Lecture 19 Arthropods and Echinoderms Flashcards
Phenotypic plasticity is
the ability of one genotype to produce more than one phenotype when exposed to different environments.
Parthenogenesis
a form of asexual reproduction in which the embryo develops and without the fertilization by sperm. Some species reproduce exclusively by parthenogenesis (such as the bdelloid rotifers), while others can switch between sexual reproduction and parthenogenesis.
Notochord
an elastic rod-like structure derived from the embryonic mesoderm and found in many deuterostome animals. Species that have a notochord at any stage of the life cycle (along with other features) is, by definition, a chordate. It develops dorsal to the gut tube and ventral to the neural tube.
Describe Myriapods “countless feet”
- 2 body regions
– Head with one pair of antennae, simple eyes, two jaws (lower and upper)
– Trunk (segmented) - Centipedes (Chilopoda)
– 1 pair of appendages per segment
– Carnivores (poison containing fangs)
– ~3,000 species - Millipedes (Diplopoda)
– 2 pairs of appendages per segment (each visible segment is a pair of fused segments)
– detritivores, herbivores
– ~11,000 species
Describe Chelicerates
- 100,000 species
- Includes horseshoe crabs, pycnogonids (sea spiders), arachnids (spiders, mites, scorpions)
- 2 body regions:
- cephalothorax – appendages
- abdomen – no appendages
- Scorpions and spiders unable to eat solid food b/c narrow gut, expell enzymes to partially digest prey
- no jaw (mandibles) and no antennae
- Mainly predators
- Sexes are separated
Six pairs of appendages:
* # 1 (chelicerae) – fangs
* # 2 (pedipalps) – pincers,sensory organs, locomotion.
* # 3, 4, 5, 6 – walking legs (4 pairs of walking legs)
Sea spiders (Pycnogonids)
-Not true spiders
-Often in shallow waters
-Long legs, vestigial abdomen
-Mostly carnivorous or scavengers
-Separate sexes
-Reproduce externally
Describe Crustaceans
- crabs, crayfish, barnacles, shrimp, isopods…
- 47,000 species
- dominant marine, but also in freshwater & terrestrial environments
- Larger harvested, smaller ones form one of the biggest biomass
- make up large part of “zooplankton”
- head + thorax (cephalothorax) + abdomen
- appendages off each segment
- Separate sexes (few hermaphroditic, few (barnacles) have asexual reproduction)
- Insects could be considered evolutionarily within Crustaceans
Describe Daphnia in Crustacean
- Freshwater cladoceran
- Zooplankton
- Important trophic link
- Phenotypic plasticity
- Model organism for toxicology and ecological genomics
- Reproduces by cyclical parthenogenesis
Cyclical Parthenogenetic Life Cycle and Obligate Parthenogenetic Life Cycle
Typical: parthenogenetic cycle under favored conditions; sexual under harsh conditions
Obligate: lost sexual ability. Miosis supressed in females. Few vestigial functional son
Describe Copepods
- Small crustaceans
- Zooplankton
- Important trophic link
- Feed on algae, phytoplankton
Describe Insects
- Abundant on land and in freshwater, but few marine species
– One million species described
– Dominate terrestrial environments - 3 body regions:
– Head with antennae, mouthparts (e.g., mandibles), compound eyes.
– Thorax with 3 pairs of walking legs may have wings (one or two pairs)
– Abdomen with no appendages - Sexual reproduction with separate sexes and metamorphosis (direct or indirect)
Unique to insects: external mouthparts
– herbivores, detritivores, fluid-drinkers, predators, scavengers, parasites
Diversity in mouthparts adapted for different feeding modes:
A: grasshopper (chewing)
B: bee (lapping)
C: butterfly (siphoning)
D: mosquito (sucking)
Describe the innovation of wings in insects
Outgrowth of exoskeletons
Fundamental classifying chara. for insects
Wings evolved ~ 320mya
Wings on 2nd and 3rd thoracic segments
The wing of an insect and the gill of a crayfish are homologous (pdm gene).
Describe homologous and analogous
Structures are homologous when they have a common ancestral root
Analogous structures have the same function and often similar appearance but different ancestry
Seven key orders of insects
- Coleoptera (beetles)
- Lepidoptera (butterflies, moths)
- Diptera (flies, mosquitoes, midges)
- Hymenoptera (ants, bees, wasps)
- Hemiptera (true bugs, aphids, cicadas)
- Orthoptera (grasshopers, crickets)
- Odonata (dragonflies, damselfies)
Note: Wings important in insect taxonomy, lost to a few, membraneous to hardened
Hemiptera (cicadas) lifecycles
13-17 years stay as larvae. Adults live 4-6 weeks
Describe ecosystem services of insects
- Perform important ecosystem services
– Pollination by native insects
– Decomposers: dung burial by dung beetles
– Biological control of pests
– Food source for other mammals, birds, fish
– Dispersal agents (seeds, pathogens, other invertebrates) - Insects are experiencing a sharp decline in biomass and diversity;
- This trend is worldwide
Result from insecticides, habitat loss, degeneration, pollution
Recall the differences between Protostomes & Deuterostomes
