Diversity and community structure of gastrointestinal helminths of Rhabdomys spp. and other small mammals in South Africa

Spickett, Andrea (2017-12)

Thesis ((PhD)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: Descriptive information forms the basis for broader ecological questions and therefore plays a vital role in studies that explore patterns in parasite diversity, distribution and species assemblages. Parasite-locality information can further aid in the development of species distribution maps that can be of value in the identification of disease risk and aid proactive disease management. As yet, current knowledge of helminth-host and helminth-locality associations in small mammals in South and southern Africa are scant. As a result, it is uncertain how host and environmental factors shape helminth infections and community structure across a climatically diverse landscape. To address this paucity of information the study aims to: (1) record descriptive information on helminth-host associations and the spatial and temporal distribution of helminth parasites associated with small mammals, (2) using two closely related murid hosts, Rhabdomys pumilio (Sparrman) and Rhabdomys dilectus (de Winton), as models, to investigate if between-host species differences in helminth infections are mainly caused by level of sociality (social R. pumilio and solitary R. dilectus) or environmental conditions (more xeric R. pumilio and more mesic R. dilectus), (3) investigate the effect of social and spatial behaviour, of R. pumilio and R. dilectus, on parasite community organization with reference to species co-occurrence and nestedness and (4) explore factors responsible for patterns in similarity in helminth species composition in R. pumilio and R. dilectus. In total 168433 specimens, comprising 56 helminth taxa were recovered from at least 16 rodent, and sengi and shrew species (n = 1079). The helminth species represented 26 genera of which 16 were nematodes, nine cestodes and one acanthocephalan. Overall, the most abundant helminth species was the nematode Heligmonina spira (133.8 ± 13.5), which was also the most prevalent (26.1%). Rhabdomys dilectus harboured 19 nematode and 7 cestode species while R. pumilio harboured 10 nematode and 5 cestode species. Seven helminth species (4 nematodes and 3 cestodes), were shared between the two rodent species, however, they also harboured their own specific helminths. In general, monoxenous (direct life cycle) nematodes were present in higher abundance compared to heteroxenous (indirect life cycle) nematodes and cestodes. Several novel helminth-host and helminth-locality records, in addition to several potentially new helminth species were noted. Life cycle-specific geographic distributions were recorded for monoxenous and heteroxenous nematodes. Helminth infections varied spatially and seasonally with significantly higher helminth abundance and prevalence in the months following the wet season. Cestode infection as well as nematode abundance, species richness or prevalence did not differ between R. dilectus and R. pumilio in between-host species comparisons. However, incidence of nematode infection was significantly higher in R. dilectus than in R. pumilio. Within-host species comparison showed that nematode abundance and species richness in infracommunities of R. pumilio inhabiting the relatively more xeric Karoo biome were significantly lower than in those inhabiting the relatively less xeric Fynbos biome. General patterns of helminth co-occurrence were similar (positive) in the two hosts, but the strength of positive associations increased with an increase in the mean number of helminth species in R. dilectus and in prevalence of infection in R. pumilio. The two host species differed in the relative frequency of positive and negative pairwise species co-occurrences (only positive in R. dilectus and both positive and negative in R. pumilio). Nestedness-related patterns in helminth infracommunities were only found in R. pumilio (predominantly anti-nested), whereas the opposite was the case for their component communities (only nested in R. dilectus). The level of infection was generally associated with the manifestation of non-randomness in helminth assemblages. Although species composition of infracommunities largely overlapped between R. dilectus and R. pumilio they were still significantly different between the two species. In both rodent species helminth infracommunities were more similar among individuals from the same locality than among localities or biomes. This pattern was more distinct for R. dilectus, which may be attributed to larger spatial distribution. Also, helminth species composition among localities correlated significantly negatively with geographic distance between localities, with a higher rate of decrease of similarity of helminth assemblages with an increase in geographic distance in R. pumilio than in R. dilectus. It is evident that spatial variation in helminth infections and community structure of helminth assemblage are dependent on a complex interplay of host and parasite related factors, compounded by environmental variation.

