Pocket science - sperm races and poison-stealing voles

Not Exactly Rocket Science
By Ed Yong
Mar 28, 2010 9:18 PMNov 20, 2019 5:11 AM


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Not Exactly Pocket Science is a set of shorter write-ups on new stories with, where possible, links to more detailed takes elsewhere. It is meant to complement the usual fare of detailed pieces that are typical for this blog.

Live broadcasts of sperm races

Last week, I blogged about the sperm wars of ants and bees. Even after males have mated with a queen, their semen contains chemicals that have evolved to incapacitate the sperm of their rivals. But there’s more than one way of winning the sperm wars. Some insects do it through sheer numbers.

Mollie Manier managed to set up live broadcasts of the sperm wars. She engineered male flies whose sperm was loaded with proteins that glow either red or green. By following these glows with a special microscope, Manier captured astounding and beautiful videos of the sperm racing around the female’s genital tract at high speed, like miniature formula-one cars.

When fruit flies mate, the female stores the male’s sperm in a special pouch. Because of this, the last male to mate with her gets an advantage because his sperm can flush out those of earlier suitors. To facilitate this, males ejaculate far more sperm than is actually necessary to fill the female’s stores. That gives them the best chance of ousting as many rival cells as possible. But unlike the battles of ants and bees, the sperm of fruit flies don’t actually harm those of rivals. Once the number of racers has been set, it’s a fair fight.


More from Jef Akst at The Scientist

Poisonous fungi unwittingly betray plants to voles

Meet the Southern vole – it looks unassuming but this little critter might just have a penchant for stealing biological weapons. As the vole eats grass, it sometimes gets mouthfuls of a fungus called Neotyphodium, which lives inside the stems. The fungus produces chemicals that poison plant-eaters trying to munch its home. Related species, like the field vole, lose weight and die earlier when they eat these poisons, but Susanna Saari found that the Southern voles seem to be immune. When they eat infected ryegrass, they’re perfectly healthy and neither their body weight nor their numbers fall.

If anything, they actually seem to benefit from the poisons, becoming less likely to fall prey to their greatest enemy, the least weasel. The reason for this protection is still unclear. Many animals steal biological weapons: the sea slug Glaucus protects itself with stinging cells taken from the jellyfish it eats; the tiger keelback snake eat toads to steal their poison; the hooded pitohui

nicks poisons from beetles. But Saari thinks that the voles are different. Lleast weasels, which hunt by smell, couldn’t distinguish between the urine of voles that had fed on infected or uninfected grass. When the voles faced a weasel, those that were full of fungi were actually less active but despite this tendency to freeze, they were less likely to be captured by weasels. Perhaps by freezing in the face of danger rather than fleeing, they somehow protected themselves.

Meanwhile, the discovery could recast the relationship between the fungus and the grass. Neotyphodium infects 20-30% of all grass species and the two are typically viewed as accomplices, whose interests are aligned. The fungus doesn’t harm the health of the grass, and its toxins deter grazers. But if the fungus’s poisons are actually a boon to some grass-eaters, its presence might actually harm the grass by drawing hungry voles. In that case, the fungus would be less a beneficial tenant than a resident parasite.

Reference: PLoS ONE http://dx.doi.org/10.1371/journal.pone.0009845

And finally...

The biggest story of the last week was undoubtedly the tale of X-Woman's Fingerbone. Unfortunately, the timing of the story coincided with the move to Discover and other things, which meant no time to cover the story in the depth that it clearly required. But that's no big loss - there' s little chance that anyone could have produced coverage as thorough and lucid as my co-blogger(!) Carl Zimmer. Go read his take.

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