Marcos Méndez

Modification of phenotypic and functional gender in the monoecious Arum italicum (Araceae).

Other than studies on sex-labile Arisaema species, studies of gender patterns in Araceae are scarce. The modification of phenotypic and functional gender was investigated in three populations of the monoecious Arum italicum Miller. The probability of reproduction and the number of inflorescences produced increased with plant size, and flower number (total, male, staminodes, female, pistillodes) increased with both plant and inflorescence sizes. However, plant and inflorescence sizes were poor predictors of floral sex ratio (female to male flower ratio). In contrast, change in floral sex ratio towards increasing femaleness was found among inflorescences sequentially produced by a plant. This change could not be explained by either a decrease in inflorescence size or a change in the mating environment. Differences in functional gender did not appear to be related to plant size or stage in the flowering period. Instead, different patterns of functional gender were found between plants with different number of inflorescences. Multi-inflorescence plants showed a functional gender around 0.5, while plants with one inflorescence showed a more extreme functional gender (either male, female, or functionally sterile). Sex of flowers in this species did not seem to exhibit a phenotypic trade-off.

Habitat-based conservation priorities for carabid beetles within the Picos de Europa National Park, northern Spain

Quick biodiversity studies on poorly studied taxa and areas are increasingly popular for setting conservation priorities over a wide range of spatial scales. However, the implementation of such studies is complicated by the variable extent to which the different criteria used in prioritisation are correlated to each other. Using methods of constrained ordination, we examined the species-habitat relationships of carabid beetles based on ground beetle assemblages from 22 sites in the Picos de Europa National Park, northern Spain. We found characteristic species assemblages for subalpine meadows, Genista shrublands, and pastures, whereas mown meadows, heathlands, beech and riparian woodlands were occupied by more habitat generalist species. Species associated with subalpine meadows and Genista shrublands tended to be mostly brachypterous and to have geographic ranges restricted to northern Spain. In contrast, we found no relationship between the degree of species association with pastures and geographic range-wing size type. Although the species richness was higher in riparian woodlands and mown meadows, we suggest a higher conservation value for subalpine meadows and Genista shrublands across the landscape because they sustain characteristic assemblages dominated by species with restricted ranges and reduced powers of dispersal. Our study suggests that preserving areas in the landscape supporting higher biodiversity will not necessarily preserve those species potentially more susceptible to habitat loss and fragmentation. It also supports the feasibility of biodiversity studies based on multivariate techniques for setting conservation priorities over complex landscapes.

Survival costs of reproduction in a short-lived perennial plant: Live hard, die young

According to life-history theory, reproductive investments involve costs in terms of growth, future fecundity, and/or survival. However, studies to date have often failed to detect costs of reproduction, with survival costs among the less documented. We investigated the cost of reproduction in Helianthemum squamatum (Cistaceae), a short-lived perennial of semiarid Mediterranean environments. After experimental flower removal, we evaluated next seasons growth, reproduction, and survival of the plants. We also monitored an indicator of plant physiological status (F(v)/F(m)) and leaf nutrient concentration at key phenological stages during reproduction. Survival rate in deblossomed plants was significantly higher than in control plants. As far as we know, this is the first experimental evidence of a survival cost of reproduction in a perennial plant. In contrast, no cost to growth or reproduction was found during the next season, and no significant differences in F(v)/F(m) or leaf nutrients were found between control and deblossomed plants. Helianthemum squamatums success in semiarid Mediterranean ecosystems seems to rely on a persistent seed bank, combined with a sustained high reproductive output at the expense of survival. We conclude that this strategy might be more common than previously thought among short-lived shrubby plants growing in stressful Mediterranean areas.

Sexual mass allocation in species with inflorescences as pollination units: a comparison between Arum italicum and Arisaema (Araceae).

