Pattern matching of age-at-death distributions in paleodemographic analysis

Model age-at-death distributions are generated from fertility and mortality rates derived from two present-day, traditional human societies with widely differing cultural systems: the !Kung hunters-and-gatherers and Yanomamo horticulturalists. Visual examination of these models demonstrates that fertility has more of an effect than mortality on the overall configuration of the age-at-death distributions of stable populations. Comparisons with a late prehistoric Oneota skeletal sample from the American Midwest illustrate how reference age-at-death schedules can be used 1) to identify whether a given skeletal sample approximates an age-at-death distribution expected of an extant human population and 2) to provide a basis for developing further testable hypotheses about the demographic and cultural characteristics of past populations.     

Hunter-gatherer energetics and fertility: A reassessment of the !Kung San

This paper examines the question of why the total fertility rate of the !Kung San hunter-gatherers of the Northern Kalahari desert is as low as 4.69 births. When the intermediate variables involved are examined through the employment of a reproductive equation, it becomes clear that low fecundity is a major issue. Arguments offered previously to explain the low fertility of !Kung women, depending on factors such as nutrition, health status, and lactational practices are insufficient. Drawing upon recent data from sports medicine and endocrinology, I suggest that the pattern of San female energetics in their gathering and subsistence routine has a direct effect upon their fecundity. Such a correlation between activity patterns, endocrine function, and reproductive capacity may also be important for understanding the fertility of other mobile hunter-gatherer groups.     

Steroid hormone interrelationships with territorial aggression in an Arctic-breeding songbird,Gambel's white-crowned sparrow,Zonotrichia leucophrys gambelii

The breeding season is very brief for arctic-breeding passerines, and any interruptions of parental care by aggressive interactions over territory may reduce reproductive success. We tested both the testosterone insensitivity and corticosterone insensitivity hypotheses in the arctic-breeding Gambel's white-crowned sparrow, Zonotrichia leucophrys gambelii. Additionally, we tested whether simulated territorial intrusions (STIs), known to stimulate increases in luteinizing hormone (LH) and testosterone (T) in mid-latitude breeding Z. l. pugetensis, would also be effective in either the early or late phases of the brief breeding season of Z. l. gambelii. Plasma levels of T and LH were high early in the breeding season and declined as egg laying began. Exposure of free-living males to 10 min of STI significantly increased LH but not T secretion. Nonetheless, the pituitary-gonadal axis is sensitive as jugular injection of gonadotrophin-releasing hormone increased plasma T at 10 min relative to saline-challenged controls. T implants failed to increase territorial aggression following STI during incubation. These data are consistent with the T insensitivity hypothesis and contrast sharply with the response of the southerly breeding subspecies, Z. l. pugetensis, in which the territorial response to T administration is retained throughout its relatively long breeding season. However, corticosterone implants during the incubation period decreased territorial aggression during STI. This responsiveness to corticosterone is not consistent with the corticosterone insensitivity hypothesis of stress modulation. Z. l. gambelii retain sensitivity to corticosterone levels that may occur naturally in response to environmental perturbations resulting in suppression of territorial behavior.     

Maternal yolk androgens stimulate territorial behaviour in black-headed gull chicks

Avian eggs contain substantial amounts of maternal androgens. The concentrations of these yolk androgens are affected by the maternal environment, such as the level of social competition, parasite exposure or food conditions. Since yolk androgens have been shown to affect a wide array of offspring traits, they may adjust the chicks to the expected post-hatching environment, but experimental evidence is still scarce. We investigate in colonial breeding black-headed gulls whether high concentrations of yolk androgens, such as those found in environments with high numbers of social interactions, facilitate aggressiveness and territorial behaviour of the chicks. Black-headed gulls are highly suitable for this, as the semi-precocial chicks defend the natal territory and food against intruders. We manipulated yolk androgen concentrations and investigated their role in both within-nest and between-nest aggression. We found that chicks hatching from androgen-treated eggs defended the natal territory more often than their nest mates from control eggs, without increasing sibling aggression. This suggests that variation in yolk androgen concentrations in relation to the social environment of the mother may indeed allow adjustment of the offspring''s behaviour to the expected frequency of territorial interactions with conspecifics post-hatching.     

Association of Cholecystokinin 1 Receptor and β3‐Adrenergic Receptor Polymorphisms with Midlife Weight Gain

We investigated the relationship of polymorphisms in the cholecystokinin 1 receptor [CCK1R; G to T (n‐128), A to G (n‐81)] and the β₃‐adrenergic receptor (β₃‐AR; Trp64Arg) with midlife weight gain. The participants were 1012 Japanese men and women (40 to 59 years of age). Their weight at 18 years old was obtained from a questionnaire. Weight change was defined as the current weight minus the weight at 18 years old. Subjects were grouped into four categories by these genotypes: W/W = noncarriers, W/H = Arg⁶⁴ carriers of the β₃‐AR, H/W = T (n‐128) or G (n‐81) carriers of the CCK1R, H/H = T (n‐128) or G (n‐81) and Arg⁶⁴ carriers. In men, the interaction between the CCK1R and β₃‐AR polymorphisms was significant (two‐way ANOVA, p < 0.05), but neither the CCK1R nor the β₃‐AR was individually associated with weight gain. The H/H group showed a higher possibility of weight gain of 10 kg or more compared with the W/W group in men. The odds ratio for weight gain (≥10 kg) of H/H was 2.54 (95% confidence interval: 1.50 to 4.30) compared with W/W. In women, neither main effect nor interaction was significant. These results suggest that the combination of CCK1R and the β₃‐AR polymorphisms is a contributing factor for midlife weight gain in men.