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Data from: Transcriptomics in the wild: hibernation physiology in free‐ranging dwarf lemurs

Hibernation is an adaptive strategy some mammals use to survive highly seasonal or unpredictable environments. We present the first investigation on the transcriptomics of hibernation in a natural population of primate hibernators: Crossley's dwarf lemurs (Cheirogaleus crossleyi). Using capture–mark–recapture techniques to track the same animals over a period of 7 months in Madagascar, we used RNA‐seq to compare gene expression profiles in white adipose tissue (WAT) during three distinct physiological states. We focus on pathway analysis to assess the biological significance of transcriptional changes in dwarf lemur WAT and, by comparing and contrasting what is known in other model hibernating species, contribute to a broader understanding of genomic contributions of hibernation across Mammalia. The hibernation signature is characterized by a suppression of lipid biosynthesis, pyruvate metabolism and mitochondrial‐associated functions, and an accumulation of transcripts encoding ribosomal components and iron‐storage proteins. The data support a key role of pyruvate dehydrogenase kinase isoenzyme 4 (PDK4) in regulating the shift in fuel economy during periods of severe food deprivation. This pattern of PDK4 holds true across representative hibernating species from disparate mammalian groups, suggesting that the genetic underpinnings of hibernation may be ancestral to mammals.

Data from: Noninvasive physiological markers demonstrate link between habitat quality, adult sex ratio and poor population growth rate in a vulnerable species, the Cape mountain zebra

Effective conservation and species management requires an understanding of the causes of poor population growth. Conservation physiology uses biomarkers to identify factors that contribute to low individual fitness and population declines. Building on this, macrophysiology can use the same markers to assess how individual physiology varies with different ecological or demographic factors over large temporal and spatial scales. Here, we use a macrophysiological approach to identify the ecological and demographic correlates of poor population growth rates in the Cape mountain zebra metapopulation. We use two non-invasive biomarkers: faecal glucocorticoids as a measure of chronic stress, and faecal androgens as an indicator of male physiological status. We found that faecal glucocorticoid concentrations were highest in the spring prior to summer rainfall, and were elevated in individuals from populations associated with low quality habitat (lower grass abundance). In addition, faecal androgen concentrations were higher in populations with a high proportion of non-breeding stallions (where male:female adult sex ratios exceed 2:1) suggesting sex ratio imbalances may intensify male competition. Finally, population growth rate was negatively associated with faecal glucocorticoid concentrations and female fecundity was negatively associated with faecal androgens, indicating a relationship between hormone profiles and fitness. Together, our results provide cross population evidence for how poor population growth rates in Cape mountain zebra can be linked to individual physiological biomarkers. More broadly, we advocate physiological biomarkers as indicators of population viability, and as a way to evaluate the impact of variable ecological and demographic factors. In addition, conservation physiology can be used to assess the efficacy of management interventions for this subspecies, and this approach could inform models of species' responses to future environmental change.

Data from: How maternal investment varies with environmental factors and the age and physiological state of wild tsetse Glossina pallidipes and Glossina morsitans morsitans

Theory suggests females should optimize resource allocation across reproductive bouts to maximize lifetime reproduction, balancing current and future reproductive efforts according to physiological state and projected survival and reproduction. Tests of these ideas focus on long-lived vertebrates: few measure age-related reproductive output in iteroparous invertebrates, or partition reserves between those allocated to offspring versus mothers. We investigated how maternal age, and environmental and physiological factors influence reproductive investment in wild tsetse, Glossina pallidipes Austen and G. morsitans morsitans Westwood. Tsetse provide a tractable system to measure reproductive allocation. Females exhibit high maternal investment, producing single, large offspring that rely exclusively on maternal reserves. We find that mothers in better physiological condition and experiencing cooler temperatures produce larger offspring. Pupal size increases significantly but weakly with age. In both species, females with less fat invest proportionately more in offspring. Post-partum fat decreases in flies with badly frayed wings: poor flight capability may limit their feeding efficiency, or they may sacrifice more reserves as a terminal investment. Our results support evidence that offspring size increases with maternal size, investment depends on the environment, and females with lower chances of future reproduction invest more into current offspring. We discuss the implications of maternal effects for predicting vector population responses to environmental change.

