The Diversity of Parasite Species Lecture Notes PDF

The Diversity of Parasite Species ❑Reading ▪ Chapter 2- pp 21-35; 43-64 ❑The Diversity of Parasite Species I. Species concepts II. The tree of life III. Eukaryote classification 1) Protozoan parasites 2) Metazoan (animal) parasites IV. Insights into parasitism from the study of...

The Diversity of Parasite Species ❑Reading ▪ Chapter 2- pp 21-35; 43-64 ❑The Diversity of Parasite Species I. Species concepts II. The tree of life III. Eukaryote classification 1) Protozoan parasites 2) Metazoan (animal) parasites IV. Insights into parasitism from the study of diversity 1 The Diversity of Parasite Species I. Species concepts ❑Biological species concept (BSC) ▪ A group of individuals with similar properties that interbreed with each other or could possibly breed under natural conditions and are reproductively isolated from other such groups ▪ BSC emphasizes absence of gene flow ▪ Applicable to many parasite species but there are some problems associated with its definition 2  The Diversity of Parasite Species I. Species concepts ❑Biological species concept (BSC) ▪ Some problems with the BSC with respect to parasites: ‒ Asexual species→ reproduction by binary fission; some protozoan parasites are not known to undergo sexual reproduction (e.g. Entamoeba) or rarely undergo sexual reproduction (e.g. Giardia → distinct clonal lines) ‒ Horizontal (lateral) gene transfer → one organism acquiring genetic information from another organism without being the offspring of that organism (e.g some parasitic nematodes & bacteria) ‒ Cryptic exchange of gametes- e.g. Trypanosoma & Leishmania ‒ Hybridizing species- the interbreeding of closely related species (e.g. Fasciola hepatica x Fasciola gigantica, 3 Schistosoma hematobium x Schistosoma bovis)  Detection of cryptic gamete exchange in Trypanosoma brucei Fluorescence microscopy of tse tse fly salivary gland 4 Case study: Pennisi, E. 2019. Hybridization may give some parasites a leg up. Science 361: 832-833 Cercariae penetrate host skin Eggs excreted with host urine Life cycle of Schistosoma hematobium 5 Pennisi, E. 2019. Hybridization may give some parasites a leg up. Science 361: 832-833 Cavu River ‒ In 2014, physicians in France & Germany began reporting cases of schistosomiasis → diagnosis revealed that the causative agent was Schistosoma hematobium ‒ The disease was traced back to travellers who visited the Cavu River, Corsica ‒ DNA analysis from infected patients showed that the parasite eggs were a hybrid of S. hematobium x S. bovis which originated in Senegal ‒ A local Corsican snail (Bulinus truncatus) was apparently serving as a suitable intermediate host ‒ An infected person(s) from Africa likely released the parasite’s eggs into the water ‒ S. hematobium miracidia does not infect Corsican snails but the hybrid miracidia readily does so ‒ Studies also revealed that the hybrid develops faster and has greater pathogenicity than either of the parental species 6  The Diversity of Parasite Species I. Species concepts ❑ Morphological species concept (MSC) ▪ A group of individuals that is morphologically, distinct from other groups in some important characteristic ▪ Most commonly used by taxonomists because it relies on structural features & is widely applicable 7  The Diversity of Parasite Species I. Species concepts ❑Morphogical species concept (MSC) ▪ Some problems with the MSC: ‒ Phenotypic variation → variability exists in a population (e.g. sexual dimorphism → not all members of the same species look alike) ‒ Cryptic species → different undescribed species that have been incorrectly classified and grouped together since they have similar appearance ‒ Phenotypic plasticity → a single genotype produces different phenotypes, depending on the environment ‒ The MSC is subjective → lump similar organisms together or split? This can result in underestimation or overestimation of species numbers 8  The Diversity of Parasite Species I. Species concepts ❑Evolutionary species concept (ESC) ▪ A group of interbreeding organisms, reproductively isolated from other lineages, that has distinct, beginning, an end, and a shared evolutionary trajectory ▪ Combines aspects of phylogeny (evolutionary history of an organism) together with aspects of the BSC ▪ A lineage is an ancestor-descendant series of populations followed over time ▪ Cannot be used if the evolutionary history of a taxonomic group has not been carefully studied 9  The Diversity of Parasite Species I. Species concepts ❑Evolutionary species concept (ESC) ▪ Sources of information that can be derived from living (and sometimes fossil) material include: ‒ Comparative morphology- organismal structures, including developmental ones ‒ Comparative biochemistry- mtDNA, rRNA, amino acid sequences ‒ Molecular clock → relies on the constant