Regina Berjano

GENDER VARIATION AND TRANSITIONS BETWEEN SEXUAL SYSTEMS IN MERCURIALIS ANNUA (EUPHORBIACEAE)

Evolutionary transitions between hermaphroditism and dioecy have occurred numerous times in the land plants. We briefly review the factors thought to be responsible for these transitions, and we provide a synthesis of what has been learned from recent studies of the annual herb Mercurialis annua, in which dioecy (males and females), monoecy (functional hermaphrodites), and androdioecy (males and hermaphrodites) occur in different parts of its geographic range. Previous research on M. annua has revealed the importance of genome duplication and hybridization in the origin of much of the observed variation. Here we show, however, that spatial transitions in the sexual system also occur within the same ploidy level. In particular, we present an analysis, using flow cytometry data, of ploidy variation across a previously unstudied transition between hermaphroditism and androdioecy, in which we find that the sexual‐system transition is uncoupled from the shift in ploidy levels. We review recent research that shows that such transitions between sexual systems in M. annua are consistent with differential selection at the regional level for reproductive assurance during colonization. We also present new experimental data that highlight both the importance of the resource status of plants and that of their local mating context in regulating gender strategies and sex ratios. The studies reviewed and the new results presented emphasize the role that shifts in the ecological and genetic context of plant populations may play in causing transitions between sexual systems.

Abiotic factors may explain the geographical distribution of flower colour morphs and the maintenance of colour polymorphism in the scarlet pimpernel

Summary1. Flower colour polymorphism is traditionally attributed to pollinator selection although otherfactors, such as indirect selection on correlated traits, can play an important role.2. Lysimachia arvensis is a widespread annual species with two colour morphs differing in anthocy-anin composition. We explored the hypothesis that colour polymorphism is maintained by selectionrelated to environmental heterogeneity. Morph frequencies and environmental traits were recorded in51 populations along a wide geographical range. To explore the existence of morph-by-environmentinteractions, we conducted an experimental study comparing the two morphs under treatments differ-ing in water and light availability.3. A geographical pattern was found with a negative association between blue frequencies and lati-tude. The proportion of the blue morph increased with temperature and sunshine hours, butdecreased with precipitation. Flowering onset and flower size differed between morphs and scarcelyvaried across treatments. In contrast, several fitness components such as germination, seedlingsurvival, seedling mass and flower production showed important morph-by-environment interactions.The blue morph showed higher overall male and female fitness in all the treatment combinationsexcepting in sun-wet conditions where the red morph had higher fitness.4. Synthesis. Our results indicate that the mechanism of selection on flower colour seems to berelated to differences in fitness of both morphs due to abiotic factors. These differences couldexplain the geographical distribution of flower colour morphs and the maintenance of the colourpolymorphism. The marked difference in flowering time between morphs leaves open the potentialfor assortative mating and speciation in Lysimachia arvensis.Key-words: Anagallis, anthocyanins, clinal variation, flower phenology, morph-by-environmentinteraction, pleiotropy, reproductive ecology, selectionIntroduction

A multi-year study of factors affecting fruit production in Aristolochia paucinervis (Aristolochiaceae)

Pollen limitation, resource limitation, fruit abortion, and predation have all been proposed as factors explaining low fruit set in hermaphroditic plants. We conducted a 5-year study combining field observations and pollination experiments to determine the causes of the low fruit set in Aristolochia paucinervis, a Mediterranean species with a specialized pollination system in two populations in SW Spain. Fruit initiation was markedly low, and between 28.6 and 75.0% of the flowering stems did not initiate any fruit. In most flowers, the number of germinated pollen grains was less than the number of ovules, and supplemental pollination significantly increased fruiting, indicating deficient pollination. In A. paucinervis, autonomous self-pollination seems to be a decisive factor in fruit production because the number of germinated pollen and the fruit set from flowers bagged before anthesis were similar to those in free-pollinated flowers. Only in 2005 did flowers that were successfully pollinated outnumber ripened fruits, suggesting that other factors limit fruiting. We found a significant positive correlation between tuber mass and fruit set. Deficient pollination and lack of resources could explain the low fruit set, but the relative consequences seem to vary spatially and temporarily.

