Response of Antarctic soil fauna to climate-driven changes since the Last Glacial Maximum.

Understanding how terrestrial biotic communities have responded to glacial recession since the Last Glacial Maximum (LGM) can inform present and future responses of biota to climate change. In Antarctica, the Transantarctic Mountains (TAM) have experienced massive environmental changes associated with glacial retreat since the LGM, yet we have few clues as to how its soil invertebrate-dominated animal communities have responded. Here, we surveyed soil invertebrate fauna from above and below proposed LGM elevations along transects located at 12 features across the Shackleton Glacier region. Our transects captured gradients of surface ages possibly up to 4.5 million years and the soils have been free from human disturbance for their entire history. Our data support the hypothesis that soils exposed during the LGM are now less suitable habitats for invertebrates than those that have been exposed by deglaciation following the LGM. Our results show that faunal abundance, community composition, and diversity were all strongly affected by climate-driven changes since the LGM. Soils more recently exposed by the glacial recession (as indicated by distances from present ice surfaces) had higher faunal abundances and species richness than older exposed soils. Higher abundances of the dominant nematode Scottnema were found in older exposed soils, while Eudorylaimus, Plectus, tardigrades, and rotifers preferentially occurred in more recently exposed soils. Approximately 30% of the soils from which invertebrates could be extracted had only Scottnema, and these single-taxon communities occurred more frequently in soils exposed for longer periods of time. Our structural equation modeling of abiotic drivers highlighted soil salinity as a key mediator of Scottnema responses to soil exposure age. These changes in soil habitat suitability and biotic communities since the LGM indicate that Antarctic terrestrial biodiversity throughout the TAM will be highly altered by climate warming.

Global change effects on plant communities are magnified by time and the number of global change factors imposed.

Global change drivers (GCDs) are expected to alter community structure and consequently, the services that ecosystems provide. Yet, few experimental investigations have examined effects of GCDs on plant community structure across multiple ecosystem types, and those that do exist present conflicting patterns. In an unprecedented global synthesis of over 100 experiments that manipulated factors linked to GCDs, we show that herbaceous plant community responses depend on experimental manipulation length and number of factors manipulated. We found that plant communities are fairly resistant to experimentally manipulated GCDs in the short term (<10 y). In contrast, long-term (≥10 y) experiments show increasing community divergence of treatments from control conditions. Surprisingly, these community responses occurred with similar frequency across the GCD types manipulated in our database. However, community responses were more common when 3 or more GCDs were simultaneously manipulated, suggesting the emergence of additive or synergistic effects of multiple drivers, particularly over long time periods. In half of the cases, GCD manipulations caused a difference in community composition without a corresponding species richness difference, indicating that species reordering or replacement is an important mechanism of community responses to GCDs and should be given greater consideration when examining consequences of GCDs for the biodiversity-ecosystem function relationship. Human activities are currently driving unparalleled global changes worldwide. Our analyses provide the most comprehensive evidence to date that these human activities may have widespread impacts on plant community composition globally, which will increase in frequency over time and be greater in areas where communities face multiple GCDs simultaneously.

High Return to Play and Low Reinjury Rates in National Collegiate Athletic Association Division I Football Players Following Anterior Cruciate Ligament Reconstruction Using Quadrupled Hamstring Autograft.

