Induction of female sex pheromone production in male houseflies by ovary implants or 20-hydroxyecdysone

Implanting ovaries or injecting 20-hydroxyecdysone into male houseflies induced sex pheromone production, including (Z)-9-tricosene (muscalure), 9,10-epoxytricosane and (Z)-14-tricosen-10-one, which normally occurs only in vitellogenic females. Control males did not produce detectable amounts of these compounds. Injection of 20-hydroxyecdysone (5 μg/insect per day) for 3 days resulted in the accumulation of 1.81 μg/insect of (Z)-9-tricosene, 0.97 μg/insect of 9,10-epoxytricosane and 0.12 μg/insect (Z)-14-tricosen-10-one. Multiple injections of 20-hydroxyecdysone at doses as low as 50 ng resulted in the accumulation of 23:1, C₂₃ epoxide and C₂₃ ketone; shifted the distribution of label within the alkenes from 27:1 to 23:1 and decreased the amount of label in the hydrocarbon fractions as alkenes. Structures of the C₂₃ alkene and epoxide produced by the males were verified by gas chromatography-mass spectrometry. Radioactivity from [1-¹⁴C] acetate was incorporated into the C₂₃ alkene, epoxide and ketone in male insects after ovaries were implanted or they were injected with 20-hydroxyecdysone. Synthesis of the C₂₃ pheromone components decreased rapidly within several days after the administration of 20-hydroxyecdysone ceased, indicating that the enzymes involved in sex pheromone production were not permanently induced by hormone treatment. Ecdysone was also effective in initianing pheromone production in males, whereas inokosterone and cholesterol were not effective. Data presented demonstrate that male houseflies possess the metabolic capability to produce the sex pheromone components, and this suggests that 20-hydroxyecdysone alters the production of cuticular hydrocarbons such that the C₂₃ sex pheromone components become major products.     

The coevolution of male and female genitalia in a mammal: A quantitative genetic insight

Male genitalia are among the most phenotypically diverse morphological traits, and sexual selection is widely accepted as being responsible for their evolutionary divergence. Studies of house mice suggest that the shape of the baculum (penis bone) affects male reproductive fitness and experimentally imposed postmating sexual selection has been shown to drive divergence in baculum shape across generations. Much less is known of the morphology of female genitalia and its coevolution with male genitalia. In light of this, we used a paternal half-sibling design to explore patterns of additive genetic variation and covariation underlying baculum shape and female vaginal tract size in house mice (Mus musculus domesticus). We applied a landmark-based morphometrics approach to measure baculum size and shape in males and the length of the vaginal tract and width of the cervix in females. Our results reveal significant additive genetic variation in house mouse baculum morphology and cervix width, as well as evidence for genetic covariation between male and female genital measures. Our data thereby provide novel insight into the potential for the coevolutionary divergence of male and female genital traits in a mammal.     

Population differences in female resource abundance, adult sex ratio, and male mating success in Dendrobates pumilio

In this study I examined the relationship among abundance ofreproductive resources, population density, and adult sex ratioin the strawberry dart-poison frog, Dendrobates pumilio, andhow these variables in turn influence the mating system, malereproductive success, and sexual selection. I studied the matingbehavior in two populations of D. pumilio living in a primaryand secondary rainforest on the Caribbean slope of Costa Rica.The abundance of tadpole-rearing sites (reproductive resourcesfor females) was approximately 10-fold higher in the secondary forest. Accordingly, the population density was higher and theadult sex ratio was strongly female biased in the secondaryforest, whereas the adult sex ratio was even in the primaryforest. The female-biased sex ratio was associated with a higherlevel of polygyny and higher male mating and reproductive successin the secondary forest. In contrast, the level of polyandrydid not differ between habitats. As expected, the opportunityfor sexual selection on male mating success was lower in thesecondary forest, the habitat with high female density. Inconclusion, my results suggest that ecological variables suchas resource availability have a great impact on the matingsystem and sexual selection through their effect on population structure. Moreover, the results of this study give furtherevidence that the opportunity for sexual selection is influencedby the adult sex ratio and hence by the operational sex ratioin a population.     

