Animal Diversity and Adaptation Notes

Module Introduction

  • Module focuses on animal diversity and adaptation.
  • Reference to http://tolweb.org/tree/ for phylogenetic information.
  • Origin of animals is obscure.
  • Prokaryotes are not considered more 'primitive'.
  • Arthropods are a dominant group.
  • Horizontal gene transfer occurs.
  • Origin of organelles is discussed.
  • Annelids (e.g., earthworms) are used as examples of animals.
  • Table 1 refers to a list of ranks used in the hierarchy of classification, with the number of taxa per rank (Ruggiero et al., 2015).

Diversity and Classification

  • Addresses the challenges of dealing with the vast diversity of life.
  • Questions whether we can name and classify everything, even to the level of phylum, class, or order.
  • Raises the issue of how much we know about the basic biology and ecology of different species.
  • Table 2 presents catalogued and predicted total number of species on Earth and in the ocean (Mora et al., 2011).

Kingdom Animalia

  • Animals are also known as Metazoa.
  • Over 1.1 million described species, with a predicted 9.92 million species actually present, meaning >88% are yet to be described.
  • There are far more animal species than plant species.
  • The number of parasitoid wasp species exceeds 100,000.
  • Example given of Dinocampus coccinellae parasitoid wasp attacking a ladybird beetle.

Defining Animals

  • Most animals are:
    • Multicellular.
    • Generally large compared to protozoans.
    • Heterotrophic: consuming herbivores, carnivores, parasites, and detritivores.
    • Motile (capable of movement).
    • Body polarized along an anterior-posterior locomotory axis.
    • Possess muscle and nervous systems.
    • Have epithelia.
    • Have an extracellular matrix (and connective tissue).
    • Conserved extracellular signalling pathways.
    • Employ sexual reproduction.

Size Comparison

  • Fig. 1 compares the size of the smallest insect (Megaphragma mymaripenne) with two protozoans (Paramecium caudatum and Amoeba proteus).
  • Scale bar for the images is 200 μm.
  • Reference to Alexey A. Polilov's work on the smallest insects evolving anucleate neurons.

Animal Characteristics

  • Animals are heterotrophs, contrasting with primary (autotrophic) producers like green plants (photoautotrophs).
  • Animals include decomposers, herbivores (insects are dominant), predators, and parasites.
  • Many animals move actively through the environment, exhibiting anterior-posterior differentiation/patterning during embryogenesis.
  • Animals possess epithelia, an extracellular matrix (ECM), and connective tissue.
  • The ECM includes collagens, proteoglycans, and adhesive glycoproteins like integrins.
  • Conserved extracellular signalling pathways are present.
  • Sexual reproduction is a common characteristic.

Sexual Reproduction

  • The existence of sexual reproduction is considered an outstanding puzzle in evolutionary biology.
  • Advantages of sexual reproduction:
    • Reduction of the effect of deleterious mutations.
    • Rapid adaptation to changing environments.
    • Parasite-host coevolution in the maintenance of sexual reproduction.
  • Asexual and sexual life cycles in Daphnia are referenced (Ebert, 2005).

Module Details

  • Module title: Animal Diversity and Adaptation.
  • Module leader: Sarah Perkins.
  • Deputy module leader: Pablo Orozco ter Wengel.
  • Assessment lead: Wynand van der Goes van Naters.
  • Assessment: 50% exam and 50% coursework.
  • Exam format: 3-hour exam with two parts (90 minutes each).
    • Part 1: Short answers, data analysis, and interpretation.
    • Part 2: Two essays (from a choice of 6).
  • Exams are on-site, invigilated, and limited open book.
  • Seven courseworks/practicals planned, with two assessed.
    • Question in Animal Diversity essay (25%).
    • Physiological and behavioural adaptations: susceptibility of moth morphs to predation (25%).
    • Questions in Animal Diversity: group presentation (formative).
    • Taxonomic keys (formative).
    • Canimalcules (formative).
    • Fish Form and Function practical (formative).
    • Visit to zoo (formative).

