For most men, the thought of taking on the burden of pregnancy from their partners would seem like a nightmare, but it’s all part and parcel of seahorse life. After mating, female seahorses and pipefish lay their eggs into a special pouch in the male’s belly and he carries the developing babies to term. They may seem like a shoe-in for a Dad-of-the-year award but this apparent display of paternal perfection has several macabre twists.
A recent study showed that pregnant pipefishes can also become vampiric cannibals, absorbing some of their brood for nutrition if their own food supplies are running low. Now, Kimberley Paczolt and Adam Jones from Texas A&M University have found that male pipefishes are also selective abortionists. They’ll kill off some of the youngsters in their pouches if they’ve mated with an unattractive female, or if they’ve already raised a large group of young in an earlier pregnancy.
The pouch isn’t just an incubator for the next generation. It’s a battleground where male and female pipefish fight a war of the sexes, and where foetal pipefish pay for this conflict with their lives.
Not Exactly Pocket Science is a set of shorter write-ups on new stories with links to more detailed takes by the world’s best journalists and bloggers. It is meant to complement the usual fare of detailed pieces that are typical for this blog.
Geneticist sequences own genome, finds genetic cause of his disease
If you’ve got an inherited disease and you want to find the genetic faults responsible, it certainly helps if you’re a prominent geneticist. James Lupski (right) from the Baylor College of Medicine suffers from an incurable condition called Charcot-Marie-Tooth (CMT) disease, which affects nerve cells and leads to muscle loss and weakness.
Lupski scoured his entire genome for the foundations of his disease. He found 3.4 million placed where his genome differed from the reference sequence by a single DNA letter (SNPs) and around 9,000 of these could actually affect the structure of a protein. Lupski narrowed down this list of candidates to two SNPs that both affect the SH3TC2 gene, which has been previously linked to CMT. One of the mutations came from his father and the other from his mother. Their unison in a single genome was the cause of not just Lipson’s disease but that of four of his siblings too.
It’s a great example of how powerful new sequencing technologies can pinpoint genetic variations that underlie diseases, which might otherwise have gone unnoticed. The entire project cost $50,000 – not exactly cheap, but far more so than the sequencing efforts of old. The time when such approaches will be affordable and commonplace is coming soon. But in this case, Lupski’s job was easier because SH3TC2 had already been linked to CMT. A second paper tells a more difficult story.
Jared Roach and David Gallas sequenced the genomes of two children who have two inherited disorders – Miller syndrome and primary ciliary dyskinesia – and their two unaffected parents. We don’t know the genetic causes of Miller syndrome and while the four family genomes narrow down the search to four possible culprits, they don’t close the case.
For great takes on these stories and their wider significance, I strongly recommend you to read Daniel Macarthur’s post on Genetic Future, Mark Henderson’s piece in the Times and Nick Wade’s take in the NYT (even if he does flub a well-known concept). Meanwhile, Ivan Oranksy has an interesting insight into the political manoeuvres that go into publicising two papers from separate journals. And check out this previous story I wrote about how genome sequencing was used to reverse the wrong diagnosis of a genetic disorder.
Male moths freeze females by mimicking bats
Flying through the night sky, a moth hears the sound of danger – the ultrasonic squeak of a hunting bat. She freezes to make herself harder to spot, as she always does when she hears these telltale calls. But the source of the squeak is not a bat at all – it’s a male moth. He is a trickster. By mimicking the sound of a bat, he fooled the female into keeping still, making her easier to mate with.
The evolutionary arms race between bats and moths has raged for millennia. Many moths have evolved to listen out for the sounds of hunting bats and some jam those calls with their own ultrasonic clicks, produced by organs called tymbals. In the armyworm moth, only the males have these organs and they never click when bats are near. Their tymbals are used for deceptive seductions, rather than defence.
Ryo Nakano found that the male’s clicks are identical to those of bats. When the males sung to females, Nakano found that virtually all of them mated successfully. If he muffled them by removing the tymbals, they only got lucky 50% of the time. And if he helped out the muted males by playing either tymbal sounds or bat calls through speakers, their success shot back up to 100%. Nakano says that this is a great example of an animal evolving a signal to exploit the sensory biases of a receiver.