AFRIKAANSE OPSOMMING: Beskrywende inligting vorm die basis vir breër ekologiese vraagstukke en speel 'n belangrike rol in studies wat poog om patrone in parasietverskeidenheid, verspreiding en spesies-samestellings bloot te lê. Inligting oor parasietvoorkoms verskaf basieseinsette vir die opstel van verspreidingskaarte wat waardevol kan wees met die identifisering van siekterisiko en proaktiewe siekte bestuur. Huidige kennis van helmint-gasheer en helmint-lokaliteit assosiasies by kleiner soogdiere in Suid- en suider-Afrika is tans gebrekkig. Daar bestaan dus onsekerheid oor die vormingseffek van gasheer- en omgewingsfaktore op helmint infeksies en gemeenskapstrukture binne ‘n klimatologiese diverse landskap. Ten einde hierdie gebrek van inligting aan te spreek het hierdie studie ten doel: (1) om beskrywende inligting oor helmint-gasheerverhoudings en die ruimtelike en temporale verspreiding van helmintparasiete wat met klein soogdiere geassosieer is, te bepaal, (2) deur die gebruik van twee naverwante knaagdier gashere, Rhabdomys pumilio (Sparrman) en Rhabdomys dilectus (de Winton), as toonbeelde, te bepaal of tussen-gasheerspesies verskille in helmint infeksies hoofsaaklik veroorsaak word deur sosialiteitsvlak (sosiale R. pumilio teenoor enkellopende R. dilectus) of verskille in omgewingstoestande (meer xeriese R. pumilio teenoor die meer mesiese R. dilectus); (3) om die effek van sosiale en ruimtelike gedrag van R. pumilio en R. dilectus op parasietgemeenskapsorganisasie met verwysing na mede-voorkoms en genestheid, te ondersoek en (4) om faktore verantwoordelik vir ooreenkomspatrone van helmintspesie- samestellings van R. pumilio en R. dilectus te te verken. Vanuit ten minste 16 spesies van knaagdiere, klaasneusmuise en skeerbekmuise (n = 1079), is 168433 helminte, wat 56 helmint taksa verteenwoordig, versamel. ‘n Totaal van 26 helmint genera, bestaande uit 16 rondewurm, nege lintwurm en een akantokefalied is gevind. Die helmintspesies met die hoogste voorkoms was die rondewurm Heligmonina spira (133.8 ± 13.5), wat dan ook die volopste (26.1%) was. Rhabdomys dilectus was besmet met 19 rondewurm en 7 lintwurm spesies, en R. pumilio, 10 rondewurm en 5 lintwurm spesies. Sewe helmintspesies (4 rondewurm en 3 lintwurm) het by beide knaagdierspesies voorgekom, maar elk was ook besmet met unieke helmintspesies. Oor die algemeen was monoxenous (direkte lewensiklus) rondewurms teenwoordig in hoër getalle in vergelyking met heteroxenous (indirekte lewensiklus) ronde- en lintwurms. Verskeie nuwe helminh-gasheer- en helmint-lokaliteit rekords, asook verskeie moontlik tot nog toe onbeskryfde en dus vermoedelik nuwe helmintspesies, is aangeteken. Lewenssiklus-spesefieke geografiese verspreidings is gekarteer vir monoxenous en heteroxenous rondewurms. Helmintinfeksies het ruimtelik en seisoenaal verskil met betekenisvolle hoër volopheid en voorkoms gedurende die maande wat volg op die reënvalseisoen. Met tussen-gasheervergelykings het lintwurm asook rondewurm volopheid, spesiesrykheid en voorkoms nie beduidend tussen R. dilectus and R. pumilio verskil nie. Die insidens of trefwydte van rondewurm infeksie was egter aansienlik meer by R. dilectus as by R. pumilio. Binne-gasheerspesies vergelykings het getoon dat rondewurm volopheid en spesiesrykheid van helmintinfragemeenskappe beduidend laer was by R. pumilio wat die droër Karoo bioom bewoon in vergelyking met dìe woonagtig in die relatief minder droër Fynbos bioom. Algemene patrone vertoon deur helmint mede-voorkomste was eenders (positief) by beide gasheerspesies. Positiewe assosiasies het egter versterk met toename in gemiddelde aantal helmintspesies by R. dilectus en met infeksie-volopheid by R. pumilio. Die relatiewe frekwensie van positiewe en negatiewe paarsgewyse spesie medevoorkomste (slegs positief by R. dilectus en beide postief en negatief by R. pumilio) het tussen die twee gasheerspesies verskil. Van die twee gasheerspesies het slegs R. pumilio genestheid-verwante patrone van sy helmint infragemeenskappe getoon (hoofsaaklik teen-genestheid), terwyl die teenoorgestelde die geval was by die helmint komponente gemeenskappe (slegs genestheid-verwante patrone is gevind met R. dilectus). Die vlak van helmint infeksie was oor die algemeen geassosieerd met die bevestiging van nie-toevalligheid by die samestelling van helmintversamelings. Samestellings van helmintspesies het grootliks oorvleuel tussen R. dilectus and R. pumilio, maar het steeds beduidend verskil tussen die twee gasheerspesies. Daar was meer ooreenstemming by beide gasheerspesies in helmint-infragemeenskappe tussen individue vanaf dieselfde lokaliteit as tussen die van verskillende lokaliteite of biome. Diè patroon was dan ook meer beslis so by R. dilectus, heel moontlik as gevolg van die gasheerspesies se groter ruimtelike verspreiding. By beide gasheerspesies het tussen-lokaliteit helmintspesie-samestellings beduidend negatief gekorreleer met geografiese afstand tussen lokaliteite, met ‘n hoër tempo van afname van ooreenkomste tussen helmint-samestellings met ‘n toename in geografiese afstand by R. pumilio as by R. dilectus. Dit is duidelik dat die ruimtelike variasie van helmint infeksies asook gemeenskapstrukture van helmint-samestellings afhanklik is van ‘n komplekse wisselwerking van gasheer- en parasietverwante faktore, met omgewingsvariasie as ‘n bykomende oorsaak.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/102653
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