ABSTRACT
Human mothers an efficient screening system to eliminate genetically abnormal embryos. However, the incidence of certain birth defects - most notably Down's syndrome - rises with maternal age. Conventional eplanations have focused on a rising production of defective zygotes; in contrast, an evolutionary approach suggest a relaxed maternal screen. Relaxed screening potentially explains the rising incidenee of chromosomal abnormalities in live-births, the incidence of normal embryos in spontaneous abortions, and the incidence of spontaneous abortions with maternal age. If true, then restoration of the screen may be possible, reducing the incidence of birth defects.
ABSTRACT
In choosing how many offspring to rear per cycle, parents commonly starts with more than they really can afford, then allow/encourage some to die. Multiple incentives for overproduction exist. By creating marginal young, parents may: (1) capitalize when unpredictable resources prove unusually rich; (2) supply these as food or servants for core brood members; and/or (3) have a stock of replacements for any core offspring that either fail to survive or develop poorly.
ABSTRACT
Avian brood reduction is widely viewed as a potential source of parent-offspring conflict. Yet empirical evidence belies the existence of conflict; for example, parents create the initial competitive asymmetries that facilitate brood reduction and, in fratricidal species, rarely intervene to stop sibling aggression. Here I examine parent-offspring conflict over brood reduction using a simple game model. Parents establish an initial brood size and level of effort that optimizes their lifetime reproductive success. Offspring can respond by reducing brood size, but if they do so, parents are free to readjust their level of effort. Brood reduction is an evolutionarily stable strategy (ESS) only when offspring fitness is higher following parental readjustment of effort. Model analysis revealed that both conflict and cooperation over brood size are possible ESS(s). Two parental policies of resource allocation among contemporary siblings were examined: equal, in which food is distributed evenly, and despotic, in which food is distributed according to a sibling dominance hierarchy. Parental fitness was diminished slightly by despotic allocation, but the risk of parent-offspring conflict was also diminished. When conflict did occur, the fitness costs and benefits for parents and offspring, respectively, were modest, particularly for despotic allocation. Where parents add "insurance" offspring to the brood, parents and elder offspring may agree over the elimination of redundant offspring, even though the proximate cause of infanticide is sibling rivalry.
ABSTRACT
The theory of parent-offspring conflict (POC) provides a plausible evolutionary foundation for the dissonant behavioral interactions commonly observed between adults and their progeny. It has been modelled extensively, but its predictions for phenotypes are murky and have been subjected to scant empirical testing. The least ambiguous cases are likely to involve taxa where offspring exert real power. Recent experimental work indicates that worker bees manipulate brood sex ratios differently from the queen. By contrast, most studies of avian brood reduction and mammalian 'weaning conflict' remain open to multiple interpretations. In general, POC may owe its current hegemony to the paucity of alternative explanations for parent-offspring squabbles. Reassessments of basic assumptions about what both parties 'really want' need to be linked to experimentation, field-oriented modelling and pluralism for this provocative theory to become broadly useful.
ABSTRACT
Minute dissection of carcasses infected with Taenia saginata cysts revealed that heart and masticatory muscles were more heavily and more frequently infected with Taenia saginata cysts than were any other muscle groups. Increasing the number of inspection cuts in the heart and masseter muscles, while omitting cuts in such sites as the diaphragm, during meat inspection would increase the efficiency in detecting beef cysticercosis. Complete dissection of cattle found to have a single viable or dead cyst by routine inspection revealed dead or viable cysts in portions of the carcass not routinely examined. These findings justify the recent change in routine meat inspection procedures whereby all carcasses with a single cyst (whether viable or dead) are now cooked or refrigerated, instead of having the offending cysts excised.
