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Why Bother With Sex - T Gilbert and A Harding


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Why Bother With Sex - T Gilbert and A Harding

  1. 1. • Despite sexual reproduction being very costly in both time and energy, it remains one of the predominant methods of continuing a species across many complex organisms, both terrestrial and aquatic (Kawatsu, 2013). • Evolutionary theory suggests that this is in order to increase the genetic variation and allow for faster, more efficient adaptation and greater preference for sexual competition (Roze, 2012). However, due to the negative costs induced by this mechanism, females that are able to reproduce through parthenogenesis (asexually) gain a large advantage over obligatory sexual females. • Conversely, males engaging in sexual reproduction with a parthenogen increases species fitness by outcompeting other males and maintain healthy gene selection (Kawatsu, 2013). Given how sexual competition still occurs in parthenogenic species, it is implied that there is still a preference over males with stronger genes. • The theory we aim to test is that, in a species which can reproduce both sexually and parthenogenically, preference and dominance will be shown toward the individuals with greater genetic variance which can only be achieved through sexual reproduction. In our proposed experiment, this species will be the Komodo Dragon. • In our hypothesis, we highlight that individuals with greater genetic variance are preferred when being chosen as a sexual mate over those with less variance due to facultative parthenogenesis, therefore indicating that sexual reproduction is necessary for maintaining good sexual fitness. • However, this doesn’t mean asexuality is without benefits. For example, parthenogenic species have advantages over sexually reproducing species, in terms of being able to colonise new ecological niches (Beukeboom & Vrijenhoek, 1998). This is due to the fact that parthenogenic reproducers are able to produce offspring without the wasting the time needed to find a mate for sexual reproduction. • In this case, if the species’ habitat were to become over-crowded, making competition for resources more intense; or if there were more predators moving into the area, causing threat to their existence; being able to migrate, colonise and populate into a new habitat or ecological niche quickly is clearly more advantageous. Furthermore, the advantage for parthenogenic species, such as Komodo Dragons in this case, is that even with low population numbers, there is still a greater chance of repopulation compared to that of sexual reproducers- albeit at the cost of losing genetic variance. • The implications this question has on the field of evolutionary ecology, therefore, are significant. Asexuality, when analysed in contexts of overarching threats to a population, is a fast, efficient method of population growth and development. However, this does not address the fact that through sexual reproduction there is greater addition to genotypic variation, thus creating more potential for plasticity and adaptation to aspects of the environment that otherwise cannot be corrected through migratory colonisation of marginalised niches. • Sexual Reproduction involves the combination of genes from two individuals, which allow for greater plasticity and superior fitness in varying environmental changes. • Asexual Reproduction requires no partner and no gene combining, essentially cloning the parent. This prevents fitness alteration, which may be beneficial, but also fixes plasticity in a constant state (Agrawal, 2001). • In our Komodo Dragons, parthenogenesis always results in all males being born. The parent will then go on to sexually reproduce with the male with the greatest fitness to continue the species, but at the cost of inbreeding. Figure 1. How genes are spread throughout different reproductive mechanisms Figure 2. How we propose to test the potential risk of parthenogenesis in Komodo Dragons Original Komodo Dragon Image Credit: Oleksander Kovalenko