Forget about the season; virgin births can happen any time of year... and anywhere.
So there is an Ask a Scienceblogger question about virgin births. In zoology this is called "parthenogenesis" (which means "virgin birth"), and in botany it is either called "vegetative reproduction" (think: cuttings) or "apomixis", in which unfertilised seeds germinate. I want to talk today about what that means for our taxonomies.
A long-standing reaction to the notion of there being asexual reproduction is that every novel individual, or any individual who has a mutant gene, would necessarily be its own species. In more common terms, every strain would be a species of its own. But bacteriologists and fungi specialists (mycologists) identify asexual species without any more trouble than those who study sexual species do (and sometimes less).
There is a group of species of lizards in northern Mexico and the southern United States, known as Cnemidophorus, or whiptail lizards. There are some 15 asexual species in this group, out of an approximate 50 species, apparently all formed by hybridisation between species, which causes clonal reproduction by interfering with the reduction of the egg cells to a haploid chromosome count. It turns out that the egg cells remain diploid, which means they have a full complement of chromosomes, and can, with the right hormonal trigger, start dividing into a fetus.
This means that, if a species is necessarily sexual, that there are groups within this cluster of species that are not species, but in all other respects, such as ecological adaptation, behaviour identity, morphology, coloration, etc., are just like species.
Virgin births turn out to be much more common than we used to think. Cases have been reported in turkeys (but to my knowledge no other birds, as the females are the heterogametic sex - that is, bird females have the sex difference chromosome, unlike in mammals and many other vertebrates, where the males have it). It may be thought to be "rare" simply because we haven't gone looking for it, under the general prejudice that sex is needed for something to be a species.
Like horizontal, or lateral, genetic transfer and indeed hybridism itself, asexual reproduction turns out to be a fact of Life, but one that is neither ubiquitous nor rare. It is another example of biology showing that the Rules aren't really rules, so much as a mix of prior presumption and ignorance on the one hand, and summaries of knowledge and data on the other.
The media, as always, tend to run this as "males will become unnecessary", egged on by some academic hype. Is this true? I really doubt it. The major hypothesis about the evolution of sex is that sexual populations have a higher diversity of genes and a much more rapid recombining of these novel genes when under threat from disease, ecological challenge, or just sexual selection for brighter and more gaudy mates. Apart from the third, sex carries benefits that lead groups that are sexual to last longer, evolutionarily speaking, even despite some apparent long-standing asexuals like many rotifers and ostracods. There are good evolutionary reasons for thinking that males will persist. However, males can become little more than appendages for females, as they do in some species of Darwin's old favourite group, barnacles. Will that happen to us?
Unlikely. Species far older than us (for instance, chimpanzees, which appear to be about three million years old compared to our 200,000 years) still have males. It takes special circumstances for males to degenerate in that way, or to disappear altogether, and those conditions don't seem to apply to us. In fact, being apes, male hierarchies are a crucial part of the social structure (as are female hierarchies - in some ape species and potentially ours, even more so), and so there'd be immediate selection against any degeneration of the male sex, although it's not impossible.
But the basic argument why human males will be around indefinitely is that otherwise, who would brewers make beer for?
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Beer and the Y chromosone. Is it genetic?
You have it the wrong way about:
Y? Beer!
Interesting. Theoretically, a human female could have a genetic mutation that led to her gametes never becoming haploid. The resulting diploid cells, combined with the right hormonal triggers could result in a virgin pregnancy. The fun part is that the resulting offspring would always be female. Society of Amazons perhaps?
The offspring would be XX but does that require them to develop as females? As I understand there are cases of humans who are physically male but have XX chromosomes.
It does appear that one X is paternal and one is maternal though.
http://www.the-scientist.com/news/display/25087/
In those cases there is one mutant gene on one of the X's that results in the fetus developing into a male. I suppose both mutations could occur, the first happening in the mother, the second happening only in the offspring. The question then would be whether or not the production of bar bodies would make the sex random, or always male.
Well it may not require a second mutation, just too much testosterone.
http://www.vancouver.wsu.edu/fac/morgan/lecture/hormone.html
It did suprise me that XX males are infertile.
Didn't find anything explaining why this should be so.
Another interesting case of unisexuality in vertebrates is the Ambystoma (salamander family Ambystomatidae) unisexual complex. The unisexuals have nuclear genomes derived from 2-4 sexual species (jeffersonianum, tigrinum, texanum, and laterale) but oddly the mtDNA is all from another: A. barbouri. A couple of recent papers are Robertson et al. 2006 doi:10.1111/j.1365-294X.2006.03005.x , and Bogert et al 2007 doi:10.1139/G06-152 .
Unfortunately a human embryo with maternal copies of both chromosomes probably wouldn't be viable: there are enough genes in a human with parent-specific chromosomal imprinting that things would start to go wrong pretty early, and get worse. The imprinted genes tend to control things like energy metabolism and brain development. Stuff you need.
Now, as for stick insects... no-one's too sure how widespread it is, but Australian stick insects at least can produce asexual eggs when they haven't been able to find a male.
Got around do reading your exposition carefully. This is the first I have heard that species identity requires sexual reproduction. I suppose there might be a narrow species definition which would say so, but there are others which do not. The fact of the matter is that the species definition of widest applicability is, "A species is what a competent taxonomist says it is." By that I mean I think the majority of living species are so poorly known that we cannot apply other definitions.
Can you imagine the self control necessary to avoid making snide comments about the need for males in human society? Or the many, many witty things I could say about bright and gaudy mates? Since I do know that almost all readers here are men, I will simply call upon my inner Spock and say, "Fascinating".
Jim, in a recent work by Jerry Coyne and H. Allen Orr, entitled Speciation, regarded as the definitive statement so far on the topic, this is just the definition of "species" they use. So it's not exactly atypical. And you comment about competent taxonomists - well that joke was around in the 1850s, if not earlier. I have blogged on this before.
Oh go on I won't mind :o) Not sure about the others here.
Does not being snide truly require self control?
The fact that in many species the male is the bright gaudy one has always been of interest, very common amongst birds, and metro-man may be a human example.
Would it be "human" society without males? I suppose you could just define human to only apply to the female half of the species or are you thinking about a world without men.
Chris,
You might find this article http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1684785 interesting it is about 45,X males.
As the summary says, they had one paitent for which no Y specific repeats where found. So perhaps parthogenisis in humans is a possibility.
Now to test it one way or another you'ld have to identify a lot of X or XX males and then compare their DNA whith their mothers and supposed fathers DNA and show that it all could have come from the mother; then you could say that it might have been parthenogenesis.