Segraves. 2019. A meta-analysis of whole genome duplication and the effects on flowering traits in plants. American Journal of Botany 106(3): 469-476. PREMISE OF THE STUDY:Polyploidy, or whole genome duplication (WGD), is common in plants despite theory suggesting that polyploid establishment is challenging and polyploids should be evolutionarily transitory. There is renewed interest in understanding the mechanisms that could facilitate polyploid establishment and explain their pervasiveness in nature. In particular, premating isolation from their diploid progenitors is suggested to be a crucial factor. To evaluate how changes in assortative mating occur, we need to understand the phenotypic effects of WGD on reproductive traits. METHODS:We used literature surveys and a meta-analysis to assess how WGD affects floral morphology, flowering phenology, and reproductive output in plants. We focused specifically on comparisons of newly generated polyploids (neopolyploids) and their parents to mitigate potential confounding effects of adaptation and drift that may be present in ancient polyploids.KEY RESULTS: The results indicated that across a broad representation of angiosperms, floral morphology traits increased in size, reproductive output decreased, and flowering phenology was unaffected by WGD. Additionally, we found that increased trait variation after WGD was uncommon for the phenotypic traits examined. CONCLUSIONS:Our results suggest that the phenotypic effects on traits important to premating isolation of neopolyploids are small, in general. Changes in flowering phenology, reproductive output, and phenotypic variation resulting from WGD may be less critical in facilitating premating isolation and neopolyploid establishment. However, floral traits for which size is an important component of function (e.g., pollen transfer) could be strongly influenced by WGD.

Plant communities are disturbed by several stressors and they are expected to be further impacted by increasing anthropogenic stress. The consequences of these stressors will depend, in part, upon the ability of plants to compensate for herbivory. Previous studies found that herbivore impacts on plants can vary from negative to positive because of environmental control of plant compensatory responses, a.k.a. the Compensatory Continuum Hypothesis. While these influential studies enhanced our appreciation of the dynamic nature of plant-herbivore interactions, they largely focused on the impact of resource limitation. This bias limits our ability to predict how other environmental factors will shape the impact of herbivory. We examined the role of salinity stress on herbivory of salt marsh cordgrass, Spartina foliosa, by an herbivore previously hypothesized to influence the success of restoration projects (the scale insect, Haliaspis spartinae). Using a combination of field and mesocosm manipulations of scales and salinity, we measured how these factors affected Spartina growth and timing of senescence. In mesocosm studies, Spartina overcompensated for herbivory by growing taller shoots at low salinities but the impact of scales on plants switched from positive to neutral with increasing salinity stress. In field studies of intermediate salinities, scales reduced Spartina growth and increased the rate of senescence. Experimental salinity additions at this field site returned the impact of scales to neutral. Because salinity decreased scale densities, the switch in impact of scales on Spartina with increasing salinity was not simply a linear function of scale abundance. Thus, the impact of scales on primary production depended strongly upon environmental context because intermediate salinity stress prevented plant compensatory responses to herbivory. Understanding this context-dependency will be required if we are going to successfully predict the success of restoration efforts and the ecological consequences of anthropogenic disturbances.

PREMISE:Although polyploidy has been studied since the early 1900s, fundamental aspects of polyploid ecology and evolution remain unexplored. In particular, surprisingly little is known about how newly formed polyploids (neopolyploids) become demographically established. Models predict that most polyploids should go extinct within the first few generations as a result of reproductive disadvantages associated with being the minority in a primarily diploid population (i.e., the minority cytotype principle), yet polyploidy is extremely common. Therefore, a key goal in the study of polyploidy is to determine the mechanisms that promote polyploid establishment in nature. Because premating isolation is critical in order for neopolylpoids to avoid minority cytotype exclusion and thus facilitate establishment, we examined floral morphology and three common premating barriers to determine their importance in generating reproductive isolation of neopolyploids from diploids. METHODS:We induced neopolyploidy in Trifolium pratense and compared their floral traits to the diploid progenitors. In addition to shifts in floral morphology, we examined three premating barriers: isolation by self-fertilization, flowering-time asynchrony, and pollinator-mediated isolation. RESULTS:We found significant differences in the morphology of diploid and neopolyploid flowers, but these changes did not facilitate premating barriers that would generate reproductive isolation of neopolyploids from diploids. There was no difference in flowering phenology, pollinator visitation, or selfing between the cytotypes. CONCLUSIONS:Our results indicate that barriers other than the ones tested in this study-such as geographic isolation, vegetative reproduction, and pistil-stigma incompatibilities-may be more important in facilitating isolation and establishment of neopolyploid T. pratense.

Together, the results demonstrate that foliar sugar can indeed enhance the efficacy of domatia-mediated plant-mite mutualisms, and suggest that this synergism has the potential to influence the co-distribution of foliar nectar and mite domatia across plants.

Greater attention to habitat-specific species interactions should improve our ability to predict the context-dependency of species interactions. Predator avoidance depends upon resource traits that can vary predictably between habitats, but few studies have linked predator avoidance to habitat-specific resource traits. For example, predator avoidance in herbivores may depend upon wave exposure, because wave-exposed and wave-protected seaweeds display strong intraspecific differences in morphology and physiology that likely influence their value to herbivores. In 2 sets of laboratory mesocosm experiments we compared predator avoidance in the herbivorous snail Littorina obtusata offered the bladder wrack Fucus vesiculosus from either wave-exposed or protected shores. The effect of predation risk by the green crab Carcinus maenas on avoidance by L. obtusata depended on wave exposure, with a stronger effect of predation risk for snails on wave-exposed F. vesiculosus. To explore the traits responsible for this pattern, we conducted multi-choice feeding experiments with F. vesiculosus from 3 wave-exposed and 3 protected sites. F. vesiculosus from protected sites (where avoidance behaviors were weak) was more palatable than F. vesiculosus from wave-exposed sites. Although several morphological (e.g. blade width and vesicle number) and physiological traits (e.g. C:N ratio) of F. vesiculosus depended upon wave exposure, these were unrelated to snail feeding and predator avoidance. Therefore, L. obtusata displayed stronger predator avoidance on less palatable, wave-exposed seaweed. We suggest that the different effects of predators on rocky shores may partly reflect the influence of exposure-specific seaweed traits that determine predator avoidance.

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