What makes a good research paper?

The annual round of refereeing for the ARCOM conference always prompts a stimulating debate among the committee members as to what constitutes a good research paper. Clearly, there is a good deal of subjectivity in distinguishing good from bad, but there may be some basic characteristics that mark out a research paper from any other kind of paper, and it is good research papers that we would like to encourage at the annual conference.

Speciation in fig wasps

There are over 700 species of fig trees in the tropics and several thousand species of fig wasps are associated with their syconia (inflorescences). These wasps comprise a monophyletic family of fig pollinators and several diverse lineages of non-pollinating wasps. The pollinator larvae gall fig flowers, while larvae of non-pollinating species either initiate their own galls or parasitise the galls of other wasps. A single fig species has 1-4 pollinator species and also hosts up to 30 non-pollinating wasp species. Most wasps show a high degree of host plant specificity and are known from only a single fig species. However, in some cases wasps may be shared across closely related fig species. There is impressive morphological coevolution between figs and fig wasps and this, combined with a high degree of partner specificity, led to the expectation that figs and pollinators have cospeciated extensively. Comparison of deep phylogenies supports long-term codivergence of figs and pollinators, but also suggests that some host shifts have occurred. Phylogenies of more closely related species do not match perfectly and may even be incongruent, suggesting significant roles for processes other than strict cospeciation. Combined with recent evidence on host specificity patterns, this suggests that pollinator wasps may often speciate by host shifts between closely related figs, or by duplication (the wasp speciates but the fig doesn't). The frequencies and biological details of these different modes of speciation invite further study. Far less is known about speciation in non-pollinating fig wasps. Some lineages have probably coevolved with figs and pollinators for most of the evolutionary history of the symbiosis, while others appear to be more recent colonisers. Many species appear to be highly host plant specific, but those that lay eggs through the fig wall without entering the syconium (the majority of species) may be subject to fewer constraints on host-shifting than pollinators. There is evidence for substantial host shifting in at least one gens, but also evidence for ecological speciation on the same host plant by niche shifts in other cases. Finally, recent work has begun to address the issue of “community phylogeny” and provided evidence for long-term co-divergence of multiple pollinating and non-pollinating wasp lineages with their host figs.

Characterization of microsatellite markers for Sycoscapter nonpollinating fig wasps

We isolated 18 microsatellites from Sycoscapter australis, a nonpollinating fig wasp that develops in figs of Ficus macrophylla, and assessed their variability in 20 wasps. We further optimized nine of these loci for use in three other Sycoscapter species that develop in Ficus rubiginosa figs and assessed their variability in 47-140 wasps per species. These are the first microsatellites developed for nonpollinating fig wasps and show sufficient polymorphism to become important tools in evolutionary and genetical studies of Sycoscapter wasps.

Molecular dating and biogeography of fig-pollinating wasps

Figs and fig-pollinating wasps are obligate mutualists that have coevolved for over 60 million years. But when and where did pollinating fig wasps (Agaonidae) originate? Some studies suggest that agaonids arose in the Late Cretaceous and the current distribution of fig-wasp faunas can be explained by the break-up of the Gondwanan landmass. However, recent molecular-dating studies suggest divergence time estimates that are inconsistent with the Gondwanan vicariance hypothesis and imply that long distance oceanic dispersal could have been an important process for explaining the current distribution of both figs and fig wasps. Here, we use a combination of phylogenetic and biogeographical data to infer the age, the major period of diversification, and the geographic origin of pollinating fig wasps. Age estimates ranged widely depending on the molecular-dating method used and even when using the same method but with slightly different constraints, making it difficult to assess with certainty a Gondwanan origin of agaonids. The reconstruction of ancestral areas suggests that the most recent common ancestor of all extant fig-pollinating wasps was most likely Asian, although a southern Gondwana origin cannot be rejected. Our analysis also suggests that dispersal has played a more important role in the development of the fig-wasp biota than previously assumed. (C) 2009 Elsevier Inc. All rights reserved.

Interference competition and high temperature reduce the ‘virulence’ of fig wasps and contribute to stability of a fig-wasp mutualism

Fig trees are pollinated by fig wasps, which also oviposit in female flowers. The wasp larvae gall and eat developing seeds. Although fig trees benefit from allowing wasps to oviposit, because the wasp offspring disperse pollen, figs must prevent wasps from ovipositing in all flowers, or seed production would cease, and the mutualism would go extinct. In Ficus racemosa, we find that syconia (‘figs’) that have few foundresses (ovipositing wasps) are underexploited in the summer (few seeds, few galls, many empty ovules) and are overexploited in the winter (few seeds, many galls, few empty ovules). Conversely, syconia with many foundresses produce intermediate numbers of galls and seeds, regardless of season. We use experiments to explain these patterns, and thus, to explain how this mutualism is maintained. In the hot summer, wasps suffer short lifespans and therefore fail to oviposit in many flowers. In contrast, cooler temperatures in the winter permit longer wasp lifespans, which in turn allows most flowers to be exploited by the wasps. However, even in winter, only in syconia that happen to have few foundresses are most flowers turned into galls. In syconia with higher numbers of foundresses, interference competition reduces foundress lifespans, which reduces the proportion of flowers that are galled. We further show that syconia encourage the entry of multiple foundresses by delaying ostiole closure. Taken together, these factors allow fig trees to reduce galling in the wasp-benign winter and boost galling (and pollination) in the wasp-stressing summer. Interference competition has been shown to reduce virulence in pathogenic bacteria. Our results show that interference also maintains cooperation in a classic, cooperative symbiosis, thus linking theories of virulence and mutualism. More generally, our results reveal how frequency-dependent population regulation can occur in the fig-wasp mutualism, and how a host species can ‘set the rules of the game’ to ensure mutualistic behavior in its symbionts.

Diverse mariner-like elements in fig wasps

Mariner transposable elements are widespread and diverse in insects. We screened 10 species of fig wasps (Hymenoptera: Agaonidae) for mariner elements. All 10 species harbour a large diversity of mariner elements, most of which have interrupted reading frames in the transposase gene region, suggesting that they are inactive and ancient. We sequenced two full-length mariner elements and found evidence to suggest that they are inserted in the genome at a conserved region shared by other hymenopteran taxa. The association between mariner elements and fig wasps is old and dominated by vertical transmission, suggesting that these 'selfish genetic elements' have evolved to impart only very low costs to their hosts.

Quantitative thermal imaging analysis of aircraft materials: through skin sensing (Invited Paper)

Thermal non-destructive testing (NDT) is commonly used for assessing aircraft structures. This research work evaluates the potential of pulsed -- transient thermography for locating fixtures beneath aircraft skins in order to facilitate accurate automated assembly operations. Representative aluminium and carbon fibre aircraft skin-fixture assemblies were modelled using thermal modelling software. The assemblies were also experimentally investigated with an integrated pulsed thermographic evaluation system, as well as using a custom built system incorporating a miniature un-cooled camera. Modelling showed that the presence of an air gap between skin and fixture significantly reduced the thermal contrast developed, especially in aluminium. Experimental results show that fixtures can be located to accuracies of 0.5 mm.