Losing the desire: selection can promote obligate asexuality.
King KC., Hurst GD.
Whilst parthenogenesis has evolved multiple times from sexual invertebrate and vertebrate lineages, the drivers and consequences of the sex-asex transition remain mostly uncertain. A model by Stouthamer et al. recently published in BMC Evolutionary Biology shows a pathway by which obligate asexuality could be selected for following endosymbiont infection. See research article http://www.biomedcentral.com/1471-2148/10/229.