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28 juin 2018

Triggers of tree mortality under drought [Nature]

Severe droughts have caused widespread tree mortality across many forest biomes with profound effects on the function of ecosystems and carbon balance. Climate change is expected to intensify regional-scale droughts, focusing attention on the physiological basis of drought-induced tree mortality. Recent work has shown that catastrophic failure of the plant hydraulic system is a principal mechanism involved in extensive crown death and tree mortality during drought, but the multi-dimensional response of trees to desiccation is complex. Here we focus on the current understanding of tree hydraulic performance under drought, the identification of physiological thresholds that precipitate mortality and the mechanisms of recovery after drought. Building on this, we discuss the potential application of hydraulic thresholds to process-based models that predict mortality.

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28 juin 2018

Orangutans venture out of the rainforest and into the Anthropocene [Science Advances]

Conservation benefits from understanding how adaptability and threat interact to determine a taxon’s vulnerability. Recognizing how interactions with humans have shaped taxa such as the critically endangered orangutan (Pongo spp.) offers insights into this relationship. Orangutans are viewed as icons of wild nature, and most efforts to prevent their extinction have focused on protecting minimally disturbed habitat, with limited success. We synthesize fossil, archeological, genetic, and behavioral evidence to demonstrate that at least 70,000 years of human influence have shaped orangutan distribution, abundance, and ecology and will likely continue to do so in the future.(...)

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27 juin 2018

The Tortoise and the Finch : Testing for island effects on diversification using two iconic Galápagos radiations [Journal of Biogeography]

Keywords : diversification, islands, phylogeny, speciation, Testudinidae, Thraupidae

Islands are widely recognized as natural laboratories for evolutionary studies, but many questions about evolution on islands remain unresolved. Here we address two general questions from a macroevolutionary perspective. First, do lineages on islands have increased diversification rates relative to mainland lineages ? Second, does the same geographical context (e.g., same archipelago) have similar effects on diversification in unrelated groups ? We focused on Darwin’s finches and Galápagos tortoises, two endemic radiations from the Galápagos Islands, and the larger families in which they are embedded.(...)

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27 juin 2018

The rate of facultative sex governs the number of expected mating types in isogamous species [Nature Ecology & Evolution]

It is unclear why sexually reproducing isogamous species frequently contain just two self-incompatible mating types. Deterministic theory suggests that since rare novel mating types experience a selective advantage (by virtue of their many potential partners), the number of mating types should consistently grow. However, in nature, species with thousands of mating types are exceedingly rare. Several competing theories for the predominance of species with two mating types exist, yet they lack an explanation for how many are possible and in which species to expect high numbers. Here, we present a theoretical null model that explains the distribution of mating type numbers using just three biological parameters : mutation rate, population size and the rate of sex.(...)

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27 juin 2018

A note on measuring natural selection on principal component scores [Evolution Letters]

Keywords : flowering time, life history, multicollinearity, principal component analysis, principal component regression, selection gradients

Measuring natural selection through the use of multiple regression has transformed our understanding of selection, although the methods used remain sensitive to the effects of multicollinearity due to highly correlated traits. While measuring selection on principal component (PC) scores is an apparent solution to this challenge, this approach has been heavily criticized due to difficulties in interpretation and relating PC axes back to the original traits. We describe and illustrate how to transform selection gradients for PC scores back into selection gradients for the original traits, addressing issues of multicollinearity and biological interpretation.(...)

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