Plant–pollinator interactions along the pathway to paternity

Minnaar, Corneile; Anderson, Bruce; Jager, Marinus L. de; Karron, Jeffrey D.

doi:10.1093/aob/mcy167

Cited by 137 publications

(191 citation statements)

References 197 publications

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“…However, because pollen removal is only the first step in the chain of events leading to successful pollen delivery (Minnaar et al. ), this should not be taken to mean that selection on spur length and other traits affecting morphological fit and efficiency of pollen transfer is necessarily stronger through female than through male function. Successful transfer of pollen to a compatible plant should depend as much on precise pollen placement on the pollinator body as does pollen receipt, and the relationship between trait expression and pollen removal need therefore not reflect the relationship between trait expression and pollen export (cf.…”

Section: Discussionmentioning

confidence: 99%

Manipulation of trait expression and pollination regime reveals the adaptive significance of spur length

2020

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Understanding the mechanisms of adaptive population differentiation requires that both the functional and adaptive significance of divergent traits are characterized in contrasting environments. Here, we (a) determined the effects of floral spur length on pollen removal and receipt using plants with artificial spurs representing the species‐wide variation in length, and (b) quantified pollinator‐mediated selection on spur length and three traits contributing to floral display in two populations each of the short‐spurred and the long‐spurred ecotype of the orchid Platanthera bifolia. Both pollen receipt and removal reached a maximum at 28–29 mm long spurs in a short‐spurred population visited by short‐tongued moths. In contrast, pollen receipt increased linearly across the tested range (4–52 mm) and pollen removal was unrelated to spur length in a long‐spurred population predominantly visited by a long‐tongued moth. The experimentally documented effects on pollen transfer were not reflected in pollinator‐mediated selection through female fitness or pollen removal indicating that the natural within‐population variation in spur length was insufficient to result in detectable variation in pollen limitation. Our study illustrates how combining trait manipulation with analysis of causes and strength of phenotypic selection can illuminate the functional and adaptive significance of trait expression when trait variation is limited.

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Section: Discussionmentioning

confidence: 99%

Manipulation of trait expression and pollination regime reveals the adaptive significance of spur length

2020

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“…Analyzing pollen placement sites on pollinators is often not possible for closely related species (Minnaar et al. ,b), although in this case, unique pollen color and shape characters have allowed us to present this aspect of the study (c.f. Muchhala and Potts who use pollen color to distinguish pollen on stigmas but not on pollinators).…”

Section: Discussionmentioning

confidence: 99%

“…Consequently, IPT among sympatric Pelargonium species in Bosfontein is expected to affect male fitness negatively because Pelargoniums are not cross compatible (Minnaar et al. ; Muchhala and Thomson ). Taken together with the correlations between style length and IPT, these results suggest that style length similarity has negative fitness consequences for co‐occurring species and that this has the potential to select for phenotypic divergence in sympatry (Moreira‐Hernández and Muchhala ).…”

Section: Discussionmentioning

confidence: 99%

Character displacement drives floral variation inPelargonium(Geraniaceae) communities

Newman

Anderson

2020

Evolution

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Interactions between plant community members are an underexplored driver of angiosperm floral variation. We investigate character displacement as a potential contributor to floral variation in Pelargonium communities. Pelargoniums all place pollen on the ventral sides of their pollinators, potentially leading to interspecific pollen transfer (IPT) in sympatry. We show that the positions of pollen placement and receipt are determined by anther and style exsertion lengths. Using field experiments, we demonstrate that heterospecific species experience higher IPT if they have similar style lengths than when they have greater style length differences. Using crosses, we show that IPT has negative consequences on seed set. In combination, these results suggest that character displacement in style length is likely to reduce IPT and increase female fitness in sympatry. Patterns of style length variation across 29 different Pelargonium communities suggest that character displacement has occurred in multiple communities. Furthermore, analyses using a wide‐ranging species pair show that style lengths are more different between sympatric populations than they are between allopatric populations. In addition to pollinators as agents of floral divergence, this study suggests that variation in Pelargonium community structure has driven style length variation through character displacement.

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“…Traits of flowering plants may be under sexual selection if they are associated with increased reproductive success for one of the sexes (Queller, ; Stanton et al., ; Willson, ). Floral traits that contribute specifically to male sexual success through pollen export such as optimal floral morphology to fit certain pollinators (Minnaar et al., ) are analogous to exaggerated ornamentation in male animals (Biernaskie and Elle, ). Sexual selection should act on pollen traits to increase the likelihood of fertilization success for the male gametophyte, while natural selection mediates traits affecting survival of the pollen grain, including its defense from consumption (Moore and Pannell, ).…”

mentioning

confidence: 99%

“…Animal‐mediated pollination is a multistep process comprising sequential stages for selection on pollen morphology (Fig. , Minnaar et al., ). Pollen must first be transferred from the donor flower to the pollinator, a process mediated by the interaction between traits of pollen and pollinator.…”

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confidence: 99%

Sexual and natural selection on pollen morphology in Taraxacum

Lynn

Piotter

Harrison

et al. 2020

American J of Botany

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Premise Spiny pollen has evolved independently in multiple entomophilous lineages. Sexual selection may act on exine traits that facilitate male mating success by influencing the transfer of pollen from the anther to the body of the pollinator, while natural selection acts to increase pollen survival. We postulated that relative to sexual congeners, apomictic dandelions undergo relaxed selection on traits associated with male mating success. Methods We explored sexual selection on exine traits by measuring the propensity for Taraxacum spp. pollen to attach to hairs of flower‐visiting bumblebees (Bombus spp.) or flies (Diptera: Syrphidae and Muscoidea) and assessed natural selection by testing whether pollen traits defend against consumption. Results Pollen picked up by bumblebees exhibited a narrower subset of spine‐spacing phenotypes, consistent with stabilizing selection. Flies picked up larger pollen from flowers than expected at random. Surveys of corbiculae (pollen basket) contents from foraging bumblebees and feces of flies showed that pollen grains consumed by both kinds of visitors are similar in spine characteristics and size to those produced by the donor. When bees visit inflorescences of apomictic T. officinale, they pick up pollen with spine‐spacing phenotypes above the mean and shifted toward those of sexual T. ceratophorum. Conclusions We demonstrate that traits under sexual selection during pollen pickup vary among pollinators, while natural selection for pollen defense is nil in T. ceratophorum. In hybrid zones between apomictic and sexual dandelions, pollen traits place apomictic donors at a dispersal disadvantage, potentially reinforcing reproductive isolation.

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Plant–pollinator interactions along the pathway to paternity

Cited by 137 publications

References 197 publications

Manipulation of trait expression and pollination regime reveals the adaptive significance of spur length

Manipulation of trait expression and pollination regime reveals the adaptive significance of spur length

Character displacement drives floral variation inPelargonium(Geraniaceae) communities

Sexual and natural selection on pollen morphology in Taraxacum

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