At "only" three tons, it is the smallest of all baleen whales: researchers have now also sequenced the genome of the pygmy right whale, opening up interesting possibilities for comparison. Its genome therefore sheds light on the evolutionary history of the sea giants and could also benefit cancer research. Because some hereditary factors that have now been identified, which differ between the "small" and its giant relatives, could be linked to the medically interesting tumor resistance of the large baleen whales, the scientists explain.
Humpback whale, fin whale... and the top is the blue whale, which can weigh up to 200 tons: the group of baleen whales (Mysticeti) has produced the largest animals that have ever existed on our planet. The evolutionary success of these marine mammals is based on an extremely effective diet: the baleen in their mouths act as a kind of sieve system through which they can filter and swallow large quantities of small prey from the water. Due to the plentiful food supply, the baleen whales were then able to produce their sometimes gigantic body dimensions. However, one representative has remained comparatively modest: the pygmy right whale (Caperea marginata) is a tiny one among its relatives with a length of six meters and a weight of up to around three tons.
Oncologically interesting whale genetics
Since the pygmy right whale has always been rare and lives in remote waters around Antarctica, comparatively little was known about this species until now. However, specific body features already suggested that it is the last surviving member of an otherwise extinct branch of the baleen whale family. For other members of the group, genetic data could provide additional information. In order to make this possible in the case of the smallest representative as well, the researchers led by Magnus Wolf from the Senckenberg Biodiversity and Climate Research Center in Frankfurt am Main sequenced the genome of the pygmy right whale. The tissue came from a specimen found dead.
As the researchers explain, there were both biological and medical reasons for the project. They wanted to get on the track of a paradox: Actually, the large representatives of the whales with their huge bodies should be predestined for tumor diseases. Because the more cells are present and dividing, the more likely it is that a mutation at a crucial point can damage the genetic material and trigger the development of cancer. Nevertheless, the gigantic marine mammals do not get cancer very often. Information on the genetic mechanisms on which this resistance is based could thus provide clues for cancer research. The idea is that less cancer protection appears necessary for the comparatively small right whale than for blue whales and the like.
Differences between small and large
As Wolf and his colleagues report, this hope was confirmed: they came across various genes that have significantly more mutations in large whales, such as the blue whale, fin whale or bowhead whale, than in their smaller relatives. From this it can be deduced that they were subject to strong adaptations in the course of their development history. The team emphasizes that there is already evidence that some of the genes may actually play a role in cancer resistance. Because among them there were also candidates who had already attracted attention in tumor research but had not yet been extensively researched.
The researchers also found interesting information about the evolutionary history of baleen whales: "Our new findings show that almost all large whale species appear to have different positively selected genes in their genomes. "This can possibly be explained by the idea, already discussed in paleontology, that the gigantism that is so typical of baleen whales probably arose several times and independently of one another in the course of evolution," says Wolf. This also fits in with clues about the relationships within the baleen whales, to which the new genome of the pygmy right whale has also contributed. Among other things, the researchers were able to use the genetic clues to show a point in evolution at which the whales split into three new developmental lines.
In order to focus again on the application-oriented perspective of the study, Wolf says in conclusion: "It could be that each large whale species has also developed its own form of tumor resistance, which hopefully can be used medically in the future," says the scientist .
Source: Senckenberg Research Institute and Natural History Museums, specialist article: BMC Biology, doi: 10.1186/s12915-023-01579-1