Indirect Selection on Flower Color in Silene littorea

Abstract

Flower color, as other floral traits, may suffer conflicting selective pressures mediated by both mutualists and antagonists. The maintenance of intraspecific flower color variability has been usually explained as a result of direct selection by biotic agents. However, flower color might also be under indirect selection through correlated traits, since correlations among flower traits are frequent. In this study, we aimed to find out how flower color variability is maintained in two nearby populations of Silene littorea that consistently differ in the proportions of white-flowered plants. To do that, we assessed natural selection on floral color and correlated traits by means of phenotypic selection analysis and path analysis. Strong directional selection on floral display and flower production was found in both populations through either male or female fitness. Flower color had a negative indirect effect on the total male and female fitness in Melide population, as plants with lighter corollas produced more flowers. In contrast, in Barra population, plants with darker corollas produced more flowers and have darker calices, which in turn were selected. Our results suggest that the prevalence of white-flowered plants in Melide and pink-flowered plants in Barra is a result of indirect selection through correlated flower traits and not a result of direct selection of either pollinators or herbivores on color.

Flower Color Evolution and the Evidence of Pollinator-Mediated Selection

“…Moreover, of these studies, only six used a hand-pollination treatment to estimate selection gradients associated with pollinator interactions ( Caruso et al, 2010 ; Parachnowitsch and Kessler, 2010 ; Lavi and Sapir, 2015 ; Sletvold et al, 2016 ; Zhang et al, 2017 ; Souto-Vilarósa et al, 2018 ; Supplementary Table 3 ). Some other studies used modeling approaches linking the flower color phenotype - fitness relationship to pollinator visitation data to determine the contribution of pollinators to observed total selection (e.g., Veiga et al, 2015 ; Rodriguez-Castañeda et al, 2020 ; Brunet et al, 2021 ; Supplementary Table 3 ).…”

“…Flower color may correlate with other traits influencing the number of pollinator visits and pollination efficiency ( Gómez, 2000 ; Armbruster, 2002 ). Such traits may include overall plant stature and flower morphology ( Gómez, 2000 ; Frey et al, 2011 ; Rodriguez-Castañeda et al, 2020 ), or, due to possible linkage in biosynthetic pathways, floral scent ( Majetic et al, 2007 ; Zvi et al, 2008 ; Dormont et al, 2019 and references therein). Depending on the genetic variance-covariance matrix for all traits involved in pollinator interaction in a population, selection on flower color can therefore also act indirectly through pleiotropic links or in a correlative fashion favoring trait integration ( Armbruster, 2002 ; Strauss and Whittall, 2006 ; Rausher, 2008 ).…”

“…For example, experimenting may be through manipulation of the pollination environment (i.e., a hand-pollination treatment to remove variation in fitness that is not associated with variation in the interaction with pollinators; Caruso et al, 2018 ; Sletvold, 2019 ). On the other hand, statistical estimation approaches may be used with structural equation modeling estimation (i.e., estimating the causal relationship of pollinator interactions with plant fitness; Souto-Vilarósa et al, 2018 ; Rodriguez-Castañeda et al, 2020 ; Brunet et al, 2021 ).…”

Divergent Responses of Floral Traits of Lonicera nervosa to Altitudinal Gradients at the Eastern Margin of Hengduan Mountains

“…Flower color shows both a strong genetic basis and a sharp geographic transition (Streisfeld and Kohn, 2005), and both biotic and abiotic agents of selection may affect floral traits (Rodríguez-Castañeda et al, 2020). However, the intensity of different biotic and abiotic interactions varies spatially, resulting in divergent selection along with maintenance of the variability of floral traits that influence these interactions (Mitchell-Olds et al, 2007;Ågren et al, 2013;Vaidya et al, 2018).…”