Does my asinina look big in these genes?

15 July 2008

in 2008

The world’s fastest growing abalone—the tropical donkey’s ear abalone, Haliotis asinina—can be bred to grow rapidly and reliably for aquaculture, Queensland biologists have found. And that makes it potentially a high value alternative crop for struggling prawn farmers.

The researchers looked at whether they could speed up breeding of abalone for aquaculture using modern technology to identify and select genes that are activated in fast-growing animals. By linking the abundance of specific genes with fast growth rates, they have now shown their proposal is practical.

“If we can select breeding individuals who grow rapidly, the chances are that they have the right underlying genetic instruction manual, which can be passed on, ensuring their progeny grow fast as well,” says Tim Lucas from the Queensland Department of Primary Industries and Fisheries, who worked on the project with Prof Bernie Degnan of the University of Queensland.

The work has already demonstrated that growth rate is highly heritable—that fast-growing animals from the wild are likely to lead to fast-growing progeny in aquaculture. And the researchers have also developed methods for a simple blood test to measure the abundance of rapid-growth genes in wild abalone. This opens the possibility of pre-selecting fast-growing broodstock, reducing the level of undesirable genes from the start.

“Using these molecular techniques to select individuals for breeding rather than traditional physical traits, we can get one step closer to the fundamental genetic differences that control growth rate,” Tim says.

“It is difficult to go out onto the reef, tag and release abalone, and physically measure growth as it’s occurring. Using these molecular tools, however, we can take a blood sample and determine the activity of the growth genes. That immediately provides us with a snapshot of how fast individuals are growing at a particular point in time.”

The availability of these molecular tools increases the feasibility of farming donkey’s ear abalone in Australia, leading to rapid improvements in profitability.

“Not only are donkey’s ear abalone potentially of high value, but they are also plant-eaters,” Tim says. “This is important because it means they could provide a sustainable alternative option for tropical prawn farmers who are currently struggling to compete with cheaper imports and the soaring price of fishmeal.”

Because all abalone species are closely related and share most of their genes, says Degnan, it is likely the findings of the research team could also be applied to the more lucrative temperate abalone aquaculture industries in Australia and around the world.

Tim Lucas is one of 16 early-career scientists chosen for Fresh Science, a national program sponsored by the Federal and Victorian governments. He is presenting his research to the public for the first time.

Background

Abstract

The tropical abalone Haliotis asinina is a wild-caught and cultured species that is found throughout the Indo-Pacific. It is also an emerging model species for the study of growth, reproduction and development of haliotids and other vetigastropods. 

H. asinina has the fastest recorded natural growth rate of any abalone and reaches sexual maturity within one year.  As such, it is a suitable abalone species for studying genetic and molecular aspects of commercially important traits such as growth.

My thesis reports the analysis of growth and other traits in a single cohort of H. asinina that consisted of 84 families that were generated via a full-factorial mating design consisting of 14 sires and 6 dams.  Progeny were measured and then tested for parentage and RNA expression to explain the differences in size.  During this study a shell disease was discovered and investigated.

 Estimating the amount of variation in size that is attributable to heritable genetic differences can assist the development of a selective breeding program. I estimated heritability for growth-related traits at 12 months of age in these 84 H. asinina families. 

Of 500 progeny sampled, 465 were successfully assigned to their parents based on shared alleles at 5 polymorphic microsatellite loci.  Using an animal model, heritability estimates were 0.48 ± 0.15 for shell length, 0.38 ± 0.13 for shell width 0.36 ± 0.13 for weight. 

Genetic correlations were > 0.98 between shell parameters and weight, indicating that breeding for weight gains could be successfully achieved by selecting for shell length.  A novel method for analysis of shell colour revealed that the proportion of blue in the shell was a very good indicator of shell length in this study.

Large and small abalone from the aforementioned experiment were compared for differences in RNA expression levels, using microarray gene expression profiling.  Comparing RNA from 3 large and 3 small pools of abalone each containing 4 individuals, the microarray experiment identified 14 genes were found to be significantly differentially regulated between fast and slow growers (p<0.05). 

From this list and another list generated by the disease study, 7 genes were selected for further interrogation using qPCR.  This experiment aimed to compare gene expression for these 7 genes in fast and slow growing individuals.  Expression levels in different individuals revealed high levels of variation in expression levels between individuals, and that several of these genes have potential for use as markers for fast growth in aquaculture.  These include the genes ferritin, metallothionein and ribosomal protein L22.

Images

Click on image for high resolution image for download

The genetic difference between two abalone grown in the same tank. Tim Lucas compared the genes that they use to grow at different rates with the aim of developing a test that can sort out the fast from the slow growers in the wild.

Photo: Tim Lucas

Young abalone growing.

Photo: Tim Lucas

Tim Lucas displays abalone growing in the lab.

Photo: Tim Lucas

 

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