lecture 16: induced defenses

Question 1

what are induced defenses?

Answer 1

a part of Adaptive Polyphenisms

example: snails on different islands
- some egg capsule wall thickness are different
- in presence of some environmental cue (like predator, increased wave action) egg capsules would be thicker
** default phenotype = cheapest
** some environmental cue would need to happen to trigger a change to conditional phenotype

which phenotype they would produce would be determined by if experienced environmental cue
- default (cheaper) option
- or conditional (expensive) phenotype
*** NOT ALWAYS PRESENT

Question 2

what are the conditions for selecting an induced defense? (4)

Answer 2

heterogeneous environment - the environmental cue only some of the time (not all) - sometimes has predator, sometimes not
– also has to be a v intense threatening predator - really effecting fitness

reliable cue signalling impending risk from predator - has to be something like a chemical effluent involved - something that the species can pick up on

conditional phenotype reduces predation risk
- has to help against attack

conditional phenotype is costly when predator is absent
- otherwise would be always (fixed genotype)

Question 3

examples of induced defenses

Answer 3

rotifer
- rotifer species called Keratella

in presence of predator, one of the spines would grow longer

• has predator called Asplanchna

***STUDY
- HYP: chemical effluent from Asplanchna was inducing long posterior spines in Keratella
- had diff water w diff organisms
– RESULTS:
- when cultured in water w Asplanchna, Keratella had long spine –> KAIROMONE

NOTE: not the individual species having this phenotypic change, but next generation of offspring

Question 4

study abt Asplanchna and Keratella

Answer 4

Keratella (prey) with long spines were captured less than short spines

long spine also helped protecting against ingestion

asymmetrical spine elongation bc why use energy to elongate two when just one works

Question 5

what is the cost of induced defense?

Answer 5

1) example of rotifers

no effect on production of eggs by amitotic females

BUT

Significant effect on production of resting eggs by mictic females (sexual reproduction)
– when looked at overwintering —> ones w long spines (expensive induced defense) - could produce less expensive overwintering eggs

2) daphnia and helmets (exuberant morphs)
**cost of this takes away from other things

Question 6

induced defense - bryozoans

Answer 6

bryozoans can get environmental cue and will start adding spines to newer individuals of colony, but needs to be within window of competence = DURING DIFFERENTIATION STAGE

by putting energy towards these spines, bryozoans then reduce growth rates

Question 7

induced defense example: solitary organism

Answer 7

barnacles

• more protected from gastropod predator in bent over morphology bc the labial tooth of gastropod cant get in as well

when in contact w kairomone - from snail mucus, there were more bent over

more costly – bent over morphotype produced less eggs

** the snails exist here and attract the bent phenotype bc they clear the conal ones and make a niche space for bent phenotype