How to define nativeness in vagile organisms: lessons from the cosmopolitan mossBryum argenteumon the island of Tenerife (Canary Islands)

Abstract

The distinction between native and introduced biotas presents unique challenges that culminate in organisms with high long-distance dispersal capacities in a rapidly changing world. Bryophytes, in particular, exhibit large distribution ranges, and some species can truly be qualified as cosmopolitan. Cosmopolitan species, however, typically occur in disturbed environments, raising the question of their nativeness throughout their range. Here, we employ genetic data to address the question of the origin of the cosmopolitan, weedy moss Bryum argenteum on the island of Tenerife. The genetic diversity of B. argenteum on Tenerife was comparable to that found in continental areas due to recurrent colonisation events, erasing any signature of a bottleneck that would be expected in the case of a recent colonisation event. The molecular dating analyses indicated that the first colonisation of the island took place more than 100,000 years ago, i.e. well before the first human settlements. Furthermore, the significant signal for isolation-by-distance found in B. argenteum within Tenerife points to the substantial role of genetic drift in establishing the observed patterns of genetic variation. Together, the results support the hypothesis that B. argenteum is native on Tenerife; although the existence of haplotypes shared between Tenerife and continental areas suggests that more recent, potentially man-mediated introduction also took place. While defining nativeness in organisms that are not deliberately introduced, and wherein the fossil record is extremely scarce, is an exceedingly challenging task, our results suggest that population genetic analyses can represent a useful tool to help distinguish native from alien populations.

Climate threat on the Macaronesian endemic bryophyte flora

“…Furthermore, recent phylogeographic evidence suggests that formerly endemic Macaronesian species have colonized several times the western Atlantic fringe of Europe since the last glacial maximum 28 . Within the endemic element of the Macaronesian bryophyte flora, the strong genetic structure observed at small scales 39 40 41 and significant shifts in the expression of mating systems and associated dispersal life-history traits 2 point, however, to dispersal limitations. These observations raise substantial concerns on the ability of Macaronesian bryophyte species to migrate to macroclimatically suitable areas on the continent as a response to the dramatic decrease of their suitable areas on the islands during the next decades.…”

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

“…, though see Collins and Cruickshank for a critique) or methods that utilize molecular clocks coupled with population genetics to determine whether a species arrived in a location prior to human colonization (Pisa et al. ). While our approach cannot provide species identifications for specimens absent from the reference library, it can be used to prioritize which specimens are examined by trained taxonomists.…”

“…Yet, DNA approaches fail to identify potential quarantine species when previously sequenced individuals of that species are missing from the reference library. While previous research has shown that the utility of DNA sequences to improve biosecurity monitoring can further be increased through the integration of multiple forms of analysis (Collins et al 2012), other approaches that might improve the identification of these "known-unknown" and "unknown-unknown" specimens that are absent from reference libraries includes the use of multi-species multi-locus coalescent (Dowton et al 2014, though see Collins and Cruickshank 2014 for a critique) or methods that utilize molecular clocks coupled with population genetics to determine whether a species arrived in a location prior to human colonization (Pisa et al 2015). While our approach cannot provide species identifications for specimens absent from the reference library, it can be used to prioritize which specimens are examined by trained taxonomists.…”

Island biogeography: an avenue for research in bryology

“…the limited number of population genetic studies in island bryophytes prevents the emergence of robust conclusions on the effects of founder events in insular bryophytes (Q26). No signature of a bottleneck was found in populations of Bryum argenteum in tenerife, possibly because of recurrent immigrations events (Pisa et al 2015). If this pattern is indeed recurrent, it could prevent endemic speciation due to gene flow intensity (Vanderpoorten et al 2008(Vanderpoorten et al , 2011 or niche pre-emption (Silvertown et al, 2005), assuming that competition could play a sufficient role to shape bryophyte communities.…”

“…despite that variation of genetic diversity and similarity along elevation gradients (Pisa et al 2015, Sim-Sim et al 2015 suggests that island bryophytes may diversify as a response to environmental variation, they are characterized by non-radiating speciation modes within archipelagic regions (Patiño et al 2014a) and thus do not seem to be prone to ecological diversification (Q23-24). Pócs (2006) discussed potential radiations in Caribbean Pilotrichum P. Beauv.…”