A complex view of breeding strategy and life-history in one population of Sphaerium corneum Linnaeus 1758 (Bivalvia: Sphaeriidae): Sphaerium corneum breeding strategy
Abstrakt
A population of viviparous freshwater bivalve Sphaerium corneum from an artificial mill race subjected to irregular changes of water level was investigated using quantitative monthly sampling, paraffin histological sections and chromosome preparations. Unlike most of the previously studied populations of the genera Sphaerium and Musculium, the one presented in this paper exhibits less synchronised life-spans.
Despite two main birth periods, many specimens release their broods also individually during the season. An adult usually breeds at least twice in a season.
The life span is more than one, more often one and half year. All age and length classes are able to overwinter.
Spermatogenesis and oogenesis apparently proceed simultaneously from spring to autumn and they occur also in fully developed larvae which are still retained inside their parents' gills. Relationship between the observed breeding strategy and the fluctuations of environment was discussed, as well as the intraspecific and interspecific variation in life-history traits within Sphaeriidae.