BIOL 371: Theme 2 - Animal Diversity and Classification

clades

groups of organisms which are all descended from a unique common ancestor, exhibit certain characteristics inherited from said common ancestor and don’t share with organisms outside of the clade, share synapomorphies/shared derived characters/homologies

nest within one another, some are more inclusive or exclusive

opisthokonts

single, posterior (opisthios) flagellum (kontos), flattened cristae (folds) in mitochondria (but variable), eg. animals, fungi, choanoflagellates

choanoflagellates

unicellular, opisthokont, eukaryotes, sessile (planted/don’t move), reproduce asexually, closest to Animalia among opisthokonts

“collar” around flagellum consists of contractile microfibrils, currents set up by flagellar action carry food particles into collar, trapped and carried down to cell (filter feeding)

choanocytes in Porifera (sponges) strongly resemble individual choanoflagellates

opisthokont animals

origin - theory that ancestral animal was descended from a colonial choanoflagellate, multicellular eukaryote, chemoheterotrophic, extracellular digestion, no cell walls, contact between adjacent cell membranes, motile (self-directed movement), oxidative phosphorylation to supply ATP

4 diagnostic characters of animals

1. develop from a blastula and undergo gastrulation (sac within a sac)

2. cell membranes contain cholesterol

3. certain extracellular matrix molecules, eg. the proteoglycan collagen

4. certain cell-cell membrane junctions, eg. tight/septate, anchoring, gap

archaeplastida

eg. plants, multicellular eukaryotes, photoautotrophic (mostly) - fix organic carbon to be biologically useful using light energy, cell walls (no contact between cell membranes), sessile, alternation of generations life cycle

systematics

the science of classification of the living world, including fossil forms, organisms classified based on inferences of evolutionary relatedness (genetics, morphology, physiology, behaviour, heritable traits - shared derived characters), today we use cladistic principles to derive phylogenies for the groups that we are classifying

shared derived character (homology)

a character (morphological, behavioural, molecular) found in all members of a group of species that is derived from a character found in the common ancestor of that group of species

must be careful to avoid using characters that are similar in different organisms, but were not derived from a common ancestor, instead produced by convergent evolution

monophyletic taxa

includes an ancestral species and all of it's descendants

polyphyletic taxa

includes species from different evolutionary lineages, does not include the most recent common ancestor

paraphyletic taxa

includes an ancestral species and only some of its descendants (some are excluded)

parsimony

the likeliest phylogeny is the one requiring the least amount of proposed evolutionary change in a character

linnean classification

implicitly based on presumed rough phylogenies, usually map well onto later phylogenies, nested (species < genus < family), today members are assumed to be clades, they share a more recent common ancestor with each other than with members of other such groups

difficult to accomodate modern findings with linnean system, groups such as archaeoplastida or opisthokonta are clades that lie above the kingdom level but below the domain level

Ediacaran Fauna

635-541 Mya (before cambrian explosion), simple multicellular “animals,” uncertain affinities, some have been identified as animals because cholesterol has been isolated from their fossils

The Cambrian Explosion

refers to sudden appearance of diverse complex fauna, apparently without antecedents, ~525 Mya, slow diversification, small shelly fauna, represents an evolutionary radiation of Animalia

Burgess Shale fauna

525-515 Mya, first diverse fauna of large complex multicellular animals, first recognizable representatives of most modern animal phyla, first fauna with jaws and eyes (sense organs) and largely bilaterian component (right, left, head, tail ends)

homeotic genes

specify the development of specific structures at particular locations during embryogenesis, responsible for symmetry, antero-posterior and dorsal-ventral axes, establish segmentation, appear to be strongly conserved among Animalia, eg. Hox genes

may have enabled rapid diversification of body forms

hox genes

a special class of homeotic genes

animal classification

a major monophyletic group originally distinguished by a unique basic body plan, grouped into more inclusive higher order groups based upon general shared derived characters

animal characters

symmetry, developmental patterns, body cavities (coelom), body segmentation

asymmetric

no major axis of symmetry

radial symmetry

body can be cut into identical pie segments, no right or left, no anterior or posterior

bilateral symmetry

body has mirror-image left-right symmetry, group called bilateria

diploblastic

two embryonic tissue layers - ectoderm and endoderm

triploblastic

three embryonic layers - ectoderm, mesoderm, and endoderm

acoelomate

no cavity enclosing the gut

pseudocoelomate

cavity enclosing the gut lined with mesoderm on outer side

coelomate

gut suspended in cavity lined with mesoderm on both sides

metameric segmentation

repeating, chordates, arthropods, annelids, both protostomes and deuterostomes, may be highly modified, eg. insects

