Origin of Mediterranean insular endemics in the Boraginales: integrative evidence from molecular dating and ancestral area reconstruction

Publication Type:Journal Article
Year of Publication:2009
Authors:Mansion, G., F. Selvi, A. Guggisberg, E. Conti
Journal:Journal of Biogeography
Start Page:1282
Keywords:Anchusa, Borago, Canary Islands, continental fragment island, Corsica, Echium, endemism, oceanic island, Sardinia.

Aim The presence of numerous reliable fossils and the occurrence of many
endemic island species make the Boraginales particularly suitable for integrative
biogeographical studies. In this paper we aim to elucidate the time frame
and events associated with the origin of selected borages endemic to the
Mediterranean climate zone. More specifically, we describe and examine the
alternative palaeo- and neoendemic hypotheses for their origin.
Location Corsica and Sardinia (continental fragment islands) and the Canary
Islands (an oceanic island archipelago).
Methods Eighty-nine accessions, representing 30 genera from five families
ascribed to the Boraginales, were examined for six chloroplast DNA regions. We
used an integrative approach including phylogenetic analyses (MrBayes),
Bayesian molecular dating (T3 package) with four fossil constraints on nodes,
and biogeographical reconstructions (diva) to elucidate the temporal and spatial
origins of the Corso-Sardinian and Canary Island endemics.
Results Species of Echium endemic to the Canary Islands diverged from their
continental sister clade during the Miocene (15.3 ± 5.4 Ma), probably after the
rise of the oldest islands (c. 20 Ma). Corso-Sardinian endemics of Borago
diverged from their primarily North African sister clade during the late
Miocene-Pliocene (c. 6.9 ± 3.6 Ma), well after the initial fragmentation of the
islands (c. 30 Ma). Similarly, Corso-Sardinian endemics of Anchusa diverged
from the South African Anchusa capensis during the Pliocene–Pleistocene (c. 2.7 ± 2.1 Ma).

Main conclusions The present study reveals an Anatolian origin for Anchusa,
Borago and Echium and underlines the importance of the Eastern Mediterranean
region as a possible reservoir for plant evolution in the Mediterranean Basin. For
Anchusa and Borago, the divergence from their respective sister clades on the two
types of islands post-dated the formation of the islands, thus supporting the neo-
endemic hypothesis, whereas the dating results for the origin of Echium endemics
were less conclusive.


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