Is There Any Evidence for Rapid,Genetically-Based,Climatic Niche Expansion in the Invasive Common Ragweed?

Climatic niche shifts have been documented in a number of invasive species by comparing the native and adventive climatic ranges in which they occur. However, these shifts likely represent changes in the realized climatic niches of invasive species, and may not necessarily be driven by genetic changes in climatic affinities. Until now the role of rapid niche evolution in the spread of invasive species remains a challenging issue with conflicting results. Here, we document a likely genetically-based climatic niche expansion of an annual plant invader, the common ragweed (Ambrosia artemisiifolia L.), a highly allergenic invasive species causing substantial public health issues. To do so, we looked for recent evolutionary change at the upward migration front of its adventive range in the French Alps. Based on species climatic niche models estimated at both global and regional scales we stratified our sampling design to adequately capture the species niche, and localized populations suspected of niche expansion. Using a combination of species niche modeling, landscape genetics models and common garden measurements, we then related the species genetic structure and its phenotypic architecture across the climatic niche. Our results strongly suggest that the common ragweed is rapidly adapting to local climatic conditions at its invasion front and that it currently expands its niche toward colder and formerly unsuitable climates in the French Alps (i.e. in sites where niche models would not predict its occurrence). Such results, showing that species climatic niches can evolve on very short time scales, have important implications for predictive models of biological invasions that do not account for evolutionary processes.     

Invasive species distribution models – how violating the equilibrium assumption can create new insights

Aim Two core assumptions of species distribution models (SDMs) do not hold when modelling invasive species. Invasives are not in equilibrium with their environment and niche quantification and transferability in space and time are limited. Here, we test whether combining global‐ and regional‐scale data in a novel framework can overcome these limitations. Beyond simply improving regional niche modelling of non‐native species, the framework also makes use of the violation of regional equilibrium assumptions, and aims at estimating the stage of invasion, range filling and risk of spread in the near future for 27 invasive species in the French Alps. Innovation For each invader we built three sets of SDMs using a committee averaging method: one global model and two regional models (a conventional model and one using the global model output to weight pseudo‐absences). Model performances were compared using the area under the receiver operating characteristic curve, the true skill statistic, sensitivity and specificity scores. Then, we extracted the predictions for observed presences and compared them to global and regional models. This comparison made it possible to identify whether invasive species were observed within or outside of their regional and global niches. Main conclusions This study provides a novel methodological framework for improving the regional modelling of invasive species, where the use of a global model output to weight pseudo‐absences in a regional model significantly improved the predictive performance of regional SDMs. Additionally, the comparison of the global and regional model outputs revealed distinct patterns of niche estimates and range filling among the species. These differences allowed us to draw conclusions about the stage of invasion and the risk of spread in the near future, which both correspond to experts' expectations. This framework can be easily applied to a large number of species and is therefore useful for control of biological invasions and eradication planning.     

Nucleocytoplasmic interactions during ontogenesis in individuals obtained by intra- and interspecific nuclear transplantation in the genus Pleurodeles (urodele amphibian)

Nuclei derived from a single blastula of Pleurodeles waltlii or Pleurodeles poireti are transplanted to the cytoplasm of eggs of both species (P. waltlii and P. poireti). Animals with identical genomes are obtained, some resulting from an intraspecific nucleocytoplasmic association, the others from an interspecific association (nucleocytoplasmic hybrids). A marked lethality results from the heterospecific association. Morphological and physiological effects, concomitant to initial egg conditioning, occur during the first stages of development. The study of lactic dehydrogenase (LDH) and malic dehydrogenase (MDH) zymograms reveals the genomic activity in the embryo from stage 28 (heart beat). A regionalization of this activity is evident; the nuclear activity can be shown in the ectomesodermic tissue sooner than in the endodermal cells. From stage 38 (feeding), the functional substitution of transplanted nucleus for effects of initial cytoplasmic conditioning appears to be total. No cytoplasmic heredity can be shown: the genetic effect of the transplanted nucleus is dominant. This is corroborated by the results of cutaneous cross-grafts between adult allocytoplasmic twins. Those animals present strictly identical immune reactions; their antigenic constitution seems to be independent from the specific origin of the egg cytoplasm.     

