A pre-impoundment study of the biological diversity of the benthic macro-invertebrate fauna of the Sabie-Sand River system

Bibliography: p. 177-205.The Kruger National Park (KNP) in the Eastern Transvaal provides a classic example of the potential conflict of interests between the industrial, agricultural and domestic sectors and conservation. The KNP is situated on the north-eastern border of South Africa and receives the flow of six rivers (Figure 0.1), all •of which originate outside the jurisdiction of the Park authorities. Thus, there are demands for water outside the boundaries of the KNP from other sectors of South Africa, as well as several self-governing states that have been set up as political entities within South Africa (see Chunnett, Fourie & Partners 1987, 1990). Due to human development •of catchments there has been regulation of these rivers, which are rapidly changing in terms of their flow regimes. (O'Keeffe. & Davies 1991). For example, the Letaba and the Luvhuvhu rivers have both changed from perennial to annual flow regimes (O'Keeffe & Davies 1991), a condition which is detrimental to the maintenance of river ecosystem functioning, while the Crocodile River has been regulated to an almost unvarying flow of ca 5m3 s•1 (O'Keeffe & Davies 1991). Recognising the need to address the problem of water allocation to the KNP, the Department of Water Affairs (DW A) convened a workshop on minimum flow needs for the environment in 1987 (Bruwer in press). Although tentative values were suggested for minimum flows, the value of the workshop was its recognition of the need for more research into the problem. Such research is currently being undertaken under the auspices of the multi-disciplinary KNP Rivers Research Programme. The goal of the programme is to " ... develop the means to predict the impact on the KNP river systems of changing flow regimes and water quality as the basis of a protocol for managing the• allocation of water for ecological purposes" (Kruger National Park Rivers Research Programme 1990). One of the studies initiated within this programme was a pre-impoundment study of the Sabie River, including its main tributary, the Sand River, which together are referred to as the Sabie-Sand River system

Distribution, age, and growth of young-of-the year greater amberjack (Seriola dumerili) associated with pelagic Sargassum

Patterns of distribution and growth were examined for young-of-the-year (YOY) greater amberjack (Seriola dumerili) associated with pelagic Sargassum in the NW Gulf of Mexico. Seriola dumerili were collected off Galveston, Texas, from May to July over a two-year period (2000 and 2001) in both inshore (<15 nautical miles [nmi]) and offshore zones (15−70 nmi). Relative abundance of YOY S. dumerili (32−210 mm standard length) from purse-seine collections peaked in May and June, and abundance was highest in the offshore zone. Ages of S. dumerili ranged from 39 to 150 days and hatching-date analysis indicated that the majority of spawning events occurred from February to April. Average daily growth rates of YOY S. dumerili for 2000 and 2001 were 1.65 mm/d and 2.00 mm/d, respectively. Intra-annual differences in growth were observed; the late-season (April) cohort experienced the fastest growth in both years. In addition, growth was significantly higher for S. dumerili collected from the offshore zone. Mortality was approximated by using catch-curve analysis, and the predicted instantaneous mortality rate (Z) of YOY S. dumerili was 0.0045 (0.45%/d)

A Small Family of Elements with Long Inverted Repeats is Located Near Sites of Developmentally Regulated DNA Rearrangement in \u3cem\u3eTetrahymena thermophila\u3c/em\u3e

Extensive DNA rearrangement occurs during the development of the somatic macronucleus from the germ line micronucleus in ciliated protozoans. The micronuclear junctions and the macronuclear product of a developmentally regulated DNA rearrangement in Tetrahymena thermophila, Tlr1, have been cloned. The intrachromosomal rearrangement joins sequences that are separated by more than 13 kb in the micronucleus with the elimination of moderately repeated micronucleus-specific DNA sequences. There is a long, 825-bp, inverted repeat near the micronuclear junctions. The inverted repeat contains two different 19-bp tandem repeats. The 19-bp repeats are associated with each other and with DNA rearrangements at seven locations in the micronuclear genome. Southern blot analysis is consistent with the occurrence of the 19-bp repeats within pairs of larger repeated sequences. Another family member was isolated. The 19-mers in that clone are also in close proximity to a rearrangement junction. We propose that the 19-mers define a small family of developmentally regulated DNA rearrangements having elements with long inverted repeats near the junction sites. We discuss the possibility that transposable elements evolve by capture of molecular machinery required for essential cellular functions

Population history and ecology, in addition to climate, influence human stature and body proportions.

Worldwide variation in human stature and limb proportions is widely accepted to reflect thermal adaptation, but the contribution of population history to this variation is unknown. Furthermore, stature and relative lower limb length (LLL) show substantial plastic responses to environmental stressors, e.g., nutrition, pathogen load, which covary with climate. Thus ecogeographic patterns may go beyond temperature-based selection. We analysed global variation in stature, sitting height and absolute and relative LLL using large worldwide samples of published anthropometric data from adult male (n = 571) and female (n = 268) populations in relation to temperature, humidity, and net primary productivity (NPP). Population history was modeled using spatial eigenvector mapping based on geographic distances reflecting the hypothesized pattern for the spread of modern humans out of Africa. Regression models account for ~ 50% of variation in most morphological variables. Population history explains slightly more variation in stature, sitting height and LLL than the environmental/climatic variables. After adjusting for population history, associations between (usually maximum) temperature and LLL are consistent with Allen's "rule" and may drive similar relationships with stature. NPP is a consistent negative predictor of anthropometry, which may reflect the growth-limiting effects of lower environmental resource accessibility (inversely related to NPP) and/or pathogen load

A trade-off between cognitive and physical performance, with relative preservation of brain function.

