Microsatellites and petal morphology reveal new patterns of admixture in Orchis hybrid zones

Abstract

The genetic structure of hybrid zones provides insight into the potential for gene flow to occur between plant taxa. Four closely related European orchid species (Orchis anthropophora, O. militaris, O. purpurea, and O. simia) hybridize when they co-occur. We aimed to characterize patterns of hybridization in O. militaris-O. purpurea, O. purpurea-O. simia, and O. anthropophora-O. simia hybrid zones using molecular and morphological data. Methods: We used 11 newly isolated nuclear microsatellites to genotype 695 individuals collected from seven hybrid zones and six allopatric parental populations in France. Geometric morphometric analysis was conducted using 15 labellum landmarks to capture the main aspects of petal shape. Results: Backcrossing was asymmetric toward O. militaris in multiple O. militaris-O. purpurea hybrid zones. Hybrids in O. purpurea-O. simia and O. anthropophora- O. simia hybrid zones were largely limited to F1 and F2 generations, but further admixture had occurred. These patterns were reflected in labellum geometric morphometric data, which correlated strongly with nuclear microsatellite data in all three species combinations. Conclusions: The coexistence of parental and admixed individuals in these Orchis hybrid zones implies they are likely to be tension zones being maintained by a balance between gene flow into the hybrid zone and selection acting against admixed individuals. The pattern of admixture in the three species combinations suggests intrinsic selection acting on the hybrids is weaker in more closely related taxa.

Traditional, Therapeutic Uses and Phytochemistry of Terrestrial European Orchids and Implications for Conservation

“…However, apart for the latter which specifies that local native orchids are propagated with the aim to help dwindling populations, other companies do not indicate the provenience of seed material. This sets potential problems of genetic pollution, increasing hybridization with local orchid species ([ 277 ] and references therein), and also the introduction of allochthonous microorganisms used in the potting mix, in particular bacteria and fungi, which could compete with the endophytes found in native populations, i.e., [ 278 , 279 , 280 ]. Given that recent studies seem to suggest that orchids can act as reservoir of orchid mycorrhizal fungi [ 281 ], conservation efforts would not only be pivotal for orchid populations persistence but also for the hosted microorganisms, which deserve more scientific attention as potential sources of active signalling molecules of ecological, agronomical, and industrial interest [ 263 ].…”

Novel Approaches for Species Concepts and Delimitation in Polyploids and Hybrids

“…A hybrid zone emerges when populations of two species overlap spatially and temporally and cross to form viable offspring. In such hybrid zones, intrinsic or extrinsic selection against hybrids may further block hybrid establishment, as demonstrated in Senecio [37][38][39], in Rhododendron [40], or in Orchis [41].…”

Extracting Quantitative Information from Images Taken in the Wild: A Case Study of Two Vicariants of the Ophrys aveyronensis Species Complex

“…Over the past decade, image-based approaches have kept their promises in biology, enabling automated species identification in taxonomy [7][8][9] or high-throughput phenotyping of cultivars in agronomy [10]. In ecology and evolutionary studies, however, image-based phenotyping is still the exception rather than the norm [6].…”