Habitat and food preferences of European rabbits in core and edge populations along the invasion front Patagonia-Monte, Argentina.

The European rabbit Oryctolagus cuniculus is an exotic herbivorous mammal undergoing an active phase of geographical expansion in the arid ecosystems of Argentina. The Adaptive Flexibility Hypothesis states that populations at the range edge (new populations) will exhibit greater flexibility in the use of resources compared with populations located in the range core (older populations). The objective of this work was to compare the rabbit's use of spatial and trophic resources in relation to the establishment time of their populations. The sampling was carried out for 2 years (2017 and 2018) in sites with different establishment times for rabbit populations. Random sampling stratified by type of habitat was applied using 115 fixed strip transects of 1,000 m2 laid out across the study areas. Fresh rabbit signs were recorded in each transect, and environmental and anthropic variables were measured. Our results show that the individuals from the range edge are more selective in the use of habitat than those from the range core. At the microhabitat level, we observed a pattern in the particular components of habitat use by rabbits mainly linked to food availability and proximity to water. From a trophic perspective, rabbits could show flexible adjustment to novel conditions and environments in the range edge. The variability in resource use by the European rabbit confirms its ecological flexibility, pivotal for their advance toward new environments in Argentina.

Environmental effects on genetic variance are likely to constrain adaptation in novel environments.

Adaptive plasticity allows populations to cope with environmental variation but is expected to fail as conditions become unfamiliar. In novel conditions, populations may instead rely on rapid adaptation to increase fitness and avoid extinction. Adaptation should be fastest when both plasticity and selection occur in directions of the multivariate phenotype that contain abundant genetic variation. However, tests of this prediction from field experiments are rare. Here, we quantify how additive genetic variance in a multivariate phenotype changes across an elevational gradient, and test whether plasticity and selection align with genetic variation. We do so using two closely related, but ecologically distinct, sister species of Sicilian daisy (Senecio, Asteraceae) adapted to high and low elevations on Mt. Etna. Using a quantitative genetic breeding design, we generated and then reciprocally planted c. 19,000 seeds of both species, across an elevational gradient spanning each species' native elevation, and then quantified mortality and five leaf traits of emergent seedlings. We found that genetic variance in leaf traits changed more across elevations than between species. The high-elevation species at novel lower elevations showed changes in the distribution of genetic variance among the leaf traits, which reduced the amount of genetic variance in the directions of selection and the native phenotype. By contrast, the low-elevation species mainly showed changes in the amount of genetic variance at the novel high elevation, and genetic variance was concentrated in the direction of the native phenotype. For both species, leaf trait plasticity across elevations was in a direction of the multivariate phenotype that contained a moderate amount of genetic variance. Together, these data suggest that where plasticity is adaptive, selection on genetic variance for an initially plastic response could promote adaptation. However, large environmental effects on genetic variance are likely to reduce adaptive potential in novel environments.

Sexual selection buffers the negative consequences of population fragmentation on adaptive plastic responses to increasing temperatures.

Whether sexual selection facilitates or hampers the ability to plastically respond to novel environments might depend on population structure, via its effects on sexual interactions and associated fitness payoffs. Using experimentally evolved lines of the seed beetle Callosobruchus maculatus, we tested whether individuals evolving under different sexual selection (monogamy vs. polygamy) and population spatial structure (metapopulation vs. undivided populations) treatments differed in their response across developmental thermal conditions (control, hot, or stressful) in a range of fitness and fitness-associated traits. We found that individuals from subdivided populations had lower lifetime reproductive success at hot temperatures, but only in lines evolving under relaxed sexual selection, revealing a complex interaction between sexual selection, population structure, and thermal environmental stress on fitness. We also found an effect of population structure on several traits, including fertility and adult emergence success, under exposure to high thermal conditions. Finally, we found a strong negative effect of hot and stressful temperatures on fitness and associated traits. Our results show that population structure can exacerbate the impact of a warming climate, potentially leading to declines in population viability, but that sexual selection can buffer the negative influence of population subdivision on adaptation to warm temperatures.

Does the definition of a novel environment affect the ability to detect cryptic genetic variation?

