Reinforcement of pre-zygotic isolation and karyotype evolution in Agrodiaetus butterflies

Abstract

Theory has shown that reinforcement is a possible mechanism that can lead to speciation6-8, empirical evidence has been sufficiently scarce to raise doubts about the importance of reinforcement in nature6,9,10. Agrodiaetus butterflies (Lepidop- tera: Lycaenidae) exhibit unusual variability in chromosome number. Whereas their genitalia and other morphological characteristics are largely uniform, different species vary con- siderably in male wing colour, and provide a model system to study the role of reinforcement in speciation. Using comparative phylogenetic methods, we show that the sympatric distribution of 15 relatively young sister taxa of Agrodiaetus strongly corre- lates with differences in male wing colour, and that this pattern is most likely the result of reinforcement. We find little evidence supporting sympatric speciation: rather, in Agrodiaetus, karyo- typic changes accumulate gradually in allopatry, prompting reinforcement when karyotypically divergent races come into contact.