A threshold effect takes place in situations where the relationship between an outcome variable and a predictor variable changes as the predictor value crosses a certain threshold/change point. Threshold effects are often plausible in a complex biological system, especially in defining immune responses that are protective against infections such as HIV-1, which motivates the current work. We st...

The extent to which key biological processes, such as sex determination, respond to environmental fluctuations is fundamental for assessing species' susceptibility to ongoing climate change. Few studies, however, address how climate affects offspring sex in the wild. We monitored two climatically distinct populations of the viviparous skink Niveoscincus ocellatus for 16 years, recording environ...

Decisions over what sex ratio to produce can have far-reaching evolutionary consequences, for both offspring and parents. However, the extent to which males and females come into evolutionary conflict over aspects of sex allocation depends on the genetic system: when genes are passed to the next generation unequally by the two sexes (as in haplodiploidy, for example), this biased transmission c...

Trivers and Willard predicted that when parental condition has differential effects on the fitness of male and female offspring, parents who are in good condition will bias investment toward the sex that benefits most from additional investment. Efforts to test predictions derived from Trivers and Willard's model have had mixed results, perhaps because most studies have relied on proxy measures...

We test two models of adaptive adjustment of birth sex ratios that are expected to apply to Cercopithecine primate species. It has been predicted that when maternal investment differentially influences the reproductive success of male and female offspring, females in good condition will bias investment in favour of the sex that gains the greatest fitness returns from additional investment. This...

Effects of environmental pollutants are most obvious when mortality is increased. However, there are other nonlethal factors that may affect population size significantly. Endocrine disruption as a mechanism of action for pollutants recently has received much attention. Observations of effects likely caused by endocrine disruptors in pulp mill effluents have been made on several fish species, e...

Negative frequency-dependent selection should result in equal sex ratios in large populations of dioecious flowering plants, but deviations from equality are commonly reported. A variety of ecological and genetic factors can explain biased sex ratios, although the mechanisms involved are not well understood. Most dioecious species are long-lived and/or clonal complicating efforts to identify st...

Because workers in colonies of eusocial Hymenoptera are more closely related to sisters than to brothers, theory predicts workers should bias investment in reproductive broods to favour reproductive females over males. However, conflict between queens and workers is predicted. Queens are equally related to daughters and sons, and should act to prevent workers from biasing investment. Previous s...

Seeds of 200 accessions of alfalfa (Medicago sativa L.) were provided from Iraniannatural resource gene bank and were sown as drilled plot using alpha designs/unreplicatedwith 2 repeated entries within all of 10 blocks under dry land farming system in agriculturalresearch center of Hamadan, Iran during 2009 to 2010. The data were collected and analyzedfor plant height, stem number, leaf stem ra...

The sex ratio of the local population influences mating-related behaviours in many species. Recent experiments show that male-biased sex ratios increase the amount of financial resources men will invest in potential mates, suggesting that sex ratios influence allocation of mating effort in humans. To investigate this issue further, we tested for effects of cues to the sex ratio of the local pop...