Is self-incompatibility a reproductive barrier for hybridization in a sympatric species?

PREMISE: Barriers at different reproductive stages contribute to reproductive isolation. Self-incompatibility (SI) systems that prevent self-pollination could also act to control interspecific pollination and contribute to reproductive isolation, preventing hybridization. Here we evaluated whether SI contributes to reproductive isolation among four co-occurring Opuntia species that flower at similar times and may hybridize with each other. METHODS: We assessed whether Opuntia cantabrigiensis, O. robusta, O. streptacantha, and O. tomentosa, were self-compatible and formed hybrid seeds in five manipulation treatments to achieve self-pollination, intraspecific cross-pollination, open pollination (control), interspecific crosses or apomixis, then recorded flowering phenology and synchrony. RESULTS: All species flowered in the spring with a degree of synchrony, so that two pairs of species were predisposed to interspecific pollination (O. cantabrigiensis with O. robusta, O. streptacantha with O. tomentosa). All species had distinct reproductive systems: Opuntia cantabrigiensis is self-incompatible and did not produce hybrid seeds as an interspecific pollen recipient; O. robusta is a dioecious species, which formed a low proportion of hybrid seeds; O. streptacantha and O. tomentosa are self-compatible and produced hybrid seeds. CONCLUSIONS: Opuntia cantabrigiensis had a strong pollen-pistil barrier, likely due to its self-incompatibility. Opuntia robusta, the dioecious species, is an obligate outcrosser and probably partially lost its ability to prevent interspecific pollen germination. Given that the self-compatible species can set hybrid seeds, we conclude that pollen-pistil interaction and high flowering synchrony represent weak barriers; whether reproductive isolation occurs later in their life cycle (e.g., germination or seedling survival) needs to be determined.

Bee Assemblage in the Southern Chihuahuan Desert: The Role of Season, Year, and Trap Color in Abundance.

Recognizing how populations fluctuate over time is a crucial factor in determining the environmental elements affecting population persistence. However, the limited information on wild bee populations complicates the estimation of the impact of anthropogenic threats leading to changes in population size. To address this, we conducted a study capturing and monitoring nine species of wild bees through monthly samplings over four years. Tray traps were placed in permanent plots, and capture records were used to determine population size (N) and density (D). A generalized linear model (GLM) was employed to determine how the use of traps affected bee species captures. The families Apidae and Halictidae represented the most captures. Apis mellifera, the Lasioglossum (Dialictus spp.) complex, and Macrotera sinaloana exhibited the largest number of captures and highest population density. Most species (77.7%) showed a tendency to remain constant over the years and to have a higher number of captures in the spring months. Moreover, yellow traps were the most effective in capturing bee individuals. We suggest that the availability of essential resources and the reduction in environmental stressors positively affected the capture of wild bee populations.

The floral biology and the role of staminal connective appendages during pollination of the endoparasite Bdallophytum americanum (Cytinaceae).

Bdallophytum americanum (Cytinaceae) is an endoparasitic plant species, meaning only the flowers emerge from the host during the reproductive season. Reports on the pollination biology of this species state that its primary pollinators are carrion flies attracted by the smell of the flowers and nectar as a reward. However, the functional role of one of the most outstanding attributes of B. americanum has been neglected. These are the staminal appendages formed by the apical overgrowth of connective tissue during anther development. To determine whether these staminal appendages play a role in pollination, we monitored a nectarless population of B. americanum. We described the inflorescence emergence, floral movements, and pollination and performed field experiments to test whether the absence of the staminal connective appendages affected the visitation frequency. Male inflorescences emerge early, and both male and female flowers open during the day and do not close. Hoverflies are the most frequent visitors to both floral sexes and carry the most pollen. Moreover, the movement of staminal appendages matching the pollen viability changes is reported for the first time. The staminal appendages are the structures where pollinators land before foraging. The field experiments showed that the visitation frequency decreased sharply without staminal appendages. As a landing platform, the staminal connective appendages in B. americanum are crucial for pollinator positioning and collecting viable pollen.

Prescriptions for the Control of a Clonal Invasive Species Using Demographic Models.