Data from: Coupling biogeochemical tracers with fish growth reveals physiological and environmental controls on otolith chemistry

Biogeochemical tracers found in the hard parts of organisms are frequently used to answer key ecological questions by linking the organism with the environment. However, the biogeochemical relationship between the environment and the biogenic structure becomes less predictable in higher organisms as physiological processes become more complex. Here, we use the simultaneous combination of biogeochemical tracers and fish growth analyzed with a novel modeling framework to describe physiological and environmental controls on otolith chemistry in an upwelling zone. First, we develop increasingly complex univariate mixed models to describe and partition intrinsic (age effects) and extrinsic (environmental parameters) factors influencing fish growth and otolith element concentrations through time. Second, we use a multivariate mixed model to investigate the directionality and strength between element-to-element and growth relationships and test hypotheses regarding physiological and environmental controls on element assimilation in otoliths. We apply these models to continuous element (Na, Sr, Mg, Ba, Li) and growth increment profiles (monthly resolution over 17 years) derived from otoliths of reef ocean perch (Helicolenus percoides), a wild-caught, site-attached, fully marine fish. With a conceptual model, we hypothesize that otolith traits (elements and growth) driven by environmental conditions will correlate both within an otolith, reflecting the time dependency of growth and element assimilation, and among individuals that experience a similar set of external conditions. We found some elements (Sr:Ca and Na:Ca) are mainly controlled by physiological processes, while other elements (Ba:Ca and Li:Ca) are more environmentally influenced. Within an individual fish, the strength and direction of correlation varies among otolith traits, particularly those under environmental control. Correlations among physiologically regulated elements tend to be stronger than those primarily controlled by environmental drivers. Surprisingly, only Ba:Ca and growth are significantly correlated among individuals. Failure to appropriately account for intrinsic effects (e.g. age) led to inflated estimates of among individual correlations and a depression of within individual correlations. Together, the lack of among-individual correlations of otolith traits in properly formulated models and the biases that can be introduced by not including appropriate intrinsic covariates suggest that caution is needed when assuming multi-elemental signatures are reflective solely of shared environments.

opencc-zeroDec 2012View details →

Data from: Leaf form and photosynthetic physiology of Dryopteris species distributed along light gradients in eastern North America

1.Despite the ubiquity of ferns and at least tacit recognition by botanists that their physiology is unique among land plants, most studies on fern physiology have focused on only a few, locally distributed, usually distantly related species. No previous study has attempted to examine physiological adaptations in a group of widespread taxa that are closely related and whose relationships are well understood. Here we report leaf form and physiological measures for such a group, the eleven eastern North American species of Dryopteris (Dryopteridaceae), and examine differences in these parameters for evidence of adaptation to light availability. 2.Economic theory predicts that species from sunnier habitats should have narrower, more steeply inclined leaves, lower specific leaf area, higher stomatal density, higher rates of maximum photosynthesis, respiration, and stomatal conductance, and require more light to saturate photosynthesis. Species should show adaptive cross-over in net carbon uptake per unit leaf mass, with a relative advantage by sun-associated species at high photon flux densities (PFDs) and by shade-associated species at low PFDs. 3.Field studies allow us to begin characterizing the range of native light environments occupied by members of this group, and to examine interspecific variation in several aspects of leaf form and photosynthetic light response for evidence of adaption to light availability. We also present a novel means for incorporating phylogeny in tests of correlated evolution in a reticulate lineage. 4.Synthesis. Observed trends in physiology and morphology generally agree with qualitative predictions, but are often not statistically significant. We found no support for adaptive cross-over in mass-based carbon uptake, and thus for light availability being the most important variable driving morphological and physiological adaptation in these ferns. We propose that hydraulic factors related to water balance may have played a larger role in determining their morphological and physiological variation. Allopolyploid hybrids did not show transgression in any physiological parameter that may have allowed them to coexist regionally with their parents. The results of our phylogenetically-structured analyses highlight the importance of incorporating phylogeny into comparative studies, particularly when hybrid or polyploid taxa are present.

