Relaxed selection in a Heliconius hybrid zone and the origin of adaptive variation

Hybridization is becoming increasingly recognized for its importance in generating novel adaptive variation and new species within a variety of different taxa.  Within Heliconius butterflies, hybridization is likely responsible for some of the remarkable diversity of adaptive wing-color patterns found in the genus.  An adaptive radiation of wing-color patterns, which serve as warnings to predators of their unpalatability, has resulted in a patchwork of differently colored races and species across the Americas.  When in contact, races or species often form narrow hybrid zones that are maintained by strong frequency-dependent selection against rare patterns.  This hybridization has been suggested to be responsible for the origin of even more novel warning color patterns. To test if relaxed selection in hybrid zones could facilitate the establishment of new adaptive color patterns, we conducted a capture-mark-release-re-sight (CMRR) study and warning color cline analyses across a Heliconius hybrid zone in French Guiana.  Results of the CMRR study show that both pure races, most hybrid forms, and two altered forms had high probabilities of establishment and similar life expectancies.  Additionally, cline analyses indicate that the widths of the color pattern clines are comparatively broad for a Heliconius hybrid zone.  These results suggest that selection is relatively relaxed within the hybrid zone, which would promote mixing of color pattern alleles and drive the evolution of new adaptive warning colors.  This provides much insight into the ecological and evolutionary conditions that are conducive to hybridization facilitating adaptation and speciation.