Intermediary floral traits between natural hybrid and its parents in the Xiquexique (Cactaceae)

Hybrid systems represent ‘new ecological opportunities’, as the changes in their vegetative and reproductive traits may facilitate colonization of new niches. The Cactaceae species Xiquexique gounellei and Xiquexique tuberculatus present different habitat preferences in the Brazilian Caatinga, however, across their distributions, some populations occur sympatrically and some individuals showed vegetative characteristics intermediate between these two species, suggesting a hybrid zone. These individuals also clearly did not belong to either of the two species, leading us to suppose that they could be hybrids, named as X. × heptagonus. Taking into account this assumption, we used a series of protocols to compare the floral attributes and signals, and floral biology displayed by the putative hybrid with those of its parents. The results showed that the flowers of the hybrid are morphologically intermediate to those of their parents. The colour of the external elements of the perianth is transgressive, and the white colour of the internal perianth-segments is shared between the three taxa. Scent analyses showed that X. × heptagonus has a scent profile that is intermediate to those of its parents, with only a few compounds indicating a transgressive phenotype. Both taxa of Xiquexique received visits from nectarivorous bats (Glossophaginae and Lonchophyllinae) and from the hawkmoths Agrius cingulata and Erinnyis ello. Our results reinforce the existence of this hybrid in the genus Xiquexique being derived from the possible parent species present. We also revealed how the floral morphology and the visual and olfactory cues of X. × heptagonus were shaped by the hybridization.