Biology subjects

Sigwart, J.

Publications and source records attributed to Sigwart, J..

5 recordsLinked to original sources

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↗

bioRxiv2026

Pigments and microstructure of the colour polymorphic shells of Polymita picta and P. muscarum (Gastropoda: Cepolidae), with observations on a new light-transmitting shell spot system

Colour polymorphism in the Cuban painted snails Polymita picta and P. muscarum is striking, yet the pigmentary and structural bases remain unclear. We combined spectrophotometric screening, Raman micro-spectroscopy, scanning electron microscopy (SEM) and LED transillumination to link pigments, ultrastructure and optics across shell morphs. A Sepia officinalis melanin standard yielded a robust linear calibration used to quantify total melanin pigments at 215 nm in pooled extracts. Melanin was detected in all samples with predominance in darker morphs. Raman spectra (785 nm) confirmed aragonite mineral organization and revealed carotenoid bands, consistent with a mixed-pigment model in which carotenoids contribute to ground and band colours and melanins underlie darker elements. SEM showed a canonical crossed-lamellar layer with alternating transverse and co-marginal layers. At shell spot areas, shell surfaces were cribose; fracturing shells near such spots showed a locally disordered, more porous mineral arrangement enriched in organic matrix, bounded basally by an organic layer. Under transillumination, these spots acted as discrete light-transmitting windows, abundantly in P. muscarum and also sparsely in P. picta; as the spots appear only as pigmented dots but also transmit light, we refer to them as cryptotransmissive domains, which is apparently a novel finding in terrestrial gastropods. We speculate that these may represent a pigment-structure-optics framework in which pigments and microstructural packing jointly play potential roles in photoprotection and behavioural thermoregulation. These results provide a mechanistic context for colour polymorphism in Polymita and suggest testable links to thermal ecology and conservation.

zoology↗

bioRxiv2026

Genome-wide identification of heat shock proteins (HSP70) in the Cuban painted snail Polymita picta: evolutionary constraints face climate change challenges

Climate change poses a critical threat for biodiversity. Among ectothermal animals, terrestrial molluscs are considered highly vulnerable to temperature increase and drought due to their low vagility and specialized ecological requirements. In response to thermal stress, heat shock proteins (HSP70) play a crucial role in the response syndrome and phenotypic plasticity and mediate the adaptation to fluctuating environments. Here, we performed the first genome-wide identification and characterization of the HSP70 family in a Neotropical terrestrial gastropod of high conservation concern: the Cuban painted snail Polymita picta. Using comprehensive bioinformatic approaches, we identified HSP70 paralogs, analysed their structural features and assessed sequence variation, highlighting their potential relevance for thermoresistance. Our findings reveal an HSP70 repertoire of ten diversified sequences with signatures of functional specialization and possible adaptive variation linked to environmental temperature regimes. Using novel molecular resources, this pioneering analysis establishes a baseline for early warning systems, integrating stress-related biomarkers into conservation management and climate change adaptation strategies for threatened terrestrial molluscs.

genomics↗

bioRxiv2024

Genome of the enigmatic watering-pot shell reveals adaptations of a living suction anchor

The watering pot shells have been rightly called "the weirdest bivalves" for their highly modified body plan and fused tubular shell that resemble the spout of a watering can. This adventitious tube has defied rational explanation as an adaptive pathway and yet arose twice convergently. We present the first genome for the clade Anomalodesmata: an annotated chromosome-scale genome of Verpa penis (Linnaeus, 1758). The first watering pot shell ever described ranges across southeast Asia but is nonetheless extremely rare and has never previously been sequenced. The assembly length of 507 Mb, with a contig N50 of 5.33 Mb, has 96.5% of sequences anchored onto 19 pseudochromosomes. Contrary to expectations from such a highly modified body plan, there is no evidence of chromosome reduction compared to the ancestral condition of heterodont bivalves (1N=19). A new hypothesis based on analysis of the living animals and literature explains the adaptive significance of this body form: it is structurally optimised for vertical stability in soft sediments, with parallels to engineering principles of a suction anchor. Our study offers new insights to a long-standing mystery in molluscan body forms, and provides genomic resources that are relevant to understanding molluscan evolution, biomineralisation, and biomimetic design.

evolutionary biology↗

bioRxiv2024

Long-read sequencing and genome assembly of natural history collection samples and challenging specimens

Museum collections harbor millions of samples, largely unutilized for long-read sequencing. Here, we use ethanol-preserved samples containing kilobase-sized DNA to show that amplification-free protocols can yield contiguous genome assemblies. Additionally, using a modified amplification-based protocol, employing an alternative polymerase to overcome PCR bias, we assembled the 3.1 Gb maned sloth genome, surpassing the previous 500 Mb protocol size limit. Our protocol also improves assemblies of other difficult-to-sequence molluscs and arthropods, including millimeter-sized organisms. By highlighting collections as valuable sample resources and facilitating genome assembly of tiny and challenging organisms, our study advances efforts to obtain reference genomes of all eukaryotes.

genomics↗