Unformatted text preview: Phylum Porifera (pore-bearers) Sponges PHYLUM PORIFERA ( = pore-bearer) bearer) Sponges Sponges Cellular grade Loose aggregation of cells Cells fairly independent Can reaggregate Major Features: Determined to be animals ~200 years ago ~8- 10,000 species Cellular grade of construction All aquatic – mostly marine All Sessile – can move some Size – 1-2cm ! >1m Size 2cm Symmetry – most have none, some ~radial some Early in fossil record, but don’t give rise to others Early “dead-end” phylum – but very successful phylum Unique Water Canal System OSTIA: water goes in OSCULA: water exits important for feeding, respiration, reproduction and excretion All processes depend on DIFFUSION All DIFFUSION No nervous system Poor development of contractile system Water goes OUT the Osculum Water OUT and IN the Ostia and IN SPONGIN: Protein secreted by lophocytes tough – resistant scleroprotein – bath sponges – Endangered in most parts of the world due to over harvesting Spongocoel = space within the sponge Massive CaCO3 secreted outside of the body probably secreted by epithelium has silicious spicules as well 1 3) POROCYTES (surround OSTIA) guard ostia not in all sponges 4) No Nerve or Sensory Cells but can receive sensory input by cell-cell communication 5) CONTRACTILE = MYOCYTES in mesoglia have contractile elements contact each other by filopodia - can result in coordinated behavior 6) CHOANOCYTES and FEEDING COLLAR CELLS read Sherman & Sherman & Brusca and Brusca have flagella inside collar made of pseudopodia creating microvilli flagellum creates water current food trapped in microvilli, phagocytized no coordination or coordinated movement among choanocytes choanocytes show up in other groups as well 7) MESOHYL Between outer epithelial cells and collar cells Filled with organic jellylike EXTRACELLULAR MATRIX, supports delicate cells Polysaccharide with fine fibrils Reproduction Asexual GEMMULES – resting stage, mostly in fresh water spp. formed from amoebocytes hard skeleton of spicules or spongin FRAGMENTATION/BUDDING – pieces break off, form new individual, have great regeneration abilities Sexual HERMAPHRODITIC sperm and eggs usually mature at different times (sequential hermaphroditism) Both gametes shed, fertilization in water or sperm shed into water, eggs retained sperm enter choanocyte – carried to the egg in the mesohyl Development BROODING – retained fertilized embryos/larvae Free swimming LARVA (Plural = LARVAE) - flagellated Amphiblastula larva 2 GENERAL BODY PLAN - three types SYCONOID ASCONOID – simplest structure Body – Radially Symmetric Thin Body Wall Surface Pores ! ATRIUM (= PERIGASTER) main central cavity lined with collar cells Osculum at top generally small in size example: Leucosolenia Body folded to form radial flagellated canals Atrium reduced in size, no longer with flagellated cells Increase in flagellated areas/body mass ! more efficient movement of water More Cells feeding/unit time Allows larger size asconoid syconoid LEUCONOID most complex has NO ATRIUM flagellated canals invaginated to form flagellated chambers most common type can be very large draws more water and greater feeding surface area than other types CLASSIFICATION CLASSIFICATION
still in flux, unknown evolutionary relations among groups because se very ancient very Class CALCAREA - calcareous sponges Class CaCO3 spicules, No Spongin spicules spicules mon-, tri-, or hexaxial all 3 body plans, all marine, mostly shallow, some deep leuconoid 3 Class DEMOSPONGIA - demonsponges Class SiO2 Spicules or Spongin or Both spicules mon-, or tetraxial primarily 95% of known species, 95% Marine and All Freshwater Sponges Leuconoid body plan only Leuconoid largest group of sponges SCLEROSPONGIA = Coralline Sponges - now classified with Coralline now demosponges - unclear how relate to others SiO2 spicules and Spongin and an outer casement of CaCO3 spicules and CaCO Mostly fossils, live discovered by Hartman and Goreau in 1970 Mostly Goreau very deep water, all leuconoid Fun with Sponges – Ecology, Physiology, Behavior Class HEXACTINELLIDA = Glass Sponges only have SiO2 only SiO spicules always hexaxonal always hexaxonal Bulk of Body SYNCYTIAL NETWORK skeleton rigid, attached to hard substrate all syconoid, only marine, mostly deep water all syconoid can form large reefs – shallow water B.C. can Hydrodynamics and feeding Symbiosis (mutualism) Zoochlorellae – green algal symbionts Association with Scallops (Bloom 1974) Sponge – Scallop – Seastar – Nudibranch Nudibranch (-) ! Sponge " + ! Scallop "(-) Seastar Motile escape response of a sessile prey Better Living Through Chemistry contain some of the most toxic and biologically active chemicals in animals ALLELOCHEMICALS – influence competition for space (Jackson and Buss 1975) BORING (excavating) SPONGES – example Cliona bores into CaCO3 ! mollusc shells, corals 4 Self – Non-self Recognition considered fairly advanced – but very different from vertebrate systems Text considers 4 Phyla of Uncertain Affinity = we don’t know where to put them! and one, has only been seen once! Mesozoans: Lack tissues and organs Phylum Placozoa - we will discuss next Phylum Monoblastozoa - Described in 1892, but not seen since. Read about it in your text, but you are not responsible for it here. Two Phyla we will talk about later - entirely parasitic Phylum Rhombozoa Phylum Orthonectida Mix dissociated cells – will reaggregate - grafting parts of one sponge onto another TRY a similar experiment in lab. Bigger et al. 1982. Characterization of allo-immune memory in a sponge. J. of Immunology 129:1570-1572 Sponges possess a primitive immune memory - reject 2nd graft more quickly than the first - only persists 3-4 weeks PHYLUM PLACOZOA
