The Role Of Rain And Pollinators In The Evolution Of Floral Traits

Floral traits may be shaped by both abiotic and biotic factors. Correlated floral traits, i.e., petal fusion, floral orientation and symmetry, have been proposed to be adaptive to pollinators and abiotic environment. Studies have shown that the evolution of floral traits partly attributes to pollinator-mediated selection, however, whether abiotic environment such as rainfall plays a role in evolution of flowers remains unclear. The specialization of floral traits has been assumed to associate with species diversification, as documented by families with bilateral symmetric flowers having more species than families with radial symmetric flowers. However, generalized flowers are more universe than specialized ones in certain communities and in the whole angiosperms. To explain this, previous hypothesis proposed that floral specialization would be more easily endangered and extinctive when specialized pollinators lost by chance. To explore the role of abiotic factors in the evolution of floral traits, in the dissertation we considered both the contribution of pollinators and rainfall on flower forming. We first conducted a comprehensive survey of the distribution and combination of floral traits in extant angiosperms, and then examined whether trait combinations associated with rainfall using previous investigation of community study as well as our own investigation in three communities from China. Finally, we conducted field experiments to examine the effects of pollinator preference and rain on different trait combinations.First, to illustrate which trait combinations (specialized or generalized traits) are dominant in angiosperms, we sampled over20000species from414families. We compiled floral traits including floral symmetry, orientation, petal united or separate of each species from numerous records and internet websites. Based on the APGIII phylogenetic tree, generalized traits were found more universal in angiosperms than specialized traits in all three trait series (petal situation, floral orientation and symmetry). Combinations of different series were found asymmestric rather than randomly assemblaged, suggesting that an adaptation to biotic or abiotic factors would not be separated.Floral traits can be also affected by temperature, humidity, altitude and latitude, thus species composition in communities can provide a cue to understand whether abiotic factors affect the evolution of floral traits. To test whether trait combinations associate with rainfall, we surveyed published references about community structure to observe local distribution of floral traits and rainfall. Among45communities, precipitation was negatively correlated with proportion of united petal, vertical orientation and zygomorphy, and certain combination types. These results provide evidence for rainfall affecting floral traits at community level.Finally, we conducted field experiments in Shangeri-La to quantify the differential contributions from pollinators and rainfall on reproductive success in12species. Both male and female functions of each species were measured under different flower manipulations. We changed petal situation (united vs separate) and floral orientation (upward vs downward) to examine the functional difference between these floral traits, Pollinator preference, pollen removal, pollen viability, stigma receptivity, stigmatic pollen deposition and seed set were examined in both sunny and rainy days for12species. Our results indicated that specialized traits could offer effective protection from rain and increase pollination accuracy, while generalized flowers could be beneficial in pollinator attraction. Taken together, our literature survey and empirical studies suggested that certain trait combinations would be wide spread in angiosperms by the integrative roles from pollinators and rainfall.