Lesley T. Lancaster

Life history trade-offs, the intensity of competition, and coexistence in novel and evolving communities under climate change

The consequences of climate change for local biodiversity are little understood in process or mechanism, but these changes are likely to reflect both changing regional species pools and changing competitive interactions. Previous empirical work largely supports the idea that competition will intensify under climate change, promoting competitive exclusions and local extinctions, while theory and conceptual work indicate that relaxed competition may in fact buffer communities from biodiversity losses that are typically witnessed at broader spatial scales. In this review, we apply life history theory to understand the conditions under which these alternative scenarios may play out in the context of a range-shifting biota undergoing rapid evolutionary and environmental change, and at both leading-edge and trailing-edge communities. We conclude that, in general, warming temperatures are likely to reduce life history variation among competitors, intensifying competition in both established and novel communities. However, longer growing seasons, severe environmental stress and increased climatic variability associated with climate change may buffer these communities against intensified competition. The role of life history plasticity and evolution has been previously underappreciated in community ecology, but may hold the key to understanding changing species interactions and local biodiversity under changing climates. This article is part of the themed issue ‘Human influences on evolution, and the ecological and societal consequences’.

Gene expression under thermal stress varies across a geographical range expansion front

Many ectothermic species are currently expanding their distributions polewards due to anthropogenic global warming. Molecular genetic mechanisms facilitating range expansion under these conditions are largely unknown, but understanding these could help mitigate expanding pests and disease vectors, or help explain why some species fail to track changing climates. Here, using RNA‐seq data, we examine genomewide changes in gene expression under heat and cold stress in the range‐expanding damselfly Ischnura elegans in northern Europe. We find that both the number of genes involved and levels of gene expression under heat stress have become attenuated during the expansion, consistent with a previously reported release from selection on heat tolerances as species move polewards. Genes upregulated under cold stress differed between core and edge populations, corroborating previously reported rapid adaptation to cooler climates at the expansion front. Expression of sixty‐nine genes exhibited a region x treatment effect; these were primarily upregulated in response to heat stress in core populations but in response to cold stress at the range edge, suggesting that some cellular responses originally adapted to heat stress may switch to cold‐stress functionality upon encountering novel thermal selection regimes during range expansion. Transcriptional responses to thermal stress involving heat‐shock and neural function genes were largely geographically conserved, while retrotransposon, regulatory, muscle function and defence gene expression patterns were more variable. Flexible mechanisms of cold‐stress response and the ability of some genes to shift their function between heat and cold stress might be key mechanisms facilitating rapid poleward expansion in insects.

Signatures of local adaptation along environmental gradients in a range-expanding damselfly (Ischnura elegans)

Insect distributions are shifting rapidly in response to climate change and are undergoing rapid evolutionary change. We investigate the molecular signatures underlying local adaptation in the range‐expanding damselfly, Ischnura elegans. Using a landscape genomic approach combined with generalized dissimilarity modelling (GDM), we detect selection signatures on loci via allelic frequency change along environmental gradients. We analyse 13,612 single nucleotide polymorphisms (SNPs), derived from restriction site‐associated DNA sequencing (RADseq), in 426 individuals from 25 sites spanning the I. elegans distribution in Sweden, including its expanding northern range edge. Environmental association analysis (EAA) and the magnitude of allele frequency change along the range expansion gradient revealed significant signatures of selection in relation to high maximum summer temperature, high mean annual precipitation and low wind speeds at the range edge. SNP annotations with significant signatures of selection revealed gene functions associated with ongoing range expansion, including heat shock proteins (HSP40 and HSP70), ion transport (V‐ATPase) and visual processes (long‐wavelength‐sensitive opsin), which have implications for thermal stress response, salinity tolerance and mate discrimination, respectively. We also identified environmental thresholds where climate‐mediated selection is likely to be strong, and indicate that I. elegans is rapidly adapting to the climatic environment during its ongoing range expansion. Our findings empirically validate an integrative approach for detecting spatially explicit signatures of local adaptation along environmental gradients.

