No evidence that seed predators constrain pollinator‐mediated trait evolution in a tropical vine

Citation: Panique, H. and C. M. Caruso. 2020. Simulated pollinator declines intensify selection on floral traits that facilitate selfing and outcrossing in PREMISE: Anthropogenic environmental change is causing pollinator populations to decline. These declines should intensify selection for floral traits that facilitate outcrossing by making plants more attractive to pollinators and/or for floral traits that facilitate selfing in the absence of pollinators. However, the effect of pollinator declines on selection on floral traits could be modified by other environmental factors such as herbivores. METHODS:We studied the effect of simulated pollinator declines on selection on floral traits of Impatiens capensis, a mixed-mating species that produces both obligately selfing cleistogamous flowers and primarily outcrossing chasmogamous flowers. We measured directional selection differentials via seeds per plant on two traits that facilitate outcrossing (chasmogamous flower size and number) and one trait that facilitates selfing (cleistogamous flower number) in ambient, reduced pollinator access, and reduced pollinator access combined with increased foliar herbivory treatments. RESULTS:Reduced pollinator access intensified selection for larger chasmogamous flowers and more cleistogamous flowers. In contrast, increased herbivory did not affect selection on any floral trait. CONCLUSIONS:Reduced pollinator access intensified selection for a trait that facilitates outcrossing, suggesting that even species such as I. capensis that can autonomously selfpollinate have the potential to respond to pollinator declines by evolving floral traits that reinforce interactions between plants and pollinators. However, reduced pollinator access also intensified selection for a trait that facilitates selfing, suggesting that I. capensis could adapt to pollinator declines by evolving floral traits that maintain the production of both selfed and outcrossed seeds.

Section: Discussionsupporting

confidence: 82%

“…The effect of pollinator declines on selection on floral traits may depend on biotic and abiotic environmental factors other than pollinators (Opedal et al., ). One such environmental factor is herbivory.…”

mentioning

confidence: 99%

Simulated pollinator declines intensify selection on floral traits that facilitate selfing and outcrossing in Impatiens capensis

Panique

Caruso

2019

“…Changes caused by herbivores would reduce nectar and pollen resources for floral visitors, decreasing the attractiveness to pollinators and thus their abundance, creating a negative feedback for the maintenance of pollinator fauna, and potentially decreasing outcrossing rates in animal‐pollinated plants. However, with our current data we cannot test whether the evolution of floral traits in response to changes in the abundance of interacting species (e.g., pollinators) depends on selective pressures generated by other interactors (e.g., herbivores) (Opedal et al, 2019).…”

Section: Discussionmentioning

confidence: 82%

Selective forces on the maintenance of outcrossing in an almost exclusively cleistogamous violet species

Seguí

Hervías‐Parejo

Traveset

2021

Premise Cleistogamous species constitute interesting study systems to resolve the longstanding question of how outcrossing is maintained given that seed production is ensured through selfing. In this work, we investigate the selective forces that allow the persistence of producing self‐pollinated cleistogamous (CL) and chasmogamous (CH) flowers in Viola jaubertiana Marès & Vigin. Methods We monitored three populations at different elevation for two years, and studied the flowering phenology and the relative contribution of each flower morph to parental fitness. We tested whether allocation to CH and CL flowers differed across populations and if it covaried with herbivory and water stress conditions. We also performed hand‐pollination and bagging experiments in CH flowers to estimate inbreeding depression and heterosis. Results The CH flowers open in winter under unfavorable conditions for pollination, show high pollen limitation and no‐delayed selfing, and thus produce a low amount of seeds. Conversely, CL flowers appear in early spring, are physiologically cheaper to produce (i.e., dry weight is 3.4 times lower than that of CH flowers), and yield approximately 100 times more seeds than CH flowers. The CH flowers were favored under water stress and low herbivory. Crosses between populations showed up to 25% greater fitness than those within populations. Conclusions Despite the great pollen limitation in CH flowers, we suggest that the interaction among different environmental determinants and heterosis are probably sufficient forces to maintain chasmogamy in this long‐lived species, reducing deleterious fixed mutations in the selfed lines.

“…We observed bumblebee visitation to virgin C. latistipula flowers to investigate the relationship between body size and behavior of the bees and their impact on the pollination performance and plant reproductive fitness (see Opedal et al [2023] for the definitions and components of pollination performance and reproductive fitness). We selected 5–10 flower buds from each of the 30 individuals of C. latistipula and covered them with small tulle bags to prevent visits by bees and other insects.…”

Section: Methodsmentioning

confidence: 99%

“…To evaluate fruit and seed production (female reproductive fitness, according to Opedal et al, 2023) after bumblebee visits, we inspected the plants and flowers once a week for fruit. Once fruit development began, we enclosed the immature fruit in a small tulle bag, and after its maturation (when it became dark and rattled), we collected the fruits.…”

Section: Methodsmentioning

confidence: 99%

The role of intraspecific variation in bumblebee body size and behavior on buzz pollination of a tropical legume species

Barbosa,

Delgado de Lima,

Mota

et al. 2023

PremiseThe outcomes of generalized mutualisms rely on partner trait variation. In pollination mutualisms, although less explored, intraspecific variation in pollinator traits can be pivotal for successful pollination. We investigated the role of intraspecific body size and behavioral trait variations of bumblebee Bombus morio on the pollination of a buzz‐pollinated legume species, Chamaecrista latistipula.MethodsTo explore the impact of body size and behavior of B. morio on the pollination of C. latistipula, we observed visits to virgin flowers and quantified the pollen removal and deposition (pollination performance) and fruit and seed production (reproductive fitness). By analyzing video and sound recordings, we measured B. morio body size and behavior on each flower, including bee vibration descriptors.ResultsWe observed intraspecific behavioral differences among B. morio bumblebees associated with different body sizes. Larger bumblebees had half the handling time and vibrational pulses, less angular displacement within flowers, and larger relative peak amplitudes during vibrations than smaller bumblebees did. Regardless of their large variation in size and behavior, bumblebees were equally effective in removing pollen and pollinating flowers. The high female reproductive fitness was independent of bumblebee body size and behavior, likely due to the interaction between both. On the other hand, larger bumblebees visited flowers for shorter periods, probably promoting higher male reproductive fitness.ConclusionsThis study is the first to highlight the large intraspecific variation of bumblebee body size and behavior in buzz‐pollinated flowers in the field. Together, body size and behavior effects unexpectedly cancel each other, generating a high buzz pollination efficiency.