Functional Antifreeze Glycoprotein Genes in Temperate-Water New Zealand Nototheniid Fish Infer an Antarctic Evolutionary Origin

• Published in: Molecular Biology and Evolution
• Main Authors: Cheng, Chi-Hing C., Chen, Liangbiao, Near, Thomas J., Jin, Yumi
• Format: Text
• Language: English
• Published: Oxford University Press 2003
• Subjects: Original Articles; Antarctic; The Antarctic; New Zealand; Antarctic Ocean; Antarc*; Antarctica
• Online Access: http://mbe.oxfordjournals.org/cgi/content/short/msg208v1; https://doi.org/10.1093/molbev/msg208

The fish fauna of the Antarctic Ocean is dominated by five endemic families of the Perciform suborder Notothenioidei, thought to have arisen in situ within the Antarctic through adaptive radiation of an ancestral stock that evolved antifreeze glycoproteins (AFGPs) enabling survival as the ocean chilled to subzero temperatures. The endemism results from geographic confinement imposed by a massive oceanographic barrier, the Antarctic Circumpolar Current, which also thermally isolated Antarctica over geologic time leading to its current frigid condition. Despite this voluminous barrier to fish dispersal, a number of species from the Antarctic family Nototheniidae now inhabit the non-freezing cool temperate coasts of the southern continents. The origin of these temperate-water nototheniids is not completely understood. Since the AFGP gene apparently evolved only once, prior to the Antarctic notothenioid radiation, the presence of AFGP genes in extant temperate-water nototheniids can be used to infer an Antarctic evolutionary origin. Genomic Southern analysis, PCR amplification of AFGP genes and sequencing showed that Notothenia angustata and Notothenia microlepidota endemic to southern New Zealand have two to three AFGP genes, structurally the same as those of the Antarctic nototheniids. At least one of these genes is still functional as AFGP cDNAs were obtained, and low levels of mature AFGPs were detected in the blood. A phylogenetic tree based on complete ND2 coding sequences showed monophyly of these two NZ nototheniids and their inclusion in the monophyletic Nototheniidae that comprises AFGP-bearing taxa. These analyses support an Antarctic ancestry for the NZ nototheniids. A divergence time of ∼11 myr was estimated for the two NZ nototheniids, approximating the upper Miocene northern advance of the Antarctic Convergence over New Zealand, which might have served as the vicariant event that lead to the northward dispersal of their most recent common ancestor. Similar secondary northward dispersal likely applies ...