Sex allocation models predict that cosexuality is stabilized by high allocation to attractive structures in pollen-limited species or by high allocation to shared structures that contribute to both genders. High investment in unilateral fixed costs favor the evolution of dioecy or gender change. With these predictions in mind, I studied sexual mass allocation at flowering in the monoecious Arum italicum (Araceae) and compared it with information available for its sex labile relative Arisaema dracontium. In A. italicum, 68% of biomass was allocated to structures believed to be involved in pollinator attraction and capture. This allocation pattern contrasts with that of Arisaema dracontium, in which 70% of biomass was allocated to scape, considered to be a unilateral fixed cost. The importance of attractive structures in A. italicum was further supported by a disproportionate increased allocation, in larger inflorescences, to the appendix (an attractive structure) compared to fertile flowers. In addition, an increase in inflorescence mass involved a disproportionate increase in mass allocation to male, rather than female, flowers. This pattern also contrasts with a size-related gender change from male to female in Arisaema species. These findings were consistent with sex allocation model predictions and shed light on the evolution of sex lability in Arisaema species.

Pollination context effects in the high-mountain dimorphic Armeria caespitosa (Plumbaginaceae): neighborhood is something more than density.

Frequency-dependent processes are relevant for flowering plant reproduction, especially for species with disassortative mating. In an individual-based study, we tested not only the effects of local density on reproductive success at small spatial scales, but also those of neighborhood quality. To test the neighborhood effects on the reproduction of Armeria caespitosa, a dimorphic Mediterranean high-mountain endemic, we introduce a novel pollination context (PC) index that considered the distance, floral display, and floral morph of neighbors at small scales (within 2 m from the focal plant), studying rock and pasture populations at both edges of the species altitudinal distribution. Reproductive success depended significantly on PC only at the low populations, suggesting that the PC effects are population-dependent and supporting the hypothesis that the neighborhood quality influences the reproductive success of A. caespitosa at least in stressful conditions. Moreover, fruit set was morph-dependent in the high-pasture population. The specific role of the spatial structure of compatible vs. incompatible morphs at small scales of the dimorphic self-incompatibility system in Armeria deserves further attention. Parameters other than plant density are useful for the study of small-scale density-dependent processes that affect pollination and other reproductive components, especially if they integrate neighborhood quality information at adequate spatial scales.

Linkages among life-history components through time: Carryover effects on the demography of a short-lived polycarpic plant

UNLABELLEDnnnnPREMISE OF THE STUDYnCurrent reproduction in polycarpic plants may be affected by a wide variety of factors, including carryover or historical effects derived from environments experienced early in life and from previous investments in organ preformation or other life functions, such as growth or reproduction. Historical effects as determinants of plant reproductive success in a specific season have received considerably less attention than events during the current reproductive episode, especially for short-lived plants. •nnnMETHODSnWe used structural equation modeling to assess direct and indirect relations between past reproduction and both subsequent reproduction and growth in Helianthemum squamatum, a short-lived polycarpic plant. Additionally, we explored the effects of current reproduction on future survival (binomial variable) by using logistic regression. •nnnKEY RESULTSnHistorical effects derived from previous growth positively affected current reproduction, suggesting the existence of a reproductive hierarchy in the population, in which some individuals are consistently better growers and seeders. The lack of effects of current reproduction on future reproduction, together with the existence of a negative effect on future survival, suggests that to invest maximally in reproduction at the expense of a short life span may be the optimal strategy for H. squamatum, a species inhabiting very unpredictable ecosystems. •nnnCONCLUSIONSnHistorical effects derived from past investments in growth or reproduction may have important consequences for current plant performance and may play an essential role in shaping life histories.

Do antheridiogens act via gametophyte size? A study of Woodwardia radicans (Blechnaceae)

For many plants, sex is not fixed by genotype but determined by environmental conditions during development. In homosporous pteridophytes, sex is environmentally determined by the presence or absence of antheridiogens, maleness-inducing pheromones. It has been proposed that antheridiogens primarily reduce growth rate, with small gametophyte size responsible for maleness. To test this hypothesis, the effects of antheridiogen and intergametophytic competition on gender expression and gametophyte size were studied in a culture experiment with Woodwardia radicans. We found that (1) antheridiogen inhibited growth of gametophytes; and (2) slow growth favored maleness, whereas fast growth favored femaleness, irrespective of the presence or absence of antheridiogen. Both conclusions are consistent with the hypothesis that, in W. radicans, antheridiogen effect is mediated by size. They also agree with the size-advantage hypothesis in which energetic limitations associated with relatively small individual size impose a less severe limitation for male reproductive success than for female reproductive success. The results are also discussed with regard to a genetic sex-determining pathway that has recently been identified.