Recommended Reading/Sources

  • A list of recommended books and sources is provided, including:
    • Ten Million Aliens by Simon Barnes.
    • Invertebrates by Richard C. Brusca, Wendy Moore and Stephen Shuster.
    • The Invertebrate Tree of Life by Gonzalo Giribet and Gregory Edgecombe.
    • The Diversity of Fishes: Biology, Evolution and Ecology by Helfman, G. et al.
    • An Introduction to Behavioural Ecology by Nicholas Davies et al.
    • A Review of the Population Status of British Mammals, and technical summary, by Fiona Mathews et al.
    • Organism and Environment: Ecological Development, Niche Construction, and Adaptation by Sonia Sultan
    • Invertebrate Zoology: A Functional Evolutionary Approach by Edward Ruppert et al.
    • An Introduction to Molecular Ecology by Graham Rowe, Michael Sweet and Trevor Beebee (2017)
    • Animal Behaviour by Dustin Rubenstein and John Alcock.
    • The Animal Kingdom: A Very Short Introduction by Peter Holland.
    • Molecular Evolution: A Phylogenetic Approach by Page et al.
  • Full references and links available via a specified URL.

Questions and Engagement

  • Students are encouraged to ask questions during and after lectures.
  • Students can contact lecturers for help, after attempting to find answers themselves.
  • Lecturers' contact details are available on Learning Central.
  • Students are encouraged to read and investigate as much as possible about animals and engage with lectures, workshops, and practicals.
  • The module aims to be enjoyable.

Additional Resources and Topics

  • References to ocw.mit.edu, Australian Institute of Marine Science, Wes Skiles, Natl Geographic, and Vectorbase.org.
  • Photo credits to WvdGvN.
  • Insects, Chelicerates (ticks, spiders), crustaceans, and corals/hydra are mentioned.
  • Reference to Srivastava et al., 2010 Nature doi:10.1038/nature09201.
  • Biology of several invertebrate groups: Wynand van der Goes van Naters photo credits
  • Topics covered in lectures include:
    • Animal adaptation
    • Sponges / Cnidaria
    • Flatworms
    • Molluscs
    • Worms (2)
    • Chelicerates / myriapods
    • Insects (2)
    • Nematodes
    • Vertebrate beginnings
    • Sharks
    • Bony fish
    • Fish evolutionary trends
    • Amphibians
    • Reptiles
    • Birds (2)
    • Mammals (2)
    • Phylogenetics / Phylogeography (2)
    • Molecular markers
    • Population Genetics (3)
    • Physiol / Behavioural Adaptation (2)
    • Parasitology
    • Chemical Senses
    • Animal senses and communication
    • Eusociality
    • Temperature and Life (2)
    • Predator psychology and prey warning signals
    • Behavioural ecology
    • Foraging behavior
    • Adaptations (2)

The Emergence of Vertebrates (Dr. Siân Griffiths)

  • Lecture 1: Chordates: Vertebrate beginnings. Introduction to early fish, including the evolution of hagfish and lampreys from Urochordates and Cephalochordates.
  • Lectures 2 & 3: Sharks and Rays (cartilaginous fish) vs the Bony Fish (teleosts).
  • Lecture 4: Your Inner Fish! The story of fish evolution reveals the origin of human body anatomy (jaws, skulls, air breathing, lobe-fins and walking).
  • Amphibians and Reptiles –Rhys Jones
    • The evolution of amphibians from fish.
    • Anura, Caudata, Gymnophiona
    • Origins. Basic structure and function: The Cleidoic (amniotic) egg. Extant reptile forms
    • Reptile diversity

Animal Evolution

  • Molecular data shows that animals form a monophyletic clade ('Animalia' or 'Metazoa').
  • Reference to http://tolweb.org/tree/.
  • Origin is obscure.
  • Prokaryotes are not more ‘primitive’.
  • Arthropods dominate.
  • Horizontal gene transfer occurs.
  • Origin of organelles.
  • Annelid of today shown as an example of animals.
  • Animals evolved from a choanoflagellate (collared flagellate, single-celled) like ancestor.
  • The advantage of coloniality may have been the sharing of nutrients in a colonial choanoflagellate.

First Animal

  • We don't know for sure what the first animal was.
  • It lived >600 MYBP.
  • May have resembled 1 mm long Trichoplax.
  • Trichoplax is the only member of the phylum Placozoa.
  • It has two layers of cells and six cell types.
  • Reproduces by fission but has evidence of gametes.
  • No gut; the underside absorbs microorganisms.
  • Has homologs for most (83%) gene families also found in sea anemones and bilaterians.

