Otolith growth and age estimation in the European hake

The internal sulcal rings in Merluccius merluccius otoliths cannot be considered as annuli. In the absence of a strong seasonal Zeitgeber, hake otoliths in the Mediterranean did not lay down an interpretable ring pattern that would be useful for age determination. A total of 484 sagittal otoliths from specimens ranging between 6 and 94 cm L T was studied in monthly samples from the Gulf of Lions in 1989–1990. Transverse, burnt otolith sections was analysed with an image analysis system using enhanced and filtered images and using a fast Fourier transform (FFT) function to avoid subjectivity in ring interpretation. The otolith radius-fish length relationship showed allometric growth and sexual dimorphism. The ring pattern was consistent for the sulcal rings in both sexes. Changes in the marginal increment showed the formation of multiple sulcal rings, of both environmental and physiological origin. The ring pattern depended on the sex and sexual activity.     

Could controlling mammalian carnivores lead to mesopredator release of carnivorous reptiles?

Emerging evidence increasingly illustrates the importance of a holistic, rather than taxon-specific, approach to the study of ecological communities. Considerable resources are expended to manage both introduced and native mammalian carnivores to improve conservation outcomes; however, management can result in unforeseen and sometimes catastrophic outcomes. Varanid lizards are likely to be apex- or mesopredators, but being reptiles are rarely considered by managers and researchers when investigating the impacts of mammalian carnivore management. Instances of mesopredator release have been described for Varanus gouldii as a result of fox and cat management in Australia, with cascading effects on faunal community structure. A meta-analysis showing extensive dietary niche overlap between varanids, foxes and cats plus a review of experimental and circumstantial evidence suggests mesopredator release of V. gouldii and about five other medium to large species of varanid lizard is likely in other regions. This highlights the need for managers to adopt a whole-of-community approach when attempting to manage predators for sustained fauna conservation, and that additional research is required to elucidate whether mesopredator release of varanids is a widespread consequence of carnivore management, altering the intended faunal responses.     

On confidence intervals for genotype relative risks and attributable risks from case parent trio designs for candidate-gene studies

Scherag et al. [Hum Hered 2002;54:210-217] recently proposed point estimates and asymptotic as well as exact confidence intervals for genotype relative risks (GRRs) and the attributable risk (AR) in case parent trio designs using single nucleotide polymorphism (SNP) data. The aim of this study was the investigation of coverage probabilities and bias in estimates if the marker locus is not identical to the disease locus. Using a variety of parameter constellations, including marker allele frequencies identical to and different from the SNP at the disease locus, we performed an analytical study to quantify the bias and a Monte-Carlo simulation study for quantifying both bias and coverage probabilities. No bias was observed if marker and trait locus coincided. Two parameters had a strong impact on coverage probabilities of confidence intervals and bias in point estimates if they did not coincide: the linkage disequilibrium (LD) parameter delta and the allele frequency at the marker SNP. If marker allele frequencies were different from the allele frequencies at the functional SNP, substantial biases occurred. Further, if delta between the marker and the disease locus was lower than the maximum possible delta, estimates were also biased. In general, biases were towards the null hypothesis for both GRRs and AR. If one GRR was not increased, as e.g. in a recessive genetic model, biases away from the null could be observed. If both GRRs were in identical directions and if both were substantially larger than 1, the bias always was towards the null. When applying point estimates and confidence intervals for GRRs and AR in candidate gene studies, great care is needed. Effect estimates are substantially biased towards the null if either the allele frequencies at the marker SNP and the true disease locus are different or if the LD between the marker SNP and the disease locus is not at its maximum. A bias away from the null occurs only in uncommon study situations; it is small and can therefore be ignored for applications.     

Identification of novel Babesia and Theileria genotypes in the endangered marsupials, the woylie (Bettongia penicillata ogilbyi) and boodie (Bettongia lesueur)

Piroplasms, which include the genera Theileria and Babesia, are blood-borne parasites transmitted mainly by tick vectors. Relatively little is known about their prevalence and clinical impact in Australian marsupials. In the present study the occurrence and molecular phylogeny of these parasites were studied in both wild and captive marsupials from Western Australia (WA) and Queensland (QLD). Blood samples were screened by microscopy and molecular methods, using PCR and DNA sequencing of the 18S ribosomal RNA gene (18S rDNA). Overall, 7.1% of the blood samples (8/113) were positive for piroplasm 18S rDNA. Theileria and Babesia rDNA was detected in 0.9% (1/113) and 6.2% (7/113) of the animals, respectively. The single Theileria positive was identified in one of three boodies (Bettongia lesueur) screened from a wildlife rehabilitation centre in WA, while all seven Babesia positives were detected in WA in wild captured woylies (Bettongia penicillata ogilbyi). Small intraerythrocytic inclusions were observed in blood films made from six of these individuals. This is the first report of a Babesia sp. in woylies, and Theileria sp. in boodies. Phylogenetic analysis indicated that the woylie-derived Babesia was genetically distinct and most closely related to Babesia occultans, the causative agent of a benign form of cattle babesiosis (genetic similarity 98.4%). The Theileria identified was most closely related to the marsupial-derived species Theileria penicillata from the woylie, Theileria brachyuri from the quokka (Setonix brachyurus), and Theileria sp. from the long-nosed potoroo (Potorous tridactylus).     

Spatiotemporal variation in the population structure of the European hake in the NW Mediterranean

The bathymetric distribution of Merluccius merluccius was studied as a function of length, age and maturity of specimens caught by commercial trawl and longline in Different seasons. Males matured first at 28·8 cm (3 years old), and females at 38·0 cm (3·5 years old). Reproductive activity was noted practically throughout the year with its most pronounced spawning peak in the autumn. Most fish <37–40 cm were males and >46 cm were females. Specimens occurred between 50 and 750 m depth, although density was low at >400 m. Adults were found at all depth strata studied. Recruits and juveniles were limited to inshore waters <400 m, most were found between 100 and 200 m. Spring and summer were the preferred seasons for recruitment; although for both seasons there was some interannual variation. Adult distribution also varied, according to the season. Young adults were spread over the entire depth range, with the biggest ones concentrated at the edge of the shelf (150–350 m), especially in autumn and winter. The main spawning peak coincided with this concentration of adults suggesting that spawning occurred in autumn/winter at the edge of the shelf.     

Effects of sequential mating by males on reproductive output of the stinkbug predator, Podisus nigrispinus

Reproductive output of the stinkbug predator Podisus nigrispinus (Dallas) (Heteroptera: Pentatomidae) was investigated as a function of the number of matings that the male had made with a range of females. After being placed with a female, virgin males were most likely to mate within 12 hours, while non-virgin males were most likely to mate within 12–24 hours. Although males lost weight during their first mating, the weights of mated and unmated males were not significantly different throughout their lifetime. Longevity was significantly greater for unmated males (36.0 days) than for mated males (29.8 days). Survival curves for both mated and unmated males were Type II. The capacity of males to transfer sperm to virgin females was not affected by previous matings. From 65.7 to 76.4% of eggs were viable and 206.7 to 274.6 nymphs were produced per female. Regardless of the number of matings that the male had made, females that had mated only once exhausted their stored sperm progressively and produced an increasing proportion of infertile eggs, which peaked at the end of their lives. These results show that P. nigrispinus females need more than one mating to maintain fertility, but their performance is not affected by the number of previous matings that the male has made or by male weight. Thus, the strategy of pairing with males multiple times improved production efficiency by increasing output and reducing food waste in mass production systems. This is achieved by temporarily pairing females at intervals of about 20 days during their entire lifetime.