Debate surrounds the issue of how the large, metabolically expensive brains of Homo sapiens can be energetically afforded. At the evolutionary level, decreased investment in muscularity, adiposity and the digestive tract allow for a larger brain. Developmentally, high neo-natal adiposity and preferential distribution of resources to the brain provide an energetic buffer during times of environmental stress. Through an experimental design, we investigated the hypothesis of a trade-off involving brain and muscle at the acute level in humans. Mental performance was measured by a free-recall test, and physical performance by power output on an indoor rowing ergometer. Sixty-two male student rowers performed the two tests in isolation, and then again simultaneously. Paired samples t-tests revealed that both power output and mental performance reduced when tested together compared to in isolation (t(61) = 9.699, p < 0.001 and t(61) = 8.975, p < 0.001). Furthermore, the decrease in physical performance was greater than the decrease in mental performance (t(61) = -2.069, p = 0.043). This is the first investigation to demonstrate an acute level trade-off between these two functions, and provides support for the selfish brain hypothesis due to the relative preservation of cognitive function over physical power output. The underlying mechanism is unclear, and requires further work

Human energetic stress associated with upregulation of spatial cognition

Objectives: Evolutionary life history theory has a unique potential to shed light on human adaptive capabilities. Ultra-endurance challenges are a valuable experimental model allowing the direct testing of phenotypic plasticity via physiological trade-offs in resource allocation. This enhances our understanding of how the body prioritizes different functions when energetically stressed. However, despite the central role played by the brain in both hominin evolution and metabolic budgeting, cognitive plasticity during energetic deficit remains unstudied. Materials: We considered human cognitive plasticity under conditions of energetic deficit by evaluating variability in performance in three key cognitive domains. To achieve this, cognitive performance in a sample of 48 athletes (m = 29, f = 19) was assessed before and after competing in multiday ultramarathons. Results: We demonstrate that under conditions of energetic deficit, performance in tasks of spatial working memory (which assessed ability to store location information, promoting landscape navigation and facilitating resource location and calorie acquisition) increased. In contrast, psychomotor speed (reaction time) remained unchanged and episodic memory performance (ability to recall information about specific events) decreased. Discussion: We propose that prioritization of spatial working memory performance during conditions of negative energy balance represents an adaptive response due to its role in facilitating calorie acquisition. We discuss these results with reference to a human evolutionary trajectory centred around encephalisation. Encephalisation affords great plasticity, facilitating rapid responses tailored to specific environmental conditions, and allowing humans to increase their capabilities as a phenotypically plastic species

A trade-off between cognitive and physical performance, with relative preservation of brain function

Debate surrounds the issue of how the large, metabolically expensive brains of Homo sapiens can be energetically afforded. At the evolutionary level, decreased investment in muscularity, adiposity and the digestive tract allow for a larger brain. Developmentally, high neo-natal adiposity and preferential distribution of resources to the brain provide an energetic buffer during times of environmental stress. Through an experimental design, we investigated the hypothesis of a trade-off involving brain and muscle at the acute level in humans. Mental performance was measured by a free-recall test, and physical performance by power output on an indoor rowing ergometer. Sixty-two male student rowers performed the two tests in isolation, and then again simultaneously. Paired samples t-tests revealed that both power output and mental performance reduced when tested together compared to in isolation (t(61) = 9.699, p < 0.001 and t(61) = 8.975, p < 0.001). Furthermore, the decrease in physical performance was greater than the decrease in mental performance (t(61) = -2.069, p = 0.043). This is the first investigation to demonstrate an acute level trade-off between these two functions, and provides support for the selfish brain hypothesis due to the relative preservation of cognitive function over physical power output. The underlying mechanism is unclear, and requires further work

Can persistence hunting signal male quality? A test considering digit ratio in endurance athletes

Various theories have been posed to explain the fitness payoffs of hunting success among hunter-gatherers. 'Having' theories refer to the acquisition of resources, and include the direct provisioning hypothesis. In contrast, 'getting' theories concern the signalling of male resourcefulness and other desirable traits, such as athleticism and intelligence, via hunting prowess. We investigated the association between androgenisation and endurance running ability as a potential signalling mechanism, whereby running prowess, vital for persistence hunting, might be used as a reliable signal of male reproductive fitness by females. Digit ratio (2D:4D) was used as a proxy for prenatal androgenisation in 439 males and 103 females, while a half marathon race (21km), representing a distance/duration comparable with that of persistence hunting, was used to assess running ability. Digit ratio was significantly and positively correlated with half-marathon time in males (right hand: r = 0.45, p<0.001; left hand: r = 0.42, p<0.001) and females (right hand: r = 0.26, p<0.01; left hand: r = 0.23, p = 0.02). Sex-interaction analysis showed that this correlation was significantly stronger in males than females, suggesting that androgenisation may have experienced stronger selective pressure from endurance running in males. As digit ratio has previously been shown to predict reproductive success, our results are consistent with the hypothesis that endurance running ability may signal reproductive potential in males, through its association with prenatal androgen exposure. However, further work is required to establish whether and how females respond to this signalling for fitness