Biogeography of Mediterranean Hotspot Biodiversity: Re-Evaluating the 'Tertiary Relict' Hypothesis of Macaronesian Laurel Forests

Abstract

The Macaronesian laurel forests (MLF) are dominated by trees with a laurophyll habit comparable to evergreen humid forests which were scattered across Europe and the Mediterranean in the Paleogene and Neogene. Therefore, MLF are traditionally regarded as an old, 'Tertiary relict' vegetation type. Here we address the question if key taxa of the MLF are relictual. We evaluated the relict hypothesis consulting fossil data and analyses based on molecular phylogenies of 18 representative species. For molecular dating we used the program BEAST, for ancestral trait reconstructions BayesTraits and Lagrange to infer ancestral areas. Our molecular dating showed that the origins of four species date back to the Upper Miocene while 14 originated in the Plio-Pleistocene. This coincides with the decline of fossil laurophyllous elements in Europe since the middle Miocene. Ancestral trait and area reconstructions indicate that MLF evolved partly from pre-adapted taxa from the Mediterranean, Macaronesia and the tropics. According to the fossil record laurophyllous taxa existed in Macaronesia since the Plio- and Pleistocene. MLF are composed of species with a heterogeneous origin. The taxa dated to the Pleistocene are likely not 'Tertiary relicts'. Some species may be interpreted as relictual. In this case, the establishment of most species in the Plio-Pleistocene suggests that there was a massive species turnover before this time. Alternatively, MLF were largely newly assembled through global recruitment rather than surviving as relicts of a once more widespread vegetation. This process may have possibly been triggered by the intensification of the trade winds at the end of the Pliocene as indicated by proxy data.

Pleistocene extinctions as drivers of biogeographical patterns on the easternmost Canary Islands

“…Désamoré et al., ; Franzke, Sharif Samani, Neuffer, Mummenhoff, & Hurka, ; García‐Verdugo, Mairal, Monroy, Sajeva, & Caujapé‐Castells, ; Jones, Reyes‐Betancort, Hiscock, & Carine, ; Kondraskov et al., ). Positive correlations between the geological age of a given archipelago and lineage colonization time may be therefore restricted to very few cases (Kondraskov et al., ). Rather, molecular reconstructions indicate that multiple waves of island immigrants through time, hybridization and back‐colonization are more common than initially thought (Caujapé‐Castells et al., ; Emerson, ).…”

Spatial and ecological population genetic structures within two island‐endemic Aeonium species of different niche width

“…A recent Bayesian divergence time dating based on ITS sequence data (Kondraskov et al. ; see also Thiv et al. ) found a cladogenetic origin in the late Pleistocene or even later for Ae.…”

“…; Kondraskov et al. ), suggesting rather recent species formation without sufficient time to differentiate from their respective ancestor and/or sister species. A recent Bayesian divergence time dating based on ITS sequence data (Kondraskov et al.…”

Island biogeography of the Macaronesian Gesnouinia and Mediterranean Soleirolia (Parietarieae, Urticaceae) with implications for the evolution of insular woodiness

“…However, an analysis on 18 representative and mainly woody laurel forest species by Kondraskov & al. () revealed that several of them might be too young to be Tertiary relicts. Concerning the number of colonization events within lineages, one colonization event or multiple colonization events to Macaronesia have been indicated (Carine & al., ; Silvertown, ; Silvertown & al., ).…”