Gui T. Wang

Population genetic structure of the parasitic nematode Camallanus cotti inferred from DNA sequences of ITS1 rDNA and the mitochondrial COI gene

The population genetic structure of fish parasitic nematode, Camallanus cotti, collected from the Yangtze River, Pearl River and Minjiang River in China was investigated. From these parasites, the approximately 730 bp of the first internal transcribed spacer of ribosomal DNA (ITS1 rDNA) and the 428bp of mitochondrial cytochrome c oxidase subunit I (COI) gene were sequenced. For the ITS1 rDNA data set, highly significant Fst values and low rates of migration were detected between the Pearl River group and both the Yangtze River (Fst=0.70, P<0.00001; Nm=0.21) and Minjiang River (Fst=0.73, P<0.00001; Nm=0.18) groups, while low Fst value (Fst=0.018, P>0.05) and high rate of migration (Nm=28.42) were found between the Minjiang and the Yangtze rivers. When different host/locality populations (subpopulations) within each river were considered, subpopulations between the Yangtze River and Minjiang River had low Fst values (<or=0.12) and high Nm values (>3.72), while Pearl River subpopulations were significantly different from the Yangtze River and Minjiang River subpopulations (Fst>or=0.59; Nm<1). The COI gene data set revealed a similar genetic structure. Both phylogenetic analyses and a statistical parsimony network grouped the Pearl River haplotypes into one phylogroup, while the Yangtze River and Minjiang River haplotypes formed a second group. These results suggested that the Yangtze River and Minjiang River subpopulations constituted a single reproductive pool that was distinct from the Pearl River subpopulations. In addition, the present study did not find host-related genetic differentiation occurring in the same drainage.

Genetic Variation of Fish Parasite Populations in Historically Connected Habitats: Undetected Habitat Fragmentation Effect on Populations of the Nematode Procamallanus fulvidraconis in the Catfish Pelteobagrus fulvidraco

Habitat fragmentation may have some significant effects on population genetic structure because geographic distance and physical barriers may impede gene flow between populations. In this study, we investigated whether recent habitat fragmentation affected genetic structure and diversity of populations of the nematode Procamallanus fulvidraconis in the yellowhead catfish, Pelteobagrus fulvidraco. The nematode was collected from 12 localities in 7 floodplain lakes of the Yangtze River. Using 11 intersimple sequence repeat markers, analysis of molecular variance showed that genetic diversity occurred mainly within populations (70.26%). Expected heterozygosity (He) of P. fulvidraconis was barely different between connected (0.2105) and unconnected lakes (0.2083). Population subdivision (Fst) between connected lakes (0.2177) was higher than in unconnected lakes (0.1676). However, the connected and unconnected lakes did not cluster into 2 clades. A Mantel test revealed significant positive correlation between genetic and geographic distances (R = 0.5335, P < 0.01). These results suggest that habitat fragmentation did not cause genetic differentiation among populations or a reduction of diversity in isolated populations of P. fulvidraconis. At least 2 factors may increase the dispersal range of the nematode, i.e., flash flooding in summer and other species of fish that may serve as the definitive hosts. Moreover, lake fragmentation is probably a recent process; population size of the nematode in these lakes is large enough to maintain population structure.

Communities of gastrointestinal helminths of fish in historically connected habitats: habitat fragmentation effect in a carnivorous catfish Pelteobagrus fulvidraco from seven lakes in flood plain of the Yangtze River, China

