Sabre-Toothed Sausages Have the Saddest Sperm
Posted by Michael_Byrne on Tuesday, Dec 06, 2011
Sometimes evolution fucks up, skipping over natural selection and allowing bad traits to persevere. Such is the case of the naked mole rat, e.g. the “sabre-toothed sausage.” Poor little fellas can’t feel pain on their skin, regulate their body temperatures well, see anything, and they’re, well, naked. The one thing they have is that they can move forward and backwards, which is handy when you live in dark, smelly tunnels. A new paper out in the BMC Evolutionary Biology journal blames the naked mole rat’s sperm, which is apparently the worst sperm on Earth.
This is from the paper’s results:
Our results revealed an atypical mammalian sperm structure with spermatozoa from breeding, subordinate and disperser males being degenerate and almost completely lacking a “mammalian phylogenetic stamp”. Sperm structure is characterized by extreme polymorphism with most spermatozoa classified as abnormal. Sperm head shapes include round, oval, elongated, lobed, asymmetrical and amorphous. At the ultrastructural level, the sperm head contains condensed to granular chromatin with large open spaces between the chromatin. Nuclear chromatin seems disorganized since chromatin condensation is irregular and extremely inconsistent. The acrosome forms a cap (ca 35%) over the anterior part of the head. A well defined nuclear fossa and neck with five minor sets of banded protein structures are present. The midpiece is poorly organized and contains only 5-7 round to oval mitochondria. The flagellar pattern is 9+9+2. A distinct degenerative feature of the tail principal piece is the absence of the fibrous sheath.
So there you go. Basically, naked mole rat sperm is shaped all kinds of weird, has screwed up DNA, is organized strangely, and can’t swim for anything.
But why? Shouldn’t sperm be getting better and better because they’re competing with other sperm to have naked mole rat sex and, thus, furthering evolution? No, not in the naked mole rat kingdom. Sperm and naked mole rats don’t have to be good at anything.
“Once the queen has picked her consort(s) she keeps the other females and males subordinate by using physical aggression,” says Professor Gerhard van der Horst of the University of the Western Cape, in a press release. “It seems that the resultant lack of competition between breeding males for the colony queen contributed to an overall decrease in sperm ‘fitness’. Surprisingly, despite the low motility and dismal features of their sperm, these naked mole-rat males are fertile and fathered a number of healthy offspring per litter. We are very excited about our results because this would be the first example of degenerate orthogenesis occurring at a cellular level.”
So apparently you can be the worst naked mole rat with the worst sperm in the colony and you still might get picked by the queen, who apparently couldn’t care less. Naked mole rats are just a metaphor warehouse, aren’t they.
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Michael covers physics, climate science, the future of music, and assorted things fallen through cracks at Motherboard. A native of Colorado, Michigan, and Oregon, he currently resides in Baltimore...
