Interspecies sex--Yur doin' it wrong.

The little fire ant (Wasmannia auropunctata) is "blamed for reducing species diversity, reducing overall abundance of flying and tree-dwelling insects, and eliminating arachnid populations. It is also known for its painful stings. On the Galapagos, it eats the hatchlings of tortoises and attacks the eyes and cloacae of the adult tortoises. It is considered to be perhaps the greatest ant species threat in the Pacific region." (http://www.issg.org/database/species/ecology.asp?fr=1&si=58)

Oh, but that's not the news.

The little fire ant is considered an invasive species in many areas of its current range; it's been introduced from its native Central and South America to parts of Africa, North America, additional regions of South America, and islands in the Caribbean and Pacific Oceans.  They're omnivores, so they'll eat just about anything, and they have that nasty sting.  Both of these attributes probably contribute greatly to their success.  But lots of ants and other colony-type insects do that.  Why do I care about these ones?

Sex.  No no, the topic isn't about MY interest in THEM as sexual objects.  Rather, I find the WAY they reproduce fascinating.  And, certainly, it is unique.  As far as I know, no other creature reproduces the same way as these little guys.

First, let me explain how most ants reproduce.  Well, at least I'll give a simplified overview of the genetics of ant reproduction.  There are three main types of individuals in most ant species (as well as bee and wasp species): queens, males, and workers.  Typically, only the queens and males are fertile.  The workers, all female, are sterile.  The queens are diploid.  That is, they possess paired sets of chromosomes.  One set from the female parent (another queen) and one set from the male parent.  The workers are also diploid.  The difference between queens and workers is often determined by factors other than genetics, such as the well-known "royal jelly", a substance fed to bee larvae that results in queens.  Males on the other hand, are haploid.  That is, they have only one set of chromosomes.  Males derive from unfertilized eggs, and thus, have genes only from the queen.  Already, this scheme is quite different from what we typically learn in biology, which focuses mostly on vertebrate creatures.  In this scheme, the male is just a carrier of the queens genes.  He brings those genes to a new queen, and she produces more queens and workers, each composed of a genome with half the original queen's genes.  Similarly, each queen only gets to contribute half her genes to her offspring.  Not such a bad deal, really, though.  It works that way with most animals.

However, in the little fire ant, that's just not enough.  Not enough for EITHER side.  Not only are the little buggers mean, they're greedy.  Neither the female nor the male share.  David Fournier, et al. (Nature, 435:1230-4, 2005; http://www.nature.com/nature/journal/v435/n7046/abs/nature03705.html) discovered a new way by which the little fire ant reproduces.  All males are clones and all queens are clones.  But...how?!  Males can't make more males, can they?  Yes, yes, they still need girls.  And the queens still need the males...but only to produce their sterile workers.  In order to pull this off, first, the queen clones herself through parthenogenesis.  In other words, she produces eggs that are diploid and don't require sperm to provide a second set of chromosomes to develop.  Great, right?  Well, no.  Unlike many parthenogenic species (including, for example, some lizards), queen ants still need workers.  Why waste a perfectly good clone of yourself on hard labor?!  So, she mates with a male.  So she intermingles her own pristine genes with a male's (ugh!) to produce laborers.  Hmmm.  Seems like the male's left out in the cold on this scheme.  The queen literally does not NEED him to pass on her genes.  If she wanted, she could do without her little slaves, and produce clones of herself generation after generation.  Here's the kicker.  Males are STILL produced, despite the fact that, if she had her druthers, the queen could keep her genetics pure forever by never mating.  But the males also are protective of their DNA.  In fact, some of the fertilized eggs, those that would have become workers...well, the male chromosomes occasionally somehow kick out the queen's chromosomes!  Leaving an egg with only male chromosomes, and ultimately, a clone of the male.  So, for generations and generations, the reproducing males and females get to keep their DNA clean and uncorrupted by sex.  They could almost be different species....  Two species separate, except when they mate to produce a slave class.  Sounds like a science fiction story, doesn't it?  I'm not the first to suggest it, but it did cross my mind the first time I read the article.

For some lovely schematics (taken from the original Nature article)--and another article I came across as I was researching the topic to write this--see: http://pharyngula.org/index/weblog/comments/clone_war_of_the_sexes/