Biology subjects

Lavanchy, G.

Publications and source records attributed to Lavanchy, G..

5 recordsLinked to original sources

bioRxiv2024

Recent neo-X and Y sex chromosomes in an ant cricket

In eukaryotes with separate sexes, sex determination often involves heteromorphic sex chromosomes which have diverged as a consequence of recombination suppression. In species with very old heteromorphic sex chromosomes, mechanisms such as dosage compensation and meiotic sex chromosome inactivation adjust for the fact that sex chromosomes occur as a single copy in the heterogametic sex. However, how such mechanisms evolve remains largely unknown because species with young sex chromosomes characterised by recent recombination suppression remain understudied. We discovered such young neo-sex chromosomes in the ant cricket Myrmecophilus myrmecophilus, which displays a neo-XY system. We generated a chromosomal-level assembly of the female genome and compared it to male genomic data and identified four evolutionary strata on the X, with varying degrees of Y chromosome degeneration. Phylogenetic studies and genomic comparisons with closely related species revealed two cases of taxonomic synonymies and that the Myrmecophilus neo-sex chromosomes likely evolved approximately 7 million years ago from an X-autosome fusion. The X strata subsequently emerged as a consequence of two localised events of recombination suppression. Ant crickets thus represent a promising new model for studying the early stages of sex chromosome degeneration and the establishment of processes such as dosage compensation or meiotic sex chromosome inactivation.

evolutionary biology↗

bioRxiv2024

LEVERAGING CITIZEN SCIENCE TO ASSESS RICHNESS, DIVERSITY, AND ABUNDANCE IN ANT COMMUNITIES

AO_SCPLOWBSTRACTC_SCPLOWCitizen science is a key resource in overcoming the logistical challenges of monitoring biodiversity. While datasets collected by groups of volunteers typically have biases, recent methodological and technological advances provide approaches for accounting for such biases, particularly in the context of modelling species distributions and diversity. Specifically, data integration techniques allow for the combination of scientifically collected datasets with haphazardly sampled presence-only datasets created by most citizen science initiatives. Here, we use a hierarchical Bayesian framework to integrate a set of ant presences collected by citizen scientists in the Vaud canton (Switzerland) with ant colony density data collected concurrently in the same region following a scientific sampling design. The community-level Poisson point process model included species-specific responses to the local (1.2 m2) and regional (1 km2) environment, with the presence-only samples incorporated at the regional scale to predict local and regional ant communities. At the regional scale, species richness followed a hump-shaped pattern and peaked near 1000 m while abundance increased with elevation. Low elevation and montane ant communities were composed of distinct species assemblages. At the local scale, the link between elevation and richness, diversity, and abundance was weak. At low elevations, local plots varied both in total abundance and species composition, while at higher elevations, the species composition was less variable. The citizen science dataset showed a general tendency toward under-representation of certain species, and heavy spatial sampling bias. Nonetheless, the inclusion of the citizen science data improved predictions of local communities, and also reduced susceptibility to over-fitting. Additionally, the citizen science dataset included many rare species not detected in the structured abundance dataset. The model described here illustrates a framework for capitalizing on the efforts of citizen scientists to better understand the patterns and distribution of biodiversity.

ecology↗

bioRxiv2023

Evolution of alternative reproductive systems in Bacillus stick insects

Reproduction is a key feature of all organisms, yet the way in which it is achieved varies greatly across the tree of life. One striking example of this variation is the stick insect genus Bacillus, in which five different reproductive modes have been described: sex, facultative and obligate parthenogenesis, and two highly unusual reproductive modes: hybridogenesis and androgenesis. Under hybridogenesis, the entire genome from the paternal species is eliminated, and replaced each generation by mating with the corresponding species. Under androgenesis, an egg is fertilized but the developing diploid offspring bear two paternal genomes, and no maternal genome, as a consequence of unknown mechanisms. Here, we re-evaluate previous descriptions of Bacillus lineages and the proposed F1 hybrid ancestries of the hybridogenetic and obligately parthenogenetic lineages (based on allozymes and karyotypes) from Sicily, where all these reproductive modes are found. We generate a chromosome-level genome assembly for a facultative parthenogenetic species (B. rossius) and combine extensive field sampling with RADseq and mtDNA data. We identify and genetically corroborate all previously described species and confirm the ancestry of hybrid lineages. All hybrid lineages have fully retained their F1 hybrid constitution throughout the genome, indicating that the elimination of the paternal genome in hybridogens is always complete and that obligate parthenogenesis in Bacillus hybrid species is not associated with an erosion of heterozygosity as known in other hybrid asexuals. Our results provide a stepping stone towards understanding the transitions between reproductive modes and the proximate mechanisms of genome elimination.

evolutionary biology↗

bioRxiv2023

Investigating fine-scale breeding habitat use by amphibians in a continuous wetland using environmental DNA

Designing effective conservation plans to protect species from extinction requires a better understanding of their ecology. Conventional methods used to investigate habitat use are time consuming, and detectability of cryptic species is often insufficient. Environmental DNA (eDNA)-based approaches now provide an alternative for ecosystems monitoring and assessment. Nevertheless, to our knowledge, such methods have never been applied to investigate habitat use at a fine scale in a continuous wetland environment. Here, we used an eDNA metabarcoding approach to characterize the breeding habitat use of local amphibian species in a wet meadow expanse along the southern shore of Lake Neuchatel, Switzerland. We retrieved DNA from six out of the seven species expected to be present. We tested the influence of six abiotic environmental variables on overall species communities as well as individual species occurrences. We showed that the main factor structuring species communities was water temperature, and that the distribution of three amphibian species was associated with several environmental variables. Our results indicate that the eDNA approach is a promising tool to study species ecology at a small scale in continuous wetland habitats.

ecology↗

bioRxiv2022

Facultative parthenogenesis in an asexual stick insect: re-evolution of sex or vestigial sexual capacity?

Transitions from obligate sex to obligate parthenogenesis have occurred repeatedly across the tree of life. Whether these transitions occur abruptly or via a transient phase of facultative parthenogenesis is rarely known. We discovered and characterised facultatively parthenogenetic populations of the North American stick insect Timema douglasi, a species in which only obligately parthenogenetic populations were known so far. These populations comprised three genetic lineages. Females from all lineages were capable of parthenogenesis (with variable efficiency) but their propensity to reproduce sexually after mating varied extensively. In all three lineages, parthenogenesis resulted in the complete loss of heterozygosity in a single generation. Obligately parthenogenetic Timema have also lost all heterozygosity, suggesting that the transition to obligate parthenogenesis did not require a modification of the proximate mechanism, but rather involved a gradual increase in frequency. We speculate that facultative parthenogenesis may often be transient and be replaced by obligate strategies (either sex or parthenogenesis) because of a trade-off between the efficiency of the two reproductive modes. Such a trade-off could help explain why facultative parthenogenesis is rare among animals, despite its potential to combine the known benefits of sex and parthenogenesis.

evolutionary biology↗