Graham R. Brown

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

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.

Caught in the act: Pollination of sexually deceptive trap-flowers by fungus gnats in Pterostylis (Orchidaceae)

BACKGROUND AND AIMS Pterostylis is an Australasian terrestrial orchid genus of more than 400 species, most of which use a motile, touch-sensitive labellum to trap dipteran pollinators. Despite studies dating back to 1872, the mechanism of pollinator attraction has remained elusive. This study tested whether the fungus gnat-pollinated Pterostylis sanguinea secures pollination by sexual deception. METHODS The literature was used to establish criteria for confirming sexual deception as a pollination strategy. Observations and video recordings allowed quantification of each step of the pollination process. Each floral visitor was sexed and DNA barcoding was used to evaluate the degree of pollinator specificity. Following observations that attraction to the flowers is by chemical cues, experimental dissection of flowers was used to determine the source of the sexual attractant and the effect of labellum orientation on sexual attraction. Fruit set was quantified for 19 populations to test for a relationship with plant density and population size. KEY RESULTS A single species of male gnat (Mycetophilidae) visited and pollinated the rewardless flowers. The gnats often showed probing copulatory behaviour on the labellum, leading to its triggering and the temporary entrapment of the gnat in the flower. Pollen deposition and removal occurred as the gnat escaped from the flower via the reproductive structures. The labellum was the sole source of the chemical attractant. Gnats always alighted on the labellum facing upwards, but when it was rotated 180 ° they attempted copulation less frequently. Pollination rate showed no relationship with orchid population size or plant density. CONCLUSIONS This study confirms for the first time that highly specific pollination by fungus gnats is achieved by sexual deception in Pterostylis. It is predicted that sexual deception will be widespread in the genus, although the diversity of floral forms suggests that other mechanisms may also operate.

Molecular genetic analysis and ecological evidence reveals multiple cryptic species among thynnine wasp pollinators of sexually deceptive orchids

Sexually deceptive Chiloglottis orchids lure their male thynnine wasp pollinators to the flower by emitting semiochemicals that mimic the specific sex pheromone of the wasp. Sexual deception is possible because chemical rather than visual cues play the key role in wasp mate search, suggesting that cryptic wasp species may be frequent. We investigated this prospect among Neozeleboria wasp pollinators of Chiloglottis orchids, drawing on evidence from molecular phylogenetic analysis at three genes (CO1, rhodopsin and wingless), population genetic and statistical parsimony analysis at CO1, orchid associations and their semiochemicals, and geographic ranges. We found a compelling relationship between genetically defined wasp groups, orchid associations, semiochemicals and geographic range, despite a frequent lack of detectable morphological differences. Our findings reveal multiple cryptic species among orchid pollinators and indicate that chemical changes are important for wasp reproductive isolation and speciation. The diversity of Neozeleboria may have enabled, rather than constrained, pollinator-driven speciation in these orchids.

Pollinator specificity, cryptic species and geographical patterns in pollinator responses to sexually deceptive orchids in the genus Chiloglottis: the Chiloglottis gunnii complex

Australian sexually deceptive orchids are typically highly pollinator specific, each species having a single unique hymenopteran pollinator species. Pollinator specificity in six of the nine described species in the Chiloglottis gunnii Lindl. complex was investigated by using field pollinator-choice tests, with Chiloglottis taxa translocated within and among biogeographical regions. Specific pollinators revealed the existence of five undescribed cryptic taxa in the C. gunnii complex, three within C. pluricallata D.L.Jones and two within C. valida D.L.Jones, in addition to the six described species. Of the 11 Chiloglottis taxa, 10 had a single thynnine-wasp pollinator throughout their sometimes large distributions, whereas one, C. valida, had a second pollinator in parts of its distribution. Eleven pollinators belonged to the genus Neozeleboria and one to Eirone. Pollinator-choice testing showed that cross-attraction of pollinators occurs between three geographically isolated Chiloglottis taxa on the New South Wales (NSW) New England Tableland and taxa in the South Eastern Highlands of NSW and Victoria. The data suggested there is sharing of chemical attractants and supported the recognition of at least five odour types within Chiloglottis, each encompassing one to three orchid taxa and their pollinators. The following two broad generalisations are made: (1) there is no cross-attraction of pollinators among sympatric Chiloglottis species, i.e. sympatric orchid taxa do not share attractant odours; and (2) all Chiloglottis species have different specific pollinators, although they may share attractant odours allopatrically. Some 28 thynnine-wasp species were attracted as minor non-pollinating responders to Chiloglottis taxa; five of these were pollinators of other Chiloglottis species. These wasps were much more taxonomically diverse than the pollinators, belonging to six genera, and suggest that some orchid-odour components are widely shared within the sex pheromones of the Thynninae.

