Fig 1.
Two hypotheses for the divergence of reproductive traits expected under reinforcement.
While allopatric populations of two species (plain ellipses and +) may retain widely overlapping variation for reproductive traits, reinforcement predicts a reduction of this overlap in the hybrid zone (empty ellipses and ×) as a selective response against maladaptive hybridization. This can be achieved by reproductive character displacement, which increases mean interspecific differences (left), or by reducing intraspecific variation without shifting the average phenotypes (right).
Fig 2.
Genetic structure of the A. o. obstetricans / A. a. almogavarii hybrid zone.
(A) Distributions of the mitochondrial lineages. (B) Individual (barplots) and population (piecharts on the map) nuclear ancestry estimated from 1,642 unlinked SNPs. (C) Sigmoid clines fitted on mitogroup frequencies (dashed cline), average ancestries (black plain cline, with the 95% confidence interval) and frequencies of 4,092 species-diagnostic SNPs (grey clines) along the geographic transect. (D) Variation in cline center (as the deviation Δc from the average center) and cline width w. Arrows point to potential barrier loci (null width). Photo credit: J. Ambu.
Fig 3.
Bioacoustic variation among 71 individuals in (parapatric) and out (allopatric) of the hybrid zone.
(A) PCA on four mating call parameters. (B) Geographic origin and group assignments of calls.
Table 1.
Comparison of the bioacoustic variation between allopatric and parapatric species across the four axes of the PCA (Fig 3).