Spatial and Temporal Variation in the Ant Occupants of a Facultative Ant-Plant1

Striking variation in ant occupation of a facultative ant-plant, Conostegia setosa (Melastomataceae), was found at three scales: local spatial, geographic, and temporal. C. setosa provides housing for ants and grows in groups of stems (clones). The ant occupants of 14 C. setosa clones were censused four times over a 14-mo period at the La Selva Biological Station, Costa Rica, and twice over a 9-mo period at the Nusagandi Station, Panama. Twelve facultative ant species occupied C. setosa stems at La Selva, compared to six facultative and one obligate species at Nusagandi. Occupancy (as % of stems ever occupied/clone) was higher at Nusagandi (median = 89%) compared to La Selva (65%). Occupancy varied among clones at La Selva but not at Nusagandi. C. setosa clones differed between sites, with larger clones and more small stems/clone at La Selva. Occupancy was influenced by clone structure; larger clones contained more ant species at both sites and had lower occupancy at La Selva. Occupancy was highest in larger stems and lowest in small stems at both sites. Temporally, percent occupation/clone did not differ among censuses at either site, but overall occupancy was lower in the dry season at La Selva. Turnover in ant occupants was higher at La Selva than at Nusagandi. The variation observed in this study is likely due to a number of factors, including differences between sites in plant population structure and history, differences between and within sites in ant faunas and their nesting requirements, and changes over space and time in microclimatic variables. Such high variation at multiple scales draws attention to the importance of long-term comparative studies of facultative animal-plant interactions.     

Facultative Ant-Plant Interactions: Nectar Sugar Preferences of Introduced Pest Ant Species in South Florida1

We observed nectar use by native and exotic ant species in nature, garden, and urban situations, and found ants utilizing floral and extrafloral nectar of a variety of flowering plant species. We collected 31 plant nectars (29 floral, 2 extrafloral) and used them in feeding preference tests against standard solutions of sugars (20 percent fructose, glucose, and sucrose, and their mixture), 10 trials for each nectar-ant comparison. We compared time-to-discovery and total ant visits to each droplet using ANOVA, and found that both trial and solution contributed significantly to the variation in most experiments. Seven of the floral nectars tested were significantly more attractive to certain ant species than the sugar solutions. Not only do ants use floral nectar, but it appears that some floral nectars contain compounds that are especially attractive to ants.     

Carbon Flux of an Urban System in México

We estimated vertical and lateral fluxes of carbon for the isolated coastal city of Ensenada (Baja California, México). In 2005, the city had a resident population of about 261,000, with tourism adding about 1.5%; it occupied an area of roughly 68 square kilometers (km²). Carbon (C) export was estimated at 400 gigagrams of carbon per year (Gg C/yr); notable sources to the atmosphere were combustion engines (42%), cement production (38%), water heating and cooking (7%), and human respiration (6%). Solid waste (6%) was exported for burial, but efflux to the bay was minor (about 0.1 Gg C/yr). Local deposition was limited to sewage sludge (about 2 Gg C/yr), asphalt, and extremely low primary production. Remote fluxes driven by local demand could be estimated only for electricity (61 Gg C/yr), but local flux from cement and other industrial production might be attributed largely to external demand. The urban system output to the atmosphere was about 6.4 kilograms of carbon per square meter per year (kg C/m²/yr), or roughly 23.6 kg/m²/yr in CO₂ equivalence. By comparison, net ecosystem productivity in the surrounding watershed has been estimated at 0.04 kg C/m²/yr, so the city's atmospheric output of C might be balanced by productivity over about 11,000 km² of the surrounding ecosystems. Between 2000 and 2005, C output increased faster than population growth, particularly from engine fuels.     

