AOBPreview originally published online on November 3, 2006
Annals of Botany 2007 99(1):29-38; doi:10.1093/aob/mcl229
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Reproductive Biology and Mating System Estimates of Two Andean Melocacti, Melocactus schatzlii and M. andinus (Cactaceae)
1 Instituto Venezolano de Investigaciones Científicas, Centro de Ecología, Aptdo. 21827, Caracas 1020-A, Venezuela
2 Universidad Central de Venezuela, Facultad de Ciencias, Centro de Botánica Tropical, Aptdo. 48312, Caracas 1041-A, Venezuela
3 Universidad de Los Andes, Facultad de Ciencias, Departamento de Biología, Mérida 5101, Venezuela
* For correspondence. E-mail: jnassar{at}ivic.ve
Received: 15 July 2006 Returned for revision: 24 August 2006 Accepted: 6 September 2006 Published electronically: 3 November 2006
BACKGROUND AND AIMS: The genus Melocactus comprises 36 species of globose cacti with the most derived traits in the Cereeae tribe. It is the proper study system to examine what are the most derived reproductive strategies within that tribe. This study aims to characterize the reproductive biology and to estimate the mating system parameters of two Andean melocacti, Melocactus schatzlii and M. andinus.
METHODS: The reproductive attributes of the two species were described, including floral morphology, anthesis patterns, floral rewards, floral visitors and visitation patterns. Levels of self-compatibility and autonomous self-pollination were estimated by hand-pollination experiments. Mating system estimates were obtained by conducting progeny array analyses using isozymes.
KEY RESULTS: The flowers of the two species present the typical hummingbird-pollination syndrome. Despite their morphological resemblance, the two species differ in flower size, pollen and ovule production and anthesis pattern. Their main pollinator agents are hummingbirds, four species in M. schatzlii and one species in M. andinus. Both cacti are self-compatible and capable of self-pollination without the aid of pollen vectors. Population-level outcrossing rate was higher for M. schatzlii (tm=0·9) than for M. andinus (tm=0·4). At the family level, outcrossing rates for most mothers of M. schatzlii were higher (tm>0·8) than for M. andinus (tm<0·5).
CONCLUSIONS: Although the two cacti are capable of selfing, M. schatzlii is a predominantly outcrossing species, while M. andinus behaves as a mixed-mating cactus. Hummingbirds are the only pollinators responsible for outcrossing and gene flow events in these species. In their absence, both melocacti set seeds by selfing. Based on its low population size, restricted distribution in Venezuela, low rates of floral visits, and high levels of inbreeding, M. andinus is considered to be an endangered species deserving further study to define its conservation status.
Key words: Andes, Cactaceae, hummingbird, isozymes, mating system, Melocactus andinus, Melocactus schatzlii, reproductive biology
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