Androgenesis: where males hijack eggs to clone themselves.

Androgenesis is a form of quasi-sexual reproduction in which a male is the sole source of the nuclear genetic material in the embryo. Two types of androgenesis occur in nature. Under the first type, females produce eggs without a nucleus and the embryo develops from the male gamete following fertilization. Evolution of this type of androgenesis is poorly understood as the parent responsible for androgenesis (the mother) gains no benefit from it. Ultimate factors driving the evolution of the second type of androgenesis are better understood. In this case, a zygote is formed between a male and a female gamete, but the female genome is eliminated. When rare, androgenesis with genome elimination is favoured because an androgenesis-determining allele has twice the reproductive success of an allele that determines sexual reproduction. Paradoxically, except in hermaphrodites, a successful androgenetic strain can drive such a male-biased sex ratio that the population goes extinct. This likely explains why androgenesis with genome elimination appears to be rarer than androgenesis via non-nucleate eggs, although both forms are either very rare or remain largely undetected in nature. Nonetheless, some highly invasive species including ants and freshwater clams are androgenetic, for reasons that are largely unexplained.This article is part of the themed issue 'Weird sex: the underappreciated diversity of sexual reproduction'.