Until recently, little research has focused on determination of the population dynamics of invasive species and evaluating their genetic variation. Consequently, not much is known of what drives clonal invasive species and their demography. Here, we describe the population dynamics of Kalanchoe delagoensis (Crassulaceae), considered invasive to several countries. We quantified the demography of a population in central Mexico using integral projection models (IPM) in a population that reproduced asexually exclusively through plantlets. The effect of clonal recruitment on population growth rate (λ) was evaluated by changing plantlet survival and simulating management scenarios that used previous data of watering and seven experimental herbicide treatments. The finite rate of population increase indicated that this Kalanchoe delagoensis population is growing (above one) and with water availability, growth rates will only accelerate. The IPM showed that plantlet survival and recruitment were the most critical steps in the cycle for the population, and simulations of different management scenarios showed that reducing plantlet survival significantly decreased λ only in two out of the seven herbicides used.

Inferring space from time: On the relationship between demography and environmental suitability in the desert plant O. rastrera.

Demographic analyses and ecological niche modeling (ENM) are two popular tools that address species persistence in relation to environmental conditions. Classic demography provides detailed information about the mechanisms that allow a population to grow or remain stable at a local scale, while ENM infers distributions from conditions suitable for species persistence at geographic scales by relating species' occurrences with environmental variables. By integrating these two tools, we may better understand population processes that determine species persistence at a geographic scale. To test this idea, we developed a model that relates climate to demography of the cactus Opuntia rastrera using 15 years of data from one locality. Using this model we determined the geographic area where populations would have positive growth rates given its climatic conditions. The climate-dependent demographic model showed poor performance as a distribution model, but it was helpful in defining some mechanisms that determine species' distributions. For instance, high rainfall had a negative impact on the population growth rate by increasing mortality. Rainy areas to the west of the distribution of O. rastrera were identified as unsuitable both by our climate-dependent demographic model and by a popular ENM algorithm (MaxEnt), suggesting that distribution is constrained by excessive rains due to high mortality. Areas projected to be climatically suitable by MaxEnt were not related with higher population growth rates. Instead, we found a strong correlation between environmental distance to the niche centroid (center of the niche hypervolume, where optimal conditions may occur) and population growth rate, meaning that the niche centroid approach is helpful in finding high-fitness areas.

Influence of fruit dispersal on genotypic diversity and migration rates of a clonal cactus from the Chihuahuan Desert.

The diverse offspring of clonal species differ in their dispersability, influencing genotypic diversity and clonal structure. Here, we determined dispersal patterns and their impact on genetic structure in Opuntia microdasys, a self-incompatible cactus with three dispersal units (one sexual and two clonal). We analyzed dispersal, using experiments at three populations, and assessed multilocus genotypes (ISSR markers) of all individuals in 10 clumps per population with known reproductive origin (sexual or clonal). Genotype of all samples, population structure, and migration between clumps and populations were assessed with GenAlEx and GenoDive, assuming higher genotypic diversity and migration when sexual reproduction is more frequent. We determined the most likely number of genetic clusters with STRUCTURE and geneland. Dispersal differed among populations; primary dispersal occurred at short distances and was farthest on steep slopes, and dispersal distance increased after secondary dispersal. Clumps had 116 different multilocus genotypes in three spatially explicit genetic clusters. We detected genetic structure at small scale, genotypic diversity among clumps varied between populations; diversity decreased while clonal dominance increased, and the most variation occurred among clumps. Genetic structure was moderate, suggesting gene flow by seed dispersal allows slight differentiation among population at large scales. Genetic diversity within clumps was the lowest because dispersal of clonal propagules was limited and caused genotypic dominance at local scale. However, the combined dispersal pattern of sexual and clonal dispersal units is fine-tuned by environmental factors, generating a range of genetic diversity among clusters and populations. This pattern suggests that genetic structure of clonal plants is more dynamic than thought, and dispersal of different types of offspring affects genetic structure at many scales.

[Demography of Caulerpa paspaloides var. wudermanni (Bryopsidales: Caulerpaceae) in the coastal zone of Campeche, México]. / Demografía de Caulerpa paspaloides var. wudermannii (Bryopsidales: Caulerpaceae) en la zona costera de Campeche, México.

