Biology subjects

Martelossi, J.

Publications and source records attributed to Martelossi, J..

5 recordsLinked to original sources

bioRxiv2026

A new phased assembly of the Antarctic spiny plunderfish provides novel insights into the evolution of the notothenioid radiation.

BackgroundNotothenioids are a well characterised species flock endemic to the Antarctic and an important model group for the study of genome adaptation to extreme cold. We used a new reference assembly and clade-wide comparative genomic analysis to investigate cryonotothenioid evolution and the appearance of novel functionalities linked to cold adaptation. ResultsA new phased assembly of a model notothenioid, Harpagifer antarcticus, demonstrated low levels of haplotypic variability across the genome. Nevertheless, numerous insertions from multiple LINE-L2 clades were found, suggesting ongoing transposition with potential contribution to speciation. Contrary to expectations the afgp locus was highly similar between haplotypes, except for large length allelic variants of afgp genes. Analysis suggests a model for the afgp locus expansion in H. antarcticus through segmental tandem duplications involving two pairs of afgp genes at time. Syntenic reconstruction of genomes from across the clade demonstrates conserved macrosyntenic relationships and group specific chromosomal fusions of notothenioids. Quantification of genome gain and transposition rates during cryonotothenioid diversification showed a first ancestral slow genome expansion concurrent with historic temperature drops. This was followed by lineage-specific massive peaks of genomic gain and transposition activity. Finally, we identified a set of genes that underwent ancestral diversifying selection and acquired novel conserved non-coding elements during the cryonotothenioid emergence. These were related to antioxidants and proteostasis, which may have facilitated the notothenioid Antarctic radiation. ConclusionDiversifying selection and genomic gain linked to transposon activity are primary contributors to lineage-specific evolutionary dynamics through the clade which facilitated adaptation to life in the cold.

genomics↗

bioRxiv2026

Transposable element activity and polymorphisms drive structural variability within and between individual in bivalves

Structural variants (SVs) represent one of the most abundant sources of genetic variation across eukaryotes, with transposable elements (TEs) standing out as primary contributors in their emergence. While the growing availability of chromosome-scale genomes has revealed the central role of SVs in species diversification and adaptation, non-model invertebrates remain critically understudied in this context. Here, we explore how SVs and their interaction with TEs shape genetic diversity at both the individual and population levels. To achieve this, we leverage four high-quality oyster genomes and a large-scale dataset of the Estuarine oyster (Crassostrea ariakensis) collected across a wide range of different temperature and salinity conditions. We explicitly account for strengths and limitations of current SV-calling software, and benchmark our results through simulations. We uncover pervasive within-individual structural variability, with up to 14% of oyster genome basepairs being in an hemizygous state. The strong enrichment of TEs within these SVs is driven by a prevalence of insertions over deletions, reflecting population-level TE activity. Strikingly, both SVs and de novo TE insertions -- driven by the concurrent mobilization of diverse TE families -- segregate among C. ariakensis populations and contribute to genomic differentiation associated with local adaptation to contrasting sea salinity and temperature levels. Our study demonstrates the power of integrating long- and short-read sequencing to recover a high-confidence catalogue of SVs and de novo TE insertions, and provides empirical evidence that structural variation is an active evolutionary force generating potentially adaptive genetic variation in a key lineage of ecologically and economically important bivalves.

evolutionary biology↗

bioRxiv2024

The high quality Chinese white truffle genome and novel fossil-calibrated estimate of Pezizomycetes divergence reveal the tempo and mode of true truffles genome evolution