Data from: Isotopic niche reflects stress-induced variability in physiological status

The isotopic niche has become an established concept in trophic ecology. However, the assumptions behind this approach have rarely been evaluated. The evidence is accumulating that physiological stress can affect both magnitude and inter-individual variability of the isotopic signature in consumers via alterations in metabolic pathways. We hypothesized that stress factors (inadequate nutrition, parasite infestations, and exposure to toxic substances or varying oxygen conditions) might lead to suboptimal physiological performance and altered stable isotope signatures. The latter can be misinterpreted as alterations in isotopic niche. This hypothesis was tested by inducing physiological stress in the deposit-feeding amphipod Monoporeia affinis exposed to either different feeding regimes or contaminated sediments. In the amphipods, we measured body condition indices or reproductive output to assess growth status and δ13C and δ15N values to derive isotope niche metrics. As hypothesized, greater isotopic niche estimates were derived for the stressed animals compared to the control groups. Moreover, the δ15N values were influenced by body size, reproductive status and parasite infestations, while δ13C values were influenced by body size, oxygen conditions and survival. Using regression analysis with isotope composition and growth variables as predictors, we were able to discriminate between the amphipods exposed to nutritionally or chemically stressful conditions and those in the control groups. Thus, interpretation of isotopic niche can be confounded by natural or anthropogenic stressors that may induce an apparent rather than a dietary change in isotopic niche. These findings stress the importance of including measures of growth and health status when evaluating stable isotope data in food web studies.

Data from: Complementary responses of morphology and physiology enhance the stand-scale production of a model invasive species under elevated CO2 and nitrogen

1. Elevated atmospheric carbon dioxide (eCO2) concentrations and nitrogen (N) enrichment are known to enhance plant productivity and invasion. However, the implications of their interactive effects for plant productivity are not well understood, especially at the stand scale, presumably because morphological and physiological responses to these global change factors are rarely studied together in the field or assessed at the stand-level. 2. We first determined how leaf-level morphological and physiological traits responded to factorial combinations of ambient and elevated CO2 and N. We collected trait data from the model invasive species Phragmites australis (common reed) that were measured over three years in a long-term global change field experiment. We then combined the trait data and additional descriptions of P. australis canopies in a simulation model of carbon assimilation to determine how morphology and physiology contribute to P. australis' stand scale productivity. 3. At the leaf level, we found that light-saturated rates of photosynthesis were strongly stimulated by eCO2 (37%) and that this effect was enhanced by increasing salinity. N had a smaller effect (17% stimulation) on physiological responses than eCO2, but leaf morphological traits responded primarily to N; plant height increased by 27% and leaf area increased by 47%. 4. Stand scale simulations demonstrated that that morphological and physiological adjustments induced approximately additive responses when P. australis experienced both eCO2 and N enrichment. The simulations also indicated that morphological changes (which were primarily associated with canopy size) influenced stand scale carbon assimilation more than physiological changes. Moreover, 97% of the N response was due to changes in morphology, whereas 62% of the eCO2 response was caused by physiological shifts. 5. Our analysis indicates that morphological and physiological trait responses to elevated CO2 and nitrogen are likely to enhance the productivity of P. australis in complementary ways, potentially accelerating its invasion in North America. Furthermore, our data suggest that changes in morphological traits may have a greater influence on carbon gain than leaf-level physiology under near-future environmental conditions. Our study also highlights the importance of accounting for both morphological and physiological responses when attempting to infer global change responses from leaf-level data.