Extrafloral nectaries in the genus Macaranga (Euphorbiaceae) in Malaysia: comparative studies of their possible significance as predispositions for myrmecophytism

Some species of the paleotropical tree genus Macaranga (Euphorbiaceae) live in close association with ants. The genus comprises the full range of species from those not regularly inhabited by ants to obligate myrmecophytes. In Malaysia (Peninsular and Borneo) 23 of the 52 species are known to be ant-associated (44%). The simplest structural adaptation of plants to attract ants are extrafloral nectaries. We studied the distribution of extrafloral nectaries in the genus Macaranga to assess the significance of this character as a possible predisposition for the evolution of obligate myrmecophytism. All species have marginal glands on the leaves. However, only the glands of non- myrmecophytic species function as nectaries, whereas liquids secreted by these glands in myrmecophytic species did not contain sugar. Some non-myrmecophytic Macaranga and transitional Macaranga species in addition have extrafloral nectaries on the leaf blade near the petiole insertion. All obligatorily myrmecophytic Macaranga species, however, lack additional glands on the lamina. The non-myrmecophytic species are visited by a variety of different ant species, whereas myrmecophytic Macaranga are associated only with one specific ant-partner. Since these ants keep scale insects in the hollow stems, reduction of nectary production in ant-inhabited Macaranga seems to be biologically significant. We interpret this as a means of (a) saving the assimilates and (b) stabilization of maintenance of the association's specificity. Competition with other ant species for food rewards is avoided and thereby danger of weakening the protective function of the obligate ant- partner for the plant is reduced. A comparison with other euphorb species living in the same habitats as Macaranga showed that in genera in which extrafloral nectaries are widespread, no myrmecophytes have evolved. Possession of extrafloral nectaries does not appear to be essential for the development of symbiotic ant-plant interactions. Other predispositions such as nesting space might have played a more important role.     

Natural selection on extrafloral nectar production in Chamaecrista fasciculata: the costs and benefits of a mutualism trait

Cost-benefit models of the evolution of mutualism predict that the current state of mutualism results from trade-offs between fitness costs of mutualist traits and the fitness benefits of association. We test the assumptions of such models by measuring patterns of natural selection on a mutualist trait, extrafloral nectar production in Chamaecrista fasciculata. Selection was measured on plants from which ants had been excluded (removing the mutualist benefit of the trait), from which all insects had been excluded (removing costs of herbivory in addition to mutualist benefits), and unmanipulated plants (where both costs and benefits were present). Selection analysis based on half-sibling-mean regressions of fitness on the trait revealed no evidence of costs of extrafloral nectar production in the absence of all insects or in the absence of ants. However, examination of the selective surfaces for these treatments suggest that costs of nectar production may exist and are exacerbated by the presence of herbivory. In the presence of ants, natural selection favors high extrafloral nectar production, consistent with a fitness benefit to this mutualist trait in the presence of the mutualist partner. In this study, the interaction of costs and benefits did not produce an evolutionary optimum for the trait within the range of variation observed, suggesting that application of a cost-benefit framework to this trait will benefit from considering the influence of temporal and spatial variation on the quality of costs and benefits.     

1H‐NMR Based Metabolomics Profiling of Citrus Juices Produced in Veracruz,México

This study describes the ¹H‐NMR‐based metabolomics profiling of juices from citrus fruits harvested in the state of Veracruz, México. The hydrophilic profile of commercial lemons (Agrio and Persian), tangerines (Fremont and Mónica), oranges (Valencia and Washington Navel), and grapefruits (Red Ruby and Rio Red) was determined. According to our results, 35 metabolites were identified in the ¹H‐NMR profiling. The statistical differences obtained by PCA and OPLS‐DA revealed that specific amino acids, sugars, and organic acids were differential metabolites in the species and cultivars studied. High endogenous levels of sucrose (10–190 mM), α‐glucose, β‐glucose (α‐ and β‐isomers, 40–205 mm ), and fructose (36–170 mm ) were detected in the juices of grapefruits, oranges, and tangerines, whereas citric acid (40–530 mm ) was the principal organic acid in the juices of lemons. To calculate the specific amounts of metabolites from these species and their cultivars, the results were finely analyzed using the qNMR method. According to these calculations, Valencia oranges had the highest concentration of ascorbic acid (>2 mm ). The described ¹H‐NMR method is highly reproducible, inexpensive, and highly robust in comparison to other analytical methods used to determine the hydrophilic profile of citrus juices.     