PURPOSE: The purpose of this study was to examine the outcomes of anterior cruciate ligament (ACL) reconstruction using quadrupled hamstring (QH) autograft in a cohort of National Collegiate Athletic Association (NCAA) Division I football players. METHODS: A retrospective analysis was performed on NCAA Division I football players at a single institution who had transtibial ACL reconstruction using QH autograft between 2001 and 2016. Primary outcomes were ACL reinjury and return to play (RTP). Secondary outcomes were position, percent of eligibility used after surgery, graft diameter, Tegner-Lysholm scores, concomitant injuries/surgeries, and postcollegiate professional play. RESULTS: Between 2001 and 2016, 34 players had QH autograft ACL reconstruction, and 29 players achieved RTP. Of the 29, 2 (6.9%) sustained ACL reinjuries. The average RTP was 318 days (range 115-628) after surgery. Players used 79.5% of their remaining collegiate eligibility after surgery. Nine players sustained multiligamentous knee injuries. This did not have a significant effect on RTP (P = 0.709; mean 306±24 days for isolated ACL, mean of 353±51 for 2 ligaments, mean of 324±114 for 3 + ligaments) and none sustained reinjury. Associated meniscal injuries were sustained by 28, and 8 sustained chondral injuries. The mean postoperative Tegner-Lysholm score was 90.7 of 100, with mean follow-up of 102 months. Of these players, 18 went on to play professionally, with 17 joining National Football League rosters and 1 an arena team roster. CONCLUSION: QH demonstrated an ACL reinjury and RTP rates similar to those in previously published, predominantly bone-patella tendon-bone ACL reinjury data in elite athletes. This study demonstrates that QH autograft may be a viable option in elite athletes. LEVEL OF EVIDENCE: IV, case series.

Positional Differences in Pre-Season Scrimmage Performance of Division I Collegiate Football Players.

This study aimed to describe the physical demands of American football players using novel performance analysis techniques. Heart rate (HR) and accelerometer-based activity levels were observed across two pre-season scrimmages in 23 Division I collegiate football players (age: 19 ± 1 y, height: 1.90 ± 0.06 m, weight: 116.2 ± 19.4 kg). Data were analyzed using a MATLAB program and inter-rater reproducibility assessed using inter-class correlations (ICC). Players were analyzed by side (offense/defense) and position (skill/non-skill). Performance variables assessed in bursts of activity included burst duration, HRmean and HRmax (bpm), and mean activity (vector magnitude units [vmu]). Exercise intensity was categorized as time spent in % HRmax in 5% increments. The burst duration (8.1±3.9 min, ICC = 0.72), HRmean (157 ± 12 bpm, ICC = 0.96) and mean activity (0.30 ± 0.05 vmu, ICC = 0.86) were reproducible. HRmean (p = 0.05) and HRmax (p = 0.001) were greater on defense. Offense spent more time at 65-70% HRmax (p = 0.01), 70-75% HRmax (p = 0.02) while defense spent more time 90-95% HRmax and ≥95% HRmax (p = 0.03). HRmean (p = 0.70) and HRpeak (p = 0.80) were not different between positions across both sides. Skilled players demonstrated greater mean activity (p = 0.02). The sport-specific analysis described HR and activity level in a reproducible manner. Automated methods of assessing HR may be useful in training and game time performance but ultimately provides support to coaching decision making.

Temporal variability in production is not consistently affected by global change drivers across herbaceous-dominated ecosystems.

Understanding how global change drivers (GCDs) affect aboveground net primary production (ANPP) through time is essential to predicting the reliability and maintenance of ecosystem function and services in the future. While GCDs, such as drought, warming and elevated nutrients, are known to affect mean ANPP, less is known about how they affect inter-annual variability in ANPP. We examined 27 global change experiments located in 11 different herbaceous ecosystems that varied in both abiotic and biotic conditions, to investigate changes in the mean and temporal variability of ANPP (measured as the coefficient of variation) in response to different GCD manipulations, including resource additions, warming, and irrigation. From this comprehensive data synthesis, we found that GCD treatments increased mean ANPP. However, GCD manipulations both increased and decreased temporal variability of ANPP (24% of comparisons), with no net effect overall. These inconsistent effects on temporal variation in ANPP can, in part, be attributed to site characteristics, such as mean annual precipitation and temperature as well as plant community evenness. For example, decreases in temporal variability in ANPP with the GCD treatments occurred in wetter and warmer sites with lower plant community evenness. Further, the addition of several nutrients simultaneously increased the sensitivity of ANPP to interannual variation in precipitation. Based on this analysis, we expect that GCDs will likely affect the magnitude more than the reliability over time of ecosystem production in the future.

Effects of Field Position on Fluid Balance and Electrolyte Losses in Collegiate Women's Soccer Players.

