A comparative study on the reproductive success of two rewarding Habenaria species (Orchidaceae) occurring in roadside verge habitats

Wenliu Zhang,Jiangyun Gao

doi:10.1186/s12870-021-02968-w

Abstract

BackgroundMost orchid species have been shown to be severely pollination limited, and the factors affecting reproductive success have been widely studied. However, the factors determining the reproductive success vary from species to species. Habenaria species typically produce nectar but exhibit variable fruit set and reproductive success among species. Here, we investigated the influence of the flowering plant density, inflorescence size, breeding system, and pollinator behaviour on the reproductive success of two rewarding Habenaria species.ResultsOur observations indicated that Habenaria limprichtii and H. petelotii co-occur in roadside verge habitats and present overlapping flowering periods. Both species were pollination limited, although H. limprichtii produced more fruits than H. petelotii under natural conditions during the 3-year investigation. H. petelotii individuals formed distinct patches along roadsides, while nearly all H. limprichtii individuals clustered together. The bigger floral display and higher nectar sugar concentration in H. limprichtii resulted in increased attraction and visits from pollinators. Three species of effective moths pollinated for H. limprichtii, while Thinopteryx delectans (Geometridae) was the exclusive pollinator of H. petelotii. The percentage of viable seeds was significantly lower for hand geitonogamy than for hand cross-pollination in both species. However, H. limprichtii may often be geitonogamously pollinated based on the behaviours of the pollinators and viable embryo assessment.ConclusionsIn anthropogenic interference habitats, the behaviours and abundance of pollinators influence the fruit set of the two studied species. The different pollinator assemblages in H. limprichtii can alleviate pollinator specificity and ensure reproductive success, whereas the more viable embryos of natural fruit seeds in H. petelotii suggested reducing geitonogamy by pollinators in the field. Our results indicate that a quantity-quality trade-off must occur between species with different breeding strategies so that they can fully exploit the existing given resources.

Highlights

Most orchid species have been shown to be severely pollination limited, and the factors affecting reproductive success have been widely studied
We studied the flowering plant density, pollinators, floral biology and breeding systems of H. petelotii and H. limprichtii to compare their reproductive success and identify the factors that may contribute to the differences between these species
Flowering phenology and morphology The two orchids flowered in August in our study site, and the flowering periods of the two species overlapped according to our observations in 2014, with H. petelotii flowering from 23 July to 26 August and H. limprichtii flowering from 31 July to 23 August (Fig. 2)

Summary

Introduction

Most orchid species have been shown to be severely pollination limited, and the factors affecting reproductive success have been widely studied. Habenaria species typically produce nectar but exhibit variable fruit set and reproductive success among species. We investigated the influence of the flowering plant density, inflorescence size, breeding system, and pollinator behaviour on the reproductive success of two rewarding Habenaria species. Rewarding species secrete nectar that can be a substantial source of energy for pollinators and may encourage repeated visits by pollinators [3]; rewarding orchids are more successful at producing fruits than their rewardless counterparts. Fruit set varies among species, and numerous studies have investigated the factors affecting reproductive success in orchids, especially in deceptive species [2]. The factors that determine reproductive success vary from species to species

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