The evolution of the upright posture and gait—a review and a new synthesis

During the last century, approximately 30 hypotheses have been constructed to explain the evolution of the human upright posture and locomotion. The most important and recent ones are discussed here. Meanwhile, it has been established that all main hypotheses published until the last decade of the past century are outdated, at least with respect to some of their main ideas: Firstly, they were focused on only one cause for the evolution of bipedality, whereas the evolutionary process was much more complex. Secondly, they were all placed into a savannah scenario. During the 1990s, the fossil record allowed the reconstruction of emerging bipedalism more precisely in a forested habitat (e.g., as reported by Clarke and Tobias (Science 269:521–524, 1995) and WoldeGabriel et al. (Nature 412:175–178, 2001)). Moreover, the fossil remains revealed increasing evidence that this part of human evolution took place in a more humid environment than previously assumed. The Amphibian Generalist Theory, presented first in the year 2000, suggests that bipedalism began in a wooded habitat. The forests were not far from a shore, where our early ancestor, along with its arboreal habits, walked and waded in shallow water finding rich food with little investment. In contrast to all other theories, wading behaviour not only triggers an upright posture, but also forces the individual to maintain this position and to walk bipedally. So far, this is the only scenario suitable to overcome the considerable anatomical and functional threshold from quadrupedalism to bipedalism. This is consistent with paleoanthropological findings and with functional anatomy as well as with energetic calculations, and not least, with evolutionary psychology. The new synthesis presented here is able to harmonise many of the hitherto competing theories

In vivo implants of β-sitosterol cause reductions of reactive cholesterol pools in mitochondria isolated from gonads of male goldfish (Carassius auratus)

߭Sitosterol, a phytosterol found in high concentrations in pulp mill effluents, has been proposed as one of the causative agents for steroid depressions observed in fish exposed to pulp mill effluents. Previous studies have suggested a cholesterol-mediated mechanism; however, it is unknown how ߭sitosterol depresses gonadal steroidogenesis. In this study, adult male goldfish (Carassius auratus) were exposed for 24-31 days to ߭sitosterol (55% of a phytosterol mixture or 96% pure; 150 lg/g; Silastic implant) after which gonadal mitochondria were isolated. Pregnenolone production, an indicator of the size of the pool of reactive cholesterol, was then measured in the isolated mitochondria. Sterol exposure did not affect P450 side-chain cleavage enzyme (converts cholesterol to pregnenolone) activity but did decrease the size of the mitochondrial pool of reactive cholesterol, suggesting ߭sitosterol is impeding cholesterol transfer across the mitochondrial membrane. This finding is supported by the observation that 25-hydroxycholesterol, which passes through mitochondrial membranes without need for a membrane transporter, restores ߭sitosterol-induced reductions in pregnenolone production.No Full Tex

Effects of a phytosterol mixture on male fish plasma lipoprotein fractions and testis P450scc activity

Plant sterols (phytosterols) have been identified as one potential source of reproductive effects in fish living downstream of pulp mills. ߭Sitosterol, the predominant plant sterol in pulp mill effluent, has previously been shown to decrease plasma sex steroid and cholesterol levels and in vitro gonadal steroid production in fish. In this study, male brook trout (Salvelinus fontinalis) and goldfish (Carassius auratus) were exposed to a phytosterol mixture (72% ߭sitosterol) via Silastic intraperitoneal implants to help elucidate the mechanisms of action of phytosterols on steroid depression. As cholesterol is exogenously supplied for gonadal steroidogenesis, changes in plasma cholesterol fractions were examined. In male brook trout, low-density lipoprotein cholesterol and triglyceride levels decreased significantly, 43 and 50%, respectively, in phytosterol-treated fish. It is improbable, however, that these decreases are linked to depressed gonadal steroidogenesis in fish. The activity of P450scc, which converts cholesterol to pregnenolone (the first step in the steroidogenic pathway), was not affected in testis mitochondria isolated from brook trout or goldfish. Further investigation of the mechanisms of action of phytosterols is required.No Full Tex

Development of a short-term in situ caging methodology to assess long-term effects of industrial and municipal discharges on salmon smolts

Trial experiments to develop an in situ method for determining effects of short-term exposure to contaminants on salmon during the sensitive smolt stage were carried out. Wild Atlantic salmon (Salmo salar) smolts were caged at various estuarine locations in northeast New Brunswick, Canada at different levels of anthropogenic impact in 2000 and 2001. Survival, growth (weight and K), and feeding (d13C and d15N) parameters were measured following summer grow-out at a hatchery. A summary of distributions of the four parameters indicated that smolts caged at locations receiving lower levels of industrial and municipal discharges feed and grow better than those caged at sites receiving higher levels. The findings, however, were not repeatable between the 2 years studied. The observed inconsistency between years may be a consequence of the relatively low concentrations of alkylphenolic contaminants (putative causative agents) and overall steroidogenic potency in river water at the time of caging. Differences in temperature and salinity from 2000 to 2001 may have further confounded comparisons across treatments and between years. In future studies, caging in closer proximity to industrial and municipal discharges or in systems with higher concentrations of waterborne contaminants or impoundments would help further the assessment and applicability of this methodology and allow a more robust comparison of smolt feeding and growth among reference and exposure sites.No Full Tex

Rapid carbon turnover during growth of Atlantic salmon (Salmo salar) smolts in sea water, and evidence for reduced food consumption by growth-stunts

Wild Atlantic salmon smolts were captured during spring out-migration in the NorthwestMiramichi River, New Brunswick, Canada, and placed on an isotopically distinct hatchery diet to determine the relative contributions of growth and metabolic turnover to isotopic change. As expected for an ectothermic species, growth explained a large amount of isotopic variation in changing stable carbon ratios of muscle tissue (average r2 젰.46) for the 3 years of study. Turnover rates of muscle carbon in all 3 years in growing fish (0.24-0.66 month)1) were higher than previously reported values for other ectothermic species, but there was little evidence for isotopic change in non-growers (average r2 젰.041, p>0.1). It is unlikely that nongrowers had consumed any of the hatchery diet over a 2-month period, thus preventing them from acquiring the new carbon isotopic signature. This period of food deprivation resulted in nitrogen-15 enrichment in liver relative to muscle (p 젰.003). It is advised that future isotope studies of metabolic turnover rates in ectotherms be conducted on slow-growing animals over a long time period. This would serve to avoid the obscuring effects of growth on isotopic change, and provide stronger comparisons to endothermic tissue turnover rates.No Full Tex