Biology subjects

Satokangas, I.

Publications and source records attributed to Satokangas, I..

4 recordsLinked to original sources

bioRxiv2024

Introgression and divergence in a young species group

The process of speciation concerns often not only pairs of species but rather groups of diverging and interacting taxa, as highlighted by recent research. Hence, to understand the evolution of species diversity and their persistence, it is crucial to understand how gene flow and evolution of reproductive isolation shape groups of closely related species. Using resequencing data, we disentangle here genomic patterns of divergence and introgression in five Formica rufa group wood ant species that are at the early stage of speciation. We first revise earlier mitochondrial phylogenies with a nuclear genomic tree, and demonstrate then introgression that is in line with observations of their current day natural hybridisation. Investigating the genome-wide differentiation and divergence we find correlations between population genetic parameters of divergence, differentiation, and diversity, that are in line with theoretical expectations for young species. Despite previously found evidence for polygenic species barriers, our data lacks the genome-wide correlation between differentiation and divergence that would be expected under a model of polygenic barriers. The likely explanation for this lack is the dominating effect of ancestral diversity at these early stages of speciation. As hybridisation has led to both deleterious and adaptive consequences within the group, we examined the signatures of introgression. We find no strong positive correlation between introgression and recombination, suggesting introgression does not have a predominantly deleterious effect. We also infer low diversity in the genomic regions with high proportions of introgression, consistent with the idea that selection has locally favoured introgression. This could be due to sharing of adaptive alleles or reduction of genetic load in the receiving species. Interestingly, gene flow in this group could potentially cross multiple species boundaries even in the absence of direct interbreeding between all the species. We discuss the long-term benefits and costs of introgression in young species, including the effect of environmental fluctuations and multi-species introgression.

evolutionary biology↗

bioRxiv2024

The loss of a supergene in obligately polygynous Formica wood ant species

Some of the most striking examples of phenotypic variation within species are controlled by supergenes. However, most research on supergenes has focused on their emergence and long-term maintenance, leaving the later stages of their life cycle largely unexplored. Specifically, what happens to a derived supergene haplotype when the trait it controls reaches fixation? Here we answer this question using the ancient supergene system of Formica ants, where (monogynous) single-queen colonies carry only the ancestral haplotype M while the derived haplotype P is exclusive to (polygynous) colonies with multiple queens. Through comparative genomics of all seven European wood ant species, we found that the P haplotype was present in only one of the three obligate polygynous species (F. polyctena). In the two others (F. aquilonia and F. paralugubris) the P haplotype was completely missing except for duplicated P-specific paralogs of two genes, Zasp52 and TTLL2, with Zasp52 being directly involved in wing muscle development. We hypothesize that these genes play a direct role in polygyny and contribute to differences in body size and/or dispersal behaviour between monogynous and polygynous queens. A complete lack of P/P genotypes among the 136 workers suggest strong selection against such genotypes. While our analyses did not reveal evidence of increased mutation load on the P, it is possible that this skew in genotype distributions is driven by a few loci with strong fitness effects. We propose that selection to escape P-associated fitness costs underlies the loss of this haplotype in obligate polygynous wood ants.

genomics↗

bioRxiv2023

Extensive hybridisation between multiple differently adapted species may aid persistence in a changing climate

Hybridisation and gene flow can have both deleterious and adaptive consequences for natural populations and species. To better understand the extent and consequences of hybridisation in nature, information on naturally hybridising non-model organisms is required, including characterising the structure and extent of natural hybrid zones. Here we study natural populations of five keystone mound-building wood ant (Formica rufa group) species across Finland. No genomic studies across the species group exist and the extent of hybridisation and genomic differentiation in sympatry is unknown. Combining genome-wide and morphological data, we show that Formica rufa, F. aquilonia, F. lugubris, and F. pratensis form distinct gene pools in Finland. We demonstrate more extensive hybridisation than previously thought between all five species and reveal a mosaic hybrid zone between F. aquilonia, F. rufa and F. polyctena. We show that hybrids between these climatically differently adapted species occupy warmer habitats than the cold-adapted parent F. aquilonia. This suggests hybrids occupy a different microclimatic niche compared to the locally abundant parent. We propose that wood ant hybridisation may increase with a warming climate, and warm winters, in particular, may provide a competitive advantage for the hybrids over F. aquilonia in the future. In summary, our results demonstrate how extensive hybridisation may help persistence in a changing climate. Additionally, they provide an example on how mosaic hybrid zones can have significant ecological and evolutionary consequences because of their large extent and independent hybrid populations that face both ecological and intrinsic selection pressures.

evolutionary biology↗

bioRxiv2018

Hybridizing wood ants allow testing for natural selection at candidate barrier loci underlying speciation

While speciation underlies novel biodiversity, it is poorly understood how natural selection shapes genomes during speciation. Selection is assumed to act against gene flow at barrier loci, promoting reproductive isolation and speciation. However, evidence for gene flow and selection is often indirect. Here we utilize haplodiploidy to identify candidate barrier loci in hybrids between two wood ant species and integrate survival analysis to directly measure if natural selection is acting at candidate barrier loci. We find multiple candidate barrier loci but surprisingly, proportion of them show leakage between samples collected ten years apart, natural selection favoring leakage in the latest sample. Barrier leakage and natural selection for introgressed alleles could be due to environment-dependent selection, emphasizing the need to consider temporal variation in natural selection in future speciation work. Integrating data on survival allows us to move beyond genome scans, demonstrating natural selection acting on hybrid genomes in real-time.

evolutionary biology↗