Stabilizing Selection on Egg Size in the Euphausiid, Thysanoessa Raschii (M. Sars, 1861)(Euphausiacea) in the Barents Sea.

The size of the eggs (alive and dead) of the euphausiid, Thysanoessa raschii (M. Sars, 1864) was studied in the various parts of the Barents Sea. There is a relationship between mortality and size in euphausiid eggs. Dead embryos dominated among eggs with both minimal or maximal diameters (embryos smaller than 300μm and bigger than 350μm; perivitelline space smaller than 25μm and bigger than 50μm). We suggest that this size-dependent mortality of euphausiid eggs is a result of stabilizing selection, thus establishing an equilibrium between egg size and number of eggs (=fecundity) in the Barents Sea population of T. raschii . [ABSTRACT FROM AUTHOR]