Eduardo Narbona

Explosive seed dispersal in two perennial Mediterranean Euphorbia species (Euphorbiaceae)

The distance of explosive dispersal, its pattern in time, and the relative importance of autochory have been studied in two diplochorous species: Euphorbia boetica and E. nicaeensis. The seeds of E. boetica released by explosive dispersal reached a median distance of 156 cm and a maximum of almost 8 m, while the distances reached by the seeds of E. nicaeensis were lower: a median of 132 cm and a maximum of 5 m. The differences in explosive dispersal distance between species seem to depend on both seed mass and caruncle retention. The seeds of both species present a caruncle, but in E. boetica this is tiny, and in most cases is shed during the explosion of the capsules. The distances reached by the seeds of these species, dispersed just by capsule explosion, were similar to or greater than the distances to which ants disperse seeds in the Mediterranean sclerophyllous vegetation. Diplochorous plants may maximize either the distance of primary dispersal or that of secondary dispersal. Given that the seeds of E. boetica, that lose their caruncles, are not gathered by myrmecochorous ants, the results suggest that E. boetica maximizes its primary dispersal distance, whereas E. nicaeensis favors its secondary dispersal.

Experimental defoliation affects male but not female reproductive performance of the tropical monoecious plant Croton suberosus (Euphorbiaceae).

BACKGROUND AND AIMS Monoecious plants have the capacity to allocate resources separately to male and female functions more easily than hermaphrodites. This can be advantageous against environmental stresses such as leaf herbivory. However, studies showing effects of herbivory on male and female functions and on the interaction with the plants pollinators are limited, particularly in tropical plants. Here, the effects of experimental defoliation were examined in the monoecious shrub Croton suberosus (Euphorbiaceae), a wasp-pollinated species from a Mexican tropical dry forest. METHODS Three defoliation treatments were applied: 0 % (control), 25 % (low) or 75 % (high) of plant leaf area removed. Vegetative (production of new leaves) and reproductive (pistillate and staminate flower production, pollen viability, nectar production, fruit set, and seed set) performance variables, and the abundance and activity of floral visitors were examined. KEY RESULTS Defoliated plants overcompensated for tissue loss by producing more new leaves than control plants. Production of staminate flowers gradually decreased with increasing defoliation and the floral sex ratio (staminate : pistillate flowers) was drastically reduced in high-defoliation plants. In contrast, female reproductive performance (pistillate flower production, fruit set and seed set) and pollinator visitation and abundance were not impacted by defoliation. CONCLUSIONS The asymmetrical effects of defoliation on male and female traits of C. suberosus may be due to the temporal and spatial flexibility in the allocation of resources deployed by monoecious plants. We posit that this helps to maintain the plants pollination success in the face of leaf herbivory stress.

A reassessment of the function of floral nectar in Croton suberosus (Euphorbiaceae): a reward for plant defenders and pollinators.

Typically, plant-pollinator interactions are recognized as mutualistic relationships. Flower visitors, however, can potentially play multiple roles. The floral nectar in Croton suberosus has been proposed to operate as a reward for predators, especially the wasp Polistes instabilis (Vespidae), which kills herbivorous insects, while the plant has been thought to be mainly wind-pollinated. In this study, we reassessed the pollination mode of C. suberosus and the possible role of its flower visitors. Pollinator exclusion experiments demonstrated that C. suberosus should be considered a strictly entomophilous species. Inflorescences of C. suberosus were visited by a diverse entomofauna involving 28 taxa belonging to six orders; however, wasps and bees were the only visitors that carried C. suberosus pollen. The visitation rate of wasps was approximately four times that of bees. This observation, combined with the fact that the small size of bees makes effective contact of their bodies with the stigma difficult, strongly suggests that large wasps are responsible for most of the effective pollination of C. suberosus. Among the wasp visitors, P. instabilis seems to be one of the most important. These findings expose an unusual plant-insect interaction, in which the plant provides nectar and wasps pollinate and defend the plant.

Investigating reproductive incompatibility barriers in a Mediterranean rockrose (Cistus ladanifer)

Cistus ladanifer L. (Cistaceae) is a shrubby species, primarily found as a dominant species of the Mediterranean evergreen scrub. Intervarietal (var. ladanifer and var. maculatus) cross compatibility and self-incompatibility (SI) were studied in six Iberian populations of C. ladanifer. In addition, temporal variation in SI across 2 years and variability in the strength of SI throughout the flowering season were analysed in a subset of two populations. The two coloured floral morphs of C. ladanifer were compatible, and pollination had statistically similar ability to fruit set when crossing individuals of the two varieties (440 flowers). Results from hand self-pollination indicate negative self-compatibility, regardless of individuals being sampled from different populations, varieties and years (160 flowers in 2003 and 1620 flowers in 2006). In addition, SI strength did not vary along the flowering season. All these results lead us to argue that, in contrast to the results of its sister species (Cistus salviifolius), the highly polymorphic C. ladanifer possesses an extremely stable SI system but a weak reproductive barrier between varieties.

