Simulating Natural Conditions in the Laboratory: A Re-Examination of Sexual Isolation between Sympatric and Allopatric Populations of Drosophila pseudoobscura and D. persimilis

Abstract

Simulating natural conditions in the laboratory poses one of the most significant challenges to behavioral studies. Some authors have argued that laboratory "choice" experiments reflect mate choice in nature more accurately than "no-choice" experiments. A recent choice experiment study questioned the conclusions of several earlier studies by failing to detect a published difference in sexual isolation between populations of Drosophila pseudoobscura, and suggested their result was more robust because of the more realistic design. Here, we re-examine the methods and analyses of this recent study, and we find there was indeed a difference in sexual isolation between populations of D. pseudoobscura. We also conduct a more rigorously controlled choice experiment and, in agreement with previous studies, note that D. pseudoobscura females from populations sympatric to their sibling species, D. persimilis, exhibit greater sexual isolation than those from allopatric populations. Our results confirm the existence of a geographic pattern in sexual isolation in D. pseudoobscura, and we discuss differences in experimental designs in light of the biology of this species.

Character Displacement as the "Best of a Bad Situation": Fitness Trade-Offs Resulting From Selection to Minimize Resource and Mate Competition

“…First, such fitness trade-offs may explain why traits that evolve in sympatry often do not spread back into allopatry even in the face of high gene flow (for discussion see Servedio and Noor 2003 and references therein). For example, Drosophila pseudoobscura exhibits high intraspecific gene flow (see Noor et al 2000 and references therein), yet females express divergent mating behaviors between sympatric and allopatric populations (Noor 1995;Noor and Ortiz-Barrientos 2005). If traits that evolve in sympatry confer a selective disadvantage in allopatry, then phenotypes that evolve in response to heterospecifics should remain localized in sympatry.…”

Time in a Bottle: The Evolutionary Fate of Species Discrimination in Sibling Drosophila Species

“…Drosophila pseudoobscura males court on average 16 seconds faster and have 2 more copulation attempts than males of D. persimilis . Although such interspecific differences in courtship intensity could have important evolutionary consequences if females select between directly competing males, such scenarios are likely limited in nature [31].…”

“…Males court females of both species indiscriminately and mate choice is driven largely by female preference for conspecific males [2], [42]. Documented patterns of species discrimination within D. pseudoobscura indicate that reinforcement is occurring; preference for conspecific males is greater in females from populations where D. pseudoobscura and D. persimilis are sympatric than in females from allopatric populations, and species discrimination ability varies in females among sympatric populations [31].…”

“…To reduce potential inbreeding depression, lineages from the same species, time point, and where possible, populations were crossed in both directions (Table 1) [2], [25], [31], [32], [43]. When crosses from the same population were not possible, crosses were made using the nearest locality from that time period.…”

Asymmetry in Reproductive Character Displacement

“…However, the effect of gene flow is generally dilution, rather than elimination, of divergence created by selection (Liou andPrice 1994, Pfennig andRyan 2006). Drosophila pseudoobscura exhibits high intraspecific gene flow (Noor and Smith 2000), yet females express divergent mating behaviors in sympatric and allopatric populations (Noor 1995, Noor andOrtíz-Barrientos 2006).…”