1. Ecology
  2. Evolutionary Biology
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Inbreeding in a dioecious plant has sex- and population origin-specific effects on its interactions with pollinators

  1. Karin Schrieber  Is a corresponding author
  2. Sarah Catherine Paul
  3. Levke Valena Höche
  4. Andrea Cecilia Salas
  5. Rabi Didszun
  6. Jakob Mößnang
  7. Caroline Müller
  8. Alexandra Erfmeier
  9. Elisabeth Johanna Eilers
  1. Kiel University, Institute for Ecosystem Research, Geobotany, Germany
  2. Bielefeld University, Faculty of Biology, Department of Chemical Ecology, Germany
  3. German Centre for Integrative Biodiversity Research (iDiv) Halle–Jena–Leipzig, Germany
Research Article
Cite this article as: eLife 2021;10:e65610 doi: 10.7554/eLife.65610
3 figures, 2 tables and 2 additional files

Figures

Figure 1 with 8 supplements
Graphical sketch of the applied methods.

Each of the eight listed methodologies is illustrated in detail in a figure supplement.

Figure 1—figure supplement 1
Map of the geographic locations of the sampled European (left) and North American (right) Silene latifolia populations.
Figure 1—figure supplement 2
Overview of the experimental crossings within each of the 16 Silene latifolia populations.

The crossings were performed with five families (numbered grey circles). Females (red plants, leaf pointing to left) were fertilised with pollen from males (blue plants, leaf pointing to right) from the same family for inbreeding (dashed arrows), and with pollen from males from a different family for outbreeding (solid arrows). Inbreeding and outbreeding were performed at distinct flowers of the same female individual.

Figure 1—figure supplement 3
Experimental plants.

Our study involved 320 plant individuals from two origins (Europe, North America) × 8 populations × 5 maternal families × 2 sexes (male, female) × 2 breeding treatments (outbred, inbred).

Figure 1—figure supplement 4
Spatial flower traits.

(a) Spatial flower trait assessment. (A) Maximal synflorescence height above ground, (B) flower number, (C) petal limb area, (D) corolla expansion. (b) Variation in flower shape of Silene latifolia plants in our experiment. Photographs from female (upper row) and male (lower row) flowers with maximal deviation in flower shape were randomly chosen from the entire pool of experimental plants.

Figure 1—figure supplement 5
Setup for the collection of headspace volatile organic compounds (VOC) from flowers of Silene latifolia (left: side view, right: front view).

Flowers were inserted into VOC collection units (consisting of 50 mL PE cups with lids, both with 15 mm holes), which were fixed via wooden sticks at the plant pot exterior. Two polydimethylsiloxane (silicone) tubes of standardised size were inserted into the collection units and absorbed VOC for a period of 8 hr.

Figure 1—figure supplement 6
Setup for the acquisition of digital images for flower colour analyses.

The camera was fixed on a tripod positioned on an exact horizontal platform, which was oriented towards the setting sun (a) to take images of flowers in the visible light spectrum (b) and the ultraviolet light spectrum (c). Images included an intact and fully opened flower (i) that was carefully plugged into a black ethylene vinyl acetate sheet equipped with a label (ii), a size standard (iii), a 10% polytetrafluorethylene light standard (iv), and a 99% spectralon light standard (v).

Figure 1—figure supplement 7
Nectar analyses.

Nectar was extracted into 1 or 2 µL microcapillary tubes. The length of the nectar column was measured with a calliper to determine the exact volume. Nectar sugar content was analysed with a refractometer adjusted for small sample sizes.

Figure 1—figure supplement 8
Experimental setup for pollinator observations.

The plots consisted of eight individuals representing all eight populations within one of the eight possible breeding treatment × sex × range combinations. Each of these combinations was replicated five times on the maternal family level, resulting in 40 plots. Plots were spaced at a distance of 6 m to provide pollinators with the choice of visiting plants of specific breeding treatment × sex × range combinations.

Figure 2 with 2 supplements
Effects of breeding treatment, sex, and origin on spatial flower traits (a–d), floral scent traits (e–f), flower colour as perceived by crepuscular moths (g–h), and floral rewards in Silene latifolia.

Graphs show estimated marginal means and standard errors for outbred (Ou, filled bars) and inbred (In, open bars), female (Fe, red bars) and male (Ma, blue bars) plants from Europe (Eu, dark coloured bars) and the North America (Na, bright coloured bars). Estimates were extracted from (generalised) linear mixed effects models for significant interaction effects and main effects of factors not involved in an interaction (significance levels based on Wald χ² tests denoted at top of plot). Interaction effect plots additionally indicate significant differences among breeding treatments, sexes, or origins within levels of other factors involved in the respective interaction (estimated based on post hoc comparisons, denoted within plots). Exact sample sizes for all traits are listed in Table 1. Significance levels: ***p<0.001, **p<0.01, *p<0.05, •p<0.06.