Research investigating hydration strategies specialized for women's soccer players is limited, despite the growth in the sport. The purpose of this study was to determine the effects of fluid balance and electrolyte losses in collegiate women's soccer players. Eighteen NCAA Division I women's soccer players were recruited (age: 19.2 ± 1.0 yr; weight: 68.5 ± 9.0 kg, and height: 168.4 ± 6.7 cm; mean ± SD), including: 3 forwards (FW), 7 mid-fielders (MD), 5 defenders (DF), and 3 goalkeepers (GK). Players practiced outdoor during spring off-season training camp for a total 14 practices (WBGT: 18.3 ± 3.1 °C). The main outcome measures included body mass change (BMC), sweat rate, urine and sweat electrolyte concentrations, and fluid intake. Results were analyzed for comparison between low (LOW; 16.2 ± 2.6° C, n = 7) and moderate risk environments for hyperthermia (MOD; 20.5 ± 1.5 °C, n = 7) as well as by field position. The majority (54%) of players were in a hypohydrated state prior to practice. Overall, 26.7% of players had a %BMC greater than 0%, 71.4% of players had a %BMC less than -2%, and 1.9% of players had a %BMC greater than -2% (all MD position). Mean %BMC and sweat rate in all environmental conditions were -0.4 ± 0.4 kg (-0.5 ± 0.6% body mass) and 1.03 ± 0.21 mg·cm-2·min-1, respectively. In the MOD environment, players exhibited a greater sweat rate (1.07 ± 0.22 mg·cm-2·min-1) compared to LOW (0.99 ± 0.22 mg·cm-2·min-1; p = 0.02). By position, DF had a greater total fluid intake and a lower %BMC compared to FW, MD, and GK (all p < 0.001). FW had a greater sweat sodium (Na+) (51.4 ± 9.8 mmol·L-1), whereas GK had the lowest sweat sodium (Na+) (30.9 ± 3.9 mmol·L-1). Hydration strategies should target pre-practice to ensure players are adequately hydrated. Environments deemed to be of moderate risk of hyperthermia significantly elevated the sweat rate but did not influence fluid intake and hydration status compared to low-risk environments. Given the differences in fluid balance and sweat responses, recommendations should be issued relative to soccer position.

A reality check for climate change experiments: Do they reflect the real world?

Experiments are widely used in ecology, particularly for assessing global change impacts on ecosystem function. However, results from experiments often are inconsistent with observations made under natural conditions, suggesting the need for rigorous comparisons of experimental and observational studies. We conducted such a "reality check" for a grassland ecosystem by compiling results from nine independently conducted climate change experiments. Each experiment manipulated growing season precipitation (GSP) and measured responses in aboveground net primary production (ANPP). We compared results from experiments with long-term (33-yr) annual precipitation and ANPP records to ask if collectively (n = 44 experiment-years) experiments yielded estimates of ANPP, rain-use efficiency (RUE, grams per square meter ANPP per mm precipitation), and the relationship between GSP and ANPP comparable to observations. We found that mean ANPP and RUE from experiments did not deviate from observations. Experiments and observational data also yielded similar functional relationships between ANPP and GSP, but only within the range of historically observed GSP. Fewer experiments imposed extreme levels of GSP (outside the observed 33-yr record), but when these were included, they altered the GSP-ANPP relationship. This result underscores the need for more experiments imposing extreme precipitation levels to resolve how forecast changes in climate regimes will affect ecosystem function in the future.

Drought timing, not previous drought exposure, determines sensitivity of two shortgrass species to water stress.

Climate change will alter global precipitation patterns, making it increasingly important that we understand how ecosystems will be impacted by more frequent and severe droughts. Yet most drought studies examine a single, within-season drought, and we know relatively little about the impacts of multiple droughts that occur within a single growing season. This distinction is important because many plant species are able to acclimate physiologically, such that the effects of multiple droughts on ecosystem function deviate significantly from the effects of cumulative, independent droughts. Unfortunately, we know relatively little about the ability of dominant species to acclimate to drought in drought-sensitive ecosystems like semi-arid grasslands. Here, we tested for physiological acclimation to multiple drought events in two dominant shortgrass steppe species: Bouteloua gracilis (C4) and Elymus elymoides (C3). Neither species exhibited physiological acclimation to drought; leaf water potential, stomatal conductance, and photosynthesis rates were all similarly affected by a single, late period drought and a second, late period drought. Biomass was lowest in plants exposed to two droughts, but this is likely due to the cumulative effects of both an early and late period drought. Our results suggest that late period droughts do exert weaker effects on biomass production of two dominant shortgrass species, but that the weaker effects are due to ontogenetic changes in plant physiology as opposed to physiological acclimation against multiple droughts. As a consequence, current ecosystem models that incorporate grass phenology and seasonal physiology should provide accurate predictions of primary production under future climates.

