ABSTRACT
Nonadaptive hypotheses on the evolution of eukaryotic genome size predict an expansion when the process of purifying selection becomes weak. Accordingly, species with huge genomes, such as lungfish, are expected to show a genome-wide relaxation signature of selection compared with other organisms. However, few studies have empirically tested this prediction using genomic data in a comparative framework. Here, we show that 1) the newly assembled transcriptome of the Australian lungfish, Neoceratodus forsteri, is characterized by an excess of pervasive transcription, or transcriptional leakage, possibly due to suboptimal transcriptional control, and 2) a significant relaxation signature in coding genes in lungfish species compared with other vertebrates. Based on these observations, we propose that the largest known animal genomes evolved in a nearly neutral scenario where genome expansion is less efficiently constrained.
Subject(s)
Fishes , Genomics , Animals , Australia , Fishes/genetics , Genome Size , Selection, GeneticABSTRACT
Nine microsatellite DNA loci for the Australian broad-shelled freshwater turtle (Chelodina expansa) are presented. Markers were tailed with 20-mer oligonucleotides for use in four-colour fluorescent multiplex PCRs. The markers show high allelic richness (mean N(A)=10.9, range 2-38) and expected heretozygosity (mean H(E)=0.643; range 0.161-0.963) indicating that they will be valuable for population genetics studies in C. expansa. Cross-species amplification in three Australian freshwater turtle species further highlights the potential utility of these markers, particularly in the side-neck species C. longicollis and C. rugosa.