What initiates parthenogenesis?

Question

please don't tell me what parthenogenesis is. i already know. what i want to know is what causes it? thanks in advance.

Answer 1

Hey Fiel!

Really interesting question this one. Let me try and answer it-

In 1936, Gregory Pincus induced parthenogenesis in mammalian (rabbit) eggs by temperature change and chemical agents. While keeping in mind the possibility of artificially introducing parthenogenesis, let's discuss the conditions that might cause parthenogenesis-

In colonies where males and females live together, there is slim chance of occurrence of parthenogenesis as once sexual reproduction is underway, it is difficult to turn back. The complex mechanisms of sexual reproduction make it evolutionarily difficult for an organism to go back to asexual or vegetative forms of reproduction.

Also, the presence of a male negates the need of parthenogenesis.

But in aphids where some species like Brevicoryne brassicae (cabbage aphids) are all females, parthenogenesis is the only way. When in nature, a female population or individual is deprived of male intervention, natural selection and evolution make way for parthenogenesis.

As you already might be knowing, in higher mammals, progesterone secreted from corpus luteum raises the body temperature and helps in converting the proliferative endometrium into a secretory lining receptive for implantation. If in a chance occurrence, the secretion of progesterone stays there for a longer period and the body temperature as a result also, is higher and thus optimized for implantation-- the ovum might undergo mitosis and act as a zygote.

The ovum already has the cytoplasmic content and the genetic information. It is just that it is haploid (which also might not be the case if the parthenogenesis is apomictic i.e. non-meiotic). The only reasons for it to not act as a zygote are genetic. It is supposed to wait for the sperm but what if it doesn't? There is nothing stopping it from chancing upon parthenogenetic reproduction.

So, if one chance occurrence of the ovum being developed parthenogenetically gets successful, it may lead to a whole bunch of parthenogenetic individuals living happily ever after!

You might observe in the third link given in the source section that some species like humans and apes cannot reproduce parthenogenetically because the embryo dies due to genetic reasons but still, the development of a haploid embryo shows that there IS a possibility always.

Now, coming to the Gregory Pincus experiment where he experimentally made parthenogenesis possible, you can easily see that regular administration of progesterone and higher body temperature can provide continuous suitable conditions to the rabbit's ovary which ultimately results in parthenogenesis.

I hope I was able to answer at least a part of your question.

Answer 2

Parthenogenesis can arise in a species due to exceptional environmental pressures. A species that is able to reproduce through parthenogenesis can settle an isolated area because a single female is enough to create a new population. If some sort of disease or other circumstance decimates the male population of a species, parthenogenesis would be the only way for the species to persist. However, parthenogenesis is not something that can necessarily happen in any given species. Rather, those species that were able to do it are the species we know about, because they survived. Many species have faced hardships like these, but were unable to initiate parthenogenesis, so they died out. I don't know exactly why some species can do it and some can't, but it is probably some vestigial ability left over through evolution from simpler species.