Theme 2 Flashcards
Opisthokonts
- Animals, fungi, choanoflagellates
- single posterior (opisthios) flagellum (kontos)
- Flattened cristae in mitochondria (but variable)
Choanoflagellates
- opisthokont eukaryotes
- sessile
- closest to Animalia among opisthokonts
- “collar” around the 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
Origins of Opisthokont ANIMALS
Likely originated from a colony of choanoflagellates
Opisthokont ANIMALS
- Multicellular eukaryote
- Chemoheterotrophic
- Cell membranes contact adjacent cell membranes (no cell walls)
- Motile (capable of self-directed movement at some life stage)
- Oxidative Phosphorylation to supply ATP
- Sense and respond to the environment rapidly
- Extracellular digestion
- Sexual reproduction featuring eggs and sperm
- Sperm and eggs are single cells
- Diploid is dominant (usually), haploid short-lived
- 3 diagnostic characteristics, only found in animals: Develop from a blastula, Certain extracellular matrix molecules (e.g. the proteoglycan collagen), Certain cell-cell membrane junctions
Archaeplastida PLANTS
- multicellular eukaryote
- photoautotrophic (mostly) – fix inorganic carbon using light energy
- Cell walls– cell membranes not in contact
- Sessile
- Alternation of generations life cycle
- haploid (gametophyte) stage alternates with a diploid (sporophyte) stage
- both are prominent/multicellular
Secondary endosymbiosis:
- heterotrophic eukaryote cell engulfs symbiotic photoautotrophic eukaryote
- photoautotroph evolves into chloroplast with four membranes
Opisthokonts and Archaeplastida Diverge
- Cell Structures differ
- In plants, we see: cell wall, large vacuole, chloroplasts
- Photoautotrophs vs. chemoheterotrophs
- Mobility (in Plants): don’t need to move to acquire energy and carbon, but move in different ways i.e growing
- Mobility and motility (in Animals): Eat things to acquire energy and carbon, must be mobile (usually) to acquire food, many consequences of being mobile
- Most animals are diploid as the dominant stage with haploid stage reduced to unicellular gametes
- Alternation of Generations in land plants
Consequences of being mobile for animals:
- Muscle
- Well developed senses and cephalization
- Nervous systems
- Digestive system
- Excretory system – eliminate nitrogenous wastes
- Skeletal system – endo- and exo-, hydrostatic
locomotory mechanism - High metabolic rate – cells; requires bulk flow and gas exchange systems
Classification of Plants and Animals
- systematics is the science of classification of the living world (including fossil forms)
- Organisms classified/grouped based on inferences of evolutionary relatedness: genetics, morphology, physiology, behaviour, heritable traits – shared derived characters
- use cladistic principles to derive phylogenies for the groups that we are classifying
What is a clade?
a monophyletic group composed of taxa with a unique common ancestor and sharing synapomorphies (shared derived characters)
cladistic phylogenies are:
hypotheses, which estimate evolutionary relationships based upon distribution and congruence of synapomorphies
- can be used to make predictions about data not yet found (intermediate forms, fossil history)
the likeliest phylogeny is the one requiring the least amount of:
proposed evolutionary change in a character – the most parsimonious
History Of Animals – The Cambrian Explosion
- 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 eyes and jaws
- first fauna with bilaterian component
The Cambrian Explosion
sudden appearance of this diverse complex fauna, apparently without antecedents
Homeotic genes
Genes specifying the development of specific structures at particular locations during embryogenesis - responsible for symmetry, antero-posterior and dorso-ventral axes
Appear to be strongly conserved among Animalia
How do homeotic genes map onto phylogenies?
Predictions:
- strong relationship between chronological order of appearance of major groups, morphological complexity and body size, and number of homeotic genes
- unique body plans associated with unique homeotic genes
Hox genes
- linear cluster of homeotic genes involved in embryonic pattern formation
- number varies among taxa
- number increases with phylogenetic position and complexity (with some losses - insects vs crustaceans, myriapods)
- linear increase most parsimoniously explained by gene duplication
Strong inference that Cambrian Explosion closely associated with:
Elaboration of hox clusters. However, morphological complexity not directly correlated with Hox cluster complexity.
