Sexy sons : a dead end for 44 cytoplasmic genes

50 Recd 21.12.03; Accptd 19.01.04; Online 51 Critics of sexual conflict theory argue that females 52 may gain a net reproductive benefit to mating with 53 manipulative males because the direct costs that 54 they suffer may be offset by the production of sexy, 55 i.e. manipulative, sons. However, this exclusive 56 focus on nuclear gene effects represents an incom57 plete view of female f itness. Females differ funda58 mentally from males in transmitting not only 59 nuclear genes but also a wide range of cytoplasmic 60 genetic elements (CGEs) that can have profound 61 effects, from male killing to influencing development 62 of the nervous system and cognitive ability. 63 Maternal transmission of CGEs has two major 64 implications for sexual selection. First, the evolution 65 of male fitness traits, such as sperm competitive 66 ability, may be constrained because response to 67 selection on mitochondrial genomes can occur only 68 through the female line. Second, CGEs bear the 69 direct costs of male manipulation but gain no 70 indirect benefits when females produce sexy sons. 71 This should result in perpetual antagonistic coevol72 ution between nuclear genes involved in male 73 manipulation and CGEs that promote female resist74 ance to male sexually selected traits. Explicit con75 sideration of the consequences of selection acting on 76 CGEs is therefore necessary for a better understand77 ing of the relationship between sexual selection and 78 sexual conflict. 79