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Abstract PremiseCo‐occurring plant species that share generalist pollinators often exchange pollen. This heterospecific pollen transfer (HPT) impacts male and female reproductive success through pollen loss and reductions in seed set, respectively. The resulting fitness cost of HPT imposes selection on reproductive traits (e.g., floral color and shape), yet we currently lack strong predictors for the post‐pollination fate of heterospecific pollen, especially within community and phylogenetic contexts. MethodsWe investigated the fate of heterospecific pollen at three distinct stages of plant reproduction: (1) pollen germination on the stigma, (2) pollen tube growth in the style, and (3) fertilization of ovules. We experimentally crossed 11 naturally co‐flowering species in the subalpine meadows of the Colorado Rocky Mountains, across a spectrum of phylogenetic relatedness. Using generalized linear mixed models and generalized linear models, we evaluated the effect of parental species identity and phylogenetic relatedness on pollen tube growth at each reproductive stage. ResultsWe found that heterospecific pollen tubes can germinate and grow within pistils at each reproductive stage, even when parental species are >100 My divergent. There was no significant effect of phylogenetic distance on heterospecific pollen success, and no evidence for a mechanism that suspends heterospecific pollen germination or pollen tube growth within heterospecific stigmas or styles. ConclusionsOur results show that even in communities where HPT is common, pre‐zygotic post‐pollination mechanisms do not provide strong barriers to interspecific fertilization. HPT can result in the loss of ovules even between highly diverged plant species.
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REPRODUCTIVE ECOLOGY OF ERIGERON SPECIOSUS, A MONTANE PERENNIAL HERB: EVIDENCE OF SELF-INCOMPATIBILITY
We conducted an experiment to determine the reproductive biology of Erigeron speciosus (Asteraceae), a perennial montane herb that is widespread throughout Western North America. Pollination of E. speciosus was manipulated to understand the following questions: (1) What is the mating system for E. speciosus (outcrossing vs. selfing)? (2) Is E. speciosus self-incompatible? (3) Does pollen donor distance affect reproductive success? (4) Is reproductive success limited by pollen receipt (i.e., pollen limitation)? We compared seed set and seed viability among five pollination treatments: ambient pollination (control), pollinator exclusion (bagged capitula), self-pollination only, and two outcrossing treatments (near and far pollen donors). We found that E. speciosus is largely self-incompatible and depends on outcrossing for its reproduction. Despite this, reproduction was not pollen-limited at our study site. We also found some evidence that E. speciosus reproduction is susceptible to outbreeding depression.
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- Award ID(s):
- 1754518
- PAR ID:
- 10526040
- Publisher / Repository:
- The Southwestern Naturalist
- Date Published:
- Journal Name:
- The Southwestern Naturalist
- Volume:
- 68
- Issue:
- 1
- ISSN:
- 0038-4909
- Page Range / eLocation ID:
- 13–19
- Subject(s) / Keyword(s):
- breeding system mating system outbreeding depression pollination
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Premise Herbivores directly influence plant reproduction by damaging reproductive tissue which reduces seed production in consumed plants. Consumption of reproductive tissue may also indirectly depress reproduction in unconsumed plants by isolating unconsumed individuals from prospective mates and reducing pollination. However, empirical support for such hypothesized indirect effects remains limited. Methods To investigate potential indirect effects of herbivory on mating opportunities and pollination, we quantified spatial patterns of white-tailed deer (Odocoileus virginianus) herbivory and reproductive outcomes in Lilium philadelphicum (Liliaceae). We mapped 708 flowering plants, monitored deer herbivory, and examined how distance to prospective mates influenced rates of ovule fertilization, a proxy for pollen receipt. Results Most floweringL. philadelphicum plants (83%) failed to produce seed. Deer consumption of flowers prevented seed production in 35% of individuals. The probability of deer herbivory declined with distance to flowering conspecifics. Sixty-five percent of the remaining, unconsumed plants failed to produce seed due to apparent pollen limitation. While ovule fertilization rates declined with multiple predictors quantifying distances to flowering conspecifics, isolation metrics that excluded plants consumed by deer significantly improved predictions of ovule fertilization. Conclusions Our results offer empirical support for the hypothesis that herbivory reduces pollination and seed production in unconsumed plants by altering spatial mating opportunities. This feedback between deer herbivory and distance-dependent pollination contributes to widespread reproductive failure in L. philadelphicum, though the extent to which deer reduce seed production varies with plant isolation. Herbivory may exacerbate pollen limitation in other species by isolating unconsumed plants from prospective mates.more » « less
