Queer Birds

November 22, 2014 2:31 PM

Birds, like quite a few other animals, can exhibit Gynandromorphism. Homosexual behavior in birds is also common. The phenomenon of avian spontaneous sex reversal has been well-documented, starting with Aristotle. Now modern researchers have uncovered yet another way in which birds are hacking sex roles: scientists think white-throated sparrows may actually be evolving a second pair of sex chromosomes.
posted by helpthebear (14 comments total)

Life, uh, finds a way.
posted by brundlefly at 2:56 PM on November 22, 2014 [7 favorites]

Life, uh, finds a way.
posted by brundlefly

Eponygoldblumical.
posted by Sys Rq at 3:21 PM on November 22, 2014 [11 favorites]

Wait, Aristotle underwent avian spontaneous sex reversal? My teacher really left out all the juicy bits.
posted by nebulawindphone at 3:36 PM on November 22, 2014 [12 favorites]

(Holy shit though that last article is fascinating.)
posted by nebulawindphone at 3:37 PM on November 22, 2014 [1 favorite]

Psh, amateurs. The humble platypus has five sets of overlapping sex chromosomes. All at once.

Actually, having read the full article, this is really very cool, but I'm not sure if I'd call these non-recombining sets of genes sex chromosomes per se because they don't function in any way related to sex determination. This isn't the first case of a life history polymorphism mediated by an inversion I've heard of, and inversions actually mean that crossing over is much, much more difficult just by their nature--since they make it hard for homologous regions to line up with each other to cross over in the first place. Accumulating inversions over time is one of the proximal mechanisms by which sex chromosomes lose their homology and stop recombining with each other over time, yes--but that doesn't mean that this inversion is involved with a sex chromosome.
posted by sciatrix at 3:44 PM on November 22, 2014 [3 favorites]

I'm in total agreement with sciatrix. This doesn't seem like a de novo sex chromosome formation as much as an incipient speciation event, given the behavioral isolation it engenders.
The one example I can think of a new sex chromosome forming is in flies. Drosophila miranda has a neo-X, or new sex chromosome derived from a massive translocation from the old X to an autosome (Ch.3, I think, in this case).
posted by Cold Lurkey at 5:27 PM on November 22, 2014

Someone get a hackerspace for those avian hackers! They are hacking their genes, the hackers.
posted by clvrmnky at 6:11 PM on November 22, 2014 [1 favorite]

After the duck penis, nothing is surprising.
posted by BlueHorse at 6:22 PM on November 22, 2014 [1 favorite]

Cold Lurkey, except that the most common and successful pairings are cross-morph. You can't have a speciation event when the 'species' are primed to mate preferentially with the other 'species'. It's exactly the opposite of a species definition. And the two possible combos of crossmorph can't speciate from each other, because the male/female aspect is not linked to the morph. So a crossmorph pair can produce all 4 possible variations.
posted by tavella at 9:31 PM on November 22, 2014 [4 favorites]

Add "Sam Peabody" to the tags.
Fascinating! I see a lot of white-throats but had no idea that the two morphs pair up.
posted by Jode at 4:51 AM on November 23, 2014

i like watching the word 'hack' develop into an all-inclusive verb that can mean literally anything
posted by p3on at 9:57 AM on November 23, 2014

It's a more complicated sexual system. But that's just super interesting, not all that novel. I mean, the Podarcis lizard "paper-rock-scissors" system is pretty cool, where orange males beat yellow males, yellow males beat blue males, but blue males beat orange males.

I think the reason she's speculatively calling it a second pair of "sex chromosomes" (which I'm not endorsing) is precisely because the chromosomal inversion means that genes specific to each morph are protected from recombination, and so have, in a sense, a distinct evolutionary fate. They're only exposed to selection in some individuals, not all individuals, and so accumulating variation can be subject to different kinds of pressures in the same generations. I'm not really all that sure what recommends the definition of sex-chromosome anyway. Is it just when there are heterosomal chromosomes one of which must be present for one type of gamete to be formed? Sex determination systems are weird anyway, and heterosomes aren't the only way to get more than one sex.

(lizards get ALL the sex.)
posted by Made of Star Stuff at 10:13 AM on November 23, 2014

Basically, sex chromosomes are the ones where you have a sex-determining gene or genes (as in the ZW system birds use) on them. Not all species have sex chromosomes--for example, bees have haplodiploid sex determination, so there's no particular chromosome that determines whether a given bee egg will be male or female. Fish that transition from one sex to another depending on their environment or age also don't have sex chromosomes, and neither do species who have temperature dependent sex determination.

However, they've been defined by the entire field for decades as chromosomes that play a defining role in sex determination. It really weirds me out to see the term applied to different life history strategies within sexes, even those which are inherited as a haplotype that no longer recombines with the rest of the chromosome. As I mentioned, sex chromosomes are not the only chunk of genes that exist which do that. It might be worth looking into the t haplotype in mice, which is also blocked off from recombining with "normal" haplotypes by a series of inversions on chromosome 17. There's even some evidence that T-haplotype mouse males have a different behavioral strategy than wild-type males, in that they're more aggressive and may survive better than wild-type males.
posted by sciatrix at 10:37 AM on November 23, 2014

This is really neat.

Genderfluid indeed.
posted by ana scoot at 3:58 PM on November 23, 2014