Biology subjects

Van Dooren, T.

Publications and source records attributed to Van Dooren, T..

5 recordsLinked to original sources

bioRxiv2018

Mild drought induces phenotypic and DNA methylation plasticity but no transgenerational effects in Arabidopsis

Whether environmentally induced changes in phenotypes can be heritable is a topic with revived interest, in part because of observations in plants that heritable trait variation can occur without DNA sequence mutations. This other system of inheritance, called transgenerational epigenetics, typically involves differences in DNA methylation that are stable across multiple generations. However, it remains unknown if such a system responds to environmental changes and if it could therefore provide a rapid way for plants to generate adaptive heritable phenotypic variation. Here, we used a well-controlled phenotyping platform and whole-genome bisulfite sequencing to investigate potential heritable effects of mild drought applied over two successive generations in Arabidopsis thaliana. Plastic phenotypic responses were observed in plants exposed to drought. After an intervening generation without stress, descendants of stressed and non-stressed plants were phenotypically indistinguishable, except for very few trait-based parental effects, and irrespective of whether they were grown in control conditions or under water deficit. Moreover, while mild drought induced changes to the DNA methylome of exposed plants, DNA methylation variants were not inherited. These findings add to the growing body of evidence indicating that transgenerational epigenetics is not a common response of plants to environmental changes.

plant biology↗

bioRxiv2018

Predicting and Analyzing the Response to Selection on Correlated Characters

The breeders equation generally provides robust predictions for the short-term evolution of single characters. When selection targets two or more characters simultaneously, there are often large discrepancies between predicted and observed responses. We assessed how well this standard model predicts responses to bivariate selection on wing color pattern characteristics in the tropical butterfly Bicyclus anynana. In separate laboratory selection experiments, two sets of serially repeated eyespots were subjected to ten generations of concerted and antagonistic selection for either size or color composition. We compared predicted and actual selection responses over successive generations, using the phenotypic data, selection differentials, and estimates of the genetic variance-covariance matrix G. We found differences in the precision of predictions between directions of selection but did not find any evidence of systematic biases in our predictions depending on the direction of selection. Our investigation revealed significant environmental effects on trait evolution across generations. When these were accounted for, predictions using the standard model improved considerably. In the experiment on eyespot size, secondary splitting of selection lines allowed the estimation of changes in G after nine generations of selection. Changes were not in general agreement with expectations from the breeders equation. A contour plot of prediction errors across trait space suggests that directional epistasis in the eyespot genotype-phenotype map might occur but estimates of changes in G are too model-dependent to verify whether they agree with that hypothesis. Altogether, our results underscore the need for quantitative genetics to investigate and estimate potential effects of multivariate non-linear genotype-phenotype maps and of environmental effects on G.

evolutionary biology↗

bioRxiv2017

POLLINATOR SPECIES RICHNESS TRENDS: NO DECELERATING DECLINES IN DUTCH BEES AND BUMBLEBEES

Temporal trends (1946-2013) in the species richness of wild bees from the Netherlands are analysed. We apply two methods to estimate richness change which both incorporate models for sampling effects and detection probability. The analysis is repeated for records with specimens deposited in collections, and a subset restricted to spatial grid cells that have been sampled repeatedly across three periods. When fitting non-linear species accumulation curves to species numbers, declines are inferred for bumblebees and at most limited declines for other bees. Capture-recapture analysis applied to species encounter histories infers a constant colonization rate per year and constant (bumblebees) or decreasing (other) local species survival. However, simulations suggest that the method estimates time trends in survival with a negative bias. Species richness trends predicted by the second approach are a 10% reduction in non-Bombus species richness and 29% fewer Bombus species since 1946, comparable to the predictions of the first approach. Neither analysis provides reliable evidence that decelerating declines in species richness occur in these taxa. Therefore we should not infer decelerating declines in pollinator species richness in N-W Europe as previously claimed.

ecology↗

bioRxiv2017

Desiccation plasticity and diapause in the Argentinian pearlfish Austrolebias bellottii

BackgroundThe annual life history strategy with diapauses evolved repeatedly in killifish. To understand their and to characterize their variation between species, patterns of desiccation plasticity seem central. Plasticity might have played a role in the origin of these developmental arrests, when annual fish evolved from non-annual ones. The consequences of desiccation on survival and developmental rates of embryos of annual fish are poorly known. Using detailed demographic modelling of embryonal life histories, we investigate plasticity for desiccation in the Argentinian pearlfish Austrolebias bellottii. The treatment protocol contains changing environmental conditions with successive phases of mild desiccation and rewetting.\n\nResultsWe observed no clear diapause II and thus no increased incidence caused by mild and prolonged desiccation. Embryos arrest development in the pre-hatching stage (DIII) or in the dispersed cell phase (DI) irrespective of environmental conditions. There are limited effects of desiccation on survival, limited developmental delays and an acceleration of development into the pre-hatching stage. We found significant parental variance components on developmental rates, but hardly any effect of parental age. Hatching probabilities increased with age, when embryos had been in air at 100% RH and increased further when embryos were rewetted a second time after a two month interval.\n\nConclusionsMild desiccation and rewetting affect survival, rates of development and hatching probability, but not the fractions of embryos that arrest development in particular stages. We can conclude that the incidences of diapause have become relatively independent of the occurrence of mild desiccation, as if they have become assimilated. In contrast to the responses to mild desiccation observed in the non-annual rivulids, Austrolebias accelerates development into the pre-hatching stage.

evolutionary biology↗

bioRxiv2017

A case for sympatric speciation by cannibalism in South-American annual killifish (Austrolebias)

A trophic radiation in the South-American annual killifish genus Austrolebias has led to the evolution of large specialized piscivores from small generalized carnivores. It has been proposed that this occurred in a single series of vicariant speciation events. An alternative hypothesis is denoted giant-dwarf speciation: piscivores would have evolved in sympatry by character displacement and cannibalism. We test the plausibility of both scenarios using size measures combined with distributional data and new phylogenetic trees based on mitochondrial and nuclear molecular markers.\n\nOur analysis uses historical biogeography models and Ornstein-Uehlenbeck processes describing trait evolution across the posterior distributions of phylogenetic trees. Large species most likely evolved three times from small ones. For the clade containing A. elongatus, we argue that vicariance was not involved in the origin of these large and specialized piscivores. They experience stabilizing selection with an optimum shifted towards larger bodies and longer jaws. The branch leading to this clade has the fastest evolving jaw lengths across the phylogeny, in agreement with expectations for giant-dwarf speciation. For A. wolterstorffi, the support for giant-dwarf speciation is weaker. When the species is placed at the root of Austrolebias, ancestral reconstructions are unreliable and vicariance cannot be ruled out. For the remaining large species, we can reject vicariance and giant dwarf speciation. Our results give rise to two new additional scenarios for the evolution of specialized piscivores. In the first, two successive speciation events in sympatry or parapatry produced large and piscivorous species. In the second, the immigration of a different annual killifish genus (Cynopoecilus) in the Patos area of endemism has contributed to in-situ diversification of Austrolebias species.

evolutionary biology↗