Hormone Specificity, Androgen Metabolism, and Social Behavior

SYNOPSIS. The ability of different sex hormones to activatesocial signals can provide important clues to the biochemicalmechanisms underlying these signals. A pattern of hormone specificityin which testosterone (T) and estradiol (E), but not dihydrotestosterone(DHT), are effective suggests that conversion (aromatization)of T to E in the brain may be involved or required; a patternin which T and DHT, but not E, are effective suggests that conversionof T to DHT may be involved. The hormone specificity of socialsignals in diverse species of vertebrates is reviewed. Aromatizationseems to be of widespread behavioral significance in mammalsandbirds. A role for conversion of T to DHT is suggested forsome signals. Aromatization of T mayalso be important for theactivation of adult female behavior in mammals and lizards,and for the early organization of behavior in mammals and birds.Patterns of hormone specificity differ both across species fora given social signal, and within a given species when differentsignals are compared. An attempt is made to integrate thesefindings by relating patterns of hormone specificity to hormonelevels, steroid receptor and enzyme concentrations and distributions,signal function and dimorphism, and phylogenetic status.     

Effect of Ethylene and Culture Environment on Rice Callus Proliferation

Modifications to the gaseous envelope by callus during culturein Petri dishes were shown to reduce growth and promote necrosisof several rice (Oryza sativa L.) cultivars. Incubatingcallusunder a continuous flow of gas mixtures of known compositionsuggested that the inhibition of growth was caused by the accumulationof ethylene, the depletion of oxygen and, to a lesser extent,the accumulation of carbon dioxide. In order to evaluate theimportance of ethylene accumulation aminoethoxyvinylglycine(AVG), 1-aminocyclopropane-l-carboxylic acid (ACC and silvernitrate (AgNO₃), were added to the nutrient medium and ethylenemeasurements performed during callus culture. Ethylene restrictedcallus growth particularly under high (35 °C) as comparedto moderate (25 °C) temperatures and under illuminated ascompared to darkened incubation. Under illuminated incubationat 25 °C AVG (5 mmol m^–3) and AgNO°(50 mmol m^–3)significantly improvedcallus growth (100 and 60% respectively)while ACC (200 mmol m^–3) significantly decreased growth(40%). AVG and AgNO₃ were less effective under dark incubationat 25 °C where ethylene production was lower. Furthermore,callus growth was significantly better in large as comparedto small culture vessels since the ethylene concentration wasdiluted and more oxygen was available for respiration. Bettercontrol of ethylene and increased oxygen availability couldbe a way ofproducing healthy callus for the formation of embryogenictissues of otherwise recalcitrant cultivars of rice (e.g. IndicaIR42) and may be a way of improving manipulation of other cerealspecies. Key words: 1-Aminocyclopropane-1-carboxylic acid, aminoethoxyvinylglycine, callus, ethylene, Oryza sativa, silver nitrate     

Sex Steroids and the Differentiation of Avian Reproductive Behavior

Experiments in which avian embryos are treated with sex steroidsor steroid antagonists suggest that sexual differentiation ofreproductive behavior (and thus differentiation of the brainmechanisms for such behavior) is controlled by steroids producedby the embryonic gonads. In chickens and Japanese quail, maleshatched from eggs treated with estradiol or testosterone duringincubation are feminized (demasculinized); they fail to exhibitmasculine sexual behavior as adults, and no longer are behaviorallydistinguishable from females. Some evidence suggests that testosteronemay mimic the feminizing action of estradiol by being convertedto an estrogen in the embryonic brain. Genetic female quailexposed to an antiestrogen during embryonic development aremasculinized; they exhibit an increased ability to display themasculine copulatory pattern. Thus the behavior of these speciesis feminized by embryonic exposure to sex steroids, the anhormonal(neutral) sex for behavioral differentiation appears to be themale, and females appear to result from estrogen produced bythe embryonic ovaries. In contrast, sex steroid treatment ofmammals early in development masculinizes behavior, the femaleis the neutral sex, and males result from fetal androgen secretion.These opposite patterns of psychosexual differentiation in birdsand mammals are correlated with a major difference between theavian and mammalian sex-determining mechanism. Implicationsfor other vertebrates are discussed.     

Pre‐zygotic parental environment modulates seed longevity

The potential for the pre‐zygotic plant growth environment to play a role in determining seed longevity was investigated for a species that inhabits arid to semi‐arid Australia. Seed longevity is particularly important for wild populations in fluctuating environments because the longer a seed‐lot is able to survive in the soil seed bank the more likely it is to buffer the population from unpredictable environments. Thus Wahlenbergia tumidifructa plants received wet or dry soil moisture within a warm or cool glasshouse until flowering. Seeds subsequently produced by flowers that opened on the day that plants were moved to a common environment were collected at maturity and longevity assessed by controlled ageing at 60% relative humidity and 45°C. Mean seed longevity was similar for seeds produced by plants that grew in warm‐wet, warm‐dry and cool‐dry conditions (P₅₀ of about 20 days), but extended for plants in cool‐wet conditions (P₅₀ = 41.7 days). Cool temperatures resulted in seeds with a wider distribution of lifespans (σ = 20 days) than warm conditions (σ = 12 days); the large σ caused the extended P₅₀ for cool‐wet plants, but not cool‐dry as a result of a concomitant reduction in initial seed germination (K_i). After moving to the common environment, all plants generated new vegetative material, which went on to produce seeds with similar longevity (P₅₀ approx. 20 days) irrespective of original environment. Visible phenotypic responses of the parent to environmental conditions correlated with longevity and quality parameters of the progeny seeds, suggesting that a parental effect modified seed longevity. Our study provides novel empirical data showing that environmental conditions expected under climate change scenarios may potentially cause seed longevity to decline for a species that inhabits arid to semi‐arid Australia. These negative impacts on population buffering may weaken the storage effect mechanism of species coexistence in fluctuating environments.