Whales and Men: genetic inferences uncover a detailed history of hunting in bowhead whale

Abstract

9After millennia of hunting and a population collapse, it is still challenging to understand the genetic 10 consequences of whaling on the circumarctic bowhead whale. Here I use published modern mtDNA 11 sequences from the Bering-Chukchi-Beaufort population and a new time calibration to show that late-12 glacial climate changes and whaling have been the major drivers of population change. Cultures that 13 hunted in the Arctic Seas from as early as 5000 years ago appear to be responsible for successive 14 declines of the population growth, bringing the effective size down to 38% of its pristine population 15 size. The Thules and the Basques (year 1000-1730) who only hunted in the North Atlantic had a major 16 impact on this North Pacific population, indicating that bowhead whale stocks respond to harvesting as 17 a single population unit. Recent positive growth is inferred only after the end of commercial whaling in 18 1915, and for levels of harvesting that are close to the current annual quota of 67 whales. By unfolding 19 the population history of the bowhead whale, I provide compelling evidence that mtDNA yields critical 20 yet undervalued information for management and conservation of natural populations. 21 22 Population dynamics; Whaling 24 (BCB). This population is showing signs of recovery, has far greater abundance than others (Moore et 48 al. 2019), and has been monitored and studied for several decades (Zeh and Punt 2005). After inferring 49 female effective population size (Ne) using a Bayesian skyline analysis (Heled and Drummond 2008), 50 I calculated population growth rates; a parameter that has a key role in describing population trends and 51 identifying potential drivers of decline (Sibly and Hone 2002). I then applied a molecular clock derived 52 from a single-point calibration and used a clustering method that groups the population growth rates 53 into distinct time periods. Remarkably, I found that bowhead whale demography is strongly influenced 54 by sea-level changes and five millennia of human harvesting. 55 56 Results and discussion 57 Validation of an LGM-based calibration of the molecular clock the following equation [R = dNe /dt = (Ne n -Nen+1)/(tn+1tn)] (with Ne: effective population size, 217 : generation time of the species, t: time and n: number of coalescent events back in time). This provided 218 the rate estimates of the population growth at every point in time associated with the coalescent events 219 recorded in the given dataset (n = 148 coalescent events for a sample size of 149), and this back to the 220 most recent common ancestor of the sequence dataset. 221 222 Calibration of molecular rates 223The calibration relies on the single assumption that the bowhead whale has a first positive population 224 growth rate (R > 0) at 20 ka (Fig. 1A). This assumption is based on the previous palaeoecological results 256 286 surface temperature predicts the movements of an Arctic cetacean: the bowhead whale. Sci Rep. 8:1-12.

Contraction-expansion dynamics of reef species in response to sea-level changes

“…To evaluate the potential role sea levels have had on past demography of coral reef species, we compared the effect of varying intensities of LGM bottlenecks on demographic inferences using a simulation study. The inferences based on the EBSP model represent fair reconstructions of the simulated population histories, which is in line with recent studies (Hoareau 2016, 2020; Pretorius and Hoareau 2020) and confirms the robustness of the analysis. Our results show an absence of expansion older than the LGM (Fig.…”

“…We argue that reef species follow a contraction-expansion model, and that the paradox observed between genetic and other evidence is linked to inadequate mutation rates used. The new calibration method specifically developed for reef species and based on the model described by Pretorius and Hoareau (2020) will help gain further insights on factors that drive the population history of tropical species.…”

Reef development and Sea level changes driveAcanthasterPopulation Expansion in the Indo-Pacific region

“…This allows a relative comparison of demographic histories to driving factor scenarios based on the timing of expansions and shape of the inferred EBSP. In addition, we used the standardized curves to estimate growth rates (Hoareau 2020) with: …”