High genetic diversity in a small population: the case of Chilean blue whales

Abstract

It is generally assumed that species with low population sizes have lower genetic diversities than larger populations and vice versa. However, this would not be the case for long-lived species with long generation times, and which populations have declined due to anthropogenic effects, such as the blue whale (Balaenoptera musculus). This species was intensively decimated globally to near extinction during the 20th century. Along the Chilean coast, it is estimated that at least 4288 blue whales were hunted from an apparently pre-exploitation population size (k) of a maximum of 6200 individuals (Southeastern Pacific). Thus, here, we describe the mtDNA (control region) and nDNA (microsatellites) diversities of the Chilean blue whale aggregation site in order to verify the expectation of low genetic diversity in small populations. We then compare our findings with other blue whale aggregations in the Southern Hemisphere. Interestingly, although the estimated population size is small compared with the pre-whaling era, there is still considerable genetic diversity, even after the population crash, both in mitochondrial (N = 46) and nuclear (N = 52) markers (Hd = 0.890 and Ho = 0.692, respectively). Our results suggest that this diversity could be a consequence of the long generation times and the relatively short period of time elapsed since the end of whaling, which has been observed in other heavily-exploited whale populations. The genetic variability of blue whales on their southern Chile feeding grounds was similar to that found in other Southern Hemisphere blue whale feeding grounds. Our phylogenetic analysis of mtDNA haplotypes does not show extensive differentiation of populations among Southern Hemisphere blue whale feeding grounds. The present study suggests that although levels of genetic diversity are frequently used as estimators of population health, these parameters depend on the biology of the species and should be taken into account in a monitoring framework study to obtain a more complete picture of the conservation status of a population.

Estimates of Abundance and Trend of Chilean Blue Whales off Isla de Chiloé, Chile

“…Torres-Florez et al [44] also noted haplotype diversity within the species is higher than might be expected considering the recent whaling impact, and hypothesized that this might be due to some degree of past sub-structuring. They suggest that the relatively high diversity seen in the Chilean blue whales (0.890) relative to pygmy blue whales [45] off Australia may be due to long-term feeding ground site fidelity along the coast (as suggested by the present study) despite the lack of evidence for genetic sub-structure.…”

Low genetic diversity in pygmy blue whales is due to climate-induced diversification rather than anthropogenic impacts

“…Samples were collected under the ethics requirements of the country, as detailed elsewhere [7,9]. rsbl.royalsocietypublishing.org Biol.…”

“…In the Northern Hemisphere, there is one subspecies (B. m. musculus), and in the Southern Hemisphere, there are two subspecies: the pygmy blue whale (B. m. brevicauda), which feeds in temperate waters, and the Antarctic blue whale (B. m. intermedia), which feeds in Antarctic waters. The lowest recorded genetic diversity in populations of blue whales is found in pygmy blue whales that feed off Australia [4][5][6][7] (table 1). Traditional genetic analyses have indicated that Australian pygmy blue whales have undergone a genetic bottleneck at an unknown time [4].…”

“…We thank Kelly M. Robertson and Paula A. Olson for their input. Acknowledgements are detailed elsewhere for sampling [7,9]. …”

A preliminary investigation into the ecology and behavior of blue whales (Balaenoptera musculus) in the Gulf of Corcovado, Chile

“…The species has been slow to recover from almost total decimation and hence a valuable discovery was made in 1993, when a small blue whale population of 232 individuals was found in the Gulf of Corcovado in the Chiloense Ecoregion of Southern Chile (Hucke-Gaete et al 2004). Genetic, acoustic and morphometric studies indicate that these blue whales are part of a wider Southeast Pacific population that is distinct from both the Antarctic (B. musculus intermedia) and "pygmy" (B. musculus brevicauda) blue whale subspecies (Branch et al 2007, Buchan et al 2014, Torres-Florez et al 2014. Further investigations are required to establish the degree of isolation of the population and the health and viability of the individuals within it.…”