Posts Tagged ‘sex’

The red queen, sex and nematode worms

// July 28th, 2011 // 1 Comment » // Recent Research, Sex and Reproduction


Alice and the Red Queen by John Tenniel

In Lewis Carroll’s Through the looking-glass– a whacky book if I ever read one – the laws of physics don’t really apply. Hills can become valleys, straight can become curvy, and forward is really backward.

In one scene, Alice chases after the Red Queen, both running as fast as they can, but when they stop Alice realises they are still right where they started. “Now, here, you see, it takes all the running you can do to keep in the same place” says the Red Queen.

And it might be the same with the evolution of predator and prey, host and parasite. Running doesn’t get you anywhere. So says the Red Queen Hypothesis.

c elegans embryo

C elegans embryo. Image by Monica Gotta

As the host adapts to fight the parasite, the parasite evolves to infect the host. It’s an endless race, and extinction faces the first organism to stop running.

So what’s this got to do with sex? Sex is evolution on turbo. Mixing and matching genes increases genetic diversity, giving a species more opportunities to outlast in the ultimate game of survivor.

Field data supports the Red Queen Hypothesis as describing an adaptive advantage of sex. Models and maths support the idea that coevolving species could select for rare genes and unusual combination randomly created by sex. Direct experimentation of coevolution and nookie is tricky business.

New research, published in Science, grew several populations of nematode worms (C. elegans, roundworms) which are usually asexually, but reproduce sexually 20% of the time.

The populations were differently exposed to bacterial parasites (Serratia marcescens) as shown.

C Elegans Sex Research

C Elegans image by Bob Goldstein, University of Carolina, Chapel Hill, remixed by Science Journal. Creative Commons License

One population was given the parasites and left to their own devices. They and their bacteria could evolve together. These nematode worms increased their rate of sexual reproduction to 80-90% over time, and maintained a high level of sexy-times.

The other nematodes were given frozen stocks of bacteria every generation, so the parasites weren’t evolving as the worms did. At first, sexual reproduction increased in the worms, but then it dropped back down to 20% – the same level as nematodes which hadn’t been exposed to the bacteria at all.Alice meets dodo

Parasites on their own don’t increase sex – coevolution does.

A second experiment supported their conclusion. Nematodes mutated to be unable to reproduce sexually (asexual obligates) became extinct after 20 generations when exposed to the parasites. But mutants that always required sex to reproduce (sexual obligates) never became extinct.

When it comes to coevolution, it’s fall behind and be left behind.

Never stop running.

Morran, L. et al (2011). Running with the Red Queen: Host-Parasite Coevolution Selects for Biparental Sex Science, 333 (6039), 216-218 DOI: 10.1126/science.1206360
Brockhurst, M. (2011). Sex, Death, and the Red Queen Science, 333 (6039), 166-167 DOI: 10.1126/science.1209420

Sex and mosquitoes – transmitting the Zika virus

// April 8th, 2011 // 5 Comments » // Recent Research, Sex and Reproduction

Senegal. Image by Mathieu Dammon

When Brian Foy returned home to America from a field trip in Senegal, Africa, he didn’t know he was infected with the mosquito spread Zika virus.

But just a few days later he was sick with extreme fatigue and joint pain, and so was his wife Chilson. A new study coauthored by the pair and colleagues suggests that this is the first documented case of an insect-borne disease being transmitted sexually.

Though the paper lists the patients as Anonymous, in an interview to Science Brian revealed he was patient 1, and his wife was patient 3.

The lucky person who was patient 2 was Brian’s PhD student Kevin Kobylinski, who had been collecting mosquitoes with him as part of his malaria research. Being bitten came with the job, so they were vaccinated against some of the major disease, including Dengue fever.

The symptoms, when they arrived, seemed to suggest they had nonetheless caught Dengue fever. Headaches, torso rashes and fatigue all round lasting for a week, then muscle pains which lingered longer. They sent blood samples to the U.S. Centers for Disease Control and Prevention, who ran a number of antibody tests. The tests showed that all three had antibodies against Zika virus, which infects monkeys and humans in Africa and Asia.

But Brian’s wife, Chilson, has never travelled to Africa or Asia. The cool climate of Colorado supports different mosquito species to those tropical varieties which spread Zika. In fact, Zika had never been recorded in the Western Hemisphere.

They concluded that Zika had been transmitted human to human, and probably sexually, as their four children didn’t get the disease.

If Zika virus can be spread by sexual transmission, it could change the way the disease is prevented. Zika is considered an emerging pathogen, having infected about 70% of the people on Yap Island in the Pacific during 2007.

ResearchBlogging.orgFoy, B. (2011). Probable Non–Vector-borne Transmission of Zika Virus, Colorado, USA Emerging Infectious Diseases DOI: 10.3201/eid1705.101939 (pdf)

Platypus. Poisonous, egg laying mammal with ten sex chromosomes

// October 13th, 2010 // 7 Comments » // Recent Research, Science Communication, Sex and Reproduction, The Realm of Bizzare


Image by Urville Djasim

Ah, the elusive platypus. The water dwelling animal with fur, webbed feet and a beak. It may just be the strangest animal on the planet. Not only does it look weird, it’s poisonous, can sense electricity, lays eggs and secrete milk through their skin, and have an excessive number of sex chromosomes.

