Relative effectiveness of insects versus hummingbirds as pollinators of Rubiaceae plants across elevation in Dominica, Caribbean.

Most angiosperms rely on animal pollination for reproduction, but the dependence on specific pollinator groups varies greatly between species and localities. Notably, such dependence may be influenced by both floral traits and environmental conditions. Despite its importance, their joint contribution has rarely been studied at the assemblage level. At two elevations on the Caribbean island of Dominica, we measured the floral traits and the relative contributions of insects versus hummingbirds as pollinators of plants in the Rubiaceae family. Pollinator importance was measured as visitation rate (VR) and single visit pollen deposition (SVD), which were combined to assess overall pollinator effectiveness (PE). In the wet and cool Dominican highland, we found that hummingbirds were relatively more frequent and effective pollinators than insects, whereas insects and hummingbirds were equally frequent and effective pollinators at the warmer and less rainy midelevation. Furthermore, floral traits correlated independently of environment with the relative importance of pollinators, hummingbirds being more important in plant species having flowers with long and wide corollas producing higher volumes of dilute nectar. Our findings show that both environmental conditions and floral traits influence whether insects or hummingbirds are the most important pollinators of plants in the Rubiaceae family, highlighting the complexity of plant-pollinator systems.

Involvement of the anterodorsal thalami nuclei on the hypophysoadrenal response to chronic stress in rats.

Anterodorsal thalami nuclei (ADTN) exert an inhibitory influence on the hypophysoadrenal system (HAS) under basal and acute stress conditions; however, after chronic stress, the effect is different. The response to chronic immobilization stress (IMO) (forced immobilization for 15 min/day for 12 days) and variable chronic stress (V) (24-day exposure to different stressors per day) of plasma ACTH and corticosterone (C) in rats with anterodorsal thalami nuclei lesions was studied. In sham-lesioned rats, chronic immobilization stress and variable chronic stress induced a significant increase in plasma ACTH and C and a reduction of adrenal C content. After exposure of lesioned rats to chronic immobilization stress, there was a decrease of plasma ACTH compared to that in unstressed lesioned rats. In contrast, there was significant increase in ACTH levels after variable chronic stress, this increase being smaller than the variable increase elicited in sham-lesioned rats. In all stressed lesioned animals, plasma C remained unchanged. However, adrenal C content decreased significantly compared to that in unstressed lesioned rats. These findings demonstrate that anterodorsal thalami nuclei lesions attenuated the hypophysoadrenal system response to chronic stress. These data are in contrast to those obtained in previous studies under basal and acute stress conditions. The reason for this discrepancy is at present unknown, and its elucidation will require further studies.