Males Not Required!

In most cases, mating is required to produce off spring, but in certain instances, particularly in the case of insects as well as some reptiles and amphibians, a single female may be able to create the next generation on her own. Paul Donovan investigates.

- Karen Arnold

I am sure that at some stage or other, most of us have bought a particular species of insect, which then produces off spring. Perhaps we had no idea that the individual which we were acquiring was a female, and assumed that because it had young, it must have been mated before we bought it. This may not necessarily be correct though.

If we delve a bit deeper, into what is described as asexual reproduction or parthenogenesis, we come across a fascinating mode of reproduction, whereby a female can give birth to off spring which involved no intervention or indeed a genetic contribution by a male. This phenomenon was first discovered by the naturalist and philosopher Charles Bonnet when he was studying aphids in the 1740s.

Over the next century, parthenogenesis was observed in a number of insect species, including bagworm and silkworm moths, as well as drone bees. However, it was not until the 1840s that it was actually named ‘parthenogenesis’ which literally means ‘virgin creation’, often described today also as ‘virgin birth’.

What is it?

In the broadest biological sense of the term, parthenogenesis simply means an unfertilised ovum that ultimately produces a fully functional adult. In other words, at cellular level, the difference between species that reproduce parthenogenetically, as distinct from sexually, is that in the latter case, meiosis - the name for the process that divides a cell so that only half the chromosomes are present - is followed by fusion of a male and female gametes. This takes place as a result of fertilisation of the egg by a sperm. In parthenogenesis, however, meiosis is changed so that only one particular set of chromosomes is transferred in a non-random fashion.