The distribution of tyrosine hydroxylase immunoreactivity in the brains of male and female zebra finches

A system of brain nuclei controls song learning and behavior in zebra finches (Poephila guttata). The size of song-control nuclei are much larger in males, which sing, than in females, which do not sing. This study examined the distribution of fibers, terminals, and cell bodies that are immunoreactive for tyrosine hydroxylase (TH) (the rate-limiting enzyme in the synthesis of catecholamines) in song-control nuclei of adult males and females and juvenile males. In addition, the broad pattern of TH staining throughout the brain was described. There was a sex difference in TH immunoreactivity within song-control nuclei: males had light to moderate staining in all three cortical nuclei examined, whereas females had little or no label in corresponding areas [lateral magnocellular nucleus of the anterior neostriatum (IMAN), higher vocal center (HVC), and robust nucleus of the archistriatum (RA)]. The song-control nucleus area X (X), located in the striatum of avian basal ganglia, was more darkly stained than the surrounding striatum only in males; X was not defined by more intense immunoreactivity in females and hence could not be visualized. There were no apparent differences in TH staining in males ranging in age from 50 days to adulthood (>90 days). Outside of the song-control system there were no substantive differences as a function of sex or age in the pattern or intensity of TH labeling. Major areas of telencephalic staining included the striatal region of basal ganglia, which was covered with dense, fine-grained label, and the septum, where cell bodies were encircled by extremely well-labeled thick processes. In the diencephalon, the preoptic area and hypothalamus included a complex pattern of darkly stained somata and fiber and terminal labeling. Darkly stained somata surrounded the pretectal nucleus, and labeled processes ramified throughout the superficial layers of the optic tectum. The midbrain and hindbrain contained a dense plexus of extremely dark cell bodies corresponding to mammalian substantia nigra, adjacent tegmental areas, and locus ceruleus. Labeled hindbrain cells were also seen in the pontine region, around nucleus solitarius, and in the ventrolateral medulla. © 1993 John Wiley & Sons, Inc.     

Change of the heterogametic sex from male to female in the frog

Two different types of sex chromosomes, XX/XY and ZZ/ZW, exist in the Japanese frog Rana rugosa. They are separated in two local forms that share a common origin in hybridization between the other two forms (West Japan and Kanto) with male heterogametic sex determination and homomorphic sex chromosomes. In this study, to find out how the different types of sex chromosomes differentiated, particularly the evolutionary reason for the heterogametic sex change from male to female, we performed artificial crossings between the West Japan and Kanto forms and mitochondrial 12S rRNA gene sequence analysis. The crossing results showed male bias using mother frogs with West Japan cytoplasm and female bias using those with Kanto cytoplasm. The mitochondrial genes of ZZ/ZW and XX/XY forms, respectively, were similar in sequence to those of the West Japan and Kanto forms. These results suggest that in the primary ZZ/ZW form, the West Japan strain was maternal and thus male bias was caused by the introgression of the Kanto strain while in the primary XX/XY form and vice versa. We therefore hypothesize that sex ratio bias according to the maternal origin of the hybrid population was a trigger for the sex chromosome differentiation and the change of heterogametic sex.     

Regulation of urine marking in male and female mice: effects of sex steroids

Effects of sex steroids on urine-marking activity were studied in male, female, and neonatally androgenized female mice. Urine marking was estimated by suspending ceramic tubes that were connected in a horizontal row with a steel rod into the home cage of an isolated mouse. Intact males showed high marking activity, which was diminished after castration. Both testosterone propionate (TP) and estradiol benzoate (EB) were effective in restoring the marking activity of castrated males, while 5-alpha-dihydrotesterone (DHT) did not have any stimulative effects. Intact normal females showed quite low marking activity and ovariectomy further depressed it. TP and DHT enhanced the marking of ovariectomized females, but EB restored the activity only to the preovariectomy level. In intact females which were neonatally androgenized, the marking activity was much higher than that of normal females. The pattern of the change induced by gonadectomy and hormone treatment in these females resembled that in males. Thus, ovariectomy reduced the activity and both TP and EB restored the level. These results indicate that the sexual dimorphism in the urine marking in mice is primarily determined by hormonal environment during early postnatal age. Hormonal control of scent marking is discussed in relation to the studies in other rodents.     

Mated pairs of owl monkeys (Aotus nancymaae) exhibit sex differences in response to unfamiliar male and female conspecifics

In socially monogamous species, mate‐guarding could be a reproductive strategy that benefits both males and females, especially when males contribute to parental care. By actively guarding mates, males may reduce their chances of being cuckolded, whereas females that mate‐guard may reduce the likelihood that their mates will desert them or acquire additional mates, and hence limit or reduce paternal care of offspring. Owl monkeys (Aotus spp.) are socially monogamous with biparental care of young and, hence, potential beneficiaries of mate‐guarding. We presented mated pairs of captive owl monkeys (A. nancymaae) with unfamiliar male and female conspecifics, to determine if either member of the pair exhibits intraspecific aggression toward an intruder or stays close to its mate, behaviors indicative of mate‐guarding. Male mates were more responsible for the maintenance of close proximity between mates than females. Male mates also exhibited elevated levels of behavior that signify arousal when presented with a male conspecific. These responses by mated male owl monkeys are consistent with patterns that may help prevent cuckoldry. Am. J. Primatol. 72:942–950, 2010. © 2010 Wiley‐Liss, Inc.