Comparison of mechanisms of reproductive interference in Taraxacum.

Akane Takemori,Sachiko Nishida,Masahiro M Kanaoka,Ko-Ichi Takakura,Akiyo Naiki

doi:10.1093/aob/mcz007

Abstract

Background and AimsReproductive interference may reduce fitness of either of the involved species, with potentially important ecological and evolutionary consequences. Except for the effect of shared pollinators on reproductive success, however, mechanisms underlying reproductive interference have been little studied, even though the severity of its impact may depend on the specific mechanism. The aim of this study was therefore to explore the mechanisms of reproductive interference between Taraxacum japonicum (native to Japan) and Taraxacum officinale (alien).MethodsIn a field survey, the association between alien species density and seed set in T. japonicum, and whether pollinator behaviour indicated a preference for the alien, were examined. Effects of heterospecific pollen deposition were measured in a series of hand pollination experiments, including mixed pollination experiments in which the order of application of conspecific and heterospecific pollen was varied. Finally, to investigate hybridization frequency, the parentage of seedlings produced following natural, mixed or heterospecific pollination was compared.Key ResultsAlien species density did not negatively affect native seed set, nor did pollinators appear to have a preference for alien flowers. The hand pollination experiments showed that heterospecific pollen deposition adversely affected native seed set, especially when alien pollen was applied before conspecific pollen. No viable hybrids were found following natural pollination, which suggests that hybridization might be a rare event.ConclusionAmong the examined mechanisms, heterospecific pollen deposition might have the largest deleterious effect on the native species. This effect is frequency dependent; thus, a positive feedback loop may cause the effect on the population dynamics to increase over time, with the result that the alien might eventually displace the native in a population. Effects of the examined mechanisms on population dynamics should be investigated further to improve understanding of the impact of reproductive interference on the structure of plant communities.

Highlights

Reproductive interference, defined as a negative effect of interspecific sexual interaction on the fitness of either species, is an important mechanism that can explain patterns of exclusion among closely related species (Hochkirch et al, 2007; Gröning and Hochkirch, 2008)
Field survey of the association between alien density and native reproductive success Seed set of the native species did not decrease significantly as the number of surrounding alien inflorescences increased, which suggests that alien density did not negatively affect the reproductive performance of the native species (Table 1; Fig. 2)
Our study pointed to heterospecific pollen deposition from the alien to the native Taraxacum species as the major mechanism of reproductive interference exerting a deleterious effect on the native species, other mechanisms should be further investigated to gain a comprehensive understanding of reproductive interference in Taraxacum

Summary

Introduction

Reproductive interference, defined as a negative effect of interspecific sexual interaction on the fitness of either species, is an important mechanism that can explain patterns of exclusion among closely related species (Hochkirch et al, 2007; Gröning and Hochkirch, 2008). Competition for pollination is defined by Waser (1983) as any interaction in which co-occurring plant species (or phenotypes) suffer reduced reproductive success because they share pollinators. With the exception of the effect of shared pollinators on reproductive success of the plant species involved, the mechanisms underlying reproductive interference have been less studied, even though Arceo-Gómez and Ashman (2011) have reported that the severity of its impact, as well as its ecological or evolutionary consequences, depends on the specific mechanism involved. Pollinator sharing can cause a reduction of seed set in the focal species by two processes: by reducing conspecific pollen transfer, which may cause a pollen limitation (conspecific pollen loss), or by increasing heterospecific pollen deposition, which may interfere with reproduction of the focal species The decrease in conspecific pollen transfer is expected to become more severe as the density of the counterpart species increases, whereas an increase in the density of the counterpart species should not affect heterospecific pollen deposition unless its frequency in the total population increases (Takakura et al, 2009; Nishida et al, 2017)

Objectives

Methods

Results

Discussion

Conclusion