Magazine R256 Orchids are one of the most fascinating and diverse plant groups. With an estimated 18,500 species worldwide they show remarkable floral diversity and reproduction strategies. Plant breeders have found that it is often easy to produce hybrids artificially between species but this does not often occur in the wild. So one of the key questions about these plants is how species that occur together and flower at similar times prevent hybridisation. One strategy developed by members of the Ophrys group of orchids has been to attract just one species of pollinator for each orchid species, a phenomenon much investigated and which attracted the interest of Charles Darwin. But in the Mediterranean region, many species of orchids co-exist, flower at similar times and are visited by the same pollinating insects. How do such species survive and avoid hybridisation? This was the question asked by Salvatore Cozzolino, at the University of Naples, Saverlo D’Emerico at the University of Bari and Alex Widmer at the Geobotanical Institute in Zurich. Reporting in the Proceedings of the Royal Society (published online), the team have examined 13 species of orchid that grow in the same areas and flower at similar times. Six species pairs were identified as having shared pollination insects and seven species pairs which use different, specific pollinators. The team studied chromosomal features of the different species to determine whether the karyotype of the different orchids might be a mechanism for a post-pollination means of preventing fertilisation and therefore hybridisation. The researchers found that there was a higher degree of intrachromosomal asymmetry between the species pairs that shared a pool of common pollinators compared with species pairs that have different pollinators. Moreover, they found that the differences in karyotype were not significantly correlated with genetic divergence, further suggesting that co-existing orchids may have evolved karyotypic differences as a means of reproductive isolation. The authors believe the absence of post-pollination isolation mechanisms in species that have evolved to have specific pollinators suggests that such specificity is important and may help explain the karyotypic differences in species that share common pollinators and thus prevent easy hybridisation in the natural environment. Orchids show an astonishing floral diversity yet an ability to hybridise in the hands of breeders. Nigel Williams reports on a new study that shows how neighbours appear to avoid the hybrid trap in the wild. Feature Keeping up appearances Separation: Orchids, including this early spider orchid (Ophrys sphegodes), appear to have evolved different methods to prevent hybridisation.

Keeping up appearances - COnnecting REpositoriescore.ac.uk/download/pdf/82540043.pdfKeeping up appearances Separation: Orchids, including this early spider orchid ( Ophrys sphegodes),

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Page 1: Keeping up appearances - COnnecting REpositoriescore.ac.uk/download/pdf/82540043.pdfKeeping up appearances Separation: Orchids, including this early spider orchid ( Ophrys sphegodes),

MagazineR256

Orchids are one of the mostfascinating and diverse plantgroups. With an estimated 18,500species worldwide they showremarkable floral diversity andreproduction strategies. Plantbreeders have found that it isoften easy to produce hybridsartificially between species butthis does not often occur in thewild. So one of the key questions

about these plants is howspecies that occur together andflower at similar times preventhybridisation. One strategydeveloped by members of theOphrys group of orchids hasbeen to attract just one speciesof pollinator for each orchidspecies, a phenomenon muchinvestigated and which attractedthe interest of Charles Darwin.

But in the Mediterraneanregion, many species of orchidsco-exist, flower at similar timesand are visited by the samepollinating insects. How do suchspecies survive and avoidhybridisation? This was thequestion asked by SalvatoreCozzolino, at the University ofNaples, Saverlo D’Emerico at theUniversity of Bari and AlexWidmer at the GeobotanicalInstitute in Zurich. Reporting inthe Proceedings of the RoyalSociety (published online), theteam have examined 13 speciesof orchid that grow in the sameareas and flower at similar times.Six species pairs were identifiedas having shared pollinationinsects and seven species pairswhich use different, specificpollinators.

The team studiedchromosomal features of thedifferent species to determinewhether the karyotype of thedifferent orchids might be amechanism for a post-pollinationmeans of preventing fertilisationand therefore hybridisation.

The researchers found thatthere was a higher degree ofintrachromosomal asymmetrybetween the species pairs thatshared a pool of commonpollinators compared withspecies pairs that have differentpollinators. Moreover, they foundthat the differences in karyotypewere not significantly correlatedwith genetic divergence, furthersuggesting that co-existingorchids may have evolvedkaryotypic differences as ameans of reproductive isolation.

The authors believe theabsence of post-pollinationisolation mechanisms in speciesthat have evolved to havespecific pollinators suggests thatsuch specificity is important andmay help explain the karyotypicdifferences in species that sharecommon pollinators and thusprevent easy hybridisation in thenatural environment.

Orchids show an astonishing floral diversity yet an ability to hybridise inthe hands of breeders. Nigel Williams reports on a new study thatshows how neighbours appear to avoid the hybrid trap in the wild.

Feature

Keeping up appearances

Separation: Orchids, including this early spider orchid (Ophrys sphegodes), appear tohave evolved different methods to prevent hybridisation.