Arthropods and climate change - arctic challenges and opportunities

A circumpolar study unveils a positive non-linear effect of temperature on arctic arthropod availability that may reduce the risk of warming-induced trophic mismatch for breeding shorebirds

Seasonally abundant arthropods are a crucial food source for many migratory birds that breed in the Arctic. In cold environments, the growth and emergence of arthropods are particularly tied to temperature. Thus, the phenology of arthropods is anticipated to undergo a rapid change in response to a warming climate, potentially leading to a trophic mismatch between migratory insectivorous birds and their prey. Using data from 19 sites spanning a wide temperature gradient from the Subarctic to the High Arctic, we investigated the effects of temperature on the phenology and biomass of arthropods available to shorebirds during their short breeding season at high latitudes. We hypothesized that prolonged exposure to warmer summer temperatures would generate earlier peaks in arthropod biomass, as well as higher peak and seasonal biomass. Across the temperature gradient encompassed by our study sites (>10°C in average summer temperatures), we found a 3-day shift in average peak date for every increment of 80 cumulative thawing degree-days. Interestingly, we found a linear relationship between temperature and arthropod biomass only below temperature thresholds. Higher temperatures were associated with higher peak and seasonal biomass below 106 and 177 cumulative thawing degree-days, respectively, between June 5 and July 15. Beyond these thresholds, no relationship was observed between temperature and arthropod biomass. Our results suggest that prolonged exposure to elevated temperatures can positively influence prey availability for some arctic birds. This positive effect could, in part, stem from changes in arthropod assemblages and may reduce the risk of trophic mismatch.

California Serogroup Viruses in a Changing Canadian Arctic: A Review

The Arctic is warming at four times the global rate, changing the diversity, activity and distribution of vectors and associated pathogens. While the Arctic is not often considered a hotbed of vector-borne diseases, Jamestown Canyon virus (JCV) and Snowshoe Hare virus (SSHV) are mosquito-borne zoonotic viruses of the California serogroup endemic to the Canadian North. The viruses are maintained by transovarial transmission in vectors and circulate among vertebrate hosts, both of which are not well characterized in Arctic regions. While most human infections are subclinical or mild, serious cases occur, and both JCV and SSHV have recently been identified as leading causes of arbovirus-associated neurological diseases in North America. Consequently, both viruses are currently recognised as neglected and emerging viruses of public health concern. This review aims to summarise previous findings in the region regarding the enzootic transmission cycle of both viruses. We identify key gaps and approaches needed to critically evaluate, detect, and model the effects of climate change on these uniquely northern viruses. Based on limited data, we predict that (1) these northern adapted viruses will increase their range northwards, but not lose range at their southern limits, (2) undergo more rapid amplification and amplified transmission in endemic regions for longer vector-biting seasons, (3) take advantage of northward shifts of hosts and vectors, and (4) increase bite rates following an increase in the availability of breeding sites, along with phenological synchrony between the reproduction cycle of theorized reservoirs (such as caribou calving) and mosquito emergence.

The rising threat of climate change for arthropods from Earth's cold regions: Taxonomic rather than native status drives species sensitivity

Polar and alpine regions are changing rapidly with global climate change. Yet, the impacts on biodiversity, especially on the invertebrate ectotherms which are dominant in these areas, remain poorly understood. Short-term extreme temperature events, which are growing in frequency, are expected to have profound impacts on high-latitude ectotherms, with native species being less resilient than their alien counterparts. Here, we examined in the laboratory the effects of short periodic exposures to thermal extremes on survival responses of seven native and two non-native invertebrates from the sub-Antarctic Islands. We found that survival of dipterans was significantly reduced under warming exposures, on average having median lethal times (LT50 ) of about 30 days in control conditions, which declined to about 20 days when exposed to daily short-term maxima of 24°C. Conversely, coleopterans were either not, or were less, affected by the climatic scenarios applied, with predicted LT50 as high as 65 days under the warmest condition (daily exposures at 28°C for 2 h). The native spider Myro kerguelensis was characterized by an intermediate sensitivity when subjected to short-term daily heat maxima. Our results unexpectedly revealed a taxonomic influence, with physiological sensitivity to heat differing between higher level taxa, but not between native and non-native species representing the same higher taxon. The survival of a non-native carabid beetle under the experimentally imposed conditions was very high, but similar to that of native beetles, while native and non-native flies also exhibited very similar sensitivity to warming. As dipterans are a major element of diversity of sub-Antarctic, Arctic and other cold ecosystems, such observations suggest that the increased occurrence of extreme, short-term, thermal events could lead to large-scale restructuring of key terrestrial ecosystem components both in ecosystems protected from and those exposed to the additional impacts of biological invasions.

