Arthropod Diversity
- Myriapods
- Crustaceans
- Chelicerates
- Hexapods
Myriapods
- Chilopoda (centipedes)
- Diplopoda (millipedes)
Chilopoda (centipedes)
- 300 species
- 1 pair of appendages per segment
- carnivores
Diplopoda (millipedes)
- 11,000 species
- herbivores and detrivores
- 2 pairs of appendages per segment
Chelicerates (Horseshoe carb, sea spider, spiders, scorpians))
- Merostomata (Horseshoe carb)
- Pycnogonids (sea spider)
- Arachnids (spiders, scorpians) Scorpians shine blue under UV
Chelicera
Two appendages next to mouth
Pedipalps
Used for warning/sexual selection
Crustaceans (Isopods, Thecostraca, Decapods, Cladocerans, Copepods)
Isopods - Wood lice Thecostraca - Barnacles Decapods - Shrimp, crayfish, lobster Cladocerans - Water flea like Daphnia Copepods - Zooplankton
Body Plan: Crustaceans
- 5 pereiopods are used for swimming
- 5 pleopods which are legs
- carapace which covers and protects cephalothorax and abdomen
Hexapods
- Most diverse group
- 73% of all animal species are insects
- In a common house, insects are most abundant in arthropods
Homologous (same ancestor) mouth parts that evolved into different functions
- Sucking/Siphoning (butterfly, cicada)
- Chewing (grasshopper, beetle)
- Lapping (bee, housefly)
Wings evolved - 320 MYA
- Ancestral multi-branched appendages –> modern crayfish –> Drosophila
- House fly: posterior wings are not retained
- Butterfly: have scales on wings
Respiration (Insects, Decapods, horseshoe crabs, spiders/scorpions):
Insects: O2 comes in the trachea and spiracles circulates O2
Decapods: have gills protected by carapace, water flow allows O2 exchange
Horseshoe crab: Book gills at the back
Spiders/Scorpions: Book lungs at the lamella, allow high surface area to volume ratio
Metamorphosis - Arthropods
- Transformation from one to other body types
- Moulting enables changes in morphology
- Each intar produces a new exoskeleton
- insects cease moulting as adults, crustaceans do not
- 2 types of metamorphosis insects: complete & incomplete
- Many eat the exoskeleton they just shed
Incomplete Metamorphosis
- indirect/ hemimetabolous metamorphosis
- wings not developed until 3rd/4th nymphs
- Nymphs resemble adults
Complete Metamorphosis
- gradual/ holometabolous metamorphosis
- involves changes in larvae
- exoskeleton hardens
- larvae looks completely different from adult
Chagas disease
- More common in South America, can result in death after a few years
- An individual gets infected by feces of the insect
Wigglesworth’s experiment on R. Prolixus
Result: Hormone in the head causes moulting
Hormones
- Chemical messengers secreted by endocrine cells
- distributes by blood, bind to target receptor to produce a response
How do hormones work? (3)
- change the permeability of the cell
- alter the activity of an existing enzyme
- affect the expression of the gene
Types of chemical signals (3) (autocrine signals, paracrine signals, endocrine signals)
- Local hormones that do not travel through the whole body
Autocrine signals: act on the same cell that secretes them
Paracrine signals: diffuse locally and act on neighbouring cells
Endocrine signals: are hormone carried btwn cells by blood or other body fluids
Hormones - 2 pathways
- Neuroendocrine
- Neuroendocrine to endocrine pathway
Both: Hypothalamus - pituitary - peripheral hormone glands
3 main families of hormones
- Peptides and Polypeptides - not liquid soluble, attach to messengers on cell membrane
- Amino acid - not liquid soluble, attach to messenger on cell membrane
- Steriods - liquid soluble, can go through membrane
PTTH (brain hormone)
- stored and produced in brain
- production influenced by environmental cues
- controls activity of prothoracic gland
- triggers periodic release of ecdysone
