Density dependence of the Addo Elephant National Park (South Africa) elephants Loxodonta africana was assessed using a long-term data set. Estimated carrying capacity is 0.1–0.5 elephants km−2 but stocking rates have been up to 4 elephants km−2. Population growth rate was found to be positively correlated with increasing density. There was no relationship between birth rate, the age of first calving or calf sex ratio and elephant density but there was a positive relationship between birth rate and rainfall during conception year. Mortality rates, particularly for juveniles, were low, and mean inter-calf interval was 3.3 years. There is no evidence of density dependent regulation in this population, despite the population being consistently above the estimated sustainable carrying capacity and a loss of phytomass and biodiversity. This is interpreted in light of the characteristics of the aseasonal habitat, succulent thicket vegetation and the ability of elephants to utilize accumulated vegetation biomass. These findings indicate that density dependence should not be considered as an option in the control of elephant numbers in this Park, or where elephant resources are not seasonally limited.
BackgroundA single bout of exercise induces changes in gene expression in skeletal muscle. Regular exercise results in an adaptive response involving changes in muscle architecture and biochemistry, and is an effective way to manage and prevent common human diseases such as obesity, cardiovascular disorders and type II diabetes. However, the biomolecular mechanisms underlying such responses still need to be fully elucidated. Here we performed a transcriptome-wide analysis of skeletal muscle tissue in a large cohort of untrained Thoroughbred horses (n = 51) before and after a bout of high-intensity exercise and again after an extended period of training. We hypothesized that regular high-intensity exercise training primes the transcriptome for the demands of high-intensity exercise.ResultsAn extensive set of genes was observed to be significantly differentially regulated in response to a single bout of high-intensity exercise in the untrained cohort (3241 genes) and following multiple bouts of high-intensity exercise training over a six-month period (3405 genes). Approximately one-third of these genes (1025) and several biological processes related to energy metabolism were common to both the exercise and training responses. We then developed a novel network-based computational analysis pipeline to test the hypothesis that these transcriptional changes also influence the contextual molecular interactome and its dynamics in response to exercise and training. The contextual network analysis identified several important hub genes, including the autophagosomal-related gene GABARAPL1, and dynamic functional modules, including those enriched for mitochondrial respiratory chain complexes I and V, that were differentially regulated and had their putative interactions ‘re-wired’ in the exercise and/or training responses.ConclusionHere we have generated for the first time, a comprehensive set of genes that are differentially expressed in Thoroughbred skeletal muscle in response to both exercise and training. These data indicate that consecutive bouts of high-intensity exercise result in a priming of the skeletal muscle transcriptome for the demands of the next exercise bout. Furthermore, this may also lead to an extensive ‘re-wiring’ of the molecular interactome in both exercise and training and include key genes and functional modules related to autophagy and the mitochondrion.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-017-4007-9) contains supplementary material, which is available to authorized users.
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A 46-year-old man took a lethal dose of an agent called dinitrophenol (DNP). He presented 11 h after ingestion with loin pain, diarrhoea and vomiting. He rapidly deteriorated with profound hyperthermia, acute renal failure, hyperkalaemia, metabolic acidosis and eventually haemodynamic instability. Despite aggressive supportive measures and rapid sequence induction, he deteriorated and died 21 h after ingestion. DNP is a metabolic poison that acts by uncoupling oxidative phosphorylation, leading to uncontrolled hyperthermia. It is an illegal weight loss agent that is used by body builders and is freely available on many internet websites. This case highlights the potential for patients to obtain and ingest exotic poisons. A summary of currently recommended treatment and a review of the literature on DNP is included, as well as a discussion of therapies that may be effective in treating hyperthermia in this situation.
Adaptation to early training and racing (i.e. precocity), which is highly variable in racing Thoroughbreds, has implications for the selection and training of horses. We hypothesised that precocity in Thoroughbred racehorses is heritable. Age at first sprint training session (work day), age at first race and age at best race were used as phenotypes to quantify precocity. Using high-density SNP array data, additive SNP heritability (hSNP2) was estimated to be 0.17, 0.14 and 0.17 for the three traits respectively. In genome-wide association studies (GWAS) for age at first race and age at best race, a 1.98-Mb region on equine chromosome 18 (ECA18) was identified. The most significant association was with the myostatin (MSTN) g.66493737C>T SNP (P = 5.46 × 10 and P = 1.89 × 10 respectively). In addition, two SNPs on ECA1 (g.37770220G>A and g.37770305T>C) within the first intron of the serotonin receptor gene HTR7 were significantly associated with age at first race and age at best race. Although no significant associations were identified for age at first work day, the MSTN:g.66493737C>T SNP was among the top 20 SNPs in the GWAS (P = 3.98 × 10 ). Here we have identified variants with potential roles in early adaptation to training. Although there was an overlap in genes associated with precocity and distance aptitude (i.e. MSTN), the HTR7 variants were more strongly associated with precocity than with distance. Because HTR7 is closely related to the HTR1A gene, previously implicated in tractability in young Thoroughbreds, this suggests that behavioural traits may influence precocity.
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