New species arise through the evolution of reproductive barriers between formerly interbreeding lineages. Yet, comprehensive assessments of potential reproductive barriers, which are needed to make inferences on processes driving speciation, are only available for a limited number of systems. In this study, we estimated individual and cumulative strengths of seven prezygotic and six postzygotic reproductive barriers between the recently diverged taxa Silene dioica (L.) Clairv. and S. latifolia Poiret using both published and new data. A combination of multiple partial reproductive barriers resulted in near-complete reproductive isolation between S. dioica and S. latifolia that is consistent with earlier estimates of gene flow between the taxa. Extrinsic barriers associated with adaptive ecological divergence were most important, while intrinsic postzygotic barriers had moderate individual strength but contributed only little to total reproductive isolation. These findings are most in line with ecological divergence as driver of speciation. We further found extensive variation in extrinsic reproductive isolation, ranging from sites with strong selection against migrants and hybrids to more intermediate sites where substantial hybridization is possible. This situation may allow for or even promote heterogeneous genetic divergence.
Range-wide presence records
Longitude and latitude (digital degrees, WGS84) for presence records of the campions S. dioica (L.) Clairv. (N=293) and of S. latifolia Poiret (N=395) throughout their native Eurasian ranges. Records were obtained from Prentice et al. (2008, Plant Systematics and Evolution 272: 23-37), Hathaway et al. (2009, Botanical Journal of the Linnean Society 161: 153-170), Rautenberg et al. (2010, Molecular Phylogenetics and Evolution 57: 978-991), Muir et al. (2012, Evolution 66: 1447-1458), from the Global Biodiversity Information Facility, GBIF (https://www.gbif.org/, accessed February 2017) and included records detailed in Table S1.
range_wd_presence_recs.csv
Sub-sampled range-wide presence records
Longitude and latitude (digital degrees, WGS84) for a subsample of presence records of the campions S. dioica (L.) Clairv. (N=206) and of S. latifolia Poiret (N=119) throughout their native Eurasian ranges (one sample per 0.05° latitude x 0.05° longitude). Records were obtained from Prentice et al. (2008, Plant Systematics and Evolution 272: 23-37), Hathaway et al. (2009, Botanical Journal of the Linnean Society 161: 153-170), Rautenberg et al. (2010, Molecular Phylogenetics and Evolution 57: 978-991), Muir et al. (2012, Evolution 66: 1447-1458), from the Global Biodiversity Information Facility, GBIF (https://www.gbif.org/, accessed February 2017) and included some records detailed in Table S1.
subsampled_ range_wd_presence_recs.csv
Swiss presence records
Longitude and latitude (digital degrees, WGS84) for presence records of the campions S. dioica (L.) Clairv. (N=4,466) and of S. latifolia Poiret (synonym: Silene pratensis (Rafn) Godr., N=1,802) within Switzerland. Records were obtained from the National Data and Information Center of the Swiss Flora (https://www.infoflora.ch/de/). Latitude and longitude are rounded to one digit according to the data use policy of the National Data and Information Center of the Swiss Flora (5 x 5 km precision); more precise records are available from the National Data and Information Center of the Swiss Flora upon request.
swiss_presence_recs.csv
Sub-sampled Swiss presence records
Longitude and latitude (digital degrees, WGS84) for a sub-sample of presence records of the campions S. dioica (L.) Clairv. (N=1,842) and of S. latifolia Poiret (synonym: Silene pratensis (Rafn) Godr., N=1,106) within Switzerland (one sample within 0.01° latitude x 0.01° longitude). Records were obtained from the National Data and Information Center of the Swiss Flora (https://www.infoflora.ch/de/). Latitude and longitude are rounded to one digit according to the data use policy of the National Data and Information Center of the Swiss Flora (5 x 5 km precision); more precise records are available from the National Data and Information Center of the Swiss Flora upon request.
subsampled_swiss_presence_recs.csv
Germination responses
Data from a germination experiment with freshly harvested seeds of crosses within Silene dioica (L.) Clairv., S. latifolia Poiret and of different hybrid classes between these species under three conditions, a dormancy breaking treatment (OPT), and conditions simulating diurnal temperature profiles during the seeding time of S. dioica (SD) or S. latifolia (SL, see methods). Column names: name, unique name of each seed lot, collected on the same day; ct4, cross type (SL: Silene latifolia, SD: Silene dioica, F1: first-generation hybrid, F2: second-generation hybrid, F3: third-generation hybrid, BC-SD: backcross toward SD, BC-SL: backcross toward SL [see also Table S2, Figure S1]); No, cross identity (see Table S2); Date: seed collection date as days from the start of the experiment; OPT, SD, SL, percentage of seeds germinating under OPT, SD, and SL conditions; weight, weight per seed in g (measured for entire seed lot before splitting), no.OPT, no.SD, no.SL, number of hard (likely viable) seeds which had not germinated; dead.OPT, dead.SD, dead.SL, number of dead (soft) seeds under OPT, SD, and SL conditions; TOTAL.sum, total number of seeds per seed lot (OPT + SD + SL); TOTAL.min, minimum number of seeds per trial (petri dish); comment, information on data pooling where seed number per trial was < 15 (see methods).
