1) A study found that a parasitoid wasp, Anisopteromalus calandrae, promoted the coexistence of two prey beetle species, Callosobruchus maculatus and C. chinensis, through frequency-dependent predation in a multi-generational experimental system. 2) The parasitoid wasp developed a search image for the prey species it had previously oviposited on, showing increased preference for that species. This caused the parasitoid to switch prey as the relative abundances of the prey species changed over time. 3) Through numerical simulations, the researchers found that this frequency-dependent preference, driven by the paras

1. Learning predator
promotes prey coexistence
Yumiko Ishii*, Masakazu Shimada (2012) PNAS
Department of System Sciences (Biology) , University of Tokyo
*Present address: Center of Environmental Biology and Ecosystem Studies,
National Institute for Environmental Studies

2. Importance of Frequency-dependent predation in maintaining
species diversity in nature ?
- Since the 1970s, theoretical studies have predicted that frequency-
dependent predation is one of the strong mechanisms in
maintaining prey coexistence.
Predator Prey switching for
abundant prey species
Prey1 Prey2
Pedators that switch to more
Population
common prey types promotes the
coexistence of prey species because
it prevent rare prey types from being
eliminated.
Time
- There is a lack of empirical evidence directly testing the effect of
learning and frequency-dependent predation in a multigenerational
prey–predator system.

3. Two- host one-parasitoid host-parasitoid system
Experimental insect population as a mimic of species interaction occurring in
natural ecosystems.
Parasitoid
Anisopteromalus
calandrae
Predation Predation
Host1: CM Competition Host2：CC
Callosobruchus For resource beans Callosobruchus
maculatus chinensis
 Does the presence / absence of a predator contribute to
coexistence of two prey species?
 How does learning of a predator affect the dynamics?

4. Life cycle of seed beetles and parasitoids.
The adult female lay their eggs
on the surface of beans. Seed beetles
- Insect Pests of stored beans.
Challosobruchus
chinensis Parasitoids
- A parasite that oviposits
Larvae feed and develop
Challosobruchus inside the beans.
on and eventually kills the
maculatus 4 weeks host organism.
Anisopteromalus
Adult emergence from
calandrae
the bean, and mating. Female wasp attacks
2weeks the host of about 2
week of age.

5. Methods: Multi-generation experimental system
-Introduction of CC, CM, and Parasitoids.
-Renew the resource once a week.
-Count the number of adults once a week.
The predation pressure was altered by changing the ratio of the black-eye
bean, BR.
low
Azuki beans BR = 0
Predation pressure
Low parasitization rate.
Refuge for host. BR = 0.5
Black-eye beans: ♪
BR = 1
High parasitization rate.
high

6. Host-parasitoid population dynamics at varying predation pressure.
Ratio of Black-eye beans: BR
Number of Adults
BR = 0 BR = 0 BR = 0
CM outcompeted CC.
low
Number of Adults
BR = 0.2 BR = 0.2
Predation pressure
Number of Adults
BR = 0.5 BR = 0.5
Long coexistence of CM and CC.
Number of Adults
BR = 0.8
Outbreak of parasitoids.
Number of Adults
high
BR = 0.8 BR = 1 BR = 1 Extinction of CM and CC.
BR = 1
Time (weeks)‫‏‬ Time (weeks)‫‏‬ Time (weeks)‫‏‬

7. Parasitoid promoted the coexistence of host species !
Number of Adults
Parasitoid absent
Number of Adults
Parasitoid present
BR = 0.8
Time (week)

8. The coexistence time of CC and CM.
Parasitoid absent
Parasitoid present
low Predation pressure high
Parasitoid introduction prolonged the coexistence time of CC and CM
at intermediate predation pressure (BR=0.2, BR=0.5, BR=0.8).

