Filatov, D. | Search bioRxiv

bioRxiv2026

Recent hybridisation and ghost introgression among a trio of island passerines

Hybridisation between species was once considered a relatively uncommon occurrence but is now recognised to occur frequently across many different taxa. It can result in homogenisation of previously distinct forms, a potential conservation issue, but can also act as a catalyst for diversification through introgression and sharing of favourable genes. Repeated rounds of island colonisation followed by speciation result in secondary sympatry, with the potential for hybridisation between early and late arrivers. In the southwest Pacific, this situation has arisen in the avian family Zosteropidae (the white-eyes). Here we use whole genome sequencing of live birds and historical specimens to characterise hybridisation between three white-eye species on Norfolk Island: two island endemics, Zosterops tenuirostris and the now-extinct Zosterops albogularis, and Zosterops lateralis, which colonised the island in 1904. Despite over two million years of divergence between Z. lateralis and the two endemics, we provide genomic evidence of their hybridisation. First, we confirm the identities of three Z. lateralis x Z. tenuirostris hybrids and additionally identify one Z. lateralis x Z. albogularis hybrid. We also report asymmetric, genome-wide introgression from both endemics into Z. lateralis, with introgressed regions enriched for a range of potential functions. However, despite this introgression, species boundaries have been maintained, and the extant endemic Z. tenuirostris does not appear to be at risk of genetic extinction. Our work additionally demonstrates an unusual case of recent ghost introgression from the extinct Z. albogularis into Z. lateralis. This study sheds light on the genomic outcomes of secondary sympatry and its potential consequences for single-island endemics.

evolutionary biology↗

bioRxiv2020

Ecology and evolutionary history determine plastic responses to environmental variation in two closely related species

The evolution of plastic responses to external cues allows species to track the environmental variation they regularly experience. However, it remains unclear how plasticity evolves during adaptation. To test whether distinct patterns of plasticity is associated with recent adaptive divergence, we quantified plasticity for two closely related but ecologically divergent Sicilian daisy species (Senecio, Asteraceae). We sampled c.40 genotypes of each species from natural populations on and around Mt Etna and then reciprocally transplanted multiple clones of each genotype into four field sites along an elevational gradient representing each species native range, the edge of their range, and conditions outside their native range. At each elevation we quantified survival and measured leaf traits that included investment (specific leaf area), morphology, chlorophyll fluorescence, pigment content and gene expression. As evidence of adaptive divergence, both species performed better at their native site and better than the species from the other habitat. Traits and differentially expressed genes that changed with elevation in one species often showed little change in the other species, or changed in the opposite direction. Adaptive divergence is therefore associated with the evolution of distinct plastic responses to environmental variation, despite these two species sharing a recent common ancestor.

evolutionary biology↗