beyond the current northern range limit in the US. 4. Synthesis and applications. These results demonstrate rapid (~ 3 decades) local adaptation of egg diapause, a key trait facilitating overwinter survival and range expansion for the invasive Asian tiger mosquito. In light of these results, control efforts could shift from targeting satellite populations to a focus on preventing dispersal into locally adapted, range-edge locations and to aim removal efforts towards areas surrounding locally adapted populations. Adopting new approaches to target rapidly adapting populations will require large-scale collaboration among control agencies and research institutions, and should begin in the northern US range to better control Ae. albopictus mosquito populations in the face of rapid adaptation.
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