Anthropogenic change exposes populations to environments that have been rare or entirely absent from their evolutionary past. Such novel environments are hypothesized to release cryptic genetic variation, a hidden store of variance that can fuel evolution. However, support for this hypothesis is mixed. One possible reason is a lack of clarity in what is meant by 'novel environment', an umbrella term encompassing conditions with potentially contrasting effects on the exposure or concealment of cryptic variation. Here, we use a meta-analysis approach to investigate changes in the total genetic variance of multivariate traits in ancestral versus novel environments. To determine whether the definition of a novel environment could explain the mixed support for a release of cryptic genetic variation, we compared absolute novel environments, those not represented in a population's evolutionary past, to extreme novel environments, those involving frequency or magnitude changes to environments present in a population's ancestry. Despite sufficient statistical power, we detected no broad-scale pattern of increased genetic variance in novel environments, and finding the type of novel environment did not explain any significant variation in effect sizes. When effect sizes were partitioned by experimental design, we found increased genetic variation in studies based on broad-sense measures of variance, and decreased variation in narrow-sense studies, in support of previous research. Therefore, the source of genetic variance, not the definition of a novel environment, was key to understanding environment-dependant genetic variation, highlighting non-additive genetic variance as an important component of cryptic genetic variation and avenue for future research.

Novel environments induce variability in fitness-related traits.

Environmental change from anthropogenic activities threatens individual organisms, the persistence of populations, and entire species. Rapid environmental change puts organisms in a double bind, they are forced to contend with novel environmental conditions but with little time to respond. Phenotypic plasticity can act quickly to promote establishment and persistence of individuals and populations in novel or altered environments. In typical environmental conditions, fitness-related traits can be buffered, reducing phenotypic variation in expression of traits, and allowing underlying genetic variation to accumulate without selection. In stressful conditions, buffering mechanisms can break down, exposing underlying phenotypic variation, and permitting the expression of phenotypes that may allow populations to persist in the face of altered or otherwise novel environments. Using reciprocal transplant experiments of freshwater snails, we demonstrate that novel conditions induce higher variability in growth rates and, to a lesser degree, morphology (area of the shell opening) relative to natal conditions. Our findings suggest a potentially important role of phenotypic plasticity in population persistence as organisms face a rapidly changing, human-altered world.

Hidden genetic variation in plasticity provides the potential for rapid adaptation to novel environments.

Rapid environmental change is forcing populations into environments where plasticity will no longer maintain fitness. When populations are exposed to novel environments, evolutionary theory predicts that genetic variation in fitness will increase and should be associated with genetic differences in plasticity. If true, then genetic variation in plasticity can increase adaptive potential in novel environments, and population persistence via evolutionary rescue is more likely. To test whether genetic variation in fitness increases in novel environments and is associated with plasticity, we transplanted 8149 clones of 314 genotypes of a Sicilian daisy (Senecio chrysanthemifolius) within and outside its native range, and quantified genetic variation in fitness, and plasticity in leaf traits and gene expression. Although mean fitness declined by 87% in the novel environment, genetic variance in fitness increased threefold and was correlated with plasticity in leaf traits. High fitness genotypes showed greater plasticity in gene expression, but lower plasticity in most leaf traits. Interestingly, genotypes with the highest fitness in the novel environment had the lowest fitness at the native site. These results suggest that standing genetic variation in plasticity could help populations to persist and adapt to novel environments, despite remaining hidden in native environments.

Evaluating the correlation between genome-wide diversity and the release of plastic phenotypic variation in experimental translocations to novel natural environments.

Phenotypic reaction norms are often shaped and constrained by selection and are important for allowing organisms to respond to environmental change. However, selection cannot constrain reaction norms for environmental conditions that populations have not experienced. Consequently, cryptic neutral genetic variation for the reaction norm can accumulate such that a release of phenotypic variation occurs upon exposure to novel14 conditions. Most genomic diversity behaves as if functionally neutral. Therefore, genome-wide diversity metrics may correlate with levels of cryptic genetic variation and, as a result, exhibit a positive relationship with a release of phenotypic variation in novel environments. To test this hypothesis, we conducted translocations of juvenile brook trout (Salvelinus fontinalis) from 12 populations to novel uninhabited ponds that represented a gradient of environmental conditions. We assessed reaction norms for morphological traits (body size and four morphometric relative warps) across pond environmental gradients and evaluated the effect of genome-wide heterozygosity on phenotypic variability. All traits displayed plastic reaction norms. Overall, we found some evidence that a release of phenotypic variation consistent with cryptic genetic variation can occur in novel environmental conditions. However, the extent to which this release correlated with average genome-wide diversity was limited to only one of five traits examined. Our results suggest a limited link between genomic diversity26 and the accumulation of cryptic genetic variation in reaction norms. Similarly, reaction norms were constrained for many of the morphological traits examined. Past conditions may have constrained reaction norms in the putatively novel environments despite significant deviations from contemporary source population habitat. Additionally, as a generalist colonizing species brook trout may exhibit plastic phenotypes across a wide range of environmental conditions.

Population climatic history predicts phenotypic responses in novel environments for Arabidopsis thaliana in North America.