Most animal phyla was established in the:
Cambrian Explosion
Changes in homeotic genes and in gene regulation enabled:
Rapid diversification of body form - Cambrian Explosion represents an adaptive radiation of Animalia
Animal Classification: Tissue layers and Symmetry
- Ectoderm, mesoderm, and endoderm
- diploblastic (radial) have ecto/endoderm
- triplovlastic (bilateral) have ecto/meso/endoderm
Development of Bilateria
- Protostome (mouth first)
- Deuterostome (anus first)
Protostome
- Spiral cleavage
- Schizeocoelous coelom
- Blastopore forms the mouth
- Determinate cleavage
- Ventral nerve cord that surrounds the digestive tract anteriorly
Deuterostome
- Radial cleavage
- Enterocoelous coelom
- blastopore forms the anus
- Indeterminate cleavage
- Dorsal nerve cord, brain does not surround digestive tract
Protostomes are further divided into:
- Lophotrochozoans (some have a trochophore larva, some have lophophore feeding structure)
- Ecdysozoans (external cuticle that is shed to grow (ecdysis))
Other cues to taxonomy
- Body segmentation (metameric segmentation repeating: chordates, arthropods, earthworms)
- Dorso-ventral orientation of C.N.S and main elements of circulatory system
- Molecular evidence like DNA and proteins are now primary source of info about phylogenies
Phylum Ctenophora: The Comb Jellies
- Sister group to all other animals
- Gelatinous body
- “Combs” are rows of fused cilia that are used in locomotion
Phylum Porifera (sponges)
- Asymmetrical
- para(beside)zoans - no true tissues - neither diploblasts or triploblasts
- sessile as adults (no nerves, filter feeders)
- choancytes’ coordinated flagellar action produces inward water currents
- suspension feeders - choanocytes filter food particles out of water
- very similar to choanoflagellates
Phylum Cnidaria
- Radial (or biradial/rotational) symmetry, diploblastic
- jellyfish, sea anemones, coral, hydra (cnidaria)
Cnidocytes and Nematocysts
- Harpoon-like nematocysts are microscopic structures found in epidermis of cnidarians
- Contact triggers the ejection of nematocysts
- nematocysts of some cnidarians inject toxins into predators or prey
- some forms are colonial with specialized individuals
Phylum Rotifera
- 1mm, crown of cilia for feeding
Bilaterally Symmetrical
- Protostomes and Deuterostomes - all Triploblasts
- Protostomes - most diverse animal group
Phylum Platyhelminthes
Platy = flat, helminthe = worm
- scavengers, predators, ectoparasites, liver fluke, tapeworms
Phylum Mollusca
- calms, oysters, scallops, mussels, snails, octopi, squid
- all have head/foot, visceral mass, mantle
Phylum Annelida
- segmented worms
- earthworms, marine/bristle worms, leeches
Ecdysozoans
- external cuticle of chirin protects animal, must be shed for animal to grow, this is shared derived morphological and developmental feature that is secreted by epidermal cells
Phylum Nematoda
- roundworms
- v important in agriculture, medicine, and research
Phylum Arthopoda
- largest animal phylum
- arthro (joint), poda (feet), exoskeleton, segmented body
- insects, spiders/mites, scorpions, crustaceans, centipedes and milllipedes
Phylum Echinodermata
- echino (spiny) dermata (skin)
- starfish, urchins, sand dollars, brittle stars, sea cucumbers
- bilaterally symmetrical larvae
- pentaradiate (5) symmetry as adults
- water vascular system and tube feet
Phylum Hemichordata
Acorn worms
Phylum Chordata
- Supbphyla Urochordata, Cephalochordata, and Vertebrata
- notochord, pharyngeal gills silts, dorsal hollow nerve cord, segmented muscle/posr-anal tail
