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"PHYSIOLOGICAL ECOLOGY"
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role of isohydric and anisohydric species in determining ecosystem-scale response to severe drought
Ongoing shifts in the species composition of Eastern US forests necessitate the development of frameworks to explore how species-specific water-use strategies influence ecosystem-scale carbon (C) cycling during drought. Here, we develop a diagnostic framework to classify plant drought-response strategies along a continuum of isohydric to anisohydric regulation of leaf water potential (Ψ L). The framework is applied to a 3-year record of weekly leaf-level gas exchange and Ψ measurements collected in the Morgan-Monroe State Forest (Indiana, USA), where continuous observations of the net ecosystem exchange of CO₂ (NEE) have been ongoing since 1999. A severe drought that occurred in the middle of the study period reduced the absolute magnitude of NEE by 55 %, though species-specific responses to drought conditions varied. Oak species were characterized by anisohydric regulation of Ψ L that promoted static gas exchange throughout the study period. In contrast, Ψ L of the other canopy dominant species was more isohydric, which limited gas exchange during the drought. Ecosystem-scale estimates of NEE and gross ecosystem productivity derived by upscaling the leaf-level data agreed well with tower-based observations, and highlight how the fraction of isohydric and anisohydric species in forests can mediate net ecosystem C balance.
Journal Article
Reproduction and adaptation
\"In the space of one generation major changes have begun to take place in the field of human reproduction. A rapid increase in the control of fertility and the understanding and treatment of sexual health issues have been accompanied by an emerging threat to reproductive function linked to increasing environmental pollution and dramatic changes in lifestyle. Organised around four key themes, this book provides a valuable review of some of the most important recent findings in human reproductive ecology. Major topics include the impact of the environment on reproduction, the role of physical activity and energetics in regulating reproduction, sexual maturation and ovulation assessment and demographic, health and family planning issues. Both theoretical and practical issues are covered, including the evolution and importance of the menopause and the various statistical methods by which researchers can analyse characteristics of the menstrual cycle in field studies\"-- Provided by publisher.
BOOK
Measuring stress in wildlife: techniques for quantifying glucocorticoids
Stress responses play a key role in allowing animals to cope with change and challenge in the face of both environmental certainty and uncertainty. Measurement of glucocorticoid levels, key elements in the neuroendocrine stress axis, can give insight into an animal's well-being and can aid understanding ecological and evolutionary processes as well as conservation and management issues. We give an overview of the four main biological samples that have been utilized [blood, saliva, excreta (feces and urine), and integumentary structures (hair and feathers)], their advantages and disadvantages for use with wildlife, and some of the background and pitfalls that users must consider in interpreting their results. The matrix of choice will depend on the nature of the study and of the species, on whether one is examining the impact of acute versus chronic stressors, and on the degree of invasiveness that is possible or desirable. In some cases, more than one matrix can be measured to achieve the same ends. All require a significant degree of expertise, sometimes in obtaining the sample and always in extracting and analyzing the glucocorticoid or its metabolites. Glucocorticoid measurement is proving to be a powerful integrator of environmental stressors and of an animal's condition.
Journal Article
Paradise falls : the true story of an environmental catastrophe
Lois Gibbs, Luella Kenny, and Barbara Quimby thought they had found a slice of the American dream when they and their families moved onto the quiet streets of Love Canal, a picturesque middle-class hamlet by Niagara Falls in the winter of 1977, the town had record snowfalls, and in the spring, rains filled the earth with water like a sponge and the basements of the neighbourhood's homes with a pungent odour. It was the sweet, synthetic smell of chemicals. Then, one by one, the children of the more than 800 families that made Love Canal their home started getting very sick. In this propulsive work of narrative reportage, Keith O'Brien uncovers how Lois, Luella, Barbara and other local mothers uncovered the poisonous secret of Love Canal - that they were living on the site where industrial employer Hooker Chemical had been dumping toxic waste for years, and covering it up.
Book
Fasting affects amino acid nitrogen isotope values: a new tool for identifying nitrogen balance of free-ranging mammals
Changes in the nutritional status of free-ranging animals have a strong influence on individual fitness, yet it remains challenging to monitor longitudinally. Nitrogen (δ15N) and carbon (δ13C) isotope values measured chronologically along the length of metabolically inert keratinous tissues can be used as a nutritional biomarker to retrospectively reconstruct the foraging ecology and eco-physiology of consumers. We quantitatively describe the physiological effects of fasting on amino acid metabolism using sequentially measured bulk tissue and amino acid δ15N values along the length of whiskers sampled from free-ranging juvenile, subadults, adult female, and male southern elephant seals (SES; Mirounga leonina) on Marion Island in the Southern Ocean. For both juveniles and adult females, whisker segments representing fasting had significantly higher bulk tissue δ15N values of 0.6 ± 0.5‰ and 1.3–1.8‰, respectively, in comparison to segments unaffected by fasting. We also found a large increase (2–6‰) in δ15N values for most glucogenic amino acids and a simultaneous depletion (2–3‰) of alanine in segments reflecting fasting, which enabled us to accurately predict (74%) the nutritional status of our model species. We hypothesize that the glucose-alanine cycle is the mechanism driving the observed depletion of alanine δ15N values during fasting. We demonstrated that keratinaceous tissues can be used as a longitudinal nutritional biomarker to detect changes in the nitrogen balance of an individual. Moreover, it is evident that physiological factors have an important influence on tissue δ15N values and can lead to erroneous bulk tissue or amino acid isotope-based reconstructions of foraging habits.
