Sexual ornaments, including plumage ornamentation, are often studied during breeding periods even though signal development can take place months earlier. This temporal disconnect potentially obscures the proximate mechanisms that underlie signal expression and development. We studied the correlation between androgen levels and expression of ornamented plumage in adult Red-backed Fairywrens (Ma...

The advent of the molecular techniques used to assign paternity has focused attention on the differences between the social and the genetic mating systems of sexual species. In particular, the interrelations between breeding synchrony-the degree to which the fertility periods of individual females in a population overlap and the degree of extra pair paternity (EPP) in that population, has becam...

The ability of animals to orient based on pheromonal cues in the environment can have significant consequences to their reproductive success and survival. For example, it is hypothesized that snakes use pheromone trails to locate potential mates during the breeding season and to locate winter hibernacula. Numerous studies have demonstrated that snakes are capable of detecting and following pher...

The pea aphid, Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae), shows wing polyphenism (winged and wingless morphs) in its life cycle. The winged morph is adapted for dispersal; its two developmental adult stages (for dispersal and reproduction) are based on its breeding periods. The two morphs show different phototactic behavior and the winged can change its preference to light according t...

the objective of this study was to investigate the effect of birth weight (bw) on future milk production and reproductive performance in iranian holstein cattle. records of holstein cows between 1967 and 2010 were obtained from the animal breeding center of iran. birth weights within each herd were grouped into five categories based on the standard normal distribution curves (z ≤-0.8416, -0.841...

Morphological changes in the sexual organs of the pulmonates were observed throughout a year and correlated with reproductive-cycle periods. Reproductive-organ weights of the snail Megalobulimus abbreviatus were recorded seasonally and gonad sections were analyzed morphologically. The weights were used to obtain the organosomatic index. Mean oocytic diameter and oocytic maturation index were ba...

In an earlier paper' I have reported findings concerning the male reproductive cycle in a population of Andean sparrows, Zonotrichia capensis, at equatorial latitudes. It was shown that each male has a double cycle in the course of a year so that there are two periods of breeding capability, the length of each averaging about four months. Thus any one bird is at reproductive capacity eight mont...