Biology subjects

Coudret, J.

Publications and source records attributed to Coudret, J..

5 recordsLinked to original sources

bioRxiv2026

Comparison of the performance of sporophytes derived from narrow and wide genetic crosses between strains of the cultivated kelp Saccharina latissima

Seaweed mariculture allows sustainable production of large quantities of biomass for multiple downstream applications but the genotypes cultivated by this industry need to be improved to increase efficiency and cost-effectiveness. It is important that the genetic improvement of cultivated strains does not lead to the introduction of foreign genetic material into wild seaweed populations, which are already under threat from global heating. To circumvent this problem, efforts are being made to develop breeding approaches based on the use of locally-resourced genetic material. The aim of this study was to evaluate the potential effectiveness of this 'local' breeding strategy compared to a classical breeding approach based on wide genetic crosses. Analyses of growth rates and cell wall composition of F1 hybrids derived from either intra- or inter-population crosses between Saccharina latissima strains from two localities, southern Brittany, France and the Faroe Islands, did not identify any clear advantage of inter- compared to intra-population crosses. Breeding based on locally-resourced strains would therefore appear to be a valid approach for current strain selection programs. The study also established a large collection of gametophyte strains from multiple sites for future breeding programs and showed that these strains retained the capacity to become fertile after more than ten years in culture.

genetics↗

bioRxiv2026

Haplotype tagging sheds light on speciation between two divergent cryptic species of the brown algae Ectocarpus

Understanding how genome-wide divergence translates to barriers to gene flow is a central question in speciation research, particularly in marine environments where interconnected habitats frequently accommodate cryptic diversity. Using linked-read whole-genome data from the brown alga Ectocarpus, we investigated genome-wide reproductive isolation between two cryptic brown algal species E. siliculosus and E. crouaniorum across replicated hybrid zones in Europe and Chile. We first uncover deep genetic structure within E. crouaniorum, revealing a more intricate species complex than previously recognized. Despite this complexity, we found parallel patterns of asymmetric introgression that emerged independently in Europe and Chile, where we detected both, F1 and low-level introgressed individuals. However, the specific lineage pairs involved in hybridization depended on local demographic history. Demographic modeling further indicated that reproductive isolation strengthens gradually with divergence time and differs markedly between geographic regions, with ongoing asymmetric gene flow even between lineage pairs where hybrids were not detected in the field. In all cases, the genomic landscape of hybridization is consistent with a polygenic, genome-wide barrier to gene flow rather than a few large-effect regions. Our results show that cryptic speciation in brown algae is driven by repeatable, regionally parallel architectures of genome-wide reproductive isolation which is shaped by ecological and demographic context.

evolutionary biology↗

bioRxiv2025

Wild and farmed Saccharina latissima in Europe: genetic insights for sustainable cultivation, traceability and environmental challenges

Kelp cultivation is expanding rapidly worldwide, although the aquaculture of Saccharina latissima (sugar kelp) in Europe remains in its early stages. However, major concerns have emerged about the potential impact of selected cultivars of the species on native populations of S. latissima which are already vulnerable to stressors including climate change. To address these concerns and support sustainable cultivation, it is essential to characterise genetic diversity and structure of wild kelp populations to monitor potential farm-to-wild gene flow. In this study we used 21 microsatellite loci to characterise the genetic structure of 24 natural and 3 farmed populations of S. latissima along European coasts. Results confirmed strong genetic differentiation between the northern and southern coasts, refining the boundaries between these two clusters compared to previous studies. Within each cluster, a clear genetic substructure was detected, with population differentiation being far more pronounced in the southern cluster. Cultivated sporophytes exhibited pedigrees that were all traced back to the local parent populations. Bayesian model-based structure analysis, discriminant analysis of principal components and assignment tests revealed no significant genetic differentiation between the farms and their wild populations. This indicates that farmed populations and neighbouring populations share the same gene pool, reflecting current cultivation practices. These findings contribute to understanding risks of gene flow between wild and farmed populations and demonstrate that strain traceability is feasible. Additionally, the study highlights the challenge European seaweed farmers face in securing reliable seedling stock, especially in the context of global change.

genetics↗

bioRxiv2025

Sex chromosomes and chromosomal rearrangements are key to behavioural sexual isolation in Jaera albifrons marine isopods

The lack of sexual attraction between individuals from different populations is a direct barrier to gene flow between these populations. Here we focus on the evolution of this class of isolating mechanism, behavioural sexual isolation, through the empirical study of two closely related species of small marine isopods. The males of Jaera albifrons and J. praehirsuta similarly engage females in tactile courtship by brushing a specific region of the females back, but they do so with divergent sets of specialised setae and spines, and female choice results in strong reproductive isolation. Using bi-allelic SNP genotypes obtained from double-digest RAD sequencing of individuals from natural populations and controlled crosses, we found that secondary contacts between J. albifrons and J. praehirsuta resulted in different levels of heterospecific gene flow depending on the ecological context. Comparison of the genomic landscapes of differentiation in the two most contrasting situations (extremely low heterospecific gene flow in one region of western France, but strong introgressive hybridisation in another), combined with linkage map analyses, allowed us to conclude that genomic regions resistant to interspecies gene flow are primarily located either on the sex chromosomes or on rearranged chromosomes (several fusion-scissions and one reciprocal translocation). These genomic regions show low recombination, and in two cases QTL analyses found genetic variation associated with several male courtship traits. These results suggest that a long period of allopatry may have allowed the divergent co-evolution of male traits and female preferences, with genetic bases located at least in part in non-recombining regions on sex chromosomes and rearranged chromosomes. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=182 SRC="FIGDIR/small/631900v4_ufig1.gif" ALT="Figure 1"> View larger version (54K): org.highwire.dtl.DTLVardef@6b7df8org.highwire.dtl.DTLVardef@11b4d00org.highwire.dtl.DTLVardef@15c760aorg.highwire.dtl.DTLVardef@1498d45_HPS_FORMAT_FIGEXP M_FIG C_FIG

evolutionary biology↗

bioRxiv2018

Sexual isolation with and without ecological isolation between sympatric isopods Jaera albifrons and J. praehirsuta

Sexual isolation is often coupled with other barriers, and sexual isolation mechanisms can be intrinsically tied to ecological conditions or natural selection against heterospecific gene flow. The independence and relative strength of sexual isolation are thus difficult to assess. Here we take advantage of a pair of isopod species (Jaera albifrons and J. praehirsuta) that show sexual isolation and coexist in populations where they share the same habitat or not (i.e. without or with ecological isolation). Using no-choice trials and a free-choice experimental population, we estimated the strength of sexual isolation between J. albifrons and J. praehirsuta individuals originating from these different ecological contexts. We found that sexual isolation is strong in presence and absence of ecological isolation, but that it is asymmetric and fails to prevent gene flow entirely. Post-zygotic barriers were low, and there was no sexual isolation within J. praehirsuta across habitats. The J. albifrons / J. praehirsuta species pair thus provides an example where the role of sexual isolation as a barrier to gene flow i) does not depend upon current ecological isolation, ii) seems to have evolved independently of local ecological conditions and hybridization costs, but iii) is unable to complete speciation entirely on its own.

evolutionary biology↗