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. 2022 Jun 13:10:e13362.
doi: 10.7717/peerj.13362. eCollection 2022.

Pollen transfer and patterns of reproductive success in pure and mixed populations of nectariferous Platanthera bifolia and P. chlorantha (Orchidaceae)

Emilia Brzosko  1 , Krzysztof Frąckiel  2 , Edyta Jermakowicz  1 , Paweł Mirski  1 , Beata Ostrowiecka  1 , Izabela Tałałaj  1
Affiliations

Pollen transfer and patterns of reproductive success in pure and mixed populations of nectariferous Platanthera bifolia and P. chlorantha (Orchidaceae)

Emilia Brzosko et al. PeerJ. .

Abstract

Plant species evolution is driven by many factors that have different roles in space and time. Using different field and laboratory methods, we studied reproductive patterns and their determinants in pure and mixed P. bifolia and P. chlorantha populations in different habitats. We also considered the probability of hybridisation between these two species and the role of intra-population processes in maintaining species integrity. Generally, we found a high level of reproductive success in both Platantherans. In both species, male (MRS) and female (FRS) reproductive success depended on floral display, and male reproductive success additionally on population structure. The flower traits were only weakly related to reproductive success. Moths' assemblages varied spatially and temporally, and their diversity and numbers were correlated with MRS in the year, when their abundance was markedly lower. Analysis of patterns of pollen transfer showed that pollen was transported up to 25 m (average 8.2 ± 4.83 m) and showed gene exchange between these two Platanthera species. The germination level of both species was significantly lower than seed viability, although P. bifolia seed germinated with higher frequency than P. chlorantha seeds. We noted differences in viability and germination of seeds developed as an effect of experimental interspecies crossings and those developed from natural pollination. The presence of intermediate ecotypes together with observations of spontaneous interspecies crosses in the field and viability of seeds produced in interspecies crossing suggest that both pre- and postzygotic reproductive barriers are not complete and do not prevent hybrid production.

Keywords: Female reproductive success; Floral display; Flower traits; Male reproductive success; Moths; Pollen flow; Putative hybrids; Seed germination; Seed viability.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Figure 1
Figure 1. PCA analysis of floral traits in P. bifolia and P. chlorantha studied populations in 2016 and 2017.
LL, labellum length; LW, labellum width; PL, pollinaria length; VD, distance between viscidia; ES, width of spur entrance.
Figure 2
Figure 2. Distance of registered pollen flow observed between color-marked flowers of two Platanthera species.
Figure 3
Figure 3. Comparison of seed viability in Platanthera bifolia, P. chlorantha and their crossings.
Figure 4
Figure 4. Comparison of seed germination rate in Platanthera bifolia, P. chlorantha and their crossings.
See this image and copyright information in PMC

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