Subtribes Goodyerinae and Cranichidinae - The Pollination Biology of North American Orchids: North of Florida and Mexico - page 10

(Kallunki 1981 ). Their different, though overlapping, flowering periods; partial
mechanical isolation based on size differences of the flowers; and partial ethologi-
cal isolation related to differences in ultraviolet reflectance, odor, and nectar
REWARDMAYAFFECTTHEFREQUENCYOFHYBRIDIZATION/NTHEOTHERHANDSINCETHE
flowers of G. tesselata resemble those of G. oblongifolia in ultraviolet reflectance
and odor production and are intermediate between those of G. repens and G.
oblongifolia in size, bees may have greater difficulty distinguishing them from
flowers of the other two species. The presence of G. tesselata may therefore
INCREASETHEPROBABILITYOFHYBRIDIZATIONWHENEVERITOCCURSINMIXEDPOPULATIONS
with one or both of the diploids (Kallunki 1981 ).
Goodyera pubescens , with a different base chromosome number, is also interfer-
tile with the other three species, producing a median of 46-68% fertile seed in hand
pollinations (Table 1.3 .ATURALHYBRIDSMIGHTTHEREFOREOCCURINMIXEDPOPULA-
tions, but again, none have yet been reported. Kallunki ( 1981 ) did not study this
species in detail, and information on ultraviolet reflectance, floral odor, and many
other details are not available. However, differences in lip shape and ornamentation
might contribute to its apparent reproductive isolation. It has been reported to attract
different pollinators than the other three Goodyera species (see below), but further
study is needed.
Phenological separation might play an important, perhaps a primary role in the
reduction of hybridization between G. tesselata and the two diploids in some areas.
!LTHOUGHmOWERINGPERIODSOVERLAPTHEMEDIANBLOOMINGDATESINMIXEDPOPULA-
tions for all pairwise comparisons of the three species differ significantly in north-
ern Michigan (Kallunki 1981 ). Goodyera tesselata blooms first followed by G.
repens and then G. oblongifolia (Kallunki 1976, 1981 ). Backcrosses between trip-
loid offspring and their diploid as well as probably their tetraploid parents may be
largely sterile. If so, selection for a prezygotic isolating mechanism, such as phe-
NOLOGICALSEPARATIONTOREDUCETHENUMBEROFWASTEDGAMETESMIGHTBEEXPECTED
Levin and Kerster ( 1967 ) have demonstrated that such selection can occur in
perennial as well as in short-lived annual species.
Brown ( 1985 ), in a 20-year study, confirmed the order of flowering reported
FROM-ICHIGANINMIXEDPOPULATIONSONTHE"RUCE0ENINSULAIN/NTARIO(OWEVER
Barclay-Estrup et al. ( 1991 FOUNDADIFFERENTSEQUENCEOFOVERLAPPINGmOWERING
periods in the Thunder Bay District. Here, G. repens apparently blooms earlier than
G. tessselata with G. oblongifolia again blooming last. The significance of these
differences remains to be determined.
Finally, in plants with a clonal outbreeding system each intraspecific pollination
event results in the production of a large number of seeds. Both geitonogamy and
cross-pollination, therefore, also counter the detrimental effects of hybridization.
Pollinators and Pollination Mechanisms
Bumblebees, attracted by nectar at the base of the saccate lip, are the most important
pollinators of G. oblongifolia , G. repens , and G. tesselata in North America