Karyotypes and Sex Chromosomes in Two Australian Native Freshwater Fishes, Golden Perch (Macquaria ambigua) and Murray Cod (Maccullochella peelii) (Percichthyidae)

Foyez Shams,Fiona Dyer,Ross Thompson,Jason D Thiem,Tariq Ezaz,Zuzana Majtánová,Richard P Duncan

doi:10.3390/ijms20174244

Abstract

Karyotypic data from Australian native freshwater fishes are scarce, having been described from relatively few species. Golden perch (Macquaria ambigua) and Murray cod (Maccullochella peelii) are two large-bodied freshwater fish species native to Australia with significant indigenous, cultural, recreational and commercial value. The arid landscape over much of these fishes’ range, coupled with the boom and bust hydrology of their habitat, means that these species have potential to provide useful evolutionary insights, such as karyotypes and sex chromosome evolution in vertebrates. Here we applied standard and molecular cytogenetic techniques to characterise karyotypes for golden perch and Murray cod. Both species have a diploid chromosome number 2n = 48 and a male heterogametic sex chromosome system (XX/XY). While the karyotype of golden perch is composed exclusively of acrocentric chromosomes, the karyotype of Murray cod consists of two submetacentric and 46 subtelocentric/acrocentric chromosomes. We have identified variable accumulation of repetitive sequences (AAT)10 and (CGG)10 along with diverse methylation patterns, especially on the sex chromosomes in both species. Our study provides a baseline for future cytogenetic analyses of other Australian freshwater fishes, especially species from the family Percichthyidae, to better understand their genome and sex chromosome evolution.

Highlights

Morphological characteristics of chromosomes, like the size and number may vary within taxonomic groups such as families, genera and even species [1]
The golden perch karyotype consisted of 24 pairs of acrocentric chromosomes (Figure 3a,b), while the Murray cod karyotype consisted of one pair of submetacentric and 23 pairs of subtelocentric/acrocentric chromosomes (Figure 3e,f)
In Murray cod, one chromosome from the largest pair was shorter in the male karyotype, while in females, the largest chromosome pair was equal in size, suggesting a male heterogametic sex determining system (XX/XY) in this species (Figure 3e,f)

Summary

Introduction

Morphological characteristics of chromosomes, like the size and number (including ploidy) may vary within taxonomic groups such as families, genera and even species [1]. Functional differences (e.g., accumulation of repetitive sequences, location of a certain gene or DNA methylation) often occur among species as well as among populations or among individuals of the same species [2,3,4]. Cytogenetic studies provide a useful tool for establishing phylogenetic and evolutionary relationships among species. Karyotype analysis can facilitate the discovery of heteromorphic or heterochromatic sex chromosomes. Identification of sex chromosomes is important in dioecious species as it provides information on the evolution of sex determination and insights into the effect of environment in driving sex ratios.

Methods

Results

Discussion

Conclusion