|Other Abstract||The nematode Camallanus cotti Fujita, 1927 (Spirurida: Camallanidae), originally reported from the freshwater fishes of Japan, has now become widespread in the world. In the present study, its population biology and molecular ecology was investigated in relation to its host range, population dynamics and maturation cycle, population genetic structure, phylogeography, molecular variation and the cophylogeny relationship between parasites and hosts.
During 5 times of extensive investigations into the fish parasite fauna of the Danjiangkou Reservoir, C. cotti was found in 26 fish hosts, of these 14 were new hosts. The cypriniform fishes were typical hosts. The nematode’s mean prevalence, prevalence, mean abundance and intensity of infection varied in different fish species. Distribution of C. cotti in greatly diverse fish species might reflect high adaptation of the parasite to different hosts. However, the difference of infection of the nematode in different hosts indicates a possible host preference.
Studies on the population dynamics and maturation cycle of C. cotti (Nematoda: Camallanidae) in the Chinese hooksnout carp Opsariichthys bidens (Osteichthyes: Cyprinidae) revealed that there was a positive relationship between fish length and the number of the parasites on individual host. The dynamics of infection of the nematode showed significant seasonal pattern in changes of mean abundance, and a similar rhythmic pattern was also found in changes of prevalence although it was not statistically significant. The higher levels of infection existed in summer and autumn and the lower in winter and spring. In addition, researches on the development and maturation of the parasite in the Chinese hooksnout carp revealed that continuous development (maturation), recruitment of next generation and reproduction occurred all the year round, although reproduction might be at its peak in winter.
The genetic structure and phylogeography of different population of C. cotti collected from 3 water systems in central and southern China were investigated using the mitochondrial COI gene and ITS1 rDNA markers. The results showed that the significant geographical structuring of C. cotti population was only presented between the Pearl River population and the Yangtze River - Minjiang River population. There was no significant differentiation among different host/geographic populations in the same drainage. The Yangtze River geographical population was the ancestral population, which gave rise to the geographical populations of the Minjiang River and Pearl River. The evidence suggested demographic expansions varied among drainages.
Molecular analyses indicated that there were only two species of Camallanus found in freshwater fishes in China, i.e. C. cotti and C. hypophthalmichthys. The evolutionary associations of C. cotti strains and their host species resulted from frequent and recent colonization, (incomplete) host-switching events or failure to speciate, and subsequent adaptive radiation and incomplete isolation of the worm in diverse host species, over a short time-span.
In addition, phylogenetic relationship of the philometrid nematodes collected from freshwater fishes in China was evaluated by using ITS rDNA and 18S rDNA marker. The results suggested that 18S rDNA was the more reliable marker for analyzing the phylogenetic position of the philometrids. The genus Philometra appeared to be paraphyletic, confirming that the homoplastic evolution of morphological characters of this group was extensive. The current system according to morphological characters didn’t reflect its real phylogenetic relationships.
Finally, a new philometrid, Philometra siniperci sp. nov., parasitizing among the pyloric caecum of the Chinese perch, Siniperca chuatsi, was described based on its morphological characters and validated by the molecular data.|