![]() ![]() We, as likely with other programs, have found men referred for isolated low morphology to be greatly stressed needlessly. ![]() ![]() Most, if not all, fertility specialists can say that they have had patients referred to them because of an isolated abnormal morphology on semen analysis. Sperm structure and motility in the eusocial naked mole-rat, Heterocephalus glaber : a case of degenerative orthogenesis in the absence of sperm competition? BMC Evolutionary Biology in press.Kristin Van Heertum, M.D., Anupama Kotha, M.D., Mabel Lee, B.A., Sara Maskal, B.S., Gretchen Collins, M.D., Kiranpreet Khurana, M.D., Rachel Weinerman, M.D., Brooke Rossi, M.D., James Liu, M.D., James Goldfarb, M.D.ĭivision of Reproductive Endocrinology & Infertility, University Hospitals Cleveland Medical CenterĬase Western Reserve University School of Medicineĭepartment of Urology, University Hospitals Cleveland Medical Center Consider This: Reference: Van der Horst, Maree, Kotze & O’Riain. The rats won’t be lovers, so there’s no point for their sperm to be fighters. They’re like the wings of island birds that often shrivel in the absence of land predators, or the eyes of cave-dwellers that deteriorate in the absence of light. With such fixed fates, there is no reason for the other males to compete for mating rights, and no reason to have Olympic-level sperm.Įvolution prunes wastefulness and over time, the naked mole rat’s sperm degenerated to the point where most are useless. In any single colony, with around 40 to 90 individuals, the only ones that can reproduce are the queen and her male consort (with a couple of possible affairs on the side). When competition is intense, every sperm counts.īut the naked mole rat has no sperm competition at all. Others win the competition by simply being very long and fast – some fruit flies, for example, have sperm cells that are a couple of inches long. Some have chemicals that incapacitate their rivals, some have barbs, and some team up with their brothers. This “ sperm competition ” is the norm in the animal kingdom, and it has driven the evolution of longer and ever more elaborate sperm. In these cases, the sperm do battle inside the female’s body for fertilisation rights. In many other animals, females mate with many males, or can store sperm inside their bodies. Van der Horst thinks that the rodent’s odd social structure is responsible for its malformed sperm. Their sperm may largely consist of deformed weaklings, but there are clearly enough normal ones to make more naked mole rats. Still, that seems to be enough.Īll of van der Horst’s breeding males had raised healthy litters of pups. The vast majority move at a slow crawl they might even be the slowest sperm of any mammal. Only between 1 and 15 percent of them can actually swim, and just 1 percent of these can swim quickly. With all these deviations, it’s no surprise that the naked mole rat’s sperm won’t be winning any races. Even mammals with more primitively shaped sperm, like the platypus, still have sheathed tails. Behind the midpiece lies the tail, which is coated with a sheath of fibres that provide support as it beats back and forth. By contrast, the naked mole rat’s midpiece is short and disorganised, with just 7 rings of mitochondria. Humans have around 15 of these rings, and some rodents have up to 300. These power the cells’ frenzied swimming. In most mammal sperm, there is a distinctive midpiece, loaded with rings of energy-producing structures called mitochondria. And all the males – whether breeding or not – had the same misshapen sperm.īehind the heads, things don’t get better. The DNA inside them isn’t packaged properly. There are sperm with shrunken heads, two heads, conical heads. Rather than the sleek, smooth tadpoles that other mammals have, the mole rat’s sperm had all manner of abnormally shaped heads. For a start, he found that they are smaller than those of other mammals, and produced in lower amounts. Gerhard Van der Horst form the University of the Western Cape, South Africa, sampled the sperm from a wide variety of male naked mole rats. Now, just when you thought they couldn’t get any weirder, we can add another bizarre trait to the naked mole rat’s extensive list: they have really rubbish sperm. ![]() Their sight is poor, they can’t control their body temperature very well, and their teeth jut out beyond their lips. They feel no pain in their skin, they live unusually long lives, they can cope with chokingly low levels of oxygen, and they seem to be immune to cancer. They live in underground colonies like those of ants and bees, with a fertile queen lording over sterile workers. The naked mole rat must be one of the strangest mammals in existence. ![]()
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