First discovered in 1883 minute metazoan - similar to an amoeba Austrian seawater aquarium has now been found in many places BUT no idea about where they live in nature, what they feed on, etc. soft-bodied, about 0.5 - 3 mm across Trichoplax adhaerens Genome sequenced this past year - smallest amount of DNA in any metazoan Mitochondrial genome sequenced Largest mt genome of any metazoan Phylogenetic analysis puts placozoa at the base of the eumetazoa (metazoa other than sponges) Has genes that code for complex systems (e.g., nervous system) in other taxa Cellular grade Cellular four cell types can reproduce by fission, budding, do not know about sexual reproduction - but appears about likely given genetic diversity seen No anterior/posterior Two species described 5 Concepts and Comparison
Study of Biology divided into two modes: 1) Functional Biology – how do organisms work 1) Functional 2) Historical Biology – how and why has life come to be this way? 2) Historical Historical Biology Never really know answer – can only be inferred Never can Determine what the actual history of evolution has been Determine ANAGENESIS: directional change within a single line directional CLADOGENESIS: branching of phylogenic tree branching Phylogenetic relationships: evolutionary patterns of relatedness All animals are mosaics of characteristics – changing at different rates. ANCESTRAL: ( = PRIMATIVE) inherited without change DERIVED: undergone recent change Character states – the forms that a character may have PLESIOMORPHIC: ancestral character state APOMORPHIC: derived character state SYMPLESIOMORPHIC: ancestral character shared by many species SYNAMPOMORPHIC: derived character shared by two or more species How do we figure out how change happened? Can we figure out what Can characters are ancestral, derived? characters Classification = Taxonomy Categories = levels of classification Using the Linnean hierarchy Phylum Class Order Family Genus Species Systematics = Study of Relationships TAXON (Pl. = TAXA) = set of real organisms that fill a category Systematics determines evolutionary relationships among taxa. MONOPHYLETIC Groups = members derived from a single common ancestor A taxon is assumed to be a monophyletic group CLADE: entire portion of a phylogeny descended from a single ancestor Therefore is a single monophyletic group, but not necessarily a taxon 6 Systemic Constructions: POLYPHYLETIC: group with multiple unrelated ancestors mistakes made frequently due to convergence = similarity not due to common ancestor GRADE: group with the same level of structural organization Some taxa may actually represent grades rather than clades. - A taxon containing more than one clade = POLYPHYLETIC - A taxon that does not include all of the descendents of an ancestor = PARAPHYLETIC CLADISTICS: classification should express branching relationships, regardless of similarities or differences ! CLADOGRAM STRICTLY monophyletic classification PHENETICISTS: base classification on overall similarity ! PHENOGRAM may not portray phylogeny – convergences Convergent Evolution: same or similar character of independent origin same common when different species under similar selective pressures Parallel Evolution: similar pattern of evolution independent developmental modification of the same kind of Evolutionary Reversals: evolves one direction and then another evolves CONSERVATIVE = slowly evolving, shared in a similar slowly condition by all or most members of a group – may be due may to canalization to GENERAL ADAPTION = shared by many for a general shared function function SPECIAL ADAPTION = specific task HOMOLOGOUS – character state in 2 species inherited from common ancestry Homoplasy – independently evolved more than once – not independently not shared by common ancestry but both have it. shared 7 How do we attempt to estimate true phylogenies? How can we avoid being misled by convergences How or variation in evolutionary rate? or Particularly given a mosaic evolution Particularly – differences in rates of evolution of differences different characters within a lineage. different How do we construct phylogenies without being misled by things such as homoplasy and differences in evolutionary rates? Hennig: key to recognizing monophyletic groups – members share uniquely derived character states – Synapomorphies – that have arisen only once. How do we find primitive characteristics? Fossils? Embryology? Define homologies? Embryology? Use of Morphological Characters, Developmental Characters Molecular Characters --- more on this later Origins & Diversity of Metazoa
Today > 40 phyla of animals more have existed in the past more Fossil record - good for animals with hard parts - rare for soft animals hard Funtional Biology: How organisms work ADAPTATION: Futuyma - “a feature that – because it increases fitness, has been shaped by specific forces of natural selection acting on genetic variation” How do we test for adaptation? Because it looks like it “should be” does it mean it is? DEMONSTRATE a trait has been developed by natural selection and specify the nature of the selective agent or agents Very Hard!! 8 Gould and Vrba (1982) Paleobiology 8:4-15 APTATION: structure that has a certain function ADAPTATION: a structure with a given function that evolved for that purpose EXAPTATION: a structure with a given function that evolved for a different purpose. Exaptations can be co-opted by natural selection ! PREADAPTATION Not all features of organisms are adaptations. How do we determine if adaptive? 1) Determine Function 2) Compare design with engineering designs for optimal performance 3) Comparative method – correlate differences among species with ecological factors and phylogenetic analysis. Using these three – we can make predictions that constitute tests of hypotheses about adaptation. 9 ...
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- Fall '10
- Cladistics, Phylogenetics, Ostia, Sponges Sponges, Sponges Leuconoid body