The effects of intensity of exercise on excess postexercise oxygen consumption and energy expenditure in moderately trained men and women

This experiment investigated the effects of intensity of exercise on excess postexercise oxygen consumption (EPOC) in eight trained men and eight women. Three exercise intensities were employed 40%, 50%, and 70% of the predetermined maximal oxygen consumption (VO_2max). All ventilation measured was undertaken with a standard, calibrated, open circuit spirometry system. No differences in the 40%, 50% and 70% VO_2max trials were observed among resting levels of oxygen consumption (V0₂) for either the men or the women. The men had significantly higher resting VO₂ values being 0.31 (SEM 0.01) 1·min^–1 than did the women, 0.26 (SEM 0.01) 1·min^–1 (P < 0.05). The results indicated that there were highly significant EPOC for both the men and the women during the 3-h postexercise period when compared with resting levels and that these were dependent upon the exercise intensity employed. The duration of EPOC differed between the men and the women but increased with exercise intensity: for the men 40% – 31.2 min; 50% – 42.1 min; and 70% – 47.6 min and for the women, 40% – 26.9 min; 50% – 35.6 min; and 70% – 39.1 min. The highest EPOC, in terms of both time and energy utilised was at 70% VO_2max. The regression equation for the men, where y=O₂ in litres, and x=exercise intensity as a percentage of maximum was y=0.380x + 1.9 (r ²=0.968) and for the women is y=0.374x–0.857 (r ²=0.825). These findings would indicate that the men and the women had to exercise at the same percentage of their VO_2max to achieve the maximal benefits in terms of energy expenditure and hence body mass loss. However, it was shown that a significant EPOC can be achieved at moderate to low exercise intensities but without the same body mass loss and energy expenditure.     

Exogenous 13C glucose oxidation during exercise: North American vs Western European studies

The purpose of this study was to test the hypothesis that the well-documented changes in background ¹³C enrichment of expired CO₂ observed in response to exercise and carbohydrate ingestion, in subjects living on a North American diet, are not present in subjects living on a Western European diet. The experimental protocol used by Pirnay et al. in 1977 and by Krzentowski et al. in 1984 in subjects living on a Western European diet (4 h of exercise on a treadmill at 50% VO_2max with ingestion of 100 g of glucose in 400 ml of water) was duplicated as closely as possible in six subjects living on a North American diet. The actual amounts of exogenous glucose oxidized, computed with a high artificial ¹³C enrichment of glucose (+189.7 ¹³C PDB-1) which allows one to neglect the 1–2 changes in ¹³C background, were [mean (SEM)] 54.7 (5.4) and 84.2 (3.4) g over 2 h and 4 h of exercise, respectively. These values compare well with data computed by Pirnay et al. [56.6 (13.1) and 94.9 (4.2) g] and by Krzentowski et al. [55.0 (6.2) and 88.0 (4.5) g] using a natural enrichment of glucose (–11.21 and –10.63 ¹³C PDB-1, respectively) assuming no change in ¹³C background in their Western European subjects. Under the same assumption and using a natural enrichment of glucose (–11.30 ¹³C PDB-1) the oxidation of exogenous glucose was overestimated by 30–40% in our North American subjects. This result indicates that because of a lower input of ¹³C in their diet, the difference between the isotopic composition of carbohydrate and fat stores are smaller, and changes in ¹³C background are small or absent in response to moderate workload in Western European subjects, when compared to their North American counterparts.     

Effects of sexual differences of age at maturity and survival on population sex ratio

Summary Five demographical factors influencing the sex ratio of a population are classically considered. The influence of two of them is dependent on the longevity of individuals in the population. The effect of differential age at maturity between males and females is higher for animals with low annual survival, whereas the effect of differential annual survival between males and females is higher for animals with high annual survival. Such a conclusion applied to turtles, which are long life-span animals, allows us to retain differential survival between sexes as a major factor influencing the population sex ratio.     

Effect of host availability on reproduction and survival of the parasitoid wasp Trichogramma minutum

Abstract.

