A tale of three morphs I: Variations in nectar, reproductive compatibility, and abundance explain reproductive success of the morphs in a polymorphic ginger from Western Ghats, India
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Background and aims
Floral color polymorphism is common in angiosperms, yet in perennial, clonal plants, proximate trait differences and reproductive differences among sympatric morphs remain poorly understood. This is primarily because perennial individuals can carry signatures of past selection regimes. We studied bract color polymorphism in a nocturnal ginger Curcuma caulina to ask: (i) Do nectar rewards, reproductive compatibility and pollinator visitation differ among color morphs? (ii) Does morph abundance correlate with fitness via ecological (pollinator-mediated) or physiological (compatibility) pathways? (iii) Do these traits predict realized reproductive success?
Methods
We measured 22 floral/vegetative traits (n=30 per morph), nectar rewards (106 flowers), pollinator visitation rates (648 hours), and physiological compatibility (471 hand-pollinations treatments) and natural fruit and seed set (≥50 per morph) across three dominant morphs. Path analysis tested direct and indirect effects of morph abundance, nectar traits, pollinator visitation, and compatibility on reproductive fitness.
Key results
Morphs did not differ in their morphological traits but showed differential nectar and reproductive compatibility traits. The rare red-white morph produced the highest nectar energy, received the most visits, had a leaky self-compatibility, and yet showed lowest seed count per fruit, while the most common green-red morph was self-incompatible, showed higher cross-compatibility and had highest seeds per fruit. The second common green-white morph showed intermediate abundance and also showed leaky self-compatibility. Path analysis indicated that morph abundance had both direct and indirect effects on reproductive fitness, mediated by nectar, pollinator visitation and compatibility.
Conclusions
Reproductive success of the polymorphic C. caulina is a result of multi-trait interactions including pollinator interaction. That is, nectar traits and mating-system differences shape reproductive fitness of the morphs. We also highlight that in polymorphic perennial plants contemporary selection regimes may be acting alongside genotypic vestiges (historical genotypes present in extant population), thus complicating any frequency-dependent selection regime.
