Reproductive endocrinology of the Wandering Albatross Diomedea exulans in relation to biennial breeding and deferred sexual maturity

first_imgThe reproductive endocrinology of the Wandering Albatross Diomedea exulans was studied at South Georgia to investigate the potential endocrine correlates of biennial breeding and of the acquisition of sexual maturity. Gonads of breeding birds and of known‐age immature birds of both sexes were examined by laparoscopy throughout the period that they were at the nest site. Blood samples, subsequently analysed to determine concentrations of luteinizing hormone (LH), prolactin, progesterone, testosterone and oestradiol‐17/i, were obtained from samples of breeding birds of both sexes at regular intervals from first arrival until the chicks fledged nearly a year later. Before laying in December, breeding birds had mature testes and ovarian follicles and high concentrations of LH, prolactin and sex steroids. Gonadal regression and a rapid drop in hormone levels (except for LH in females) occurred in early incubation (January). Testes (and follicles to a lesser extent) enlarged in mid‐incubation, coinciding with high levels of LH and increases in prolactin and testosterone. Gonads finally regressed completely near hatching time. LH, prolactin and testosterone remained at low levels throughout chick rearing (April to November), but females had several periods of active progesterone and oestradiol secretion, and progesterone was detectable in males only late in the chick‐rearing period. Although some changes in hormone levels are difficult to explain, the patterns are fairly typical of temperate birds. The persistence of progesterone secretion in both female breeders and non‐breeding ‘immature’ birds is viewed as part of a mechanism inhibiting an ovary from becoming vitellogenic. Although testis size and testosterone concentrations increased with age in immature males (of ages 4–10 years), birds of 5 years and older are probably physiologically mature, even though breeding does not start until they are 7 years of age and only half an age group has bred by an age of 11 years. Immature females (of age 4–7 years) had undeveloped follicles, very low oestradiol concentrations but high progesterone levels, providing further support for the role of this hormone in inhibiting gonadotropin secretion. The condition of the female is therefore probably decisive in determining when a pair first attempts to breed but it is unknown what factors initiate normal ovarian development.last_img read more

Aerial dispersal of lichen soredia in the maritime Antarctic

first_imgAn aerobiological monitoring programme was carried out for over a year on Signy Island, South Orkney Islands, Antarctica. Collections were made using arrays of rotorod samplers at three sites. Lichen soredia were found to be the most abundant air borne propagules, more so than ascospores, the sexual propagules of lichen fungi. The dominance of soredia over ascospores appeared to decrease with increasing maturity of fellfield sites. No correlations were found with temperature, relative humidity or wind speed. Collections at 1 m above ground level were shown not to be significantly different to those at 0·15 m at two of the sites. Size range distribution also differed at two of the sites. Soredial clumps in excess of 100 μm in diameter were collected at 1 m above ground level and at some distance from potential source plants, though most fell in the range 30–60 μm. Peaks in numbers of air borne soredia were found after winter snow melt, demonstrating that soredial production continues at subzero temperatureslast_img read more