The differential allocation hypothesis predicts that reproductive investment will be influenced by mate attractiveness, given a cost to reproduction and a tradeoff between current and future reproduction. We tested the differential allocation hypothesis in the swordtail fish Xiphophorus multilineatus, where males have genetically influenced (patroclinous inheritance) alternative mating tactics ...

Human immunodeficiency virus (HIV) infection has increased considerably among middle-aged women. In this work we reviewed recent studies aimed at identifying possible factors related to HIV infection in climacteric women. Several associated factors are considered, such as: climacteric symptoms, partner's change in sexual behavior in face of new drugs, negotiation for use of condoms in sexual in...

heritability, environmentaland genetic correlations between body weight at hatch (bw0), eight (bw8) and twelve (bw12) weeksof age, body weight at sexual maturity (bwm), age at sexual maturity (afe),the weight of the first egg laid by the hen (ewm), the mean egg weight from 28 to 32 wks (ew28-32) and egg numbers (ens) were estimated by the restricted maximum likelihood method under an animal mod...

A target BW is often used to estimate sexual maturity in beef heifers. The target BW, a percentage of mature BW, is generally an average for the breed, herd, or both. Heifer development is done in groups or herds, and not all heifers respond similarly to the same development regimen. Generally, heifers fed at a higher plane of nutrition gain more BW and tend to have increased pregnancy rates, b...

BACKGROUND Few human studies have evaluated the impact of childhood exposure to organochlorine pesticides (OCP) on pubertal development. OBJECTIVE We evaluated associations of serum OCP concentrations [hexachlorobenzene (HCB), β-hexachlorocyclohexane (βHCH), and p,p-dichlorodiphenyldichloroethylene (p,p´-DDE)] with age at attainment of sexual maturity among boys. METHODS From 2003 through 2...

As the U.S. EPA begins its program to test endocrine-disrupting effects of pesticides, researchers caution that routine screening methods could distort results [EHP 115:1717–1726; Thigpen et al.]. The team discovered that some commercially available rodent diets can cause early sexual maturation similar to that induced by chemical endocrine disruptors. Furthermore, one rat strain commonly used ...