Molecular phylogeny of Scorzoneroides (Asteraceae): Evolution of heterocarpy and annual habit in unpredictable environments

It has been hypothesized that annual life history and heterocarpy are an adaptation to unpredictable habitats. In this paper, we infer a phylogenetic history for Scorzoneroides from the analysis of internal transcribed spacer (ITS) and plastid ndhF-rpl32 and rpl32-trnL sequences, on which we trace the evolution of one ecological (predictable vs unpredictable habitats) and two morphological (annual vs perennial and dimorphic vs homomorphic achenes) characters. Our results confirm the monophyly of Scorzoneroides and reveal the existence of two significant evolutionary lineages that do not coincide with major taxonomic subdivisions traditionally proposed for this genus. The first major group comprises taxa with all types of possible combinations of character states. The second major group includes exclusively homocarpic perennial taxa occurring in predictable habitats. It is strongly inferred that the most recent common ancestor of Scorzoneroides was perennial and homomorphic, and occurred in predictable habitats. The evolution of both annual life history and dimorphic achenes was significantly associated with occurrence in unpredictable habitats, which may suggest an adaptation process.

Sexual Dimorphism in the Andromonoecious Euphorbia nicaeensis: Effects of Gender and Inflorescence Development

BACKGROUND AND AIMS In andromonoecious taxa with separate floral types along the inflorescence, architectural or plastic effects can simulate floral sexual dimorphism. Both the primary and secondary sexual characteristics of the cyathia of the protogynous andromonoecious species Euphorbia nicaeensis were analysed according to their sex and arrangement on the inflorescence. METHODS The production of male and hermaphrodite cyathia at each inflorescence level was surveyed in two natural populations. The longevity, size, pollen production and viability, and nectar secretion of both types of cyathia were checked between inflorescence levels and between sexes at the only level at which they occur together. This sampling method makes it possible to know whether differences between cyathia types are based on sex or are attributable to inflorescence development. KEY RESULTS Male cyathia were produced predominantly at the first and second inflorescence levels, whereas at levels 3-5, the cyathia were almost exclusively hermaphrodite. Viable pollen production by male cyathia at the second inflorescence level was higher than that of hermaphrodite cyathia at the third level but, when males and hermaphrodites at the same level were compared, their pollen production was similar. Male and hermaphrodite cyathia were similar in size, irrespective of the inflorescence level, although the exclusively hermaphrodite cyathia of the last level were smaller. Both cyathium types produced similar amounts of sugar. However, male cyathia produced nectar during their whole lifespans, whereas hermaphrodites produced it exclusively during their male phase. Moreover, the nectary activity of male cyathia started earlier in the day than that of hermaphrodites. CONCLUSIONS An apparent floral dimorphism exists in the primary sexual characteristics of Euphorbia nicaeensis because differences in pollen production between cyathium types are due to theirs positions. Similarly, differences affecting most secondary sexual characteristics are only apparent between the two cyathium types. However, E. nicaeensis shows a true but slight floral dimorphism in some of the secondary sex characters related to nectar secretion. The lack of nectar production by the female phase of the hermaphrodite cyathia of E. nicaeensis indicates that this is a deceit-pollinated species.

Linking self-incompatibility, dichogamy, and flowering synchrony in two Euphorbia species: alternative mechanisms for avoiding self-fertilization?

