Biology subjects

Olivieri, E.

Publications and source records attributed to Olivieri, E..

5 recordsLinked to original sources

bioRxiv2026

Reproductive isolation emerges from coordinated barriers during mating system divergence in plants

Background and AimsUnderstanding how reproductive barriers combine to restrict gene flow remains a central challenge in speciation research. Although reproductive isolation is inherently a composite process, most empirical studies have focused on individual barriers in isolation, limiting our ability to capture their joint effects particularly in systems undergoing evolutionary transitions such as shifts in mating system. MethodsHere, we provide a comprehensive, life-cycle-wide quantification of reproductive isolation between two closely related species of the Erysimum incanum complex that differ strikingly in mating system: the predominantly selfing E. incanum and the outcrossing E. wilczekianum. Key ResultsBy integrating ecological, phenological, behavioural, and post-pollination components, we show that total reproductive isolation is nearly complete (T{approx}0.999), but overwhelmingly driven by pre-pollination barriers. Ecogeographical differentiation and, most prominently, pollinator-mediated isolation dominate, with pollinators exhibiting a strong bias toward E. wilczekianum. Floral traits linked to mating system divergence, particularly flower size, emerge as key drivers of assortative mating, supporting their role as "magic traits" coupling ecological divergence with reproductive isolation. In contrast, post-pollination barriers are weaker but strongly asymmetric. Hybrid seed formation is largely prevented when E. wilczekianum acts as the maternal parent, consistent with expectations from mating system differences, whereas reciprocal crosses are relatively successful. Despite reduced germination, hybrids display enhanced growth and no evidence of hybrid breakdown, suggesting that intrinsic incompatibilities remain incomplete. ConclusionsThese findings reveal that mating system divergence restructures the entire architecture of reproductive isolation rather than acting as a single barrier. More broadly, our results highlight that early-stage speciation can be driven by coordinated shifts in ecological and reproductive traits, emphasizing the need for integrative approaches to fully understand how barriers interact to generate species boundaries.

plant biology↗

bioRxiv2023

Effects of ploidy and genetic diversity on competitive outcomes.

O_LIGenetic diversity affects evolutionary trajectories but their ultimate effects on ecological interactions and community dynamics remains poorly understood. It has been hypothesized that phenotypic novelties produced by ploidy and heterozygosity modify the ecological interactions between novel genotypes and more ancient locally adapted ones, and therefore, their opportunities to coexist. C_LIO_LIWe performed a greenhouse competition experiment with three taxa of the Erysimum incanum species complex differing in ploidy (2x, 4x and 6x) and heterozygosity (high and low). This experiment allows us to parameterize a population model to test the effect of genetic diversity on modulating the ecological forces that determine the outcome of competition, niche and fitness differences. C_LIO_LIDepending on whether ploidy variation and the level of heterozygosity made interspecific competition greater or smaller than intraspecific competition, we predicted either priority effects or coexistence. Such competitive outcome differences were explained by the phenotypic expression in the number of stalks (plant size surrogate) with genotypes under priority effects showing more stalks. C_LIO_LIAltogether, our results show that non-polyploid plants can coexist with polyploids contravening theoretical expectations of polyploidy dominance under stable conditions. However, historical contingency such as order of arrival promotes priority effects when adaptive phenotypic optimums strongly compete for space. C_LI

ecology↗

bioRxiv2022

The origin and evolution of mitochondrial tropism in Midichloria bacteria

Midichloria are intracellular bacterial symbionts of ticks. Some representatives of this genus have the unique capability to colonize mitochondria in the cells of their hosts. Hypotheses on the nature of this interaction have proven difficult to test, partly due to a lack of data. Indeed, until now, mitochondrial tropism information and genomes were available only for symbionts of three and two tick host species, respectively. Here we analyzed the mitochondrial tropism of three additional Midichloria and sequenced nine novel genomes, showing that the tropism is pnon-monophyletic, either due to losses of the trait or multiple parallel acquisitions. Comparative genome analyses support the first hypothesis, as the genomes of non-mitochondrial symbionts appear to be reduced subsets of those capable of colonizing the organelles. We detect genomic signatures of mitochondrial tropism, showing a set of candidate genes characteristic of the strains capable of mitochondrial colonization. These include the type IV secretion system and the flagellum, which could allow the secretion of unique effectors, direct interaction with, or invasion of the mitochondria. Other genes, including putative adhesion molecules, proteins possibly involved in actin polymerization, cell wall and outer membrane proteins, are only present in mitochondrial symbionts. The bacteria could use these to manipulate host structures, including mitochondrial membranes, in order to fuse with the organelles or manipulate the mitochondrial network.

