An increase in temperature, within bounds, will accelerate development of reptile embryos, and morphogenesis can be normal over a range of temperatures despite those varying rates of development. Less well understood is the form of the relationship that best describes variation in developmental rate with temperature. In this article, we apply a linear degree.hour model, an empirical curvilinear model, a biophysical model, and a polynomial model to data on rates of embryonic development and temperature in the pig-nosed turtle Carettochelys insculpta from northern Australia. The curvilinear models, which have been applied with success to development of insects, describe the embryonic development of turtles well. When fluctuating temperatures extend beyond the constant temperatures that support successful incubation, the curvilinear models continue to perform well, whereas the linear model predictions fail. Sensitivity analysis indicates that under some circumstances, incubation duration may be increased by diel temperature fluctuations, independent of an influence of mean temperature. In other circumstances, incubation duration may be decreased, and in still other circumstances, diel temperature fluctuations will have no impact on incubation duration. This adds an additional dimension to our understanding of how thermal regimes can be selected or manipulated by reptiles to optimise incubation duration and the timing of offspring emergence.

Standard series of embryonic stages are the primary basis for organising information in embryological studies and for ageing eggs and embryos in field studies. In this paper we calibrate the developmental series for the pignosed turtle, Carettochelys insculpta, from northern Australia against an established series for Chelydra serpentina, carefully noting unique attributes of C. insculpta. We also extend existing non-destructive approaches to staging embryos by identifying several additional specific embryological attributes visible externally or by candling. A chronological sequence of attributes visible by candling is established as a viable alternative to the destructive approaches requiring direct examination of embryos.Résumé : Des séries-étalons de stades embryonnaires constituent la base de l'organisation de l'information en embryologie et elles sont essentielles à la détermination de l'âge des oeufs et des embryons au cours d'études sur le terrain. Nous avons calibré une série de stades de développement de Carettochelys insculpta, une tortue du nord de l'Australie, en les confrontant à une série déjà établie de stades de Chelydra serpentina, notant les particularités de C. insculpta. Nous apportons également des détails supplémentaires au sujet des approches non destructrices déjà existantes de déter-mination des stades embryonnaires en identifiant plusieurs caractéristiques embryonnaires spécifiques additionnelles par observation externe ou par mirage. L'établissement d'une séquence chronologique des attributs visibles par mirage est une alternative intéressante aux approches destructrices qui supposent l'examen direct des embryons.[Traduit par la Rédaction] 392Beggs et al.

Invasive plants are recognised as a major threat to biodiversity conservation worldwide. Despite this recognition, our understanding of the mechanisms controlling the invasion process and its impact on flora and fauna is often poor. We examined the impact of an invasive aquatic grass species, para grass (Urochloa mutica), on seasonally inundated wetlands in tropical northern Australia. Flora and avifauna were surveyed at sites invaded by para grass and in native vegetation. Spatial information systems were used to design surveys and determine environmental correlates of para grass distribution and so predict the potential future spread of para grass and infer impacts in the absence of control. Where para grass was present the median number of plant taxa was ~75% lower. Few birds showed preference for habitats invaded by para grass, and most birds were associated with areas of native vegetation or other habitats with little or no para grass. The study identified several wetland habitats that are at greater risk of invasion, based on the apparent habitat preferences of para grass. The degradation or loss of some of these 'at-risk' habitats, including Oryza meriodionalis grasslands that play an integral role in the wetland food chain, has important ramifications for the levels of biodiversity supported by the wetlands.

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