The spatial scale of competition from recruits on an older cohort in Atlantic salmon

Competitive effects of younger cohorts on older ones are frequently assumed to be negligible in species where older, larger individuals dominate in pairwise behavioural interactions. Here, we provide field estimates of such competition by recruits on an older age class in Atlantic salmon (Salmo salar), a species where observational studies have documented strong body size advantages which should favour older individuals in direct interactions. By creating realistic levels of spatial variation in the density of underyearling (YOY) recruits over a 1-km stretch of a stream, and obtaining accurate measurements of individual growth rates of overyearlings (parr) from capture–mark–recapture data on a fine spatial scale, we demonstrate that high YOY density can substantially decrease parr growth. Models integrating multiple spatial scales indicated that parr were influenced by YOY density within 16 m. The preferred model suggested parr daily mass increase to be reduced by 39% when increasing YOY density from 0.0 to 1.0 m−2, which is well within the range of naturally occurring densities. Reduced juvenile growth rates will in general be expected to reduce juvenile survival (via increased length of exposure to freshwater mortality) and increase generation times (via increased age at seaward migrations). Thus, increased recruitment can significantly affect the performance of older cohorts, with important implications for population dynamics. Our results highlight that, even for the wide range of organisms that rely on defendable resources, the direction of competition among age classes cannot be assumed a priori or be inferred from behavioural observations alone

A new parasite that infects eggs of the mud crab, Scylla serrata, in Australia

The mud crab, Scylla serrata, is currently being evaluated for its feasibility for mass aquaculture in Australia. As part of the evaluation process, pathogens that can affect this species need to be identified. This research note describes a possible new parasite that infects the eggs of S. serrata. The parasite was discovered in two separate cases (three months apart) in a broodstock research program and appears to cause 100% egg mortality. The parasite consists of a cluster of cells with rhizoids that appear to function as an anchorage and a feeding organ. The individual cells range from 3 to 6 μm with a single nucleus. The parasite could not be classified to a phylum by morphology alone. However, BLAST analysis of the DNA sequence from a PCR amplicon generated using universal 18S ribosomal RNA gene primers indicated similarity to pathogenic thraustochytrids, Dermocystidium sp. and Rhinosporidium seeberi. All except R. seeberi are protistan parasites of fish and crustaceans. A neighbour-joining phylogenetic tree confirmed the homology with the thraustochytrids; however, further molecular techniques need to be exploited for absolute classification of this new parasite

Family by environment interactions in shell size of 43-day old silver-lip pearl oyster (Pinctada maxima), five families reared under different nursery conditions

To understand the influence the environment and associated genotype by environment interactions will exert on future silver-lip pearl oyster (Pinctada maxima) selective breeding programs, this study assessed the relative performance in four shell growth traits of spat from five full-sib families, when spat were communally reared at different salinities (29, 34 and 40 ppt), food availability (high, medium and low), food quality (high, medium and low), and in a hatchery vs. ocean environment for 43 days. Rearing environment was found to influence growth expression, with significant differences evident when oysters were grown at different salinities in the ocean instead of hatchery, or when fed algae of differing\ud nutritional quality. As indicated by MANOVA, family comparative growth performances were also altered\ud when the environment changed, with significant environment by family interactions apparent in the food quality, food availability and hatchery vs. ocean rearing treatments. Changes in salinity, however, did not affect relevant family performances. These results indicate that growth and relative family performance in P. maxima may change dependent on local environmental conditions and that genotype by environment effects may need to be considered in breeding programs for this species

Donor-oyster derived heritability estimates and the effect of genotype × environment interaction on the production of pearl quality traits in the silver-lip pearl oyster, Pinctada maxima

The silver-lip pearl oyster, Pinctada maxima, produces the largest and most valuable pearls in the world. Despite the importance of this species very little is known about genetic parameters of commercially important pearl traits. As an initial step towards developing a selective breeding program, site selection effects, donor oyster derived genetic parameters and genotype by environment (G × E)interactions were estimated for pearl quality traits of P. maxima, originating from three populations (Aru, Bali, West Papua), reared at two commercial grow-out locations in Indonesia (Bali and Lombok). Microsatellite-based DNA parentage analyses were used to assign oysters to families and population of origin. Six pearl traits that are together the major determinants of pearl value (pearl weight (g), size (mm), shape, colour, complexion and lustre) were recorded at harvest. Pearls produced at the Lombok site were bigger and more valuable compared to pearls produced at the Bali site (P < 0.05). G × E interactions were present for size (rg = − 0.22), colour (rg = 0.28), weight (rg = 0.38), shape (rg = 0.56) and lustre (rg = 0.59) due to re-ranking of relative family performances at the two sites, although there were large standard errors associated with these estimates. Complexion was the only trait that showed little evidence for re-ranking (rg = 0.85). Donor related-heritability estimates for size (h2 = 0.13), lustre (h2 = 0.14), weight (h2 = 0.15), colour (h2 = 0.15) and shape (h2 = 0.06) were low, while for complexion estimates were moderate (h2 = 0.25). A positive and high genetic correlation was found between pearl size and weight (rg = 0.99), shape and complexion (rg = 0.65) and shape and colour (rg = 0.62); however, interestingly pearl weight was negatively genetically correlated with shape (rg = − 0.46), complexion (rg = − 0.11), colour (rg = − 0.03) and lustre (rg = − 0.15). Given the complex relationship amongst pearl quality traits and the likelihood for G × E interaction effects care should be executed when designing breeding objectives for the genetic improvement of these traits in P. maxima

Population and family growth response to different rearing location, heritability estimates and genotype×environment interaction in the silver-lip pearl oyster (Pinctada maxima)

Genetic parameters and genotype by environment interactions were estimated from the growth responses of silver-lip pearl oyster (Pinctada maxima) families originating from three populations (Aru, Bali, West Papua) reared at two Indonesian commercial sites (Bali and Lombok). Microsatellite-based DNA parentage analyses were used to assign oysters to their family and population of origin and four shell growth traits (anterior–posterior measurement (APM), dorsal–ventral measurement (DVM), shell width (SW) and wet weight (WW)) recorded at 14 and 18 months of age. Significant size differences were observed in all shell growth traits between oyster populations, and between oysters cultured at the different locations. Oysters from Bali and West Papua grew faster than those sourced from Aru at both culture sites, whilst the Lombok site produced the fastest growing oysters overall. Significant size differences were also present in shell traits among families, indicating a large amount of genetic variability present for potential breeding programs. Although there were significant familial size differences for shell traits, genetic correlation analyses showed little evidence for re-ranking of family performance among the two culture sites (rg = 0.89–0.99), suggesting low genotype by environment deviations among sites. Heritability of the shell traits DVM, APM and WW was moderate (0.15 ± 0.003 (DVM), 0.23 ± 0.030 (APM)) and as a consequence should respond to targeted selection