Predation Risk Reverses the Potential Effects of Warming on Plant-Herbivore Interactions by Altering the Relative Strengths of Trait- and Density-Mediated Interactions.

Climate warming will initiate numerous changes in ecological community structure and function, and such high-level impacts derive from temperature-driven changes in individual physiology. Specifically, top-down control of plant biomass is sensitive to rising temperatures, but the direction of change depends on a complex interaction between temperature, predation risk, and predator thermal preference. Here, I developed an individual-based optimal foraging model of three trophic levels (primary producers, herbivores, and predators) to examine how warming affects top-down control of primary producers via both trait- and density-mediated indirect interactions (TMII and DMII). This model also factorially crossed warm- and cold-adapted herbivores and predators to determine how local adaptation modifies the effects of warming on food web interactions. Regardless of predator thermal preference, warming increased herbivore foraging effort and by extension predation rates. As a result, TMII declined in importance at high temperatures regardless of predator thermal adaptation. Finally, predation risk reduced herbivore fitness via both indirect (i.e., reduced herbivore size) and direct (i.e., reduced herbivore survival) pathways. These results suggest that, contrary to previous predictions, warming might stimulate primary productivity by reducing herbivore population sizes, releasing plants from immediate top-down control.

Responses of plant phenology, growth, defense, and reproduction to interactive effects of warming and insect herbivory.

Climate warming can modify plant reproductive fitness through direct and indirect pathways. Direct effects include temperature-driven impacts on growth, reproduction, and secondary metabolites. Indirect effects may manifest through altered species interactions, including herbivory, although studies comparing the interactive effects of warming and herbivory are few. We used experimental warming combined with herbivore exclusion cages to assess the interactive effects of climate warming and herbivory by Popillia japonica, the Japanese beetle, on flowering phenology, growth, defense, and lifetime reproduction of a biennial herb, Oenothera biennis. Regardless of temperature, herbivory delayed flowering phenology and, surprisingly, led to decreased levels of foliar defenses. At ambient temperatures, plants were able to compensate for herbivory by producing smaller seeds and increasing total seed production, leading to similar investment in seed biomass for plants exposed to and protected from herbivores. At elevated temperatures, plants had elevated total seed production, but herbivory had negligible impacts on flower and fruit production, and total lifetime seed biomass was highest in plants exposed to herbivores in warmed conditions. We speculate that warming induced a stress response in O. biennis resulting from low soil moisture, which in turn led to an increase in seed number at the expense of maternal investment in each seed. Plant-insect interactions might therefore shift appreciably under future climates, and ecologists must consider both temperature and herbivory when attempting to assess the ramifications of climate warming on plant populations.

Asymmetric responses of primary productivity to precipitation extremes: A synthesis of grassland precipitation manipulation experiments.

Climatic changes are altering Earth's hydrological cycle, resulting in altered precipitation amounts, increased interannual variability of precipitation, and more frequent extreme precipitation events. These trends will likely continue into the future, having substantial impacts on net primary productivity (NPP) and associated ecosystem services such as food production and carbon sequestration. Frequently, experimental manipulations of precipitation have linked altered precipitation regimes to changes in NPP. Yet, findings have been diverse and substantial uncertainty still surrounds generalities describing patterns of ecosystem sensitivity to altered precipitation. Additionally, we do not know whether previously observed correlations between NPP and precipitation remain accurate when precipitation changes become extreme. We synthesized results from 83 case studies of experimental precipitation manipulations in grasslands worldwide. We used meta-analytical techniques to search for generalities and asymmetries of aboveground NPP (ANPP) and belowground NPP (BNPP) responses to both the direction and magnitude of precipitation change. Sensitivity (i.e., productivity response standardized by the amount of precipitation change) of BNPP was similar under precipitation additions and reductions, but ANPP was more sensitive to precipitation additions than reductions; this was especially evident in drier ecosystems. Additionally, overall relationships between the magnitude of productivity responses and the magnitude of precipitation change were saturating in form. The saturating form of this relationship was likely driven by ANPP responses to very extreme precipitation increases, although there were limited studies imposing extreme precipitation change, and there was considerable variation among experiments. This highlights the importance of incorporating gradients of manipulations, ranging from extreme drought to extreme precipitation increases into future climate change experiments. Additionally, policy and land management decisions related to global change scenarios should consider how ANPP and BNPP responses may differ, and that ecosystem responses to extreme events might not be predicted from relationships found under moderate environmental changes.

