| dc.description.abstract | The nature of genetic divergence between the Artemia population native to San Francisco
Bay, (SFB) USA and those from the introductions of SFB material in the Kenyan coast
(Fundisha and Kensalt) 2 decades ago were investigated using the mitochondrial DNA
(mtDNA) and heat shock protein 70 (Hsp70) gene molecular markers. Control samples were
obtained from Great Salt Lake (GSL), Utah, USA and Vinh Chau (VC), Vietnam, while
Artemia cysts from Tanga, Tanzania were for additional study. The DNA was extracted from
80 single Artemia cysts (10 cysts per sample) using the Chelex protocol for mtDNA analysis
while the Promega method was used in the Hsp70 gene analysis. The 1,500 bp fragment of
the 12S - 16S region of the mtDNA and a 1,935 bp fragment of the Hsp70 gene were
amplified through Polymerase Chain Reaction (PCR) using appropriate primers followed by
Restriction Fragment Length Polymorphism (RFLP) digestion based on 6 restriction
endonucleases (AluI, HaeIII, HinfI, RsaI, XbaI and HpaII) for mtDNA and 4 restriction
endonucleases (AluI, Sau3A, HinfI and RsaI) for the Hsp70 gene. The mtDNA analysis
indicated higher haplotype diversity (0.76 ± 0.07) in Artemia samples from Fundisha
saltworks while the rest of the samples were monomorphic. The presence of 3 haplotype
genotypes in Fundisha (AAAAAA, AAAABA and AAABBA) signified a molecular evidence of
a systematic genetic differentiation. However, the haplotype frequencies within Fundisha
were statistically insignificant (P > 0.05). The existence of haplotypes AAAAAA and AAAABA
in Fundisha, GSL and SFB cyst samples was a molecular evidence of SFB and GSL Artemia
strains co-existing in Fundisha saltwork while the Kensalt and Tanga Artemia samples were
purely SFB strains. The non-polymorphic DNA fingerprint observed in Kensalt Artemia cysts
was probably caused by the non-sequential Artemia culture system, lack of ecological
isolation and limited genetic drift. Also, the limited mtDNA fragment analysed might have
excluded valuable genetic information from the study. The Hsp70 gene RFLP fingerprint
showed lack of unique gene signatures in the Kenyan Artemia samples suggesting that other
factors besides Hsp70 could be involved in their superior thermotolerance compared to their
SFB ancestors. In conclusion, if indeed there was significant genetic differentiation between
the Kenyan Artemia population and their SFB ancestors, then the tools used in the study
were not sufficiently adequate to detect this microevolutionary divergence. Further genetical
studies based on the larger mtDNA fragment using robust genetic markers are
recommended. Also, evolutionary and ecological studies of the heat shock protein family and
the stress response are highly encouraged. | en_US |