Genetic races associated with the genera and sections of host species in the holoparasitic plant Cytinus (Cytinaceae) in the Western Mediterranean basin

* Speciation via race formation is an important evolutionary process in parasites, producing changes that favour their development on particular host species. Here, the holoparasitic plant Cytinus, which has diverse host species in the family Cistaceae, has been used to study the occurrence of such races. * Amplified fragment length polymorphism (AFLP) analyses were performed on 174 individuals of 22 populations parasitizing 10 Cistaceae species in the Western Mediterranean basin. * Neighbour-joining, multivariate ordination analyses, and individual-based Bayesian analyses, clustered Cytinus populations into five well-characterized genetic races that, overall, agreed with the taxonomic sections of their hosts. In the AMOVA, among-races differences accounted for almost 50% of the genetic variation. The isolation-by-distance model was not supported by a Mantel test among Cytinus populations (r = 0.012; P = 0.456). All races showed low within-population genetic diversity, probably as a result of restricted pollen flow aggravated by flowering asynchrony, restricted seed dispersion, or stochastic processes. * The genetic differentiation among the five races of Cytinus is congruent with the view that these races are well-characterized lineages that have evolved independently as a result of selective pressures imposed by their hosts. This pattern, with genetically distinctive groups associated with the infrageneric sections of the host species, has not been reported previously for parasitic angiosperms.

Pollinators, flowering phenology and floral longevity in two Mediterranean Aristolochia species, with a review of flower visitor records for the genus.

The pollination of Aristolochia involves the temporary confinement of visitors inside the flower. A literature review has shown that some species are visited by one or a few dipteran families, while others are visited by a wider variety of dipterans, but only some of these are effective pollinators. We observed flowering phenology and temporal patterns of pollinator attendance in diverse populations of Aristolochia baetica and A. paucinervis, two species that grow in SW Spain, frequently in mixed populations. The two species had overlapping floral phenologies, extended flowering periods and long-lived flowers. A. baetica attracted a higher number of visitors than A. paucinervis. Drosophilids and, to a lesser extent, phorids, were the main pollinators of A. baetica, whereas in A. paucinervis, phorids were the only pollinators. Attendance to A. paucinervis flowers by phorids in mixed populations was markedly lower than in pure populations. This effect was more evident in years with lower pollinator density. Our results suggest that A. baetica and A. paucinervis may compete for pollinators in mixed populations.

The role of resources and architecture in modeling floral variability for the monoecious amphicarpic Emex spinosa (Polygonaceae)

Determining the sources of floral variation is crucial to the understanding of floral evolution. Architectural effects and phenotypic plasticity in development can play an important role in intraplant floral variation, giving rise to gender dimorphism or sexual specialization. Amphicarpic plants have another source of floral variation that could also be influenced by positional effects. We studied the effects of resource availability and architecture in intraplant floral variability in two ecotypes of the amphicarpic Emex spinosa. Male flowers were smaller than females, irrespective of position or resource availability. Emex spinosa shows gender dimorphism not influenced by positional effects. Flower size differences among positions were mainly due to architecture, because the effects of resources on flower size were minimal. Architectural effects caused a decrease in female flower size from ground to apical positions but an increase in most male traits that resulted in sexual specialization at the end of flowering. In general, the ecotypes were similarly affected by resources or architecture. Differences between subterranean and aerial female flowers seem also to be a consequence of architecture. Our results contribute to the evidence that resource limitation is an overestimated effect and that architectural effects must be considered in studies of floral or fruit variation.

Contrasting strategies to cope with drought by invasive and endemic species of Lantana in Galapagos

This study compares how Lantana camara, an invasive species, and L. peduncularis, an autochthonous one, cope with drought in Galapagos. Soil surface temperature was the abiotic environmental parameter that best explained variations in photosynthetic stress. Higher soil surface temperatures were recorded in the lowlands and in rain-shadow areas, which were also the driest areas. L. peduncularis, with a shallow root system, behaved as a drought-tolerant species, showing lower relative growth rates, which decreased with leaf water content and higher photosynthetic stress levels in the lowlands and in a northwest rain-shadow area in comparison with higher and wetter locations. Its basal and maximal fluorescences decreased at lower altitudes, reflecting the recorded drops in chlorophyll concentration. In contrast, L. camara with a deep root system behaved as a drought-avoiding species, showing leaf and relative water contents higher than 55% and avoiding permanent damage to its photosynthetic apparatus even in the driest area where it showed very low chlorophyll content. Its relative growth rate decreased more in dry areas in comparison to wetter zones than did that of L. peduncularis, even though it had greater water content. Furthermore, L. camara showed higher water contents, growth rate, and lower photosynthetic stress levels than L. peduncularis in the arid lowlands. Thus, L. peduncularis maintained lower maximum quantum efficiency of photosystem II photochemistry (Fv/Fm) than L. camara even at sunrise, due to higher basal fluorescence values with similar maximal fluorescence, which indicated permanent damage to PSII reaction centres. Our results help to explain the success and limitations of L. camara in the invasion of arid and sub-arid environments.

