Biology subjects

Jaron, K.

Publications and source records attributed to Jaron, K..

4 recordsLinked to original sources

bioRxiv2026

Hybrid breakdown is temporary and not expressed in a novel environment during 50 generations of experimental evolution in Tetranychus urticae hybrids

Hybridization, the interbreeding between species or genetically distinct populations, can lead to deleterious fitness consequences, but simultaneously it can boost adaptive potential by increasing genetic variation, especially in novel environments. However, how incompatibilities and beneficial genetic combinations interplay across generations remains poorly understood. Here, we tracked how two fitness proxies, the absolute number of adult offspring and the proportion of eggs that reached adulthood, evolve in parental and hybrid populations at three different time points over 50 generations, in both novel and ancestral environments. To test this, we used two geographically distinct populations with low divergence (Dxy=0.002) of the two-spotted spider mite (Tetranychus urticae). Across the first three generations, hybrids showed significantly lower fitness than parental populations in the ancestral environment, indicating incompatibilities between the parental genomes. In contrast, hybrid and parental fitnesses were similar in the novel environment, indicating that the impact of incompatibilities was minor compared to the selection imposed by the novel environment. However, after 50 generations, hybrids displayed similar fitness relative to parental populations in all environments, suggesting resolution of the incompatibilities. Furthermore, around generation 45, hybrids temporarily outperformed parental populations in a novel environment, suggesting a transient window of higher adaptive potential, before fitness stabilized again by generation 50. In conclusion, we show that hybrid populations of T. urticae can swiftly purge incompatibilities when genetic divergence is low. These findings suggest that the dynamics of incompatibility resolution and adaptive potential of novel haplotypes play out over a long time frame, highlighting the importance of tracking hybrid fitness past the first few generations.

evolutionary biology↗

bioRxiv2025

Forty New Genomes Shed Light on Sexual Reproduction and the Origin of Tetraploidy in Microsporidia

Microsporidia are single-celled, obligately intracellular parasites with growing public health, agricultural, and economic importance. Despite this, Microsporidia remain relatively enigmatic, with many aspects of their biology and evolution unexplored. Key questions include whether Microsporidia undergo sexual reproduction, and the nature of the relationship between tetraploid and diploid lineages. While few high-quality microsporidian genomes currently exist to help answer such questions, large-scale biodiversity genomics initiatives, such as the Darwin Tree of Life project, can generate high-quality genome assemblies for microsporidian parasites when sequencing infected host species. Here, we present 40 new microsporidian genome assemblies from infected arthropod hosts that were sequenced to create reference genomes. Out of the 40, 32 are complete genomes, eight of which are chromosome-level, and eight are partial microsporidian genomes. We characterised 14 of these as polyploid and five as diploid. We found that tetraploid genome haplotypes are consistent with autopolyploidy, in that they coalesce more recently than species, and that they likely recombine. Within some genomes, we found large-scale rearrangements between the homeologous genomes. We also observed a high rate of rearrangement between genomes from different microsporidian groups, and a striking tolerance for segmental duplications. Analysis of chromatin conformation capture (Hi-C) data indicated that tetraploid genomes are likely organised into two diploid compartments, similar to dikaryotic cells in fungi, with evidence of recombination within and between compartments. Together, our results provide evidence for the existence of a sexual cycle in Microsporidia, and suggest a model for the microsporidian lifecycle that mirrors fungal reproduction.

genomics↗

bioRxiv2021

Monomorphic Trypanozoon: towards reconciling phylogeny and pathologies

2.Trypanosoma brucei evansi and Trypanosoma brucei equiperdum are animal infective trypanosomes conventionally classified by their clinical disease presentation, mode of transmission, host range, kDNA composition and geographic distribution. Unlike other members of the subgenus Trypanozoon, they are non-tsetse transmitted and predominantly morphologically uniform (monomorphic) in their mammalian host. Their classification as independent species or subspecies has been long debated and genomic studies have found that isolates within T. b. evansi and T. b. equiperdum have polyphyletic origins. Since current taxonomy does not fully acknowledge these polyphyletic relationships, we re-analysed publicly available genomic data to carefully define each clade of monomorphic trypanosome. This allowed us to identify, and account for, lineage specific variation. We included a recently published isolate, IVM-t1, which was originally isolated from the genital mucosa of a horse with dourine and typed as T. equiperdum. Our analyses corroborate previous studies in identifying at least four distinct monomorphic T. brucei clades. We also found clear lineage specific variation in the selection efficacy and heterozygosity of the monomorphic lineages, supporting their distinct evolutionary histories. The inferred evolutionary position of IVM-t1 suggests its reassignment to the T. b. evansi type B clade, challenging the relationship between the Trypanozoon species, the infected host, mode of transmission and the associated pathological phenotype. The analysis of IVM-t1 also provides the first evidence of the expansion of T. b. evansi type B, or a 5th monomorphic lineage represented by IVM-t1, outside of Africa, with important possible implications for disease diagnosis. 3. Impact statementTrypanosoma brucei are unicellular parasites typically transmitted by tsetse flies. Subspecies of T. brucei cause human African trypanosomiasis and the animal diseases, nagana, surra and dourine. T. b. evansi and T. b. equiperdum have branched from T. brucei and, by foregoing tsetse transmission, expanded their geographic range beyond the sub-Saharan tsetse belt. These species can only reproduce asexually and exhibit morphological uniformity in their host ( monomorphism). T. b. evansi and T. b. equiperdum have historically been classified based on fragmentary information on the parasites transmission routes, geographic distribution, kDNA composition and disease phenotypes. Our analysis of genome sequencing data from monomorphic T. brucei supports at least four independent origins with distinct evolutionary histories. One isolate, IVM-t1, typed as T. equiperdum, is a closer relative to T. b. evansi, highlighting the risk of using pathognomonic descriptors for subspecies assignment. We show clear lineage specific variation in the selection efficacy in monomorphic T. brucei. Using the evolutionary relationships between lineages, we suggest it would be beneficial to reconcile phylogeny and pathology in monomorphic trypanosomes. 4. Data summaryThe data used in this study is available from the Sequence Read Archive or the Wellcome Sanger Institute. The accessions can be found in Supplementary file 1.

genomics↗

bioRxiv2018

Asexual reproduction drives the reduction of transposable element load

Theory predicts that sexual reproduction can both facilitate and restrain transposable element (TE) accumulation by providing TEs with a means of spreading to all individuals in a population and facilitating TE load reduction via purifying selection. By quantifying genomic TE loads over time in experimental sexual and asexual Saccharomyces cerevisiae populations, we provide direct evidence that asexual reproduction drives a reduction of TE loads. We show, using simulations, that this reduction occurs via evolution of TE activity, most likely via increased excision rates. Thus, sex is a major driver of genomic TE loads and at the root of the success of TEs.

evolutionary biology↗