Environmental variation in sex ratios and sexual dimorphism in three wind‐pollinated dioecious plant species

Variation in plant sex ratios is often attributable to sex-specific mortality in heterogeneous environments that differentially limit male and female plant reproduction. Yet sexual dimorphism and plastic responses to environmental heterogeneity are common and may co-vary with variation in sex ratios. Here, we show that the sex ratio and the degree of sexual dimorphism for a number of plant traits varied along climatic and elevation gradients in three wind-pollinated dioecious species, Rumex lunaria, Urtica dioica and Salix helvetica. Some of the observed sex-specific responses to climatic variation are consistent with greater sensitivity of females to water scarcity, but most responses rather point to the greater sensitivity of males to ecological stress, consistent with larger male reproductive effort, as has been commonly reported for wind-pollinated plants. In contrast, we found no evidence for variation in either sex ratios or sexual dimorphism expected under sexual selection. Interestingly, sex ratios and sexual dimorphism varied both along distinct and the same ecological axes of variation, suggesting that the evolution of sexual dimorphism in the measured traits was not sufficient to prevent sex-specific mortality

Functional traits explain the Hutchinsonian niches of plant species

CITATION: Martina, T. et al. 2019. Functional traits explain the Hutchinsonian niches of plant species. Global Ecology and Biogeography, 29(3):534–54. doi:10.1111/geb.13048The original publication is available at https://onlinelibrary.wiley.com/journal/14668238Aim: The Hutchinsonian niche is a foundational concept in ecology and evolutionary biology that describes fundamental characteristics of any species: the global maximum population growth rate (rmax); the niche optimum (the environment for which rmax is reached); and the niche width (the environmental range for which intrinsic population growth rates are positive). We examine whether these characteristics are related to inter- and intraspecific variation in functional traits. Location: Cape Floristic Region, South Africa. Time period: Present day. Major taxa studied: Twenty-six plant species (Proteaceae). Methods: We measured leaf, plant-architectural and seed traits across species geographical ranges. We then examined how species-mean traits are related to demographically derived niche characteristics of rmax, in addition to niche optima and widths in five environmental dimensions, and how intraspecific trait variation is related to niche widths. Results: Interspecific trait variation generally exceeded range-wide intraspecific trait variation. Species-mean trait values were associated with variation in rmax (R2 = 0.27) but were more strongly related to niche optima (mean R2 = 0.56). These relationships generally matched trait–environment associations described in the literature. Both species-mean traits and intraspecific trait variability were strongly related to niche widths (R2 = 0.66 and 0.59, respectively). Moreover, niche widths increased with intraspecific trait variability. Overall, the different niche characteristics were associated with few, largely non-overlapping sets of traits. Main conclusions: Our study relating functional traits to Hutchinsonian niches demonstrates that key demographic properties of species relate to few traits with relatively strong effects. Our results further support the hypothesis that intraspecific trait variation increases species niche widths. Given that niche characteristics were related to distinct sets of traits, different aspects of environmental change might affect axes of trait variation independently. Trait-based studies of Hutchinsonian niches thus yield important insights into the mechanisms shaping functional biodiversity, which should reinforce the role of traits in functional biogeography.https://onlinelibrary.wiley.com/doi/10.1111/geb.13048Publishers versio

