Allopolyploid origin and niche expansion of Rhodiola integrifolia(Crassulaceae)

Polyploidy after hybridization between species can lead to immediate post-zygotic isolation,causing saltatory origin of new species.Although the incidence of polyploidization in plants is high,it is thought that a new polyploid lineage can succeed only if it establishes a new ecological niche divergent from its progenitor lineages.We tested the hypothesis that Rhodiola integrifolia from North America is an allopolyploid produced by R. rhodantha and R.rosea and determined whether its survival can be explained by the niche divergence hypothesis.To this end,we sequenced two low-copy nuclear genes(ncpGS and rpb2) in a phylogenetic analysis of 42 Rhodiola species and tested for niche equivalency and similarity using Schoener’s D as the index of niche overlap.Our phylogeny-based approach showed that R integrifolia possesses alleles from both R. rhodantha and rosea Dating analysis showed that the hybridization event that led to R.integrifolia occurred ca.1.67 Mya and niche modeling analysis showed that at this time,both R.rosea and R.rhodantha may have been present in Beringia,providing the opportunity for the hybridization event.We also found that the niche of R.integrifolia differs from that of its progenitors in both niche breadth and optimum.Taken together,these results confirm the hybrid origin of R.integrifolia and support the niche divergence hypothesis for this tetraploid species.Our results underscore the fact that lineages with no current overlapping distribution could produce hybrid descendants in the past,when climate oscillations made their distributions overlap.

Realized niche shift associated with Galinsoga quadriradiata(Asteraceae)invasion in China

Shifts in the realized niches of exotic species may play an important role in their invasion.Galinsoga quadriradiata has invaded China widely and occupied many climate zones that are different from its native range.We addressed the climatic niche shift of G.quadriradiata and evaluated how this could contribute to its invasion in China.We used the Maxent model to predict the potential distribution of G.quadriradiata using its native and invaded range occurrences and climatic variables.Principal component analysis was conducted to measure climatic niche shifts of G.quadriradiata during its invasion in China.The models revealed only 32.7%niche overlap between the native and invasive populations.The niche similarity of the two populations was significantly low(Schoener’s D=0.093,P<0.005),suggesting the occurrence of a niche shift.The envelop and center of the realized climatic niche in China has shifted to lower temperature and less precipitation compared to that in its native range.The majority of invaded areas in southern China are in the stabilizing zone,whereas the colonization and adaptation zones are predicted to be at the leading edge of G.quadriradiata invasion in northern China.This suggests that the regional distribution of G.quadriradiata may be in a quasi-equilibrium state,and that the species continues to invade environmentally suitable areas.Alterations in G.quadriradiata’s niche would help to explain why this species is so invasive in China.

Climatic niche shift of an invasive shrub (Ulex europaeus): a global scale comparison in native and introduced regions

Aims Invasive species,which recently expanded,may help understand how climatic niche can shift at the time scale of the current global change.Here,we address the climatic niche shift of an invasive shrub(common gorse,Ulex europaeus)at the world and regional scales to assess how it could contribute to increasing invasibility.Methods Based on a 28187 occurrences database,we used a combination of 9 species distribution models(SDM)to assess regional climatic niche from both the native range(Western Europe)and the introduced range in different parts of the world(North-West America,South America,North Europe,Australia and New Zealand).Important Findings Despite being restricted to annual mean temperature between 4℃ and 22℃,as well as annual precipitation higher than 300 mm/year,the range of bioclimatic conditions suitable for gorse was very large.Based on a native versus introduced SDM comparison,we highlighted a niche expansion in North-West America,South America and to a lesser degree in Australia,while a niche displacement was assessed in North Europe.These niche changes induced an increase in potential occupied areas by gorse by 49,111,202 and 283%in Australia,North Europe,North-West America and South America,respectively.On the contrary,we found no evidence of niche change in New Zealand,which presents similar climatic condition to the native environment(Western Europe).This study highlights how niche expansion and displacement of gorse might increase invasibility at regional scale.The change in gorse niche toward new climatic conditions may result from adaptive plasticity or genetic evolution and may explain why it has such a high level of invasibility.Taking into account the possibility of a niche shift is crucial to improve invasive plants management and control.

Northwestward range expansion of the bumblebee Bombus haematurus into Central Europe is associated with warmer winters and niche conservatism

Species range expansions are crucial for understanding niche formation and the interaction with the environment.Here,we studied the bumblebee Bombus haematurus Kriechbaumer,1870,a species historically distributed from northern Serbia through northern Iran which has very recently started expanding northwestward into Central Europe without human-mediated dispersal(i.e.,it is a natural spread).After updating the global distribution of this species,we investigated if niche shifts took place during this range expansion between newly colonized and historical areas.In addition,we have explored which climatic factors may have favored the natural range expansion of the species.Our results indicated that Bombus haematurus has colonized large territories in 7 European countries outside the historical area in the period from the 1980s to 2018,a natural expansion over an area that equals 20%of the historical distribution.In addition,this bumblebee performs generalism in flower visitation and it occurs in different habitats,although a preference for forested areas clearly emerges.The land-use associated with the species in the colonized areas is similar to the historical distribution,indicating that no major niche shifts occurred during the spread.Furthermore,in recently colonized localities,the range expansion was associated with warming temperatures during the winter and also during both queen overwintering and emergence phases.These findings document a case of natural range expansion due to environmental change rather than due to niche shifts,and specifically they suggest that warmer winters could be linked to the process of natural colonization of new areas.