Influence of larval and juvenile life history on age at first maturity in two tropical amphidromous fish species

This study investigates how age at first maturity of two tropical amphidromous species Sicyopterus lagocephalus (Pallas, 1770) and Cotylopus acutipinnis (Guichenot, 1863) varies in relation to their larval and juvenile life history. Reproductive stage was estimated based on histological observation of ovaries of more than 200 females of each species caught monthly over 1 year. The age of fish was estimated by interpreting the daily increments deposited on otoliths during the oceanic larval phase, and the juvenile phase in the river. The age at first maturity was approximately 9 months for S. lagocephalus and 7 months for C. acutipinnis, corresponding to approximately 70–130 and 90–130 days after they returned to freshwater respectively. For both species, the time spent in freshwater before maturity was significantly influenced by the duration of the pelagic larval stage at sea (PLD) and the season of return in freshwater. Individuals with a long PLD, or returning in freshwater during the warmer season, maturated faster once in freshwater. This reproductive advantage may minimise the risk of extirpation due to catastrophic events at each generation and thus probably benefits amphidromous species living in very unpredictable tropical rivers.     

High productivity gel diets for rearing of Queensland fruit fly, <Emphasis Type="Italic">Bactrocera tryoni</Emphasis>

The Queensland fruit fly or ‘Q-fly,’ Bactrocera tryoni (Froggatt) (Diptera: Tephritidae), is Australia’s most damaging insect pest of horticulture. The sterile insect technique (SIT) is being developed as a sustainable approach to management of Q-fly. New larval diets are needed for economical production of millions of artificially reared sterile flies that are required for use in SIT. Solid diets that incorporate biological bulking agents present problems of variable quality and waste disposal. Liquid diets emerged as a promising alternative, but these also suffer drawbacks, including separation of components, fermentation and need for cleaning and regular replacement of substrates that support developing larvae. The present study considers whether two promising liquid diet formulations might be improved by incorporating agar (0, 0.25, 0.5, 1.0 and 1.5%) to create semiliquid or gel diets that maintain consistent composition, suppress fermentation, negate the need for supporting substrates and minimize waste. Overall, gel diets containing greater than 0.5% agar outperformed liquid diets (0% agar) and semiliquid diets (0.25% agar) of identical nutritional composition, especially in terms of development rate and productivity. Flies from the two tested diet formulations differed in flight performance, and this likely reflects differences in concentration of wheat germ oil and/or the type of yeast used. Overall, gel diets show great promise for rearing of Q-fly, overcoming many of the constraints of both traditional solid diets and more recently developed liquid diets. There is now a need for larger-scale trials that test and refine these diets for use in operational SIT settings.     

Morphological and molecular characterisation of a mixed Cryptosporidium muris/Cryptosporidium felis infection in a cat

To date Cryptosporidium muris has been identified by microscopy and genotyping in cats in two studies. We report morphological and genetic evidence of a mixed C. muris and C. felis infection in a cat and provide the first histological, immunohistochemical, in situ hybridisation and genetic confirmation of a C. muris infection in the stomach of a cat. The cat suffered persistent diarrhoea after the initial consultation, which remained unresolved, despite several medical interventions. Further studies are required to determine the range, prevalence and clinical impact of Cryptosporidium species infecting cats.     

Assessment of novel inhibitors of Helicoverpa aminopeptidases as anti-insect agents

Helicoverpa species present problems worldwide as pests on a variety of agricultural crops. In Australia, the costs of controlling H. armigera (Hübn.) and H. punctigera (Wall.) are a major burden on the cotton industry, and novel mechanisms are continually sought to combat these pests. Potential new targets for insecticides are the digestive proteases of the insect, including the aminopeptidases (APs). A variety of compounds, designed to be similar in structure to known AP inhibitors, were synthesized and screened for activity in inhibiting H. armigera larval growth and AP activity. The most effective compounds in both assays proved to be hydroxamic acids and methylphosphonic acids. Compounds that incorporated both of these groups were also found to have significant potential as control agents. The most inhibitory compounds included valine methylphosphonic acid and a leucine methylphosphonic acid/hydroxamic acid derivative. The valine methylphosphonic acid compound was tested further in vitro, with the aim of producing a new active capable of restricting the viability of Helicoverpa populations on commercial crops.     

Vertical variations in wood basic density for two softwood species

European Journal of Forest Research - Studies on wood basic density (BD) vertical variations become essential to predict more accurately the within-stem distributions of biomass and wood quality in...     

