No borders during the post‐glacial assembly of European bryophytes

Abstract

Climatic fluctuations during the Last Glacial Maximum (LGM) exerted a profound influence on biodiversity patterns, but their impact on bryophytes, the second most diverse group of land plants, has been poorly documented. Approximate Bayesian computations based on coalescent simulations showed that the post‐glacial assembly of European bryophytes involves a complex history from multiple sources. The contribution of allochthonous migrants was 95–100% of expanding populations in about half of the 15 investigated species, which is consistent with the globally balanced genetic diversities and extremely low divergence observed among biogeographical regions. Such a substantial contribution of allochthonous migrants in the post‐glacial assembly of Europe is unparalleled in other plants and animals. The limited role of northern micro‐refugia, which was unexpected based on bryophyte life‐history traits, and of southern refugia, is consistent with recent palaeontological evidence that LGM climates in Eurasia were much colder and drier than what palaeoclimatic models predict.

Bryophytes are predicted to lag behind future climate change despite their high dispersal capacities

“…If, due to dispersal constraints, a species is absent from climatically suitable conditions, climatic suitability models may therefore underestimate species niche range 63 . Although bryophytes are extremely good dispersers, so that, unlike in some angiosperm species 18 , there is no mismatch between the predicted and observed northern limit of distribution 39 , the present analyses suggest that there is a time-lag of more than a century before newly suitable areas are fully colonized. Nevertheless, our datapoints were sampled across the entire European range of the species, encompassing the full range of climatic conditions that they can experience, so that the potential failure to incorporate localities where the species had not time to disperse yet would not affect the boundaries of our global niche estimate.…”

“…While bryophytes successfully back-colonized areas of suitable climate since the end of the last glacial maximum, 18,000 years ago 39 , our results suggest that, at best,~30% of the species would be at equilibrium with their environment by 2050. This indicates that bryophytes are not equipped to track the very fast rates of ongoing climate change projected for the course of the next decades.…”

“…Finally, in addition to short-distance dispersal events with a probability defined by the kernel described above, any pixel located at >10 km from a potential source could be colonized by LDD. The maximum LDD distance was set to unlimited based on phylogeographic evidence 39 . Following Robledo-Arnuncio et al 31 , we employed the results of previous Approximate Bayesian Computation methods for LDD inference from genetic structure data in bryophytes 39 , 77 to define the range of LDD probability values, set to 0, 10 −4 , 10 −3 , 10 −2 and 10 −1 .…”

Welcome to migrants in a borderless Europe: bryophytes show the way to go

“…Although several species-specific studies have been published (see Kyrkjeeide et al 2014 for review), there has been to date no comprehensive effort to reconstruct the Quaternary history of bryophytes. Here, we review most recent phylogeographic evidence (Patiño et al 2015;Ledent et al 2019) to show that post-glacial recolonization patterns in European bryophytes are unique among previously published work on other groups of plants and animals due to the substantial contribution of allochtonous migrants, with a substantial input of the Macaronesian islands that would, at first sight, not be expected. 1.1.…”

“…In this framework, Patiño et al (2015) and Ledent et al (2019) attempted at reconstructing the post-glacial history of 11 and 12 bryophyte species whose distribution range is restricted to the North-East Atlantic region, encompassing the Macaronesian islands and the western fringe of Europe, and encompasses the entire European continent as well as large portions of the Holarctic, respectively. Coalescence simulations were performed in both cases to determine whether the post-gla- cial recolonization of Europe took place from (1) local refugia located in the southern (1a) or northern (1b) regions or (2) from allochtonous migrants.…”