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).