Acclimatization to 4100 m does not change capillary density or mRNA expression of potential angiogenesis regulatory factors in human skeletal muscle

[EN] Increased skeletal muscle capillary density would be a logical adaptive mechanism to chronic hypoxic exposure. However, animal studies have yielded conflicting results, and human studies are sparse. Neoformation of capillaries is dependent on endothelial growth factors such as vascular endothelial growth factor (VEGF), a known target gene for hypoxia inducible factor 1 (HIF-1). We hypothesised that prolonged exposure to high altitude increases muscle capillary density and that this can be explained by an enhanced HIF-1alpha expression inducing an increase in VEGF expression. We measured mRNA levels and capillary density in muscle biopsies from vastus lateralis obtained in sea level residents (SLR; N=8) before and after 2 and 8 weeks of exposure to 4100 m altitude and in Bolivian Aymara high-altitude natives exposed to approximately 4100 m altitude (HAN; N=7). The expression of HIF-1alpha or VEGF mRNA was not changed with prolonged hypoxic exposure in SLR, and both genes were similarly expressed in SLR and HAN. In SLR, whole body mass, mean muscle fibre area and capillary to muscle fibre ratio remained unchanged during acclimatization. The capillary to fibre ratio was lower in HAN than in SLR (2.4+/-0.1 vs 3.6+/-0.2; P<0.05). In conclusion, human muscle VEGF mRNA expression and capillary density are not significantly increased by 8 weeks of exposure to high altitude and are not increased in Aymara high-altitude natives compared with sea level residents.

Colonization of gastropods on subtidal reefs depends on density in adjacent habitats, not on disturbance regime

[EN] Habitats dominated by algal canopies are often altered by physical disturbances of varying severity, changing environmental conditions and biological processes. We used Artificial Seaweed Units (ASUs) to test whether severity of physical disturbances on algal canopies affects the post-disturbance colonization of gastropods on subtidal reefs. Specifically, we examined patterns of assemblage structure of gastropods to test the hypothesis that the extent and intensity of canopy removal affects the post-disturbance colonization of ASUs, testing the consistency of these effects among four regions encompassing a 68 latitudinal gradient in southwestern Australia. Because adjacent habitats can act as a source of new colonists (either as drifting migrants or as a source of propagules) from the perimeter surrounding perturbed areas, we also predicted that patterns of colonization (types and total abundances of colonizers) were influenced by the available pool of individuals at the scale of reefs. Three reefs were selected within each region. On each reef, ASUs were placed in the centre of circular canopy clearings of different size (0, 3, 13 and 50 m2) and intensity (50% vs 100%), and retrieved after 3 months. Resulting assemblages occupying the ASUs were quantitatively representative of the adjacent (undisturbed), algal-associated, assemblages at the scale of reef. Within reefs, recruited assemblages largely mimicked those associated with erect red algae. However, neither disturbance size nor intensity affected the colonization patterns across reefs and regions. These results suggest that algal-associated gastropods, regardless of the prevalent mode of dispersion, are resilient to physical disturbances to canopies across broad geographical regions as long as the pool of potential colonists is maintained. A high dispersal ability of gastropods likely ensures a quick colonization of recovering algal habitats.