Discuss the Comparative Evolutionary Costs and Benefits of Parthenogenesis vs. Sexual Reproduction.

This essay will discuss the comparative benefits and costs of two forms of reproductions; parthenogenesis and sexual reproduction. To narrow the scope of the piece, the area of parthenogenesis is going to be largely limited to organisms that are obligately parthenogenetic. Parthenogenesis is the “production of an embryo from a female gamete without any genetic contribution from a male gamete” (Mittwoch, 1978). Sexual reproduction is the process of cross-fertilisation in which the genomes of two parents via gametes are brought together in one cell forming a zygote (Hörandl E, 2009). It is necessary to clarify that parthenogenesis is a different mechanism to self-fertilisation and asexual reproduction. In these mechanisms offspring either do not originate form an egg or incorporate paternal.
It should be established that offspring produced by parthenogenesis are called parthenogenones (Mittwoch, 1978). The implications of both reproductive mechanisms will be compared in this essay.

The Cost of Sexual Reproduction
Many costs of reproduction compared to parthenogenesis are derived from the presence of males. The cost of males is associated with the fact that males do not directly produce offspring. Thus in a population containing males and females (sexually reproducing) the birth rate per capita is lower than in a population solely made up of parthenogenetic females (Maynard Smith, 1978). This means parthenogenetic populations can produce twice as many progeny compared to populations with males (assumed 1:1 sex ratio), as each parthenogenetic female in the population can bare progeny. This is called the “twofold cost” of sexual reproduction (Maynard Smith, 1978, Morran, Parmenter & Phillips, 2009, Tobler & Schlupp, 2010). With the ability to reproduce in greater numbers parthenogenetic species can spread into areas where conditions are favourable more quickly that sexual species (Hörandl, E. 2009). Maynard (1978) also suggested that without males, populations

References: D 'Souza TG, Michiels, N.K. (2008), “Correlations between sex rate estimates and fitness across predominantly parthenogenetic flatworm populations”. Journal of Evolutionary Biology 21 (1), pp. 276-277 Green RF, Noakes DLG (1995) “Is a little bit of sex as good as a lot?” Journal of Theoretical Biology 174 (1), pp. 87 Hörandl E (2009), “A combinational theory for maintenance of sex”. Heredity 103 (6), pp. 445-450, 453-455 Lively CM (2010) “Parasite virulence, host life history, and the costs and benefits of sex”. Ecology 91 (1), pp.3 -6 Mittwoch U (1978), "Parthenogenesis". Journal of Medical Genetics 15, pp. 165-181 Morran LT, Parmenter MD, Phillips PC (2009) “Mutation load and rapid adaptation favour outcrossing over self-fertilization”. Nature 462 (7271), pp. 350-352 Peck, J.R., Waxman, D. (2000) “What 's wrong with a little sex?” Journal of Evolutionary Biology 13 (1), pp. 63-69 Rice WR, Chippindale AK (2001), “Sexual recombination and the power of natural selection”. Science 294 (5542), pp.555–559. Tobler M, Schlupp I (2010) “Differential susceptibility to food stress in neonates of sexual and asexual mollies (Poecilia, Poeciliidae)”. Evolutionary Ecology 24 (1), pp. 39-47