Among-sibling differences in the phenotypes of juvenile fish depend on their location within the egg mass and maternal dominance rank.

We investigated whether among-sibling differences in the phenotypes of juvenile fish were systematically related to the position in the egg mass where each individual developed during oogenesis. We sampled eggs from the front, middle and rear thirds of the egg mass in female brown trout of known dominance rank. In the resulting juveniles, we then measured traits that are related to individual fitness: body size, social status and standard metabolic rate (SMR). When controlling for differences among females in mean egg size, siblings from dominant mothers were initially larger (and had a lower mass-corrected SMR) if they developed from eggs at the rear of the egg mass. However, heterogeneity in the size of siblings from different positions in the egg mass diminished in lower-ranking females. Location of the egg within the egg mass also affected the social dominance of the resulting juvenile fish, although the direction of this effect varied with developmental age. This study provides the first evidence of a systematic basis for among-sibling differences in the phenotypes of offspring in a highly fecund organism.

Hematodinium infection seasonality in the Firth of Clyde (Scotland) Nephrops norvegicus population: a re-evaluation.

Hematodinium infections in Norway lobster Nephrops norvegicus from the Clyde Sea area (CSA) population, Scotland, UK, have previously been undetected in summer. This study aimed to establish if the CSA is actually devoid of infected N. norvegicus in this season. Two PCR assays, an ELISA and 2 tests that detect only patent infection (pleopod and body colour methods) were applied in a 21 mo study. Patent infection was seasonal, appearing predominantly in spring, while subpatent infection diagnosed by ELISA and PCR was highly prevalent in all seasons. Generalised linear modelling supported this assertion, as sampling in September and February significantly increased the probability of finding infected N. norvegicus (p < 0.01); infections were predominantly subpatent and patent respectively, at these times. Therefore, Hematodinium seasonality in N. norvegicus populations is likely to have been an artefact of insensitive diagnostic tests. Light Hematodinium infections were found using PCR assays when patent infections were at their most prevalent and intense, suggesting that infection develops at different rates in different N. norvegicus individuals and that only a portion of the total number of infected N. norvegicus die within a single year. These new data were added to a long-term data series for the CSA (1990 to 2008), which showed that after an initial 5 yr epidemic period, prevalence stabilised at 20 to 25%. Comparisons with 'susceptible-infected-recovered/removed' (SIR) models suggest that this high prevalence is maintained through high birth rates of susceptible host N. norvegicus.