ANALYSIS OF POPULATION STRUCTURE AND GENE FLOW IN

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Right whales belong to the sub order of Baleen whales or Mysticetes, which includes the blue whale and grey whale. These are one among the 14 large species found in whale (www1) and are the most endangered species among cetaceans (mammals which are best suited for aquatic life) (Rosenbaum et al 2000). They are in small numbers and there are 3 species discovered by the scientist which are found in the Atlantic, Pacific in the northern hemisphere and in Atlantic, Pacific, and Indian oceans in the southern hemisphere. Previously there was an abundant population but now they are becoming extinct due to human exploitation over a period of years (www1).

Right whales tend to travel long distance between the specific feeding and breeding grounds in a cyclic way annually. (Rus Hoelzel 1994). Southern right whales present in coastal waters starts moving towards the offshore for feeding during the summer time. They are found calving in the winter months. The migrating pattern tends to appear from north-south and also east-west. The mitochondrial DNA is been isolated from the southern hemisphere right whales and northern hemisphere right whales. Northern right whales had been hunted more compared to the southern right whales and hence those were exploited a lot comparatively.

It was found that there was a population differentiation and genetic variation between the Indo-Pacific and South Atlantic oceans. These findings together gave significant genetic variation at the nucleotide levels and the haplotype levels in the four calving grounds. The calving grounds were South Africa in South Atlantic basin, south-western Australia and New Zealand in Indo-Pacific basin (Luciano O. Valenzuela et al). But among the ocean basins the mtDNA haplotype was shared between the feeding grounds and the two different nursery grounds. It was identified that southern right whales had site fidelity to feeding grounds and suggested that in different breeding populations among the oceans the whales would be mixed in the common feeding grounds (Luciano O. Valenzuela et al 2009). In the northern right whales it was seen that most of the reproductive females bought their calves to the feeding grounds in the Bay of Fundy (Catherine M. Schaeff 1993). But the substructuring within this population is not known. The reason might be due to the lack of food abundance equally spread among the feeding regions. If nursery ground was considered then changes would be found in the haplotype frequency of standard whales or the haplotype of reproductive females.

In case of gray whales, the calves are nursed by their mothers considerably in less time than the humpback whales and the North Atlantic right whales. The calves learn the migration routes of the feeding grounds through repeatedly following their mothers for a few months (Timothy R. Frasier et al). There is significant genetic differentiation was present between the calving females and the mating females but not so much between the calving females with the two lagoons (Luciano O. Valenzuela et al).

The degree of genetic differentiation between the southern right whales in the wintering grounds was very similar to that of the humpback whales (C.S. Baker et al 1999). Samples for the genetic analysis were taken from different regions. The samples collected must be stored in the liquid nitrogen or in -70°C ethanol. Then complete DNA is to be extracted following the standard methods.

There are different statistical methods found which can determine the differentiation using software. For example phylogeny of a whale mtDNA haplotype can be found using parsimony methods with the help of software referred to as PAUP. Similarly the diversity and the geographical variation of haplotype can be found using the AMOVA (ANALYSIS OF MOLECULAR VARIANCE) which is found in software called "Arlequin". This helps in the calculation of standard variance and different haplotype correlation measures known as φ-statistics (φst) and F-statistics (Fst) for population structures. The diversity of right whale mtDNA was determined at the levels, the nucleotide level and the haplotype level. At the nucleotide level the diversity and the standard deviation was found based on the pair wise distances between the mtDNA and in the haplotype level same way was carried out but without considering the genetic distance between the two sequences (C.S. Baker et al 1999).

Comparing the southern right whale with the northern right whale there was a difference in consensus segment of control region. In southern right whales 3 to 7 % less was found when compared to north's. There were no conversions among these two haplotype (C.S. Baker et al 1999).

Statistics NZ SWA SA AR NP NA Mean s.d.

