Energetic mechanisms for coping with changes in resource availability.
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ABSTRACT:
SUBMITTER: Auer SK
PROVIDER: S-EPMC7728673 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:In many organisms, food availability is a proximate cue that synchronizes seasonal development of the reproductive system with optimal environmental conditions. Growth of the gonads and secondary sexual characteristics is orchestrated by the hypothalamic-pituitary-gonadal (HPG) axis. However, our understanding of the physiological mechanisms by which food availability modulates activity of the HPG axis is limited.It is thought that many factors, including energetic status, modulate seasonal reproductive activation. We tested the hypothesis that food availability modulates the activity of the HPG axis in a songbird. Specifically, we food-restricted captive adult male Abert's Towhees Melozone aberti for 2 or 4 weeks during photoinduced reproductive development. A third group (control) received ad libitum food throughout. We measured multiple aspects of the reproductive system including endocrine activity of all three levels of the HPG axis [i.e. hypothalamic gonadotropin-releasing hormone-I (GnRH-I), plasma luteinizing hormone (LH) and testosterone (T)], and gonad morphology. Furthermore, because gonadotropin-inhibitory hormone (GnIH) and neuropeptide Y (NPY; a potent orexigenic peptide) potentially integrate information on food availability into seasonal reproductive development, we also measured the brain levels of these peptides.At the hypothalamic level, we detected no effect of food restriction on immunoreactive (ir) GnRH-I, but the duration of food restriction was inversely related to the size of ir-GnIH perikarya. Furthermore, the number of ir-NPY cells was higher in food-restricted than control birds. Food restriction did not influence photoinduced testicular growth, but decreased plasma LH and T, and width of the cloacal protuberance, an androgen-sensitive secondary sexual characteristic. Returning birds to ad libitum food availability had no effect on plasma LH or T, but caused the cloacal protuberance to rapidly increase in size to that of ad libitum-fed birds.Our results support the tenet that food availability modulates photoinduced reproductive activation. However, they also suggest that this modulation is complex and depends upon the level of the HPG axis considered. At the hypothalamic level, our results are consistent with a role for the GnIH and NPY systems in integrating information on energetic status. There also appears to be a role for endocrine function at the anterior pituitary gland and testicular levels in modulating reproductive development in the light of energetic status and independently of testicular growth.
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Project description:OBJECTIVES:Cardiovascular disease (CVD) remains the leading cause of death in the USA. Reducing the population-level burden of CVD disease will require a better understanding and support of cardiovascular health (CVH) in individuals and entire communities. The objectives for this study were to examine associations between community-level healthcare resources (HCrRes) and CVH in individuals and entire communities. SETTING:This study consisted of a retrospective, cross-sectional study design, using multivariable epidemiological analyses. PARTICIPANTS:All participants in the 2011 Behavioral Risk Factor Surveillance System (BRFSS) survey were examined for eligibility. CVH, defined using the American Heart Association CVH Index (CVHI), was determined using self-reported responses to 2011 BRFSS questions. Data for determining HCrRes were obtained from the Area Health Resource File. Regression analysis was performed to examine associations between healthcare resources and CVHI in communities (linear regression) and individuals (Poisson regression). RESULTS:Mean CVHI was 3.3±0.005?and was poorer in the Southeast and Appalachian regions of the USA. Supply of primary care physicians and physician assistants were positively associated with individual and community-level CVHI, while CVD specialist supply was negatively associated with CVHI. Individuals benefiting most from increased supply of primary care providers were: middle aged; female; had non-Hispanic other race/ethnicity; those with household income <$25 000/year; and those in non-urban communities with insurance coverage. CONCLUSIONS:Our results support the importance of primary care provider supply for both individual and community CVHI, though not all sociodemographic groups benefited equally from additional primary care providers. Further research should investigate policies and factors that can effectively increase primary care provider supply and influence where they practice.
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Project description:Numerous experiments, mostly performed in particular environments, have shown positive diversity-productivity relationships. Although the complementary use of resources is discussed as an important mechanism explaining diversity effects, less is known about how resource availability controls the strength of diversity effects and how this response depends on the functional composition of plant communities. We studied aboveground biomass production in experimental monocultures, two- and four-species mixtures assembled from two independent pools of four perennial grassland species, each representing two functional groups (grasses, forbs) and two growth statures (small, tall), and exposed to different combinations of light and nutrient availability. On average, shade led to a decrease in aboveground biomass production of 24% while fertilization increased biomass production by 36%. Mixtures were on average more productive than expected from their monocultures (relative yield total, RYT>1) and showed positive net diversity effects (NE: +34% biomass increase; mixture minus mean monoculture biomass). Both trait-independent complementarity effects (TICE: +21%) and dominance effects (DE: +12%) positively contributed to net diversity effects, while trait-dependent complementarity effects were minor (TDCE: +1%). Shading did not alter diversity effects and overyielding. Fertilization decreased RYT and the proportion of biomass gain through TICE and TDCE, while DE increased. Diversity effects did not increase with species richness and were independent of functional group or growth stature composition. Trait-based analyses showed that the dominance of species with root and leaf traits related to resource conservation increased TICE. Traits indicating the tolerance of shade showed positive relationships with TDCE. Large DE were associated with the dominance of species with tall growth and low diversity in leaf nitrogen concentrations. Our field experiment shows that positive diversity effects are possible in grass-forb mixtures irrespective of differences in light availability, but that the chance for the complementary use of resources increases when nutrients are not available at excess.
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