Nutrient loading alters the performance of key nutrient exchange mutualisms.

Nutrient exchange mutualisms between phototrophs and heterotrophs, such as plants and mycorrhizal fungi or symbiotic algae and corals, underpin the functioning of many ecosystems. These relationships structure communities, promote biodiversity and help maintain food security. Nutrient loading may destabilise these mutualisms by altering the costs and benefits each partner incurs from interacting. Using meta-analyses, we show a near ubiquitous decoupling in mutualism performance across terrestrial and marine environments in which phototrophs benefit from enrichment at the expense of their heterotrophic partners. Importantly, heterotroph identity, their dependence on phototroph-derived C and the type of nutrient enrichment (e.g. nitrogen vs. phosphorus) mediated the responses of different mutualisms to enrichment. Nutrient-driven changes in mutualism performance may alter community organisation and ecosystem processes and increase costs of food production. Consequently, the decoupling of nutrient exchange mutualisms via alterations of the world's nitrogen and phosphorus cycles may represent an emerging threat of global change.

Underappreciated problems of low replication in ecological field studies.

The cost and difficulty of manipulative field studies makes low statistical power a pervasive issue throughout most ecological subdisciplines. Ecologists are already aware that small sample sizes increase the probability of committing Type II errors. In this article, we address a relatively unknown problem with low power: underpowered studies must overestimate small effect sizes in order to achieve statistical significance. First, we describe how low replication coupled with weak effect sizes leads to Type M errors, or exaggerated effect sizes. We then conduct a meta-analysis to determine the average statistical power and Type M error rate for manipulative field experiments that address important questions related to global change; global warming, biodiversity loss, and drought. Finally, we provide recommendations for avoiding Type M errors and constraining estimates of effect size from underpowered studies.

Phylogenetic relatedness and leaf functional traits, not introduced status, influence community assembly.

Considerable debate focuses on whether invasive species establish and become abundant by being functionally and phylogenetically distinct from native species, leading to a host of invasion-specific hypotheses of community assembly. Few studies, however, have quantitatively assessed whether similar patterns of phylogenetic and functional similarity explain local abundance of both native and introduced species, which would suggest similar assembly mechanisms regardless of origin. Using a chronosequence of invaded temperate forest stands, we tested whether the occurrence and abundance of both introduced and native species were predicted by phylogenetic relatedness, functional overlap, and key environmental characteristics including forest age. Environmental filtering against functionally and phylogenetically distinct species strongly dictated the occurrence and abundance of both introduced and native species, with slight modifications of these patterns according to forest age. Thus, once functional and evolutionary novelty were quantified, introduced status provided little information about species' presence or abundance, indicating largely similar sorting mechanisms for both native and introduced species.

Differing nutritional constraints of consumers across ecosystems.