Background Plant species have several mechanisms to avoid selfing such as dichogamy or a self-incompatibility response. Dichogamy in a single flower may reduce autogamy but, to avoid geitonogamy, plants must show flowering synchronization among all their flowers (i.e. synchronous dichogamy). It is hypothesized that one species would not simultaneously show synchronous dichogamy and self-incompatibility because they are redundant mechanisms to reduce selfing; however, this has not been accurately assessed. Methodology/Principal Findings This expectation was tested over two years in two natural populations of the closely related Mediterranean spurges Euphorbia boetica and E. nicaeensis, which completely avoid autogamy by protogyny at the cyathia level. Both spurges showed a high population synchrony (Z<79), and their inflorescences flower synchronously. In E. nicaeensis, there was no overlap among the cyathia in anthesis of successive inflorescence levels and the overlap between sexual phases of cyathia of the same inflorescence level was uncommon (4–16%). In contrast, E. boetica showed a high overlap among consecutive inflorescence levels (74–93%) and between sexual phases of cyathia of the same inflorescence level (48–80%). The flowering pattern of both spurges was consistent in the two populations and over the two successive years. A hand-pollination experiment demonstrated that E. nicaeensis was strictly self-compatible whereas E. boetica was partially self-incompatible. Conclusions/Significance We propose that the complex pattern of synchronized protogyny in E. nicaeensis prevents geitonogamous crosses and, consequently, avoids selfing and inbreeding depression. In E. boetica, a high probability of geitonogamous crosses may occur but, alternatively, this plant escapes selfing through a self-incompatibility response. We posit that synchronous dichogamy and physiological self-incompatibility do not co-occur in the same species because each process is sufficiently effective in avoiding self-fertilization.

Similar reproductive success of the two petal colour polymorphisms of Cistus ladanifer (Cistaceae)

Abstract Variation in flower colour can reflect adaptive responses to selective pressures generated by pollinators. Cistus ladanifer is a Mediterranean shrub that displays self-incompatibility, entomophyly and polymorphism for the presence of a dark coloured blotch in the base of their petals (var. maculatus with blotched petals and var. ladanifer with unblotched petals). In order to investigate the effect of the petal blotch and geography in C. ladanifer reproductive success, variation in female reproductive output (flower production, fruit set, seed set) was analysed in four and three Iberian populations of var. ladanifer and var. maculatus, respectively. Additionally, we tested whether co-existence of these two C. ladanifer phenotypes yielded different reproductive output (ovule production, seed set) in a subset of two populations. Significant differences in flower production (56.4–229.4%), fruit set (64.9–93.8%) and seed set (82.8–98.0%) among populations were reported. Geographical and taxonomic variables did not significantly explain this variation. Significant results between floral morphs within a single population were found neither for ovule nor for seed production. Our findings suggest that the petal blotch in C. ladanifer should be considered to be neutral in its effect on fruit and seed production and its occurrence may simply reflect a relaxed selection under current conditions.

Transcriptome and Biochemical Analysis of a Flower Color Polymorphism in Silene littorea (Caryophyllaceae).

Flower color polymorphisms are widely used as model traits from genetics to ecology, yet determining the biochemical and molecular basis can be challenging. Anthocyanin-based flower color variations can be caused by at least 12 structural and three regulatory genes in the anthocyanin biosynthetic pathway (ABP). We use mRNA-Seq to simultaneously sequence and estimate expression of these candidate genes in nine samples of Silene littorea representing three color morphs (dark pink, light pink and white) across three developmental stages in hopes of identifying the cause of flower color variation. We identified 29 putative paralogs for the 15 candidate genes in the ABP. We assembled complete coding sequences for 16 structural loci and nine of ten regulatory loci. Among these 29 putative paralogs, we identified 622 SNPs, yet only nine synonymous SNPs in Ans had allele frequencies that differentiated pigmented petals (dark pink and light pink) from white petals. These Ans allele frequency differences were further investigated with an expanded sequencing survey of 38 individuals, yet no SNPs consistently differentiated the color morphs. We also found one locus, F3h1, with strong differential expression between pigmented and white samples (>42x). This may be caused by decreased expression of Myb1a in white petal buds. Myb1a in S. littorea is a regulatory locus closely related to Subgroup 7 Mybs known to regulate F3h and other loci in the first half of the ABP in model species. We then compare the mRNA-Seq results with petal biochemistry which revealed cyanidin as the primary anthocyanin and five flavonoid intermediates. Concentrations of three of the flavonoid intermediates were significantly lower in white petals than in pigmented petals (rutin, quercetin and isovitexin). The biochemistry results for rutin, quercetin, luteolin and apigenin are consistent with the transcriptome results suggesting a blockage at F3h, possibly caused by downregulation of Myb1a.

Diversity of sexual systems within different lineages of the genus Silene

Species or populations may be categorized by sexual system. Here, we examine the frequency of sexual systems in Silene. We found that hermaphroditism is the most common sexual system, followed by dioecy, gynodioecy and gynodioecy-gynomonoecy (females, hermaphrodites and gynomonoecious plants) with similar frequency. These sexual systems are equally represented in the two phylogenetically supported subgenera Silene and Behenantha. We specifically studied the sexual systems of section Psammophilae (four species and 26 populations), and found that most populations are gynodioecious-gynomonoecious. Hermaphrodites are the most common sexual morph, and females tend to produce fewer flowers than other morphs.