Killer splits

Although killer whales showed overall low levels of mitochondrial sequence variation, the researchers found three fixed differences between the open-sea type A whales compared with the two ice-inhabiting, other forms. " The genetic pattern suggests that, for females at least, there is no gene flow between them, " the authors write. But they do point out that the evidence for reproductive isolation between types B and C is weaker, as the variation within the types is equivalent to the differences between them. One single fixed sequence difference was found between them, which the authors say could be consistent with geographical variation within a single species. More extensive sampling will be needed to clarify this relationship, they believe. But they point out that killer whales are perhaps one of the best-studied large animals on earth, making the discovery of one or perhaps two new species all the more surprising. Recently, " a number of studies have detected the presence of other previously unrecognised cetacean species based on morphological and genetic data, " the authors write. " Taken together these findings indicate that cetacean diversity in the world's oceans may be substantially underestimated, and that there is still much to learn about even the largest of mammals. " Nigel Williams Killer splits Killer whales and humans share one thing in common: almost global ubiquity. While humans occupy almost all land regions on the earth, killer whales are found in all the oceans, although most densely occurring in polar regions. Like many of their cetacean relatives they are capable of travelling great distances so it is entirely possible that the global population remains homogeneous. But, in the northern Pacific, researchers have considered that up to three different types occur, specialising on different prey that also appear to some extent to be reproductively isolated. More recently, researchers in the Antarctic have been noticing quite distinctive markings on killer whales that have led to the consideration that they comprise three distinct groups there too. Further, these three groups appear to show distinct food preferences. One of the groups, type A, shows the typical black and white colouration, lives in ice-free water and appears to hunt primarily other cetaceans, particularly the Antarctic minke whale. The second group, type B, is grey, black and white, with a larger eyepatch and a distinct dorsal cape — it lives in the pack ice where it prefers to hunt seals. …