Evolution of reproductive isolation as a by‐product of divergent life‐history evolution in laboratory populations of Drosophila melanogaster

• Published in: Ecology and evolution Vol. 2; no. 12; pp. 3214 - 3226
• Main Authors: M. Ghosh, Shampa, Joshi, Amitabh
• Format: Journal Article
• Language: English
• Published: England John Wiley & Sons, Inc 01.12.2012; Blackwell Publishing Ltd
• Subjects: Adaptation; Animal behavior; Animal reproduction; Body size; development time; Divergence; divergent selection; Drosophila melanogaster; Evolution; Females; Fruit flies; Gene expression; Insects; Laboratories; laboratory selection; Males; mate choice; Mating; Original Research; Populations; postcopulatory prezygotic isolation; premating isolation; Reproductive isolation; sexual conflict; Sexual selection; Studies; Success; divergent selection; postcopulatory prezygotic isolation; sexual conflict; development time; Body size; sexual selection; laboratory selection; reproductive isolation; mate choice; premating isolation
• ISSN: 2045-7758; 2045-7758
• DOI: 10.1002/ece3.413

We show that two complementary asymmetric isolating mechanisms, likely mediated by divergence in body size, underlie the evolution of incipient reproductive isolation between a set of Drosophila melanogaster populations selected for rapid development and their ancestral controls. Selection has led to great reduction in body size in the fast developing lines. Small males belonging to fast developing lines obtain few matings with large control females, both in presence and absence of large control line males, giving rise to unidirectional, premating isolation caused by sexual selection. Conversely, small selected line females suffer greatly increased mortality following mating with large control males, causing unidirectional postcopulatory prezygotic isolation. We discuss preliminary evidence for evolution of reduced male harm caused to females upon mating in the fast developing lines, and speculate that the females from these lines have coevolved reduced resistance to male harm such that they can no longer resist the harm caused by males from control lines. This potentially implicates differing levels of sexual conflict in creating reproductive barrier between the selected line females and the control males. We also show that a large difference in development time is not sufficient to cause postzygotic incompatibilities in the two sets of populations reaffirming the belief that prezygotic isolation can evolve much earlier than postzygotic isolation. We show that long‐term selection for rapid development and early reproduction in laboratory populations of Drosophila melanogaster led to the evolution of reproductive isolation between the selected populations and their ancestral controls presumably due to body size divergence. Small females of fast developing lines show high mortality rate after mating with large ancestral line males giving rise to unidirectional postcopulatory prezygotic isolation. Small males from the fast developing lines, on the other hand, obtain few matings with large control line females showing evolution of a premating barrier in the other direction. Flies from ancestral populations shown in the upper row; lower row showing individuals from fast developing populations.