Biology subjects

Brochmann, C.

Publications and source records attributed to Brochmann, C..

5 recordsLinked to original sources

bioRxiv2026

Shared genomic signatures of Arctic adaptation among distantly related plant lineages

Extreme environments impose strong selection pressures that can drive convergent adaptation among distantly related species. Arctic plants survive low temperatures, 24-hour light in summer and darkness in winter, short growing seasons, limited precipitation, nutrient-poor soils, and extreme seasonal variation. To test if these conditions are associated with shared genomic signatures, we generated a chromosome-level genome assembly for Oxyria digyna and compared it with existing reference genomes for three distantly related Arctic species (Cochlearia groenlandica, Draba nivalis, Dryas octopetala) and for 16 non-Arctic species from the same families. We identified 214 orthogroups with signatures of positive selection in all Arctic species, 1.6 times the number shared among the non-Arctic species. Although no gene ontology (GO) categories remained significantly enriched after multiple-testing correction, descriptive annotations included genes involved in general functions including protein folding, glycolysis, transcription, and oxidative-stress responses. Orthogroups showing copy number variation were associated with biotic interactions, sexual reproduction, and nutrient acquisition, suggesting that species may respond to biotic and nutrient stresses by shifts in gene copy number. Arctic and alpine genomes contained lower proportions of some repetitive elements, including terminal inverted repeats, and smaller regions of centromeric repeats than non-Arctic genomes. Overall, we see shared genes under positive selection, similar functions of genes with high copy number variation, and lower counts of some repetitive elements in the Arctic plant genomes. Our findings reveal a shared genomic signature of Arctic adaptation across deeply diverged plant lineages, suggesting that evolution in extreme environments repeatedly targets similar genomic features.

genomics↗

bioRxiv2024

Different resource partitioning explains plant species richness patterns in tropical alpine ecosystems

Species co-existence based on resource partitioning modulates biodiversity patterns across latitudes and altitudes. Resource partitioning can occur via specialisation or separation in the geographic range or niche. Here, we compare two tropical alpine ecosystems with similar climates to test for geographic range and climatic niche partitioning strategies in explaining species richness difference. We compare the species-rich tropical alpine ecosystem in the South American Andes with the more species-poor one in the eastern African mountains. We combine phylogenomic data for three locally diversified plant lineages in each region with occurrence records and estimate climatic niche and geographic range metrics (size and overlap). We found that the Andean species have overall larger niches than the African species, thus smaller niches indicating specialisation is not the explanation for the higher species richness in the Andes. Instead, for species with overlapping geographic ranges, we found that the Andean species tend to show less niche overlap than the African species, indicating more effective niche separation. Taken together, we propose that different degrees of niche separation in geographically overlapping species, and hence, a different pattern of resource partitioning, explain the differences in species richness between the two tropical alpine ecosystems.

ecology↗

bioRxiv2024

Low parental conflict, no endosperm hybrid barriers, and maternal bias in genomic imprinting in selfing Draba species

In flowering plants, a distinct post-zygotic hybridization barrier between closely related species can arise during seed maturation, resulting in embryo lethality due to abnormal endosperm development. The endosperm initially works as a nutrient sink, acquiring nutrients from adjacent tissues, but later undergoes cellularization, switching to serve as a nutrient source. In hybrid seeds, this cellularization switch can be hampered if the endosperm genomic ratio is imbalanced. Disruption in the genomic ratio can be caused when species of different ploidy are crossed, but also by crosses between species with identical ploidy, if the effective ploidy differs. One factor proposed to influence effective ploidy is the epigenetic phenomenon genomic imprinting, the parent-of-origin specific expression of alleles inherited either maternally or paternally. It has been proposed that outbreeding species exhibit higher effective ploidy compared to selfing species, as a consequence of parental conflict in resource allocation to the developing progenies. This suggests a low anticipation of endosperm-based post-zygotic hybridization barriers between selfing species of similar ploidy. Here, we show that in crosses between the diploid selfing arctic species Draba fladnizensis, D. nivalis and D. subcapitata, the endosperm-based post-zygotic hybridization barrier is absent, supporting low parental conflict. To investigate parent-of-origin allele specific expression, we conducted a genomic imprinting study in D. nivalis and compared to previous studies in other Brassicaceae species. We report a high number of maternally expressed genes (MEGs) and concomitantly low numbers of paternally expressed genes (PEGs). Our results suggest rapid evolution of MEGs and loss of PEGs in a mating system with low parental conflict, proposing that selfing arctic species may exhibit a generally stronger maternal expression bias as an adaptive mechanism to efficiently cope with an extreme environment.

