You might think that animals with different appearances and habitats would genetically be very different. But this is not the case for a group of lizards found on island arcs in the Pacific Ocean.
Weirdly, a new study published in the Proceedings of the Royal Society B has discovered that a variety of different lizard species found in the Pacific are all unexpectedly closely related to beach-dwelling mourning geckos. This finding suggests that these creatures are all descended from a common ancestor that once lived along an ancient archipelago in the Western Pacific Ocean.
The team conducted phylogenetic analyses on 12 major lizard lineages. Nine belonged to the genus Lepidodactylus, the scaly-toed geckos, two to Luperosaurus, the fringed geckos, and one to Pseudogekko, the false geckos.
"The slender, long-bodied geckos of the genus Pseudogekko live deep in forests, and we didn't think they were related to the small, primarily coastal scaly-toed geckos," said study co-author Rafe Brown. "Another is Luperosaurus, the flap-legged geckos. They're big and robust and have thorns and flaps all over their bodies, and some are orders of magnitude larger than mourning geckos. It's astounding that these lizards that are so physically different have turned out to be close relatives."
The closest relatives of mourning geckos, members of Lepidodactlyus, all look very different, but according to the researchers, they all live along island arcs or areas where long-lost arcs have merged into continents. Therefore, the locations of these lizards include the Philipines, Fiji, Christmas Island, Borneo, and eastern Melanesia.
The team used DNA sequencing data and conducted statistical analysis to investigate the divergence of the lizards, which probably took place between 30 and 40 million years ago.
A very long time ago, there was a chain of islands running through the Pacific called the Vitiaz Arc. It is likely that the fragmentation of the Vitiaz Arc, which later became islands like the Philipines, Fiji, and the Solomon Islands, allowed Lepidoactylus lizards to gain a broad and varied distribution across these areas, thus shaping their evolution.
This is why the lizards were unexpectedly found to be closely related – they must be descended from a common ancestor that once lived along the Vitiaz Arc.
Interestingly, the new findings relate to the taxon cycle, a model created by biologist and world-class ant expert Edward O. Wilson. He proposed that when species spread out and colonize new areas on islands, they must be adapted to survive harsh coastal conditions. They then evolve and adapt to more inland parts of the island, and spread into these habitats. Meanwhile, those on the coast get outcompeted and replaced by new colonizers, and the cycle starts again.
However, the new findings didn’t always match up with the model. “In some cases, we did not find the most ancient lizards to be specialists from interior habitats on the oldest land masses. Some ancient lineages are found today on the margins of arc islands or just on the edges of larger landmasses,” explained Brown.
"To me, this work underscores how much we have yet to understand about the complexity of species diversification on our planet, particularly in island systems," added study co-author Cameron Siler. "It is amazing to think about the role these ancient island systems played in the evolution of endemic communities in Wallacea, the West Pacific and Australasia."