Reinforcement and Sexual Selection: Interaction and Effect on Mate Recognition

Higgie, Megan (2008). Reinforcement and Sexual Selection: Interaction and Effect on Mate Recognition PhD Thesis, School of Integrative Biology, The University of Queensland.

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Author Higgie, Megan
Thesis Title Reinforcement and Sexual Selection: Interaction and Effect on Mate Recognition
School, Centre or Institute School of Integrative Biology
Institution The University of Queensland
Publication date 2008-09-01
Thesis type PhD Thesis
Supervisor Prof Mark Blows
Dr Steve Chenoweth
Total pages 165
Language eng
Subjects 270000 Biological Sciences
Formatted abstract
Closely related species often differ most dramatically in the appearance of mating traits,
suggesting that selection on these traits is important to the formation of new species.
Reinforcement can cause the evolution of traits involved in species recognition where species
co-occur in sympatry with a closely related species. If these traits are also used for withinspecies
mate choice, then there is the potential for reinforcement to interfere with the action of
sexual selection. Reinforcing selection acts on the cuticular hydrocarbons (CHCs) of
Drosophila serrata where it is sympatric with a closely-related species, Drosophila birchii,
generating a pattern of reproductive character displacement in CHCs between sympatric and
allopatric populations of D. serrata. These same CHCs have also been shown to be under
sexual selection within D. serrata. Here, I studied the interaction between reinforcement and
sexual selection in populations of D. serrata.
Along a 36 km transect across the transition between sympatric and allopatric populations of
D. serrata, reinforcing selection generates reproductive character displacement in male and
female CHCs. The transition in male CHCs was markedly abrupt, suggesting strong
reinforcing selection acting to create the sympatric phenotype, and at the same time, strong
selection acting to maintain an allopatric phenotype. Consistent with the hypothesis that the
allopatric phenotype is favoured by sexual selection, females from allopatric populations prefer
males with allopatric-like CHCs over sympatric-like CHCs. This result suggests that sexual
selection within D. serrata is compromised by reinforcing selection and may be preventing the
spread of sympatric-like blends to the area of allopatry. Reinforcing selection and sexual
selection therefore interact to maintain reproductive character displacement at the transition
between sympatric and allopatric populations.To confirm that sexual selection was responsible for the allopatric phenotype, the opportunity
for sexual selection was manipulated in sympatry–allopatry hybrid populations of D. serrata.
The CHCs of hybrid male D. serrata evolved under the influence of sexual selection (and no
reinforcing selection) to resemble those of allopatric populations, and this was driven by
female choice alone. Female preference evolved to prefer allopatric males to sympatric males
in the populations where hybrid females were allowed to choose their mates.
The evolution of CHCs and preferences under sexual selection to an allopatric phenotype
demonstrated that the allopatric phenotype is the sexual selection optimum in D. serrata.
Therefore I conclude that sexual selection causes the allopatric phenotype, while a combination
of reinforcing selection and sexual selection cause the sympatric phenotype. As a consequence
of both the processes of reinforcement and sexual selection, the allopatric and sympatric
populations of D. serrata have different blends of CHCs, and importantly, different female
preferences for those blends. These different preferences result in positive assortative mating
between sympatric and allopatric populations that could eventually result in higher premating
isolation between these populations in the future. More broadly, I discuss how other types of
species interactions that are carried out on the basis of mating traits can also generate divergent
mate choice within species.
Keyword reinforcement, reproductive character displacement, sexual selection, natural selection, mate recognition, species recognition, mate choice, mating signals, female preference, cuticular hydrocarbons

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Created: Sat, 06 Dec 2008, 00:59:01 EST by Dr Megan Higgie on behalf of School of Biological Sciences