Evolutionary relationships among pollinators and repeated pollinator sharing in sexually deceptive orchids

The mechanism of pollinator attraction is predicted to strongly influence both plant diversification and the extent of pollinator sharing between species. Sexually deceptive orchids rely on mimicry of species‐specific sex pheromones to attract their insect pollinators. Given that sex pheromones tend to be conserved among related species, we predicted that in sexually deceptive orchids, (i) pollinator sharing is rare, (ii) closely related orchids use closely related pollinators and (iii) there is strong bias in the wasp lineages exploited by orchids. We focused on species that are pollinated by sexual deception of thynnine wasps in the distantly related genera Caladenia and Drakaea, including new field observations for 45 species of Caladenia. Specialization was extreme with most orchids using a single pollinator species. Unexpectedly, seven cases of pollinator sharing were found, including two between Caladenia and Drakaea, which exhibit strikingly different floral morphology. Phylogenetic analysis of pollinators using four nuclear sequence loci demonstrated that although orchids within major clades primarily use closely related pollinator species, up to 17% of orchids within these clades are pollinated by a member of a phylogenetically distant wasp genus. Further, compared to the total diversity of thynnine wasps within the study region, orchids show a strong bias towards exploiting certain genera. Although these patterns may arise through conservatism in the chemical classes used in sex pheromones, apparent switches between wasp clades suggest unexpected flexibility in floral semiochemical production. Alternatively, wasp sex pheromones within lineages may exhibit greater chemical diversity than currently appreciated.

Absence of nectar resource partitioning in a community of parasitoid wasps

Parasitoid wasps occur in diverse communities, with the adults of most species sourcing carbohydrates from nectar or honeydew. However, the role of niche partitioning of nectar resources in maintaining diverse communities of parasitoid Hymenoptera is poorly known. To elucidate patterns of nectar resource use and test whether species partition resources, we investigated pollen loads in a community of parasitoid thynnine wasps in the biodiversity hotspot of southwestern Australia. In total, 304 thynnine wasps from 28 species were captured. Eighteen of these species are undescribed, highlighting the high diversity of unrecognized species in southwestern Australia. Pollen loads were detected on 111 individuals representing 19 species. Six pollen types were identified. All species that carried pollen primarily visited two tree species, Agonis flexuosa and Eucalyptus marginata, in the Myrtaceae. The other four pollen types were only recorded from single wasps. There was no evidence of nectar-resource partitioning. This may be due to these Myrtaceae producing abundant, open-faced flowers. Wasp species that were not recorded carrying pollen may utilise other carbohydrate sources, such as homopoteran honeydew. Niche partitioning is predicted to occur during the parasitoid larval phase of the life cycle. This study highlights the importance of nectariferous Myrtaceae in supporting diverse wasp communities. Further, two species of nectar-foraging wasps collected here are involved in the pollination of rare orchid species. Hence, conservation and management of habitats that support floriferous Myrtaceae are important for both the maintenance of diverse wasp communities, and the plants they pollinate.

When did Homo sapiens first reach Southeast Asia and Sahul

Anatomically modern humans (Homo sapiens, AMH) began spreading across Eurasia from Africa and adjacent Southwest Asia about 50,000–55,000 years ago (ca. 50–55 ka). Some have argued that human genetic, fossil, and archaeological data indicate one or more prior dispersals, possibly as early as 120 ka. A recently reported age estimate of 65 ka for Madjedbebe, an archaeological site in northern Sahul (Pleistocene Australia–New Guinea), if correct, offers what might be the strongest support yet presented for a pre–55-ka African AMH exodus. We review evidence for AMH arrival on an arc spanning South China through Sahul and then evaluate data from Madjedbebe. We find that an age estimate of >50 ka for this site is unlikely to be valid. While AMH may have moved far beyond Africa well before 50–55 ka, data from the region of interest offered in support of this idea are not compelling.

Rugosothynnus gen. nov. (Hymenoptera: Tiphiidae: Thynninae: Rhagigasterini), a newly recognised Australian genus

Rugosothynnus gen. nov. (type species Rhagigaster corrugatus Turner, 1910) is erected for 12 Rhagigaster-like species. Nine species are described and illustrated from Australia: R. brunneus sp. nov., R. clypeatus sp. nov., R. confusus sp. nov., R. depressus sp. nov., R. fulvescens sp. nov., R. houstoni sp. nov., R. monteithae sp. nov., R. neocorrugatus sp. nov. and R. schichai sp. nov. New combinations are proposed for R. burnsi (Given, 1959), comb. nov., R. corrugatus (Turner, 1910), comb. nov. and R. tristis (Smith, 1859), comb. nov. (all previously from genus Rhagigaster Guérin-Ménéville, 1838). A key to both sexes of all species is provided except for the females of R. clypeatus sp. nov., R. depressus sp. nov., R. neocorrugatus sp. nov. and R. schichai sp. nov. which are unknown.