Ghosts of the Past: How DNA Reveals an Extinct Island Lineage

Islands offer an ideal setting to study evolution in action. Their isolation allows scientists to explore how new species form, a process known as speciation. When a few individuals colonise a new island, they often adapt to its unique conditions and then gradually evolve into a separate species from their mainland relatives. But not all colonisation attempts are successful. Many species fail to establish or eventually disappear, leaving only traces behind in the genetic record. A new study from the Canary Islands, published as part of the Special Issue “Evolution on Islands” in the Evolutionary Journal of the Linnean Society by Emerson, Campedel & Noguerales, uses molecular genetics to uncover these hidden stories.

Insects are particularly valuable for studying evolution on islands because their diversity, abundance, and often limited ability to disperse make them sensitive indicators of how species form and disappear. Because of their small size and the variety of habitats they occupy, insects often evolve unique lineages even when separated by short distances. The weevils from the Canary Islands offer a unique opportunity to explore these patterns. In this study, researchers examined the Laparocerus tessellatus group (species complex of closely related weevils) to understand how different island populations are related, focusing on Laparocerus auarita from La Palma. Earlier research hinted that this species might have arisen from a mix of colonists from Tenerife and Gran Canaria. Emerson et al. set out the following questions: (i) was L. auarita formed through hybridisation between these two island lineages, or (ii) does an undiscovered second species exist on La Palma?

To investigate these questions, more than 200 weevils were collected from three Canary Islands: La Palma, Tenerife, and Gran Canaria. Each island’s populations were sampled from several sites to capture as much genetic variation as possible. The team extracted DNA from each specimen and used modern genomic techniques to analyse thousands of differences across the genome, allowing them to look beyond single genes and compare overall genetic patterns among islands. They focused on two types of genetic information: mitochondrial DNA, which is inherited from the mother and helps trace lineage history, and nuclear DNA, which represents the full genetic makeup of each individual.

To interpret these data, the researchers examined population structure and genetic diversity to see how variation is distributed within and between islands. They also reconstructed phylogenetic relationships to identify how island populations are evolutionarily related, and applied demographic modelling, which tests different historical scenarios such as isolation, colonisation, or hybridisation. By combining these approaches, the team built a detailed picture of how the weevils on each island are related and whether La Palma’s species shows signs of hybridisation.

The analyses revealed a clear pattern of colonisation and loss. Nuclear genetic data showed that the La Palma weevil population, Laparocerus auarita, originated from Tenerife, not from Gran Canaria, as once suspected (Figure 1a). The researchers found no evidence of a second, hidden species on La Palma and little sign of hybridisation in the nuclear genome, which reflects overall ancestry. Yet the mitochondrial DNA (inherited through the mothers) told a different story, showing traces of ancestry from both Tenerife and Gran Canaria (Figure 1b). This mismatch suggests that after Tenerife weevils colonised La Palma, a second, short-lived colonisation from Gran Canaria occurred. The two lineages briefly interbred, but the Gran Canaria population eventually disappeared, leaving behind only its mitochondrial signature in the surviving species. The scientists suggest that the already-established Tenerife weevils may have outcompeted the newcomers, but with selection favouring the persistence of the Gran Canaria mitochondrial DNA within La Palma. This work shows how genetic data can reveal the traces of species that no longer exist, offering new insight into the outcomes of island colonisation.

This research demonstrates how modern genetic tools can reveal extinction events that would otherwise go unnoticed. By using genome-wide data, scientists can detect when a species colonised an island, briefly established, and then disappeared, leaving only genetic traces behind. The findings suggest that colonisation between islands may be more common than previously thought, but success is limited when closely related species are already present. Importantly, this study demonstrates that even short-lived species can leave a lasting mark on the genetic landscape, highlighting the hidden dynamics of island biodiversity. By revealing these “ghost lineages”, studies like this help us better understand how colonisation, hybridisation, and extinction together shape the diverse and fragile ecosystems of islands.