Ecological mechanisms explaining interactions within plant-hummingbird networks: morphological matching increases towards lower latitudes

Interactions between species are influenced by different ecological mechanisms, such as morphological matching, phenological overlap and species abundances. How these mechanisms explain interaction frequencies across environmental gradients remains poorly understood. Consequently, we also know little about the mechanisms that drive the geographical patterns in network structure, such as complementary specialization and modularity. Here, we use data on morphologies, phenologies and abundances to explain interaction frequencies between hummingbirds and plants at a large geographical scale. For 24 quantitative networks sampled throughout the Americas, we found that the tendency of species to interact with morphologically matching partners contributed to specialized and modular network structures. Morphological matching best explained interaction frequencies in networks found closer to the equator and in areas with low-temperature seasonality. When comparing the three ecological mechanisms within networks, we found that both morphological matching and phenological overlap generally outperformed abundances in the explanation of interaction frequencies. Together, these findings provide insights into the ecological mechanisms that underlie geographical patterns in resource specialization. Notably, our results highlight morphological constraints on interactions as a potential explanation for increasing resource specialization towards lower latitudes.

Age-related changes of the multidrug resistance P-glycoprotein function in normal human peripheral blood T lymphocytes

The multidrug resistance P-glycoprotein is a transmembrane efflux pump expressed by lymphocytes and is involved in their cytolytic activity. In the present study, we investigated the age-related changes of P-glycoprotein function in normal peripheral blood lymphocytes. Blood samples from 90 normal volunteers (age range, 0 to 86 years) were analyzed. P-glycoprotein function was assessed by the flow cytometric rhodamine 123 assay. P-glycoprotein function was highest in cord blood and progressively declined with age in peripheral blood T CD4+ and CD8+ cells. In contrast, P-glycoprotein function did not vary with age in CD19+ B or CD16+CD56+ natural killer cells. These data suggest that the decline in P-glycoprotein function in T CD4+ and CD8+ lymphocytes as a function of age may contribute to the decrease in T cell cytolytic activity with aging.

Idiopathic juxtafoveolar retinal telangiectasis: clinical pattern in 19 cases

BACKGROUND

Idiopathic juxtafoveolar telangiectasis (IJT) is a rare retinal vasculopathy of adulthood that may cause central loss of visual acuity. The purpose of this paper is to evaluate the type and distribution of fundus changes in patients with this disorder.

METHODS

Medical records of 19 patients with IJT using the Gass & Blodi classification were studied. Eight patients in group 1A (42%) and 11 in group 2A (58%) were analyzed. By projecting color photographs we divided the macula into four quadrants and studied the fundus changes in each one.

RESULTS

All patients in group 1A presented unilateral disease with easily seen telangiectasis, lipid deposits and cystic macular edema. The mean age of this group was 55.8 years. Five (63%) patients were male and 3 (37%) were female. All patients in group 2A, 2 males (18%) and 9 females (82%), had bilateral disease evidenced by fluorescein angiography. The mean age of this group was 54.5 years. Fundoscopic findings included: intraretinal pigment plaques, grayish coloring of the macular retina, superficial crystalline deposits, right-angle venules, subretinal and intraretinal neovascularization.

CONCLUSIONS

All patients in this survey were adults. In group 1A, men were affected 2 times more often than women, and the main affected macular quadrant was the inferior temporal, followed by the inferior nasal. In group 2A, women were affected 4 times more often than men and all eyes had inferior and superior temporal macular quadrant involvement.