Uma abordagem genômica no estudo da história demográfica da população de baleias jubarte (Megaptera novaeangliae) do Atlântico sul ocidental

Abstract

Currently there are seven recognized reproductive stocks (A-G) of humpback whales (Megaptera novaeangliae) in the southern hemisphere. The breeding stock 'A' spreads along the Brazilian coast (between 5 ° and 23 ° S) and the Abrolhos Bank- BA is the main breeding area of the Southwest Atlantic Ocean. During the commercial whaling period (early 20th century) the breeding stock ‘A’ had reached nearly of 2% of its historical size. Recent researches, using different techniques to study the demographic history, have found different values for recent and historical abundance for this population. The knowledge about population size at specific times and its dynamics during time is very important to draw conservations strategies. Here we sequenced a ddRADseq library of 25 DNA samples extracted from tissues of individuals from the Brazilian humpback whales population. The data suggests absence of population structure in the population. The analysis with 5145 locus with migrate-n estimated the genetic diversity of the population as 0.00237 in per site, indicating an effective size of approximately 40,000 and a census size ~140,000. The ABC approach (Approximate Bayesian Computation), used to test different demographic scenarios related to the commercial whaling period, supported a constant population scenario (<10 generations) (against scenarios with population changes in this period) corroborating previous studies using microsatellites and a few nuclear loci. The Ne estimated in the constant scenario was similar to that obtained with the migrate-n method. Finally, the skyline plot obtained with the migrate-n suggests an increase in the effective size of more than an order of magnitude extending for hundreds of thousands of generation in the past. This very long time frame suggests that this estimate may actually reflects the population size of a metapopulation covering the entire Southern Hemisphere or even entire species, a hypothesis that needs to be tested with the addition of other populations and appropriate demographic scenarios.