Data from: Life on the edge: a comparative study of eco-physiological adaptations of frogs to tropical semiarid environments

A key goal of ecology and evolution is to understand the relative contributions of environment and history in determining the geographic distribution of organisms. For the Neotropical lowlands, where temperatures are similar across landscapes, we hypothesize that water balance may be a critical but understudied factor in determining the distribution of species. Amphibians are especially sensitive to variation in precipitation due to their permeable skin. Here we focused on lowland frogs of north-western South America and investigated variation among 17 species in potentially important ecologically relevant performance variables related to water balance, and tested for possible adaptations to semiarid conditions within species. We studied frogs from coastal xeric, savannah and wet forest biomes under common laboratory conditions and quantified rates of evaporative water loss, rates of water uptake, and variation in water-searching behavior and performance. We found significant differences in all three performance variables among species, even after accounting for shared evolutionary history. A phylogenetic ANCOVA showed that categorizing species by ecological habits (terrestrial vs. arboreal) explained much of the eco-performance trait variation among species. Secondarily, environment explained additional variation, e.g., coastal xeric species showed reduced rates of water loss and terrestrial savannah amphibians showed lower rates of water uptake. Conspecific frog populations from different biomes exhibited similar performance. We compare our results with previous studies and conclude that ecological habit is the principle factor that predicts eco-physiological trait variation and the possible geographic distribution of lowland Neotropical frogs.

Data from: Physiological, morphological, and ecological tradeoffs influence vertical habitat use of deep-diving toothed-whales in the Bahamas

Dive capacity among toothed whales (suborder: Odontoceti) has been shown to generally increase with body mass in a relationship closely linked to the allometric scaling of metabolic rates. However, two odontocete species tagged in this study, the Blainville's beaked whale Mesoplodon densirostris and the Cuvier's beaked whale Ziphius cavirostris, confounded expectations of a simple allometric relationship, with exceptionally long (mean: 46.1 min & 65.4 min) and deep dives (mean: 1129 m & 1179 m), and comparatively small body masses (med.: 842.9 kg & 1556.7 kg). These two species also exhibited exceptionally long recovery periods between successive deep dives, or inter-deep-dive intervals (M. densirostris: med. 62 min; Z. cavirostris: med. 68 min). We examined competing hypotheses to explain observed patterns of vertical habitat use based on body mass, oxygen binding protein concentrations, and inter-deep-dive intervals in an assemblage of five sympatric toothed whales species in the Bahamas. Hypotheses were evaluated using dive data from satellite tags attached to the two beaked whales (M. densirostris, n = 12; Z. cavirostris, n = 7), as well as melon-headed whales Peponocephala electra (n = 13), short-finned pilot whales Globicephala macrorhynchus (n = 15), and sperm whales Physeter macrocephalus (n = 27). Body mass and myoglobin concentration together explained only 36% of the variance in maximum dive durations. The inclusion of inter-deep-dive intervals, substantially improved model fits (R2 = 0.92). This finding supported a hypothesis that beaked whales extend foraging dives by exceeding aerobic dive limits, with the extension of inter-deep-dive intervals corresponding to metabolism of accumulated lactic acid. This inference points to intriguing tradeoffs between body size, access to prey in different depth strata, and time allocation within dive cycles. These tradeoffs and resulting differences in habitat use have important implications for spatial distribution patterns, and relative vulnerabilities to anthropogenic impacts.

opencc-zeroDec 2014View details →

Data from: Micro-scale environmental variation amplifies physiological variation among individual mussels

