Endohelminth Diversity

Author : Kyle E. Luth
Publisher :
ISBN 13 :
Total Pages : 339 pages
Book Rating : 4.:/5 (962 download)

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Download or read book Scale-dependent Variation in Molecular and Ecological Patterns of Infection for Endohelminths from Centrarchid Fishes written by Kyle E. Luth and published by . This book was released on 2016 with total page 339 pages. Available in PDF, EPUB and Kindle. Book excerpt: Few studies exist addressing the intraspecific molecular variability of helminths in a widely distributed freshwater fish host. Equally rare are studies considering both large- and small-scale patterns of infection of helminth communities in a widely distributed aquatic host(s). Vanishingly few studies exist making large-scale population-level comparisons of numerous helminth species occurring in multiple host species. Typically, such studies are meta-analyses, which incorporate data from numerous independent studies, thereby introducing issues of sampling (or sampler) bias, inconsistent reporting of information, etc. The purpose of the current work was to attempt to fill some of these voids in the parasitological/ecological literature, with a single, concise series of studies using the internal helminths of a commonly encountered group of freshwater fishes (Centrarchidae) across the United States (US). Intraspecific molecular variation in the bass tapeworm, Proteocephalus ambloplitis, was assessed by sequencing the mitochondrial (16S) and nuclear (ITS2) loci of tapeworms recovered from numerous centrarchid host species, from freshwater bodies of water across a large portion of the US. The goal of the study was to determine whether crypticity in this tapeworm could explain the pattern of adult presence in definitive hosts during summer mo in the northern portion of the US, and during the winter mo in the southern portion of the country. Sequences were obtained from 191 individual worms, taken from various locations, host species, and host tissues. Sequences were concatenated and used to construct a maximum likelihood (ML) phylogenetic tree which evidenced a large amount of sequence heterogeneity in these worms across the US. Four distinct groups appeared to resolve, based on branch length; however, branch support values did not recapitulate this topography. In neither case was the prediction of crypticity as a driving force behind the pattern of seasonal, regional presence of adults in definitive hosts supported. Furthermore, no patterns in molecular structuring were observed on the basis of host species, host tissue, or even within a lake. Rejection of the crypticity hypothesis suggests that perhaps differential seasonal presence/absence of first intermediate hosts, changes in water temperature, fluctuations in definitive-host hormone levels, or a combination of 2, or more, of these factors may be responsible for the observed patterns of adult cestode infections. Prevalence and intensity values are common metrics for analyzing and comparing the endohelminth populations infecting various hosts. Even so, few studies exist assessing these measures on a large geographic scales. In the current study, the endohelminths of 1,962 hosts of 3 species, i.e., bluegill sunfish (Lepomis macrochirus), green sunfish (Lepomis cyanellus), and largemouth bass (Micropterus salmoides), were used for comparison. Prevalence and intensity were used to compare population-level differences between host species, and total richness (S), total average endohelminth richness (S[subscript T]), average allogenic endohelminth richness (S[subscript AL]), and average autogenic endohelminth richness (S[subscript AU]) were used to make community-level comparisons. Thirteen of 25 endohelminth species encountered, infected all 3 host species, 6 infected a combination of 2, and 6 infected only 1 host species. The most commonly encountered endohelminth species infecting all 3 species included Neoechinorhynchus cylindratus, Proteocephalus ambloplitis, Camallanus oxycephalus, Contracaecum spiculigerum, Spinitectus spp., and Posthodiplostomum minimum. As might be expected, some endohelminth species differentially infected these closely related hosts, based on prevalence and intensity comparisons with permutational ANOVA, while others did not. Likely, behavioral differences between these hosts, including discrepancies in food/prey choice and habitat preference, influence these patterns. The endohelminth communities of bluegill sunfish were characterized by the greatest richness (S = 25), but lowest diversity (0.36), of all host species. Conversely, largemouth bass endohelminth communities were characterized by the lowest total richness (S = 15), but had the second highest diversity (0.65), of all host species. Largemouth bass also possessed the greatest S[subscript T] and S[subscript AL] values, and bluegill sunfish and largemouth possessed the same S[subscript AU] values. Although bluegill sunfish possessed the greatest total endohelminth richness at the host population level, individual largemouth bass possessed 1 of the highest diversities, and the highest S[subscript T], S[subscript AL], and S[subscript AU] values. The results of the current study confirms the value of large-scale studies in detecting patterns in endohelminth community structure which allow general conclusions to be made (and tested) concerning the parasite communities of widely distributed hosts. The resolution of patterns in parasite communities is highly dependent on both geographic and temporal scale. Although the impact of geographic scale on pattern resolution has received much attention as it pertains to free-living organisms, the parasitological literature remains depauperate in this area. Redundancy analysis (RDA) ordination using environmental variables, or host physical traits, in combination with the binary community matrix for 24 endohelminth species of bluegill sunfish (obtained from 200 freshwater bodies of water), was used to determine to what extent these factors structured the endohelminth communities of these hosts. Additionally, Mantel tests were employed to evaluate whether internal helminth communities of bluegill sunfish decay significantly with distance, both at a nearly countrywide scale, and at a regional scale, i.e., freshwater ecoregions. Average internal helminth richness was calculated for each freshwater ecoregion, and for each body of water from which 5 (or more) bluegill sunfish were recovered. These values were compared between freshwater ecoregions, as well as between bodies of water within ecoregions using either permutational ANOVAs or permutational t-tests. Additionally, average internal helminth richness was plotted against latitude and longitude to determine whether significant relationships existed for either. The data showed that bluegill internal helminth communities are both rich and quite consistent across the entire sampled range. Even so, community similarity decayed significantly with geographic distance, and average internal helminth richness was significantly influenced by both latitude and longitude across the sampled area. These trends were greatly mitigated at the intermediate geographic scale, i.e., within freshwater ecoregions, with only 2 of 16 showing a significant decay of similarity in endohelminth community similarity as inter-lake distance increased. At the smallest scale, e.g., between lakes within a given ecoregion, average internal helminth richness differed significantly, suggesting heterogeneity like that seen at the largest geographic scale. Thus, the data suggest that relatively small, or gradual, changes in internal helminth community structure at the local scale, such as adding or removing rare or regionally distinct endohelminth species, may be amplified at larger scales, but diminished at regional scales. Additionally, it appears that relatively few ecoregions, those characterized by particularly rich, or depauperate, endohelminth communities, may have a disproportionate impact on the countrywide patterns observed. Few modern-day studies exist attempting to single-handedly summarize the endohelminth communities of a widely distributed group of hosts, across a large geographic area. Often such studies must rely on multiple sources, potentially from numerous authorities, time frames, and widely distributed sampling sites. The final contribution of the current body of work is a survey the endohelminths of 18 different centrarchid species, or hybrids, collected from across a large portion of the US, during the summer mo of 2011-2013. No recent surveys exist considering the endohelminths of a single group of hosts, let alone such a closely related, yet behaviorally diverse group of hosts. The majority of endohelminths encountered were recovered from a variety of host species, suggesting broad utility of centrarchid hosts in the life cycles of many generalist endohelminth species of fishes occurring across the sampled region of the US.