More on bats vs. moths from me
Reference: Biology Letters http://dx.doi.org/10.1098/rsbl.2010.0058
The animal on the right is no ordinary chicken. Its right half looks like a hen but its left half (with a larger wattle, bigger breast, whiter colour and leg spur) is that of a cockerel. The bird is a ‘gynandromorph‘, a rare sexual chimera. Thanks to three of these oddities, Debiao Zhao and Derek McBride from the University of Edinburgh have discovered a truly amazing secret about these most familiar of birds – every single cell in a chicken’s body is either male or female. Each one has its own sexual identity. It seems that becoming male or female is a very different process for birds than it is for mammals.
In mammals, it’s a question of testicles, ovaries and the hormones they produce. Embryos live in sexual limbo until the sex organs (gonads) start to develop. This all depends on a sexual dictator called SRY, a gene found on the Y chromosome. If it’s present, the indifferent gonads go down a male route; if not, they take a female one. The sex organs then secrete a flush of hormones that trigger changes in the rest of the body. The sex chromosomes are only relevant in the cells of the gonads.
But the gynandomorphs show that something very different happens in birds. Birds have Z and W chromosomes; males are ZZ and females are ZW. Zhao and McBride used glow-in-the-dark molecules that stick to the two chromosomes to show that the gynandromorphs do indeed have a mix of ZZ and ZW cells. However, they aren’t split neatly down the middle. Their entire bodies are suffused with a mix of both types, although the male half has more ZZ cells and the female half has more ZW ones.
Even though the three chickens were both male and female, one of them only had a testicle on one side, the second only had an ovary on one side, and the third had a strange hybrid organ that was part testis and part ovary. These malformed organs pumped the same soup of hormones throughout the birds’ bodies but, clearly, each side responded differently.
Zhao and McBride started to suspect that each cell has its very own sexual identity, and that this individuality exists from the chicken’s first days of embryonic life. They proved that by transplanting cells from embryonic sex organs from one animal to another. All the transplants produced a glowing green protein so Zhao and McBride could track their whereabouts, and those of their daughters.
Sex might be fun but it’s not without risks. As your partner exposes themselves to you, they also expose you to whatever bacteria, viruses or parasites they might be carrying. But some animals have a way around that. Ekaterina Litvinova has found that when male mice get a whiff of female odours, their immune systems prepare their airways for attack, increasing their resistance to flu viruses.
Litvinova worked with a group of mice that were exposed to bedding that had previously been soiled by females in the sexually receptive parts of their cycle. She compared them to a second more monastic group that were isolated from female contact.
Male mice use smells to track down females who are ready to mate. They’ll follow markings of faeces and urine and when they actually find the female, they’ll continue sniffing her nose and genitals. Each of these nasal encounters could be a source of infection. She then pitted both groups against a flu virus. Influenza doesn’t affect wild populations of house mice, so the virus in this case is acting as more of an indicator of the animals’ defences, rather than a representative of a real threat.
Both groups of mice lost a bit of weight, but at certain doses of virus, those that had been exposed to female aromas kept more of their grams on. They also fared better in the long run – just 20% of them died, compared to 46% of those that had only smelled male odours.
In science, we don’t often get to talk about male repression, but a new discovery gives us just such a chance. It turns out that ovaries can only remain ovaries by constantly suppressing their ability to become male. Silence a single gene, and adult ovaries turn into testes. That adult tissues can be transformed in this way would be surprising enough, but doing so by changing a single gene is truly astonishing.
As embryos, our gonads aren’t specific to either gender. Their default course is a female one, but they can be diverted through the action of a gene called SRY that sits on the Y chromosome. SRY activates another gene called Sox9, which sets off a chain reaction of flicked genetic switches. The result is that premature gonads develop into testes. Without SRY or Sox9, you get ovaries instead.
But Henriette Uhlenhaut from the European Molecular Biology Laboratory has found that this story is woefully incomplete. Maleness isn’t just forced onto developing gonads by the actions of SRY – it’s permanently kept at bay by another gene called FOXL2.