mutation rate of particular DNA sequences (e.g. DNA barcoding in animals → mitochondrial cytochrome c oxidase 1 (CO1); for plants → chloroplast genes (e.g. rbcL or Mat K) ‒ Comparative cytology- chromosome number, shape, size, etc 10  The Diversity of Parasite Species II. Tree of life- describes the relationships between organisms on Earth ‒ 3 domains of life based on rRNA sequences 11  Relationships among the major groups of eukaryotes [Stramenopila-Alveolata- Rhizaria (SAR) lineage] 12  The Diversity of Parasite Species III. Eukaryote classification ❑Stramenopila-Alveolata-Rhizaria (SAR) Lineage ▪ Stramenopila (Heterokonts) ‒ Motile stages possess two unequal flagella ‒ Chloroplasts, when present, are comprised of four membranes ‒ Mainly free-living (e.g. diatoms, golden & brown algae) but some parasitic forms (e.g. oomycetes or water molds) ‒ Blastocystis (parasitic) & Chilomastix (commensal) are present in the human gut Phytophthora infestans Blastocyctis hominis Chilomastix mesnili 13  The Diversity of Parasite Species III. Eukaryote classification ❑Stramenopila-Alveolata-Rhizaria (SAR) Lineage ▪ Alveolata ‒ Possess flattened vesicles/sacs (alveoli) which lie beneath the cell membrane; mitochondria with tubular cristae ‒ Comprises many important groups which cause human & animal diseases [e.g. Apicomplexa (mostly parasitic-.e.g Plasmodium, Toxoplasma), ciliates (e.g. Balantidium coli, Ichthyophthirius multifilis), dinoflagellates (Pfiesteria piscicida) “Ich” or “ick” Balantidium coli Ichthyophthirius multifilis Pfiesteria piscicida 14  The Diversity of Parasite Species III. Eukaryote classification ❑Stramenopila-Alveolata-Rhizaria (SAR) Lineage ▪ Rhizaria ‒ Mostly unicellular eukaryotes having pseudopods, some produce skeletons ‒ e.g. Cercozoa, Foraminifera (free-living), Polycystinea, Phytomyxea (parasites that cause plant galls), Acetosporea (e.g. Haplosporidium nelsoni) Haplosporidium nelsoni Marine foraminifera 15 Multinucleate Sphere Unknown X  The Diversity of Parasite Species III. Eukaryote classification ❑ Archaeplastida Lineage ▪ Glaucophyta (microscopic, unicellular FW algae- e.g. Glaucocystis), Chloroplastida (e.g. green algae & all land plants), Rhodophycaea (red algae) ▪ Some forms are parasitic on other algae Glaucocystis Spirogyra Lilium ❑ Excavata Lineage ▪ Unicellular eukaryotes possessing a mitochondrion or a highly derived mitochondrion (e.g. mitosome) or structures associated within mitochondrion (e.g. kinetoplast) ▪ Many parasitic groups, most are flagellated [e.g. Trypanosoma, Leishmania, Giardia, Histomonas, Trichomonas, except 16 Dientamoeba (no flagellum)]  The Diversity of Parasite Species III. Eukaryote classification ❑Amoebozoa Lineage ▪ Locomotion via pseudopodia ▪ E.g. Entamoeba histolytica, Endolimax, Acanthamoeba, Balamuthia Endolimax E. nana Balamuthia B. mandrillaris nana cyst trophozoite mandrillaris cyst trophozoite ❑Opisthokonta Lineage ▪ Cells possess posteriorly directed flagellum ▪ Fungi & Animalia 17  The Diversity of Parasite Species III. Eukaryote classification ❑Opisthokonta Lineage ▪ Kingdom Animalia- mobile, multicellular heterotrophs − Approximately 36 animal phyla − Parasitism is thought to have arisen independently at least on 60 occasions in animals ▪ 3 major monophyletic clades of animals: 1) Deuterostomia- radial cleavage; first opening (blastopore) to form during embryonic development becomes the anus 2) Lophotrochozoa- one of the major grouping of protostome (radial cleavage; first opening to form becomes the mouth) animals; possess trochophore larva or lophophore feeding apparatus (e.g. Mollusca, Platyhelminthes, Annelida, Bryozoa, Brachiopoda) 3) Ecdysozoa- protostome animals with tough outer cuticle that 18 is shed by molting (e.g. Nematoda, Arthropoda, Onycophora) Overview of animal phylogeny showing selected parasitic groups covered in this course (dashed lines) 19  The Diversity of Parasite Species III. Eukaryote classification ❑ Opisthokonta Lineage ▪ Horizontal (or lateral) gene transfer (HGT or LGT) may have played a role in the evolution of some parasitic animals − LGT is the lateral transfer of genetic information between organisms without sexual reproduction or other conventional modes of reproduction (i.e. parent to offspring) − Increasing evidence suggests that some parasites have obtained genes from symbiotic organisms that occupy the same host − Symbionts may provide genes that allow parasites to exploit novel metabolic pathways & DNA repair 20 mechanisms  Meloidogyne incognita (root knot nematode) acquired cellulase and pectinase genes from plant microbes → breaks down cell wall Meloidogyne incognita Onchocerca volvulus filarial larva “River blindness” Onchocerca adult worm “River blindness” (cross section) Wolbachia-filarial nematode LGT LC= lateral cords Wolbachia-derived genes are