Reproductive barriers play a crucial role in hindering gene exchange between diverging species, helping to maintain species integrity. While numerous studies have explored the genomic landscape of speciation in select organisms from the plant and animal kingdoms, our objective is to shed light on the genetic bases of reproductive isolation in another major eukaryotic supergroup – the brown algae (Phaeophyceae). 

Genomic barriers to gene flow

Intrinsic postzygotic isolation, resulting in fitness decline of hybrids compared to the parental species, is typically attributed to the incompatibilities between diverged parental genomes that manifest themselves independently of the environment. These genomic incompatibilities are often associated with two major processes: 1) chromosomal rearrangements (fusions, fissions, translocations and inversions), which lead to disruption of chromosomal pairing at meiosis, prevent recombination and shelter genomic regions from introgression, and 2) accumulation of small mutations, which create negative epistatic interactions between alleles in the hybrid offspring (Bateson-Dobzhansky-Muller incompatibilities). Our objective is to elucidate the genomic architecture underlying pre- and post-zygotic reproductive barriers across a spectrum of species with varying divergence times by generating chromosome-level genome assemblies and conducting comprehensive comparative genomic analyses.

Sex chromosomes in speciation

Sex chromosomes are dynamic component of the genome and can change rapidly over time, leading to intrinsic postzygotic isolation, following well-established speciation principles like Haldane's rule and the large X effect. While previous studies on the role of sex chromosomes in reproductive isolation have primarily focused on a limited set of model organisms with a specific type of sex determination—typically those with dimorphic sex chromosomes—brown algae present a distinctive scenario. Unlike the more extensively studied diploid sex determination systems (XY, ZW), brown algae employ a haploid sex chromosome system (UV) which is largely unexplored. We are investigating the role of the U and V sex chromosomes in the speciation process. Our goal is to better understand the underlying causes of sex-chromosome-related reproductive isolation and test the generality of previous observations from diploid systems.

From loci to causative mutations

The advancement of genome sequencing technologies has not only facilitated the exploration of genetic architecture but has also enabled the identification of variant sites driving adaptation and speciation in natural populations. Unraveling the genetic foundations of phenotypic diversification and speciation in these populations is essential for addressing questions about the constraints on evolutionary processes and whether they occur gradually or rapidly. We employ a combination of studies on wild populations and controlled laboratory crosses to study the genetic underpinnings of post-mating viability and fertility. Through this approach, we aim to pinpoint genomic regions and genes potentially implicated in hybrid incompatibilities, encompassing morphological and transcriptional traits such as gametophyte sterility, diminished fertility, and developmental abnormalities.