Island Biogeography of Flexiseps Skinks in the Comoros Archipelago

Keywords: island biology, scincidae, 3D geometric morphometrics, genomics

Adaptation and diversification of species after they arrive on islands can lead to evolutionary oddities or shifts in observable traits in response to the different selective pressures of island systems. This project was my master's thesis research and examined the diversification and colonization history of two closely related skink species in the genus Flexiseps in the West Indian Ocean.

We were particualrily interested in untangling the biogeography of Flexiseps skinks on the Comoros Archipelago because, despite the geographic separation and morphological distinction between Flexiseps johannae from the Comoros Archipelago and Flexiseps ardouini from Madagascar, previous studies found very little genetic differentiation.

Here, we used an integrative approach, combining molecular and morphological data, to investigate variation among island populations and gain insight into the biogeographic history of these skinks.

What did we find?

The genomic data revealed a surprising relationship between the two species; Malagasy F. ardouini was found to be nested within the four Comoran island populations of F. johannae, and F. johannae divided into two population clusters corresponding to the eastern and western islands of the archipelago. Patterns of morphological variation, however, do not follow the same trends as molecular variation.

Our morphological data obtained through 3D geometric morphometric analysis of the skinks’ skulls and traditional morphometric analysis of external body characteristics revealed the two species are significantly morphologically distinct and can be easily distinguished by differences in body size, skull shape, and scale counts. Some morphological variation was also present among the Comoran island populations.

These results support a more complex colonization history of F. johannae on the Comoros Archipelago than previously considered. One possible dispersal route involves a there-and-back-again scenario with an initial colonization event from Madagascar and secondary re-colonization back to Madagascar.

Why does this matter?

Field sampling for this project helped inform about the status of F. johannae in the Comoros Archipelago, which was found to have a stable population trend throughout many habitats and elevations on the islands. This information was utilized in the most recent IUCN red list assessment for the species.

We hope this study initiates F. johannae in the Comoros Archipelago as an excellent new system to study dispersal and diversification in skinks, which may provide valuable insight into the mechanisms behind speciation on islands and body-form evolution in lizards.

Related Activities

Master Thesis:

Webster, KC. (2020) Island Diskinktion: An Investigation into the Molecular and Morphological Variability of a Skink Complex in the Comoros Archipelago. Ludwig-Maximilians University, Munich, Germany. Supervised by Dr. Oliver Hawlitschek, Dr. Mark D. Scherz, & Prof. Dr. Gerhard Haszprunar. (Contact me for PDF)

Conference Presentations:

Webster, KC, Glaw, F, Scherz, MD, & Hawlitschek, O. (2022) More Complex than You’d Skink: Morphological and Molecular Investigation into the Island Biogeography of Flexiseps Skinks in the Comoros Archipelago. Oral presentation. Joint Meeting of Ichthyologists & Herpetologists, Spokane, Washington, USA.
Webster, KC, Glaw, F, Scherz, MD, & Hawlitschek, O. (2019) Morphologically Diskinkt: Comparing Island Populations of Skinks in the Comoros Archipelago. Oral presentation. Societas Europaea Herpetologica (SEH) 20th European Congress, Milan, Italy.
Webster, KC, Glaw, F, Scherz, MD, & Hawlitschek, O. (2019) Morphologically Diskinkt: Comparing Island Populations of Skinks in the Comoros Archipelago. Poster presentation. Island Biology Conference, Réunion Island. (PDF)
Webster, KC, Glaw, F, Scherz, MD, & Hawlitschek, O. (2019) Morphologically Diskinkt: Comparing Island Populations of Skinks in the Comoros Archipelago. Oral presentation. 20th Meeting of the German Society for Biological Systematics, Munich, Germany.

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