Article (Scientific journals)
Why are so few island bryophytes endemic?
Mirolo, Sébastien; Ledent, Alice; González-Mancebo, Juana María et al.
In pressIn Biological Reviews
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Keywords :
speciation; endemism; evolution; island biogeography; island syndromes; hybridization; Macaronesia
Abstract :
[en] Endemism, a hallmark of island biodiversity, reaches its lowest levels among bryophytes compared with other land plants. Whether this pattern reflects low diversification rates, and why, or whether it is a result of loss of endemicity due to extinctions or subsequent continental (back-) colonization, is examined here through a review of available evidence in the Macaronesian flora. Significant genetic differentiation (GST, based on allele frequencies) was consistently found between Macaronesian and continental populations, ruling-out the hypothesis that intense migrations necessarily hamper differentiation. A significant phylogeographical signal in the data (NST > GST; NST being a GST-analog incorporating phylogenetic relationships among alleles), involving higher mutation rates than dispersal rates and evidencing incipient speciation, was further found in more than 1/3 of the species investigated. The significantly higher average NST between extra-European regions and Macaronesia compared to Europe and Macaronesia suggests, however, that incipient speciation is more likely to occur between distant (Macaronesian versus extra-European) than closer (Macaronesian versus European) populations. In line with this, ancestral area estimations in Macaronesian endemic bryophyte species revealed that at least 50% of them have an extra-European origin, in contrast with the almost exclusively (>90%) European/Mediterranean origin of Macaronesian endemic spermatophytes. Allopatric speciation via long-distance dispersal and subsequent divergence of a single endemic species prevails in island bryophytes, wherein sympatric radiations virtually never occur. Such a speciation mode does not trigger high rates of endemism, in contrast to radiations in Macaronesian spermatophytes, which contribute to 56% of the total number of endemics. Several mechanisms may explain the failure of island bryophytes to diversify in situ, including the fact that oceanic islands are too small or insufficiently isolated from each other or from continents to promote sympatric speciation, the lack of key innovations, and phylogenetic niche conservatism for stable habitats not prone to trigger radiations. In comparison with spermatophytes, continental (back-)colonization further largely prevails in bryophytes and, unlike in many instances in angiosperms, is not followed by in situ speciation on the mainland. The consequent loss of the endemic status of species that did speciate on islands but subsequently enlarged their range further accounts for the low rates of endemism among island bryophyte floras and invalidates the use of endemism rates as a proxy of speciation rates in this group.
Disciplines :
Environmental sciences & ecology
DOI :
10.1002/brv.70127
Author, co-author :
Mirolo, Sébastien  ;  Université de Liège - ULiège > Integrative Biological Sciences (InBioS)
Ledent, Alice  ;  Université de Liège - ULiège > Integrative Biological Sciences (InBioS)
González-Mancebo, Juana María;  ULL - Universidad de La Laguna > Departamento de Botanica, Ecología y Fisiología Vegetal
Gabriel, Rosalina;  University of the Azores > Centre for Ecology, Evolution and Environmental Changes
Sim-Sim, Manuela;  Universidade de Lisboa > Museu Nacional de História Natural e da Ciência > Centre for Ecology, Evolution and Environmental Changes
Collart, Flavien  ;  Université de Liège - ULiège > Integrative Biological Sciences (InBioS)
Patiño, Jairo ;  CSIC - Consejo Superior de Investigaciones Científicas > Instituto de Productos Naturales y Agrobiología (IPNA) > Island Ecology and Evolution Research Group
Vanderpoorten, Alain  ;  Université de Liège - ULiège > Département de Biologie, Ecologie et Evolution > Biologie de l'évolution et de la conservation - Unité aCREA-Ulg (Conseils et Recherches en Ecologie Appliquée)
 These authors have contributed equally to this work.
Language :
English
Title :
Why are so few island bryophytes endemic?
Publication date :
In press
Journal title :
Biological Reviews
ISSN :
1464-7931
eISSN :
1469-185X
Publisher :
John Wiley & Sons, Oxford, United Kingdom
Peer reviewed :
Peer Reviewed verified by ORBi
Data Set :
APPENDIX_Macaronesia_liverworts-hornworts_distribs.xlsx

Distribution of liverwort and hornwort species present in the Azores, Madeira, Canary Islands, Cape Verde and surrounding mainland areas. AZO, CAN, MAD and MAC refer to species that are endemic to the Azores, Canary Islands, Madeira, and Macaronesia (multiple-archipelago endemics), respectively.

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