José María Sánchez

Relationships between vegetation and environmental characteristics in a salt-marsh system on the coast of Northwest Spain

This study reports an investigation of relationships between environmental variables (electrical conductivity of groundwater, soil redox potential, water-table depth, and high-tide flooding depth) on vegetation zonation in a salt-marsh system on the coast of northwest Spain. Discriminant analysis indicated that conductivity (a measure of salinity) and redox potential are correlated with vegetation type within the study area. Conductivity declines with increasing altitude and distance from the sea, whereas redox potential does not vary along well-defined large-scale gradients. Soils with the most strongly oxidizing conditions (i.e. moderate salinity, with Eh greater than 200 mV and thus subtoxic levels of Mn2+, Fe2+ and S2-) are occupied by the Halimione portulacoides community. Communities dominated by Juncus maritimus, and Phragmites australis reedbeds, occur at more strongly reducing sites (Eh between 100 and 200 mV, with possibly toxic levels of Mn2+ but not of Fe2+); the presence of these communities may thus be limited by Fe2+ toxicity. The most strongly reducing sites (with Eh low enough for the reduction of Fe3+ to Fe2+) are occupied by Spartina maritima and Scirpus maritimus communities. These communities appear to be tolerant of Fe2+, and even of low concentrations of S2-.

A New Approach to the Quantification of Degree of Reciprocity in Distylous (sensu lato) Plant Populations

BACKGROUND AND AIMS Although evolution of sexual polymorphism has been traditionally analysed using discrete characters, most of these polymorphisms are continuous. This is the case of heterostyly. Heterostyly is a floral polymorphism successfully used as a model to study the evolution of the sexual systems in plants. It involves the reciprocal positioning of anthers and stigmas in flowers of different plants within the same population. Studies of the functioning of heterostyly require the quantification of the degree of reciprocity between morphs of heterostylous species. Some reciprocity indices have been proposed previously, but they show significant limitations that need to be dealt with. This paper analyses these existing indices, and proposes a new index that aims to avoid their main problems (e.g. takes into account population variability and offers a single value per population). METHODS The new index is based on the comparison of the position of every single sexual organ in the population with each and every organ of the opposite sex. To carry out all the calculations, a macro was programmed with MS Visual Basic in MS Excel. The behaviour of the index is tested using hypothetical data to simulate different situations of dimorphic populations; the index is also tested with some actual populations of different species of the genus Lithodora. RESULTS AND CONCLUSIONS The index of reciprocity proposed here is a sound alternative to previous indices: it compares stigma-stamen height gaps for all potential crosses in the population, it comprises stigma-stamen distance as well as dispersion, it is not skewed by the more frequent sex, and it can be meaningfully compared between populations and species. It has produced solid results for both hypothetical and natural populations.

Reproductive biology of twoPrunus species (Rosaceae) in the Northwest Iberian Peninsula

We studied the reproductive biology ofPrunus spinosa andPrunus mahaleb (Prunoideae, Rosaceae) in the northwest Iberian Peninsula. The two species flowered at the same time (peaking on March 9 and 11, respectively in 1990) but differ significantly in their fruit maturation times. Nectar volume peaked in the early morning in both species, and was ten times greater inP. spinosa than inP. mahaleb. Neither species shows apomixis, nor does fruit-set occur if pollinators are excluded. In both species self-pollination resulted in fewer fruits than open pollination. The principal pollinators belong to theApidae family (79% and 63% of visits toP. spinosa andP. mahaleb, respectively). Results are compared with those for other rosaceous plants with fleshy fruits.

Stigma–anther reciprocity, pollinators, and pollen transfer efficiency in populations of heterostylous species of Lithodora and Glandora (Boraginaceae)

According to Darwin, the reciprocal position of sexual whorls in heterostylous plants enhances disassortative pollen transfer between different floral morphs. It is believed that greater reciprocity between morphs will promote more efficient transfer of pollen. Additionally, efficient pollination will act as a selective force in achieving greater reciprocity between floral morphs. In this study we test whether variation in reciprocity of sexual organs between morphs is related to the efficiency of pollinators in transferring pollen between them. To do this, we first describe the pollinator’s array in several populations of species of the genus formerly known as Lithodora, which have different types of stylar polymorphism and degrees of reciprocity, and determine their abundance, plant visitation rate, number of flowers visited per plant and handling time in the population. We estimate the efficiency of the pollinator arrays by use of an approximation based on qualitative (location of pollen loads on different areas of insect bodies) and quantitative (plant visitation rate) measurements. Our results show a correlation between the degree of reciprocity and the efficiency of pollinators associated with the populations. These observations suggest that pollinators are a possible selective force driving the evolution of heterostyly.