The genus Tuber (family: Tuberaceae) includes the most economically valuable ectomycorrhizal (ECM), truffle-forming fungi. Previous genomic analyses revealed that massive transposable element (TE) proliferation represents a convergent genomic feature of mycorrhizal fungi, including Tuberaceae. Repetitive sequences are one of the major drivers of genome evolution shaping its architecture and regulatory networks. In this context, Tuberaceae represent an important model system to study their genomic impact; however, the family lacks high-quality assemblies. Here, we tested the interplay between TEs and Tuberaceae genome evolution by producing a highly contiguous assembly for the endangered Chinese truffle Tuber panzhihuanense, along with a novel timeline for Tuberaceae diversification and comprehensive comparative genomic analyses. We found that concurrently with a Paleogene diversification of the family, pre-existing Chromoviridae-related Gypsy clades independently expand in different truffle lineages leading to increased genome size and high gene family turnover rates, but without resulting in highly scrambled genomes. Additionally, we found an enrichment of ECM-induced gene families among ancestral duplication events. Finally, we explored the repetitive structure of nuclear ribosomal DNA (rDNA) loci for the first time in the clade. We found that most of the 45S rDNA paralogues are undergoing concerted evolution, though an isolated divergent locus raises concerns about potential issues for metabarcoding and biodiversity assessments. Our study provides a fundamental genomic resource for future research on truffle genomics and showcases a clear example on how establishment and self-perpetuating expansion of heterochromatin can drive massive genome size variation due to activity of selfish genetic elements.

evolutionary biology↗

bioRxiv2023

Teaching transposon classification as a means to crowd source the curation of repeat annotation - a tardigrade perspective

The advancement of sequencing technologies results in the rapid release of hundreds of new genome assemblies a year providing unprecedented resources for the study of genome evolution. Within this context, the significance of in-depth analyses of repetitive elements, transposable elements (TEs) in particular, is increasingly recognized in understanding genome evolution. Despite the plethora of available bioinformatic tools for identifying and annotating TEs, the phylogenetic distance of the target species from a curated and classified database of repetitive element sequences constrains any automated annotation effort. Manual curation of raw repeat libraries is deemed essential due to the frequent incompleteness of automatically generated consensus sequences. However, manual curation and classification are time-consuming processes that offer limited short-term academic rewards and are typically confined to a few research groups where methods are taught through hands-on experience. Crowd sourcing efforts could offer a significant opportunity to bridge the gap between learning the methods of curation effectively and empowering the scientific community with high-quality, reusable repeat libraries. Here, we present an example of such crowd sourcing effort developed through both in-person and online courses built around a collaborative peer-reviewed teaching process that can be used as teaching reference guide for similar projects. The collaborative manual curation of TEs from two tardigrade species, for which there were no TE libraries available, resulted in the successful characterization of hundreds of new and diverse TEs: A hidden treasure awaits discovery within non-model organisms.

evolutionary biology↗

bioRxiv2020

Macroevolutionary Analyses Provide New Evidences of Phasmids Wings Evolution as a Reversible Process.

AO_SCPLOWBSTRACTC_SCPLOWThe concept that complex ancestral traits can never be re-acquired after their loss has grown popular since its initial formulation and its often referred to as Dollos law. Nonetheless, several macroevolutionary evidences - along with molecular ones - suggest instances where complex phenotypes could have been lost throughout a clade evolutionary history and subsequently reverted to their former state in derived lineages. One of the first and most notable rejection of Dollos law is represented by wing evolution in phasmids: this polyneopteran order of insects - which comprises stick and leaf insects - has played a central role in initiating a long-standing debate on the topic. In this study, a novel and comprehensive time-tree - including over 300 Phasmatodea species - is used as a framework for investigating wings evolutionary patterns in the clade. Despite accounting for several possible biases and sources of uncertainty, macroevolutionary analyses consistently support a dynamic and reversible evolution of wings, with multiple transitions to ancestral states taking place after their loss. Our findings suggest that wings and flight are decoupled from Phasmatodea diversification dynamics and that brachyptery is an unstable state, unless when co-opted for non-aerodynamic adaptations. We also explored how different assumptions of wings reversals probability could impact their inference: we found that until reversals are assumed to be over 30 times more unlikely than losses, they are consistently retrieved despite uncertainty in tree and model parameters. Our findings demonstrate that wings evolution can be a reversible and dynamic process in phasmids and contribute to shape our understanding of how complex phenotypes evolve.

evolutionary biology↗