Decisions about whom to mate with can sometimes be difficult, but making the right choice is critical for an animal's reproductive success. The ubiquitous fruit fly, Drosophila, is clearly very good at making these decisions. Upon encountering another fly, a male may or may not choose to court. He estimates his chances of success primarily on the basis of pheromone signals and previous courtshi...

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Androgen insensitivity syndrome (AIS) is a condition that results in the partial or complete inability of the cell to respond to androgens (androgenic hormones) that stimulate or control the development and maintenance of male physiological characteristics by binding to androgen receptors. The unresponsiveness of the cell to the presence of androgenic hormones can impair, or prevent, both the m...

Whiptail lizards provide a unique system to study evolution of brain mechanisms because both ancestral (sexual) and descendant (parthenogenetic) species exist. Parthenogenetic whiptails enable us to avoid the two major confounds in sex differences research - males and females that differ both genetically and hormonally. Parthenogens are females that reproduce clonally, yet display alternately f...

What determines male mating rate? New research is highlighting the potential importance of variation in reproductive organ size in determining the limits of male mating frequency and reproductive success. The accessory glands provide the material required to synthesise the spermatophore in which the sperm, produced by the testes, are packaged. Male mating rate is both phenotypically and genetic...

At the initial stages of sex differentiation (7.5 and 8.5 days of incubation), chick embryo gonads were treated directly with testosterone or estradiol-17 beta in organ cultures. Chemically-defined media containing cholesterol as a steroid precursor were used. The differentiation of gonads in the 10 to 12-day controls, cultured in media containing no hormones, was close to that of gonads of equ...

Artificially selected aggressive (SAL) and non-aggressive (LAL) male house mice were tested in a hexagonal tunnel maze and light-dark preference (LD) box to determine if the bidirectional selection for aggressive behavior leads to a coselection for different levels of trait anxiety. The tunnel maze consists of an open, brightly lit central arena surrounded by a complex system of interconnecting...