PREMISE: Determining how species perform in novel climatic environments is essential for understanding (1) responses to climate change and (2) evolutionary consequences of biological invasions. For the vast majority of species, the number of population characteristics that will predict performance and patterns of natural selection in novel locations in the wild remains limited. METHODS: We evaluated phenological, vegetative, architectural, and fitness-related traits in experimental gardens in contrasting climates (Ontario, Canada, and South Carolina, USA) in the North American non-native distribution of Arabidopsis thaliana. We assessed the effects of climatic distance, geographic distance, and genetic features of history on performance and patterns of natural selection in the novel garden settings. RESULTS: We found that plants had greater survivorship, flowered earlier, were larger, and produced more fruit in the south, and that genotype-by-environment interactions were significant between gardens. However, our analyses revealed similar patterns of natural selection between gardens in distinct climate zones. After accounting for genetic ancestry, we also detected that population climatic distance best predicted performance within gardens. CONCLUSIONS: These data suggest that colonization success in novel, non-native environments is determined by a combination of climate and genetic history. When performance at novel sites was assessed with seed sources from geographically and genetically disparate, established non-native populations, proximity to the garden alone was insufficient to predict performance. Our study highlights the need to evaluate seed sources from diverse origins to describe comprehensively phenotypic responses to novel environments, particularly for taxa in which many source populations may contribute to colonization.

Priorities for research in soil ecology.

The ecological interactions that occur in and with soil are of consequence in many ecosystems on the planet. These interactions provide numerous essential ecosystem services, and the sustainable management of soils has attracted increasing scientific and public attention. Although soil ecology emerged as an independent field of research many decades ago, and we have gained important insights into the functioning of soils, there still are fundamental aspects that need to be better understood to ensure that the ecosystem services that soils provide are not lost and that soils can be used in a sustainable way. In this perspectives paper, we highlight some of the major knowledge gaps that should be prioritized in soil ecological research. These research priorities were compiled based on an online survey of 32 editors of Pedobiologia - Journal of Soil Ecology. These editors work at universities and research centers in Europe, North America, Asia, and Australia.The questions were categorized into four themes: (1) soil biodiversity and biogeography, (2) interactions and the functioning of ecosystems, (3) global change and soil management, and (4) new directions. The respondents identified priorities that may be achievable in the near future, as well as several that are currently achievable but remain open. While some of the identified barriers to progress were technological in nature, many respondents cited a need for substantial leadership and goodwill among members of the soil ecology research community, including the need for multi-institutional partnerships, and had substantial concerns regarding the loss of taxonomic expertise.

Plant trait effects on soil organisms and functions.

Global change alters the composition and functioning of ecosystems by creating novel environmental conditions and thereby selecting for specific traits of organisms. Thus, trait-based approaches are promising tools to more mechanistically understand compositional and functional shifts in ecological communities as well as the dependency of response and effect traits upon global change. Such approaches have been particularly successful for the study of plant communities in terrestrial ecosystems. However, given the intimate linkages between aboveground and belowground compartments as well as the significance of plants as integrating organisms across those compartments, the role of plant traits in affecting soils communities has been understudied. This special issue contains empirical studies and reviews of plant trait effects on soil organisms and functions. Based on those contributions, we discuss here plasticity in trait expression, the context-dependency of plant trait effects, time lags in soil biotic responses to trait expression, and limitations of measured plant traits. We conclude that plant trait-based approaches are an important tool to advance soil ecological research, but also identify critical limitations and next steps.

Tree invasions and biosecurity: eco-evolutionary dynamics of hitchhiking fungi.

When non-native plants reach novel environments, they typically arrive with hidden microbiomes. In general, most of these hitchhikers remain on their co-evolved hosts, some contribute to the invasiveness of their hosts, and a small number can undergo host shifts and move onto native hosts. Invasion success can vary depending upon the different categories of fungal associates. When an invader tree relies on a fungal mutualism to survive in the new environment, there is a fundamentally lower likelihood of either the tree, or the fungus, establishing novel associations. In contrast, parasitic hitchhikers could merely use their host plants to move through the landscape and to become established on new hosts (host shifts). Evidence suggests the frequency of these host shifts is low and depends upon the fungal functional group. However, epidemics caused by invasive pathogens in native ecosystems have occurred globally. Thus, elucidating the potential for hidden non-native fungi to form novel host associations in a new environment is important for biodiversity conservation.

Evolutionary response when selection and genetic variation covary across environments.

