Effect of temperature, salinity and food level on sexual and asexual reproduction inBrachionus plicatilis(Rotifera)
✍ Scribed by T. W. Snell
- Publisher
- Springer-Verlag
- Year
- 1986
- Tongue
- English
- Weight
- 585 KB
- Volume
- 92
- Category
- Article
- ISSN
- 0025-3162
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✦ Synopsis
The reproductive response of sexual and asexual female Brachionus plicatilis (Muller) was examined over temperatures ranging from 20 ~ to 40 ~ salinities from 5 to 40%0 S, and food levels from 0.25 to 20ktg Chlorella vulgaris dry-weight per ml. Reduced food levels, as well as temperature and salinity extremes, reduced reproduction of both sexual and asexual females, but did so differentially. Reproduction by sexual females was reduced to a greater extent at environmental extremes than asexual females. The broad, flat reproductive response curve of asexual females extended beyond the limits of the narrower, more sharply peaked curve of sexual females. Thus zones of exclusively asexual reproduction exist at environmental extremes where sexual reproduction is physiologically restricted. These results are corroborated by a comparison of the lifetime fecundity of individual sexual and asexual females over a 20 ~ temperature range. No differences in lifetime fecundity occurred between sexual and asexual females at 18 ~ and 28~ At 38~ however, asexual female fecundity reached its highest level, while sexual female fecundity declined 15%. The appearance of sexual females in rotifer populations is the result of both inducible and repressible factors.
The reproductive physiology of asexual (amictic) and sexual (mictic) females is substantially different. Amictic and mictic females differ in size (Gilbert, 1975;Gilbert and Litton, 1978) and in the types of eggs that they produce (Gilbert, 1983). Their mechanism for oogenesis differs, with amictic females producing d!ploid and mictic females haploid eggs (Gilbert, 1983). Egg shell composition, yolk contents and lifetime fecundity are also markedly different between amictic and mictic females (Gilbert, 1983).
As a result of these differences in reproductive physiology, amictic and mictic females may be expected to respond quite differently to extreme environments. As environmental conditions deviate from optimal, differences between these females are likely to be accentuated. The hypothesis examined in this paper is that amictic and mictic females have different reproductive requirements and their responses to environmental extremes are not identical. I have investigated this hypothesis by comparing the reproductive responses of Brachionus plicatilis amictic and mictic females over a wide range of temperatures, salinities and food levels.