Mechanisms of asexual reproduction
Invertebrates carry out the several
simplest forms of asexual reproduction.
Budding: new individuals arise from the outgrowth of existing ones; in any case of budding, you can observe the trait “connected
individuals,” because the offspring and parents are connected together.
Fission: the splitting and separation of a
parent organism into two individuals of about the same size; e.g. binary
fission in bacteria.
Fragmentation and regeneration: as the name
confirms, this type of reproduction is a two-step process; appears in annelids,
sponges, corals, cnidarians, and tunicates.
Parthenogenesis: happens when an egg
develops without being fertilized; it can be observed in both invertebrates and
vertebrate (much rare). Among invertebrates, this can occur in species of bees,
wasps, and ants. Male bees, for instance, are fertile haploid adults that are
not fertilized, while female bees are fertile diploid adults. Among vertebrates,
such as the Komodo dragon and hammerhead shark, females can produce genetically-identical
offspring as a rare response to low population density.
Variations of sexual reproduction
Normally, among vertebrates, as in humans,
sexual reproduction involves simply the mating between a male and a female
individual. However, for many sexual animals, finding a mate can be difficult,
and this is the reason for the emergence of deviations of sexual reproduction.
Hermaphroditism: characterized by an individual
having both the male and female reproductive system; this type of adaption
makes the finding of a mate easier in some vertebrates (any two individuals can
mate).Sometimes, self-fertilization is possible.
Sex reversal: individuals can transform between
male and female; this is especially useful for sedentary animals like oysters
and corals, because by transforming into males during the time of ovulation,
more gametes (sperm) is released into the environment so chances of
fertilization can greatly increase.
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| Parthenogenesis of bees. |
Reference:
Campbell, et al. Biology: A Global Approach. 11th ed., Pearson, 2017.
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