COS 135-6 - Maintenance of geographic mosaicness in floral color polymorphism is driven by variation in physiological compatibilities, floral ecology, and pollinator interactions

Background/Question/Methods

Floral Colour Polymoprhsim (FCP) is the presence of two or more floral color variants in the same population. Our understanding of their spatial variation, associated ecological traits, and evolutionary consequences among different populations is limited. We examined emergence and maintenance of FCP in a nocturnal, polymorphic ginger species- Curcuma caulina J. Graham (Zingiberaceae) which is endemic to the Western Ghats, India and where color polymorphism is restricted to the color of lateral bracts within an inflorescence. We tested if ecological traits such as pollinator activity and physiological traits such as reproductive compatibility could explain the genetic variation among population, and we asked:

1. 
   Do morphological and ecological traits (resulting pollinator response) vary among populations of C. caulina?
   
   


2. 
   Are inbreeding and outcrossing rates comparable among populations?
   
   

We quantified morph frequency, morphological traits, nectar traits, and pollinator activity across five populations and quantified self and outcrossing rates by intra- and inter-morph hand pollination treatments. We next used ddRAD sequencing for genotyping. We quantified inbreeding (Fis) and outcrossing (Fst) rates using hierfstat package in R. Population genetics structures were plotted in the Structure program and dendrograms were constructed using gdsfmt and snprelate packages in R.

Results/Conclusions

We used five populations in our study and four of them (KP, BP, KAS, RAJ) were found to be trimorphic while one population (RAI) was monomorphic. We found that floral color morphs of C. caulina do not differ in their floral or vegetative morphologies but differ in their natural densities and key ecological traits such as nectar energy, pollinator visitation rates, and physiological compatibilities. Further, in three of the five populations (KP, BP, KAS), the rarest morphs showed the highest nectar energy and received most pollinator visitations. In two populations (KAS and RAJ), self-compatibilities rates were observed to be the lowest with one morph being completely self-incompatible. Finally, the KAS population was observed to be admixtured with all populations and we propose that KAS might represent the ancestral or parent population of all C. caulina.



Our results strongly suggest that physiological compatibilities and outcrossing rates in plants may vary among population, resulting in further geographic mosaicness in polymorphic traits. We also propose that the presence of variable reproductive and ecological traits within a species is a strong indicator of its recent diversification and highlights the importance of maintaining polymorphic characters as a step towards improving within-species genetic diversity.