Evolution of fire adaptation in plants : the case of the south-african fynbos

Dans les milieux soumis au feu, les plantes ont développé une diversité de stratégies d'histoire de vie qui sont supposément adaptées à différentes conditions environnementales, comme différents régimes de feu. Au cours de ma thèse, j'ai cherché à expliquer la diversité de stratégies adoptées par les plantes pérennes en cherchant à déterminer comment des facteurs intrinsèques et extrinsèques ont influencé l'évolution de ces traits d'histoire de vie. Mais également si cette connaissance peut nous permettre d'améliorer notre compréhension de l'impact à venir de changements environnementaux ou renseigner des politiques de conservation. Les régimes de feux ont été proposés comme étant une force sélective majeure influençant les traits d'histoire de vie dans les milieux soumis au feu. J'ai donc particulièrement étudié l'impact de la distribution des intervalles de feux. Un modèle d'optimisation d'allocation des ressources a été construit afin d'étudier les stratégies d'histoire de vie optimales sous différents régimes de feu. Ce modèle prédit qu'il est optimal de diminuer l'allocation des ressources au maintien des cônes lorsque la variance des intervalles de feu augmente et lorsque la disponibilité en ressources diminue. De même, les prédictions montrent que l'allocation des ressources à la sérotinie diminue lorsque la disponibilité des ressources diminue au profit de l'allocation à la croissance et à la production de graines. De façon, à tester ces prédictions, nous utilisons des analyses comparatives appliquées le long d'une nouvelle phylogénie du genre Leucadendron. Un protocole de recherche de marqueurs permettant de maximiser le polymorphisme et la probabilité d'orthologie de ceux-ci a été construit de façon à définir de nouveaux marqueurs spécifiques du genre Leucadendron. L'estimation des valeurs de traits d'histoire de vie le long de cette nouvelle phylogénie montre une évolution complexe de tous les traits d'histoire de vie considérés ainsi qu'une évolution conjointe entre certains traits d'histoire de vie. Des analyses comparatives prenant en compte l'incertitude phylogénétique et la variabilité environnementale intra-spécifique, montrent notamment que les espèces sérotineuses ont évolué des niches environnementales impliquant des événements climatiques extrêmes (i.e. sécheresse et gel) moins importants que les espèces avec banques de graines dans le sol. De même, les espèces non-réitératives semblent avoir été moins tolérantes que les espèces réitératives à des événements climatiques extrêmes.In fire-prone environments, plants have developed a huge diversity of life history strategies that aresupposed to be adapted to different environmental conditions such as several fire regimes. My PhDproject aimed at explaining the large diversity of life history strategies of perennial plants, focusingon how intrinsic and extrinsic factors have shaped the evolution of those traits. I particularly ask, ifsuch knowledge can be used to understand the impact of future environmental changes onbiological diversity ? And finally, how does this apply to conservation policies and the maintenanceof such diversity? Because contrasted fire regimes have been suggested as a major selective factorinfluencing plant traits in fire-prone environments, I especially investigated the effect of the fireregime in terms of distribution probabilities of fire intervals. A model of optimization of resourceallocation for a serotinous non-resprouting plant predict that whenever maximal plant survivalprobability is low, the optimal strategy consists in reducing resource allocation to seed maintenancein the canopy, while increasing resource allocation to annual seed production. The model alsopredict that a low level of serotiny should evolve when the predictability of fire arrival is low, that iswhen there is a large variance in fire intervals. In order to test those predictions, I used comparativeanalyses along the newly reconstructed phylogeny of the Leucadendron genus. A bioinformaticspipeline allowed designing new nuclear markers, maximizing both polymorphism and probability oforthology that can be further used to construct the Leucadendron phylogeny. This approachgenerated seven new markers of which three contained a polymorphic 3'-UTR region. Life historytrait are further estimated along branches of this new phylogeny to assess whether life history traitswere labile across the evolutionary history of the genus. This analysis show that all five studiedtraits emerged independently several times and in correlation with one another. The joint evolutionof fire-related traits and ecological niches are finally studied to test hypotheses partly inspired byour theoretical work. Comparative analyses that account for phylogenetic uncertainty, traitreconstruction uncertainty and environmental intra-specific variability show that serotinous speciesevolved ecological niches characterised by less extreme climatic events than species havingunderground seed banks. Similarly, non-resprouting species evolved niches including less extremeclimatic events than resprouting species

Do metrics of sexual selection conform to Bateman's principles in a wind-pollinated plant?