Herbivores in Arctic ecosystems: Effects of climate change and implications for carbon and nutrient cycling

Arctic terrestrial herbivores influence tundra carbon and nutrient dynamics through their consumption of resources, waste production, and habitat-modifying behaviors. The strength of these effects is likely to change spatially and temporally as climate change drives shifts in herbivore abundance, distribution, and activity timing. Here, we review how herbivores influence tundra carbon and nutrient dynamics through their consumptive and nonconsumptive effects. We also present evidence for herbivore responses to climate change and discuss how these responses may alter the spatial and temporal distribution of herbivore impacts. Several current knowledge gaps limit our understanding of the changing functional roles of herbivores; these include limited characterization of the spatial and temporal variability in herbivore impacts and of how herbivore activities influence the cycling of elements beyond carbon. We conclude by highlighting approaches that will promote better understanding of herbivore effects on tundra ecosystems, including their integration into existing biogeochemical models, new applications of remote sensing techniques, and the continued use of distributed experiments.

Population genomic signatures of the oriental fruit moth related to the Pleistocene climates

The Quaternary climatic oscillations are expected to have had strong impacts on the evolution of species. Although legacies of the Quaternary climates on population processes have been widely identified in diverse groups of species, adaptive genetic changes shaped during the Quaternary have been harder to decipher. Here, we assembled a chromosome-level genome of the oriental fruit moth and compared genomic variation among refugial and colonized populations of this species that diverged in the Pleistocene. High genomic diversity was maintained in refugial populations. Demographic analysis showed that the effective population size of refugial populations declined during the penultimate glacial maximum (PGM) but remained stable during the last glacial maximum (LGM), indicating a strong impact of the PGM rather than the LGM on this pest species. Genome scans identified one chromosomal inversion and a mutation of the circadian gene Clk on the neo-Z chromosome potentially related to the endemicity of a refugial population. In the colonized populations, genes in pathways of energy metabolism and wing development showed signatures of selection. These different genomic signatures of refugial and colonized populations point to multiple impacts of Quaternary climates on adaptation in an extant species.

Are Bumblebees Relevant Models for Understanding Wild Bee Decline?

The unsustainable use of ecosystems by human societies has put global biodiversity in peril. Bees are, in this context, a popular example of a highly diversified group of pollinators whose collapse is a major concern given the invaluable ecosystem services they provide. Amongst them, bumblebees (Bombus) have increasingly drawn the attention of scientists due to their dramatic population declines globally. This regression has converted them into popular conservation entities, making them the second most studied group of bees worldwide. However, in addition to have become relevant models in the fields of ecology, evolution and biogeography, bumblebees have also been used as models for studying wild bee decline and conservation worldwide. Integrating evidence from the comparative ecology and resilience of bumblebees and wild bees, I discuss the relevance of using Bombus as radars for wild bee decline worldwide. Responses of bumblebees to environmental changes are generally not comparable with those of wild bees because of their relatively long activity period, their inherent sensitivity to high temperatures, their relatively generalist diet breadth and many aspects arising from their eusocial behavior. Moreover, important differences in the available historical data between bumblebees and other bees make comparisons of conservation status even more arduous. Overall, these results reinforce the need for conservation actions that consider a higher level of understanding of ecological diversity in wild bees, highlight the need for an updated and more extensive sampling of these organisms, and emphasize that more caution is required when extrapolating trends from model species.

A Survey of Potentially Pathogenic-Incriminated Arthropod Vectors of Health Concern in Botswana

Arthropod vectors play a crucial role in the transmission of many debilitating infections, causing significant morbidity and mortality globally. Despite the economic significance of arthropods to public health, public knowledge on vector biology, ecology and taxonomic status remains anecdotal and largely unexplored. The present study surveyed knowledge gaps regarding the biology and ecology of arthropod vectors in communities of Botswana, across all districts. Results showed that communities are largely aware of individual arthropod vectors; however, their 'potential contribution' in disease transmission in humans, livestock and wildlife could not be fully attested. As such, their knowledge was largely limited with regards to some aspects of vector biology, ecology and control. Communities were strongly concerned about the burden of mosquitoes, cockroaches, flies and ticks, with the least concerns about fleas, bedbugs and lice, although the same communities did not know of specific diseases potentially vectored by these arthropods. Knowledge on arthropod vector control was mainly limited to synthetic chemical pesticides for most respondents, regardless of their location. The limited knowledge on potentially pathogen-incriminated arthropod vectors reported here has large implications for bridging knowledge gaps on the bio-ecology of these vectors countrywide. This is potentially useful in reducing the local burden of associated diseases and preventing the risk of emerging and re-emerging infectious diseases under global change.

Direct and indirect effects of altered temperature regimes and phenological mismatches on insect populations

Climate change is transforming ecosystems by altering species ranges, the composition of communities, and trophic interactions. Here, we synthesize recent reviews and subsequent developments to provide an overview of insect ecological and evolutionary responses to altered temperature regimes. We discuss both direct responses to thermal stress and indirect responses arising from phenological mismatches, altered host quality, and changes in natural enemy activity. Altered temperature regimes can increase exposure to both cold and heat stress and result in phenological and morphological mismatches with adjacent trophic levels. Host plant quality varies in a heterogenous way in response to altered temperatures with both increases and decreases observed. Density-dependent effects, spatial heterogeneity, and rapid evolutionary change provide some resilience to these threats.

