Acylated and des acyl ghrelin in human portal and systemic circulations

Octanoylation of the gastric peptide ghrelin produces an active isoform that regulates appetite and other metabolic functions. Acylated ghrelin is present in the gastrointestinal tract suggesting that octanoylation may occur in these tissues and thereby affect the acylated ghrelin in the systemic circulation. In this study blood samples were collected simultaneously from portal, arterial, peripheral venous and central venous compartments from patients undergoing laparotomy. ELISA and high sensitivity Bioplex was used to measure the concentration of acylated and des acyl ghrelin. We found median (95% confidence interval (CI)) plasma acylated ghrelin (pg/ml) was 35.8 (30.0–59.6) in the portal compartment compared to 51.5 (37.6–74.8; P < 0.05, n = 11) in the arterial, 39.3 (33.3–56.3) in the portal compartment compared to 55.0 (48.5–77.0; P < 0.001, n = 12) in the peripheral venous and 36.0 (33.1–57.4) in the portal compartment compared to 48.9 (43.3–65.6; P < 0.01, n = 15) in the central venous compartment. Median (95% CI) plasma des acyl ghrelin levels (pg/ml) was 173 (125–220) in the portal compartment compared to 136 (99.3–125; P < 0.001, n = 14)in the arterial, 186 (136–233) in the portal compartment compared to 149 (111–190; P < 0.01, n = 15) in the peripheral venous and 171 (140–208) in the portal compartment compared to 152 (119–175; P < 0.01, n = 15) the central venous compartment. We conclude that plasma acylated ghrelin concentration was significantly lower in portal compared with the systemic compartments whilst plasma des acyl ghrelin was significantly higher in portal compared with systemic compartments. These findings suggest that the liver could be involved in the regulation of circulating ghrelin.     

Ecological cues, gestation length, and birth timing in African buffalo (Syncerus caffer)

We examined annual variation in the timing of conception andparturition in the African buffalo (Syncerus caffer) and thesynchrony of birth timing with resource cues, using 8 yearsof monthly birth, rainfall, and vegetation data, measured asNormalized Difference Vegetation Index (NDVI). Monthly birthshad the strongest significant correlations with NDVI and rainfalllevels 12 and 13 months in the past, respectively. In addition,the synchrony of current year births corresponds most stronglyto the synchrony of the previous year's NDVI distribution. Becausethe gestation period of buffalo has been estimated to be around11 months, these findings suggest that improved protein levels,occurring approximately a month after the first green flushof the wet season, are either a trigger for conception or conceptionhas evolved to be synchronous with correlated environmentalcues that ensure females enter a period of peak body conditionaround the time of conception and/or parturition. With a gestationperiod of approximately 340 days, parturition occurs to takeadvantage of the period when forage has its highest proteincontent. A comparative analysis of gestation periods withinthe subfamily Bovinae indicates that African buffalo have aprotracted gestation for their body size, which we suggest isan adaptation to their seasonal environment. We also found thatinterannual variation in the birth distribution suggests a degreeof plasticity in the date of conception, and variation in thenumber of calves born each year suggest further synchrony ata timescale longer than a single year.     

Risk of extinction increases towards higher elevations across the world's amphibians

Aim

Life in mountains is associated with multiple features that increase the risk of demographic collapses in populations – small geographic ranges, short breeding seasons, specialization to harsh climates – leading to the hypothesis that extinction risk is exacerbated in species inhabiting higher elevations. Here, we implement the first test of this hypothesis across the amphibian tree of life – the tetrapods with the largest proportion of montane species, and nature's most threatened animals.

Location

Global.

Time Period

Present.

Major Taxa Studied

Class Amphibia.

Methods

We collated a dataset spanning 8042 species from across all three amphibian orders (Anura, Caudata and Gymnophiona). We preformed phylogenetic logistic regressions to test the predictions that extinction risk increases with elevation, and whether this effect is caused by factors previously hypothesised to drive high-elevation declines, including restrictions on species' geographic ranges, variation in their life histories and the presence of infectious disease.

Results

Globally, extinction risk increases towards higher elevations. At order-level, this relationship holds for frogs and salamanders. Even when controlling for geographic range size, life histories and infectious disease, extinction risk increases with elevation for amphibians combined and frogs globally, and in the Americas. In contrast, whereas extinction risk is greater among high-elevation Eurasian amphibians, this relationship is explained by larger body sizes and lower fecundity.

Main Conclusions

Our analyses indicate that after considering factors previously thought to explain the increase in extinction risk towards higher elevations (e.g., geographic range size, disease), elevation remains a significant predictor of amphibian extinction risk. Given that the only available tests of this hypothesis in other tetrapods (birds and reptiles) conflict with our findings, we suggest that physiological or life-history features of amphibians may explain this observed phenomenon.