Journal Article
How and Why Chromosome Inversions Evolve
Over the next half century, inspired largely by Dobzhansky and his coworkers, much of empirical population genetics devoted itself to studying the abundant polymorphisms within and fixed differences of inversions between species of Drosophila [2]. The presence of an inversion is suggested when a certain cross consistently shows blocked recombination in part of the genome, but this observation requires genetic markers that have been mapped. [...]we will see how several of these themes are illuminated by an exciting study on an inversion in a plant that appears in this issue of PLoS Biology.
Journal Article
A Widespread Chromosomal Inversion Polymorphism Contributes to a Major Life-History Transition, Local Adaptation, and Reproductive Isolation
The role of chromosomal inversions in adaptation and speciation is controversial. Historically, inversions were thought to contribute to these processes either by directly causing hybrid sterility or by facilitating the maintenance of co-adapted gene complexes. Because inversions suppress recombination when heterozygous, a recently proposed local adaptation mechanism predicts that they will spread if they capture alleles at multiple loci involved in divergent adaptation to contrasting environments. Many empirical studies have found inversion polymorphisms linked to putatively adaptive phenotypes or distributed along environmental clines. However, direct involvement of an inversion in local adaptation and consequent ecological reproductive isolation has not to our knowledge been demonstrated in nature. In this study, we discovered that a chromosomal inversion polymorphism is geographically widespread, and we test the extent to which it contributes to adaptation and reproductive isolation under natural field conditions. Replicated crosses between the prezygotically reproductively isolated annual and perennial ecotypes of the yellow monkeyflower, Mimulus guttatus, revealed that alternative chromosomal inversion arrangements are associated with life-history divergence over thousands of kilometers across North America. The inversion polymorphism affected adaptive flowering time divergence and other morphological traits in all replicated crosses between four pairs of annual and perennial populations. To determine if the inversion contributes to adaptation and reproductive isolation in natural populations, we conducted a novel reciprocal transplant experiment involving outbred lines, where alternative arrangements of the inversion were reciprocally introgressed into the genetic backgrounds of each ecotype. Our results demonstrate for the first time in nature the contribution of an inversion to adaptation, an annual/perennial life-history shift, and multiple reproductive isolating barriers. These results are consistent with the local adaptation mechanism being responsible for the distribution of the two inversion arrangements across the geographic range of M. guttatus and that locally adaptive inversion effects contribute directly to reproductive isolation. Such a mechanism may be partially responsible for the observation that closely related species often differ by multiple chromosomal rearrangements.
Journal Article
Fine-scale variation in microhabitat conditions influences physiology and metabolism in an Antarctic insect
Microhabitats with distinct biotic and abiotic properties exist within landscapes, and this microhabitat variation can have dramatic impacts on the phenology and physiology of the organisms occupying them. The Antarctic midge Belgica antarctica inhabits diverse microhabitats along the Western Antarctic Peninsula that vary in macrophyte composition, hygric qualities, nutrient input, and thermal patterns. Here, we compare seasonal physiological changes in five populations of B. antarctica living in close proximity but in different microhabitats in the vicinity of Palmer Station, Antarctica. Thermal regimes among our sample locations differed in both mean temperature and thermal stability. Between the warmest and coldest sites, seasonal mean temperatures differed by 2.6°C and degree day accumulations above freezing differed by a factor of 1.7. Larval metabolic and growth rates varied among the sites, and adult emergence occurred at different times. Distinct microhabitats also corresponded with differences in body composition, as lipid and carbohydrate content of larvae differed across sites. Further, seasonal changes in carbohydrate and protein content were dependent on site, indicating fine-scale variation in the biochemical composition of larvae as they prepare for winter. Together, these results demonstrate that variation in microhabitat properties influences the ontogeny, phenology, physiology, and biochemical makeup of midge populations living in close proximity. These results have implications for predicting responses of Antarctic ecosystems to environmental change.
Journal Article
Light and VPD gradients drive foliar nitrogen partitioning and photosynthesis in the canopy of European beech and silver fir
While foliar photosynthetic relationships with light, nitrogen, and water availability have been well described, environmental factors driving vertical gradients of foliar traits within forest canopies are still not well understood. We, therefore, examined how light availability and vapour pressure deficit (VPD) co-determine vertical gradients (between 12 and 42 m and in the understorey) of foliar photosynthetic capacity (Amax), ¹³C fractionation (Δ), specific leaf area (SLA), chlorophyll (Chl), and nitrogen (N) concentrations in canopies of Fagus sylvatica and Abies alba growing in a mixed forest in Switzerland in spring and summer 2017. Both species showed lower Chl/N and lower SLA with higher light availability and VPD at the top canopy. Despite these biochemical and morphological acclimations, Amax during summer remained relatively constant and the photosynthetic N-use efficiency (PNUE) decreased with higher light availability for both species, suggesting sub-optimal N allocation within the canopy.Δ of both species were lower at the canopy top compared to the bottom, indicating high water-use efficiency (WUE). VPD gradients strongly co-determined the vertical distribution of Chl, N, and PNUE in F. sylvatica, suggesting stomatal limitation of photosynthesis in the top canopy, whereas these traits were only related to light availability in A. alba. Lower PNUE in F. sylvatica with higher WUE clearly indicated a trade-off in water vs. N use, limiting foliar acclimation to high light and VPD at the top canopy. Species-specific trade-offs in foliar acclimation to environmental canopy gradients may thus be considered for scaling photosynthesis from leaf to canopy to landscape levels.
Journal Article