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Nematode Sinusoidal Movement Major muscles are down dorsal and ventral sides. Contraction makes nematodes slide on their sides. Pushing force must exceed adhering force. Movement of nematodes in different thicknesses of water film Peristaltic movement of Criconemoides curvatum Rear end contracts Wave of contraction passes forward, pushes head forward Opposite of earthworm Backward-directed annules resist slipping backward Structure of the Stoma Relative to Feeding Nematodes eat living organisms or their tissues Feeding Behaviors Holophagic = bacteria, algae, yeasts, protozoa (A) Fluid-feeders = stylet pierces algae, plants, small fauna; sucks out contents (B, C, D) Predators capture prey and swallow whole or in parts (E) Animal parasites = primarily blood feeders (F, G, H) Stoma structure infers trophic position! Ingestion by Holophagic Feeding A - Contractions open lumen, negative pressure sucks in particles B - Muscles relax, lumen narrows, water goes back out mouth C - Wave of contractions move food particles into intestine Variations in Holophagic Feeding A - Panagrellus B - Ascaris C - Aplectana Pumping rate = 1-5/sec, bursts = 20/sec Nematode Esophageal Types Kathy Merrifield K. Merrifield www.fcps.k12.va.us J.D. Eisenback Nemapix 1 Some nematodes pierce the cuticle of prey with a stylet, inject enzymes and ingest the internal body fluids. (Seinura sp.) Fluid-Feeding Predators Fluid-Feeding Fungal Feeders Fluid-Feeding Plant Feeders Scott Edwards U. Wyss Fluid-Feeding Plant Feeders Locating Host Exploration = find roots by chance Attraction = respond to gradients in: CO2 exudates rhizosphere microbial products Attraction may reach ½ meter > mile in human scale U. Zunke Fluid-Feeding Plant Feeders Locating Feeding Site - Exploration of root = probe w/o puncturing - Head rocks side to side, papillae touch root - Arches body to bring stylet at right angles to root for maximum thrust - Polysaccharide plug may glue lips to root Fluid-Feeding Plant Feeders Stylet Penetration -Nematode penetrates cell wall with stylet -Only part of stylet used so many thrusts required, up to 2-6 thrusts/sec -Nematode may move head back and forth -Show film clip Fluid-Feeding Plant Feeders Ingestion -Pause after stylet penetration (1) -Enzymes may be secreated into cell for predigestion (2), 20 sec-2 hrs, cyclosis may stop -Median bulb pumps cell contents into esophagus (3) -Turgor pressure in cell may assist -Cell may collapse (4) -Feeding time/cell 1-5 min to 1 wk Fluid-Feeding Plant Feeders Ingestion -In other cases cyclosis may continue while cell is fed upon -Cell not damaged Fluid-Feeding Plant Parasites - Invasion Migratory ectoparasites – withdraw stylet, move to new cell, & repeat process Endoparasites – penetrate further into tissues Root-knot J2 collect behind apical meristem, perforate epidermal cell with stylet until cell wall collapses, push head inside = 3-24 hrs High populations = competition for invasion sites. J2 may follow in the same hole, enlarging it and the hole may become surrounded by necrotic cells. Fluid-Feeding Plant Parasites - Invasion W. Wergi Fluid-Feeding Plant Parasites - Invasion Enter through natural openings -Lenticels in potato tubers -Junctions between primary and lateral roots -Stomata in leaves Fluid-Feeding Plant Parasites - Tunneling -“Cut” holes through cell walls with stylet - Force between cells = “unzip” middle lamella (Root-knot, Meloidogyne) - Digest holes through cell walls with enzymes (Burrowing nematode, Radopholus similis) Fluid-Feeding Plant Parasites - Tunneling Movement through the root is periodic as the nematode occasionally stops to feed. D. Wixted Fluid-Feeding Plant Parasites - Feeding Endoparasites disrupt tissues during feeding Enzymes secreted = tissues enlarge, separate & collapse to form cavities (D) Specialized feeding cells are formed (E) = nurse cells (F) = giant cells Animal Parasites Discuss Later Nematode Reproduction “Sex of an individual depends on gamete produced” Sperm = male Eggs = female Both = hermaphrodite Eggs embryo w/o sperm = parthenogenic female Nematodes are extremely varied in their patterns of reproduction. Nematode Reproduction Amphimixis = eggs and sperm come from separate individuals during cross fertilization where male deposits sperm in reproductive tract of female. Most common type Males with a bursa align “parallel” to female Males without bursae align “perpendicular” to the female's body and the entire posterior region folds over and grasps the vulva. “Cement” may hold nematodes together. Nematode Reproduction Amphimixis Sex attractants aid males and females to find each other. Sedentary = only females produce Migratory = both sexes produce & respond Nematode Reproduction Under normal conditions, most amphimictic populations maintain a 1:1 sex ratio. Stress in environment can alter the sex ratio. Usually the response is to inadequate nutrition. Developing population = predominantly male. Differential survival, more female mortality. High temperatures, increased CO2 and accumulation of certain chemicals may also increase the ratio of males to females. Nematode Reproduction Automixis = self fertilization by hermaphrodites Egg and sperm come from same individual Syngonic hermaphrodites = eggs and sperm produced in the “same gonad” ovotestis. Sperm produced first, stored while eggs are produced. Fertilized as move towards uterus. Diagonic hermaphrodites have “separate structures” for producing eggs and sperm. Different gametes produced at same time. Nematode Reproduction Pseudomixis (pseudogamy) Participation of male gamete necessary for oocyte development but no fertilization. Facultative pseudogamy = unfertilized eggs become males, fertilized eggs become females. Redundant pseudogamy = sperm is deposited in reproductive tract but doesn't penetrate egg. Nematode Reproduction Parthenogenesis = “females beget females” Reproduction from unfertilized eggs without participation of a male gamete. Mitotic parthenogenesis = Retains the somatic number of chromosomes = no pairing of homologous chromosomes during prophase. Oocytes remain diploid. (n 2n without cell division = mitosis without cytokinesis) Nematode Reproduction Parthenogenesis = “females beget females” Meiotic parthenogenesis = two maturation divisions = Results in eggs that are haploid. Diploid condition restored by fusion of egg nucleus with nucleus of nonextruded polar body. Facultative meiotic parthenogenesis occurs in noninseminated females or non-fertilized eggs. Fertilized eggs = amphimictic development. Both processes can occur in same female. Nematode Reproduction Nematode Reproduction Oviparous = eggs released Ovoviviparous = living young released Endotokia matricida = eggs hatch in uterus, juveniles burrow through the uterus into the body cavity and feed on body of the mother. Nematode Reproduction Migratory nematodes eggs move down the ovary into the uterus and are laid one at a time as soon as they reach the vulva. Sedentary parasites eggs are in a cluster either outside (root-knot) or inside (cyst) the body. Most nematodes lay eggs in the soil but endoparasites lay eggs in the soil or inside plant tissues. Juveniles develop within egg, may go through one or two molts before hatching. Most hatch spontaneously as soon as they reach the end of embryonic development. Temperature and moisture regulate developmental time. Some plant parasites need stimulus such as elevated CO2, or root exudate to trigger hatching sequence. Some species require diapause During the hatching process, either the shell is softened by enzymes, or the nematode uses its stylet to puncture a hole in the shell.