Stoichiometric mismatches between resources and consumers may drive a number of important ecological interactions, such as predation and herbivory. Such mismatches in nitrogen (N) or phosphorus (P) content between resources and consumers have furthered our understanding of consumer behavior and growth patterns in aquatic systems. However, stoichiometric data for multiple consumers from the same community are lacking in terrestrial systems. Here, we present the results of a study designed to characterize nutritional constraints within a terrestrial arthropod community. In order to place our results in a broader context, we compared our data on resource-consumer stoichiometry to those of stream and lake ecosystems. We found that N and P varied among trophic levels, and that high N:P content of herbivores suggests that herbivores might experience strong N-limitation. However, incredibly low P-content of plant foliage leads to potential P-limitation in herbivores that is nearly as strong as potential N-limitation. Moreover, arthropod predators may also be strongly P-limited. In fact, potential nutrient limitation of terrestrial herbivores in our study is similar to nutrient limitation from streams and lakes, suggesting that similar nutritional constraints may be operating across all three study systems. Importantly, our data suggest that consumers in lakes experience a trade-off between N- and P-limitation, while terrestrial consumers experience simultaneous strengthening or weakening of N- and P-limitation. We suggest that P may be overlooked as an important limiting nutrient in terrestrial ecosystems.

Schizachyrium scoparium (C4) better tolerates drought than Andropogon gerardii (C4) via constant CO2 supply for photosynthesis during water stress.

Climate change is dramatically altering global precipitation patterns across terrestrial ecosystems, making it critically important that we understand both how and why plant species vary in their drought sensitivities. Andropogon gerardii and Schizachyrium scoparium, both C4 grasses, provide a model system for understanding the physiological mechanisms that determine how species of a single functional type can differ in drought responses, an issue remains a critical gap in our ability to model and predict the impacts of drought on grassland ecosystems. Despite its greater lability of foliar water content, previous experiments have demonstrated that S. scoparium maintains higher photosynthetic capacity during droughts. It is therefore likely that the ability of S. scoparium to withstand drought instead derives from a greater metabolic resistance to drought. Here, we tested the following hypotheses: (H1) A. gerardii is more vulnerable to drought than S. scoparium at both the population and organismal levels, (H2) A. gerardii is less stomatally flexible than S. scoparium, and (H3) A. gerardii is more metabolically limited than S. scoparium. Our results indicate that it is actually stomatal limitations of CO2 supply that limit A. gerardii photosynthesis during drought. Schizachyrium scoparium was more drought-resistant than A. gerardii based on long-term field data, organismal biomass production and physiological gas exchange measurements. While both S. scoparium and A. gerardii avoided metabolic limitation of photosynthesis, CO2 supply of A. gerardii was greatly reduced during late-stage drought stress. That two common, co-occurring C4 species possess such different responses to drought highlights the physiological variability inherent within plant functional groups and underscores the need for more studies of C4 drought tolerance.

Blood and MRI biomarkers of mild traumatic brain injury in non-concussed collegiate football players.

Football has one of the highest incidence rates of mild traumatic brain injury (mTBI) among contact sports; however, the effects of repeated sub-concussive head impacts on brain structure and function remain under-studied. We assessed the association between biomarkers of mTBI and structural and functional MRI scans over an entire season among non-concussed NCAA Division I linemen and non-linemen. Concentrations of S100B, GFAP, BDNF, NFL, and NSE were assessed in 48 collegiate football players (32 linemen; 16 non-linemen) before the start of pre-season training (pre-camp), at the end of pre-season training (pre-season), and at the end of the competitive season (post-season). Changes in brain structure and function were assessed in a sub-sample of 11 linemen and 6 non-linemen using structural and functional MRI during the execution of Stroop and attention network tasks. S100B, GFAP and BDNF concentrations were increased at post-season compared to pre-camp in linemen. White matter hyperintensities increased in linemen during pre-season camp training compared to pre-camp. This study showed that the effects of repeated head impacts are detectable in the blood of elite level non-concussed collegiate football players exposed to low-moderate impacts to the heads, which correlated with some neurological outcomes without translating to clinically-relevant changes in brain anatomy or function.

Do invasive species perform better in their new ranges?

A fundamental assumption in invasion biology is that most invasive species exhibit enhanced performance in their introduced range relative to their home ranges. This idea has given rise to numerous hypotheses explaining "invasion success" by virtue of altered ecological and evolutionary pressures. There are surprisingly few data, however, testing the underlying assumption that the performance of introduced populations, including organism size, reproductive output, and abundance, is enhanced in their introduced compared to their native range. Here, we combined data from published studies to test this hypothesis for 26 plant and 27 animal species that are considered to be invasive. On average, individuals of these 53 species were indeed larger, more fecund, and more abundant in their introduced ranges. The overall mean, however, belied significant variability among species, as roughly half of the investigated species (N=27) performed similarly when compared to conspecific populations in their native range. Thus, although some invasive species are performing better in their new ranges, the pattern is not universal, and just as many are performing largely the same across ranges.

