Asymmetric habitat isolation and sexual isolation predicted by the cost of migration and hybridization generate novel signatures of reinforcing selection

Reinforcement is an evolutionary process whereby increased prezygotic reproductive isolation evolves in response to the cost of hybridization. Despite theory predicting that multiple prezygotic barriers can evolve via reinforcement, most empirical studies examine a single barrier. We test novel predictions for the reinforcement of both habitat isolation and sexual isolation between ecologically divergent lineages under asymmetric migration: the lineage that emigrates more should evolve stronger habitat isolation due to the lower fitness of immigrants in the alternative habitat, while the lineage that receives more immigrants should exhibit stronger sexual isolation due to the lower fitness of hybrids. We found both signatures of reinforcement in two sympatric sister species of gall wasps that are host specific to the southern live oaks, Quercus virginiana and Q. geminata, respectively. Specifically, we observed stronger habitat isolation in the species with higher emigration rates, Belonocnema treatae, and stronger sexual isolation in the species facing more immigrants, B. fossoria. In contrast, comparisons of both species to a third, allopatric, species showed that B. kinseyi exhibited both lower habitat isolation and sexual isolation than the sympatric species, consistent with the classic predictions of reinforcement. Our study provides a rare examination of the interplay of ecology and geography in the evolution of multiple reproductive barriers to gene flow. Given that asymmetric migration between ecologically divergent lineages increasingly appears to be the rule rather than the exception, concomitant asymmetries in the strength of habitat and sexual isolation could be more widespread than currently understood.

Interspecific Variation between the American Quercus virginiana and Mediterranean Quercus Species in Terms of Seed Nutritional Composition, Phytochemical Content, and Antioxidant Activity

This study aimed to evaluate a complete nutritional composition in the seeds Quercus virginiana to compare this nutritional composition with three Mediterranean Quercus species. We analyzed the seed morphometry, proximate composition, phytochemicals, and antioxidant capacity. The seed of Q. virginiana presented the smaller seed size and weight, while Q. suber presented the highest values. Moreover, Q. virginiana seeds showed the highest amounts of sugar and total lipids, digestibility, energy, palmitic acid, and stearic acid. On the other hand, Q. virginiana seeds showed the lowest values of linoleic acid. Moreover, Q. coccifera seeds presented the highest total phenolics and flavonoids contents and antioxidant activity. The clustering analysis revealed a significant similarity in seed morphometry and nutritional composition between the Mediterranean Q. ilex and Q. suber, grouping with the American Q. virginiana, but to a considerable distance; by contrast, the Mediterranean Q. coccifera was the most distant in the clustering analysis. The content of phenolics and flavonoids and digestibility value were the variables that contributed to the separation to a greater extent in the clustering of the four species. The nutritional and biological activity assessment of plant seed may be considered as an essential mission to find new sustainable sources and novel chemical agents. In this sense, Quercus seeds may be an alternative and a competitive food source for the agri-food industry.

Caracterización del arbolado urbano de la ciudad de Montemorelos, Nuevo León

En el presente estudio se hizo una caracterización de la estructura y diversidad del arbolado urbano de la ciudad de Montemorelos, Nuevo León, al noreste de México. Se censaron los árboles de todos los camellones y parques urbanos y se les midió la altura total (h), el diámetro normal (d1.30 m) y el diámetro de copa (k). Se calculó su abundancia (Ar), dominancia (Dr) y frecuencia (Fr), así como el Índice de Valor de Importancia (IVI) de las especies arbóreas presentes; se evaluó su diversidad con los índices de Margalef (DMg), Shannon (H’), Diversidad Real (1D) y el área verde por habitante. Se registraron un total 918 árboles de 13 especies, pertenecientes a 11 géneros, de las cuales siete son introducidas. El área verde por habitante fue de 0.87. Fraxinus americana fue el taxón con mayor IVI (53.82 %.), seguido de Quercus virginiana (21.37 %). El arbolado urbano reúne una mayor proporción de organismos de porte alto (entre 4 y 6 m), y un diámetro normal de tamaño medio (entre 20 y 30 cm); asimismo la comunidad registró un índice de Margalef (DMg) de 1.9, una diversidad de Shannon (H’) de 1.17 y un Índice de Diversidad Real de 3.22. El área verde urbana por habitante es inferior a lo recomendado en estudios previos, y presenta una baja diversidad, con respecto a otras de este tipo en distintas localidades.

Arthropod Community Associated With the Asexual Generation of Bassettia pallida (Hymenoptera: Cynipidae)

Cynipid gall wasps play an important role in structuring oak arthropod communities. Wasps in the Cynipini tribe typically lay their eggs in oaks (Quercus L.), and induce the formation of a ‘gall’, which is a tumor-like growth of plant material that surrounds the developing wasp. As the wasp develops, the cynipid and its gall are attacked by a diverse community of natural enemies, including parasitoids, hyperparasitoids, and inquilines. Determining what structures these species-rich natural enemy communities across cynipid gall wasp species is a major question in gall wasp biology. Additionally, gall wasps are ecosystem engineers, as the abandoned gall is used by other invertebrates. The gall-associated insect communities residing on live oaks (Quercus geminata Small and Quercus virginiana Mill.) are emerging as a model system for answering ecological and evolutionary questions ranging from community ecology to the evolution of new species. Documenting the arthropods associated with cynipids in this system will expand our understanding of the mechanisms influencing eco-evolutionary processes, record underexplored axes of biodiversity, and facilitate future work. Here, we present the community of natural enemies and other associates of the asexual generation of the crypt gall wasp, Bassettia pallida Ashmead. We compare the composition of this community to communities recently documented from two other cynipid gall wasps specializing on live oaks along the U.S. Gulf coast, Disholcaspis quercusvirens Ashmead and Belonocnema treatae Mayr. B. pallida and their galls support a diverse arthropod community, including over 25 parasitoids, inquilines, and other associated arthropods spanning 5 orders and 16 families.

