Drosophila stocks and maintenance
Four strains obtained from the National Drosophila Species Stock Center were used in this study. The stocks were Drosophila willistoni willistoni 14030–0814.10 (G: Guadeloupe) and 14030–0811.12 (P: Toro Negro, Puerto Rico), and D. w. winge 14030–0811.13 (S: Saint Vincent and the Grenadines), and 14030–0811.16 (U: Rocha, Uruguay). A previously established postzygotic isolation of Central America, North America, and northern Caribbean islands from South American and southern Caribbean island strains and suggested a subdivision of D. w. willistoni into two subspecies namedD. w. willistoni and D. w. winge (Mardiros et al ., 2016).
Flies were kept in bottles containing cornmeal-yeast-agar-molasses (CYAM) medium and kept in a 12:12 light–dark cycle at 22-24°C. Adult flies used in mating experiments, in interrupted mating assays or to produce hybrids were collected as newly emerged every 4 hours to ensure virginity. Virgin females and naïve males were separated, maintained at a density of 20 flies per vial, and aged post-eclosion before being used.