Occurrences of Prorocentrum minimum (Pavillard) in México

Prorocentrum minimum is a planktonic dinoflagellate known to produce red tides that can be harmful. To recognize localities and understand occurrences of Prorocentrum minimum blooms in Mexico, published data of plankton from 1942 to present, as well as unpublished data from the authors, were reviewed. Studies and reports covered marine and coastal waters of México during different periods. Presence of P. minimum were reported in the Pacific coast, Gulf of California, Gulf of México, and the Caribbean, but blooms have been only reported since 1990. Thirteen bloom events were recorded. Six occurred in shrimp ponds and seven near aquaculture regions or coastal areas where intensive agriculture is practiced. Most of the blooms can be associated with damage to the surrounding marine biota either in aquaculture ponds or open waters. Direct toxicity has not been fully evaluated, but data suggest that low oxygen may not easily explain all of the damage. Interestingly, for yet unknown reasons, cells belonging to the triangular morphotype have seldom been reported in México.     

Reproductive biology of the invasive species Pseudoxiphophorus bimaculatus and Poecilia sphenops in the Teuchitlán River,México

Reproductive biology of invasive species is not often studied relative to the invasion process, although it may provide an accurate indicator of the invasion stage. We evaluated the reproductive biology of the exotic fish species Pseudoxiphophorus bimaculatus and Poecilia sphenops in the Teuchitlán River, Jalisco, Mexico by fertility, size at first maturity, sex ratio, gonad maturity stage, gonadosomatic index, condition factor, size‐structure, and habitat. The reproductive variables were related to environmental characteristics using the non‐metric analysis of multidimensional scaling. A total of 1374 specimens of P. bimaculatus and 571 of P. sphenops were captured by seine netting and electrofishing. Maximum fertility of P. bimaculatus was 15.99 ± 2.27 embryonated eggs and embryos and, for P. sphenops, 31.26 ± 4.17. Females predominated among P. bimaculatus, while in P. sphenops the sex ratio was ~1:1. We found mature female and male of P. bimaculatus in degraded sites and juveniles in the springs. Poecilia sphenops reproduced along the river. The establishment of both invasive species in the Teuchitlán River is evidence that they share the reproductive habitat with native fish species, and tend to spread and colonize new areas.     

Interaction between lithification and resource availability in the microbialites of Río Mesquites,Cuatro Ciénegas,México

Lithified microbial structures (microbialites) have been present on Earth for billions of years. Lithification may impose unique constraints on microbes. For instance, when CaCO₃ forms, phosphate may be captured via coprecipitation and/or adsorption and potentially rendered unavailable for biological uptake. Therefore, the growth of microbes associated with CaCO₃ may be phosphorus‐limited. In this study, we compared the effects of resource addition on biogeochemical functions of microbial communities associated with microbialites and photoautotrophic microbial communities not associated with CaCO₃ deposition in Río Mesquites, Cuatro Ciénegas, México. We also manipulated rates of CaCO₃ deposition in microbialites to determine whether lithification reduces the bioavailability of phosphorus (P). We found that P additions significantly increased rates of gross primary production (F_2,13 = 103.9, P < 0.001), net primary production (F_2,13 = 129.6, P < 0.0001) and ecosystem respiration (F_2,13 = 6.44, P < 0.05) in the microbialites, while P addition had no effect on photoautotrophic production in the non‐CaCO₃‐associated microbial communities. Growth of the non‐CaCO₃‐associated phototrophs was only marginally stimulated when nitrogen and P were added simultaneously (F_1,36 = 3.98, P = 0.053). In the microbialites, resource additions led to some shifts in the abundance of Proteobacteria, Bacteroidetes and Cyanobacteria but mostly had little effect on bacterial community composition. Ca²⁺ uptake rates increased significantly with organic carbon additions (F_1,13 = 8.02, P < 0.05). Lowering of CaCO₃ deposition by decreasing calcium concentrations in the water led to increased microbial biomass accumulation rates in terms of both organic carbon (F_4,48 = 5.23, P < 0.01) and P (F_6,48 = 13.91, P < 0.001). These results provide strong evidence in support of a role of lithification in controlling P limitation of microbialite communities.     

