The Resilience of Polar Collembola to Climate Change

Polar Collembola have adapted over millions of years to an environment that is changing faster than any other on earth. Globally, Collembola (springtails) are among the most abundant and widely-distributed arthropods and are key components of species-poor polar ecosystems. Understanding the resilience of polar collembola to climate change is therefore an urgent research priority. Here we explore the links between genetic diversity and physiology in shaping the resilience of polar Collembola to climate change. I have reviewed the resilience of polar Collembola considering genetic diversity, behavioural avoidance and physiological tolerances along with an examination of the potential impacts of biotic interactions. I also explored potential recovery dynamics with reference to temperate taxa and colonisation patterns of new habitat exposed by glacial retreat. This review illustrated that polar Collembola exhibit a suite of traits that have enabled their survival in extreme conditions and may serve as pre-adaptations to changing conditions. However, if resistance capacities are insufficient, complete community level recovery following disturbances is exceedingly slow, especially among Collembola that inhabit deeper microhabitats within the soil column (deeper-dwelling). Overall, it appears that deeper-dwelling species that fail to resist climate changes may not recover in ecologically realistic timescales, especially given the projected pace of climate changes. The largest spatial scale study and analysis of the genetic diversity of Collembola from the central Canadian High Arctic location of Cambridge Bay (Ikaluktuktiak) was undertaken to refine species identifications, examine levels of population diversity, and explore the role of geological processes and glacial dynamics in shaping the current Arctic collembolan fauna. I identified 68 Barcode Index Numbers (BINs, as a proxy for species diversity) representing an estimated 43 morphological species, with 29 BINs unique to Cambridge Bay. The geographic linkages between populations across the High Arctic supported hypothesised east to west dispersal patterns in accordance with prevailing ocean currents. The physiology of five of the most abundant surface-active species from the Canadian High Arctic was explored to determine how resistant local species are likely to be to rising temperatures and increasing drought pressure. Some individuals were found to exhibit remarkably high heat tolerances (>40 ℃) with only limited cold tolerance capacities (64 % had supercooling points higher than -10 ℃). Survival rates in response to a desiccation stress were also variable among individuals (range: 1.0-13.5 hrs). This indicated that Arctic Collembola may be pre-adapted to a level of climate warming. I also explored the specific relationship between two populations of the Antarctic collembolan Gomphiocephalus hodgsoni found in the largest ice-free area in continental Antarctica, McMurdo Dry Valleys. I tested whether the genetic variation found between coastal and inland individuals of G. hodgsoni corresponded with differences in physiological tolerances of hot and cold temperatures was tested. Individuals from the population nearest the warmer coastal site had higher upper thermal limits (mean CTmax 31.3 ℃) compared to individuals from the more inland population (mean CTmax 27.2 ℃). However, these differences in heat tolerance weren’t significant until accounting for microhabitat temperature at time of collection (site + microhabitat at time of collection, p=0.0029). Coastal individuals also had higher mean supercooling points (coastal: -14.3 ℃; inland: -22.6 ℃, p=0.011). Under climate change associated warming warm-adapted populations may have a selective advantage relative to more cold adapted individuals, leading to changes in population genetic structure, a decline in genetic diversity, and associated decline in resilience. Collectively my thesis chapters have identified that the biggest threats to the ongoing survival of polar Collembola are sustained heat stress, desiccation stress, changing biotic interactions, and the arrival and spread of invasive species. Despite this, polar Collembola exhibit considerable levels of genetic diversity and physiological tolerances that may make them pre-adapted to climate change induced environmental changes

The Trichoptera barcode initiative: a strategy for generating a species-level Tree of Life

DNA barcoding was intended as a means to provide species-level identifications through associating DNA sequences from unknown specimens to those from curated reference specimens. Although barcodes were not designed for phylogenetics, they can be beneficial to the completion of the Tree of Life. The barcode database for Trichoptera is relatively comprehensive, with data from every family, approximately two-thirds of the genera, and one-third of the described species. Most Trichoptera, as with most of life’s species, have never been subjected to any formal phylogenetic analysis. Here, we present a phylogeny with over 16 000 unique haplotypes as a working hypothesis that can be updated as our estimates improve. We suggest a strategy of implementing constrained tree searches, which allow larger datasets to dictate the backbone phylogeny, while the barcode data fill out the tips of the tree. We also discuss how this phylogeny could be used to focus taxonomic attention on ambiguous species boundaries and hidden biodiversity. We suggest that systematists continue to differentiate between ‘Barcode Index Numbers’ (BINs) and ‘species’ that have been formally described. Each has utility, but they are not synonyms. We highlight examples of integrative taxonomy, using both barcodes and morphology for species description. This article is part of the themed issue ‘From DNA barcodes to biomes’

The resilience of Polar Collembola (Springtails) in a changing climate.

Assessing the resilience of polar biota to climate change is essential for predicting the effects of changing environmental conditions for ecosystems. Collembola are abundant in terrestrial polar ecosystems and are integral to food-webs and soil nutrient cycling. Using available literature, we consider resistance (genetic diversity; behavioural avoidance and physiological tolerances; biotic interactions) and recovery potential for polar Collembola. Polar Collembola have high levels of genetic diversity, considerable capacity for behavioural avoidance, wide thermal tolerance ranges, physiological plasticity, generalist-opportunistic feeding habits and broad ecological niches. The biggest threats to the ongoing resistance of polar Collembola are increasing levels of dispersal (gene flow), increased mean and extreme temperatures, drought, changing biotic interactions, and the arrival and spread of invasive species. If resistance capacities are insufficient, numerous studies have highlighted that while some species can recover from disturbances quickly, complete community-level recovery is exceedingly slow. Species dwelling deeper in the soil profile may be less able to resist climate change and may not recover in ecologically realistic timescales given the current rate of climate change. Ultimately, diverse communities are more likely to have species or populations that are able to resist or recover from disturbances. While much of the Arctic has comparatively high levels of diversity and phenotypic plasticity; areas of Antarctica have extremely low levels of diversity and are potentially much more vulnerable to climate change

The Trichoptera barcode initiative: a strategy for generating a species-level Tree of Life.

DNA barcoding was intended as a means to provide species-level identifications through associating DNA sequences from unknown specimens to those from curated reference specimens. Although barcodes were not designed for phylogenetics, they can be beneficial to the completion of the Tree of Life. The barcode database for Trichoptera is relatively comprehensive, with data from every family, approximately two-thirds of the genera, and one-third of the described species. Most Trichoptera, as with most of life's species, have never been subjected to any formal phylogenetic analysis. Here, we present a phylogeny with over 16 000 unique haplotypes as a working hypothesis that can be updated as our estimates improve. We suggest a strategy of implementing constrained tree searches, which allow larger datasets to dictate the backbone phylogeny, while the barcode data fill out the tips of the tree. We also discuss how this phylogeny could be used to focus taxonomic attention on ambiguous species boundaries and hidden biodiversity. We suggest that systematists continue to differentiate between 'Barcode Index Numbers' (BINs) and 'species' that have been formally described. Each has utility, but they are not synonyms. We highlight examples of integrative taxonomy, using both barcodes and morphology for species description.This article is part of the themed issue 'From DNA barcodes to biomes'