Implications of pollination by food and sexual deception for pollinator specificity, fruit set, population genetics and conservation of Caladenia (Orchidaceae)

Abstract

Caladenia is very unusual in that it contains species that attract pollinators by two different strategies, food and sexual deception. Among the sexually deceptive species, baiting for pollinators has shown that within populations orchid species are typically pollinated by a single species of thynnine wasp. However, some wasp species can be pollinators of more than one species of orchid usually when their ranges do not overlap. There is a trend for closely related orchids to exploit wasps from the same genus, with different lineages of orchids often pollinated by different genera. Very little is known about pollination of food-deceptive Caladenia species, although it is evident they attract a suite of generalist food-seeking insects. Food-deceptive species have a higher pollination rate than do sexually deceptive species. Studies of population genetics and pollen movements are few, although they suggest a pattern of fine-scale genetic structuring within populations, owing to predominantly restricted seed dispersal and low genetic differentiation among populations as a consequence of rare long-distance seed-dispersal events. Both evolutionary and ecological research of Caladenia will greatly benefit from a better understanding of the insect species involved in pollination, their ecological requirements and the ecological and genetic consequences of food and sexual deception.

Pollinator sharing by the sexually deceptive Green-comb Spider Orchids, Caladenia phaeoclavia, C. parva and C. villosissima (Orchidaceae: Caladeniinae): taxonomic considerations

“…Experimental evidence for pollinator specificity in sexually By contrast to the lack of pollinator sharing in Chiloglottis and Drakaea revealed by field choice testing, published pollinator lists suggest pollinator sharing may occur in some groups of sexually deceptive, Thynnid-pollinated Caladenia species in eastern Australia (Phillips et al 2009, Gaskett 2010. While most sexually deceptive Caladenia species attract unique pollinators, nine species in the Caladenia reticulata complex are pollinated by Phymatothynnus near nitidus 1, three species of Greencomb Spider Orchids are pollinated by Lophocheilus anilitatus and Caladenia tesselata shares P. near nitidus 1 with the C. reticulata group (Phillips et al 2009, Gaskett 2010. These data contrast markedly with results for Chiloglottis and Drakaea, and suggest that factors other than pollinator specificity may govern reproductive isolation in some Caladenia clades.…”

“…Potential factors include postzygotic incompatibility and different positioning of pollinaria on the body of the pollinator (Paulus and Gack 1990, Phillips et al 2013, Vereecken and Francisco 2014. However, all Thynnid pollinators carry the pollinia of Drakaeinae and Caladeniinae nototribically on the centre thorax discounting a role for differential pollen placement in reproductive isolation in these groups (Stoutamire 1983, Phillips et al 2009). Alternatively, it is possible that cryptic pollinator species may exist within P. near nitidus 1 and Lophocheilus anilitatus, such that pollinator sharing may not be occurring.…”

“…Alternatively, it is possible that cryptic pollinator species may exist within P. near nitidus 1 and Lophocheilus anilitatus, such that pollinator sharing may not be occurring. A further possibility is that a mismatch exists between morphospecies and biospecies boundaries in the Greencomb Spider Orchids and the C. reticulata complex (Phillips et al 2009), which would suggest the two orchid complexes may have been over-split taxonomically. Swartz et al (2014) examined these issues in the C. reticulata complex.…”

“…Extensive pollinator baiting and field choice tests throughout the distribution of the complex in western Victoria showed that ten species shared the single pollen vector P. nitidus (=P. near nitidus 1 of Phillips et al 2009) and that no cryptic species existed within the P. nitidus. Phylogenetic analyses of 31 Caladenia species, including 25 in the reticulata complex, showed limited species level resolution within the complex and no differences between species with different pollinators (Swartz et al 2014).…”

“…Overall, the sharing of the same vector species among ten reticulata complex species combined with evidence of very low genetic divergence suggested they belong to the same biological species and most likely represent an example of taxonomic over-splitting (Swartz et al 2014). This paper uses pollinator baiting and controlled field choice tests to examine putative pollinator sharing (Phillips et al 2009, Gaskett 2010 across the geographical distributions of three closely similar, sexually deceptive species of Greencomb Spider Orchids; Caladenia parva G.W. Carr, C. phaeoclavia D.L.…”