Biology subjects

Jabbour-Zahab, R.

Publications and source records attributed to Jabbour-Zahab, R..

5 recordsLinked to original sources

bioRxiv2026

Environmental tolerance, species interaction, and the link between the fundamental and realized niches: Insights from a hypersaline planktonic system

The impacts of a changing abiotic environment on fitness and performance arise not only from low tolerance to new environmental conditions, but also from changes in the abundance and interaction intensity with other species. The strength of the interaction may itself depend on how well each species performs across environments, but there is a dearth of studies investigating how intrinsic fitness and interaction intensity covary across an abiotic environmental gradient. We addressed this question in a hypersaline consumer-resource system: the microalga Dunaliella spp. grazed by the brine shrimp Artemia franciscana. We exposed four Dunaliella strains to a range of salinities above seawater, with or without brine shrimps, and tracked their population sizes over time and the survival of their predators, to estimate basic parameters of a Lotka-Volterra model. We found that the intrinsic growth rate of algae, the survival rate of predators, and the per-capita predation rate, all varied with salinity and algal strain. Significant interactions between strain and salinity further revealed that these ecological responses to salinity are evolvable. Together with correlations between demographic parameters across salinity, this suggests that predation may influence the evolution of salinity tolerance curves, blurring the line between the fundamental and realized niches.

ecology↗

bioRxiv2022

Asexual male production by ZW recombination in Artemia parthenogenetica

In some asexual species, parthenogenetic females occasionally produce males, which may strongly affect the evolution and maintenance of asexuality if they cross with related sexuals and transmit genes causing asexuality to their offspring ("contagious parthenogenesis"). How these males arise in the first place has remained enigmatic, especially in species with sex chromosomes. Here, we test the hypothesis that rare, asexually produced males of the crustacean Artemia parthenogenetica are produced by recombination between the Z and W sex chromosomes during non-clonal parthenogenesis, resulting in ZZ males through loss of heterozygosity at the sex determination locus. We used RAD-sequencing to compare asexual mothers with their male and female offspring. Markers on several sex-chromosome scaffolds indeed lost heterozygosity in all male but no female offspring, suggesting that they correspond to the sex-determining region. Other sex-chromosome scaffolds lost heterozygosity in only a part of the male offspring, consistent with recombination occurring at a variable location. Alternative hypotheses for the production of these males (such as partial or total hemizygosity of the Z) could be excluded. Rare males are thus produced because recombination is not entirely suppressed during parthenogenesis in A. parthenogenetica. This finding may contribute to explaining the maintenance of recombination in these asexuals.

evolutionary biology↗

bioRxiv2021

The origin of asexual brine shrimps

Determining how and how often asexual lineages emerge within sexual species is central to our understanding of sex-asex transitions and the long-term maintenance of sex. Asexuality can arise "by transmission" from an existing asexual lineage to a new one, through different types of crosses. The occurrence of these crosses, cryptic sex, variation in ploidy and recombination within asexuals greatly complicates the study of sex-asex transitions, as they preclude the use of standard phylogenetic methods and genetic distance metrics. In this study we show how to overcome these challenges by developing new approaches to investigate the origin of the various asexual lineages of the brine shrimp Artemia parthenogenetica. We use a large sample of asexuals, including all known polyploids, and their sexual relatives. We combine flow cytometry with mitochondrial and nuclear DNA data. We develop new genetic distance measures and methods to compare various scenarios describing the origin of the different lineages. We find that all diploid and polyploid A. parthenogenetica likely arose within the last 80,000 years through successive and nested hybridization events that involved backcrosses with different sexual species. All A. parthenogenetica have the same common ancestor and therefore likely carry the same asexuality gene(s) and reproduce by automixis. These findings radically change our view of sex-asex transitions in this group, and show the importance of considering asexuality "by transmission" scenarios. The methods developed are applicable to many other asexual taxa.

evolutionary biology↗

bioRxiv2021

Strong transgenerational effects but no genetic adaptation in zooplankton 24 years after an abrupt +10°C climate change

The climate is currently warming fast, threatening biodiversity all over the globe. Adaptation is often rapid when the environment changes quickly, but for climate warming very little evidence is available. Here, we investigate the pattern of adaptation to an extreme +10{degrees}C climate change in the wild, following the introduction of brine shrimp Artemia franciscana from San Francisco Bay, USA, to Vinh Chau saltern in Vietnam. We use a resurrection ecology approach, hatching diapause eggs from the ancestral population and the introduced population after 13 and 24 years (resp. ~54 and ~100 generations). In a series of coordinated experiments, we determined whether the introduced Artemia show increased tolerance to higher temperatures, and the extent to which genetic adaptation, developmental plasticity, transgenerational effects, and local microbiome differences contributed to this tolerance. We find that introduced brine shrimp do show increased phenotypic tolerance to warming. Yet strikingly, these changes do not have an additive genetic component, are not caused by mitochondrial genetic variation, and are not caused by epigenetic marks set by adult parents exposed to warming. Further, we do not find any developmental plasticity in response to warming, nor any protective effect of heat-tolerant local microbiota. We conclude that the evolution of shrimps extreme thermal tolerance is only due to transgenerational (great)grandparental effects, possibly epigenetic marks set by parents who were exposed to high temperatures as juveniles. This finding challenges standard models of genetic and plastic adaptive responses, and our conception of how species may cope with climate warming. Significance statementAdaptation is often rapid when environments change quickly, but for climate warming little evidence is available. Many studies report no genetic responses due to pre-existing plasticity, while others point towards epigenetics and microbiota effects. In this study, we take advantage of a natural experiment to study all of these effects. We use a set of coordinated experiments and a resurrection ecology approach, reviving resting eggs of brine shrimp up to100 generations after their introduction from a temperate to a tropical saltern. We find that heat adaptation occurs, but heritability is fully "missing". Plasticity and microbiota play no role either, indicating that only transgenerational (great)grandmaternal effects are involved. This finding prompts us to reconsider the relative importance of the different possible mechanisms by which phenotypic change can occur, especially in response to temperature variation.

evolutionary biology↗

bioRxiv2018

Long-term prevalence data reveals spillover dynamics in a multi-host (Artemia), multi-parasite (Microsporidia) community

In the study of multi-host parasites, it is often found that host species contribute asymmetrically to parasite transmission, with cascading effects on parasite dynamics and overall community structure. Yet, identifying which of the host species contribute to parasite transmission and maintenance is a recurring challenge. Here, we approach this issue by taking advantage of natural variation in the community composition of host species. We studied the horizontally transmitted microsporidians Anostracospora rigaudi and Enterocytospora artemiae in a Southern French metacommunity of their brine shrimp hosts, Artemia franciscana and Artemia parthenogenetica. Within the metacommunity, patches can contain either or both of the Artemia host species, so that long-term prevalence data can provide a direct link between the presence of the two host species and the persistence of the two parasites. First, we show that the microsporidian A. rigaudi is a spillover parasite: it was unable to persist in the absence of its maintenance host A. parthenogenetica. This result was particularly striking in light of A. rigaudis high prevalence (in the field) and high infectivity (when tested in the lab) in both hosts. Moreover, A. parthenogeneticas seasonal presence imposed seasonality on the rate of spillover, causing cyclical pseudo-endemics in the spillover host A. franciscana. Second, while our prevalence data was sufficient to identify E. artemiae as either a spillover or a facultative multi-host parasite, we could not distinguish between the two possibilities. This study supports the importance of studying the community context of multi-host parasites, and demonstrates that in appropriate multi-host systems, sampling across a range of conditions and host communities can lead to clear conclusions about the drivers of parasite persistence.

ecology↗