Demography of Caulerpa paspaloides var. wudermanni (Bryopsidales: Caulerpaceae) in the coastal zone of Campeche, México. The subaquatic vegetation of Los Petenes, Campeche, Mexico, stands out due to its considerable floristic diversity, composed of a great variety of sea grasses and several species of the genus Caulerpa sp. This is a genus of ecological relevance, with the invasive species in the Mediterranean, with negative impact on several native sub-aquatic plants; nevertheless, little is known about the demography and population dynamics of Caulerpa species and their contribution to food webs. Thus the main objective of this study was to describe the demographics of Caulerpa paspaloides var. wudermanni, using the number of stolons, complete and incomplete fronds, the diameter of the stolons and the biomass. The information was used to determine the growth rate (lambda) of this species. The study was conducted in the Biosphere Reserve of Los Petenes, which is located in the Northwest of the state of Campeche. The submerged aquatic vegetation (SAV) in the Petenes Biosphere consists of monospecific and mixed populations of seagrass species (Thalassia testudinum, Halodule wrightii and Syringodium filiforme). Although chlorophytes, brown algae and red algae, are fundamental elements in the specific composition of the SAV in Petenes, several species of Caulerpa are prominent because of their coverage and abundance. In May and June of 2010, significant differences in the quantity of stolons, their diameter, incomplete and complete fronds, and the size of the stolons and rhizomes, were observed. In 2010, the finite population growth rate (lambda) was 2.38 +/- 0.1571 for individuals and 1.20 +/- 0.1356 for the population, and in 2011 the values of lambda were 1.80 +/- 0.3608 and 1.35 +/- 0.1571, respectively. From these results it can be concluded that the population is growing; however, growth is controlled by biotic and abiotic factors. Despite there was no apparent threat, we suggest continuing the demographic studies of C. paspaloides var. wurdemannii, as well as of other species of the same genus, not only to detect invasion or explosive growth, but also their presence indicated low oxygen levels and high sulphates.

Demografía de Caulerpa paspaloides var. Wudermannii (Bryopsidales: Caulerpaceae) en la zona costera de Campeche, México / Demography of Caulerpa paspaloides var. wudermanni (Bryopsidales: Caulerpaceae) in the coastal zone of Campeche, México

The subaquatic vegetation of Los Petenes, Campeche, Mexico, stands out due to its considerable floristic diversity, composed of a great variety of sea grasses and several species of the genus Caulerpa sp. This is a genus of ecological relevance, with the invasive species in the Mediterranean, with negative impact on several native sub-aquatic plants; nevertheless, little is known about the demography and population dynamics of Caulerpa species and their contribution to food webs. Thus the main objective of this study was to describe the demographics of Caulerpa paspaloides var. wudermanni, using the number of stolons, complete and incomplete fronds, the diameter of the stolons and the biomass. The information was used to determine the growth rate (λ) of this species. The study was conducted in the Biosphere Reserve of Los Petenes, which is located in the Northwest of the state of Campeche. The submerged aquatic vegetation (SAV) in the Petenes Biosphere consists of monospecific and mixed populations of seagrass species (Thalassia testudinum, Halodule wrightii and Syringodium filiforme). Although chlorophytes, brown algae and red algae, are fundamental elements in the specific composition of the SAV in Petenes, several species of Caulerpa are prominent because of their coverage and abundance. In May and June of 2010, significant differences in the quantity of stolons, their diameter, incomplete and complete fronds, and the size of the stolons and rhizomes, were observed. In 2010, the finite population growth rate (λ) was 2.38±0.1571 for individuals and 1.20±0.1356 for the population, and in 2011 the values of λ were 1.80±0.3608 and 1.35±0.1571, respectively. From these results it can be concluded that the population is growing; however, growth is controlled by biotic and abiotic factors. Despite there was no apparent threat, we suggest continuing the demographic studies of C. paspaloides var. wurdemannii, as well as of other species of the same genus, not only to detect invasion or explosive growth, but also their presence indicated low oxygen levels and high sulphates. Rev. Biol. Trop. 62 (2): 729-741. Epub 2014 June 01.