important for worm O= ovary growth, metabolism & reproduction Red stain = Wolbachia Wolbachia-derived molecules contribute to the bacterium pathogenesis of human onchocerciasis 21  The Diversity of Parasite Species IV. Insights into parasitism from the study of diversity 1) Phylogenetic affinities of enigmatic parasites are revealed ‒ Determined by examining nucleic acid sequences (e.g. rRNA, mt DNA) Pentastomids (tongue worms)=parasitic crustaceans Argulus (fish louse) Linguatula Armillifer * Closer morphological examination reveals sperm morphology of Pentastomids is similar to Argulus → supports molecular data 22  The Diversity of Parasite Species IV. Insights into parasitism from the study of diversity 2) How particular parasites came to infect humans ‒ Humans are parasitized by 2 different genera of blood- sucking lice: Pediculus humanus (body louse) and Pthirus pubis (pubic louse) ‒ Chimps and gorillas each have only 1 species of louse, Pediculus schaeffi and Pthirus gorillae, respectively ‒ Time of divergence from the common ancestor of Pediculus and Pthirus, and between humans and primates was estimated from DNA sequencing ‒ Generate hypotheses using phylogenetic trees as to 23 how humans acquired 2 louse species  Body, head & pubic lice of humans Pediculus humanus Pthirus pubis Pediculus humanus corporis captitis 24 Phylogenetic trees for primates and anopluran lice 25 Hypothesis about how humans acquired 2 louse genera Humans & chimps acquired Pediculus from a common ancestor ~ 5-6 mya Phylogeny of humans, chimps, gorillas & OW monkeys Common ancestor of humans, gorillas & chimps Estimated time of divergence between Pthirus pubis & Pthirus gorillae is ~3-4 mya → host switch Pediculus humanus is referred to as an “heirloom parasite” Pthirus pubis is referred to as a “souvenir parasite” 26 Parasite-host species transfers inform hominin evolution 27 Perry, G.H. 2014. Evol. Anthropol. 23: 218–228.  The Diversity of Parasite Species IV. Insights into parasitism from the study of diversity 3) Reconstructing historical biogeography ▪ How geology, ecology, climate or human activities influence the distribution of parasites ▪ Example: Schistosoma mansoni is a trematode which causes schistosomiasis in Africa as well as South America ▪ S. mansoni is native to Africa but molecular & historical data suggest that schistosomiasis was not present in the New World until the 1600s → how did the parasite get to the New World? ▪ Adult worms reproduce in the veins draining the intestine of humans → eggs excreted with host feces into water → miracidia larvae → snail intermediate host (Genus: Biomphalaria) → cercariae larvae exit snail → penetrates skin of human host ▪ Ancestral Biomphalaria species are thought to have originated in South America 28 Historical biogeography of S. mansoni 3 possible scenarios (a, b, c) that may explain how the South American freshwater snail genus Biomphalaria became established in Africa & then became an intermediate host of Schistosoma mansoni Proc. R. Soc. Lond. B. 2000. 267: 2351-2358 29 Trans-Atlantic slave trade Species of Biomphalaria which evolved in Africa & are hosts of Schistosoma mansoni 30 The trans-Atlantic slave trade in the 16th century introduced schistosomiasis from Africa to the New World Huyse, T. 2014. Africa Atlanta 2014. Ivan Allen College of Liberal Arts, Georgia Tech. What is this mechanism of evolutionary change? Coloured dots represent different genetic populations of S. mansoni 31  The Diversity of Parasite Species IV. Insights into parasitism from the study of diversity 4) Cataloguing & revealing parasite diversity ▪ DNA barcoding- identifies unknown biological specimens, typically using “signature” mitochondrial DNA sequences [e.g. cytochrome c oxidase I (COI)] for animals and then comparing to known sequences in molecular sequence databases ‒ Useful for cataloguing cryptic species (e.g. Trichinella spp., Anopheles spp., trematodes of fishes) Trichinella spiralis Anopholes culicifacies At least 9 species of Trichinella have 5 cryptic species of 47 additional Diplostomum been identified- each Anopholes identified with species found in the St. have different life different distribution, host Lawrence based on CO1 histories preferences, etc 32  The Diversity of Parasite Species IV. Insights into parasitism from the study of diversity 4) Cataloguing & revealing parasite diversity ▪ Metagenomics (eDNA)- genetic material (DNA or RNA) isolated from a ”bulk” sample without the need to culture or isolate all the individual organisms in the sample ▪ Genetic material isolated from the environment it is referred to as environmental DNA (eDNA) Alexandrium minutum (dinoflagellate) Amoebophyra (a parasite of A. minutum) 33  The Diversity of Parasite Species IV. Insights into parasitism from the study of diversity 5) Improving parasite