The contributions of temporal and spatial environmental variation to physiological variation remain poorly resolved. Rocky intertidal zone populations are subjected to thermal variation over the tidal cycle, superimposed with micro-scale variation in individuals' body temperatures. Using the sea mussel (Mytilus californianus), we assessed the consequences of this micro-scale environmental variation for physiological variation among individuals, first by examining the latter in field-acclimatized animals, second by abolishing micro-scale environmental variation via common garden acclimation, and third by restoring this variation using a reciprocal outplant approach. Common garden acclimation reduced the magnitude of variation in tissue-level antioxidant capacities by ~30% among mussels from a wave-protected (warm) site, but it had no effect on antioxidant variation among mussels from a wave-exposed (cool) site. The field-acclimatized level of antioxidant variation was restored only when protected-site mussels were outplanted to a high, thermally stressful site. Variation in organismal oxygen consumption rates reflected antioxidant patterns, decreasing dramatically among protected-site mussels after common gardening. These results suggest a highly plastic relationship between individuals' genotypes and their physiological phenotypes that depends on recent environmental experience. Corresponding context-dependent changes in the physiological mean-variance relationships within populations complicate prediction of responses to shifts in environmental variability that are anticipated with global change.

opencc-zeroDec 2013View details →

Data from: Personality drives physiological adjustments and is not related to survival

The evolutionary function and maintenance of variation in animal personality is still under debate. Variation in the size of metabolic organs has recently been suggested to cause and maintain variation in personality. Here, we examine two main underlying notions: (i) that organ sizes vary consistently between individuals and cause consistent behavioural patterns, and (ii) that a more exploratory personality is associated with reduced survival. Exploratory behaviour of captive red knots (Calidris canutus, a migrant shorebird) was negatively rather than positively correlated with digestive organ (gizzard) mass, as well as with body mass. In an experiment, we reciprocally reduced and increased individual gizzard masses and found that exploration scores were unaffected. Whether or not these birds were resighted locally over the 19 months after release was negatively correlated with their exploration scores. Moreover, a long-term mark–recapture effort on free-living red knots with known gizzard masses at capture confirmed that local resighting probability (an inverse measure of exploratory behaviour) was correlated with gizzard mass without detrimental effects on survival. We conclude that personality drives physiological adjustments, rather than the other way around, and suggest that physiological adjustments mitigate the survival costs of exploratory behaviour. Our results show that we need to reconsider hypotheses explaining personality variation based on organ sizes and differential survival.

opencc-zeroDec 2018View details →

Data from: Social and ecological factors alter stress physiology of Virunga mountain gorillas (Gorilla beringei beringei)

Living in a rapidly changing environment can alter stress physiology at the population level, with negative impacts on health, reproductive rates, and mortality that may ultimately result in species decline. Small, isolated animal populations where genetic diversity is low are at particular risks, such as endangered Virunga mountain gorillas (Gorilla beringei beringei). Along with climate change‐associated environmental shifts that are affecting the entire population, subpopulations of the Virunga gorillas have recently experienced extreme changes in their social environment. As the growing population moves closer to the forest's carrying capacity, the gorillas are coping with rising population density, increased frequencies of interactions between social units, and changing habitat use (e.g., more overlapping home ranges and routine ranging at higher elevations). Using noninvasive monitoring of fecal glucocorticoid metabolites (FGM) on 115 habituated Virunga gorillas, we investigated how social and ecological variation are related to baseline FGM levels, to better understand the adaptive capacity of mountain gorillas and monitor potential physiological indicators of population decline risks. Generalized linear mixed models revealed elevated mean monthly baseline FGM levels in months with higher rainfall and higher mean maximum and minimum temperature, suggesting that Virunga gorillas might be sensitive to predicted warming and rainfall trends involving longer, warmer dry seasons and more concentrated and extreme rainfall occurrences. Exclusive use of smaller home range areas was linked to elevated baseline FGM levels, which may reflect reduced feeding efficiency and increased travel efforts to actively avoid neighboring groups. The potential for additive effects of stress‐inducing factors could have short‐ and long‐term impacts on the reproduction, health, and ultimately survival of the Virunga gorilla population. The ongoing effects of environmental changes and population dynamics must be closely monitored and used to develop effective long‐term conservation strategies that can help address these risk factors.