It’s poisonous.
It is SERIOUSLY poisonous. The males have poison barbs under their front feet which they mainly use during the spring breeding season. One scratch from these babies and you will be in terrible agony.

My friend studied platypuses (yes, that’s the plural I checked) in honours and her colleague injected himself with platypus venom in the name of science. For months he had excruciating pain for months which did not respond to any painkillers, including morphine. Because of this quality, platypus venom could help scientists develop drugs which work differently to our current repertoire.

Research into platypus venom is lacking because it is hard to come across samples. But just last month researchers identified 83 possible venom genes using DNA extracted from an active venom gland. Some of the genes are similar to those in snakes, pufferfish and starfish. Now the platypus hardly evolved from a starfish. Instead, it’s an example of convergent evolution, traits that arise separately in different species and give a selective advantage. Illustrious journal Nature says platypus venom confirms the convergent evolution theory for venom. (Research paper Whittington CM, & et al (2010). Novel venom gene discovery in the platypus. Genome biology, 11 (9) PMID: 20920228)

Electroreceptor bill
Sharks use electroreception to find prey by sensing the electricity animals have in their body. Monotromes (mammals that lay eggs) including platypuses and echidnas, are the only mammals with the same ability, and the platypus is the strongest. Closing its eyes and nose when it dives, the platypus relies almost entirely on electrolocation and touch to find the tasty crustaceans it snacks on. Sharks and platypuses are hardly related, making this another yet another example of convergent evolution.

Electroreceptors are located in rows on the bill, which might help it find prey by noticing which receptors pick up the electricity first. We do the same thing with our ears, hearing noises at slightly different times tells us which direction the sound is coming from. When the platypus hunts, it moves its bill side to side, which might reveal how far away the prey is. It’s similar to how pigeons bob their head for depth perception.

Image by TwoWings

Laying eggs
A female platypus has two ovaries, but only the left one is functional. Why? We don’t know.

Eggs spend 28 days developing inside their mother’s body and 10 days outside. The babies (often called puggles) are born with teeth, which drop out as they mature.

The mother produces milk, but she doesn’t have teats or nipples. Instead puggles lick or nibble on her skin to drink, gaining nutrients and probably an immune system. Living in mud, platypuses are born with no immune system, making them worse off than human babies which have immature immune systems at birth and rely on colostrum to boost their protection.

Sex chromosomes
Since the platypus genome was sequenced in 2008, we know a bit about these strange sex chromosomes. We know that they are more similar to birds than mammals, suggesting that our own mammal-like reptile ancestors might have had sex chromosomes like the birds of today. But there’s one big difference that makes the platypus unique.

They have ten sex chromosomes. Males have five X and five Y. Females have ten X. Humans, in fact, almost all mammals have only two. During platypus sperm production, the sex chromosomes pair up as X1Y1, X2Y2, X3Y3, X4,Y4, X5,Y5, so they can split evenly to make sperm that have 5X or 5Y. Phew. After all that, I’m surprised the males have any energy left for mating.

Female fiddler crabs have sex with the neighbours

// April 20th, 2010 // Comments Off on Female fiddler crabs have sex with the neighbours // Recent Research, Sex and Reproduction

Fiddler Crab

Fiddler crabs may be little, but they have one big appendage, the CLAW! A weapon if ever there was one. Like a lance or an over-sized boxing glove, something about it just screams MAN. So it fits that male fiddlers are the gender so endowed.

Females have two little feeding claws. No giant claw. No weapon of any kind. Unless, of course, you count her good looks and killer form. Turns out that’s all she needs.

This research comes from the ANU (me own university), and there’s apparently a fiddler crab expert here that I have to meet. His name is Richard Milner, and the paper was published in Biology Letters.

ResearchBlogging.orgRichard N. C. Milner*, Michael D. Jennions and Patricia R. Y. Backwell (2009). Safe sex: male−female coalitions and pre-copulatory mate-guarding in a fiddler crab Biology Letters (6), 180-182 : 10.1098/rsbl.2009.0767

Fiddler crabs live in burrows, which are a place to hide when predators come along. Burrows are in high demand, and males will fight for squatting rights. Females can’t fight without a big-ass claw, instead they take over empty burrows.

Burrow-owning females would be sitting ducks for homeless males to come and kick them out, if it weren’t for the male next door.

Male fiddlers will defend the territory of nearby females. The study showed that if the intruder is a male, the neighbour will try to fight him off 95% of the time. That compares to just 15% of the time when the intruder was female. So male fiddlers like to be surrounded by female fiddlers. Go figure.

When picking a sexual partner, female fiddlers chose a neighbour who shares a territory border with her 85% of the time. The remaining 15% was made up of strangers, burrowless males and non-neighbour residents.

Part of that could be convenience, as females are at risk of predation while they search for a mate. Part of it could be gratitude. Part of it could be white knight syndrome, in which the big manly fiddler roughly dispenses of all piddly competition to claim the hand of the fair maiden. Damn I have a problem with personifying animals.

It boils down to one thing: Fiddlers exchange sex for protection. It makes me wonder whether some human relationships amount to much the same thing. Give me your thoughts and complete the following: Humans exchange sex for

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