BackgroundHabitat fragmentation may result in the reduction of diversity of parasite communities by affecting population size and dispersal pattern of species. In the flood plain of the Yangtze River in China, many lakes, which were once connected with the river, have become isolated since the 1950s from the river by the construction of dams and sluices, with many larger lakes subdivided into smaller ones by road embankments. These artificial barriers have inevitably obstructed the migration of fish between the river and lakes and also among lakes. In this study, the gastrointestinal helminth communities were investigated in a carnivorous fish, the yellowhead catfish Pelteobagrus fulvidraco, from two connected and five isolated lakes in the flood plain in order to detect the effect of lake fragmentation on the parasite communities.ResultsA total of 11 species of helminths were recorded in the stomach and intestine of P. fulvidraco from seven lakes, including two lakes connected with the Yangtze River, i.e. Poyang and Dongting lakes, and five isolated lakes, i.e. Honghu, Liangzi, Tangxun, Niushan and Baoan lakes. Mean helminth individuals and diversity of helminth communities in Honghu and Dongting lakes was lower than in the other five lakes. The nematode Procamallanus fulvidraconis was the dominant species of communities in all the seven lakes. No significant difference in the Shannon-Wiener index was detected between connected lakes (0.48) and isolated lakes (0.50). The similarity of helminth communities between Niushan and Baoan lakes was the highest (0.6708), and the lowest was between Tangxun and Dongting lakes (0.1807). The similarity was low between Dongting and the other lakes, and the similarity decreased with the geographic distance among these lakes. The helminth community in one connected lake, Poyang Lake was clustered with isolated lakes, but the community in Dongting Lake was separated in the tree.ConclusionThe similarity in the helminth communities of this fish in the flood-plain lakes may be attributed to the historical connection of these habitats and to the completion of the life-cycles of this fish as well as the helminth species within the investigated habitats. The diversity and the digenean majority in the helminth communities can be related to the diet of this fish, and to the lacustrine and macrophytic characters of the habitats. The lake isolation from the river had little detectable effect on the helminth communities of the catfish in flood-plain lakes of the Yangtze River. The low similarities in helminth communities between the Dongting Lake and others may just be a reflection of its unique water environment and anthropogenic alterations or fragmentation in this lake.

MOLECULAR PHYLOGENY AND HOST SPECIFICITY OF THE LARVAL EUSTRONGYLIDES (NEMATODA: DIOCTOPHMIDAE) FROM FRESHWATER FISH IN CHINA

Abstract:  The nematodes Eustrongylides spp. collected from different fish species in China were examined for their intra- and interspecific evolutionary variations using the molecular markers mitochondrial cytochrome oxidase c subunit 1 (COI) gene and internal transcribed spacer (ITS) rDNA regions. The phylogenetic analysis indicated that Eustrongylides species are divided into 3 well-supported clades. The ITS divergence between the clades suggested that clades 2 and 3 might represent the same species, whereas clade 1 represent another cryptic species. The host specificity of these nematodes was analyzed according to prevalence data, host range, and phylogenetic information. Clade 1 was found in 4 fish species, i.e., Odontobutis obscurus, Silurus asotus, Culter mongolicus, and Acanthogobius flavimanus, but was predominant in the 2 perciform species, O. obscurus and A. flavimanus. Clade 2 was found in 3 fish species, Monopterus albus, Channa argus, and Channa asiatica, but was predominant in M. albus, reported to feed primarily on oligochaetes, the first intermediate host of Eustrongylides sp. Clade 3 was found in 9 species, but its low prevalence suggests accidental infection in all species. Although the larval nematode presented low host specificity, it exhibited some host preference.

Frequency Distribution and Seasonal Dynamics of Intestinal Helminths in the Yellowhead Catfish Pelteobagrus fulvidraco from Liangzi Lake, China

Abstract The frequency distribution and seasonal changes of intestinal helminths in Pelteobagrus fulvidraco were investigated from February 2001 to July 2002 in Liangzi Lake in the floodplain of the Yangtze River, central China. Four parasite species were found: the cestode Gangesia pseudobagri and the digeneans Orientocreadium siluri, Coitocoecum plagiorchis, and Echinoparyphium lingulatum. There was a significant difference in the mean abundance of O. siluri between male (8.12 ± 16.99) and female hosts (3.19 ± 5.42). Parasite distribution patterns were all overdispersed (s2/x¯ > 1) and followed the negative binomial distribution. In the analysis of changes in mean parasite abundance and variance to mean ratio with host age, convex curves were observed for G. pseudobagri and O. siluri. This suggests that these 2 helminths may have had deleterious effects on the hosts. Significant seasonal changes were detected in the prevalence and mean abundance of the 4 helminths other than for the prevalence of O. siluri. The mean abundance of O. siluri, C. plagiorchis, and G. pseudobagri reached a peak in the spring, and E. lingulatum had the highest infection levels in the spring and early summer.

