Biology Reference
In-Depth Information
Table 1.3
2ESULTSFORHYBRIDIZATIONEXPERIMENTSONFOURSPECIESOF
Goodyera
enclosed in nylon
net (percentage capsule set/percentage fertile seed [median (range)]) (Kallunki
1981
)
Variables
G. oblongifolia
G. pubescens
G. repens
G. tesselata
Source of plants
Michigan
Wisconsin, Rhode Island
Michigan
Michigan
Hybridized
G. pubescens
X
71/57.5 (1-96)
G. repens
X
96/34 (0-80)
82/46 (3-76)
G. tesselata
X
78/42 (0-87)
90/68 (20-98)
74/73.5 (24-96)
Chromosomes (2
n
)
30
26
30
60 (45)
tesselata
, intermediate in size and other characters between
G. oblongifolia
and
G. repens
, is apparently not mechanically or ecologically isolated from either spe-
cies. It probably hybridizes freely with one or both of the diploids in areas, where
they are sympatric. Triploids (2
n
= 45) were found only in areas, where
G. tesselata
and
G. oblongifolia
or both diploids were also present (Kallunki
1981
). These plants
had irregular meiosis and resembled
G
.
tesselata
in morphology. The presence of
occasional parthenocarpic plants (Ackerman
1975
; Kallunki
1981
) might also be
RELATEDTOTRIPLOIDY4HECONlDENCELIMITSONTHEPERCENTAGEOFPLANTSINMIXED
populations that looked like
G. tesselata
but were actually triploids ranged from
33 to 79% (Kallunki
1981
).
'IVENTHEOCCURRENCEOFMIXEDPOPULATIONSANDTHEABSENCEOFSIGNIlCANTCHRO-
mosomal sterility barriers it might be asked what, if anything, restricts the level of
HYBRIDIZATION3EEDLINGESTABLISHMENTCANOCCURWITHINEXISTINGCOLONIESOFALLFOUR
species (Ames
1921
; Reddoch and Reddoch
2007
), but rhizome growth gives rise
TOEXTENSIVECLONESANDTHECLONALPOPULATIONSTRUCTUREPLUSTHEABSENCEOFSUBSTAN-
tial self-incompatibility barriers probably results in much inbreeding (Ackerman
1975
; Kallunki
1981
3ELFCOMPATIBILITYWOULDBEEXPECTEDTOAUGMENTSEED
production in a clonal species (Estes and Brown
1973
; Estes and Thorpe
1974
) and
in combination with vegetative reproduction, contribute to the maintenance of spe-
CIESINTEGRITYINHYBRIDIZINGMIXEDPOPULATIONS!CKERMAN
1975
; Kallunki
1981
).
Clonal structure also leads to a clustering of inflorescences which could enhance the
orchid's visual and olfactory appeal to pollinators and provide a concentrated food
source (Ackerman
1975
), factors that might further reduce hybridization by restrict-
ing pollen transport and gene flow, especially in years when genets produce large
numbers of flowers (Kallunki
1981
).
A certain amount of isolation would therefore result from self-compatibility
ANDAPERENNIALCLONALGROWTHHABIT(OWEVEREXPERIMENTSWITHmORESCENTPIG-
MENTPARTICLESREVEALEDTHATVECTORSFREQUENTLYMOVEDBETWEENANDCROSSPOLLI-
nated the flowers of
G. tesselata
and
G. oblongifolia
, and hybrids resulting from
crosses between
G. tesselata
ANDEITHERDIPLOIDCOULDBEPRESENTINANYMIXED
species population (Kallunki
1981
). There are, as yet, no reports of diploid hybrids
between
G. repens
and
G. oblongifolia
despite a median of 34% fertile seed
OBTAINEDINEXPERIMENTALCROSSES4ABLE
1.3
). Apparently, cross-pollination between
THESESPECIESOCCURSINFREQUENTLYUNDERNATURALCONDITIONSORTHEREISAPROBLEM
with the establishment of the hybrid seeds. It may be significant that
G
.
repens
and
G. oblongifolia
are among the most dissimilar members of the genus in our flora
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