We suggest that unlike in more divergent species compar- isons, where sperm competition typically increases reproductive isolation, ejacu- late tailoring can reduce the potential for PMPZ isolation when recently diverged populations interbreed. Fertilisation success can thus differ dra- 1679вЂ“1691 matically between competitive and noncompetitive conditions, perhaps because the males that mate second produce higher quality ejaculates in response to doi: 10.1002/ece3.1995 sperm competition. While there were subtle differences in how P Received: 9 November 2015 Revised: 17 changed over time, suggesting that Vancouver malesвЂ™ sperm are somewhat less January 2016 Accepted: 18 January 2016 competitive in a п¬Ѓrst-male role within Colorado females, these effects did not Ecology and Evolution 2016 6(6): translate into differences in overall P. setting, indicating no difп¬Ѓculty of sperm from Vancouver males to fertilize Col- orado eggs after double matings. Surprisingly, we found no Suomen Akatemia (Grant/Award Number: PMPZ reproductive isolation between the two populations under a competitive вЂ250999вЂ™). We measured premating isolation in no-choice tests, female fecundity, fertility and egg-to-adult viability after single and double mat- Funding Information ings as well as second-male paternity success (P ). remate rapidly), we set up double matings of all possible crosses between the Tel: +374 same populations to test whether competitive effects between ejaculates inп¬‚u- Fax: +358 14 617 239 E-mail: ence this PMPZ isolation. A recent study described a potential example between populations of the Correspondence same species: single matings between Drosophila montana populations resulted Outi Ala-Honkola, Department of Biological in differential fertilisation success because of the inability of sperm from one and Environmental Science, University of population (Vancouver) to penetrate the eggs of the other population (Color- Jyvaskyla, PO Box 35, FI- 40014 Jyvaskyla, ado). Veltsos, ParisД®jaculate tailoring, ejaculateвЂ“ejaculate Postmating but prezygotic (PMPZ) interactions are increasingly recognized as a interaction, postcopulatory sexual selection, potentially important early-stage barrier in the evolution of reproductive isola- reproductive isolation, speciation. PostmatingвЂ“prezygotic isolation between two allopatric populations of Drosophila montana : fertilisation success differs under sperm competition PostmatingвЂ“prezygotic isolation between two allopatric populations of Drosophila montana.

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