evolutionary biology↗

bioRxiv2021

A dual endosymbiosis drives nutritional adaptation to hematophagy in the invasive tick Hyalomma marginatum

Many animals are dependent on microbial partners that provide essential nutrients lacking from their diet. Ticks, whose diet consists exclusively on vertebrate blood, rely on maternally inherited bacterial symbionts to supply B vitamins. While previously studied tick species consistently harbor a single lineage of those nutritional symbionts, we evidence here that the invasive tick Hyalomma marginatum harbors a unique dual-partner nutritional system between an ancestral symbiont, Francisella, and a more recently acquired symbiont, Midichloria. Using metagenomics, we show that Francisella exhibits extensive genome erosion that endangers the nutritional symbiotic interactions: Its genome includes folate and riboflavin biosynthesis pathways but deprived functional biotin biosynthesis on account of massive pseudogenization. Co-symbiosis compensates this deficiency since the Midichloria genome encompasses an intact biotin operon, which was primarily acquired via lateral gene transfer from unrelated intracellular bacteria commonly infecting arthropods. Thus, in H. marginatum, a mosaic of co-evolved symbionts incorporating gene combinations of distant phylogenetic origins emerged to prevent the collapse of an ancestral nutritional symbiosis. Such dual endosymbiosis was never reported in other blood feeders but was recently documented in agricultural pests feeding on plant sap, suggesting that it may be a key mechanism for advanced adaptation of arthropods to specialized diets.

evolutionary biology↗

bioRxiv2020

Sequence of a Coxiella endosymbiont of the tick Amblyomma nuttalli suggests a pattern of convergent genome reduction in the Coxiella genus

Ticks require bacterial symbionts for the provision of necessary compounds that are absent in their hematophagous diet. Such symbionts are frequently vertically transmitted and, most commonly, belong to the Coxiella genus, which also includes the human pathogen Coxiella burnetii. This genus can be divided in four main clades, presenting partial but incomplete co-cladogenesis with the tick hosts. Here we report the genome sequence of a novel Coxiella, endosymbiont of the African tick Amblyomma nuttalli, and the ensuing comparative analyses. Its size ([~]1 Mb) is intermediate between symbionts of Rhipicephalus species and other Amblyomma species. Phylogenetic analyses show that the novel sequence is the first genome of the B clade, the only one for which no genomes were previously available. Accordingly, it allows to draw an enhanced scenario of the evolution of the genus, one of parallel genome reduction of different endosymbiont lineages, which are now at different stages of reduction from a more versatile ancestor. Gene content comparison allows to infer that the ancestor could be reminiscent of Coxiella burnetii. Interestingly, the convergent loss of mismatch repair could have been a major driver of such reductive evolution. Predicted metabolic profiles are rather homogenous among Coxiella endosymbionts, in particular vitamin biosynthesis, consistently with a host-supportive role. Concurrently, similarities among Coxiella endosymbionts according to host genus and despite phylogenetic unrelatedness hint at possible host-dependent effects. Significance statementThe genus Coxiella includes the pathogen Coxiella burnetii and widespread nutritional mutualists in ticks. Current knowledge on their evolution is hampered by the limited genomic resources available. Here we provide the first genome sequence of a Coxiella endosymbiont of clade B, the only clade for which none was available. These data allow to infer an evolutionary scenario of parallel genome reduction among Coxiella endosymbionts, with similar constraints, leading to selective retention of biosynthetic pathways beneficial for the host. The combined predicted functional capabilities of the symbionts appear to be a subset of those of C. burnetii. Accordingly, this pathogen could be closer to an ancestral state of the endosymbionts, rather than being derived from an endosymbiotic ancestor, as previously hypothesized.

genomics↗