dorsal-ventral orientation

of central nervous system and main elements of circulatory system, both protostomes and deuterostomes

molecular evidence

a good cue for classification, DNA and proteins are now the primary source of information about phylogenies, chance of convergent evolution is not likely

bilaterians

under metazoa, divided into protostomes and deuterostomes

protostomes

bilaterian (metazoan), a superphylum, the most diverse animal group determinate spiral cleavage, schizocoely, mouth derived from blastopore, lophophores (u-shaped feeding structure)

includes lophotrochozoans and ecdyzoans

deuterostomes

bilaterian (metazoan), a superphylum, indeterminate radial cleavage, enterocoely, anus derived from blastopore, mouth develops from a second opening

includes enchinodermata, hemichordata, chordata

phylum ctenophora

comb jellies, diploblastic, biradial symmetry, sister group to all other animals (still being argued), gelatinous body, “combs” are rows of fused cilia that are used in locomotion

phylum porifera

acoelom, asymmetrical sponges, sessile as adults (no nerves, filter feeders), parazoans, no extracellular digestion (choanocytes)

parazoans

no true tissues, neither diploblasts nor triploblasts, eg. porifera

choanocytes

coordinated flagellar action produces inward water current, suspension feeders - choanocytes filter food particles out of water, very similar to choanoflagellates, found in porifera

phylum cnidaria

radial symmetry, diploblastic, jellyfish, sea anemones, coral, hydra, life cycles generally incorporate both polyp and medusa stages (body forms), have cnidocytes and nematocysts

cnidocytes and nematocysts

a shared derived character of cnidaria, special cells on the tentacles used to capture prey

siphonophores

colonial cnidarians composed of several different types of individuals, modified for different functions

corals

an example of siphonophores, colonial cnidarians that build calcareous or proteinaceous skeletons

lophotrochozoans

protostomes, some phyla have a trochophore larva and some phyla have a lophophore feeding structure

includes phyla platyhelminthes, mollusca, and annelida

phylum platyhelminthes

protostomes (lophotrochozoans), acoelomates, parasites and predators (absorbs nutrients through skin, invade host’s intestines), gut has only one opening (no anus), gut branches throughout body, triploblastic

phylum mollusca

protostomes (lophotrochozoans), 100 000 species, 1mm to over 10 m in size, body organized into foot, mantile, and visceral mass, unsegmented by some evidence of earlier segmentation, considerable morphological variation among major groups

phylum annelida

protostomes (lophotrochozoans), worms, segmented - metamerism, hydrostatic skeleton

ecdyzoans

protostomes, growth is through ecdysis of the cuticle or exoskeleton

shedding: shared derived morphological and development character, acellular - secreted by epidermal cells

includes phyla nematoda and arthropoda

phylum nematoda

protostomes (ecdyzoans), pseudocoelomate, unsegmented, no limbs, important as parasites, soil fauna, eg. pinworms, hookworms, can cause elephantiasis (lymphatic filariasis - nodes can’t drain lymph) or trichinosis, exoskeleton!!

phylum arthropoda

protostomes (ecdyzoans), joined chitinous (chitin - a polysaccharide) exoskeleton, segmented body, metamerism, jointed limbs, at least one pair of legs per segment, they can lose limbs if they don’t have a function (modification, eg. mouth parts were once limbs but modified), tagmatization

tagmatization

fusion of body segments, exhibited by most arthropods

phylum echinodermata

deuterostomes, bilaterally symmetrical larve, pentaradiate (5) symmetry as adults (eg. sea star), water vascular system and tube feet - change water pressure, tubes to ocean

phylum hemichordata

deuterostomes, pharyngeal gill slits, dorsal nerve cord, stomochord (thought to be homologous to notochord), no skeleton

phylum chordata

deuterostomes, all have 4 characteristics - notochord, dorsal hollow nerve chord (neural tube), perforated pharynx (gill slits), segmented muscles with post-anal tail

subphylum - cephalochordata, urochordata/tunicata, vertebrata

cephalochordata

subphylum under chordata (deuterostomes), posses the 4 chordate characteristics, but lack a heart, liver, blood cells and respiratory pigments, which are found in other chordates

urochordata/tunicata

subphylum under chordata (deuterostomes), have all the characteristics of chordates at some point in their life histories, flexible outer body, cover, the tunic, branchial basket for food collection and gas exchange

vertebrata

subphylum under chordata (deuterostomes), possess the chordate characteristics at some point during their lives, vertebral column and a cranium/skull, internal skeleton