Figure 2—figure supplement 1
Stacked bar plot illustrating the proportions of variance in floral trait responses explained by fixed effects (black) and the random effects of mother in the P-generation (dark grey), father in the P-generation (medium grey), and population (light grey), as well as the amount of unexplained variance, that is, residuals (white).

Please note that the amount of variation in response variables that is explained by fixed effects exceeds the amount of variance explained by the population random factor in 9 of 12 models.

Figure 2—figure supplement 2
Unsupervised random forest comparison MDS plots for floral headspace volatile organic compounds (VOC, left panel) and supervised random forest importance plots for mean decrease in accuracy (MDA, right panel) for all detected compounds (upper plots) and the subset for compounds that can be detected by Hadena bicruris (lower plots).

Patterns were compared for outbred (Ou, filled squared) and inbred (In, open squares), female (Fe, red) and male (Ma, blue) plants from Europe (Eu, dark coloured) and North America (Na, bright coloured). Each square represents one population, data within populations were averaged to improve clarity.

Figure 3 with 1 supplement
Effects of breeding treatment, sex, and origin on pollinator visitation rates in Silene latifolia.

Graphs show estimated marginal means and standard errors for outbred (Ou, filled bars) and inbred (In, open bars), female (Fe, red bars) and male (Ma, blue bars) plants from Europe (Eu, dark coloured bars) and North America (Us, bright coloured bars). Estimates were extracted for significant interaction effects from the conditional part of generalised linear mixed effects models (significance levels based on Wald χ² -tests denoted at top of plot). Plots additionally indicate significant differences between breeding treatments, sexes, or origins within levels of other factors involved in the respective interaction (estimated based on post -hoc comparisons, denoted within plots). Exact sample sizes for all traits are listed in Table 1. Significance levels: ***p<0.001, **p<0.01, and *p<0.05.

Figure 3—figure supplement 1
Estimated marginal means for zero scores in pollinator visitation responses (increasing values indicate higher proportion of zeroes in response data) and standard errors for outbred (Ou, filled bars) and inbred (In, open bars), female (Fe, red bars) and male (Ma, blue bars) plants from Europe (Eu, dark coloured bars) and North America (Us, bright coloured bars).

Estimates were extracted for significant interaction effects from the zero inflation part of generalised linear mixed effects models (significance levels based on Wald χ² tests denoted at top of plot). Plots additionally indicate significant differences between breeding treatments, sexes, or origins within levels of other factors involved in the respective interaction (estimated based on post hoc comparisons, denoted within plots). Exact sample sizes for all responses are listed in Table 1. Significance levels: ***p<0.001, **p<0.01, and *p<0.05.

Tables

Table 1
Overview of locations, times, and sample sizes for data acquisition.
Trait categoryLocationAcquisition time
(year, month, duration)
Nesting and intended
total sample size
Realised total sample sizeReplicates per group
(breeding treatment × sex ×
origin combination)
Reason for sample size reduction
Spatial flower traits (synflorescence height, flower number)Greenhouse and common garden2019
Jun., Jul., Aug.
5 days, respectively
Two breeding treatments × 2 sexes × 5 maternal families × 8 populations × 2 origins=32031636–40Four individuals died
Flower scentGreenhouse2019
Jul.
8 hr
Two breeding treatments × 2 sexes × 3 maternal families × 8 populations × 2 origins=19219223–35-
Flower colourCommon garden2019
Aug.
2 weeks
Two breeding treatments × 2 sexes × 5 maternal families × 8 populations × 2 origins=32028623–25Four individuals died, no flowers available for remaining plants
Spatial flower traits (petal limb area and expansion)Common garden2019
Aug.
2 weeks
Two breeding treatments × 2 sexes × 5 maternal families × 8 populations × 2 origins=32028623–35Four individuals died, no flowers available for remaining plants
Pollinator visitation ratesField site2020
May–Jul.
8 weeks
Two breeding treatments × 2 sexes × 5 maternal families × 8 populations × 2 origins=32031636–40Four individuals died
Floral rewardsCommon garden2020
Aug.
4 weeks
Two breeding treatments × 2 sexes × 5 maternal families × 8 populations × 2 origins=32028030–40Four individuals died, no flowers available for remaining plants
Table 2
Overview and results of statistical analyses with (generalised) linear mixed effects models.

The table summarises the model types and error distributions used for each of the responses (printed in subscript), the parameter estimates on the link function scale with significance levels assessed based on Wald χ² tests for all fixed effects (***p<0.001, **p<0.01, and *p<0.05 printed in bold), and random effect variances (printed in italic). For zero inflated responses, estimates from the conditional model parts appear in the first line and estimates from zero inflation model parts in the second line. All listed fixed effects consume 1 degree of freedom.

