lecture 13 - defensive strategies

Question 1

biotic vs abiotic threats

Answer 1

biotic:
- between same species or different
- living
- predators etc

abiotic:
- threat of wave action
- changes in temp or salinity
- things not from organisms

Question 2

predation as a major selective force

Answer 2

• Almost all organisms have predators
• Predators have a dramatic impact on fitness (no gene passing if dead)
• Predators rarely 100% successful

Question 3

biotic vs abiotic defensive strategies

Answer 3

biotic: coming from same (conspecific) or different species (predation) –> competition for space, resources, predation)

abiotic:
- threats of save action, change in salinity, etc
- NOT from organism

Question 4

predation as major selective force
- what makes predation a major selective force?

Answer 4

• almost all organisms have predators
• predators have dramatic impact on fitness (if prey dies, no genetic material passed on)
• predators rarely 100% successful –> the traits of the ones that survive will be passed on to future generations

Question 5

red queen hypothesis

Answer 5

definition: Prey and predators must continuously improve in performance just to survive over the long term

P-P interactions (predator/prey)

predator prey interactions are reciprocal and dynamic
– both organisms influencing selective environment of one another

arms race

Question 6

why is there asymmetry in strength of selection on predators & prey ?

Answer 6

• predator loses: simply misses dinner
• prey loses: loses life

asymmetry in selective force —> a lot more at stake for prey vs predator

• predator just doesnt get dinner, whereas prey loses life — natural asymmetry

Question 7

chart w phases of predatory act & selected defenses
- what are the phases of predation and explain them

Answer 7

search & detection
- self-explanatory

pursuit

subjugation (subdue)
- collected and eaten

Question 8

selected defenses against SEARCH & DETECTION phase of predation

Answer 8

camouflage (crypsis)

mimicry

hiding

activity patterns
- like DVM (of bobtail squid or zoop)

Question 9

selected defenses against PURSUIT phase of predation

Answer 9

Fast swimming/running

escape behaviours
- like tail flipping in lobsters

Question 10

selected defenses against SUBJUGATION phase of predation

Answer 10

armour
- like crab or gastropod shells

retaliation
- fighting back

toxicity

autonomy
- dropping a limb to distract

structural add ons
- creation of long spines –> such as zoop, where too big for predator

Question 11

induced defenses - definition and explanation

Answer 11

when organisms only have a defense mechanism at certain times - NOT always

induced by presence of predators - will stop growth etc to develop the defenses

can be combo of multiple different types (* Structural *Chemical
* Behavioural)

Question 12

components of gastropod shell

Answer 12

protoconch
- first part of shell developed in larval stage

whorl
- a cavity formed by calcium carbonate – laid down around central matrix

spire
- consists of all of the previously laid down whorls

body whorl
- most recently laid down
–> has aperture and apertural lip (outer lip of shell aperture)

Question 13

ways of being crushed

Answer 13

Apertural Lip Crush

Spire Crush
- small part in dactyle –> which is closer to condyle = more force to be crushed as the length output of lever arm is shorter (force advantage)

Apertural Lip Peel
- open like a can opener

Question 14

gastropod shell defenses against crushing predators

Answer 14

• Overall thickening of shell
• Thickened apertural lip
• Apertural teeth
  - waves where shell opening - adds thickness where can break
• Narrowed aperture
  - less likely to get cheliped in and pry open
• Reduced spire
  - if less pointy up top, less close to condyle (pivot point) - predator less
  advantage to crushing
• Thickened tubercles & varices
  - projections like spikes

Question 15

study done on tubercles (spines) - Palmer et al

Answer 15

tubercles are spines on gastropod shells

a porcupine fish preys on gastropods and has teeth that crush them

study done on 2 species of porcupine fish and 2 species of gastropods

3 things found looking at Effect of tubercles on crushing attempts:

Question 16

Palmer et al study

3 things found looking at Effect of tubercles on crushing attempts:

Answer 16

1) tubercles increase effective diameter
- reduce force advantage of jaws
- shell doesnt get as close to condyle (as far in mouth) so less force can be applied

2) tubercles allow the force to be distributed over a greater area (reduces stress on shell)

3) tubercles allow for the crusher to have less access to area, and the spines can damage predator
- this might be most important

Question 17

further findings of Palmer et al in relation to size of shell

Answer 17

tubercles allowed for the critical size of the shell to be smaller on average

a gastropod species w strong spines could have a smaller size overall, whereas the species with weak spines would require a larger shell to reach critical size

with weaker spines, the gastropod has to put in more energy and resources to growing to a larger size, w strong spines, need less size bc of these

Question 18

further study on tubercles (modification of shells)

Answer 18

filed off tubercles of shells and others had spines

the critical length of those with spines removed was needed to be larger than those with spines

Question 19

presence of spines on gastropods in different latitudes

Question 20

Number of fish families & species that crush molluscs
Tropical vs. Temperate

Answer 20

found high correlation between species that crush and tropical latitudes (68%)

temperate:
proportion of species crushers = 29%

Question 21

study showing evidence of convergence - gastropod shell defences

Answer 21

Lake Tanganyika - Tanzania

this freshwater system gastropods w really thick shells - normally thin shells in freshwater bc lack of calcium carbonate

when looking at presence of predators –> much higher here bc crab chelipeds are larger therefore have greater force

indepedently evolving to have thicker shells in different locations to protect themselves from shell crushing predators = CONVERGENCE

Question 22

Defensive value of gastropod operculum?

Answer 22

example of Taylors sculpin
- suction feeder
- preys on gastropods
- has pegs arising from neurocranium which puts holes in gastropods

40% of unpunched gastropod shells survived completely through fish and out of feces