The Effect of Pollen Source vs. Flower Type on Progeny Performance and Seed Predation under Contrasting Light Environments in a Cleistogamous Herb

<div><p>Dimorphic cleistogamy is a specialized form of mixed mating system where a single plant produces both open, potentially outcrossed chasmogamous (CH) and closed, obligately self-pollinated cleistogamous (CL) flowers. Typically, CH flowers and seeds are bigger and energetically more costly than those of CL. Although the effects of inbreeding and floral dimorphism are critical to understanding the evolution and maintenance of cleistogamy, these effects have been repeatedly confounded. In an attempt to separate these effects, we compared the performance of progeny derived from the two floral morphs while controlling for the source of pollen. That is, flower type and pollen source effects were assessed by comparing the performance of progeny derived from selfed CH vs. CL and outcrossed CH vs. selfed CH flowers, respectively. The experiment was carried out with the herb <i>Ruellia nudiflora</i> under two contrasting light environments. Outcrossed progeny generally performed better than selfed progeny. However, inbreeding depression ranges from low (1%) to moderate (36%), with the greatest value detected under shaded conditions when cumulative fitness was used. Although flower type generally had less of an effect on progeny performance than pollen source did, the progeny derived from selfed CH flowers largely outperformed the progeny from CL flowers, but only under shaded conditions and when cumulative fitness was taken into account. On the other hand, the source of pollen and flower type influenced seed predation, with selfed CH progeny the most heavily attacked by predators. Therefore, the effects of pollen source and flower type are environment-dependant and seed predators may increase the genetic differences between progeny derived from CH and CL flowers. Inbreeding depression alone cannot account for the maintenance of a mixed mating system in <i>R. nudiflora</i> and other unidentified mechanisms must thus be involved.</p> </div

Diversity effect on plant defenses.

<p>Effect of mahogany genotypic and species diversity on the concentration of: (A) mahogany stem polyphenolics, (B) stem tannins, (C) leaf polyphenolics, and (D) leaf tannins. The dashed line represents the mean value for mahogany genotypic monocultures (N  = 12) and the shaded area represents the standard error around that mean. Least-square means ± S.E. (N  = 12 for genotypic polycultures and N  = 12 for species polycultures). Significant differences (<i>P</i><0.05) between a given diversity treatment and the genotypic monoculture treatment are indicated by an asterisk.</p

<i>Hypsipyla grandella</i> damage.

<p>Damage caused by <i>Hypsipyla grandella</i> (Lepidoptera: Pyralidae), a stem-boring caterpillar specializing on tree species of the neotropical family Meliaceae. The images show a fourth-instar larva inside a terminal shoot of a big-leaf mahogany (<i>Swietenia macrophylla</i> King, Meliaceae) sapling and the damage caused. Photo credits: Luis Abdala-Roberts.</p

Diversity effect on growth and herbivore damage.

<p>Summary of results from generalized linear mixed models testing for the effects of (a) big-leaf mahogany (<i>Swietenia macrophylla</i> King, Meliaceae) genotypic diversity and (b) tree species diversity on mahogany growth and damage by the specialist <i>Hypsipyla grandella</i> (number of attack sites per plant). We tested the effect of mahogany genotypic diversity by comparing genotypic monocultures to genotypic polycultures, whereas to test for a species diversity effect we compared genotypic monocultures and species polycultures. F-values and associated significance levels (<i>P</i>) are shown, as well as numerator and denominator degrees of freedom (subscripts).</p

Diversity effect on growth and herbivore damage.

<p>Effect of mahogany genotypic and tree species diversity on: (A) mahogany sapling height and (B) the mean number of attack sites per plant by the specialist stem-boring insect <i>Hypsipyla grandella</i>. The dashed line represents the mean value for genotype monocultures (N  = 12) and the shaded area represents the standard error around that mean. Least-square means ± S.E. (N  = 20 genotypic polycultures and N  = 12 species polycultures). “(n.s.)” in the figures indicates non-significant differences (<i>P</i><0.05) between a given diversity treatment and the genotypic monoculture treatment.</p

Abundance herbivores of tropical trees, effects of diversity

Data is collected in the field,on the first column Species diversity with two levels monoculture and polyculture. Second column Genotypic diversity with two levels one maternal family and four maternal families. Rest of columns Ants, Sap feeders, leaf chewers (abundance) , H. grandella y P. meliacella (attacks as proxy of abundance

Abundance of sap-feeding generalist herbivores on mahogany (<i>Swietenia macrophylla</i>) plants with artificially reduced or ambient (control) ant abundances, across two levels of tree species diversity (mahogany monocultures and polycultures of four tree species, including mahogany), in a tree diversity experiment in southern Mexico.

<p>Values are means ± S.E. We found negative effects of ants on sap feeders at low diversity (F_{1, 17} = 5.7, P = 0.01), but not at high diversity (F_{1, 17} = 0.63, P = 0.42), whereas effects of diversity were significant under ambient (control) ant densities (F_{1, 17} = 10.23, P = 0.001) but not under ant-reduced conditions (F_{1, 17} = 1.52, P = 0.21). Statistics are based upon a posteriori contrasts.</p

Effects of mahogany (<i>Swietenia macrophylla</i>) genotypic diversity and tree species diversity on the abundance of ants (A, B), generalist leaf-chewing herbivores (C, D), generalist sap-feeding herbivores (E, F), specialist stem-boring herbivores (<i>Hypsipyla grandella</i>) (G, H), and specialist leaf-mining herbivores (<i>Phyllocnistis meliacella</i>) (I, J) on mahogany saplings in a tree diversity experiment in southern Mexico (bars are means ± S.E.).

<p>Values are means ± S.E. *P<0.05, **P<0.01, ***P<0.001, n.s. = not significant. G1 = plots with one mahogany maternal family, G4 = plots with four mahogany maternal families; M = monocultures of mahogany, P = polycultures of four species (including mahogany).</p

Results from generalized linear mixed models testing for the effects of an ant reduction treatment (A), tree species diversity (SD), mahogany (<i>Swietenia macrophylla</i>) genotypic diversity (GD), and their interactions on the abundance of generalist (G) and specialist (S) herbivores on mahogany.

<p>The model for ant abundance tested for the effects of SD, GD, and their interaction, but did not test for the ant reduction treatment or its interactions with SD or GD as it only considered control (ambient ant abundances) plants. All models include survey and plot as random effects. Significant effects (P < 0.05) are in bold.</p