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.

Influence of anterodorsal thalamic nuclei on the hypophyseal-adrenal axis and cardiac beta receptors in rats submitted to variable chronic stress.

The limbic structures play an important role in the control of the neuroendocrine and sympathical adrenal function in basal and stress conditions. This work was undertaken to evaluate plasma ACTH, adrenocortical activity, cardiac adrenoceptors density and affinity response to variable chronic stress (VCS) in anterodorsal thalamic nuclei (ADTN) lesioned rats. Thirty days after lesion, shamlesioned stressed animals increased plasma ACTH and corticosterone as compared to sham-lesioned unstressed animals (p < 0.05); lesioned rats increased ACTH levels after VCS (p < 0.05) as compared to unstressed-lesioned rats. Whereas in sham-lesion plasma corticosterone (C) increased after stress, in lesioned animals(C) remained unchanged as compared to unstressed-lesioned animals. In the stressed groups, adrenal C contents were below those found in unstressed rats. beta-receptors affinity, in all the experimental groups, was similar, but VCS sham-lesioned animals underwent a significant increase in cardiac D-adrenergic receptors density when compared with basal and lesioned groups (P < 0.001). Our findings would demonstrate that the increment in cardiac beta adrenoceptors density appears as a consequence of the increase in ACTH, plasma corticosterone and sympathetic response provoked by chronic stress situations. ADTN lesion attenuated this hipophisoadrenal system response to chronic stress as well as the above mentioned cardiac beta adrenoceptors density increment.

Influence of anterodorsal thalamic nuclei on the hypophyseal-adrenal axis and cardiac beta receptors in rats submitted to variable chronic stress.

The limbic structures play an important role in the control of the neuroendocrine and sympathical adrenal function in basal and stress conditions. This work was undertaken to evaluate plasma ACTH, adrenocortical activity, cardiac adrenoceptors density and affinity response to variable chronic stress (VCS) in anterodorsal thalamic nuclei (ADTN) lesioned rats. Thirty days after lesion, shamlesioned stressed animals increased plasma ACTH and corticosterone as compared to sham-lesioned unstressed animals (p < 0.05); lesioned rats increased ACTH levels after VCS (p < 0.05) as compared to unstressed-lesioned rats. Whereas in sham-lesion plasma corticosterone (C) increased after stress, in lesioned animals(C) remained unchanged as compared to unstressed-lesioned animals. In the stressed groups, adrenal C contents were below those found in unstressed rats. beta-receptors affinity, in all the experimental groups, was similar, but VCS sham-lesioned animals underwent a significant increase in cardiac D-adrenergic receptors density when compared with basal and lesioned groups (P < 0.001). Our findings would demonstrate that the increment in cardiac beta adrenoceptors density appears as a consequence of the increase in ACTH, plasma corticosterone and sympathetic response provoked by chronic stress situations. ADTN lesion attenuated this hipophisoadrenal system response to chronic stress as well as the above mentioned cardiac beta adrenoceptors density increment.

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.