Sperm speed gene improves reproduction
Deer mice and their many relatives are found in North America. They fill the mice niches in a more athletic way-hence the name, and vary in their reproductive capacity. The great interest in this paper is that the sperm mid-section proves to be very important for success in fertilisation and that could easily be true of humans and other mammals.
As one species the deer mouse, Peromyscus maniculatusmates promiscuously, it faces competition for sperm from different males as they race towards the eggs. Surprisingly for mice, the males also hang around to care for the nest and, unsurprisingly, numerous young. A related species, “the oldfield mouse,” or Peromyscus polionotus is monogamous and therefore has little or no competition among the spermatozoa, apart from between those of the husband.
How does the sperm manage to go faster? Once it gets to the egg using chemotaxis (as here in the externally fertilised mussel,) then its job is done, but superior speed would be a major factor and selection pressure. A gene was discovered here to greatly expand the sperm midsection that contains mitochondria. This would be expected to produce more energy and more power for swimming. The gene PrKar1a codes for a protein used in the sperm mid-section, and is also found in the human genome. With the gene functioning, the coded protein is abundant.
The indication is that behaviours such as reproductive patterns drive evolution. Selection is obvious for the super-fast sperm, when they are needed, but we are lucky to have 2 closely-related species that adopt totally different strategies for mating. Heidi S. Fisher. Emily Jacobs-Palmer, Jean-Marc Lassance and Hopi E. Hoekstra of the Universities of Maryland and Harvard just released their paper as a preprint in bioRxiv.org, entitled The genetic basis and fitness consequences of sperm midpiece size in deer mice.
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