First Report of Peronospora belbahrii on Sweet Basil in Baja California Sur,México

In Baja California Sur, Mexico, a foliar disease occurred on sweet basil which seriously affected its quality and yield. The most common symptoms were yellowing and necrosis on leaves, caused by a downy mycelium growth on the lower leaf surface. Symptomatic leaves from two sampling sites were collected for morphological studies and molecular analysis of pathogen DNA. Based on morphological characteristics (sporangiophore size of 240–530 × 7–11 μm, branches of 5–8 order and a sporangia size of 27–31 × 21–25 μm) and molecular analysis (the GenBank blast of the PCR assays showed unique rDNA sequence data with 99% similarity to P. belbahrii), the pathogen was identified as Peronospora belbahrii, the causal agent of basil downy mildew. This is the first report of P. belbahrii affecting sweet basil in Mexico.     

Changing light conditions in pine rockland habitats affect the intensity and outcome of ant–plant interactions

Extrafloral nectar (EFN) mediates food‐for‐protection mutualisms between plants and ants. Such mutualisms exist within a complex web of biotic interactions, and in a framework provided by the abiotic environment. Both biotic and abiotic factors, therefore, affect the outcome of ant–plant interactions. We conducted an experiment to determine the effects of ant activity, and light intensity, on herbivory rates, growth, and reproductive fitness in Senna mexicana var. chapmanii, a perennial legume native to pine rockland habitats of south Florida. Forty plants were divided among four treatments in a factorial experimental design with two independent variables: ant activity and light intensity. Plants were divided equally between sunny and shady habitats, and ants were excluded from half of the plants in each habitat type. The presence of ants significantly reduced herbivory rates in S. chapmanii. In shaded habitats, the presence of ants had no effect on plant reproductive fitness, however, in sunny habitats plants with ants produced significantly more seeds over the duration of the 1‐yr study. Ants represent an important biotic defense against herbivores in S. chapmanii; however, their effects on plant fitness are dependent on light conditions. Pine rockland habitats in south Florida have been widely destroyed or mismanaged. In fragments that remain, suppression of fire has led to increased canopy closure and shading of the understory. These changes will likely negatively impact plants that rely on ants for defense. We highlight the importance of conservation efforts to preserve the pine rocklands and the fire regimes on which they rely.     

Interacciones Planta‐Nodriza en Lophophora diffusa (Cactaceae) en un Desierto Subtropical de México1

One of the two species from the genus Lophophora is the false peyote Lophophora diffusa, an endemic cactus species of the xerophytic shrubland at Querétaro, México, considered threatened from illegal extraction due to its hallucinogenic and medicinal properties. We analyzed the spatial distribution of L. diffusa and its association with the locally dominant shrub species with the system SADIE (Spatial Analysis by Distance IndicEs). We also studied the principal microclimatic factors (light, temperature, and humidity) beneath the canopy of the possible nurse plant species. The use of SADIE is a new approach to study the mechanisms of spatial distribution. Lophophora diffusa and the shrub species presented an aggregated distribution with patches and gaps, as indicated by the values of I_a= 4.179 for L. diffusa and I_a= 1.660 for the vegetation. Lophophora diffusa was positively associated with the arboreal vegetation, particularly with Larrea tridentata and Acacia sororia, but was negatively associated with Celtis pallida and Myrtillocactus geometrizans. Microclimate evaluation indicated that C. pallida canopy significantly reduced radiation and temperature compared to the other species (L. tridentata, A.sororia y P. laevigata). We had expected L. diffusa to exhibit a positive spatial association with C. pallida; however, the reduction in light availability apparently limited seedling establishment of L. diffusa.     

Reproduction and Activity of the Snail-Eating Snake,Dipsas albifrons (Colubridae), in the Southern Atlantic Forest in Brazil

A study in a remnant of cerrado vegetation in São Paulo State, Brazil, was carried out to investigate the possible role of leaf-cutting ants in the creation of nutrient-rich patches and their consequent influence on plant establishment and growth. The results showed that leaf-cutting ants had neither detectable effect on local nutrient enrichment nor on plant community structure. It is suggested that leaf-cutting ants may affect early successional stages of the vegetation, when colonies are more abundant and disperse into the habitat. Foi feito um estudo em um remanescente de vegetação de cerrado no Estado de São Paulo, com o objetivo de testar o papel das sa£vas na criação de manchas ricas em nutrientes e sua conseqüente influência no estabelecimento e crescimento das plantas. Os resultados mostraram que as saúvas não tiveram nenhum efeito detectável no enriquecimento local de nutrientes e nem na estrutura das comunidades vegetais. Sugere-se que as saúvas possam afetar os estádios iniciais da sucessão vegetal, quando as colônias são mais abundantes e dispersam-se mais no habitat.     

