Low genetic variation among killer whales (Orcinus orca) in the eastern North Pacific and genetic differentiation between foraging specialists

Abstract

Killer whales from the coastal waters off California through Alaska were compared for genetic variation at three nuclear DNA markers and sequenced for a total of 520 bp from the mitochondrial control region. Two putative sympatric populations that range throughout this region were compared. They can be distinguished by social and foraging behavior and are known as "residents" and "transients". We found low levels of variation within populations compared to other cetacean species. Comparisons between fish (resident) versus marine mammal (transient) foraging specialists indicated highly significant genetic differentiation at both nuclear and mitochondrial loci. This differentiation is at a level consistent with intraspecific variation. A comparison between two parapatric resident populations showed a small but fixed mtDNA haplotype difference. Together these data suggest low levels of genetic dispersal between foraging specialists and a pattern of genetic differentiation consistent with matrifocal population structure and small effective population size.

Phylogenomics of the killer whale indicates ecotype divergence in sympatry

“…Environmental cycles releasing habitat or opening/closing dispersal corridors may also influence the evolution of population structure in these species (Amaral et al, 2012;Moura et al, 2013). For killer whales, some well-studied populations show strong resource specializations based on consistent prey choice (ecotypes) within stable, matrifocal social groups (pods), together with genetic and phenotypic differentiation (Hoelzel et al, 1998;Pitman and Ensor, 2003;Hoelzel et al, 2007;Morin et al, 2010). A key question is whether or not differentiation has occurred in sympatry through ecologically based divergent selection with the potential to lead to sympatric speciation.…”

“…In this study, we generate the first multilocus phylogeny based on nuclear DNA for this genus, providing an important test of earlier inference based on mitochondrial DNA (mtDNA) trees (Hoelzel et al, 1998;Pitman and Ensor, 2003;Morin et al, 2010). We compared high-resolution phylogenetic reconstructions for mtDNA (alignment length of 4370 bp) with nuclear sequence phylogenies, built from restriction-associated DNA (RAD) fragments (see methods) consisting of a total alignment of 1 730 328 bp, with 5191 bp being variable among the killer whale samples.…”

“…We compared high-resolution phylogenetic reconstructions for mtDNA (alignment length of 4370 bp) with nuclear sequence phylogenies, built from restriction-associated DNA (RAD) fragments (see methods) consisting of a total alignment of 1 730 328 bp, with 5191 bp being variable among the killer whale samples. The earlier studies based on mtDNA (based on both Control Region and whole-mitogenome studies; for example, Hoelzel et al (1998) and Morin et al (2010)) showed that a lineage comprised of the marine-mammal-eating populations in the North Pacific (known as 'transients') branched from the most basal node. A later study based on mtDNA proposed that a North Atlantic population was derived from ancestral North Pacific lineages, perhaps during an opening in the northwest passage during the last (Eemian) interglacial (Foote et al, 2011a).…”

Resource specialisation and the divergence of killer whale populations

“…Foote and Morin (2015) suggest that the co-occurrence of populations in the same ocean doesn't necessarily imply that they differentiated in sympatry, which is clearly true. However, as Moura et al (2015) and others (for example, Hoelzel et al, 1998Hoelzel et al, , 2007 have discussed, it is the life history and behaviour of killer whales that suggest the potential for differentiation in sympatry. Although the proximity of resources brings killer whale pods into sympatry, the differential pattern of spatial and temporal habitat use, as well as fidelity to pods that forage by similar learned methods, could serve to isolate resource specialist communities reproductively.…”

Genetic Structure and Low-genetic Diversity Suggesting the Necessity for Conservation of the Chinese Longsnout Catfish, Leiocassis longirostris (Pisces: Bagriidae)

“…These properties make mtDNA a valuable marker for detecting population structure at the species level. Among all the mitochondrial genome the control region, which is noncoding, has been used to detect genetic variations of fishes for the studies of population structure and phylogeny since it varies greater than the other regions (Aurelle & Berrebi 2001;Hoelzel et al 1998;Nesbo et al 1998). Although cytochrome b (Cyt b) does not show a high-sequence variation, it can provide enough genetic information on the species level and distribution of genetic variability (Bernardi & Crane 1999;Carr & Marshall 1991;Zhang et al 1999).…”