Lec 3 / Lec 4 - Zooplankton

Rotifers:

Difficult to see, needing more protection

Polymorphisms

  • Can find in species with allorica, which causes their epidermus to have hard shapes, and create these spines. In relation to change in body form, which is induced in the presence of predators.

  • These can be pssed down onto offspring, daughter cells depending on exposure to predators.

Clocedera:

  • Distinct head

Copepoda

General characteristics:

  • 2 sets of Antenna - 1st long, 2nd antenna is short (Use to detect surroundings and not swimming)

  • Tubular

  • Dont have a distinct head

  • Move fast and rapidly

Calanoids

  • Specialised 5th leg - Assymetrical on males, long to wrap around female. The fifth legs need to be spcies specific.

Feeding:

Cyclopoids:

  • Raptorial - Won’t clean lakes

Life cycle:

  • Normal life cycle - Meiosis

  • Eggs are carried by female externally

  • Go through 5 moults, before going through metamorphisis and becoming an adult.

Distribution of Calanoid Copepoda:

  • 9 native species found in New-Zealand

  • 4 calanoid species

  • Native species tend to have distinct distributions, seemingly related to geological history.

  • Grass carp, spreading invasive species.

No Polymorphisms: Don’t need protection

Change in shape of the body form, by differential growth of peripheral structures of the body, which is determined by the exposure to predators. These are typically seen as spines.

What do spines do?

  • Stop getting eaten.

Cladocerans

  • Seen to increase in head size, and tail length.

  • Grows spines externally.

Why not always have spines, to protect themselves?

There is a cost:

One with spines, decreases death rate and birth rate. This is due to more energy going towards producing thes estructures and not toward reproduction.

How do they get spines?

Moults

Diel vertical migrations:

Avoiding mortality by fish:

Cladocerns show distinct diel vertical migrations over long distances. They do this, becuase at the surface there is more food, they then sink down to darker areas to prevent predation, to not be seen by fish. So constant vertical migrations up and down, for food and prevent predation.

  • Morning - Day - Night

Invertebrate - Hunt by touch

Fish - Hunt by sight

Four main evidence for mortaility avoidance:

  1. Animals that are vsiually seen more, pigmented, carrying eggs, will need to migrate more to prevent visual predation.

  2. Migration amplitude depnds on the clarity of the water, so if the lake is dirty, it will no need as much vertical migration as its difficult to see tehm, compared to clear areas.

  3. Fish abundance affect amplitude, if there is an abundnace on fish there will be alot of zooplankton migrations, compare to an are with less fish as there is less predation risk.

  4. Inducible by providing predator cue, introcucing predator cues that will impact their migrations.

  5. Kairomones

Cyclomorphosis

Changes in body form through time

Three groups of calanoids:

  • Calenoid - Long antennae to swim (Open water)

  • Cyclopoid - Half length of body antenna’s (Mixed environment of open and movement through plants)

  • Harpacticoid -