The impact of nature and domestication on roundworms
The domestication of horses has completely changed the behaviors of warfare and transportation in human society. The usage of horses as the main transport by the Cavalry army appeared in the early Iron Age (Drews, 2004). Studies have shown that the decline in heterozygosity indicates that in recent centuries, the breeding population of horses has been greatly reduced, and this was the inevitable result of domestication and reproduction (Fages et al., 2019). During the war, humans significantly preferred the speed traits of horses. Therefore, in order to maintain the excellent traits of horses, on the one hand, people began to select excellent stallions in breeding (Fages et al., 2019), and on the other hand, the forage nutrition of horses has been gradually improved. The change of the host’s diet was an opportunity and a challenge for the parasites. From the perspective of glycolysis, we found that most of the key enzymes involved in glycolysis in zebra roundworms and donkey roundworms were subjected to a higher degree of recent selection when compared to domestic horses. As the most important way for roundworms to obtain ATP, glycolysis and tricarboxylic acid cycle seem to have ”degraded” in domestic horse roundworm populations. This may be the result of its adaptation to host domestication. Experiments have shown that the content of fatty acids such as palmitic acid, palmitoleic acid, stearic acid and oleic acid of the parasite were almost the same as that of the specific host and the changes in the ratio of fatty acids tend to be synchronized(Barlow, 1972). Immunological evasion could be the major purpose. This notion is supported by our findings in horse roundworms, which showed a strong selection of genes involved in lipid synthesis. Obviously, in addition to nutrition and maintaining physiological integrity, a more important purpose was possible to keep consistent with the host’s various fatty acid patterns. The evolution of parasites in regulating lipid composition may be a factor influencing host suitability (Wallis, 1982). The difference was that we believed the consistency in this case was more likely related to the host’s intestinal and surrounding lipid deposition rather than the total lipid ratio.