Tardigrades
have a wide variety of reproductive strategies, that are both sexual, and
asexual in nature. Normally, they are dioecious, meaning that they have a
female, and male version, and reproduce sexually. However, there are some
colonies/species where it is reported that there are no males at all.
Although some species
are parthenogenetic, both males and females are usually present, each with a
single gonad located above the intestine. Two ducts run from the testis in males,
opening through a single pore in front of the anus. In contrast, females have a
single duct opening either just above the anus or directly into the rectum,
which thus forms a cloaca.
In
sexual reproduction, females will lay anywhere from 1-30 eggs, which they often
leave in their shed molt. The males will then come along, and fertilize the
eggs by depositing his sperm. . Mating
occurs during the molt with the eggs being laid inside the shed cuticle of the
female and then covered with sperm. A few species have internal fertilization,
with mating occurring before the female fully sheds her cuticle. In most cases,
the eggs are left inside the shed cuticle to develop, but some attach them to
nearby substrate.
The eggs
hatch after no more than fourteen days, with the young already possessing their
full complement of adult cells. Growth to the adult size therefore occurs by
enlargement of the individual cells (hypertrophy), rather than by cell
division. Tardigrades live for three to thirty months, and may moult up to
twelve times.
In
asexual reproduction, as aforementioned, there are no males in some species of
tardigrades. Therefore, they under go parthenogenesis; the females will lay
eggs, which will develop without need of fertilization.
Source:
www.baertierchen.de/wb_dez03.html
www.bioweb.uwlax.edu/bio203/s2008/shifflet_bran/naughtybits.htm
www.en.wikipedia.orh/wiki/tardigrade
www.animals.jrank.org/pages/1728/Water-Bears-Tardigra-BEHAVIOUR-REPRODUCTION.html
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