Morpho-Genetic Divergence and Adaptation of Anadromous Hilsa shad (Tenualosa ilisha) Along Their Heterogenic Migratory Habitats

Md Asaduzzaman,Md Moshiur Rahman,Barun Kanti Roy,Michael J Phillips,Li Lian Wong,Md Nahiduzzaman,Mariom Mariom,Md Abdul Wahab,Md Jalilur Rahman

doi:10.3389/fmars.2020.00554

Abstract

Migration of an anadromous fish to heterogeneous environment continuously enforces a selective pressure that incorporates a wide range of life-history strategies by which individuals adapt to the prevailing conditions. Therefore, we used the landmark-based morphometric truss network method and nextRAD genotyping-based putatively adaptive SNP loci dataset to know how the anadromous Hilsa shad (Tenualosa ilisha) morpho-genetically adapt to the heterogeneous habitats across their migratory routes by investigating 300 individuals, collected from nine strategic sampling sites covering sea, estuary, and upstream freshwater rivers. Different multivariate and clustering analyses revealed that the riverine populations were morphometrically wider (broad type) than the estuarine and marine populations (slender type). In the case of riverine population, the north-western turbid population (the Padma and Jamuna rivers) had wider body depth than the north-eastern clear water population (the Meghna river). The linear model and spatial multivariate analyses further revealed that the outcomes of morphometric dataset were in complete concordance with the results of putatively adaptive SNP loci dataset for different Hilsa shad populations. The GO enrichment analysis of the 36 genes, which are encoded by the putative adaptive SNP loci, supported the presence of multiple genes involved in the growth, metabolism, homeostasis and osmoregulation related functions. Several non-mutually exclusive hypotheses were attributed to explain the observation of continuum differentiation at both phenotypes and genotypes: i) the genetic variation largely determines the morphometric discrimination, ii) the interactive evolutionary processes and salinity gradients predominantly contribute to the morphogenetic divergence between the marine-estuarine and the freshwater riverine populations, iii) the salinity levels influence the genotypes leading to the phenotypic plasticity, and iv) the local environmental heterogeneity may contribute to the morphogenetic divergence between the riverine populations. Finally, we concluded that the genetic adaptation, phenotypic plasticity and interactive ecological and evolutionary consequences jointly determine the morphogenetic divergence of Hilsa shad. The interaction of all of these forces and their relative strength in heterogeneous environments, however, made it rather challenging to determine the most probable selective pressure, which has shaped the Hilsa shad morphogenetic divergence across their diverse migratory habitats.

Highlights

Over the last few decades, many innovative studies have revealed that environmental changes have influenced the morpho-genetic alterations in both plant and animal kingdom (Bradshaw and Holzapfel, 2006; Borges, 2008; Hoffmann et al, 2015)
Different multivariate and cluster analyses initially indicated that morphogenetic divergence of Hilsa shad population from different habitats overlapped among each other, and was mostly discriminated by the salinity gradients of their diverse migratory habitats (Supplementary Figures S1, S2)
This study so far represents the first ever efforts made to combine both nextRAD genotypes and morphometric analyses of anadromous Hilsa shad populations collected from a broader sampling locations covering all types of their natural habitats

Summary

Introduction

Over the last few decades, many innovative studies have revealed that environmental changes have influenced the morpho-genetic alterations in both plant and animal kingdom (Bradshaw and Holzapfel, 2006; Borges, 2008; Hoffmann et al, 2015). The phenotypic discriminations are largely determined by the genetic differences and are affected by the interaction of ecological and evolutionary systems in response to the spatio-temporal heterogenic environmental conditions (Tamario et al, 2019). Given such complex adaptation strategies of anadromous fish, there is a need for a better understanding about the pattern of morpho-genetic variation in response to their migratory behavior in heterogeneous environments. The major overarching question for the scientists over many years is how the anadromous fish respond to the environmental heterogeneity and cope with the changing environmental conditions when they migrate from the marine waters to the freshwater rivers for breeding and/or feeding purposes

Methods

Results

Conclusion