Site fidelity and movements of an amphidromous goby revealed by otolith multi‐elemental signatures along a tropical watershed

Otolith microchemistry can provide crucial information to address gaps of knowledge in spatio‐temporal ecology of fish species. However, understanding the seasonal variability of water chemistry and its effect on otolith signatures is needed to interpret fish movements. Otolith multi‐elemental signatures were used to examine the diadromous migration and small‐scale movements of a tropical goby (Sicyopterus lagocephalus) within a watershed in La Réunion Island, Indian Ocean. The elemental ratios Sr:Ca, Ba:Ca and Sr:Ba recorded monthly in the water of nine sampling sites varied between localities and were correlated with otolith signatures, whereas the Mg:Ca signature was not. The incorporation of some trace elements in otoliths was influenced by the size of fish and site where they were caught, reflecting an effect of endogenous and exogenous factors. Despite these sources of variation, the elemental signatures did not overlap for three river sections distributed along the 26‐km‐long watershed. The diadromous migration and fish lifetime movements between these river sections were reconstructed using an original process based on random forest analysis. This approach revealed distinct migratory behaviours after fish entered in the river, with some individuals progressing slowly in the watershed whereas other rapidly reached the upper localities. As adults, S. lagocephalus showed a restricted exploratory behaviour and a strong site fidelity to a particular part of the watershed. The detection of adult movement was typically only between adjacent locations and is possibly explained by shifts in local intraspecific hierarchies and/or displacement during extreme discharge caused by cyclones.     

Measuring wood density by means of X-ray computer tomography

? Wood density is a characteristic of major interest. Usually, it is used as an indicator of wood quality; however, in the context of global change, it is increasingly used for biomass and carbon storage estimations. X-ray computer tomography is a method which enables quick estimates of wood density after applying a calibration procedure.

? A review of the literature is presented in this article. Most of the previous studies have been performed in the 80’s or at the beginning of the 90’s.

? In this study, the relationship between wood density and Hounsfield numbers was investigated using a recent medical scanner. A linear relationship was fitted using a calibration data set which consisted in tropical wood samples representing a large range of densities ranging between 133 and 1319 kg m^?3, and then validated using an independent data set (mainly temperate tree species). The fitted relationships were very strong (R ² > 0.999), whichever the tested scanner settings, with slight but significant effects of the current voltage and reconstruction filters. The RMSE values computed from the validation data set ranged between 5.4 and 7.7 kg m^?3 for densities ranging between 364 and 821 kg m^?3.

? In conclusion, this method of calibration enables the use of a medical scanner to obtain maps of wood density, in a fast and non destructive way, and with a very good accuracy. Very interesting perspectives are opened regarding biomass distribution within trees.

     

Crown plasticity reduces inter-tree competition in a mixed broadleaved forest

The objective of the study was to analyse to which extent horizontal crown plasticity reduces inter-tree competition at stand scale, and how it relates to species growth strategy. Two components of crown plasticity defined at the individual tree level (crown shape distortion, CSD and crown displacement relative to stem, CRD) were analysed and their relative importance in the reduction of competition was quantified. Inter-tree competition at stand scale was estimated using spatial pattern analysis and crown overlap estimation. Measurements were performed in a mixed broadleaved stand of Western Europe. Crown plasticity was shown to regularise the spatial distribution of crowns in comparison with the corresponding stems and to reduce inter-tree competition by optimising space occupation. A significant reduction in crown overlap was observed, mainly due to CRD and secondarily to CSD. At the species level, CSD and CRD were positively correlated. In addition, both were negatively correlated with species shade-tolerance scores. In particular, three European temperate tree species showed contrasting responses, which were related to their known specific ecological strategies. Fagus sylvatica, known to be a highly shade-tolerant species, showed large crowns, low CSD and CRD, indicating a low plasticity and suggesting a strong competitive ability. At the opposite, Quercus sp., known to be clearly less shade-tolerant, exhibited a reduced growth, associated with high CSD and CRD, indicating high crown plasticity and probably a lower competitive ability. For this species, plasticity could be described as passive. Last, Carpinus betulus, known to have a relatively good shade-tolerance, showed a contrasting behaviour with high CSD and CRD and a strong presence in the stand, suggesting high crown plasticity and a good competitive ability. In that case, plasticity was described as rather adaptive.