Wyniki wyszukiwania - Biblioteka Nauki

Nowa wersja platformy, zawierająca wyłącznie zasoby pełnotekstowe, jest już dostępna.
Przejdź na https://bibliotekanauki.pl

Ograniczanie wyników

1 Polish Journal of Ecology

1 2006

1 Jakubik B.

Znaleziono wyników: 1

Liczba wyników na stronie

Wyniki wyszukiwania

Sortuj według:

Ogranicz wyniki do:

Reproductive pattern of Viviparus viviparus (Linnaeus 1758) (Gastropoda, Viviparidae) from littoral aggregations in a through-flow reservoir (Central Poland)

100%

Jakubik B.

tom Vol. 54, nr 1

39-55

Reproductive pattern of V. viviparus was studied in the years 1990-1994. The study was carried out in selected sites of the Zegrzyński Reservoir (Central Poland) and in outlet zones of its tributaries. Distinct prevalence of females over males was found. Sex ratio varied seasonally. In spring the percentage of females was the highest and decreased later on. In spring, reservoir sites were dominated by females of the III (12.1-25.0 mm width and 12.1-20.0 mm height ) and IV (25.1-35.0 mm width and 20.1-35.0 mm height) size classes and by males of the II (8.1-12.0 mm width and height) and III (12.1-25.0 mm width and 12.1-20.0 mm height ) size classes. In the outflow zones of rivers size distribution was similar. The lowest percentage of the I (shells of the young were < 8.0 mm long and had a hair cover characteristic for young snails) size class was noted in all sites for both sexes. Fertile females dominated in both habitats. In the reservoir their contribution ranged from 50 to 90% and was the highest in spring (c. 60-70%), still increased in summer (to c. 80-90%) and decreased in autumn to c. 50%. Mean number of embryos per female in the reservoir varied between 1.3 and 10.0 with the maximum recorded number of 35 embryos. In the outlet zones of rivers (where snail density was higher than in the reservoir) a higher percentage of fertile females (over 80%) was noted in both spring and summer. In autumn this percentage decreased to c. 60%. Mean number of embryos per female was also higher there than in the reservoir. It varied between 1.8 and 24.9 with the maximum number of 63 embryos per female. Higher numbers (mean and maximum) of embryos per female in the outlet zones persisted on all sampling occasions. Mean number of embryos increased with the shell size. The results suggest that reproductive pattern is the most influential factor affecting populations of Viviparus. This is mainly associated with the snails. viviparity which results in controlling reproduction, appearance of young all year round and parental care over juveniles.