Ecdysozoa: Nematodes & Pan-Arthropods - BIO1427

Ecdysozoa: Nematodes & Pan-arthropods

• Course: BIO1427
• Recording date: 8.2
• Lecturer: Jolyon Troscianko

Learning Objectives

• Understand key features of basal Ecdysozoa: Nematoda, Tardigrada, and Onychophora
• Understand the niche and ecological importance of Nematodes
• Understand the life cycle of key nematode parasites and their interaction with hosts
• Understand the basics of pan-arthropods

Warning

• Images of parasitic worms and their hosts may be present in the material
• Content may not be considered "beautiful" natural history

Ecdysozoan Phylogeny

• Ecdysozoa is a broad animal group in Bilateria.
• Mouth develops first during embryonic development (protostomes)
• Includes nematodes, tardigrades, and arthropods
• Cambrian group split from other protostomes ~510 million years ago
• Roughly 83% of all bilaterians
• Includes over 1.2 million named and extant species (likely many more total)

Nematoda (Roundworms)

• Over 18,500 species, possibly up to 1 million
• Half of them are parasitic
• Common examples: C. elegans, human pinworm, dog roundworm, hookworm, heartworm, and canine whipworm

Nematode Basics

• Abundant in various environments, including marine sediment (up to 4 million individuals/sq meter)
• Essential for nutrient cycling
• Important in a wide range of habitats (ocean sediment, soil, inside plants and animal tissues, hot springs and polar ice)

Fungi trapping & consuming nematodes

• Some fungi prey on nematodes by trapping them in nets or nooses
• They release chemical cues to attract nematodes toward food sources

Nematode body plan

• Typically cylindrical, but some parasites can be large (e.g., Placentonema gigantissima)
• Covered by a tough, elastic cuticle
• No circulatory system, but nutrients are moved via pseudocoelom fluid
• Longitudinal muscles for undulatory movement

Flatworms vs. Annelid worms

• Flatworms are flat, lack a coelom, and move via cilia
• Annelid worms are segmented, have both circular and longitudinal muscles for movement

Caenorhabditis elegans

• Model organism in developmental biology
• Simple, transparent, and easily manipulated
• Entire development of every single cell mapped out, >4.5 million scientific papers published
• Used in research but medical models frequently fail for human results even with success in mice

Loiasis (Loa loa)

• African eye worm disease
• 12-13 million people infected
• Transmitted by deer fly bites
• Passes back into the deer fly via infected blood
• Treatable, but therapy can be dangerous for humans

Lungworms

• Important parasites of cattle
• Transmission occurs through soil, and ingestion of contaminated material
• Can cause serious illness in infected cattle

Accidental Hosts

• Certain roundworms (e.g. Ophidascaris robertsi) are normally in carpet pythons
• Humans can be accidental hosts, usually by contact and consumption of contaminated food

Anthelmitic eco-toxicity

• Anti-worming drugs used on farm animals
• Can negatively impact non-target organisms (e.g., dung beetles).
• Reduces prevalence of cattle nematode infections and pest flies

Hygiene hypothesis

• Connection exists between sanitized environments and inflammatory autoimmune diseases
• Lack of early exposure to pathogens may reduce immune system's resilience
• Th1 vs. Th2 response balance linked to autoimmune diseases

Ecdysozoa: Arthropods & their Cuticles

• Key features of arthropods
• Process of moulting and structure of arthropod cuticle & epicuticle
• Benefits and limitations of a rigid exoskeleton
• Sensory adaptations in arthropods

Arthropod Cuticle

• Thin outer layer (epidermis) with outer cuticle (procuticle, exo- and endocuticle).
• Epicuticle is thin at joints to allow for moulting
• Dermal glands secrete waxy layer after moulting

Epicuticle

• Covered by hydrophobic lipid or wax layer
• Reduces dehydration in terrestrial groups
• Used in signalling/recognition

Procuticle

• Primarily chitin (polysaccharide)
• Sclerotisation with cross-linking proteins makes cuticle darker
• Crustaceans add calcium carbonate to further strengthen cuticle

Arthropod musculature

• Have striated muscle bundles for movement
• Attached to epidermis and the hard cuticle
• Apodemes provide attachment area

Arthropod Exoskeleton

• Made of plates connected by articulation membranes
• Often has condyles and sockets for joints.

Arthropod Movement

• Muscle contraction used for locomotion and manipulation
• Exoskeleton acts as lever and joints
• Blood pressure in some cases moves body parts

Arthropod Hematocoel

• Filled with hemolymph
• Fluids transport some nutrients, hormones, and immune system components

Arthropod Conquest of Land

• Evidence suggests arthropods moved onto land in the early Cambrian period
• Exoskeletons were likely crucial for adapting to terrestrial environments (reducing desiccation, providing support for movement)

Arthropod Sense Organs

• Exoskeleton limits detection of stimuli, and requires sensilla for sensory input
• Different eye types found (pit eyes, camera eyes, compound eyes)
• Provide rapid directed feedback
• Complex visual systems evolved in the Cambrian

Arthropod Visual Adaptations

• Varied colour receptors, polarization, extreme low-light and speed vision
• Visual system requires large energy investment