Physical activity habit: Complexities and controversies

The health benefits of regular physical activity participation among adults support a reliable dose–response relationship with risk reduction of all-cause mortality, cardiovascular disease, stroke, hypertension, colon cancer, and breast cancer (Warburton, Charlesworth, Ivey, Nettlefold, & Bredin, 2010). Furthermore, regular physical activity has been linked to reduced mental health problems such as depression and anxiety symptoms (Rebar et al., 2015). The recommended dose of physical activity for optimal health benefits is 150 min of moderate intensity or 75 min of vigorous intensity activity for adults per week (World Health Organization, 2012). Unfortunately, few people meet these guidelines, particularly in higher income countries (Hallal et al., 2012). For example, less than 20% of North American adults are physically active at the recommended guidelines (Colley et al., 2011; Troiano et al., 2008). Thus, promotion of regular physical activity is paramount to public health and effective interventions are needed

\u3ci\u3eDrosophila\u3c/i\u3e Muller F Elements Maintain a Distinct Set of Genomic Properties Over 40 Million Years of Evolution

The Muller F element (4.2 Mb, ~80 protein-coding genes) is an unusual autosome of Drosophila melanogaster; it is mostly heterochromatic with a low recombination rate. To investigate how these properties impact the evolution of repeats and genes, we manually improved the sequence and annotated the genes on the D. erecta, D. mojavensis, and D. grimshawi F elements and euchromatic domains from the Muller D element. We find that F elements have greater transposon density (25–50%) than euchromatic reference regions (3–11%). Among the F elements, D. grimshawi has the lowest transposon density (particularly DINE-1: 2% vs. 11–27%). F element genes have larger coding spans, more coding exons, larger introns, and lower codon bias. Comparison of the Effective Number of Codons with the Codon Adaptation Index shows that, in contrast to the other species, codon bias in D. grimshawi F element genes can be attributed primarily to selection instead of mutational biases, suggesting that density and types of transposons affect the degree of local heterochromatin formation. F element genes have lower estimated DNA melting temperatures than D element genes, potentially facilitating transcription through heterochromatin. Most F element genes (~90%) have remained on that element, but the F element has smaller syntenic blocks than genome averages (3.4–3.6 vs. 8.4–8.8 genes per block), indicating greater rates of inversion despite lower rates of recombination. Overall, the F element has maintained characteristics that are distinct from other autosomes in the Drosophila lineage, illuminating the constraints imposed by a heterochromatic milieu