Two Cycad Species Affect the Carbon, Nitrogen, and Phosphorus Content of Soils

The influences of Cycas micronesica and Zamia integrifolia plants on soil chemistry were determined in Tinian and Florida in order to more fully understand how cycad plants affect the environments in which they grow. The introduction of C. micronesica plants into a karst habitat generated decreases in soil phosphorus after five years and increases in soil nitrogen after six years. The carbon:nitrogen:phosphorus stoichiometry beneath the cycad plants significantly diverged from those of the adjacent native forests with Pisonia grandis, Psychotria mariana, Aglaia mariannensis, Cynometra ramiflora, and Ficus sp. cover after five years. Mineralization traits were determined beneath nine-year-old C. micronesica plants and revealed the plants greatly increased net nitrification and decreased net ammonification when compared to the native forest soils with Bursera simaruba, Pinus elliottii, and Quercus virginiana cover. These flux changes increased the total available nitrogen and percent available nitrogen in the soils beneath the cycad plants. The substrates of two soil series exhibited increased carbon and nitrogen concentrations beneath Z. integrifolia plants when compared with soils away from the cycad plants. No other mineral or metal was influenced by proximity to the Z. integrifolia plants. These gymnosperms exhibit distinct interactions with their subtending soils, and some of these traits improve ecosystems by increasing recalcitrant carbon and nitrogen and increasing spatial heterogeneity of soil chemistry.

Oak trees are elemental carbon sinks in urban ecosystems: patterns and drivers

<p>Cities represent a significant source of atmospheric elemental carbon (EC), a minor constituent of particulate matter (PM) but a major climate-forcing agent and air pollutant. Urban trees scavenge PM and regulate material fluxes to the ground. As such, urban trees represent potentially important sinks—not only for PM but also for EC—in urban landscapes. Here we assess the magnitude and spatiotemporal drivers of EC removal by trees in urban atmospheres. We quantified foliar EC accumulation by, as well as throughfall EC flux under, the canopy of two oak species (<em>Quercus stellata</em>: post oak; <em>Quercus virginiana</em>: live oak), which are widespread across the southern United States. Sampling was conducted from March 2017 to March 2018 across the City of Denton, a city at the northern edge of the Dallas-Forth Worth metropolitan area in Texas. Over the year-long study period, we found that post oak tree canopies accumulated two times more EC (0.53 mg EC m<sup>-2</sup> leaf d<sup>-1</sup>) than live oak trees (0.22 mg EC m<sup>-2</sup> leaf d<sup>-1</sup>), with 95% of EC depositing to leaf surfaces as opposed to leaf waxes. Throughfall EC fluxes were also greater under post oak (0.15 mg EC m<sup>-2</sup> d<sup>-1</sup>) compared to live oak (0.12 mg EC m<sup>-2</sup> d<sup>-1</sup>) canopies, but these differences between post oak and live oak were far less pronounced than for foliar EC accumulation. These results suggest that considerable amounts of dry-deposited EC are retained in post oak canopies, reducing species differences in throughfall EC fluxes. Our findings also revealed strong, albeit, contrasting seasonal patterns for foliar EC accumulation and throughfall EC fluxes. For both tree species, EC accumulation on canopy surfaces increased, whereas throughfall EC fluxes decreased from spring to fall, providing additional evidence that EC retention on canopy surfaces results in decreased EC fluxes to the ground. In summary, our findings show that urban oak trees scavenge considerable amounts of EC from the atmosphere and that the magnitude of accumulation and delivery to soil vary by species and season. This research highlights the potential for urban trees and forests to contribute to climate and air quality mitigation.</p>

Human-mediated disturbance in multitrophic interactions results in outbreak levels of North America's most venomous caterpillar

Anthropogenic environmental change is predicted to disrupt multitrophic interactions, which may have drastic consequences for population-level processes. Here, we investigate how a large-scale human-mediated disturbance affects the abundance of North America's most venomous caterpillar species, Megalopyge opercularis . Specifically, we used a natural experiment where netting was deployed to cover the entire canopies of a subset of mature southern live oak trees ( Quercus virginiana ) to exclude urban pest birds (grackles and pigeons), throughout an 8.1 km 2 area encompassing a medical centre in Houston, Texas. We used this experimental exclusion to test the following hypothesis: release from avian predators increases caterpillar abundance to outbreak levels, which increases the risk to human health. Results from a multi-year survey show that caterpillar abundance increased, on average, more than 7300% on netted versus non-netted trees. Thus, increases in caterpillar abundance due to anthropogenic enemy release increase human exposure to this venomous pest, and should be considered a health threat in the area. This study emphasizes the unforeseen consequences of ecological disturbance for species interactions and highlights the importance of considering ecology in urban planning.