9. Can A. calandrae distinguish between CC and CM ?
Host search behavior of A. calandrae
! - Search the concealed host larvae in a bean
with antennal tapping.
- Oviposit on the host larva & pupa.
Hatched egg of the seed beetle.
Inside the bean
Larva of CM
Larva of CC
Learning in parasitoids
- Many parasitoid species have been well-studied
for their learning ability. (Godfray & Waage 1988, Turlings et
al. 1993 ).
- They prefer the experienced host by learning the
host-related odors during successful oviposition.

10. A. calandrae learned to preferred the host they experienced.
The effect of the oviposision experience on the preference were examined.
-Conditioning: A. calandrae experienced oviposition on the larvae of CM or CC for 6, 24, 48hrs.
-Choice test: The conditionded female was provided the equal numbers of CM and CC larve, and allowed to oviposit
for 3 hrs.
Experienced Experienced Control female
female on CM female on CC without experience
Number of oviposition on
Number of oviposition
mean±SE
CC
CM
Conditioning time (h) Conditioning time (h) Conditioning time (h)
A. calandrae increased preference for the Choice test
conditioned host after 24 h.

11. A. calandrae distinguished between two hosts by olfactory cues.
Host searching behavior of A. calandrae for olfactory cues.
- Female experienced oviposition on the each hosts for 3 days.
- The extracts (acetone) were made from black eye beans containing the larvae of each host species.
Experienced Experienced Control female
female on CM female on CC without experience Clean black-eye beans were
treated with aceton extract from:
CM： C. maculatus
CC：C. chinensis
CC B CC B: Clean black-eye beans
A: Control (acetone)
A CM CC A A CM
White line: the trajectories of
B CM walking A. calandrae.
B
A. calandrae walked extensively over the surface of the bean treated with the
acetone extract from the experienced host and tried to oviposit on the bean.
Ishii and Shimada (2010) Popul Ecol

12. A. calandrae showed frequency-dependent preference.
Female parasitoid preference in fluctuating host-parasitoid multi-
generation dynamics was examined.
Cross correlation：preference for CC, P (t) and the adult density of CC and CM, ( t + L ).
CCF for adult density of CC Preference test every week.
CCF for adult density of CM
CCF
CCF
Host adult density ( periodic oscillation of 4 weeks )
CM
Time shift, L (week) CC
Host larval density
CC
-Negative correlation between
preference for CC - adult CC density CM
-2 weeks lag between
adult CC density - vulnerable CC larvae density Parasitoid Preference for CC
-Positive correlation between
preference for CC - vulnerable CC larvae density
Time

13. Numerical simulation: learning / non-learning parasitoids
The effect of frequency-dependent predation on the coexistence time of CC and CM
was tested by numerical simulations using the stage-structured host-parasitoid model.
Parasitoid present
g : degree of frequency-dependence.
Non-learning parasitoids
Parasitoid absent
- Non-learning parasitoids does not prolong the coexistence time.
- Frequency-dependence of host preference is the major mechanism that prolonged
the coexistence time.

14. Conclusion : Frequency-dependent predation of A. calandrae the
promoted the prey coexistence in this host-parasitoid system.
- Olfactory search image is thought to cause frequency-dependent
predation.
- “Search image”: Perceptual change in the ability of predators to
detect cryptic prey (Tinbergen 1960).
Birds selectively search for particular cryptic insects after discovering this type of
prey because they ‘‘learn to see.’’

15. Search-image examples in insect visual predators
-Butterflies: Frequency-dependent oviposition
for two different shapes of leaves (Rausher 1978).
- Honeybees: Flower constancy.
Individuals often specialize on a few flower species
while ignoring equally rewarding flowers (Chittka et al. 1999).
- Parasitoids：Frequency-dependent oviposition for
aphid color polymorphism (Langley et al. 2006).
- Jumping spiders：
Preference for the experienced prey type (Jackson & Li 2004).
Cognitive ecology
Our result showed the possible importance of cognition
and leaning of organisms on species interaction,
population dynamics, and species diversity in ecological
communities.