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Decline and structural changes in the population and groups of the Mayotte brown lemur (Eulemur fulvus)

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Genotype and morphological data of Mercurialis annua selection gradient analysis

In a common garden at low-density and another common garden at high-density, a set of vegetative and reproductive traits have been measured in males and females of Mercurialis annua. Genotype data on height microsatellites have also been produced for all males and females along with respectively 642 and 657 juveniles for the high- and low-density garden grown from seeds sampled on the study females

Data from: Sex-specific selection on plant architecture through 'budget' and 'direct' effects in experimental populations of a wind-pollinated herb

Sexual selection may contribute to the evolution of plant sexual dimorphism by favoring architecture traits that improve pollen dispersal to mates in males. In both sexes, larger individuals may be favored if large size allows the allocation of more resources to gamete production (a ‘budget’ effect of size). In wind-pollinated plants, large size may also benefit males if it allows them to liberate pollen from greater heights, fostering its dispersal (a ‘direct’ effect of size). To assess these effects and their implications for trait selection, we measured selection gradients on plant morphology in both males and females, as well as pollen production and dispersal in males, of the wind-pollinated dioecious herb Mercurialis annua. In two separate experimental common gardens established at different densities, selection strongly favored plants dispersing their pollen further. Selection for pollen production was observed in the high-density garden only and was weak. In addition, male morphologies associated with increased mean pollen dispersal differed between the two gardens as elongated branches were favored in the high-density garden while shorter plants with longer peduncles bearing inflorescences were advantaged the low-density garden. Larger females were selected in both gardens. Our results point to the importance of selection on male traits that affect pollen dispersal, and to a lesser extent pollen production

Data from: Sex-specific selection on plant architecture through 'budget' and 'direct' effects in experimental populations of a wind-pollinated herb

Sexual selection may contribute to the evolution of plant sexual dimorphism by favoring architecture traits that improve pollen dispersal to mates in males. In both sexes, larger individuals may be favored if large size allows the allocation of more resources to gamete production (a ‘budget’ effect of size). In wind-pollinated plants, large size may also benefit males if it allows them to liberate pollen from greater heights, fostering its dispersal (a ‘direct’ effect of size). To assess these effects and their implications for trait selection, we measured selection gradients on plant morphology in both males and females, as well as pollen production and dispersal in males, of the wind-pollinated dioecious herb Mercurialis annua. In two separate experimental common gardens established at different densities, selection strongly favored plants dispersing their pollen further. Selection for pollen production was observed in the high-density garden only and was weak. In addition, male morphologies associated with increased mean pollen dispersal differed between the two gardens as elongated branches were favored in the high-density garden while shorter plants with longer peduncles bearing inflorescences were advantaged the low-density garden. Larger females were selected in both gardens. Our results point to the importance of selection on male traits that affect pollen dispersal, and to a lesser extent pollen production

On the function of flower number: disentangling fertility from pollinatormediated selection

In animal-pollinated angiosperms, the "male-function" hypothesis claims that male reproductive success should benefit from large floral displays, through pollinator attraction, while female reproductive success is expected to be mainly limited by resource availability. As appealing as this theory might be, studies comparing selection strength on flower number in both sexes rarely document the expected asymmetry. This discrepancy could arise because flower number impacts both pollinator attraction and overall gamete number. In this study, we artificially manipulate floral displays to disentangle the fertility versus pollinator attraction components of selection, both in terms of mating and reproductive success. In females, flower number was under strong fertility selection, as predicted in the absence of pollen limitation. In contrast, in males, flower number was mainly under sexual selection, which in turn increased male reproductive success. However, these selection patterns were not different in males with artificially increased floral displays. This suggests that sexual selection acting on flower number in males do not occur because flower number increases pollinator attraction, but rather because more pollen is available to disperse on more mates. Our study illustrates the power of disentangling various components of selection with potentially sex-specific effects for understanding the evolution of sexual dimorphism

The Scope for Postmating Sexual Selection in Plants

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