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Abstract:
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We report a new obligate pollination mu-
tualism involving the senita cactus, Lophocereus schottii
(Cactaceae, Pachyceereae), and the senita moth, Upiga
virescens (Pyralidae, Glaphyriinae) in the Sonoran De-
sert and discuss the evolution of specialized pollination
mutualisms. L. schottii is a night-blooming, self-incom-
patible columnar cactus. Beginning at sunset, its ¯owers
are visited by U. virescens females, which collect pollen
on specialized abdominal scales, actively deposit pollen
on ¯ower stigmas, and oviposit a single egg on a ¯ower
petal. Larvae spend 6 days eating ovules before exiting
the fruit and pupating in a cactus branch. Hand-polli-
nation and pollinator exclusion experiments at our study
site near Bahia Kino, Sonora, Mexico, revealed that
fruit set in L. schottii is likely to be resource limited.
About 50% of hand-outcrossed and open-pollinated
senita ¯owers abort by day 6 after ¯ower opening.
Results of exclusion experiments indicated that senita
moths accounted for 75% of open-pollinated fruit set in
1995 with two species of halictid bees accounting for the
remaining fruit set. In 1996, ¯owers usually closed be-
fore sunrise, and senita moths accounted for at least
90% of open-pollinated fruit set. The net outcome of the
senita/senita moth interaction is mutualistic, with senita
larvae destroying about 30% of the seeds resulting from
pollination by senita moths. Comparison of the senita
system with the yucca/yucca moth mutualism reveals
many similarities, including reduced nectar production,
active pollination, and limited seed destruction. The in-
dependent evolution of many of the same features in the
two systems suggests that a common pathway exists for
the evolution of these highly specialized pollination
mutualisms. Nocturnal ¯ower opening, self-incompati-
ble breeding systems, and resource-limited fruit pro-
duction appear to be important during this evolution |
