Mitochondrial and nuclear gene analysis of the killifish, Fundulus heteroclitus; a reconstruction of phylogenetic history

• Main Author: Smith, Michael William
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-1990
• Subjects: Aquaculture; Aquatic sciences; Biological oceanography; Fish production; Oceanography
• ISBN: 9798759983606

Mitochondrial and nuclear genomes were examined in two geographically separated coastal and estuary intergradation zones of Fundulus heteroclitus subspecies. Mitochondrial DNA from Chesapeake bay fish representative of both Fundulus heteroclitus subspecies were cloned into the lambda phage vector EMBL3. Locations of the ribosomal RNA genes and restriction sites were determined. Assuming a mammalian sequence divergence rate, the sequence divergence between the two mitochondrial genomes (2.3%) corresponds to separation approximately one million years ago. The mitochondrial DNA genome was examined in twenty-nine coastal and estuary populations of Fundulus heteroclitus. F.h. macrolepidotus haplotypes were found in populations north of the Hudson River bay along the Atlantic coast. Relic F.h. macrolepidotus fish populations were also found isolated in the upper Chesapeake and Delaware bays, and their tributaries. The southern F.h. heteroclitus mtDNA haplotypes occurred from Sandy Hook, New Jersey south and within almost all of the Chesapeake and Delaware bays. Seven genetically inherited nuclear allozyme loci were examined in nineteen Chesapeake and Delaware bay populations. Five different patterns of allozyme allele introgression occurred within and between Atlantic coastal, and Chesapeake and Delaware bay intergradation zones. Different ancestral source populations of F.h. macrolepidotus could account for the near alternate fixation of alleles at Mpi-A and 6Pgdh-A. Dispersal of neutral genetic variants can only explain one of the remaining three introgression patterns for the loci Idh-B, Gpi-B, Mdh-A and Pgm-A. By elimination, the two remaining patterns can only be explained by selection on these allozyme loci and/or closely linked genes. The freely associated genetic makeup of individuals demonstrates that the two subspecies are randomly interbreeding. There were no significant excesses or deficiencies of observed heterozygosity. The mitochondrial and nuclear genomes were not significantly associated within individuals found in four contact populations. In contrast, there was agreement between the overall geographic distributions of mitochondrial and nuclear genetic variation. The Wisconsin glaciation had a major impact on the present day subspecies distributions. Fundulus heteroclitus has undergone numerous range expansions and contractions. Glacial maxima and minima combined with corresponding sea level minima and maxima may have resulted in episodic periods of selection. The glacially induced environmental oscillations could have provided the cold and freshwater selection on small F.h. macrolepidotus populations suggested by Cashion et al. (1981).