Biology subjects

Wenzell, K. E.

Publications and source records attributed to Wenzell, K. E..

3 recordsLinked to original sources

bioRxiv2025

In-depth phenotyping reveals unexpected floral trait variation in Mimulus cardinalis across a range-wide latitudinal gradient

Background & AimsPollinators play a crucial role in the evolution and diversification of flowering plants. Intraspecific variation in floral traits occurs frequently and likely reflects variable biotic and abiotic selection pressures. The hummingbird-pollinated monkeyflower Mimulus cardinalis occurs across western North America, where geographic mosaics of selection have likely influenced its natural history, due to this wide species range. Processes driving early stages of divergence and speciation remain poorly understood, though theory predicts that trait divergence will be most likely at range edges. Within M. cardinalis, which is usually red-flowered and hummingbird-pollinated, two independent shifts to yellow flowers have occurred at the northern and southern range edges, including a population found on Cedros Island, off the coast of Baja California, Mexico. MethodsThis study characterises the local climatic variables of five accessions of M. cardinalis derived from locations across a latitudinal geographic gradient. Highly integrative methods in metabolomics and morphological analyses were used to characterise a suite of pollinator-relevant floral traits across the range of M. cardinalis species variation. We use transcriptomics and whole genome sequencing to study underlying genetic variation in two yellow-coloured, range-edge accessions. Key ResultsThis study uncovers high levels of variation in morphology, nectar properties, pigmentation and scent profile across geographically diverse Mimulus cardinalis accessions, in addition to profiling how these accessions are perceived by potential pollinators. We find high levels of phenotypic variation across M. cardinalis, particularly in the biochemistry of pigment and scent, where inflorescences that appear to be the same shade of red have completely different anthocyanin profiles. Floral trait-underlying genetic differences between different M. cardinalis lines were also investigated, revealing potential mechanisms underlying floral diversification. ConclusionsThis work highlights the importance of interplay between floral trait diversification, pollinator perception and climate. This work also highlights the importance of considering suites of floral traits in a quantitative fashion when studying intraspecific variation in relation to species range. This study also provides genetic insight into changes in these traits and provides many future directions to study the early stages of pollinator-mediated trait differentiation across a species range.

plant biology↗

bioRxiv2024

Adaptive generalization in pollinators: hawkmoths increase fitness to long-tubed flowers, but secondary pollinators remain important

Selection on floral traits by animal pollinators is important in the evolution of flowering plants, yet whether floral divergence requires specialized pollination remains uncertain. Longer floral tubes, a trait associated with long-tongued pollinators, can also exclude other pollinators from accessing rewards, a potential mechanism for specialization. Across most of its range, Castilleja sessiliflora displays much longer corollas than most Castilleja species, though tube length varies geographically and correlates partially with hawkmoth visitation. To assess if long corolla tubes reflect adaptation to hawkmoth pollinators, we performed a day/night pollinator exclusion experiment in nine natural populations that varied in corolla length across the range of C. sessiliflora and short-tubed members of the parapatric C. purpurea complex. We compared the fitness contributions of nocturnal and diurnal visitors, revealing that long-tubed populations visited predominantly by hawkmoths experienced greater fruit set at night, in contrast with short-tubed populations or those visited mainly by diurnal pollinators. Next, leveraging a range-wide multi-year dataset of pollinator visitation to these species, we identify that hawkmoth visitation is associated with increased fitness in long-tubed populations overall, and that long tubes are associated with less diverse visitor assemblages. Thus, long corollas represent an adaptation to hawkmoth pollination at the exclusion of diverse pollinators. Nonetheless, while hawkmoths were scarce in the northern range, secondary diurnal pollinators contributed to fruit set across the range, providing reproductive assurance despite possible trait mismatch. This study illustrates adaptive generalization in pollination modes and that floral divergence may proceed along a continuum of generalized and specialized pollinator interactions.

evolutionary biology↗

bioRxiv2023

Do color polymorphisms reflect pollinator shifts?: Integrating floral traits as signals to a novel pollinator to understand species divergence

Understanding how evolution proceeds from molecules to organisms to interactions is critical for evolutionary biology and requires integrative studies that span biological levels. By linking phenotypic changes with associated genes and fitness implications, we gain insight on the repeatability of evolution and how adaptive walks move organisms between fitness peaks, which remains poorly understood at intermediate stages, e.g. potential fitness valleys. Floral trait evolution can proceed rapidly, confer reproductive isolation, and provides numerous examples of convergent evolution associated with pollinator guilds. Within the monkeyflowers (Mimulus sect. Erythranthe), intraspecific shifts to yellow flowers within red hummingbird-pollinated species have arisen at least twice and may represent incipient shifts between optima of pollinator adaptation. Here, we compare two natural yellow-flowered forms of M. cardinalis and M. verbenaceus to their red conspecifics in floral phenotypes, biochemistry, transcriptomic and genomic variation, and interactions with pollinators. We find convergent evolution in the adaptive walks of yellow morphs in both species, with consistent changes in traits of large effect (floral pigments and associated gene expression), which result in strong preference for yellow flowers by bumblebees. Shifts in additional traits (scent emissions and floral opening size) are also consistent with bee pollination, which may represent smaller-effect steps in an ongoing walk from hummingbird to bee pollination. By examining intraspecific variation representing incipient pollinator shifts in two related species, this work elucidates how adaptive walks proceed at early stages by highlighting how convergent large effect mutations (floral color) may drive pollinator attraction, preceding smaller effect changes controlling pollinator fit and reward access. This work integrates phenotypic, biochemical, genomic, and behavioral evidence to shed light on how repeated steps in adaptive walks to new fitness optima may impact reproductive isolation and incipient speciation via convergent evolution.

evolutionary biology↗