After-life effects: Living and dead invertebrates differentially affect plants and their associated above- and belowground multitrophic communities

Plant science

The use of living labs to advance agro-ecological theory in the transition towards sustainable land use: a tale of two polders

Environmental Biolog

Reduced fertilization constitutes an important prezygotic reproductive barrier between two sibling species of the hybridizing Brachionus calyciflorus species complex

Brachionus calyciflorus is a species complex consisting of four recently described species. Although several lines of evidence support their species status, hybridization between two of the sibling species B. calyciflorus s.s. and B. elevatus has been inferred from both field and laboratory studies. In this study, we tested for the existence of prezygotic barriers between these species by performing two types of cross-fertilization experiments. In a ‘mate competition’ experiment we exposed mictic females to equal numbers of conspecific and allospecific males and demonstrate that intraspecific fertilizations occur at much higher frequencies than interspecific fertilizations, providing evidence for a strong prezygotic reproductive barrier. This result was consistent across numerous combinations of parental genotypes. In addition, by creating interspecific combinations of mictic females and males in a ‘no choice’ experiment, we found that interspecific fertilization success is independent of fertilization direction while it does seem to depend on maternal genotype. Our results demonstrate the existence of a strong prezygotic barrier that may play an important role in the maintenance of species boundaries. Yet, the observation of hybrids also shows a potential for gene flow between the species through hybridization

Monogonont rotifers as model systems for the study of micro-evolutionary adaptation and its eco-evolutionary implications

A better understanding of the ability of organisms to adapt to local selection conditions is essential for a better insight in their ecological dynamics. The study of micro-evolutionary adaptation and its eco-evolutionary consequences is challenging for many reasons and the choice of a suitable model organism is particularly important. In this paper, we explain why monogonont rotifers, through their unique combination of traits, are ideal study organisms for this purpose. With a literature review, we demonstrate the capacity of monogonont populations to adapt to a variety of selection conditions (e.g., salinity, food shortage, elemental limitation, and disturbance regimes) within very short-time frames and highlight some potential eco-evolutionary implications. Although monogononts are increasingly used in eco-evolution-oriented studies, their potential is still underappreciated compared to other model organisms. No doubt the high prevalence of cryptic species complexes and the lack of genomic tools form important obstacles that may discourage researchers to work with this group. Here, we argue that none of these difficulties should prevent monogonont rotifers from becoming commonly used model organisms in micro-evolutionary studies and make suggestions for future research

Genetic differentiation in life history between Daphnia galeata population: an adaptation to local predations regimes?

Species of the water flea Daphnia exhibit constitutive as well as phenotypically inducible anti-predator defence strategies, involving life history, morphological and behavioural traits. We explored the hypothesis of genetic differentiation in anti-predator defence strategies using Daphnia clones originating from two different water bodies: Tjeukemeer (the Netherlands) and Fish Pond (Belgium). Both water bodies are inhabited by zooplanktivorous fish. In contrast to Tjeukemeer, Fish Pond is also inhabited by larvae of the phantom midge Chaoborus. The life history responses of the two sets of clones to kairomones from fish (Perca), to kairomones from Chaoborus, and to a mixture of both were compared. Clones from Tjeukemeer and Fish Pond showed strong responses to the presence of fish kairomone, with reductions in adult and neonate body length, in age at first reproduction and in the total number of neonates produced during the first three adult instars. Responses to Chaoborus kairomone were much less pronounced, although there was a tendency towards an increase in the number of neonates in the first brood. Significant inter-population genetic differences were found for all the investigated traits. However, there was no indication for genetic adaptation of the Fish Pond clones to negative size-selective predation by Chaoborus. Compared to Tjeukemeer clones, Fish Pond clones had a lower size at first reproduction, produced smaller neonates and produced a higher number of neonates in their first brood. This suggests adaptation to positive rather than to negative size selective predation. Genetic differences between populations were observed mainly for constitutive life history traits, rather than for phenotypic shifts in response to the presence of predator kairomones

Experimental evidence of rapid heritable adaptation in the absence of initial standing genetic variation

The success of genetically depauperate populations in the face of environmental change is contrary to the expectation that high genetic diversity is required for rapid adaptation. Alternative pathways such as environmentally induced genetic modifications and non-genetic heritable phenotypes have been proposed mechanisms for heritable adaptation within an ecologically relevant time frame. However, experimental evidence is currently lacking to establish if, and to what extent, these sources of phenotypic variation can produce a response. To test if adaptation can rapidly occur in the absence of initial standing genetic variation and recombination in small populations, we (a) exposed replicate monoclonal populations of the microzooplankton Brachionus calyciflorus to a culturing regime that selected for phenotypic variants with elevated population growth with either high or low phosphorus food for a period of 55 days and (b) examined population level response in two fully factorial common garden experiments at day 15 and 35 of the exposure experiment. Within six generations, we observed heritable local adaptation to nutrient limitation. More specifically, populations with a history of exposure to low P food exhibited higher population growth rates under low P food conditions than populations with a high P exposure history. However, the capacity for such a response was found to vary among clones. Our study finds that although standing genetic variation is considered essential for rapid heritable adaptation, the rapid emergence of de novo genetic variation or alternative sources of phenotypic variation could aid in the establishment and persistence of low-diversity populations

Effects of connectivity, dispersal directionality and functional traits on the metacommunity structure of river benthic diatoms

Aim Dendritic ecological networks (DENs), such as river systems, combine features that challenge the traditional conceptual views and empirical approaches applied to metacommunities. As a result of their dendritic branching geometry and stream flow directionality, they are strongly hierarchical and asymmetrical. We analysed the metacommunity structure of benthic diatoms in a large-scale river system with the aim of evaluating the importance of potential causal influences. Furthermore, we hypothesized that metacommunities of diatoms that are strongly attached to their substrata show a different spatial structure than metacommunities of other, more weakly attached diatoms. Location The study was carried out in the Dong River, a 32,275 km2 subtropical river network located in southern China. Methods We surveyed benthic diatom communities during three seasons (dry, intermediate and wet). Using partial redundancy analysis, we partitioned community variation among environmental models and different spatial eigenfunction models to evaluate the influence of alternative dispersal pathways (overland versus water course dispersal), stream directionality, man-made dams and diatom functional traits on diatom metacommunity structure. Results Models based on hydrological connections and water directionality represent spatial patterns better than overland distances, suggesting that the dynamics of benthic diatom metacommunities are mainly confined to the river network and influenced by the prevailing water flow. We found significant effects of man-made dams on the spatial structure of important limnological variables and diatom metacommunity structure. The metacommunity of strongly attached diatoms also showed a weaker signature of flow directionality than that of other growth forms, especially in seasons with high water levels. Main conclusions We conclude that the consideration of among-site connectivity, flow directionality and species traits is key to a better understanding of the spatial ecology of passively dispersing microbial organisms in river systems.