Which factors have stronger explanatory power for primary wind dispersal distance of winged diaspores:the case of Zygophyllum xanthoxylon(Zygophyllaceae)?

Aims How seed dispersal distance is related to various factors is a major challenge for seed ecologists.However,there are different answers as to which factor is most important in determining wind dispersal distance.This study is to quantitatively describe the relationship between various factors and primary wind dispersal distance of winged diaspores.Methods The dispersal distances of five morphologies of winged diaspores in Zygophyllum xanthoxylum(Zygophyllaceae)were measured under controlled conditions in a wind tunnel.The explanatory power of environmental factor(i.e.wind speed),plant trait(i.e.release height)and diaspore attributes(i.e.wing loading(the ratio of diaspore mass to projected area),settlement-velocity,shape index(the variance of diaspore length,width and thickness))to the variation in dispersal distance was assessed by releasing diaspores at varying wind speeds and release heights.Important Findings Wind speed and seed release height were the strongest explanatory factors to dispersal distance,contributing 41.1%and 24.8%(P<0.01)to total variation in dispersal distance,respectively.Wind speed accounted more for relatively light disc-shaped seeds than for relatively heavy spherical seeds.Wing loading,shape index and settlement-velocity explained 9.0%(P<0.01),1.4%(P<0.01)and 0.9%(not significant)of the variation in dispersal distance,respectively.From disc-shaped to four-winged diaspores,relative contributions of wing loading and shape index decreased but contribution of settlementvelocity increased.The relative contributions of various factors to wind seed dispersal distance may change with the change in seed morphology.

Evolutionary importance of the relationship between cytogeography and climate:New insights on creosote bushes from North and South America

Relationships between genome size and environmental variables suggest that DNA content might be adaptive and of evolutionary importance in plants.The genus Larrea provides an interesting system to test this hypothesis,since it shows both intra-and interspecific variation in genome size.Larrea has an amphitropical distribution in North and South American deserts,where it is most speciose.Larrea tridentata in North America shows a gradient of increasing autopolyploidy;while three of the four studied South American species are diploids,Larrea divaricata,Larrea nitida,Larrea ameghinoi,and the fourth is an allopolyploid,Larrea cuneifolia.We downloaded available focal species’georeferenced records from seven data reservoirs.We used these records to extract biologically relevant environmental variables from WorldClim at 30 arc seconds scale,to have a broad characterization of the variable climatic conditions of both regions,and a climatic envelope for each species.We estimated relative DNA content index and relative monoploid genome values,by flow cytometry,of four most abundant Larrea species throughout their respective ranges.Then we winnow the bioclimatic dataset down to uncorrelated variables and sampled locales,to analyse the degree of association between both intra-and interspecific relative DNA content and climatic variables that are functionally relevant in arid environments using Pearson correlations,general linear and mixed effects models.Within the genus Larrea,relative DNA content increases with rising temperature and decreases with rising precipitation.At the intraspecific level,all four species show relative DNA content variation across climatic conditions.Larrea is a genus that shows genome size variation correlated with climate.Our results are also consistent with the hypothesis that extreme environmental pressures may have facilitated repeated whole genome duplication events in North America,while in South America,reticulate evolution,as allopolyploidization,and speciation might have been climate-dependent since the Oligocene.