Myosin isoenzymes and their subunits in urodelan amphibian fast skeletal muscle. Coexistence of larval and adult heavy chains in neotenic individuals

The distributions of native myosin isoforms were examined by electrophoresis under non-dissociating conditions, in the fast twitch dorsal skeletal muscle of young larvae, neotenic adults and metamorphosed adults of urodelan amphibians. Both heavy and light chains of myosin isoenzymes were analysed. In pyrophosphate acrylamide gel electrophoresis three isoenzymes were demonstrated in larval myosin; other isoforms of lower electrophoretic mobility were observed in metamorphosed adults myosin. Larval and adult isoenzymes were shown to coexist in myosin from neotenic adults. Analysis of heavy chains in denaturing conditions and proteolytic digestion revealed the sequential occurrence during development of two types of heavy chains, one larval and one adult, that coexist in the myosin of neotenic adults only. Analysis of light chain patterns under denaturing conditions revealed the existence of three fast light chains which displayed no modification during the course of development. The neotenic urodelan amphibian species model represents actually the only model in which the coexistence of larval (or neonatal) and adult heavy chains is maintained throughout life in adults.     

Exercise-induced modulation of calcineurin activity parallels the time course of myofibre transitions

This study establishes a causal link between the limitation of myofibre transitions and modulation of calcineurin activity, during different exercise paradigms. We have designed a new swimming-based training protocol in order to draw a comparison between a high frequency and amplitude exercise (swimming) and low frequency and amplitude exercise (running). We initially analysed the time course of muscle adaptations to a 6- or 12-week swimming- or running-based training exercise program, on two muscles of the mouse calf, the slow-twitch soleus and the fast-twitch plantaris. The magnitude of exercise-induced muscle plasticity proved to be dependent on both the muscle type and the exercise paradigm. In contrast to the running-based training which generated a continuous increase of the slow phenotype throughout a 12-week training program, swimming induced transitions to a slower phenotype which ended after 6 weeks of training. We then compared the time course of the exercise-induced changes in calcineurin activity during muscle adaptation to training. Both exercises induced an initial activation followed by the inhibition of calcineurin. In the muscles of animals submitted to a 12-week swimming-based training, this inhibition was concomitant with the end of myofibre transition. Calcineurin inhibition was a consequence of the inhibition of its catalytic subunit gene expression on one hand, and of the expression increase of the modulatory calcineurin interacting proteins 1 gene (MCIP1), on the other. The present study provides the first experimental cues for an interpretation of muscle phenotypic variation control.     

Intransitive competition and its effects on community functional diversity

Can competitive interactions be inferred from the analysis of community functional diversity patterns? Originally, at the scale of a community, competitive interactions were supposed to generate trait overdispersion patterns due to limiting similarity process. More recently, by highlighting the importance of competitive hierarchies, it has been shown that when only one resource limits species coexistence, competition can also lead to patterns of trait clustering. However, these two expectations (overdispersion and clustering) ignore potential multi‐species indirect competitive interactions, and especially intransitive competition. Indeed, little is yet known about intransitive competition and its influence on community's functional diversity. Here I propose a brief appraisal of empirical evidence for intransitive competition in nature, and an overview of the current understanding of this mechanism and its properties. I then demonstrate with a theoretical model that intransitive competitive interactions can actually generate random‐like functional diversity patterns. The variety of diversity patterns (overdispersion, clustering, randomness) that can emerge from diverse types of competitive interactions makes it difficult to identify the presence of competition in nature, potentially leading to an underestimation of its importance as a structuring force. New methodologies able to capture both simple and complex competition mechanisms are thus urgently needed.     

Note Sui Grani a Spighe Ramificate

Resumé

Chez les Blés branchus de l'espèce «turgidum» (Triticum turgidum compositum), il existe des sortes à thermostade plutôt froid (Blés d'hiver ou de semi-hiver) et des sortes à thermostade chaud, tièe ou «indifférent» (Blés de printemps).

Les Blés branchus de l'espèce «turgidum» apparaissent comme étant des plantes à photostade de jour long.

La plus ou moins grande rapidité de l'accomplissement du photostade, par rapport à la rapidité de l'assimilation des matières plastiques, détermine la structure, — non ramifiée ou ramifiée — de l'épi.