Trichoplax Feeding

  • Trichoplax feeding on Rhodamonas salina microalgae is shown.
  • Reference to Smith et al. (2015) on coordinated feeding behavior in Trichoplax.
  • Animal diversity in geological time shows a 'sudden' diversification of animals with the first animal fossils ~600 MYBP.

Early Animal Fossils

  • Earliest animal fossils from the Precambrian period (c. 600 MYBP).
  • These were soft-bodied, marine organisms that were mostly suspension or detritus feeders.
  • Their relationships to extant phyla are unclear, but some may have been Cnidaria (jellyfish, corals, etc.).

Cambrian Explosion

  • The Cambrian Explosion occurred around 544 MYBP.
  • This involved a sudden appearance of a diversity of marine forms.
  • The best fossils are found in the Burgess Shale, Canada.
  • Many animals developed hard body parts (calcareous exoskeletons).
  • Some animals were clearly predatory.
  • Seas became more highly oxygenated.
  • Break-up of Pannotia increased the area of shallow seas.
  • More potential niches were available than in deeper oceans.

Pannotia and Pangaea

  • Pannotia broke up.
  • Break-up of Rodinia occurred around 750 Ma.
  • Formation of Pangea, which existed from 335-175 Ma.
  • A simplified sketch of the break-up of the supercontinent Pangaea over the past 180 Myr is referenced.
  • tectonics.caltech.edu is mentioned as a resource.

Phylogeny and Evolution

  • The lecture discusses basal phyla.
  • It covers Lophotrochozoa, Ecdysozoa, Protostomes, and Deuterostomes.
  • The concept of a Trichoplax-like common ancestor with distinct cell types is introduced.
  • Evolution of 3 germ layers (mesoderm is included), i.e., triploblastic + Clear head & tail ends, i.e., cephalisation + Bilateral symmetry (radial symmetry of echinoderms is a derived trait).
  • Also includes 2 germ tissue layers (ecto- & endoderm) – i.e., diploblastic + No clear head or tail ends + Either no symmetry or radial symmetry

Homology and Analogy

  • Forelimbs of different vertebrates are homologous; They are derived from a 5-digit (pentadactyl) limb.
  • Homology implies common ancestry.
  • Insect wings are analogous to bat and bird wings.
  • Convergent evolution between placental and marsupial mammals is noted, with the Australian marsupial fauna radiating in isolation from placentals.
  • It's a response to similar selection pressures.

Convergent Evolution

  • Response to similar selection pressures, e.g., cacti & other succulents / cetaceans & fishes.
  • Limpets and barnacles are classified based on their dome-shaped armoured covering; however, the armoured covering has a different origin in the two animals (i.e., analogous not homologous).
  • There has been phenotypic convergence between limpet (mollusc) & barnacle (crustacean) – due to selection pressure of wave/current action.
  • Barnacles share homologous features with crabs (common arthropod ancestry).
  • The armoured covering has a similar origin.

Phylogeny Accuracy

  • The correct phylogeny is the one that reflects genetic relationships.
  • Taxa may resemble one another for three reasons:
    • (i) The character arose early on in the ancestry of the taxa, before the occurrence of the nearest common ancestor (e.g., jaws in amphibians, reptiles, birds, and mammals).
    • (ii) The character originated in the nearest common ancestor = shared character e.g. jaws for jawed fish + amphibians + reptiles + birds + mammals; e.g. advanced lungs for amphibians + reptiles + birds + mammals; e.g. amniotic egg for reptiles + mammals + birds.
    • (iii) The character originated independently, by convergence; similarity due to convergence is known as homoplasy (i.e., not derived from a common ancestor). Another way of saying this is that these are analogous structures and not homologous structures (e.g. elongated shape in eels).

Derived Characters

  • Characters acquired by, and restricted to, a phyletic line after it branched off from its sister-group are unshared derived characters.
  • Mammary glands in mammals are an example.
  • Feathers in birds (but not when both extinct & extant vertebrates are considered).
  • Unshared characters define each particular taxon (end-branch).