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Stigmatic receptivity in a dichogamous early-divergent angiosperm species, Annona cherimola (Annonaceae): influence of temperature and humidity.

PREMISE OF THE STUDY
A variety of mechanisms to prevent inbreeding have arisen in different angiosperm taxa during plant evolution. In early-divergent angiosperms, a widespread system is dichogamy, in which female and male structures do not mature simultaneously, thus encouraging cross pollination. While this system is common in early-divergent angiosperms, it is less widespread in more recently evolved clades. An evaluation of the consequences of this system on outbreeding may provide clues on this change, but this subject has been little explored.


METHODS
In this work, we characterized the cycle and anatomy of the flower and studied the influence of temperature and humidity on stigmatic receptivity in Annona cherimola, a member of an early-divergent angiosperm clade with protogynous dichogamy.


KEY RESULTS
Paternity analysis reveals a high proportion of seeds resulting from self-fertilization, indicating that self-pollination can occur in spite of the dichogamous system. Stigmatic receptivity is environmentally modulated--shortened by high temperatures and prolonged by high humidity.


CONCLUSIONS
Although spatial and temporal sexual separation in this system seems to effectively decrease selfing, the system is modulated by environmental conditions and may allow high levels of selfing that can guarantee reproductive assurance.