Epipodial Tentacle Gene Expression and Predetermined Resilience to Summer Mortality in the Commercially Important Greenlip Abalone, Haliotis laevigata

Brett P Shiel,Ira R Cooke,Nathan E Hall,Nicholas A Robinson,Jan M Strugnell

doi:10.1007/s10126-017-9742-z

Abstract

“Summer mortality” is a phenomenon that occurs during warm water temperature spikes that results in the mass mortality of many ecologically and economically important mollusks such as abalone. This study aimed to determine whether the baseline gene expression of abalone before a laboratory-induced summer mortality event was associated with resilience to summer mortality. Tentacle transcriptomes of 35 greenlip abalone (Haliotis laevigata) were sequenced prior to the animals being exposed to an increase in water temperature—simulating conditions which have previously resulted in summer mortality. Abalone derived from three source locations with different environmental conditions were categorized as susceptible or resistant to summer mortality depending on whether they died or survived after the water temperature was increased. We detected two genes showing significantly higher expression in resilient abalone relative to susceptible abalone prior to the laboratory-induced summer mortality event. One of these genes was annotated through the NCBI non-redundant protein database using BLASTX to an anemone (Exaiptasia pallida) Transposon Ty3-G Gag Pol polyprotein. Distinct gene expression signatures were also found between resilient and susceptible abalone depending on the population origin, which may suggest divergence in local adaptation mechanisms for resilience. Many of these genes have been suggested to be involved in antioxidant and immune-related functions. The identification of these genes and their functional roles have enhanced our understanding of processes that may contribute to summer mortality in abalone. Our study supports the hypothesis that prestress gene expression signatures are indicative of the likelihood of summer mortality.

Highlights

Over the past few decades, mass mortality of economically important mollusks, such as abalone (Vandepeer 2006), oysters (Cotter et al 2010), mussels (Mallet et al 1990), and scallops (Xiao et al 2005), has been reported during the summer months at a range of locations around the world
26 genes were matched to known proteins with a Swissprot ID, an additional 5 genes were matched to different known or predicted sequences based on the C. gigas genome using BLASTX, and another gene was matched to a similar sequence from the NCBI non-redundant protein database using BLASTX (Fig. 3)
Two genes were found to be differentially expressed between summer mortality resilient and susceptible abalone 6 months before being subjected to a heat stress event

Summary

Introduction

Over the past few decades, mass mortality of economically important mollusks, such as abalone (Vandepeer 2006), oysters (Cotter et al 2010), mussels (Mallet et al 1990), and scallops (Xiao et al 2005), has been reported during the summer months at a range of locations around the world. These events are known as Bsummer mortalities^ and they occur in both wild and aquaculture environments. Higher water temperatures are known to result in chemical changes in water quality (elevated ammonia, changes to pH, lower dissolved oxygen, and nutritional factors) which compromise the immune system and make species more vulnerable to mass mortality from diseases such as those caused by Vibrio sp. (Vandepeer 2006)

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