• 1 We tested the hypothesis that females of the egg parasitoid, Trichogramma minutum Riley (Hymenoptera: Trichogrammatidae), could adjust their fecundity schedule according to host availability and that there was a negative correlation between reproduction and survival in these wasps.
• 2 Newly-emerged females were provided with an unlimited or limited number of hosts in the first trial and with either unlimited, limited or zero hosts in the second trial.
• 3 When hosts were unlimited, wasps had the highest rate of reproduction in the first day, which decreased dramatically thereafter. When hosts were limited, wasps from the two trials differed in their response. In Trial I, females with limited hosts had lower first-day fecundity than, and the same subsequent-day fecundity as, those with unlimited hosts. However, in Trial II, females with limited host had a lower first-day but a higher subsequent-day fecundity than those with unlimited hosts. This indicates variation in Trichogramma's ability to shift its fecundity schedule in response to host availability.
• 4 There was a positive (rather than a negative) correlation between reproduction and survival. Wasps that oviposited (in host-unlimited treatment) had greater longevity than those that could not (in host-unavailable treatment).
• 5 The sex ratio of the progeny produced by wasps in both host-unlimited and limited treatments shifted gradually from a female to a male bias as the wasps aged.
• 6 We consider the ability of parasitoids to adjust their fecundity schedule as an adaptation to changing host resources and discuss our findings with regard to theories of life history evolution.

     

The evolution of unusual chromosomal systems in coccoids: extraordinary sex ratios revisited

Coccoids (scale insects) exhibit a wide variety of chromosomal systems. In many species, paternal chromosomes are eliminated from the male germline such that all of a male's sperm transmit an identical set of maternal chromosomes. In such species, an offspring's sex is determined by whether or not paternal chromosomes are inactivated in the egg's cytoplasm after fertilization. This paper presents a model of the evolution of paternal genome loss in coccoids from an ancestral system of XX-XO sex determination. The model is based on Hamilton's (1967) theory that different genetic elements within the genome have different unbeatable sex ratios. In this model (1) meiotic drive by the X chromosome in XO males causes female-biased sex ratios; (2) the maternal set of autosomes in males evolves effective sex linkage to exploit X-drive; and (3) genes expressed in mothers are selected to convert some of their XX daughters into sons. A similar model may explain the evolution of haplodiploidy.     

Are brood sex ratios adaptive?—The effect of experimentally altered brood sex ratio on nestling growth,mortality and recruitment

Brood sex ratios (BSRs) have often been found to be nonrandom in respect of parental and environmental quality, and many hypotheses suggest that nonrandom sex ratios can be adaptive. To specifically test the adaptive value of biased BSRs, it is crucial to disentangle the consequences of BSR and maternal effects. In multiparous species, this requires cross-fostering experiments where foster parents rear offspring originating from multiple broods, and where the interactive effect of original and manipulated BSR on fitness components is tested. To our knowledge, our study on collared flycatchers (Ficedula albicollis) is the first that meets these requirements. In this species, where BSRs had previously been shown to be related to parental characteristics, we altered the original BSR of the parents shortly after hatching by cross-fostering nestlings among trios of broods and examined the effects on growth, mortality and recruitment of the nestlings. We found that original and experimental BSR, as well as the interaction of the two, were unrelated to the fitness components considered. Nestling growth was related only to background variables, namely brood size and hatching rank. Nestling mortality was related only to hatching asynchrony. Our results therefore do not support that the observed BSRs are adaptive in our study population. However, we cannot exclude the possibility of direct effects of experimentally altered BSRs on parental fitness, which should be evaluated in the future. In addition, studies similar to ours are required on various species to get a clearer picture of the adaptive value of nonrandom BSRs.     