opencc-zeroNov 2019View details →

Data from: Diving into divergence: differentiation in swimming performances, physiology and gene expression between locally-adapted sympatric cichlid fishes

Sympatric speciation occurs without strict vicariance and is thought to often be driven by ecological specialization of subpopulations that eventually diverge genetically and phenotypically. Distinct morphologies between sympatric populations occupying different niches have been interpreted as such differentiating adaptive phenotypes, yet differences in performance and thus adaptiveness between them were rarely tested. Here, we investigated if divergent body shapes of two sympatric crater lake cichlid species from Nicaragua, one being a shore-associated (benthic) species while the other prefers the open water zones (limnetic), affect cruising and sprinting swimming abilities - performances particularly relevant to their respective lifestyles. Furthermore, we investigated species differences in oxygen consumption across different swimming speeds and compare gene expression in gills and white muscle at rest and during exercise. We found a superior cruising ability in the limnetic Amphilophus zaliosus compared to the benthic A. astorquii, while sprinting was not different, suggesting that their distinct morphologies affect swimming performance. Increased cruising <a>ability in A. zaliosus was however linked</a> to a higher oxygen demand, during activity (but not rest), indicating different metabolic rates during exercise - a hypothesis supported by coinciding gene expression patterns of gill transcriptomes. We identified differentially expressed genes linked to swimming physiology, regulation of swimming behaviour and oxygen intake. A combination of physiological and morphological differences may thus underlie adaptations to these species' distinct niches. This complex ecological specialization likely resulted in morphological and physiological trade-offs that contributed to the rapid establishment and maintenance of divergence with gene flow.

opencc-zeroDec 2014View details →

Data from: Quantification of correlational selection on thermal physiology, thermoregulatory behavior and energy metabolism in lizards

Phenotypic selection is widely accepted as the primary cause of adaptive evolution in natural populations, but selection on complex functional properties linking physiology, behavior, and morphology has been rarely quantified. In ectotherms, correlational selection on thermal physiology, thermoregulatory behavior, and energy metabolism is of special interest because of their potential coadaptation. We quantified phenotypic selection on thermal sensitivity of locomotor performance (sprint speed), thermal preferences, and resting metabolic rate in captive populations of an ectothermic vertebrate, the common lizard, Zootoca vivipara. No correlational selection between thermal sensitivity of performance, thermoregulatory behavior, and energy metabolism was found. A combination of high body mass and resting metabolic rate was positively correlated with survival and negatively correlated with fecundity. Thus, different mechanisms underlie selection on metabolism in lizards with small body mass than in lizards with high body mass. In addition, lizards that selected the near average preferred body temperature grew faster that their congeners. This is one of the few studies that quantifies significant correlational selection on a proxy of energy expenditure and stabilizing selection on thermoregulatory behavior.

Data from: Aging in an herbaceous plant: increases in mortality and decreases in physiology and seed mass

1. Little is known about plant age-dependent trait expression and how environmental conditions might affect aging in the wild. This study evaluates age variation in multiple traits of a short-lived perennial herb using a manipulative field experimental design. 2. Two different-aged cohorts were followed in a field plot for over a year to evaluate trait expression in response to a competition treatment and seasonal stress. Traits measured included size, mortality, reproduction, and physiology, including photosynthetic efficiency and chlorophyll content (SPAD). We hypothesized that the stress of competition and seasonal changes would accentuate age-dependent trait declines in older plants. 3. The results highlight consistent age differences in plant size, mortality, and seed size with older plants being smaller, more likely to die, and producing smaller seeds. Some of the aging declines were sensitive to environmental conditions such that it was only during certain seasons when older plants had higher mortality, lower photosynthetic efficiency, and lower chlorophyll content than young plants. Age-dependent trait expression also varied in response to competition such that age differences in size were only present in the 'no competition treatment,' and old individuals in the competition treatment had a higher mortality than all other age-environment combinations. 4. Synthesis. These findings show that aging in plants is a complex phenotype where declines in traits are uncoordinated and can be, but are not always, sensitive to environmental conditions. This study shows age-dependent maternal effects on offspring quality which, together with the decline in performance of older individuals, may have impacts on an individual's fitness and on natural population demography.