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Open top chambers (OTCs) are a popular method for studying the biological effects of climate change through passive heating, but their effects on biotic interactions are poorly understood, especially for pollination. Here we use the subalpine plants Delphinium nuttallianum and Potentilla pulcherrima to examine the possibility that the effects of OTCs on plant reproduction are not the result of warming but rather OTCs acting as barriers to pollinator movement. Pollinator observations were conducted and stigmas collected from plants inside and outside of OTCs in a meadow in the Rocky Mountains of Colorado, USA. Very few visitors were observed inside of OTCs, which led to severe reductions in visitation rates, by 92% in Delphinium and 85% in Potentilla. The number of conspecific pollen grains on stigmas was 73% lower in OTCs for Delphinium but not Potentilla, likely because it is capable of autogamous self-pollination. This study clearly shows that OTCs can reduce animal pollination, which is also likely to reduce plant reproductive output of outcrossing plants via decreases in the quantity or quality of pollen. OTCs may therefore confound effects of warming on plant reproduction with pollination effects. Although the unintended effects of OTCs on abiotic conditions are well-studied, this study highlights that their effects on biotic interactions require further investigation.more » « less
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Abstract Background Siring success plays a key role in plant evolution and reproductive ecology, and variation among individuals creates an opportunity for selection to act. Differences in male reproductive success can be caused by processes that occur during two stages, the pollination and post-pollination phases of reproduction. In the pollination phase, heritable variation in floral traits and floral display affect pollinator visitation patterns, which in turn affect variation among plants in the amount of pollen exported and deposited on recipient stigmas. In the post-pollination phase, differences among individuals in pollen grain germination success and pollen tube growth may cause realized paternity to differ from patterns of pollen receipt. The maternal plant can also preferentially provision some developing seeds or fruits to further alter variation in siring success. Scope In this review, we describe studies that advance our understanding of the dynamics of the pollination and post-pollination phases, focusing on how variation in male fitness changes in response to pollen limitation. We then explore the interplay between pollination and post-pollination success, and how these processes respond to ecological factors such as pollination intensity. We also identify pressing questions at the intersection of pollination and paternity and describe novel experimental approaches to elucidate the relative importance of pollination and post-pollination factors in determining male reproductive success. Conclusions The relative contribution of pollination and post-pollination processes to variation in male reproductive success may not be constant, but rather may vary with pollination intensity. Studies that quantify the effects of pollination and post-pollination phases in concert will be especially valuable as they will enable researchers to more fully understand the ecological conditions influencing male reproductive success.more » « less
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Summary Effective insect pollination requires appropriate responses to internal and external environmental cues in both the plant and the pollinator.Helianthus annuus, a highly outcrossing species, is marked for its uniform eastward orientation of mature pseudanthia, or capitula. Here we investigate how this orientation affects floral microclimate and the consequent effects on plant and pollinator interactions and reproductive fitness.We artificially manipulated sunflower capitulum orientation and temperature in both field and controlled conditions and assessed flower physiology, pollinator visits, seed traits and siring success.East‐facing capitula were found to have earlier style elongation, pollen presentation and pollinator visits compared with capitula manipulated to face west. East‐facing capitula also sired more offspring than west‐facing capitula and under some conditions produced heavier and better‐filled seeds. Local ambient temperature change on the capitulum was found to be a key factor regulating the timing of style elongation, pollen emergence and pollinator visits.These results indicate that eastward capitulum orientation helps to control daily rhythms in floral temperature, with direct consequences on the timing of style elongation and pollen emergence, pollinator visitation, and plant fitness.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1894/0038-4909-68.1.13