Is drift ‘directional’? Unequal breeding sex ratio revisited

Unequal breeding sex ratio can significantly reduce effective population size, allowing a rare neutral allele to jump to a high frequency through genetic drift. However, this one-way alteration to allele frequency appears inconsistent with the concept that drift is non-directional. Based on binomial sampling distribution, this study developed a method to directly and exhaustively measure drift by calculating the mean deviation of change in allele frequency, then applied it to cases of unequal breeding sex ratio. The result shows that, under those cases, (1) the mean deviation can always be divided into two halves that are equal in size but opposite in direction; (2) each half consists of one or several categories represented by various allele proportions in the rare sex; (3) this proportion is another factor that determines the outcome of drift, in addition to effective population size and allele frequency; (4) drift is non-directional on a global scale, but whether an allele will drift up or down can be predicted based on the above factors. This method enables us to dissect every component of the expected change in allele frequency caused by drift and to find out the combined effect of population size, allele frequency and allele proportion in the rarer sex under neutrality but unequal breeding sex ratio.     

Divergence in male mating tactics between two populations of the soapberry bug: I. Guarding versus nonguarding

I compared male allocation to prolonged mate guarding versusnot guarding between two populations of the soapberry bug (Jaderahaematoloma) that differ in adult sex ratio: Oklahoma, USA (mean± SD adult sex ratio, 2.70 ± 0.95 males per female),and Florida, USA (1.09 ± 0.26 males per female). To predictthe reproductive performance of each mating tactic in each population,I collected data on search time per mating, time required forguarding to be effective, sperm competition, female rematingpropensity, and female resistance to guarding. Search time alonediffered significantly between the populations, being much greaterin Oklahoma (estimated as 26.2 h per mate) than in Florida (estimatedas 9.6 h per mate). For males in each region, these data wereused to model the costs and benefits of guarding for differentnumbers of oviposition bouts versus not guarding. The reproductiverate of nonguarders in Oklahoma is exceeded by that of guarderswho remain with a female for more than one oviposition bout,but in Florida, the reproductive rate of nonguarders is onlyexceeded by that of guarders who remain with a female for atleast three ovipositions. Consistent with the model, Oklahomamales in field arenas guarded more frequently than did Floridamales. However, nonguarding was common in both populations,and guarding durations were highly variable.     

Reproductive biology of the slender smoothhound,Gollum attenuatus,collected from New Zealand waters

Synopsis The reproductive biology of 385 male and 373 female slender smoothhounds,Gollum attenuatus, collected from New Zealand waters was examined. Size at maturity for both sexes was about 700 mm TL. Litter size was usually two. The sex ratio of embryos was 1:1. The right ovary ovulated 50–100 ova, 4–8 mm in diameter, and 30–80 ova were enclosed in each egg capsule. Only one embryo developed from the many ova in each egg capsule, the other undeveloped ova were ingested and passed to an external yolk sac which formed the yolk supply for the developing embryo.     

Fish oil supplementation reduces excretion of 2,3-dinor-6-oxo-PGF1α and the 11-dehydrothromboxane B2/2,3-dinor-6-oxo-PGF1α excretion ratio in adult men

Dietary supplementation with a fish oil concentrate (FOC) reduced the endogenous synthesis of prostacyclin (PGI₂), as measured by the excretion of its major urinary catabolite, 2,3-dinor-6-oxo-PGF_1α (PGI₂-M). Thirty-four healthy men (24–57 years old) were given controlled diets and supplements that provided 40% of the energy from fat and a minimum of 22 mg/d of α-tocopherol for two consecutive experimental periods of 10 weeks each. During the experimental periods, the men received capsules containing 15 g/d of a placebo oil (PO) (period 1) or 15 g/d of the FOC (period 2). In addition to the PO or FOC, capsules contained 1 mg of α-tocopherol per g of fat as an antioxidant. The average daily excretion of PGI₂-M during the last week of FOC supplementation (period 2) was 22% less (P = 0.0001) than at the end of the first period. These results are at variance with those reported in comparable human studies conducted by other investigators during the middle and late 1980s. A 20% reduction (P = 0.003) in the 11-dehydrothromboxane B₂ to 2,3-dinor-6-oxo-PGF_1α excretion ratio at the end of period 2 in this study demonstrates that a shift of the n-6 to n-3 polyunsaturated fatty acid ratio from 12.5 to 2.3 brings about a substantial modulation of the eicosanoid system.