Abstract
BACKGROUND AND AIMS: Pollinator specificity facilitates reproductive isolation among plants, and mechanisms that generate specificity influence species boundaries. Long-range volatile attractants, in combination with morphological co-adaptations, are generally regarded as being responsible for maintaining extreme host specificity among the fig wasps that pollinate fig trees, but increasing evidence for breakdowns in specificity is accumulating. The basis of host specificity was examined among two host-specific Ceratosolen fig wasps that pollinate two sympatric varieties of Ficus semicordata, together with the consequences for the plants when pollinators entered the alternative host variety. METHODS: The compositions of floral scents from receptive figs of the two varieties and responses of their pollinators to these volatiles were compared. The behaviour of the wasps once on the surface of the figs was also recorded, together with the reproductive success of figs entered by the two Ceratosolen species. KEY RESULTS: The receptive-phase floral scents of the two varieties had different chemical compositions, but only one Ceratosolen species displayed a preference between them in Y-tube trials. Specificity was reinforced at a later stage, once pollinators were walking on the figs, because both species preferred to enter figs of their normal hosts. Both pollinators could enter figs of both varieties and pollinate them, but figs with extra-varietal pollen were more likely to abort and contained fewer seeds. Hybrid seeds germinated at normal rates. CONCLUSIONS: Contact cues on the surface of figs have been largely ignored in previous studies of fig wasp host preferences, but together with floral scents they maintain host specificity among the pollinators of sympatric F. semicordata varieties. When pollinators enter atypical hosts, post-zygotic factors reduce but do not prevent the production of hybrid offspring, suggesting there may be gene flow between these varieties.
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Claims 9
Claim · model-written summary
The two fig varieties had different receptive floral scent compositions.
- Taxon
- Ficus semicordata
Ficus semicordatae1 - Outcome
- chemical compositionse0
- Direction
- differente0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The receptive-phase floral scents of the two varieties had different chemical compositions”
e1“two sympatric varieties of Ficus semicordata”
Claim · model-written summary
Only one Ceratosolen species preferred one scent over the other in Y-tube tests.
- Taxon
- Ceratosolen
Ceratosolene0
- Outcome
- displayed a preferencee0
- Setting
- Y-tube trialse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“only one Ceratosolen species displayed a preference between them in Y-tube trials.”
Claim · model-written summary
Both pollinator species preferred entering figs of their normal hosts after walking on figs.
- Taxon
- Ficus semicordataFicus semicordatae1
- Interactor
- Ceratosolen fig waspse2pollinator
- Outcome
- preferred to enter figs of their normal hostse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Specificity was reinforced at a later stage, once pollinators were walking on the figs, because both species preferred to enter figs of their normal hosts.”
e1“two sympatric varieties of Ficus semicordata”
e2“two host-specific Ceratosolen fig wasps”
Claim · model-written summary
Both pollinators could enter and pollinate both fig varieties.
- Taxon
- Ficus semicordataFicus semicordatae1
- Interactor
- Ceratosolen fig waspse2pollinator
- Outcome
- enter figs of both varieties and pollinate theme0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Both pollinators could enter figs of both varieties and pollinate them”
e1“two sympatric varieties of Ficus semicordata”
e2“two host-specific Ceratosolen fig wasps”
Claim · model-written summary
Figs receiving extra-varietal pollen were more likely to abort.
- Taxon
- Ficus semicordataFicus semicordatae1
- Outcome
- aborte0
- Direction
- more likelye0
- Qualifier
- extra-varietal pollene0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“figs with extra-varietal pollen were more likely to abort and contained fewer seeds.”
e1“two sympatric varieties of Ficus semicordata”
Claim · model-written summary
Figs receiving extra-varietal pollen contained fewer seeds.
- Taxon
- Ficus semicordataFicus semicordatae1
- Outcome
- seedse0
- Direction
- fewere0
- Qualifier
- extra-varietal pollene0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“figs with extra-varietal pollen were more likely to abort and contained fewer seeds.”
e1“two sympatric varieties of Ficus semicordata”
Claim · model-written summary
Hybrid seeds germinated at normal rates.
- Taxon
- Ficus semicordataFicus semicordatae1
- Organ / stage
- Hybrid seedse0
- Outcome
- germinatede0
- Direction
- normale0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Hybrid seeds germinated at normal rates.”
e1“two sympatric varieties of Ficus semicordata”
Claim · model-written summary
Contact cues and floral scents together maintain pollinator host specificity.
- Taxon
- F. semicordataFicus semicordatae0
- Interactor
- fig waspe0pollinator
- Outcome
- host specificitye0
- Qualifier
- Contact cuese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Contact cues on the surface of figs have been largely ignored in previous studies of fig wasp host preferences, but together with floral scents they maintain host specificity among the pollinators of sympatric F. semicordata varieties.”
Claim · model-written summary
Post-zygotic factors reduce hybrid offspring production but allow possible gene flow.
- Taxon
- Ficus semicordataFicus semicordatae1
- Outcome
- production of hybrid offspringe0
- Direction
- reduce but do not prevente0
- Qualifier
- post-zygotic factorse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“When pollinators enter atypical hosts, post-zygotic factors reduce but do not prevent the production of hybrid offspring, suggesting there may be gene flow between these varieties.”
e1“two sympatric varieties of Ficus semicordata”