Reproductive character displacement and environmental filtering shape floral variation between sympatric sister taxa

Abstract

Divergence in reproductive traits between closely related species that co-occur contributes to speciation by reducing interspecific gene flow. In flowering plants, greater floral divergence in sympatry than allopatry may reflect reproductive character displacement (RCD) by means of divergent pollinator-mediated selection or mating system evolution. However, environmental filtering (EF) would prevail for floral traits under stronger selection by abiotic factors than pollination, and lead to sympatric taxa being more phenotypically similar. We determine whether floral UV pigmentation and size show signatures of RCD or EF using a biogeographically informed sister taxa comparison. We determine whether 35 sister pairs in the Potentilleae tribe (Rosaceae) are allopatric or sympatric and confirm that sympatric sisters experience more similar bioclimatic conditions, an assumption of the EF hypothesis. We test whether interspecific differences are greater in allopatry or sympatry while accounting for divergence time. For UV pigmentation, sympatric sisters are more phenotypically similar than allopatric ones. For flower size, sympatric sisters show increased divergence with time since speciation but allopatric ones do not. We conclude that floral UV pigmentation shows a signature of EF, whereas flower size shows a signature of RCD. Discordant results between the traits suggest that the dominant selective agent differs between them.

Ecological sorting and character displacement contribute to the structure of communities ofClarkiaspecies

“…These results follow from previous studies that have found evidence for ecological sorting and character displacement among plants that share pollinators (Table ), although most studies have not collected data both within and across communities in order to determine the relative importance of both processes in the same system (e.g. Briscoe Runquist et al ., ; but see Koski & Ashman, ; Kooyers et al ., ). Here we discuss what types of species interactions might generate the observed patterns in species co‐occurrence and trait variation, and what additional data are needed to definitively attribute these patterns to pollinator sharing.…”

“…Patterns of trait variation consistent with pollinator‐mediated ecological sorting and character displacement have been observed in a number of systems (Table ), but there are two key gaps in our understanding of these processes. First, most studies have not collected data both within and across communities in order to determine the relative importance of both processes (but see Koski & Ashman, ; Kooyers et al ., ). Pollinator‐mediated ecological sorting may occur more frequently where reproductive interactions among plants are stronger or more specialized (Collins et al ., ; Gumbert et al ., ; McEwen & Vamosi, ; Pellissier et al ., ), while pollinator‐mediated character displacement may be more common where these interactions are not strong enough to generate filtering or exclusion (Armbruster, ; Table ).…”

The evolution of floral signals in relation to range overlap in a clade of California Jewelflowers (Streptanthuss.l.)

“…Although less frequently investigated, co‐occurrence has also been hypothesized to drive convergence, rather than divergence, in floral traits (e.g., Moeller ; Koski and Ashman ). However, we found no evidence of convergence of floral traits in our study, as close relatives with range overlap had more dissimilar (rather than more similar) scent profiles than expected given their age.…”

“…In theory, this process should produce a macroevolutionary signature of increased levels or rates of phenotypic divergence among close relatives that coexist. On the other hand, floral trait convergence (rather than divergence) may be predicted if similar traits in a community positively impact the selective benefit of having those traits (Geber and Moeller ; Koski and Ashman ). For example, if convergent species share the same pollinators and either facilitate each other in attracting a critical mass of pollinators, are deceptive mimics of rewarding species, or reduce the use of flowers by enemies (e.g., Moeller ; Lev‐Yadun and Ne'eman ).…”

Digest: Trait variation in Mimulus provides new evidence for the joint action of ecological sorting and character displacement*

“…Although evidence for character displacement in plants has increased in recent years (Grossenbacher and Stanton ; Norton et al. ; Koski and Ashman ; Kooyers et al. ), reports of multiple instances of character displacement within a plant genus remain rare.…”