Comparative mitogenomics supports synonymy of the genera Ligula and Digramma (Cestoda: Diphyllobothriidae)

BackgroundAfter observing differences in the number of reproductive complexes per proglottid within the genus Ligula, the genus Digramma was erected. However, the validity of Digramma has been previously questioned due to a low variability in the cox1, nad1 and ITS rDNA sequences between the two genera. We undertook a study to greatly increase the amount of sequence data available for resolution of this question by sequencing and characterizing the complete mitogenomes of Digramma interrupta and Ligula intestinalis.ResultsThe circular mtDNA molecules of Digramma interrupta and Ligula intestinalis are 13,685 bp and 13,621 bp in size, respectively, both comprising 12 PCGs, 22 tRNA genes, two rRNA genes, and two mNCRs. Both mitogenomes exhibit the same gene order and share 92.7% nucleotide identity, compared with 85.8–86.5% to the most closely related genus Dibothriocephalus. Each gene from D. interrupta and L. intestinalis is almost of the same size, and the sequence identity ranges from 87.5% (trnD) to 100% (trnH, trnQ and trnV). NCR2 sequences of D. interrupta and L. intestinalis are 249 bp and 183 bp in length, respectively, which contributes to the main difference in length between their complete mitogenomes. A sliding window analysis of the 12 PCGs and two rRNAs indicated nucleotide diversity to be higher in nad5, nad6, nad2, nad4 and cox3, whereas the most conserved genes were rrnL and rrnS. Lower sequence identity was also found in nad2, nad4, nad5, nad6 and cox3 genes between the two diphyllobothriids. Within the Diphyllobothriidae, phylogenetic analysis indicated Ligula and Digramma to be most closely related to one another, forming a sister group with Dibothriocephalus.ConclusionsOwing to higher nucleotide diversity, the genes nad2, nad4, nad5, nad6 and cox3 should be considered optimal candidates to use as molecular markers for population genetics and species identification between the two closely related species. The phylogenetic results in combination with the comparative analysis of the two mitogenomes, consistently support the congeneric status of L. intestinalis and D. interrupta.

Seasonal dynamics and spatial distribution of the Dactylogyrus species on the gills of grass carp (Ctenopharyngodon idellus) from a fish pond in Wuhan, China.

Abstract Spatial distribution and seasonal variation in mean intensity and prevalence of monogeneans on the gills of grass carp (Ctenopharyngodon idellus) were investigated from September 2012 to December 2014 in a fish pond in Wuhan, China. During this period, 2 species of Dactylogyrus were found, i.e., Dactylogyrus lamellatus and Dactylogyrus ctenopharyngodonis. Dactylogyrus lamellatus was present during the entire duration of the investigation, whereas D. ctenopharyngodonis was only detected after January 2014, when another batch of grass carp fingerlings was added to the pond. Prevalence of the 2 Dactylogyrus spp. was relatively high throughout the year, but significant seasonal changes were detected in the mean intensity of the 2 species (P < 0.05). Mean intensity of D. lamellatus peaked in late winter and spring, and then dropped to the lowest point in summer. Dactylogyrus ctenopharyngodonis exhibited a high mean intensity in summer and autumn, but low in winter and spring. Spatial distribution of the 2 species was similar: the highest mean intensity was found on medial and distal parts of the second gill arch. Moreover, no evident change was detected in niche preference of D. lamellatus after the infection of D. ctenopharyngodonis occurred. There was no significant positive correlation in abundance between the 2 species (P > 0.05). In addition, there were no significant differences in the percentage of mean intensity of the 2 species on each gill arch among low-, medium-, and high-intensity groups (P > 0.05). These results suggest unsaturated gill niches and the absence of interspecific competition between the 2 Dactylogyrus species.

