A study was conducted on a kind of endemic marine mammal in a land locked sea. The coastal line is about 1000 km from West to East. 20 microsatellite markers had used and the results of DPAC analysis using adegenet (R package) Fig 1 and STRUCTURE software (1000000 MCMC, 10% burnin) Fig 2 were shown two different populations of this species. The results reinforce the hypothesis that there is more than one population in this closed sea. Now, I've three questions here:
a) Is there any possibility to have two populations for mentioned species in a land locked sea with 400000 km2 area?
b) With these results, can we conclude that there was a gene influence form the east population to the west population?
c) How about interpretation for DAPC graph with two curves?
P.S: In both barplots, red cluster represents west population individuals, while green cluster indicates East population individuals.
Hmm, without knowing the species and a bit about its distribution/dispersal ability it is hard to say. What you are showing could be the result of 2 diverging populations, or it could be the result of sampling 2 locations within a single population that are far-enough apart that isolation by distance accounts for the depicted differences. If the "populations" are discontinuous, I then begin to wonder if this is a natural process, or a relic of anthropogenic pressures (hunting, etc) fragmenting a once-continuous population - then drift, etc between the two "populations" resulting in the observed patterns. I'm curious what the pairwise FST, expected heterozygosity, and observed heterozygosity are? These should prove useful in determining down-stream analyses. Also, I assume no complimentary mitochondrial or SNP data is available?
I did a touch more sluthing as to what species you might be inquiring about. Without revealing the candidate species I came up with, which I assume you intentionally did not mention in the original post, I think the following article may be useful: Article Genetic Effects of Harvest on Wild Animal Populations
Since I’m not a geneticist I’m putting my thoughts for part a
a) Is there any possibility to have two populations for mentioned species in a land locked sea with 400000 km2 area?
Yes! You need gene flow between populations over longer timescales to maintain the species delineation. So knowing that broadly they are spatially accessible to each other the next good question might be a movement/behavioral one. Do the groups self segregate spatially, or are they unable/unwilling to cross what they perceive as boundaries?
Another point that often prevents similar species from mating is temporal separation. So do they breed at the same time, or is it not possible within a season to mate with each other?
Finally, courtship behavior/physiology may prevent mating. Do the two groups have a specific mating behavior or scent that is required for successful mating? Is there strong mating preferences? Are only a handful of individuals of either sex producing offspring?
Any of these scenarios could lead to differentiation or maintain differences at the same location.
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