Geography of the circadian gene clock and photoperiodic response in western North American populations of the three‐spined stickleback Gasterosteus aculeatus

Controlled laboratory experiments were used to show that Oregon and Alaskan three‐spined stickleback Gasterosteus aculeatus, collected from locations differing by 18° of latitude, exhibited no significant variation in length of the polyglutamine domain of the clock protein or in photoperiodic response within or between latitudes despite the fact that male and female G. aculeatus are photoperiodic at both latitudes. Hence, caution is urged when interpreting variation in the polyglutamine repeat (PolyQ) domain of the gene clock in the context of seasonal activities or in relationship to photoperiodism along geographical gradients.     

Positive effects of native shrubs on three specially protected cacti species in Durango,México

The spatial association between the specially protected cacti Coryphanta durangensis, Echinocereus longisetus and Peniocereus greggii and potential nurse plants was evaluated, as was their relative position to the sun under the crown of the latter in the southern Chihuahuan Desert. The soil temperature under potential nurse plants was lower than under direct sunlight. There was more nitrogen and organic matter in the soil under Prosopis laevigata trees than in soil under direct sunlight. There were 68 plants of C. durangensis, 59 plants of E. longisetus and 157 of P. greggii. Only one individual of C. durangensis and one of E. longisetus grew outside the shade of the crown of other plants. Echinocereus longisetus was not associated with any particular species, but grew more often than expected by chance in the northern segment of the crown (i.e. the area most shaded in the afternoon). Coryphanta durangensis and P. greggii grew more often under P. laevigata than expected by chance. The effect of other plants, and P. laevigata in particular, on the facilitation of growth of protected cacti species should be considered in management plans of the Chihuahuan Desert, where mesquite (P. laevigata) is often harvested for charcoal production.     

Intraspecific Variation in the Amino Acid Content of Floral Nectar

In order to evaluate the constancy of amino acid composition and concentration, several randomly collected samples of genuine floral nectar from different flowers of several plant species were analysed. Although there seems to exist a rough pattern of species-specific nectar amino acid composition, amino acid concentration varied strongly from sample to sample. Apart from the lack of constancy in concentration of floral amino acids, our samples do not show amino acid concentration values as assigned typical for the pertinent pollination mode by other workers.     

Extranuptial nectaries in flowers: ants increase the reproductive success of the ant‐plant Miconia tococa (Melastomataceae)

• Although the production of extranuptial nectar is a common strategy of indirect defence against herbivores among tropical plants, the presence of extranuptial nectaries in reproductive structures is rare, especially in ant‐plants. This is because the presence of ants in reproductive organs can generate conflicts between the partners, as ants can inhibit the activity of pollinators or even castrate their host plants. Here we evaluate the hypothesis that the ant‐plant Miconia tococa produces nectar in its petals which attracts ants and affects fruit set.
• Floral buds were analysed using anatomical and histochemical techniques. The frequency and behaviour of floral visitors were recorded in field observations. Finally, an ant exclusion experiment was conducted to evaluate the effect of ant presence on fruit production.
• The petals of M. tococa have a secretory epidermis that produces sugary compounds. Nectar production occurred during the floral bud stage and attracted 17 species of non‐obligate ants (i.e. have a facultative association with ant‐plants). Ants foraged only on floral buds, and thus did not affect the activity of pollinators in the neighbouring open flowers. The presence of ants in the inflorescences increased fruit production by 15%.
• To our knowledge, the production of extranuptial nectar in the reproductive structures of a myrmecophyte is very rare, with few records in the literature. Although studies show conflicts between the partners in the ant–plant interaction, ants that forage on M. tococa floral buds protect the plant against floral herbivores without affecting bee pollination.