Can parthenogenesis offspring reproduce
How mothers prepare their offspring for the future
Water fleas (daphnia) are among the most common crustaceans in stagnant waters. In ponds, ponds, ponds and lakes they feed on plankton algae and themselves serve as food for the predatory organisms of the waters. In short: It is impossible to imagine the food web of these aquatic ecosystems without them. Their success in asserting themselves here is based above all on their mode of reproduction.
As a rule, daphnia reproduce unisexually, via virgin generation (parthenogenesis). From a genetic point of view, water flea populations are therefore clones: the genome of the offspring is identical to that of their mother. Since water fleas do not have any larval stages, the generation times are very short, and this gives a population correspondingly high growth rates: within a few weeks it can grow to over a thousand individuals.
Most of the year, when the conditions are favorable, only female daphnia can be found in the waters, 7 to 12 in number, which lay their fertilized eggs in summer (summer eggs) in a separate brood chamber on their backs. After a few days, the hatched female young are released into the open water. These small copepods then only live a few weeks.
In unfavorable environmental conditions, e.g. beginning dehydration, cold or population pressure (lack of food due to overpopulation), however, some eggs are retuned: the smaller males now hatch from them. The female water fleas can thus switch to bisexual, i.e. bisexual, reproduction. This creates a saddle-shaped structure (ephippium) that contains two permanent eggs above the brood chamber of a female water flea. These have to be fertilized by the males and after the females have molted, they sink to the bottom of the water with their empty shell. The permanent eggs can survive in lake sediments for many years if the environmental conditions are unfavorable for water fleas. Female water fleas always hatch from them.
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