What is parthenogenesis?

Aphid adult and young produced by parthenogenesis.

Parthenogenesis is a form of asexual reproduction where a single adult can lay viable eggs that hatch into clones.  The offspring is identical to the parent genetically.  The whole purpose of sexual reproduction requiring a male and female is to recombine genes to produce unique individuals. This produces small variables in a population that will allow better-adapted members to survive.  If this is so valuable, why do some organisms reproduce parthenogenetically?

Consider plants that reproduce asexually.  Many garden plants have this ability.  Strawberries (runners), potatoes (tubers), and raspberries (cut a branch off and stick in in the soil) all make clones of themselves.  They also reproduce sexually - all of these plants produce flowers and seeds.

Certain invertebrates, including the aphids I photographed above, can reproduce in both manners.  The advantage of parthenogenesis is the ability to produce large numbers of offspring in a very short period of time, especially if mates are not available.  Another organism, cladocerans (Daphnia or water fleas), also reproduces this way.  They may be heavily predated, live in a harsh environment, or the conditions may just be really excellent; this can allow tremendous numbers to be produced in a short span of time.

I was swimming in Lightening Lakes in Manning one summer and I noticed the water was teaming with these cladocera.  You could examine a bunch of them just by scooping up a handful of water and looking into it.  Tiny, but fascinating.  I photographed the one below using a microscope.  It is red because it has been dyed and fixed on a slide.  The black spot is an eye, the branches off its head are antennae, and the near its tail are young developing in a brood pouch - all parthenogenetically.

Daphnia (water flea) with young.

Thanks for reading.

Eric Svendsen     www.ericspix.com

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