Evidence of Physiological Mutations in the Cladoceran, Moina macrocopa

Abstract

Extensive breeding experiments with Daphnia longispina (Banta and Wood, and unpublished data) give rather conclusive evidence that recessive mutations having physiological effects accumulate during parthenogenesis in this species. In order to learn whether recessive physiological mutations accumulate similarly in Moina macrocopa, 2 strains of this species were inbred (sexual reproduction). One strain, Banta's Line 1012, had a laboratory history of 1090 parthenogenetic generations before inbreeding, whereas the other line, Banta's Line 1705, had only a short history of 42 parthenogenetic generations before inbreeding. Of 151 ephippial (sexual) eggs obtained from Line 1012, 118 or 78.1% hatched. Of 321 ephippial eggs obtained from Line 1705, 282 or 87.9% hatched. Eggs in both of these groups include several series which fairly consistently showed the same differential rate of hatching as is represented by the totals given above. This is suggestive of the accumulation during long-continued parthenogenesis of semi-lethal mutations in Line 1012. Fifty-five females which hatched from the sexual eggs obtained by inbreeding Line 1012 were compared with 55 parthenogenetically-produced females of Line 1012 as to their viability, reproductive capacity, and other characteristics. Comparisons were made between the individuals of these 2 groups, on the basis of the following specific points: early mortality (died before maturity), sterility (attained maturity but died without producing young), longevity, number of broods of parthenogenetic young produced, and reproductive index (average number of young per mother per day of reproductive life).