The Advantage of Asexual Reproduction: When is it Two-fold?

The classical two-fold advantage of asexual reproduction relative to sex can arise from two distinct causes: (i) the absence of male parental investment, or (ii) the asexual females having access to male parental investment when it is available. Both of these causes arise through differences in the deployment of resources prevailing in sexual and asexual populations. This paper aims to clarify the distinction between these alternative advantages, particularly in situations where both may contribute. Advantage (i) depends on the proportion of parental investment contributed by male and female parents, and (i) and (ii) both depend on the sex ratio at maturity. The conditions under which the net advantage is two-fold are identified. In most cases, male parental investment may be negligible, and the sex ratio at maturity close 1:1, in which case an asexual clone is expected to have the classical two-fold advantage (neglecting causes other than the deployment of resources, such as “lethal fertilization” of diploid eggs). However, male parental investment may have played a role in the spread of some asexual and gynogenic populations.