The lowest–quality sperm is from the diggers
Researchers at the University of the Western Cape Province, South Africa, working under the leadership of Liana Maree, isolated the sperm of naked diggers they caught and subjected it to comprehensive testing.
The naked digger (Heterocephalus glaber) is a small burrowing rodent of the digger family. It is characterized by a unique social structure for mammals, low body temperature, insensitivity to pain and endurance to high concentrations of carbon dioxide. It is the longest-lived of rodents (up to 28 years old), which makes it one of the most important objects for studying the mechanisms of longevity.
The test results showed that the vast majority of spermatozoa had an atypical shape (round, oval, elongated, lobed, asymmetric and amorphous), while the sperm heads contained unorganized chromatin and showed all possible structural anomalies. It is not surprising that only about 7% of these "freaks" could move, while their speed was only about 35 microns per second. Apparently, this is a record for slowness among mammalian spermatozoa.
As the object of the study, the scientists selected males from colonies with a high degree of outbreeding (crossing of unrelated individuals). This makes it possible to exclude the role of inbreeding in sperm degeneration.
Apparently, such an exceptionally low quality of spermatozoa is due to the lack of competition between males. Naked diggers live in colonies dominated by female queens. Such a dominant female chooses one "favorite" for a certain period of time and suppresses the reproductive instincts of all the other males living in the colony. The chosen male has exclusive rights to mate, so his spermatozoa absolutely do not have to hurry on the way to the egg.
Experts believe that naked diggers are a very good model for studying the evolutionary processes that affect the quality of human sperm. People are relatively monogamous, which causes a lack of competition between spermatozoa of different individuals and a fairly high frequency of abnormalities of these cells. On average, only 60% of spermatozoa in men are mobile, whereas for more polygamous mammalian species this figure can be up to 95%.
Article by Gerhard van der Horst et al. Sperm structure and motility in the eusocial naked mole-rat, Heterocephalus glaber: a case of degenerative orthogenesis in the absence of sperm competition? published in the journal BMC Evolutionary Biology.
Evgeniya Ryabtseva
Portal "Eternal youth" http://vechnayamolodost.ru based on the materials of New Scientist: Naked mole rats make deformed, sluggish sperm.
08.12.2011