Unraveling the evolutionary history of the Galapagos Rail

When did this species reach the Galapagos Islands and where did it come from?

As more and more bird genomes are being sequenced (see this paper for the latest overview), it is surprising to come across bird species without genetic resources. But these species do exist, such as the Galapagos Rail (Laterallus spilonota). The lack of genetic studies on this rail might be an even bigger surprise when you took a closer look at its common name: this species occurs on the Galapagos, one of the most studied island archipelagos in the world. While some charismatic or historically relevant species attracted a lot of scientific attention – just think of the iconic Darwin’s Finches – the Galapagos Rail has not been studied with genetic tools yet. Hence, we know little about the evolutionary history of this rail and, more importantly, we have almost no knowledge about its conservation status from a genetic point of view. The Galapagos Rail might be heading for extinction and we would not have a clue. Luckily, a recent study in the journal Diversity provided the first genetic assessment of the Galapagos Rail.

Phylogenetics

Jaime Chaves and his colleagues sequenced the DNA of several recent and historical samples to reconstruct the evolutionary history of the Galapagos Rail. Phylogenetic analyses revealed that the ancestor of this species reached the Galapagos Islands about 1.2 million years ago. This timing is similar to other species, for example Darwin’s Finches arrived between 1 and 1.5 million years ago. The sister species of the Galapagos Rail turned out to be the Black Rail (Laterallus jamaicensis), which currently has a patchy distribution across North America and along the coast of Peru and Chile. The exact source population of Black Rails that gave rise to the Galapagos Rail remains to be determined with further sampling. It seems likely that the Galapagos Rail arose from birds dispersing out of the South American populations, but it is also possible that individuals migrating from North to Central America were blown off course and ended up on the Galapagos. Or perhaps an extinct “ghost” population was involved (such as in the Red-billed Chough). Plenty of hypotheses to explore.

The Galapagos Rail (#1) is most closely related to the Black Rail (#4) from which it split about 1.2 million years ago. From: Chaves et al. (2020) Diversity.

Genetic Diversity

More detailed analyses indicated little genetic differentiation between the island populations of the Galapagos Rail. This finding is rather surprising because this species is flightless and is thus not expected to disperse very far. The authors noted that these rails have been observed to forage near the coast and that they are capable of swimming significant distances. So, frequent movements between islands – which are on average 25 kilometers apart – are not impossible.

The researchers also reported low levels of genetic diversity in the Galapagos Rail, which can be explained by recent population bottlenecks. This species has suffered from human activities, such as habitat loss due to agricultural expansion and the introduction of non-native predators (mostly cats and rats). Currently, the Galapagos Rail can be found in higher numbers within restored habitats. They might thus recover from past population bottlenecks, although they still carry the genetic signatures of these events. Nonetheless, the information from this genetic study can help guide future conservation efforts to preserve the Galapagos Rail.

Only a few haplotypes (shared across different islands) were found for the different genetic markers. This low level of genetic diversity is probably due to past population bottlenecks. From: Chaves et al. (2020) Diversity.

References

Chaves, J. A., Martinez-Torres, P. J., Depino, E. A., Espinoza-Ulloa, S., García-Loor, J., Beichman, A. C., & Stervander, M. (2020). Evolutionary history of the Galápagos Rail revealed by ancient mitogenomes and modern samples. Diversity12(11), 425.

Featured image: Galapagos Rail (Laterallus spilonota) © John Gould | Wikimedia Commons

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