Sunday, February 4, 2018

[Fungi • 2018] High Diversity, High Insular Endemism and Recent Origin in the Lichen Genus Sticta (lichenized Ascomycota, Peltigerales) in Madagascar and the Mascarenes

in Simon, Goffinet, Magain & Sérusiaux, 2018. 

•  A lineage of Sticta restricted to the Indian Ocean underwent a rapid radiation.
•  The adaptive radiation gave rise to 31 species, most with small-range endemism.
•  The dramatic diversification followed a single colonization event (c. 11 Mya).

Lichen biodiversity and its generative evolutionary processes are practically unknown in the MIOI (Madagascar and Indian Ocean Islands) biodiversity hotspot. We sought to test the hypothesis that lichenized fungi in this region have undergone a rapid radiation, following a single colonization event, giving rise to narrow endemics, as is characteristic of other lineages of plants. We extensively sampled specimens of the lichen genus Sticta in the Mascarene archipelago (mainly Réunion) and in Madagascar, mainly in the northern range (Amber Mt and Marojejy Mt) and produced the fungal ITS barcode sequence for 148 thalli. We further produced a four-loci data matrix for 68 of them, representing the diversity and geographical distribution of ITS haplotypes. We reconstructed the phylogenetic relationships within this group, established species boundaries with morphological context, and estimated the date of the most recent common ancestor. Our inferences resolve a robust clade comprising 31 endemic species of Sticta that arose from the diversification following a single recent (c. 11 Mya) colonization event. All but three species have a very restricted range, endemic to either the Mascarene archipelago or a single massif in Madagascar. The first genus of lichens to be studied with molecular data in this region underwent a recent radiation, exhibits micro-endemism, and thus exemplifies the biodiversity characteristics found in other taxa in Madagascar and the Mascarenes.

Keywords: Biogeography; Indian Ocean; Lobariaceae; Photomorph; Radiation

Fig. 1. Representatives of MIOI Sticta species. 
(B) Sticta sp. 20. (C) Sticta sp. 23. (D) S. macrophylla. (E) Sticta sp. 22.
Photographs taken in the field by E. Sérusiaux (A–D) and B. Goffinet (E).

The present study demonstrates the existence of a well-supported monophyletic lineage within the genus Sticta, which is endemic to three islands of the Western Indian Ocean: Madagascar, Mauritius and Réunion (MIOI hotspot). This clade comprises an assemblage of mostly narrow endemic species six times more diverse than previously recognized, highlighting the extent of the undiscovered diversity within lichen-forming fungi in this region, especially in the genus Sticta. Our results strongly support a local species-rich radiation starting in the Late Miocene, that is concomitant with the emergence of the Mascarene archipelago. Thus, the following biogeographic scenario can be tentatively suggested for the MIOI Sticta species: their most recent common ancestor reached either Madagascar or the Mascarenes, via a single long dispersal event, most likely from an area in the Southern Hemisphere; thereafter migrations between the three islands shaped the observed evolutionary patterns and local speciation, including within each Madagascan montane area, giving rise to a rich complex of small-range endemic species.

Antoine Simon, Bernard Goffinet, Nicolas Magain and Emmanuël Sérusiaux. 2018. High Diversity, High Insular Endemism and Recent Origin in the Lichen Genus Sticta (lichenized Ascomycota, Peltigerales) in Madagascar and the Mascarenes. Molecular Phylogenetics and Evolution.  122; 15–28.  DOI: 10.1016/j.ympev.2018.01.012