The influence of gene expression time delays on Gierer-Meinhardt pattern formation systems

There are numerous examples of morphogen gradients controlling long range signalling in developmental and cellular systems. The prospect of two such interacting morphogens instigating long range self-organisation in biological systems via a Turing bifurcation has been explored, postulated, or implicated in the context of numerous developmental processes. However, modelling investigations of cellular systems typically neglect the influence of gene expression on such dynamics, even though transcription and translation are observed to be important in morphogenetic systems. In particular, the influence of gene expression on a large class of Turing bifurcation models, namely those with pure kinetics such as the Gierer–Meinhardt system, is unexplored. Our investigations demonstrate that the behaviour of the Gierer–Meinhardt model profoundly changes on the inclusion of gene expression dynamics and is sensitive to the sub-cellular details of gene expression. Features such as concentration blow up, morphogen oscillations and radical sensitivities to the duration of gene expression are observed and, at best, severely restrict the possible parameter spaces for feasible biological behaviour. These results also indicate that the behaviour of Turing pattern formation systems on the inclusion of gene expression time delays may provide a means of distinguishing between possible forms of interaction kinetics. Finally, this study also emphasises that sub-cellular and gene expression dynamics should not be simply neglected in models of long range biological pattern formation via morphogens

A new extinct species of Polynesian sandpiper (Charadriiformes: Scolopacidae: Prosobonia) from Henderson Island, Pitcairn Group, and the phylogenetic relationships of Prosobonia

We describe a new species of Polynesian sandpiper from Henderson Island, Prosobonia sauli sp. nov., based on multiple Holocene fossil bones collected during the Sir Peter Scott Commemorative Expedition to the Pitcairn Islands (1991–92). Prosobonia sauli is the only species of Prosobonia to be described from bone accumulations and extends the record of known extinct Polynesian sandpipers to four. It is readily differentiated from the extant Tuamotu Sandpiper P. parvirostris in several features of the legs and bill, implying ecological adaptations to different environments. The geographically nearest Prosobonia populations to Henderson Island were found on Mangareva, where it is now extinct. A previous record of a species of Prosobonia from Tubuai, Austral Islands, is here shown to belong to the Sanderling Calidris alba. Our analyses of newly sequenced genetic data, which include the mitochondrial genomes of P. parvirostris and the extinct Tahiti Sandpiper P. leucoptera, confidently resolve the position of Prosobonia as sister-taxon to turnstones and calidrine sandpipers. We present a hypothesis for the timing of divergence between species of Prosobonia and other scolopacid lineages. Our results further provide a framework to interpret the evolution of sedentary lineages within the normally highly migratory Scolopacidae.Vanesa L De Pietri, Trevor H Worthy, R Paul Scofield, Theresa L Cole, Jamie R Wood, Kieren J Mitchell ... et al

Journal of Molecular Spectroscopy

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