Ecological characteristics of the flora of the Northwest Iberian Peninsula

An analysis of the ecological characteristics (life form, seed-dispersal mode, pollination mode, and reproductive mode) of about 1800 species of the flora of northwest Spain indicates that the most frequent characteristics are hemicryptophyte or therophyte life form, semachorous or barochorous seed dispersal, entomophilous pollination, and hermaphroditism. Following binary classification of the above characteristics (herbaceous versus woody life form, animal-assisted versus abiotic seed dispersal, animal-assisted versus abiotic pollination, dioecous versus hermaphrodite reproductive mode), statistically significant associations were found for all pairs of characteristics except pollination mode and reproductive mode (in disagreement with the results of previous studies which have detected significant associations between dioecy and abiotic pollination) and pollination mode and life form. To investigate the evolutionary plasticity of the different characters, we used nested analysis of variance with (in the case of life form, for example) percentage of species in genus with herbaceous life form as response variable, and with genus, family, order and subclass as nested factors and class as crossed factor. The results of this analysis indicated that higher-level grouping (class or subclass) accounted for the majority of total variance only in the case of pollination mode, suggesting either that pollination mode was typically determined early in evolutionary history and that there is currently little plasticity in this characteristic (i.e., phylogenetic constraints), or that this characteristic has been subject to stabilizing selection (i.e., phylogenetic niche conservatism). The other ecological characters, by contrast, showed high variability at lower levels in the taxonomic hierarchy.

Patterns of style polymorphism in five species of the South African genus Nivenia (Iridaceae)

BACKGROUND AND AIMS Heterostylous plants have been characterized by the presence of two or three discrete morphs that differ in their sex organ position within populations. This polymorphism is widely distributed among the angiosperms, but detailed studies are limited to few taxonomic groups. Although a small representation, evolutionary meaningful variations of the heterostylous syndrome have been reported when precise measurements of the sexual whorls were taken. A thorough exploration of groups where heterostyly has been reported should offer new opportunities to further testing the evolutionary hypotheses explaining heterostyly. Here, the traits defining heterostyly were explored in half of the species in Nivenia, the only genus of Iridiaceae where heterostyly has been reported. METHODS Detailed morphometric analysis of the flower sexual whorls and some traits considered as ancillary are supplied to determine for each population (a) the kind of stylar polymorphism, (b) the morph ratio and (c) the degree of reciprocity between sexual whorls. Also the rates of assortative (within morph) versus disassortative (between morphs) pollen transfer were estimated by analysing pollen loads on stigmas. The association between floral phenotypic integration and the reciprocity between sexual whorls was estimated; both characteristics have been quoted as dependent on the accuracy of the fit between pollinators and flowers and therefore related to the efficiency of pollen transfer. KEY RESULTS Different types of polymorphism, differing in their degree of reciprocity, were found in Nivenia. Effective disassortative mating appears to be common, since (a) all dimorphic populations show equal morph-ratios (isoplethy), and (b) the pollen placed on the stigmas of each morph is likely to be coming from the other (complementary) morph. The most reciprocal populations of the heterostylous species have also the highest values of phenotypical integration. CONCLUSIONS Stigma height dimorphism, as opposed to distyly, is proven for the first time in Nivenia. The presence of different types of polymorphism within the genus is consistent with hypotheses of the evolution of heterostyly. The role of the pollinators as the leading force of the transition seems to be apparent, since floral integration is related to reciprocity.