Regional variation in sex ratios and sex allocation in androdioecious Mercurialis annua.

In androdioecious metapopulations, where males co‐occur with hermaphrodites, the absence of males from certain populations or regions may be explained by locally high selfing rates, high hermaphrodite outcross siring success (e.g. due to high pollen production by hermaphrodites), or to stochastic processes (e.g. the failure of males to invade populations or regions following colonization or range expansion by hermaphrodites). In the Iberian Peninsula and Morocco, the presence of males with hermaphrodites in the wind‐pollinated androdioecious plant Mercurialis annua (Euphorbiaceae) varies both among populations within relatively small regions and among regions, with some regions lacking males from all populations. The species is known to have expanded its range into the Iberian Peninsula from a southern refugium. To account for variation in male presence in M. annua, we test the following hypotheses: (1) that males are absent in areas where plant densities are lower, because selfing rates should be correspondingly higher; (2) that males are absent in areas where hermaphrodites produce more pollen; and (3) that males are absent in areas where there is an elevated proportion of populations in which plant density and hermaphrodite pollen production disfavour their invasion. We found support for predictions two and three in Morocco (the putative Pleistocene refugium for M. annua) but no support for any hypothesis in Iberia (the expanded range). Our results are partially consistent with a hypothesis of sex‐allocation equilibrium for populations in Morocco; in Iberia, the absence of males from large geographical regions is more consistent with a model of sex‐ratio evolution in a metapopulation with recurrent population turnover. Our study points to the role of both frequency‐dependent selection and contingencies imposed by colonization during range expansions and in metapopulations.

Persistently low fruiting success in the Mediterranean pipevine Aristolochia baetica (Aristolochiaceae): a multi-year study.

Low fruit set is common in many plant species and may be caused by a variety of factors, such as predation, resource limitation or deficient pollination, or it may be an evolutionary strategy. In this paper, we investigate factors that affect fruit set in Aristolochia baetica (Aristolochiaceae), a Mediterranean pipevine found in southwest Spain. Fruit production was monitored in two populations over 4 years (2002-2005), and the causes of flower or fruit loss were determined. Experimental hand-pollinations were performed, and germinated pollen grains on the stigmas of open-pollinated flowers were quantified. Fruit set was always very low (4-14%). Floral abscission initially reduced reproductive output by more than 50%; then herbivory (6-12%) and fruit abortion (8-26%) caused further reductions. Given that the number of efficiently pollinated flowers was always higher than that of ripe fruits, and that xenogamous hand-pollination did not increase fruit set in relation to open-pollination, the final fruit production of A. baetica seems not to be pollen-limited. Fruit abortion of effectively pollinated flowers supports the idea that resource availability limits fruit set. In A. baetica, fruit abortion could lead to mate selection of the best quality fruits. Moreover, the initiated fruits that finally abort could also satiate predators, contributing to increase progeny fitness.

Predation on Seeds of Invasive Lantana camara by Darwin's Finches in the Galapagos Islands

Abstract Observations on birds feeding on fruits of the invasive shrub Lantana camara (Supirrosa) were conducted on Santa Cruz Island, Galapagos (Ecuador) in the Dry Zone during the 2009 dry season. The endemic ground finches Geospiza magnirostris (Large Ground Finch) and G. fortis (Medium Ground Finch) were recorded eating Lantana seeds with G. fortis the main consumer (>90% of records). Both finch species crushed the seeds and ate the embryos, discarding the exocarp and empty seed coats. They also dropped entire fruits to the ground, which could contribute to short-distance dispersal, but both finches also consumed fruits of L. camara on the ground. Density of L. camara seedlings under adult plants was higher in rockier areas than in bare soil since seeds were less accessible to predators and/or found more suitable microsites for germination and establishment. Both species of finches serve as short-distance dispersers, but mainly as seed predators of L. camara fruits.