Odonata community structure and patterns of land use in the Atewa Range Forest Reserve, Eastern Region (Ghana)

Recent studies have indicated that frequent anthropogenic disturbances in tropical developing countries are primary drivers of reduction in community diversity and local extinction of many arthropods, including dragonflies. We assessed the impact of anthropogenic disturbances on odonate assemblages across three different land use types, in a biodiverse nature reserve in Ghana. A total of 37 transects (100 × 10  m) were used to survey odonate species over two seasons and three rivers which pass through agricultural, mature forest and forest margin habitats. A total of 6940 individuals, belonging to 53 species (23 Zygoptera and 30 Anisoptera) in eight families, were recorded. Sapho ciliata (15% relative abundance) was the most abundant zygopteran, whereas Orthetrum julia (4.8% relative abundance) was the dominant anisopteran. Rarer species like Umma cincta, Chlorocnemis sp. and Elattoneura sp. were represented by < 50 individuals. The effective number of species was affected by the surrounding terrestrial habitat type and this most strongly reflected the difference between agricultural habitats (8.09 ± standard error (SE) 0.41) and mature forests (5.0 ± SE 0.24). A canonical correspondence analysis revealed that turbidity, surface water temperature, canopy cover and channel width were the key factors that influenced odonate assemblages. Degraded habitats were dominated by generalist and heliophilic dragonflies, while mature forest habitat included more stenotopic damselflies and dragonflies. These findings improve our understanding of the drivers of Odonata distributions and diversity and will help river managers use odonates to monitor riverine health, as part of conservation activities.

SOCIAL STRESS AS A PRIMING MECHANISM FOR THERMAL TOLERANCE DURING A POLEWARD RANGE SHIFT

Cold tolerance plays a critical role in determining species’ geographical range limits. Previous studies have found that range shifts in response to climate warming are facilitated by cold acclimation capacities, due to increasingly colder and variable weather at high latitudes, and that cold tolerance can also be influenced by social factors. In this study we combined experiments and field studies to investigate the climatic and social factors affecting cold tolerances in range-shifting populations of the female-polymorphic damselfly Ischnura elegans in northeast Scotland. In the field, we observed both environmental (measured via habitat suitability) and social (sex ratio and density) effects on cold tolerance (CTmin). Androchrome females (male-like females) were less susceptible to beneficial social effects on cold tolerance than gynochromes (female-like females), and correspondingly, gynochrome frequency increased at colder, environmentally-limiting sites towards the range margin. Our manipulations of density in the laboratory further provide novel, experimental evidence that social interactions directly impact cold tolerance n this species. These results suggest that reciprocal effects of social environments on thermal acclimation may be an important but commonly overlooked aspect of allee effects which contribute to the formation of range margins. Moreover, our results point to a wider need to consider the role of population and social dynamics to shape both the thermal physiology of individuals and the thermal niches of species.

Towards an interactive, process-based approach to understanding range shifts: developmental and environmental dependencies matter

Many species are undergoing distributional shifts in response to climate change. However, wide variability in range shifting rates has been observed across taxa, and even among closely‐related species. Attempts to link climate‐mediated range shifts to traits has often produced weak or conflicting results. Here we investigate interactive effects of developmental processes and environmental stress on the expression of traits relevant to range shifts. We use an individual‐based modelling approach to assess how different developmental strategies affect range shift rates under a range of environmental conditions. We find that under stressful conditions, such as at the margins of the species’ fundamental niche, investment in prolonged development leads to the greatest rates of range shifting, especially when longer time in development leads to improved fecundity and dispersal‐related traits. However, under benign conditions, and when traits are less developmentally plastic, shorter development times are preferred for rapid range shifts, because higher generational frequency increases the number of individual dispersal events occurring over time. Our results suggest that the ability of a species to range shift depends not only on their dispersal and colonisation characteristics but also how these characteristics interact with developmental strategies. Benefits of any trait always depended on the environmental and developmental sensitivity of life history trait combinations, and the environmental conditions under which the range shift takes place. Without considering environmental and developmental sources of variation in the expression of traits relevant to range shifts, there is little hope of developing a general understanding of intrinsic drivers of range shift potential.