Video Transcript
When conditions are favorable, the
freshwater crustacean Daphnia shown in the figure reproduces asexually by
producing offspring that develop from unfertilized diploid eggs. What is the name of this
process?
The question asks us to name the
process by which Daphnia reproduce asexually. You may already be familiar with
some of the many methods of asexual reproduction found in the natural world,
including binary fission, budding, regeneration, vegetative propagation, the use of
spores, and parthenogenesis. Let’s first take a brief look at
the life cycle of Daphnia in order to determine the method of asexual
reproduction described in the question.
During most of the growth season,
Daphnia reproduce asexually. Mature females produce unfertilized
diploid eggs, which are held in a part of her body called the brood chamber. Because no male gametes have fused
with the eggs, both sets of chromosomes contain genes from the mother. Therefore, the offspring that arise
from these eggs will be genetically identical to their mom and to each other. After one to two days, the eggs
hatch while still inside the brood chamber and are born about three days later. The offspring, which are usually
all female, go through about four to six stages of larval development. Once they are mature, they begin to
produce their own unfertilized diploid eggs.
Changing environmental conditions
such as overcrowding, food scarcity, or cooler water temperatures can stimulate
females to enter asexual phase of reproduction. Cycling between sexual and asexual
reproduction allows organisms to take advantage of the best parts of each. They can rapidly grow their
populations in the asexual phase and increase genetic variation in the sexual
phase. The particular type of asexual
reproduction exhibited by Daphnia is called parthenogenesis, in which
offspring are produced from unfertilized eggs. The definition of parthenogenesis
matches the description given in the question. Therefore, the name of the process
in which Daphnia produce offspring asexually from unfertilized diploid eggs
is parthenogenesis.
