Cortisol advantage of neighbouring the opposite sex in utero.

Population sex ratios naturally fluctuate around equality. It is argued that the production of an equal number of male and female offspring by individual parents should be favoured by selection, if all costs and benefits are equal. Theoretically, an even sex ratio should yield the highest probability for a fetus to be adjacent to a fetus of the opposite sex in utero. This may cause developmental costs or benefits that have been overlooked. We examined the physiological and developmental parameters associated with in utero sex ratios in the nutria (Myocastor coypus), an invasive wildlife species with a strong reproductive output. Using hair testing, we found that litters with even sex ratios had the highest average cortisol levels. Fetuses neighbouring the opposite sex exhibited longer trunks than those neighbouring the same sex, which might imply better lung development. Our results are the first, to our knowledge, to link intra-utero sex ratios and fetal cortisol and suggest that fetal cortisol might be a mechanism by which even sex ratios are maintained via developmental advantages.

Assessment of pollution in road runoff using a Bufo viridis biological assay.

Road runoff is a major source of environmental pollution, significantly threatening nearby aquatic habitats. Chemical analyses indicate high pollutant concentrations in the road's "first flush", but bioassays are more advantageous for addressing the cumulative effects of the numerous pollutants within the runoff. We used Bufo viridis embryos and larvae to assess the toxicity of road runoff from two major highways in Israel. We show, for the first time, that exposure to midseason runoff not only has an adverse effect on growth and development rates of B. viridis larvae but can also lead to increased rates of morphological deformations. Seasonal first flushes, despite having higher metal concentrations, did not adversely affect the toad larvae, apparently due to a counter effect of organic matter that potentially served as a supplementary energy resource. Road runoff can be a major cause for a qualitative decrease in the quality of aquatic habitats threatening amphibians in Israel.

Brain mast cells lack the c-kit receptor: immunocytochemical evidence.

Mast cells are reported to differ from other cells of the hematopoietic lineage in that as mature cells, they retain the c-kit receptor, and are thus capable of responding to the stem cell factor (SCF) ligand. SCF is important for development and survival of mast cells. In this study, c-kit expression was examined immunocytochemically in the brains of mice, rats and doves. The results indicate that brain mast cells lack the c-kit receptor; those of the leptomeninges and other connective tissues are a mixed population of c-kit positive and negative cells. The mechanisms whereby brain mast cells might survive in the absence of SCF-c-kit signaling are discussed.

Mole-rat harderian gland secretions inhibit aggression

The harderian gland secretions of mole-rats, Spalax ehrenbergiusually released by self-grooming, include odorous substances which are sex dependent. Male secretions were the most attractive to both sexes, while female secretions were attractive to males but not to other females. The rate of attacks by females towards intact males was higher than towards males whose harderian gland had been removed. However, grooming by intact male mole-rats decreased the rate of attacks by their opponents, while grooming by males without harderian glands did not; thus the male harderian secretions appear to have appeasement qualities. Grooming by females with and without harderian glands failed to reduce aggression. Unlike intact males, those without harderian glands had almost no volatiles on their fur, and thus are probably not considered to be a threat to conspecifics. Gas chromatography spectra showed that substances of harderian origin were added to the fur during grooming. Some of these substances remained on the fur long after the animal ceased grooming, and appear to give the animal its specific odour, but some volatile substances peaked briefly after grooming, and were probably responsible for the decline of aggression that occurred after grooming. Although grooming has long been considered to be a displacement activity, we suggest that in the mole-rat its performance is too risky to be merely this, and it has acquired the meaning of appeasement through the release of chemical cues.Copyright 1997 The Association for the Study of Animal Behaviour1997The Association for the Study of Animal Behaviour

Putative melatonin receptors in the blind mole rat harderian gland.

The blind mole rat (Spalax ehrenbergi) displays daily and seasonal rhythms. Melatonin, secreted nocturnally by the pineal gland, is also produced in the harderian gland and affects its morphology in rodents. We report here on the presence of putative melatonin receptors in the blind mole rat harderian gland, located in the microsome-enriched fraction of the cells. Equilibrium 125I-melatonin binding studies indicated high- and low-affinity melatonin binding sites in the female (apparent Kd 10 pM and 2.4 nM, respectively) and low-affinity sites in the male (apparent Kd 2.6 nM) mole rat. The binding sites were not significantly affected by season. Castration increased the density of high-affinity binding sites in males and low-affinity binding in females. 125I-melatonin binding to the gonadectomized mole rat preparation was inhibited by serotonin > 2-iodomelatonin > or = memelatonin > 5-methoxytryptamine. The guanine nucleotide analogs, guanosine 5'-O-[3-thio-triphosphate] and guanosine 5'-O-[2-thio-diphosphate], inhibited specific 125I-melatonin binding, whereas 5'-guanylyl imido-diphosphate was less potent. These results indicate for the first time the presence of GTP-sensitive melatonin binding sites in the blind mole rat harderian gland, and suggest that their expression is under control of sex steroids.

Grooming secretions and seasonal adaptations in the blind mole rat (Spalax ehrenbergi).

The postulated thermoregulatory function of grooming in the "blind" mole rat (Spalax ehrenbergi), a solitary, highly aggressive subterranean rodent, was tested by subjecting individuals to extreme hot and cold environments and measuring their grooming frequency and thermoregulatory capacity. It was found that exposure to heat stress during both the winter and the summer failed to elicit grooming in isolated mole rats, even though their body temperature was significantly elevated. Thus, unlike Mongolian gerbils (Meriones unguiculatus), mole rats do not seem to have a mechanism for lowering body temperature by grooming. However, at low temperatures, grooming behavior significantly increased during both seasons, although a decline in body temperature was recorded only during the summer. Because grooming in mole rats expresses Harderian lipids onto the fur, it is suggested that in the winter, under cold stress, this behavior might prevent a drop in body temperature through spreading insulating Harderian lipids.

Quantitative histomorphology of the blind mole rat harderian gland.

Anatomical, histological and morphometric studies have been performed on the harderian gland and its surroundings in the blind mole rat (Spalax ehrenbergi). The gland is tubuloalveolar with no true duct system. All ducts within the gland are formed by a single epithelial cell type and drain into a wide secretory duct. This opens into the conjunctival sac which serves as a reservoir for harderian secretions. Drainage from the conjunctival sac follows 2 possible routes: one through the nasolacrimal duct to the external nasal cavity, the other through a unique excretory duct that emerges from the anteromedial part of the conjunctival sac and runs through the dermis to the skin, opening at the base of a hair follicle. The function of this newly described duct is discussed. Morphometric studies revealed that the lumen volume fraction in the female, slightly smaller than that of the male during the summer, becomes significantly greater during the winter breeding season. The dimorphism and seasonal variations found in the gland acini suggests that the gland may be implicated in pheromone production.