Nutrient status in tall and short forms of Spartina maritima in the salt marshes of ortigueira (NW Iberian Peninsula) as related to physicochemical properties of the soils

The existence of different growth forms (tall and short) in various species of the genus Spartina has, on occasion, been attributed to differences in the availability of nutrients. In the present work, macronutrient (N, P, K, Mg, Ca, S) and micronutrient (Fe, Mn, Zn, Cu) contents of the soils and tissues (leaves and stems) of three populations of S. maritima from the NW Iberian Peninsula were studied. The results obtained showed that although there were differences in the physicochemical properties of the soils and in the concentration of nutrients in soils and plants at the different locations, these do not explain the different growth forms of S. maritima. Since other authors have found that the growth forms displayed by different species of the same genus are in part due to genotypic differences, ecotypic differentiation, along with other environmental factors that were not assessed in this research, may control the differences in height and biomass of S. maritima. However, more detailed studies of this species are required in order to assess the importance of environmental (e.g., fertilization experiments) and genetic factors (e.g., RAPD analysis) that influence the growth form of natural populations of Spartina maritima.

The avoidance of self-interference in the endemic daffodil Narcissus cyclamineus (Amaryllidaceae)

Hermaphrodite flowers usually possess floral traits to avoid the negative effects derived from inbreeding depression and/or self-interference between pollen export and reception, both acting as the main selective pressures on those floral traits. The avoidance of self-interference is widely accepted as the primary force promoting the separation between sexes within the flowers in time (dichogamy) and/or space (herkogamy) for self-incompatible species, which are already protected from the negative effects of inbreeding depression by the incompatibility system. Different degrees of incompatibility, herkogamy, and dichogamy have been reported for the genus Narcissus. However, the only mechanism for the separation of sexes reported up to date for Narcissus cyclamineus is herkogamy, while the presence of dichogamy and the type of incompatibility in this species remain uncertain. In this study, we analyze the patterns of sexual reproduction in N. cyclamineus to ascertain whether there is any selective pressure favouring sexual segregation or its maintenance and their mechanisms. N. cyclamineus is self-incompatible and dichogamy can be rejected for this species. Even though the species is self-incompatible, when cross-pollination is preceded by self-pollination the number of ovules available for legitimate crosses is diminished (ovule discounting). Pollinators are scarce during the flowering period, resulting in pollen limitation. It is suggested that both the scarcity of pollinators and ovule discounting may be acting synergically to promote herkogamy or its maintenance in this species.

Effects of nectar robbing on male and female reproductive success of a pollinator-dependent plant

BACKGROUND AND AIMS Nectar robbers affect host fitness in different ways and by different magnitudes, both directly and indirectly, and potentially constitute an important part of pollination interactions. The aim of this study was to assess the effect of nectar robbing on several variables that characterize the reproductive success of Lonicera etrusca, a pollinator-dependent plant with long, tubular flowers that produce abundant nectar. METHODS Using fluorescent powder dye as a proxy for pollen, the distance of pollen dispersal was compared for robbed and non-robbed flowers. Artificial nectar robbing treatments were applied to test its effects on four additional measures of reproductive success, namely the quantity of pollen exported, fruit set, seed/ovule ratio and seed weight. KEY RESULTS Nectar robbing was not found to have any significant negative consequences on female and male components of reproductive success as determined through the five variables that were measured. CONCLUSIONS Although L. etrusca exhibits high levels of nectar robbing and nectar robbers are common floral visitors, no evidence was found of detrimental changes in the components of reproductive success. A combination of morphological and ecological mechanisms is proposed to explain how plants may compensate for the energetic loss caused by the nectar robbers.

Shading by invasive seaweeds reduces photosynthesis of maerl from the Ría de Vigo (NW Spain)

Abstract The overgrowth and shading of several alien species along the European Atlantic coast are expected to reduce photosynthesis of maerl, decreasing its growth and fitness. In this work, three shade levels (0, 20 and 50%) were set up under laboratory conditions to simulate different competitive scenarios potentially affecting maerl beds. Live individuals of Sargassum muticum and Undaria pinnatifida were placed over maerl cultures, and the effects of shading were assessed by chlorophyll a fluorescence using a pulse-modulated fluorescence monitoring system. Photosystem II efficiency was measured as the ratio of variable to maximal fluorescence (Fv/Fm) as a proxy for the stress experienced by maerl. According to our data, irradiance reduction results in a small, yet significant, impact on the PSII efficiency of maerl, which could have fitness consequences.