plant biology↗

bioRxiv2022

Mating system and speciation I: accumulation of genetic incompatibilities in allopatry

Self-fertilisation is widespread among hermaphroditic species across the tree of life. Selfing has many consequences on the genetic diversity and the evolutionary dynamics of populations, which may in turn affect macroevolutionary processes such as speciation. On the one hand, because selfing increases genetic drift and reduces migration rate among populations, selfing may be expected to promote speciation. On the other hand, because selfing reduces the efficacy of selection, selfing may be expected to hamper ecological speciation. To better understand under which conditions and in which direction selfing affects the build-up of reproductive isolation, an explicit population genetics model is required. Here, we focus on the interplay between genetic drift, selection and genetic linkage by studying speciation without gene flow. We test how fast populations with different rates of selfing accumulate mutations leading to genetic incompatibilities. When speciation requires the population to pass through a fitness valley caused by underdominant and compensatory mutations, selfing reduces the depth and/or breadth of the valley, and thus overall facilitates the fixation of incompatibilities. When speciation does not require the population to pass through a fitness valley, as for Bateson-Dobzhanzky-Muller incompatibilities (BDMi), the lower effective population size and higher genetic linkage in selfing populations facilitates the fixation of incompatibilities. Interestingly, and contrary to intuitive expectations, local selection does not always accelerate the build-up of reproductive isolation in outcrossing relative to selfing populations. Our work helps to clarify how selfing lineages may speciate and diversify over time, and emphasizes the need to account for interactions among segregating mutations within populations to better understand macroevolutionary dynamics. Author summaryHermaphroditic organisms may use their male gametes to fertilise their own female gametes, and species vary greatly in how much they self-fertilise. Self-fertilisation induces many genetic modifications in the population, which may ultimately affect the rates at which lineages diversify. Here we aim to build predictions on how self-fertilisation affects the rate at which reproductive isolation arises between geographically isolated populations. Specifically, we develop theoretical models in which populations varying in their rates of self-fertilisation may fixate mutations leading to reproductive isolation. We first explored scenarios in which reproductive isolation is made by mutations whose fixations necessitate the population to experience temporally deleterious effects (i.e., a fitness valley), and found that self-fertilisation reduces the breadth and depth of the fitness valley and thereby overall facilitates the accumulation of such mutations. Second, we explored scenarios in which genetic incompatibilities are caused by interactions between derived alleles of different genes (i.e., BDMi). By allowing the BDMi to occur within populations, we found that self-fertilisation reduces the manifestation of BDMi within population, and thereby facilitates their fixation. This effect prevails even in the face of local adaptation. Thus, our study clarifies how fast species are expected to arise in self-fertilisation lineages.

evolutionary biology↗

bioRxiv2021

What can the cold-induced transcriptomes of Arctic Brassicaceae tell us about the evolution of cold tolerance?

O_LILittle is known about the evolution of cold tolerance in polar plant species and how they differ from their temperate relatives. To gain insight into their biology and the evolution of cold tolerance, we compared the molecular basis of cold response in three Arctic Brassicaceae species. C_LIO_LIWe conducted a comparative time series experiment to examine transcriptional responses to low temperature. RNA was sampled at 22 {degrees}C, and after 3h, 6h, and 24h at 2 {degrees}C. We then identified sets of genes that were differentially expressed in response to cold and compared them between species, as well as to published data from the temperate Arabidopsis thaliana. C_LIO_LIMost differentially expressed genes were species-specific, but a significant portion of the cold response was also shared among species. Among thousands of differentially expressed genes, [~]200 were shared among the three Arctic species and A. thaliana, while [~]100 were exclusively shared among the three Arctic species. C_LIO_LIOur results show that cold response differs markedly between Arctic Brassicaceae species, but likely builds on a conserved basis found across the family. They also confirm that highly polygenic traits such as cold tolerance may show little repeatability in their patterns of adaptation. C_LI

evolutionary biology↗