Suck on this: predictions and patience in phytobiology

Image: Thomas William Wood, in ‘Creation by Law’ by Alfred Russel Wallace, The Quarterly Journal of Science vol. 4, 1867.

Image: Thomas William Wood, in ‘Creation by Law’ by Alfred Russel Wallace, The Quarterly Journal of Science vol. 4, 1867.

One of the great strengths of the sci­entific method is its abil­ity to make pre­dic­tions that can be tested. One of the most fam­ous of those pre­dic­tions is Charles Darwin’s oft-cited 1862 infer­ence that a long-throated flower (‘with a nec­tary a foot long’ – approx. 30 cm for non-Imperial read­ers) from Madagascar (Angraecum ses­qui­pedale or Darwin’s orchid) would be pol­lin­ated by an equally long-tongued insect. Despite being a pro­nounce­ment by the ven­er­able nat­ur­al­ist – or maybe because of that? – the asser­tion was con­tro­ver­sial at the time and not without its detract­ors. Nevertheless, this incid­ent helped to place the notion of insect–plant co-evolution firmly onto the agenda and star­ted a debate that con­tin­ues into the 21st cen­tury (e.g. Miguel Rodríguez-Gironés and Ana Llandres). Sadly, the Great Man never lived to see his pre­dic­tion con­firmed and his pres­ci­ence vin­dic­ated – that only happened in the late 20th cen­tury, but a fit­ting trib­ute to this remark­able story has been pro­duced by Joe Arditti and col­leagues. For many years the iden­tity of the nectar-sucking moth was not known. Although the appro­pri­ately named Xanthopan mor­ganii ssp. prae­dicta (Morgan’s sphinx) was mooted as the likely pol­lin­ator, this was not con­clus­ively demon­strated until 1992. It is a fas­cin­at­ing tale that is richly illus­trated – both with images and quotes from the cor­res­pond­ence that passed between the major play­ers in this saga – and is a nice bring­ing together of plants, people and per­son­al­it­ies (includ­ing the ever-interesting if much over-shadowed Alfred Russel Wallace). But those bene­fi­cial long tongues come with costs, as Brendan Borrell has demon­strated for orchid bees, not least of which is the need for their own­ers to have a firm grasp of the phys­ics of fluid flow! Closer to home, long tongues amongst humans are rare enough to be con­sidered an ‘abnor­mal­ity’ and own­er­ship thereof may incur ser­i­ous ‘lost oppor­tun­ity’ costs as one hyper­glos­sic boy dis­covered when he lost his place at a school in Malavalli (in the Mandya dis­trict of India) as a res­ult. [For the record – maybe lit­er­ally – the mean tongue (tech­nic­ally, a pro­bos­cis) length of the hawk­moth is a stag­ger­ing 22 cm; the mean spur length of the flower is 33 cm – Ed.]

Nigel Chaffey. ORCID 0000-0002-4231-9082

Nigel is a botanist and full-time academic at Bath Spa University (Bath, near Bristol, UK). As News Editor for the Annals of Botany he contributes the monthly Plant Cuttings column to that august international botanical organ. His main goal is to inform (hopefully, in an educational, and entertaining way...) about plants and plant-people interactions.