Although models of evolution usually assume that the strength of selection on a trait and the expression of genetic variation in that trait are independent, whenever the same ecological factor impacts both parameters, a correlation between the two may arise that accelerates trait evolution in some environments and slows it in others. Here, we address the evolutionary consequences and ecological causes of a correlation between selection and expressed genetic variation. Using a simple analytical model, we show that the correlation has a modest effect on the mean evolutionary response and a large effect on its variance, increasing among-population or among-generation variation in the response when positive, and diminishing variation when negative. We performed a literature review to identify the ecological factors that influence selection and expressed genetic variation across traits. We found that some factors - temperature and competition - are unlikely to generate the correlation because they affected one parameter more than the other, and identified others - most notably, environmental novelty - that merit further investigation because little is known about their impact on one of the two parameters. We argue that the correlation between selection and genetic variation deserves attention alongside other factors that promote or constrain evolution in heterogeneous landscapes.

Limits to Future Adaptation in the Invasive Plant Polygonum cespitosum: Expression of Functional and Fitness Traits at Elevated CO2.

For organisms to adapt to future environments, they must both evolve appropriate functional responses and phenotypically express those responses under future climatic and CO2 conditions. We examined these 2 components of future adaptation in an invasive annual plant (Polygonum cespitosum) by performing a "resurrection" experiment under field conditions simulating a future environment. Resurrection experiments reveal recent evolution by comparing genotypes from natural populations sampled across a multigeneration interval. We collected genotypes from the same 3 North American populations in 1994 and 2005 and raised inbred lines from these collections under free air CO2 enrichment to examine functional and fitness traits expressed in hot, dry conditions at both ambient and elevated CO2 (N = 295 plants). The species has rapidly evolved in its introduced range to increase photosynthetic rate (collection year effect P ≤ 0.011) and delay senescence (P = 0.017) under full-sun, dry field conditions, but these adaptive changes were not expressed when the field environment included elevated CO2 (within-treatment year effect P ≥ 0.20 for both traits). Populations showed different levels of reproductive output and its genetic variance in these novel, stressful conditions. These findings illustrate constraints on evolutionary adaptation to predicted future conditions at both the species and population levels.

Vocal traits and diet explain avian sensitivities to anthropogenic noise.

Global population growth has caused extensive human-induced environmental change, including a near-ubiquitous transformation of the acoustical environment due to the propagation of anthropogenic noise. Because the acoustical environment is a critical ecological dimension for countless species to obtain, interpret and respond to environmental cues, highly novel environmental acoustics have the potential to negatively impact organisms that use acoustics for a variety of functions, such as communication and predator/prey detection. Using a comparative approach with 308 populations of 183 bird species from 14 locations in Europe, North American and the Caribbean, I sought to reveal the intrinsic and extrinsic factors responsible for avian sensitivities to anthropogenic noise as measured by their habitat use in noisy versus adjacent quiet locations. Birds across all locations tended to avoid noisy areas, but trait-specific differences emerged. Vocal frequency, diet and foraging location predicted patterns of habitat use in response to anthropogenic noise, but body size, nest placement and type, other vocal features and the type of anthropogenic noise (chronic industrial vs. intermittent urban/traffic noise) failed to explain variation in habitat use. Strongly supported models also indicated the relationship between sensitivity to noise and predictive traits had little to no phylogenetic structure. In general, traits associated with hearing were strong predictors - species with low-frequency vocalizations, which experience greater spectral overlap with low-frequency anthropogenic noise tend to avoid noisy areas, whereas species with higher frequency vocalizations respond less severely. Additionally, omnivorous species and those with animal-based diets were more sensitive to noise than birds with plant-based diets, likely because noise may interfere with the use of audition in multimodal prey detection. Collectively, these results suggest that anthropogenic noise is a powerful sensory pollutant that can filter avian communities nonrandomly by interfering with birds' abilities to receive, respond to and dispatch acoustic cues and signals.

THE INCREASED POTENTIAL FOR SELECTION OF THE LAC OPERON OF ESCHERICHIA COLI.

The fitness effects of six lac operons from natural isolates of Escherichia coli were determined in chemostats, in a test of the idea that selective differences among natural alleles are greater in novel conditions than in the prevailing environment, resulting in a greater genetic variance in fitness in novel conditions. Fitnesses were determined in the common milk sugar lactose, the natural substrate of the lac operon, and in three rare ß-galactosides, lactulose, galactosyl-arabinose, and methyl-galactopyranoside, that are novel for E. coli. Significantly greater fitness differences were observed among the lac alleles in each of the novel ß-galactosides than in lactose. An alternative explanation of the experimental findings is discussed. General evolutionary causes and consequences of selection potentials are discussed, and an outline of the work necessary to further elucidate the physiological basis of the observed potential for selection of the lac operon of E. coli is presented.