La vegetación subacuática de Los Petenes, Campeche, México, se destaca por su gran diversidad florística, compuesto por una gran variedad de pastos marinos y varias especies del género Caulerpa sp. Caulerpa es un género de relevancia ecológica, con especies como la Caulerpa taxifolia, que es invasiva en el Mediterráneo, con un impacto negativo en varias plantas sub-acuáticas nativas, pero poco se sabe acerca de la demografía y la dinámica poblacional de las especies de Caulerpa y su contribución a las redes alimenticias. El objetivo general es conocer la demografía de Caulerpa sp., por medio del número de estolones, frondas completas e incompletas, el diámetro de los estolones y la biomasa. El estudio se realizó en la Reserva de la Biosfera de Los Petenes, en Campeche, México. La Vegetación Acuática Sumergida (VAS) en la Biosfera de los Petenes está constituida por poblaciones tanto monoespecíficas como mixtas de las especies de pastos marinos Thalassia testudinum, Halodule wrightii y Syringodium filiforme. Aunque las especies de algas clorófitas, feofitas y rodófitas son elementos fundamentales de la VAS, destacan por su cobertura y abundancia las especies de Caulerpa. En mayo y junio del 2010, hubo diferencias significativas de la cantidad de estolones, su diámetro, frondas completas e incompletas y el tamaño de los estolones como el de los ejes erectos. En el 2010 el valor de la tasa finita de crecimiento poblacional (l) fue de 2.38±0.15 con el método de las marcas y con el de la biomasa 1.20±0.13 y en el 2011 los valores fueron de 1.80±0.36 con las marcas y de 1.35±0.15 con la biomasa. Los resultados indican que la población está creciendo, pero es controlada por factores bióticos y abióticos. A pesar de que no se detecta la especie como una amenaza aparente, sugerimos que se continúen estos estudios demográficos sobre C. paspaloides var. wurdemannii e incluso de otras especies del mismo género. No solo para detectar una invasión o un crecimiento explosivo, sino porque la presencia de estas especies no indican condiciones bajas en oxígeno y altas en sulfatos.

How common is self-incompatibility across species of the herkogamous genus Ariocarpus?

PREMISE OF THE STUDY: Self-incompatibility (SI), the most effective mechanism to prevent selfing, may limit the number of compatible mates in populations. The seven species of Ariocarpus are endangered and predominantly outcrossers but fruit set may reach 1-20% after selfing. We aimed to determine whether SI is the underlying mechanism influencing mating in Ariocarpus species. METHODS: We characterized the presence/absence of SI using pollination treatments (self-pollination, cross-pollination, natural pollination) in one population per species. We assessed SI using epifluorescence and generalized linear models (GLMs) to compare the presence of pollen tubes in the stigma, stylar transmitting tissue, and ovary among self- and cross-pollinated pistils 48 h after pollination. Following the same treatments, production of fruit set was noted and related to pollen tube growth. KEY RESULTS: Pollen tubes were found more frequently in the ovaries of natural and cross-pollinated flowers than in ovaries of self-pollinated. Stylar rejection of self-pollen indicated gametophytic SI, although pollen tubes reached the ovaries in six species (4-33% of pistils). Fruit set was lower after hand-pollinations than expected from pollen tube observations. CONCLUSIONS: The low percentages of self-compatibility in all species in pollen tube growth and pollination experiments indicated that no species had complete self-sterility, suggesting the presence of partial SI. Reduced fruit set relative to pollen tube production could result from a threshold of insufficient pollination, early-acting inbreeding depression, or resource limitation. The origin of partial SI in Ariocarpus could respond to pressures such as pollen limitation and population size.

Seed size and photoblastism in species belonging to tribe Cacteae (Cactaceae).

The response of seed germination towards light and the relationship to seed traits has been studied particularly well in tropical forests. Several authors have shown a clear adaptive response of seed size and photoblastism, however, the evolutionary significance of this relationship for species inhabiting arid environments has not been fully understood and only some studies have considered the response in a phylogenetic context. We collected seeds from 54 cacti species spread throughout the tribe Cacteae to test whether there was correlated evolution of photoblastism, seed traits and germination using a reconstructed phylogeny of the tribe. For each species we determined the photoblastic response under controlled conditions, and seed traits, and analyzed the results using phylogenetically independent contrasts. All studied species were positive photoblastic contrasting with the basal Pereskia suggesting an early evolution of this trait. Seeds from basal species were mostly medium-sized, diverging into two groups. Seeds tend to get smaller and lighter suggesting an evolution to smaller sizes. No evidence exists of a relationship between seed size and photoblastic response suggesting that the photoblastic response within members of this tribe is not adaptive though it is phylogenetically fixed and that is coupled with environmental cues that fine tune the germination response.