taxonomy ▪ Nucleic acid sequence analyses complement traditional morphological characterization & can reconcile traditional taxonomy with phylogenetic relationships ▪ Molecular phylogenetic methods are useful for parasites since distinguishing morphological features may be absent or obscure − Myxozoan parasites were formerly classified as protozoa → now classified as parasitic Cnidaria Cnidarian nematocyst Myxozoan spore with coiled (myxospore) with thread coiled polar filaments 34  Atkinson et al 2018. Zoology 129: 66-68 Whirling disease in trout caused by infection with Myxobolus cerebralis https://www.cabi.org/isc /datasheet/73782 35  The Diversity of Parasite Species IV. Insights into parasitism from the study of diversity 5) Improving parasite taxonomy ▪ Many parasites exhibit homoplasy (=convergent evolution) in morphological structures - e.g. ectoparasitic flatworms of the Family Capsalidae → 4 members of the subfamily do not form a monophyletic clade when analyzed at the molecular level Homoplasy of anterior attachment organs of the family Capsalidae (Phylum Platyhelminthes) The taxonomic goal is to identify synapomorphies→ shared, evolutionarily- derived character traits that show patterns of common descent 36 Improving trematode taxonomy Originally, Orientobilharzia & Schistosoma were distinguished by the number of testes and placed in different clades……. ….however, after molecular analysis, O. turkestanicum is now called Schistosoma turkestanicum and is placed in the same clade 37  The Diversity of Parasite Species IV. Insights into parasitism from the study of diversity 6) Revealing important intraspecific variations ‒ Isolate- a sample of a parasite species taken from a host at a specific point in time (e.g. Plasmodium falciparum 3D7 isolate) ‒ Subspecies- a population of organisms within a species that occupy a particular geographic region and are genetically distinguishable from other populations of the same species. They can interbreed with other subspecies populations where their ranges overlap but normally do not (e.g. Trypanosoma brucei brucei, Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense) ‒ Strain- an intraspecific group of parasites that differ in one or more traits from other such groups → more often used by microbiologists to isolate genetic variants such as traits relevant to pathogen control or disease treatment in the host 38  The Diversity of Parasite Species IV. Insights into parasitism from the study of diversity 6) Revealing important intraspecific variations ‒ Intraspecific diversity can be revealed using microsatellite analysis → typically uses short tandem repeat (STR) sequences (~2-6 bp long) from non-coding regions of the genome 39 39  The Diversity of Parasite Species IV. Insights into parasitism from the study of diversity 6) Revealing important intraspecific variations ▪ Three subspecies of Trypanosoma brucei: T brucei brucei, T. brucei gambiense and T. brucei rhodesiense are morphologically indistinguishable but have different vectors & hosts ▪ The T. brucei complex ‒ Trypanosoma brucei brucei (Tbb)→ causes Nagana or animal trypanosomiasis ‒ Trypanosoma brucei gambiense (Tbg) → West African or Gambian Sleeping Sickness in humans ‒ Trypanosoma brucei rhodesiense (Tbr) → East African or Rhodesian Sleeping Sickness in humans *Why is it important to distinguish between subspecies of T. brucei as it relates to human disease? 40 Distribution of T. brucei gambiense & T. brucei rhodesiense West African or Gambian Sleeping Sickness East African or Rhodesian Sleeping Sickness 41  The Diversity of Parasite Species IV. Insights into parasitism from the study of diversity 6) Revealing important intraspecific variations ▪ Trichostrongylus colubriformis ‒ Primarily a nematode parasite of grazing herbivores which is responsible for significant economic losses ‒ Human infections are rare but can occur when food or drinking water is contaminated with infective stage larvae 42 Intraspecific variation of carbohydrate surface antigens of Trichostrongylus colubriformis Isolates of T. colubriformis have different carbohydrate surface antigens as revealed by immunohistochemistry Antibodies raised against E1 antigen and E2 antigen each recognize their specific carbohydrate antigens → important implications for vaccine design 43  Immunohistochemistry is used to localize specific antigens in cells & tissues Green fluorophore (e.g. Red fluorophore Green Fluorescent Protein) (e.g. Texas Red) Fluorophore bound to secondary antibody Goat Anti-rabbit IgG (secondary antibody) Rabbit IgG E1 antibody E2 antibody (primary antibody) which recognizes Target a specific antigen antigen E1 antigen E2 antigen Parasite surface (purple) is covered by specific antigens → an effective vaccine must recognize a specific parasite antigen, then neutralize it 44