Data from: Physiological conditions and genetic controls of phaeomelanin pigmentation in nestling barn swallows

Phaeomelanin is a common pigment that confers a reddish color to animals. Since phaeomelanogenesis requires the sulfhydryl group from cysteine or glutathione (GSH), which is an important antioxidant, this pigmentation and the associated coloration may be an honest signal, whereby only high-quality individuals (e.g., with lower oxidative stress) are able to develop showy plumage. The present study tested the mechanisms underlying the honest signal hypothesis using nestling barn swallows, Hirundo rustica gutturalis, which exhibit phaeomelanic throat plumage patches. We examined the relationship between phaeomelanin pigmentation levels and physiological condition during trait development, and the expression of the phaeomelanin-related gene agouti-signaling protein (ASIP) and the GSH-related gene glutathione S-transferase (GST) in throat feather follicles. We found that during phaeomelanogenesis, heavier nestlings produced more pigmented feathers, indicating that nestlings with high phaeomelanin concentrations are in better condition. We also found that phaeomelanin concentration was negatively correlated with total GSH level, but not significantly related with measures of oxidative stress. Among the GST genes, GSTM3 exhibited the highest expression in the developing feathers during phaeomelanogenesis. The expression levels of ASIP were positively associated with the amount of phaeomelanin deposition and negatively associated with the expression of GSTM3, reducing the amount of GSH that was available as an antioxidant. These findings suggest that high-quality individuals produce high concentrations of phaeomelanin in their plumage without experiencing increased oxidative stress, despite phaeomelanin production, which is triggered by ASIP, potentially actively consuming the sulfhydryl group from GSH.

opencc-zeroDec 2015View details →

Data from: C4 photosynthesis boosts growth by altering physiology, allocation and size

C4 photosynthesis is a complex set of leaf anatomical and biochemical adaptations that have evolved more than 60 times to boost carbon uptake compared with the ancestral C3 photosynthetic type1,2,3. Although C4 photosynthesis has the potential to drive faster growth rates4,5, experiments directly comparing C3 and C4 plants have not shown consistent effects1,6,7. This is problematic because differential growth is a crucial element of ecological theory8,9 explaining C4 savannah responses to global change10,11, and research to increase C3 crop productivity by introducing C4 photosynthesis12. Here, we resolve this long-standing issue by comparing growth across 382 grass species, accounting for ecological diversity and evolutionary history. C4 photosynthesis causes a 19–88% daily growth enhancement. Unexpectedly, during the critical seedling establishment stage, this enhancement is driven largely by a high ratio of leaf area to mass, rather than fast growth per unit leaf area. C4 leaves have less dense tissues, allowing more leaves to be produced for the same carbon cost. Consequently, C4 plants invest more in roots than C3 species. Our data demonstrate a general suite of functional trait divergences between C3 and C4 species, which simultaneously drive faster growth and greater investment in water and nutrient acquisition, with important ecological and agronomic implications.

opencc-zeroNov 2019View details →

Data from: Physical and physiological impacts of ocean warming alter phenotypic selection on sperm morphology

