PubMed · 4969566
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N D Lehner, B C Bullock, T B Clarkson. 1968. Ascorbic acid deficiency in the squirrel monkey.. https://doi.org/10.3181/00379727-128-33053
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Mammal life history traits relating to growth and reproduction are extremely diverse. Sibling rivalry may contribute to selection pressures influencing this diversity, because individuals that are relatively large at birth typically have an advantage in competition for milk. However, selection for increased growth rate is likely to be constrained by kin selection and physiological costs. Here, we present and test a model examining the ESS (evolutionarily stable strategy) balance between these constraints and advantages associated with increased prenatal growth in mammal sibling rivalry. Predictions of the model are supported by results of comparative analyses for the Carnivora and Insectivora, which demonstrate an increase in prenatal growth rate with increasing intensity of postnatal scramble competition, and a decrease in postnatal growth rate relative to size at birth. Because increased prenatal growth rates are predicted to select for reduced gestation length under certain conditions, our study also indicates that sibling rivalry may contribute to selection pressures influencing variation in altriciality and precociality among mammals.
The aim of the present study was to characterize ovarian follicular development and steroid concentrations during postpartum and the estrous cycle of Brangus Ibagé cows (3/8 Nelore + 5/8 Aberdeen Angus) with different levels of fertility. Cows were classified as having high or low fertility according to the calving interval (CI). The average CI of the herd from which cows used in this study were selected was 404.6+/-5.44 and 711.2+/-20.89 days for the high and low fertility groups, respectively. Four cows of high fertility and five cows of low fertility had calves removed between 70 and 100 days after parturition. Ovarian activity was monitored daily by ultrasound for 16 days after calf removal. Days to emergency of the first follicular wave after calf removal, number of follicles with diameter >9 mm, growth rate of largest follicle, maximum diameter of largest follicle, length (days) and number of follicular waves were recorded. During this period, blood was collected daily for measurements of serum progesterone (P(4)) and estradiol (E(2)) concentrations. In another experiment, ovarian activity and P(4) and E(2) concentrations were examined during estrous cycle in five cows of high fertility and four cows of low fertility. Ovarian activity and steroid concentrations were assessed from the day prior to estrus to the 15th day of the estrous cycle (estrus = day 0). In postpartum cows of high fertility, the total number of follicles >5mm and the maximum diameter of the largest follicle were higher than in cows of low fertility (P < 0.05). Concentrations of P(4) and E(2) did not differ between groups in the postpartum cows. However, E(2) increased 5 days after calf removal (around 90 days of postpartum) in the high fertility group, followed by an increase in P(4) with average values indicating ovulation around 100 days postpartum. In cycling cows, the profile of follicular development was similar between cows of high and low fertility. There was no difference between groups for number of follicles >5mm, but the day effect was significant (P < 0.01). Plasma concentrations of P(4) and E(2) were similar in both groups. These data suggest that cows, from a population raised in the same environment have different fertility as a consequence of individual physiological characteristics.
BACKGROUND: The insulin/IGF-1 signaling pathway controls cellular and organismal growth in many multicellular organisms. In Drosophila, genetic defects in components of the insulin signaling pathway produce small flies that are delayed in development and possess fewer and smaller cells as well as female sterility, reminiscent of the phenotypes of starved flies. RESULTS: Here we establish a causal link between nutrient availability and insulin-dependent growth. We show that in addition to the Drosophila insulin-like peptide 2 (dilp2) gene, overexpression of dilp1 and dilp3-7 is sufficient to promote growth. Three of the dilp genes are expressed in seven median neurosecretory cells (m-NSCs) in the brain. These m-NSCs possess axon terminals in the larval endocrine gland and on the aorta, from which DILPs may be released into the circulatory system. Although expressed in the same cells, the expression of the three genes is controlled by unrelated cis-regulatory elements. The expression of two of the three genes is regulated by nutrient availability. Genetic ablation of these neurosecretory cells mimics the phenotype of starved or insulin signaling mutant flies. CONCLUSIONS: These results point to a conserved role of the neuroendocrine axis in growth control in multicellular organisms.