Composition and Diversity of Communities of Dactylogyrus spp. In Wild and Farmed Goldfish Carassius auratus

Abstract Species composition and diversity of dactylogyrids were compared on gills of wild and cultured goldfish (silver crucian carp) Carassius auratus from 3 naturally populated lakes and 3 stocked aquaculture ponds in the Hubei province of China to examine the differences in the gill parasite community between these natural and farmed waters. Of the 7 Dactylogyrus spp. detected, all were found in lakes and 5 in ponds, with Dactylogyrus inexpectatus and Dactylogyrus anchoratus being absent from ponds. No significant correlation was found between the species richness and habitat area or host size, nor was there a significant difference in mean species richness between lakes (0.41–0.65) and ponds (0.30–0.76). Brillouins diversity in lakes (0.049–0.067) was higher than that in ponds (0.024–0.046), but not significantly so. Although the diversity of parasite communities was higher in wild goldfish, higher mean abundance of some Dactylogyrus spp. was found in cultured goldfish. Based on Bray–Curtis similarity, it was difficult to differentiate parasite communities in lakes from those in ponds at the infracommunity level, whereas the 3 lakes and Guanqiao pond differed markedly from the remaining 2 ponds at the component community level. Although infracommunities differed among waterbodies, no effects of fish length or waterbody type were found on infracommunity or component community structure. Together, these results suggest that abundance and species richness of Dactylogyrus spp. on goldfish in lakes and farm ponds are influenced by habitat-specific environmental factors.

Expression analysis of immune genes in goldfish (Carassius auratus) infected with the monogenean parasite Gyrodactylus kobayashii

ABSTRACT Heavy infection with the ectoparasite Gyrodactylus kobayashii commonly leads to high mortality of ornamental goldfish Carassius auratus. To understand the underlying mechanisms of goldfish against infection of gyrodactylids, transcription responses of immune‐related genes including IL‐1&bgr;2, TNF&agr;1, TNF&agr;2, IFN‐&ggr;, TGF&bgr;, MHC II &bgr;, TCR&bgr;1 and complement factor C3 were studied by real‐time quantitative PCR analysis. Significant increases of expression of inflammatory genes such as IL‐1&bgr;2, TNF&agr;1, TNF&agr;2 and TGF&bgr; were detected at days 7 and 14 post‐infection (pi). No significant differences of G. kobayashii load were observed in response to primary infection and re‐infection. In addition, the transcript levels of genes involved in adaptive immunity such as MHC II &bgr; and TCR&bgr;1 remained unchanged. Curiously, fish moderately infected with gyrodactylid showed elevated expression IL‐1&bgr;2, TNF&agr;1 and TNF&agr;2. In all the gyrodactylids‐infected fish, expression of complement factor C3 was consistently inhibited. The results extend current knowledge to the understanding of gyrodactylid infection in fish and support the previous findings that innate immunity is indispensable for controlling parasite infection. HighlightsExpression of immune genes was studied in skin of goldfish during the primary infection and re‐infection with gyrodactylid.Inflammatory genes were up‐regulated.Complement factor C3 was down‐regulated.The genes involved in adaptive immunity were not modulated.

Effects of goldfish (Carassius auratus) population size and body condition on the transmission of Gyrodactylus kobayashii (Monogenea)

Field surveys indicate that host population size, rather than density, is the most important determinant of monogenean infection dynamics. To verify this prediction, epidemic parameters were monitored for 70 days at five host population sizes held at constant density using a goldfish - Gyrodactylus kobayashii laboratory model. During the first 20 days, the rate of increase of prevalence and mean abundance was faster in small host populations. Total mean prevalence and total mean abundance throughout the experiment were not significantly affected by host population sizes. Higher transmission rates were detected in larger host populations. However, there were no significant differences in effective contact rates among the five host populations on each sampling day during the first 20 days, implying that contact rates may be saturated at a sufficiently high host density. These results demonstrate that the epidemic occurs more quickly in smaller host populations at the beginning of the experiment. However, the epidemic is independent of the host population size due to the similar effective contact rates in the five population sizes. Significant negative influence of the initial body condition (Kn) of uninfected goldfish on total mean abundance of parasites suggests that susceptibility of hosts is also a determinant of parasite transmission.