germination.csv
Climate data June-August
Average temperatures (minimum, mean, maxiumu) during the seed fall period of Silene dioica (L.) Clairv. and S. latifolia Poiret (June – August) for 20 populations of S. dioica and 19 populations of S. latifolia (Table S1). Data are calculated from long-term monthly averages (1960-1990) obtained from WorldClim – Global Climate Data (http://www.worldclim.org/, Hijmans et al., 2005, Int. J. Climatol. 25:1965-1978). Colum names: pop, population name; Sp, species [SD: S. dioica, SL, S. latifolia]; Max, maximum temperature June-August; Mean, mean temperature June-August; Min, minimum temperature June-August.
orig.climate.csv
Transplant experiment
Cumulative fitness (times flowered + 1 if the plant survived to the end of the experiment) in crosses within the campions Silene dioica (L.) Clairv. and S. latifolia Poiret, as well as their first- and second-generation hybrids, in a four-year transplant experiment at three sites of each species (data from Favre et al., 2017, New Phytologist 213, 1487-1499). Individuals that died soon after transplantation (transplant shock) or due to mole disturbance or could not be sexed were excluded from the dataset here (see Favre et al. 2017). Column names: Site.ID, identification of individuals across sites; site, transplant site; ID, identification number of individuals within sites; cross, cross type [SD: within S. dioica, SL: within S. latifolia, HD: SD female x SL male, HL: SL female x SD male, F2: second-generation hybrids (pooled)]; habitat, SD: transplanted within SD population, SL: transplanted within SL population; dblock, block within site; family, full-sib family; sex, plant sex; fitness.rev, cumulative fitness (times flowered + 1 if the plant survived to the end of the experiment).
transplant.data.RI.csv
Pollen competition
Percent hybrid offspring after mixed pollination with 1:1 mixed pollen loads in the campions Silene dioica (L.) Clairv. and S. latifolia Poiret (data from: Rahmé et al., 2009, Journal of Evolutionary Biology 22, 1637-1943). Column names: mother, individual; mother.sp, species [SD: S. dioica, SL: S. latifolia]; conspecific, number of offspring with con-specific father; heterospecific, number of offspring with hetero-specific father (hybrids); Unknown, number of offspring with unknown father (not considered); date.poll, pollination date(s); prop.consp, proportion of offspring with con-specific father, prop.heterosp, proportion of offspring with hetero-specific father (hybrids).
PollenComp_180607.csv
R script: Range wide SDM and PCA
Species distribution modeling (SDM) with 10-fold cross validation and principal components analysis (PCA) for range-wide records of Silene dioica (L.) Clairv. and S. latifolia Poiret as well as principal components analysis of climatic variables.
SDM range_wide_20180605.R
Cross fertility
Seed set after pollination within the campions Silene dioica (L.) Clairv. and S. latifolia Poiret, as well as between these species (data from: Rahmé et al., 2009, Journal of Evolutionary Biology 22, 1637-1943 ). Column names: female, female individual; mother.species, species [Dioica: S. dioica, Latifolia: S. latifolia]; treatment, pollination treatment [D.pollen: S. dioica pollen, L.pollen: S. latifolia pollen, M.pollen: 1:1 mixed pollination (not considered)]; normal, number of normal seeds; deformed, number of deformed seeds; aborted, number of aborted seeds; weight, seed weight of normal seed in mg; mean.weight, mean weight per seed in mg, Seed.set, normal seeds divided by total seeds (normal+deformed+aborted), date, pollination date.
CrossFertility_180607.csv
R script: Swiss SDM and PCA
Species distribution modeling (SDM) with 10-fold cross validation and principal components analysis (PCA) for records of Silene dioica and S. latifolia within Switzerland, where dispersal between habitats scan be expected.
SDM_swiss_20180605.R
R script: Germination responses
Analysis of a seed germination experiment using interval in freshly harvested seeds of Silene dioica, S. latifolia and of different hybrid classes between these species under three conditions, a dormancy breaking treatment and conditions simulating diurnal temperature profiles during the seeding time of S. dioica or S. latifolia. Analyses of seed weight and climate condition during seed fall as well as of reproductive isolation indices with bootstrap confidence intervals are also included.
Germination_180607.R
R script: Transplant experiment
Analysis of cumulative fitness and associated reproductive isolation indices with bootstrap confidence intervals in crosses within the Silene dioica and S. latifolia as well as their first- and second-generation hybrids a four-year transplant experiment at three sites of each species (data from Favre et al. 2017, New Phytologist 213, 1487-1499).
Transplant_RI_20181015.R
R script: Cross fertility and pollen competition
Analysis of seed set after pollination within and between the campions Silene dioica (L.) Clairv. and S. latifolia Poiret, as well as hybrid production after mixed pollination (pollen competition) together with associated reproductive isolation indices with bootstrap confidence intervals.
CrossFert_and_PollenComp_180608.R