<ol> <li>Global warming may threaten fertility, which is a key component of individual fitness and vital for population persistence. For males, fertility relies on the ability of sperm to collide and fuse with eggs; consequently, sperm morphology is predicted to be a prime target of selection owing to its effects on male function.</li> <li>In aquatic environments, warming will expose gametes of external fertilisers to the physiological effects of higher temperature and the physical effects of lower viscosity. However, the consequences of either effect for fertility, and for selection acting on sperm traits to maintain fertility, are poorly understood.</li> <li>Here, we test how independent changes in water temperature and viscosity alter male fertility and selection on sperm morphology in an externally-fertilising marine tubeworm. To create five fertilisation environments, we manipulate temperature to reflect current-day conditions (16.5°C), projected near-term warming (21°C), and projected long-term warming (25°C), then adjust two more environments at 21°C and 25°C to the viscosity of environments at 16.5°C and 21°C, respectively. We then use a split-ejaculate design to measure the fertility of focal males, and selection on their sperm, in each environment.</li> <li>Projected changes in temperature and viscosity act independently to reduce male fertility, but act jointly to alter selection on sperm morphology. Specifically, environments resulting from projected warming alter selection on the sperm midpiece in ways that suggest shifts in the energetic challenges of functioning under stressful conditions. Selection also targets sperm head dimensions and tail length, irrespective of environment.</li> <li>We provide the first evidence that projected changes in ocean temperature and viscosity will not only impact the fertility of marine external fertilisers, but expose their gametes to novel selection pressures that may drive them to adapt in response if gamete phenotypes are sufficiently heritable.</li> </ol>

Data from: Increasing photoperiod stimulates initiation of spring migratory behaviour and physiology in a facultative migrant, the pine siskin

The transition to a migratory state involves coordinated changes in physiology and behaviour. In species with regular, predictable (obligate) migrations, increasing day length triggers the expression of a spring migratory state and androgens play an important role in stimulating its development. In contrast, we know very little about the environmental cues and endocrine mechanisms that regulate migration in species with less predictable (facultative) migrations. Here, we tested whether photoperiod stimulates a migratory state in a facultative nomadic migrant, the pine siskin (Spinus pinus). We exposed wintering birds to either a naturally increasing or short-day photoperiod and measured physiological and behavioural changes indicative of a migratory state. We also examined changes in circulating hormones that may play a role in the migratory transition. Natural-day, but not short-day, birds displayed physiological preparations for migration, including increases in fat deposition, and expressed increased levels of migratory restlessness. We found no evidence for a role of corticosterone in the migratory transition, but testosterone may be important. This study is the first experimental test of the role of photoperiod in regulating facultative migration and demonstrates that the predictive cue used by many obligate migrants to time spring migration is also important in a facultative migrant.

Data from: Stress in biological invasions: introduced invasive grey squirrels increase physiological stress in native Eurasian red squirrels

1. Invasive alien species can cause extinction of native species through processes including predation, interspecific competition for resources, or disease-mediated competition. Increases in stress hormones in vertebrates may be associated with these processes and contribute to the decline in survival or reproduction of the native species. 2. Eurasian red squirrels (Sciurus vulgaris) have gone extinct across much of the British Isles and parts of Northern Italy following the introduction of North American invasive grey squirrels (Sciurus carolinensis). We extracted glucocorticoid metabolites from faecal samples to measure whether the presence of the invasive species causes an increase in physiological stress in individuals of the native species. 3. We show that native red squirrels in seven sites where they co-occurred with invasive grey squirrels had glucocorticoid concentrations that were three times higher than those in five sites without the invasive species. Moreover, in a longitudinal study, stress hormones in native red squirrels increased after colonisation by grey squirrels. When we experimentally reduced the abundance of the invasive grey squirrels, the concentration of faecal glucocorticoid metabolites in co-occurring red squirrels decreased significantly between pre- and post-removal periods. 4. Hence, we found that the invasive species acts as a stressor which significantly increases the concentrations of glucocorticoids in the native species. 5. Given that sustained elevations in glucocorticoids could reduce body growth and reproductive rate, our results are consistent with previous studies where the co-occurrence of the invasive grey squirrel was associated with smaller size and lower reproductive output in red squirrels.