Positive assortative mating among populations and no evidence of non-competitive postmating prezygotic isolation
Multiple mating tests show, for the most part, significant sexual isolation among strains. Tests between strains of different subspecies (heterotypic) showed strong positive assortative mating with no asymmetry in female’s preference. This departure from random mating indicates strong, but not complete, premating isolation between the subspecies. The same assay using strains of the same subspecies (homotypic) also showed positive assortative mating between island and geographically distant mainland populations (Saint Vincent and Uruguay) but not between geographically closer island populations (Guadeloupe and Puerto Rico) (IPSI= 0.20; P = 0.145). There was also no evidence of asymmetry in female’s preference in homotypic mating assays (IAPSI) (Table 1). When the data was analyzed within each replicate, we found that the detected premating isolation was not consistent across replicates (Table S1). Altogether, any indication of premating isolation is not driven by the subspecies status of the strains assayed but rather by its population origin.
We compared overall fecundity of females crossed to males of the same population to estimates from crosses between individuals of different subspecies. This is a non-competitive setting, as females were not offered an opportunity to doubly-mate with both males of the same population and of a different population or. subspecies. We found significant differences among crosses in fecundity (F7,37= 9.8; p< 0.001). Crosses among individuals of the same populations were non-significantly different from crosses between individuals of different subspecies (Figure 1).