Floral Trait and Mycorrhizal Similarity between an Endangered Orchid and Its Natural Hybrid

Jacopo Calevo,Mariangela Girlanda,Samuele Voyron,Martino Adamo,Laura Cornara,Miriam Bazzicalupo,Karl J Duffy,Francesco Saverio Robustelli Della Cuna,Annalisa Giovannini

doi:10.3390/d13110550

Abstract

Hybridization can often lead to the formation of novel taxa which can have traits that resemble either or both parental species. Determining the similarity of hybrid traits to parental taxa is particularly important in plant conservation, as hybrids that form between rare and common taxa may more closely resemble a rare parental species, thereby putting the rare parental taxon at further risk of extinction via increased backcrossing and introgression. We investigated the floral (morphological and chemical) traits and orchid mycorrhizal (OrM) fungal associations of the endangered orchid Orchis patens, its more common sister species O. provincialis, and their natural hybrid O. × fallax in natural sympatric populations. We found that both morphological and chemical floral traits of O. × fallax are shared by the parents but are more similar to O. patens than O. provincialis. OrM fungi were shared among all three taxa, indicating that the availability of OrM fungi should not represent a barrier to establishment of individuals of any of these taxa. These results suggest that O. × fallax may be able to expand its distribution within a similar niche to O. patens. This highlights the importance of quantifying differences between hybrids and parental taxon in species conservation planning.

Highlights

Hybridization among plant species is common in the wild and is thought to be a driving force in evolution [1,2]
The longitudinal section of the spurs revealed that the inner surface of Orchis patens and O. × fallax were covered with papillae having different length (Figure 2a,b), while O. provincialis presented more or less protuberant epidermal cells as already stated by Bell et al [69] (Figure 2c,i)
In O. provincialis, cells located near the spur entrance were prolate and covered by linear cuticular striations which sometimes turned into vermiform (Figure 2f), while cells at the spur apex were more swollen and rounded/sub-prolate with sinuous vermiform striations (Figure 2i)

Summary

Introduction

Hybridization among plant species is common in the wild and is thought to be a driving force in evolution [1,2]. Hybridization can lead to introgression and the loss of unique genetic identities within populations [6,7] This is true when rare species co-occur and hybridize with more common and widespread related taxa [8,9]. The maintenance of species boundaries depends on reproductive barriers to isolate sexually compatible species which grow sympatrically [13,14] These barriers can be divided in pre-zygotic, which prevent individuals of different species from mating (e.g., by emitting different scents that attract different pollinators, different flowering phenology, habitat separation or geographic distribution) and post-zygotic barriers, such as hybrid sterility, fruit abortion, production of non-viable seeds or, in the case of plants that depend on fungi to recruit from seed, limitation of suitable mycorrhizas [15,16]

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Conclusion