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The article, Low Genetic Variability in the Geographically Widespread Andean Condor by Hendrickson et al., presents the study conducted with the aim of characterizing “DNA sequence variation in the mitochondrial control region and 12S ribosomal subunit for a sample Andean Condors” (Hendrickson et al.).
The study observes that critical data on genetic variability that existed before most species become endangered has been lacking. The lacking data is essential in providing critical controls for the interpretation of potential implications of declining populations such as losing genetic diversity. As such, the Andean Condor (Vultur gryphus) presents an opportunity for studying a threatened species for three reasons (Hendrickson et al.).
Firstly, they have the desired demographic and physical attributes among living birds. Secondly, the species continues to maintain a considerable geographical range in western South America enabling the examination of “large-bodies species” in a wider region. Thirdly, there are two distinctive structures that are expressed in the condor range. These demonstrate the effects of population structure on genetic variability.
The study required the use of blood and tissue samples from the condors. However, since these cannot be easily obtained from wild condors, the researchers obtained the required samples from zoos, museum specimens, birds in recovery programs and feathers salvaged from wild condors. Blood and feather samples were also obtained from captured birds from capture locations that were known. In order to ensure equitable geographical representation in the condor range, the researchers acquired samples from north and south of the Northern Peruvian Low.
The obtained blood samples were stored at 0 degrees Celsius in tubes containing EDTA (Hendrickson et al.). Museum skin and feather calami samples were stored in sterilized tubes. Specimens from museum calami were acquired through cutting of the skin on the body’s side, where it is believed that the sample is less likely to be contaminated. DNA extractions were acquired through the use of Blood Kits and QIAamp Tissue (Hendrickson et al.).
The researchers ivided the control area into three domains on the basis of their varied evolution rates. Domains I and III were observed to have the highest variability; hence they provide adequate genetic markers for studying the population. Meanwhile, the 12S Ribosomal RNA gene is less variable and located downstream from the control region since it has functional limitations.
The study integrated nucleotide and haplotype diversity to indicate variability levels in condor populations. Tajima’s D and the mismatch distribution were incorporated with the aim of testing departures from neutrality in the condor population (Hendrickson et al.). Meanwhile, Fisher’s exact test was used to analyze the differentiation between allele frequency in the northern and southern Andean condor populations.
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The study led to the detection of five haplotypes on the basis of two variable sites in the control area (domains II and III) and two in 12S (Hendrickson et al.). One additional variable site was identified in the five sequences. The population of the Andean Condors presented a low genetic diversity. The northern and southern regions had few haplotypes; therefore, nucleotide and haplotype diversity had no significant diversity between the northern and southern samples.
This indicates that diversity is not a reflection of the regional differences in the degree of isolation or ecology; however, larger samples sizes are required to substantiate this finding. The study found that the diversity of mitochondrial genes in the Andean condor appeared to be relatively low compared to outbred birds. Evidently, the only species with “close observed and expected values are those which have experienced recent bottleneck” (Hendrickson et al.).
The results of the study indicate a low genetic variability in mitochondrial genes of Andean Condors. Particularly, no association was found between the quantity of mitochondrial haplotypes, heterogeneity, patterns of population scarcity or degree of isolation. As such, the results reinforce previous recorded evidence of low genetic variability among large-bodied species. As such, genetic variability is perceived to be low in larger predatory or scavenging birds because of the small effective poopulation given its high position in the food chain, home-range size and scarcity (Hendrickson et al., 2003). Since Andean Condors fall in the category of scavengers, they exemplify such attributes; furthermore, they raise a single offspring in every brood and attempt to nest at least once every two years. In addition, condors attain sexual maturity when they are eight years old. As such, this causes a slow recovery from population bottlenecks as a result of significantly reduced population numbers.
A smaller effective population has the potential to produce low variability “through conventional population-genetic processes such as non-selective loss of alleles by random genetic drift” (Hendrickson et al.). In addition, a sparsely distributed population can present a slow spread of new mutations. Meanwhile, decreased genetic variability in mega-fauna can result from various processes at the molecular level. Larger body mass, and lower metabolic rate have the potential to slow the accumulation of new genetic variants through a reduction of overall mutation rates (Hendrickson et al., 2003).
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While there are established methods of identifying historical bottlenecks that are identified as the main cause of low variability in various species, the study found that the condor data yielded conflicting results. The conflicting results are attributed to the limited sites available for the analyses. In spite of the observed low variability of the control region, a number of geographical structures were detected. Significant differences observed in the frequencies of haplotypes were “found between northern and southern populations indicating that geography or philopatry and breeding structure is affecting gene distributions” (Hendrickson et al., 2003).
Genetic Variability and Conservation
The low levels of genetic variability observed in widespread species that are not in immediate danger of extinction present critical conservation implications. In most cases, genetic studies are only conducted when populations have been significantly reduced “in size and abundance” (Hendrickson et al.). The results obtained in the study suggest that genetic variability in larger animals may be low in spite of the absence of known restrictions to their natural population sizes.
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