Changes in floral traits and higher reproductive success after management in Cereus jamacaru, a cactus endemic to Brazil and obligatorily cross-pollinated by Sphingids

Abstract

Pollination is a key component for plant reproduction and maintenance and can be directly altered by anthropogenic disturbances, such as traditional plant management. Plant management causes changes in several floral and reproductive traits, including floral morphology, number of reproductive structures, and reproductive success. We investigated floral morphology, pollination biology and ecology, and quantified measures of investment in male function (i.e., amount of pollen/anther, pollen/flower, and pollen viability); female function and reproductive success (i.e., number of ovules/ovary, fruit set, and seed set) of managed and unmanaged Cereus jamacaru DC. (Cactaceae) individuals in the Caatinga. For this purpose, we conducted observations, pollination experiments and analysed flower buds, flowers and fruits. We observed that managed individuals exhibited flowers with greater a) corolla area (64%), b) corolla diameter (30%) and c) floral tube length (16%), d) herkogamy (i.e., stigma-anther distance; 600%), e) number of ovules (16%) f) pollen/flower (7.1%), fruit set (133%) and seed set (49%) in relation to the unmanaged population. The flowers of the managed population were visited exclusively by Manduca rustica and those of the unmanaged population by M. paphus. Our findings reveal that traditional management favours C. jamacaru individuals in the Caatinga dry forest. Furthermore, pollination by species of Sphingids exclusive to each population, together with herkogamy, can act as a barrier to pollen/gene flow between managed and unmanaged individuals. Thus, traditional management may not be able to maintain C. jamacaru populations in the Caatinga, as well as its associated fauna, i.e., pollinating and dispersing animals.