Signorini, S. G. | Search bioRxiv

bioRxiv2026

Dynamic genomes uncover opposite sex determination in the invasive quagga and zebra mussels

Sex determination is a fundamental developmental switch, yet the genetic architectures that underlie transitions between sex-determining systems remain poorly understood, especially in non-model animals with homomorphic sex chromosomes. Here, we combine chromosome-scale genomes, whole-genome resequencing of 80 sexed individuals, sex-specific k-mer analyses, and developmental transcriptomics to resolve and compare sex determination in zebra and quagga mussels, two closely related and globally invasive freshwater bivalves. We find that these species have evolved sharply contrasting sex-determining architectures since their divergence. Zebra mussels show signatures of a polygenic ZZ/ZW system, with sex-linked regions on multiple chromosomes, including signal at the conserved ovarian regulator FoxL2. In contrast, quagga mussels possess a localized [~]800 kb XX/XY sex-determining region containing FoxL2-Y, a duplicated and structurally modified FoxL2 paralog and candidate male-determining locus. In quagga mussels, SNP-based differentiation, model-based inference, sex-biased read coverage, and male-specific k-mers independently converge on this Y-linked region, while diagnostic k-mer screening of staged embryonic transcriptomes reveals rare, early developmental expression of FoxL2-Y, consistent with a transient regulatory role. The quagga sex-determining region is enriched for C-type lectins and other genes implicated in reproductive interactions, suggesting that haploid selection may have contributed to the stabilization of this region. Together, these findings show that closely related species can rapidly evolve different genetic solutions to sex determination and identify gene duplication, genome dynamism, and reproductive selection as potential contributors to sex-determining system turnover. Because zebra and quagga mussels are major freshwater invaders, resolving their divergent reproductive architectures also provides essential genomic context for assessing the future feasibility of sex-ratio-based biocontrol strategies.

genomics↗

bioRxiv2023

The genome of the rayed Mediterranean limpet Patella caerulea (Linnaeus, 1758)

Patella caerulea (Linnaeus, 1758) is a molluscan limpet species of the class Gastropoda. Endemic to the Mediterranean Sea, it is considered to be a keystone species in tidal and subtidal habitats due to its primary role in structuring and regulating the ecological balance of these habitats. It is currently being used as a bioindicator to assess the environmental quality of coastal marine waters and as a model species to understand adaptation to ocean acidification. Here we provide a high-quality reference genome assembly and annotation for Patella caerulea. We used a single specimen collected in the field to generate [~]30 Gb of PacBio HiFi data. The final assembly is 749.8 Mb large and contains 62 contigs, including the mitochondrial genome (14,938 bp). With an N50 of 48.8 Mb and 98% of the assembly contained in the 18 largest contigs, this assembly is near chromosome-scale. BUSCO scores were high (Mollusca: 87.8% complete; Metazoa: 97.2% complete) and similar to metrics observed for other chromosome-level Patella genomes, highlighting a possible bias in the Mollusca database for Patellids. We generated transcriptomic Illumina data from a second individual collected at the same locality, and used it together with protein evidence to annotate the genome. 23,938 protein coding gene models were found. By comparing this annotation with other published Patella annotations, we found that the distribution and median values of exon and gene lengths was comparable to other Patella species despite different annotation approaches. The present high-quality Patella caerulea reference genome is an important resource for future ecological and evolutionary studies. SignificanceReference genomes are essential resources for biodiversity conservation and management. Patella caerulea (Linnaeus, 1758) is a gastropod species occurring in the Mediterranean Sea that is currently used as a model to understand the impact of pollution and ocean acidification on marine biodiversity. Here we present a high-quality reference genome of P. caerulea, that almost reaches chromosome-level contiguity. We further provide a high-quality genome annotation supported by transcriptomic evidence. This reference genome will be of interest for researchers working on the ecology and evolution of marine biodiversity. All data is available on the public database NCBI for future use by researchers.

genomics↗