InterceptBtmt
[outbred –inbred]
Sex
[female –male]
Origin
[Europe –US]
Btmt × sexBtmt × originSex × originBtmt × sex × originLatitudePlant ageObs. timePopPop: motherPop : fatherPlotObs. trial
Spatial flower traits
Synflorescence heightLMM(G)81.03 3.56***−0.40NS1.840.670.111.07Ns−0.151.00Nt.Nt. 5.42 16.76 0.00Nt.Nt.
No. flowersGLMM(NBQ)2.61 0.14***−0.70***−0.25**0.08**−0.040.010.010.12Nt.Nt. 0.03 0.02 0.02Nt.Nt.
Petal limb areaLMM(G)2.76 0.16**−0.38***0.070.060.040.100.030.19Nt.Nt. 0.15 0.08 0.00Nt.Nt.
Corolla expansionLMM(G)5.21 0.21**−0.44***0.33 0.23**0.02 0.21**0.110.06Nt.Nt. 0.290.30 0.00Nt.Nt.
Flower scent traits
Shannon index VOCLMM(G)1.860.03−0.13*−0.060.010.040.020.010.03−0.02*Nt.0.010.000.00Nt.Nt.
Lilac aldehyde AZI-GLMM(NBQ)15.110.02−0.060.020.01−0.08−0.04−0.16*0.01−0.08Nt.0.010.000.00Nt.Nt.
−1.93***Nt.Nt.Nt.Nt.Nt.Nt.Nt.Nt.Nt.Nt.Nt.Nt.Nt.Nt.Nt.
Lilac aldehyde B/CZI-GLMM(NBL)15.78−0.08−0.090.120.06−0.10−0.01−0.03−0.09−0.03Nt.0.010.000.03Nt.Nt.
−1.93***Nt.Nt.Nt.Nt.Nt.Nt.Nt.Nt.Nt.Nt.Nt.Nt.Nt.Nt.Nt.
Lilac aldehyde DZI-GLMM(NBQ)13.70−0.050.14−0.07−0.09−0.16−0.06−0.080.08−0.17Nt.0.002.750.47Nt.Nt.
0.02NsNt.Nt.Nt.Nt.Nt.Nt.Nt.Nt.Nt.Nt.Nt.Nt.Nt.Nt.Nt.
Flower colour
Reflectance UVLMM(G)2.04−0.05−0.27***0.050.040.08Ns−0.040.020.01Nt.Nt.0.010.030.01Nt.Nt.
Reflectance blueLMM(G)26.72−0.02−0.95***0.100.240.050.210.14Ns0.47Nt.Nt.0.470.850.00Nt.Nt.
Reflectance greenLMM(G)39.87−0.10−0.190.400.260.170.120.31Ns0.05Nt.Nt.1.120.370.07Nt.Nt.
Floral rewards
Excreted sugarLMM(G)5.700.03−0.18***−0.080.04−0.02−0.020.040.04Nt.Nt.0.070.000.00Nt.Nt.
Pollinator visitation
No. plant visitsZI-GLMM(P)0.280.09 −0.67***0.090.22−0.20−0.16−0.29*Nt.Nt.−0.11*Nt.Nt.Nt.0.270.15
−0.48Ns0.050.29−0.21−0.11−0.110.10−0.46*Nt.Nt.0.10Nt.Nt.Nt.0.140.44
No. flowers visitedZI-GLMM(P)0.790.04−0.56***−0.03 0.34*−0.23−0.22−0.46**Nt.Nt. 0.19***Nt.Nt.Nt.0.680.23
−0.09Ns−0.04 0.47**−0.23−0.19−0.020.17−0.31*Nt.Nt. 0.47**Nt.Nt.Nt.0.160.47
  1. Abbreviations. Btmt: breeding treatment, LMM: linear mixed effects model, (NBQ): negative binomial distribution with quadratic parametrisation and log-link, (NBL): negative binomial distribution with linear parametrisation and log-link, No.: number, Nt.: not tested, GLMM: generalised linear mixed effects model, Obs: observation, (P): Poisson distribution with log-link, Pop: population, ZI-GLMM: zero inflation generalised mixed effects model, (G): Gaussian distribution with identity link.

Additional files

Supplementary file 1

Mean ± SE abundance (e-06) of 70 volatile organic compounds (VOC) emitted by Silene latifolia plants in all breeding treatment × sex × origin combinations, as determined by silicone tubing headspace collection combined with thermal desorption–gas chromatography–mass spectrometry.

The 20 VOC, which evidently trigger antennal responses in Hadena bicruris (Dötterl et al., 2006) and were thus analysed as a sub-dataset, are highlighted in bold.

https://cdn.elifesciences.org/articles/65610/elife-65610-supp1-v3.docx
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