How to gain the benefits of sexual reproduction without paying the cost: a worm shows the way

Abstract

Sexual reproduction is perhaps the greatest of all evolutionary puzzles. It's a puzzle because sexually reproducing species pay the cost of spending half their resources (over and above what is needed for vegetative growth) in producing males, whereas parthenogenetic species utilize all their resources meant for reproduction in producing only females (or hermaphrodites) like themselves. This twofold cost of sexual reproduction [1,2] is sometimes referred to as the twofold cost of producing males. Three advantages of sexual reproduction that might offset this cost have been proposed. Genetic recombination and cross fertilization permit sexually reproducing species to (1) bring together, in the same individual, mutations arising in different individuals [3,4]; (2) generate genetic variability and thus adapt to changing environments[2, 5, 6]; and (3) shuffle their genes in every generation and thus keep parasites at bay [7,8,9]. While evolutionary biologists are busy testing their favourite ideas for offsetting the twofold cost of producing males, recent work by Craig LaMunyon and Samuel Ward[10] shows that a nematode, Caenorhabditis briggsae, appears to have found a way of gaining the benefits of sexual reproduction without paying the cost of producing males.