Signature selection forces and evolutionary divergence of immune-survival genes compared between two important shrimp species

Abstract

In recent years, shrimp aquaculture industry had grown significantly to become the major source of global shrimp production. Despite that, shrimp aquaculture production was impeded by various shrimp diseases over the past decades. Interestingly, different shrimp species demonstrated variable levels of immune strength and survival (immune-survival) ability towards different diseases, especially the much stronger immune-survival ability shown by the ancient shrimp species,Macrobrachium rosenbergiicompared to other shrimp species. In this study, two important shrimp species,M.rosenbergiiandPenaeus monodon(disease tolerant strain) (uninfected control andVpAHPND-infected) were compared to uncover the potential underlying genetic factors. The shrimp species were sampled, followed by RNA extraction and cDNA conversion. Five important immune-survival genes (C-type Lectin, HMGB, STAT, ALF3, and ATPase 8/6) were selected for PCR, sequencing, and subsequent genetics analysis. The overall genetic analyses conducted, including Analysis of Molecular Variance (AMOVA) and population differentiation, showed significant genetic differentiation (p<0.05) between different genes ofM.rosenbergiiandP.monodon. There was greater genetic divergence identified between HMGB subgroups ofP.monodon(uninfected control andVpAHPND-infected) compared to other genes. Besides that, based on neutrality tests conducted, purifying selection was determined to be the main evolutionary driving force ofM.rosenbergiiandP.monodonwith stronger purifying selection exhibited inM.rosenbergiigenes. Potential balancing selection was identified forVpAHPND-infected HMGB subgroup whereas directional selection was detected for HMGB (both species) and ATPase 8/6 (onlyP.monodon) genes. The divergence times betweenM.rosenbergiiandP.monodongenes were estimated through Bayesian molecular clock analysis, which were 438.6 mya (C-type Lectin), 1885.4 mya (HMGB), 432.6 mya (STAT), 448.1 mya (ALF3), and 426.4 mya (ATPase 8/6) respectively. In conclusion, important selection forces and evolutionary divergence information of immune-survival genes betweenM.rosenbergiiandP.monodonwere successfully identified.