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Populations of the same species vary in their secondary metabolite content. This variation has been attributed to biotic and abiotic environmental conditions as well as to historical factors. Some studies have focused on the geographic variation of chemical diversity in plant populations, but whether this structure conforms to a central-marginal model or a mosaic pattern remains unclear. Furthermore, assessing the chemical diversity of invasive plants in their native distribution facilitates the understanding of their relationships with natural enemies. We examined the geographic variation of chemical diversity in Mexican populations of the bittervine weed Mikania micrantha and its relationship to herbivore damage. The foliar volatile terpenoid blend was analyzed in 165 individuals of 14 populations in the Pacific and Gulf of Mexico tropical watersheds. A cluster analysis grouped individuals with similar terpenoid blends into 56 compositional types. Chemical diversity was measured using the number of compounds and their concentration within the blends for individuals, and the number and frequency of compositional types for populations. A stepwise multiple regression analysis performed with geographic, climatic, and chemical diversity variables explained herbivore damage. However, population-level chemical diversity was the only variable found to be significant (β = -0.79, P = 0.042) in the model (R(2) = 0.89). A Mantel test using Euclidean distances did not indicate any separation by geographic origin; however, four barriers were identified using Monmonier's algorithm. We conclude that variation in population-level chemical diversity follows a mosaic pattern in which geographic factors (i.e., natural barriers) have some effect and that variation is also associated with the local intensity of herbivore attack.

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Phytochemical diversity (PD) can be considered as a defensive trait; it can operate through single plant secondary metabolites or usually as complex mixtures of them. We tested the more diversity-better defense hypothesis correlating the leaf plant secondary metabolites (PSMs) with the incidence of plant enemies on Hass avocado trees. We expected a negative correlation between the occurrence of plant enemies and PD metrics. Also, as intraspecific PSMs polymorphisms in plant populations are common, we studied the incidence of plant enemies on Hass avocado trees representing chemical variants (chemotypes). We expected a differential incidence of plant enemies among trees grouped by their mono and sesquiterpene + phenylpropanoid chemotypes. We analyzed foliar hexane extracts from 236 trees in 17 orchards by gas chromatography and for the incidence of red mite, thrips, whitefly, avocado branch borer, fruit rot, scab, and peduncle collar blight. The predicted negative correlation between the plant enemies’ incidence and the phytochemical metrics did not occur. To determine the relationship between enemy incidence and chemotypes we grouped the trees by cluster analysis using a matrix of PSMs in each tree. Most trees were grouped under four out of 23 chemotypes. Branch borers attacked trees of low-frequency chemotypes more frequently than trees with common chemotypes. The incidence of five plant enemies was different among the predominant chemotypes. The hypothesis of more diversity-better defense was not supported by the correlations between the phytochemical diversity and the incidence of pests and pathogens in Hass avocado orchards. Based on our results, we hypothesize that phytochemical diversity function as a defensive trait relies more on differentiation among individuals in a population than on the sole increase of chemical diversity. Also, the differential incidence of pests and pathogens on trees classified by their foliar chemotypes implies that these susceptibility or resistance markers represent potential useful tools for Hass avocado orchard pest management.

This study evaluated the response of bat communities, from a taxonomic and functional perspective, to variation in the vegetation and landscape attributes produced by anthropogenic activities. We characterized the following: (1) the community of phyllostomid and mormoopid bats associated with the initial successional stages of a tropical dry forest, (2) the response of these communities to the variation in the attributes of the vegetation and the landscape, and (3) how the seasonality modulates such response. This allowed us to identify potential mechanisms underlying the response of bat communities to human disturbance. Our results showed that the species negatively affected by the anthropoghenic disturbance are those with greater body mass, larger nose-leaves, or a lower wing aspect ratio and relative wing loading, which perform low-speed flights and have high maneuverability and, potentially, a high directionality in their emissions. We also detected a greater sensitivity of bats to changes in the landscape attributes regarding the riparian than the dry forest, and that the effect of anthropic transformation on bats was intensified during the dry season. Then, the continued loss of the original vegetation can lead to a loss of certain groups of bat species in neotropical landscapes, reducing the resilience of the system.

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Fresh cheese is one of the most consumed products of the dairy industry in México. This study aimed to determine the frequency, antimicrobial resistance, and genetic characteristics of extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli in fresh cheese. From fresh cheese samples, E. coli was isolated and the production of ESBL, the antibiotic resistance patterns, the frequency of resistance genes, and the genetic relationship were analyzed. Sixty ESBL-producing E. coli belonging to phylogenetic groups A, C, and B1 were isolated and were highly resistant to the beta-lactam antibiotics, tetracycline, streptomycin, and trimethoprim-sulfamethoxazole. The bla CTX-M gene was detected in all isolates, either alone or in combination with bla TEM and bla SHV . Similarly, a high frequency of resistance genes tetA, strA, and strB and class 1 integrons were found. According to their ERIC-PCR fingerprints, the E. coli were clustered into eight groups. In conclusion, a high frequency of ESBL-producing, genetically diverse, and multidrug-resistant E. coli was found in fresh cheese. The presence of ESBL-producing E. coli in fresh cheese constitutes a public health issue because these bacteria may be pathogenic or contribute to the dissemination of resistance genes to other pathogenic and non-pathogenic bacteria.

The quantification of plant secondary metabolites at levels higher than the population (i.e. community and ecosystem) requires the implementation of efficient, low-cost, and small-scale assays. We propose a modified protocol based on the Folin-Ciocalteu colorimetric assay that integrates the simultaneous quantitative determination of total phenols and total tannins from 40 µL of methanolic extract, and a modified aluminum chloride assay to quantify total flavonoids from 20 µL of methanolic extract. These miniaturized microplate colorimetric assays were tested and adjusted to work with as little as 50 mg of foliar tissue and to encompass the variation of secondary metabolite concentrations present in trees of 77 species, 58 genera, and 27 families from conserved and secondary tropical dry forest. At present, these new protocols are of great relevance to study ecological processes in highly diverse and strongly threatened ecosystems.