Mating systems in a natural hybrid of Cephalocereus (Cactaceae) and comparative seed germination

Abstract

The Cactaceae family has a strong predisposition for hybridization, which is a mechanism suggested to be relevant to its evolution. However, a few studies evidence the consequences of hybridization in members of this family. A population of Cephalocereus columna-trajani × C. tetetzo cohabits with both parental species in the Tehuacán-Cuicatlán Reserve, Mexico. A comparative analysis was conducted between these three taxa with three principal aims: a) determine, through in situ experiments, the mating system of a hybrid taxon; b) compare seed morphology; and c) evaluate seed germination under controlled conditions. Our results show that the mating success was higher between hybrid individuals than between hybrids and C. tetetzo members. The hybrid seed showed the typical morphology of the tribe Pachycereeae but was statistically smaller than the seed of C. columna-trajani. Under white and red light the total germination percentage of hybrid seeds was higher than that of both parental species, which was interpreted as hybrid vigor. In summary, the successful mating between individuals preceding the formation of viable seeds with better germination capacity than both parental species is evidence of the reproductive success of hybrids, disproving their sterility and challenging the view that the hybrid taxon represents an “evolutionary endpoint”.