How to define nativeness in vagile organisms: lessons from the cosmopolitan moss Bryum argenteum on the island of Tenerife (Canary Islands)

Categorization of species as native or nonnative using DNA sequence signatures without a complete reference library

New genetic diagnostic approaches have greatly aided efforts to document global biodiversity and improve biosecurity. This is especially true for organismal groups in which species diversity has been underestimated historically due to difficulties associated with sampling, the lack of clear morphological characteristics, and/or limited availability of taxonomic expertise. Among these methods, DNA sequence barcoding (also known as "DNA barcoding") and by extension, meta-barcoding for biological communities, has emerged as one of the most frequently utilized methods for DNA-based species identifications. Unfortunately, the use of DNA barcoding is limited by the availability of complete reference libraries (i.e., a collection of DNA sequences from morphologically identified species), and by the fact that the vast majority of species do not have sequences present in reference databases. Such conditions are critical especially in tropical locations that are simultaneously biodiversity rich and suffer from a lack of exploration and DNA characterization by trained taxonomic specialists. To facilitate efforts to document biodiversity in regions lacking complete reference libraries, we developed a novel statistical approach that categorizes unidentified species as being either likely native or likely nonnative based solely on measures of nucleotide diversity. We demonstrate the utility of this approach by categorizing a large sample of specimens of terrestrial insects and spiders (collected as part of the Moorea BioCode project) using a generalized linear mixed model (GLMM). Using a training data set of known endemic (n = 45) and known introduced species (n = 102), we then estimated the likely native/nonnative status for 4,663 specimens representing an estimated 1,288 species (412 identified species), including both those specimens that were either unidentified or whose endemic/introduced status was uncertain. Using this approach, we were able to increase the number of categorized specimens by a factor of 4.4 (from 794 to 3,497), and the number of categorized species by a factor of 4.8 from (147 to 707) at a rate much greater than chance (77.6% accuracy). The study identifies phylogenetic signatures of both native and nonnative species and suggests several practical applications for this approach including monitoring biodiversity and facilitating biosecurity.

Evolutionary origin of the latitudinal diversity gradient in liverworts

A latitudinal diversity gradient towards the tropics appears as one most recurrent patterns in ecology, but the mechanisms underlying this pattern remain an area of controversy. In angiosperms, the tropical conservatism hypothesis proposes that most groups originated in the tropics and are adapted to a tropical climatic regime, and that relatively few species have evolved physiological adaptations to cold, dry or unpredictable climates. This mechanism is, however, unlikely to apply across land plants, and in particular, to liverworts, a group of about 7500 species, whose ability to withstand cold much better than their tracheophyte counterparts is at odds with the tropical conservatism hypothesis. Molecular dating, diversification rate analyses and ancestral area reconstructions were employed to explore the evolutionary mechanisms that account for the latitudinal diversity gradient in liverworts. As opposed to angiosperms, tropical liverwort genera are not older than their extra-tropical counterparts (median stem age of tropical and extra-tropical liverwort genera of 24.35 ± 39.65 Ma and 39.57 ± 49.07 Ma, respectively), weakening the 'time for speciation hypothesis'. Models of ancestral area reconstructions with equal migration rates between tropical and extra-tropical regions outperformed models with asymmetrical migration rates in either direction. The symmetry and intensity of migrations between tropical and extra-tropical regions suggested by the lack of resolution in ancestral area reconstructions towards the deepest nodes are at odds with the tropical niche conservatism hypothesis. In turn, tropical genera exhibited significantly higher net diversification rates than extra-tropical ones, suggesting that the observed latitudinal diversity gradient results from either higher extinction rates in extra-tropical lineages or higher speciation rates in the tropics. We discuss a series of experiments to help deciphering the underlying evolutionary mechanisms.

Climate threat on the Macaronesian endemic bryophyte flora

Oceanic islands are of fundamental importance for the conservation of biodiversity because they exhibit high endemism rates coupled with fast extinction rates. Nowhere in Europe is this pattern more conspicuous than in the Macaronesian biogeographic region. A large network of protected areas within the region has been developed, but the question of whether these areas will still be climatically suitable for the globally threatened endemic element in the coming decades remains open. Here, we make predictions on the fate of the Macaronesian endemic bryophyte flora in the context of ongoing climate change. The potential distribution of 35 Macaronesian endemic bryophyte species was assessed under present and future climate conditions using an ensemble modelling approach. Projections of the models under different climate change scenarios predicted an average decrease of suitable areas of 62-87% per species and a significant elevational increase by 2070, so that even the commonest species were predicted to fit either the Vulnerable or Endangered IUCN categories. Complete extinctions were foreseen for six of the studied Macaronesian endemic species. Given the uncertainty regarding the capacity of endemic species to track areas of suitable climate within and outside the islands, active management associated to an effective monitoring program is suggested.