NP

NA

Mean

s.d

No. of transitions 16 15 25 28 15 7 17.667 6.968

16

15

25

28

15

7

17.667

6.968

No. of transversions 2 0 0 0 0 0 0.333 0.745

2

0

0

0

0

0

0.33

0.745

No. of substitutions 18 15 25 28 15 7 18.000 6.928

18

15

25

28

15

7

18

6.928

No. of indels 0 0 0 0 0 0 0.000 0.000

0

0

0

0

0

0

0

0

No. of ts. sites 16 15 25 28 15 7 17.667 6.968

16

15

25

28

15

7

17.667

6.968

No. of tv. sites 16 15 25 28 15 7 0.333 0.745

16

15

25

28

15

7

0.333

0.745

No. of subst. sites 18 15 25 28 15 7 18.000 6.928

18

15

25

28

15

7

18

6.928

No. of indel sites 0 0 0 0 0 0 0.000 0.000

0

0

0

0

0

0

0

0

Pi 3.819 6.058 6.812 8.234 4.712 1.755 5.23172 2.10333

6.812

8.234

4.712

1.755

5.23172

2.1033

Fig 1: molecular diversity indexes (obtained from ARLEQUIN SOFTWARE)

The Fst values was found using AMOVA. First the project file is opened in Arlequin. Then the settings are modified. For Fst conventional F statistics is selected with the number of permutations being 1000. Apart from that standard indices and molecular indeces were selected.

----------------------------------------------------------------------

Source of Sum of Variance Percentage

variation d.f. squares components of variation

----------------------------------------------------------------------

Among

populations 5 1015.036 4.48193 Va 73.92

Within

populations 406 642.124 1.58159 Vb 26.08

----------------------------------------------------------------------

Total 411 1657.160 6.06351

----------------------------------------------------------------------

Fixation Index FST: 0.73916

Fig 2: AMOVA results for φst (obtained from Arlequin software)

Population specific FST indices

--------------------------

Pop# Name FST

--------------------------

1 NZ 0.73802

2 SWA 0.73425

3 SA 0.73259

4 AR 0.73020

5 NP 0.73692

6 NA 0.74171

--------------------------

Fig 3: amova results for population specific φst indices (obtained from Arlequin software)

Similar procedure is followed for the analysis of Fst and the following results were obtained.

----------------------------------------------------------------------

Source of Sum of Variance Percentage

Variation d.f. squares components of variation

----------------------------------------------------------------------

Among

populations 5 27.425 0.11386 Va 23.64

Within

populations 406 149.298 0.36773 Vb 76.36

----------------------------------------------------------------------

Total 411 176.723 0.48159

----------------------------------------------------------------------

Fixation Index FST : 0.23643

----------------------------------------------------------------------

Fig 4: amova results obtained for Fst (obtained from Arlequin software)

-------------------------------

Population specific FST indices

--------------------------

Pop# Name FST

--------------------------

1 NZ 0.23841

2 SWA 0.23701

3 SA 0.23203

4 AR 0.23175

5 NP 0.23389

6 NA 0.23733

--------------------------

Fig 5: amova results for population specific Fst indices (obtained from Arlequin software)

The differentiation of right whales along with the mtDNA nucleotide diversity was found and was then compared with the humpback whales. They were similar in nature depending on same regions. At the haplotype level the mtDNA diversity was more for humpback whales (0.974) when compared to that of the right whales (0.7932). The number of haplotypes was considerably more and even the percentage of polymorphic sites was more compared to that of right whales (C.S. Baker 1999)

The range of geographic variation found using the φ-st and Fst was relatively large and it was found to be significant statistically when both the permutations procedure and chi-square test of independence for haplotype frequencies were tested. The φ-st explained that nearly 75% of molecular variance was shared to the different basins but in the Fst using haplotype frequency only showed 80 % of variance found in the ocean regions (H.C. Rosenbaum et al 2000). However they are similar to the humpback whales, the overall haplotype was significantly lower n the right whales. There might be few reasons which were predicted to be the cause of low diversity (C.S. Baker 1999). They were lower mutation rate smaller effective population size and loss of greater lineage due to the repeated whaling and decline of population size. The hunting of right whales is much more than the humpback whales in the southern hemisphere the reasons being these right whales are slow movers and can be easily exploited. Due to large exploitation and very slow recovery of these right whales there is a decline in the current rate of population. Australian population is much more than the New Zealand for right whales. The humpback whales are present in large numbers as they are not much exploited. These are the few variations of the hump back whales and the right whales based on the haplotypes and the nucleotides and their feeding grounds

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