Sympatric speciation in killer whales?

Resource specialisation and the divergence of killer whale populations

“…However, these resources are found within the same waters, though the timing and technique for capture may differ. 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.…”

“…They are not alone in this view, but alternative interpretations are well established (see review in Via (2001)), and indeed some of the most thoroughly investigated putative examples of sympatric speciation do not fit the scenarios proposed by Foote and Morin (2015), such as habitat-shift systems (for example, Filchak et al, 2000). Although Foote and Morin (2015) contend that killer whale ecotypes are too differentiated to represent even 'sister taxa or a monophyletic endemic species flock' and therefore rule out speciation in sympatry, we point out that levels of differentiation are comparatively low, and propose that if speciation is relevant for killer whales it is at a very early stage (see Moura et al, 2014a,b). However, Moura et al (2014a) using restriction-associated DNA (RAD) sequencing to identify 3281 single-nucleotide polymorphisms (SNPs) compared differentiation at neutral loci and those putatively under directional selection based on outlier analysis and fixed differences, and found stronger differentiation at linked loci with relevant functions (associated with digestion, growth etc.).…”

“…Foote and Morin (2015) propose that differentiation in sympatry is exceptional, restricted to 'geographically isolated 'island' populations, such as found in small crater lakes or on small remote oceanic islands'. They are not alone in this view, but alternative interpretations are well established (see review in Via (2001)), and indeed some of the most thoroughly investigated putative examples of sympatric speciation do not fit the scenarios proposed by Foote and Morin (2015), such as habitat-shift systems (for example, Filchak et al, 2000).…”

“…Foote and Morin (2015) propose that differentiation in sympatry is exceptional, restricted to 'geographically isolated 'island' populations, such as found in small crater lakes or on small remote oceanic islands'. They are not alone in this view, but alternative interpretations are well established (see review in Via (2001)), and indeed some of the most thoroughly investigated putative examples of sympatric speciation do not fit the scenarios proposed by Foote and Morin (2015), such as habitat-shift systems (for example, Filchak et al, 2000). Although Foote and Morin (2015) contend that killer whale ecotypes are too differentiated to represent even 'sister taxa or a monophyletic endemic species flock' and therefore rule out speciation in sympatry, we point out that levels of differentiation are comparatively low, and propose that if speciation is relevant for killer whales it is at a very early stage (see Moura et al, 2014a,b).…”

“…This is consistent with disruptive selection between ecotypes, thought to be an important mechanism in the process of sympatric speciation (see Via, 2001). Foote and Morin (2015), following inference from Foote et al (2011), propose that the demographic history indicated by mitochondrial DNA (mtDNA) phylogenies reflects the true history, and that it implies re-convergence of resource specialist populations that differentiated in allopatry. However, it is well-established (for example, see Shaw, 2002) that single gene trees can be misleading based on stochastic factors or introgression.…”