THE ADVANTAGE OF ASEXUAL REPRODUCTION - WHEN IS IT 2-FOLD

The classical two-fold advantage of asexual reproduction relative to s ex can arise from two distinct causes: (i) the absence of male parenta l investment, or (ii) the asexual females having access to male parent al investment when it is available. Both of these causes arise through differences in the deployment of resources prevailing in sexual and a sexual populations. This paper aims to clarify the distinction between these alternative advantages, particularly in situations where both m ay contribute. Advantage (i) depends on the proportion of parental inv estment contributed by male and female parents, and (i) and (ii) both depend on the sex ratio at maturity. The conditions under which the ne t advantage is two-fold are identified. In most cases, male parental i nvestment 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-f old advantage (neglecting causes other than the deployment of resource s, such as ''lethal fertilization'' of diploid eggs). However, male pa rental investment may have played a role in the spread of some asexual and gynogenic populations. (C) 1995 Academic Press Limited