Seasonal changes in physiological and psychological parameters of stress in collegiate swimmers.

To investigate the seasonal changes in physiological and psychological parameters of stress in collegiate swimmers. Fifteen NCAA Division I swimmers (8 men) participated in a tethered anaerobic swim test to determine physiological responses in an ecologically-relevant, graded exercise test. Wisconsin Upper Respiratory Symptom Survey (WURSS-21), Activation-Deactivation Adjective Check List (AD-ACL), Daily Analysis of Life Demands of Athletes (DALDA), and Pittsburgh Sleep Quality Index were assessed at post-season in April (V1), the end of off-season in June (V2), and pre-season in October (V3). The percent change was determined from V2-V1 (off-season phase), V3-V2 (pre-season phase), V1-V3 (in-season phase). Spearman's rho correlation was used to examine associations between change in physiological and psychological outcomes. All data results showed a better swim performance occurred at V2. Men tended to have faster speed (p = 0.07) in fewer strokes (p = 0.10) and greater work per stroke (p = 0.10) at V2 than V1. Women were faster during V2 compared to V1 (p = 0.02) and V3 (p = 0.05). Women had fewer strokes (p = 0.02) and greater work per stroke (p = 0.01) at V2 compared to V3. Women had the lowest HR and lactate concentration at V3 compared to other visits (p < 0.05). During the in-season phase, swim speed decreased the greatest extent and stress sources and symptoms assessed by DALDA had greatest elevation (p < 0.05). An increased in stress sources and symptoms assessed by DALDA was associated with an increase in upper respiratory illness from WURSS-21 (rho = 0.44, p = 0.009), being less energetic (rho = - 0.35, p = 0.04) and greater tension state (rho = 0.49, p = 0.003; AD-ACL), and a decrease in swim speed (rho =- 0.38, p = 0.03). Swim performance peaked at off-season when psychological stress was at its lowest. The relationship between DALDA scores with psychological parameters and swim performance suggested physiological and psychological parameters of stress is an important aspect to avoid overtraining when approaching high swim performance.

Strong Dispersal Limitation of Microbial Communities at Shackleton Glacier, Antarctica.

Microbial communities can be structured by both deterministic and stochastic processes, but the relative importance of these processes remains unknown. The ambiguity partly arises from an inability to disentangle soil microbial processes from confounding factors, such as aboveground plant communities or anthropogenic disturbance. In this study, we characterized the relative contributions of determinism and stochasticity to assembly processes of soil bacterial communities across a large environmental gradient of undisturbed Antarctic soils. We hypothesized that harsh soils would impose a strong environmental selection on microbial communities, whereas communities in benign soils would be structured largely by dispersal. Contrary to our expectations, dispersal was the dominant assembly mechanism across the entire soil environmental gradient, including benign environments. The microbial community composition reflects slowly changing soil conditions and dispersal limitation of isolated sites. Thus, stochastic processes, as opposed to deterministic, are primary drivers of soil ecosystem assembly across space at our study site. This is especially surprising given the strong environmental constraints on soil microorganisms in one of the harshest environments on the planet, suggesting that dispersal could be a driving force in microbial community assembly in soils worldwide. IMPORTANCE Because of their diversity and ubiquity, microbes provide an excellent means to tease apart how natural communities are structured. In general, ecologists believe that stochastic assembly processes, like random drift and dispersal, should dominate in benign environments while deterministic processes, like environmental filtering, should be prevalent in harsh environments. To help resolve this debate, we analyzed microbial community composition in pristine Antarctic soils devoid of human influence or plant communities for eons. Our results demonstrate that dispersal limitation is a surprisingly potent force of community limitation throughout all soil conditions. Thus, dispersal appears to be a driving force of microbial community assembly, even in the harshest of conditions.