Male pygmy hippopotamus influence offspring sex ratio

What is it about?

Some populations have a male-to-female ratio that is different from the expected unity. It has traditionally been assumed that if a parent can influence the offspring sex ratio it would be the female due to her much larger investment. In this study we show that the male also have a say. Only ~42% of the pygmy hippos born in captivity are males. We found by sampling semen from 10% of the adult male population that the sex ratio of their sperm is similarly shifted (43% with chromosome Y).

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Why is it important?

This finding suggests two things - first that males may also influence the offspring sex ratio, and second, that males may have a mechanism by which they eliminate spermatozoa carrying the undesired sex chromosome. Finding how they do it will put a valuable reproductive and conservation tool in our hands. It may also provide explanation to hitherto unexplained shifts such as the excess in male offspring among humans in most countries around the world.