Age At Sexual Maturity Research Articles

Estimating mean age at sexual maturity in the crabeater seal (Lobodon carcinophagus)

Mean age at sexual maturity (ASM) in crabeater seals (Lobodon carcinophagus) was estimated according to two different methods. Samples were from 1964, 1977, and 1989. Using the first method, the estimated ASM in 1989 was 6.57 ± 0.82 years, which was considerably older than reported earlier. This estimate is the only one existing for crabeater seals that can be used to compare populations and species. The first method was based on the maturity rate at age. Behavioural segregation of mature and immature seals could give skewed maturity rates in samples. Because the 1964 and the 1977 samples were collected during a season when segregated behaviour was expected (breeding season), results from these years were not comparable with the 1989 estimate (collected during moult). The second method does not produce absolute values of ASM, but the estimates could be used as indices of ASM within a specific population. There was a statistically significant increase in the ASM index in 1989 (4.93 ± 0.57), compared with 1964 (3.75 ± 0.31) and 1977 (3.80 ± 0.44). This is a strong indication of a true increase in ASM in crabeater seals. Recommendations are made to improve future procedures for studying reproductive status in seals.

Reproduction and reproductive seasonality in Danish harbour porpoises,Phocoena Phocoena

Abstract The reproduction and reproductive seasonality of 365 Danish harbour porpoises (Phocoena phocoena (L.)) incidentally caught in various gill nets or stranded, was studied. The animals were collected from all Danish waters throughout the year from 1985 to 1991. Ovulations were only found in the left ovary whilst the right was permanently sub mature. Large vesicular follicles are found in July, with the largest size (14 mm) in the end of July. Developing corpora lutea with mean diameters of 13.5 mm were found in early August. These findings suggest that ovulation and conception occur in late July and early August. Testicular mass and spermatogenic activity peak in July. Foetuses are first detectable in early September. Gestation lasts for approximately 10.5 months and parturition occurs in the middle of June and early July. Age at sexual maturity (ASM) was estimated by the sum of fraction immature method for both females and males. The average age at attainment of sexual maturity for females was 3.64...

Studies on the Sexual Cycle in Birds. VI. Effects of White, Green, and Red Lights of Equal Luminous Intensity on the Testis Activity of the European Starling (Sturnus vulgaris)

Studies on the Sexual Cycle in Birds. VI. Effects of White, Green, and Red Lights of Equal Luminous Intensity on the Testis Activity of the European Starling (Sturnus vulgaris)