Sympatric speciation still remains a controversial issue in biology. The general framework for sympatric speciation is disruptive selection for a fitness trait, the formation of coadapted gene complexes and their maintenance through the action of linkage and assortative mating. Although many theoretical models show sympatric speciation is possible, empirical support for these ideas in wild populations is harder to come by. In this thesis we use the polymorphic population structure of the side-blotched lizard (Uta stansburiana) to investigate possible mechanisms of incipient sympatric species formation and maintenance. Inherent in populations of the side-blotched lizard are three genetically determined throat colour morphs, orange, blue and yellow. Each throat colour is linked to a distinct reproductive strategy in males and females. Male morphs cycle in frequency in response to negative frequency dependent selection of male mating success. In females only two throat colours are expressed (orange and yellow); these cycle as a function of density dependent selection of female reproductive allocation strategies. We found strong support for the role of correlational selection as a mechanism for the build up of coadapted gene complexes (morphs) in a runaway process as a result of selection in fluctuating social environments. In addition, favourable genetic combinations were perpetuated by a positive assortative mate preference function in females. However, variation in mating pattern, because of the context dependent nature of female preference functions and changes in morph specific male mating success in response to fluctuations in socially determined male-male competition, acted to maintain cross-morph mating, reducing reproductive isolation of the different morphs. Therefore, despite the presence of a structured population gene pool around three fitness peaks (that correspond to orange, blue and yellow morphs) speciation is prevented by the loss of prezygotic isolation because of the context dependent nature of decisions and as a result of sexual conflict.
|Translated title of the contribution||Processes of incipient speciation: The formation and maintenance of alternative strategies in the side blotched lizard, Uta stansburiana|
|Number of pages||155|
|Publication status||Published - 2004|