Biting insects in a rapidly changing Arctic

Biting insects have a long-standing reputation for being an extreme presence in the Arctic, but it is unclear how they are responding to the rapid environmental changes currently taking place in the region. We review recent advances in our understanding of climate change responses by several key groups of biting insects, including mosquitoes, blackflies, and warble/botflies, and we highlight the significant knowledge gaps on this topic. We also discuss how changes in biting insect populations could impact humans and wildlife, including disease transmission and the disruption of culturally and economically important activities. Future work should integrate scientific with local and traditional ecological knowledge to better understand global change responses by biting insects in the Arctic and the associated consequences for the environmental security of Arctic communities.

Thermal acclimation has limited effect on the thermal tolerances of summer-collected Arctic and sub-Arctic wolf spiders

High-latitude ectotherms contend with large daily and seasonal temperature variation. Summer-collected wolf spiders (Araneae; Lycosidae) from sub-Arctic and Arctic habitats have been previously documented as having low temperature tolerance insufficient for surviving year-round in their habitat. We tested two competing hypotheses: that they would have broad thermal breadth, or that they would use plasticity to extend the range of their thermal performance. We collected Pardosa moesta and P. lapponica from the Yukon Territory, Canada, P. furcifera, P. groenlandica, and P. hyperborea from southern Greenland, and P. hyperborea from sub-Arctic Norway, and acclimated them to warm (12 or 20 °C) or cool (4 °C) conditions under constant light for one week. We measured critical thermal minimum (CT_min) or supercooling point (SCP) as a measure of lower thermal limit, and critical thermal maximum (CT_max) as a measure of upper thermal limit. We found relatively little impact of acclimation on thermal limits, and some counterintuitive responses; for example, warm acclimation decreased the SCP and/or cool acclimation increased the CT_max in several cases. Together, this meant that acclimation did not appear to modify the thermal breadth, which supports our first hypothesis, but allows us to reject the hypothesis that spiders use plasticity to fine-tune their thermal physiology, at least in the summer. We note that we still cannot explain how these spiders withstand the very cold winters, and speculate that there are acclimatisation cues or processes that we were unable to capture in our study.

Responses of terrestrial polar arthropods to high and increasing temperatures

Terrestrial arthropods in the Arctic and Antarctic are exposed to extreme and variable temperatures, and climate change is predicted to be especially pronounced in these regions. Available ecophysiological studies on terrestrial ectotherms from the Arctic and Antarctic typically focus on the ability of species to tolerate the extreme low temperatures that can occur in these regions, whereas studies investigating species plasticity and the importance of evolutionary adaptation to periodically high and increasing temperatures are limited. Here, we provide an overview of current knowledge on thermal adaptation to high temperatures of terrestrial arthropods in Arctic and Antarctic regions. Firstly, we summarize the literature on heat tolerance for terrestrial arthropods in these regions, and discuss variation in heat tolerance across species, habitats and polar regions. Secondly, we discuss the potential for species to cope with increasing and more variable temperatures through thermal plasticity and evolutionary adaptation. Thirdly, we summarize our current knowledge of the underlying physiological adjustments to heat stress in arthropods from polar regions. It is clear that very little data are available on the heat tolerance of arthropods in polar regions, but that large variation in arthropod thermal tolerance exists across polar regions, habitats and species. Further, the species investigated show unique physiological adjustments to heat stress, such as their ability to respond quickly to increasing or extreme temperatures. To understand the consequences of climate change on terrestrial arthropods in polar regions, we suggest that more studies on the ability of species to cope with stressful high and variable temperatures are needed.

Nonlinear trends in abundance and diversity and complex responses to climate change in Arctic arthropods

Time series data on arthropod populations are critical for understanding the magnitude, direction, and drivers of change. However, most arthropod monitoring programs are short-lived and restricted in taxonomic resolution. Monitoring data from the Arctic are especially underrepresented, yet critical to uncovering and understanding some of the earliest biological responses to rapid environmental change. Clear imprints of climate on the behavior and life history of some Arctic arthropods have been demonstrated, but a synthesis of population-level abundance changes across taxa is lacking. We utilized 24 y of abundance data from Zackenberg in High-Arctic Greenland to assess trends in abundance and diversity and identify potential climatic drivers of abundance changes. Unlike findings from temperate systems, we found a nonlinear pattern, with total arthropod abundance gradually declining during 1996 to 2014, followed by a sharp increase. Family-level diversity showed the opposite pattern, suggesting increasing dominance of a small number of taxa. Total abundance masked more complicated trajectories of family-level abundance, which also frequently varied among habitats. Contrary to expectation in this extreme polar environment, winter and fall conditions and positive density-dependent feedbacks were more common determinants of arthropod dynamics than summer temperature. Together, these data highlight the complexity of characterizing climate change responses even in relatively simple Arctic food webs. Our results underscore the need for data reporting beyond overall trends in biomass or abundance and for including basic research on life history and ecology to achieve a more nuanced understanding of the sensitivity of Arctic and other arthropods to global changes.