Scientists from the University of Connecticut, the University of Massachusetts, and the University of Wisconsin-Madison found that three-spined spiny ridges sacrifice 80% of their offspring for resistance to tapeworms. The study was published in the journal Science.
Some populations of three-spined barbs have developed a defense against tapeworms: their immune systems form scar tissue around the parasite, stopping its growth. The scientists studied the rebounds from Lakes Roberts and Gosling in British Columbia. The barb fish here are very similar, both lakes have tapeworms, but only in Lake Roberts the fish use scarring to protect themselves from parasites. In addition, they breed worse due to the many scars and inflammations in the abdominal cavity of the fish.
The team crossed individuals from these two populations to mix their genes. This step was necessary to reduce the number of genetic differences between fish – after all, there were too many and the “scarring” gene could be lost among them. They then selected fish with and without parasite protection from the offspring of these hybrids. To do this, the fish were “baited” with tapeworms on each fish for several weeks.
The scientists found that one of the most active genes in worm-protective prickly spines is a gene that is also strongly associated with scarring in mice. This is surprising and predictable: scarring is controlled by the immune system, which is more or less the same in all vertebrates, from fish to mice.
About 12,000 years ago, three spiky spiny ridges in the sea lived in northern freshwater lakes, where they encountered freshwater tapeworms. Due to the lack of adaptation, the tapeworms in his body reached a third of the mass of the fish. Parasites do not affect the fish’s reproduction, but slow it down, making it easy prey for predators.
This study showed that, contrary to common misconception, evolution did not always move towards developing resistance with parasites. Sometimes it is more profitable for animals to endure the fight against parasites than to pay for their own reproductive success. These principles probably apply to humans as well. To successfully manage infectious diseases, we need to understand the balance of costs and benefits that result from the immune response.