Transcript Predation & Parasitism

Predation & Parasitism
DEFINITIONS (Gullen & Cranston, 2000)
Predator. “An organism that eats more than one other
organism (animal) during its life.” Usually larger than prey
(exception: social predators).
Parasite. “An organism that lives at the expense of another
(host), which it does not usually kill.” Usually smaller than
host.
Parasitoid. “A parasite that kills its host.” Usually smaller
than host.
(DEFINITIONS)
Cleptoparasite. ‘A “thief” parasite, one that consumes the food
stored by another insect in a nest. (Evans, 1984) Smaller or
similar size as host; often closely related.
Hyperparasite. Parasite of a parasite. Usually smaller than host.
Inquiline. “An organism that lives in the home of another,
sharing food; in entomology, used particularly of residents in the
nests of social insects or in plant galls induced by another
organism.” (Gullen & Cranston 2005)
Social Parasite. “An insect that invades or lays its eggs in the
nest of a social insect and eats and develops on food stores or on
host immatures.” (Evans, 1984)
Predators
Predation by social insects challenges the usual rule that the
predator must be larger than the prey unless one considers the
entire colony the predator.
Predation
Paleohistory. 1st hexapods were likely predaceous.
Modern Representatives. All ARACHNIDA, all CHILOPODA,
most “Soil Arthropods”, all ODONATA, representatives in most
other orders, some predominantly. Exceptions: a few minor insect
orders with only saprophagous or parasitic members, ISOPTERA,
LEPIDOPTERA (but counter-exceptions even here).
The evolution of plant-feeding by insects was a major adaptive
leap, leading to huge increases in species diversity. But many
species remained predaceous (or parasitic), eventually diversifying
in response to more varied prey. Also, as has happened many times
in insect evolution, there have been reversions to previous food
habits, so some plant-eaters branched off into secondarily evolved
predation, e.g. some stink bugs.
How to be a Predator (Behavior & Ecology).
Some major quantifiable factors in the life of a predator.
1) Prey Distribution in Space & Time
a) Coarse vs. Fine-grained
b) Patchy vs. Even
c) Continuous vs. Intermittent
>> Terms relative to predator’s “viewpoint”
2) Foraging Strategy: Cost vs. Benefit
Costs: Time (T), energy (e)
Benefit: Nutrition (energy, protein)
>> “Optimal Foraging Theory”: Successful strategies optimize
Benefit/Cost ratio by maximizing prey capture while minimizing
inputs, either T or e or both.
Resource Dispersion models influencing adaptations of
predators &/or parasites.
Patch or perch departure
criteria (thresholds):
• Elapsed Overall Time
• Elapsed Search time
• Prey encounter rate
• Prey capture rate
Mother may play a role in selecting prey
patch choice of offspring, e.g. syrphid flies.
Major Types of Prey
Searching Behavior
Sit & Wait
Trapping
Active Searching
Random
Directional
Generalized Predator Foraging Strategies with Examples
Time & energy are balanced in any strategy.
T
e
Strategy


Sit & Wait
≈

-
Immature
Adult
dragonfly, mantid,
(dragonfly), mantid,
tiger beetle,
spider
≈
Trapping
spider, ant lion, tiger
beetle, cave midge

Active
Foraging
(dragonfly), robber fly,
syrphid fly
spider (some nonweb species),
dragonfly, robber fly
-
Non-feeding or
non-predatory
-
ant lion, cave midge,
syrphid fly (nectar
only)
Dragonfly nymph switches strategies depending on prey density; adult
strategy depends on species. Immature & adult strategies often the same in
hemimetabolous species. Some holometabolous adults do not feed at all.
Parasites & Parasitoids
Paleohistory & Evolution
• Small size => poor fossil record of parasites.
• Probable radiation with increased importance of
phytophagy.
• ~25% of all insect species are parasitic in one or more
stages of development.
• The parasitic life style represents a major adaptive
advantage and has arisen many times. Only 3 orders are
completely parasitic (probably relatively recent in
evolutionary terms; 2 linked to vertebrate hosts). But
there are parasitic representatives in 4 hemimetabolous
orders and all but two (minor) endopterygote orders.
Various Parasites,
Parasitoids, &
Cleptoparasites in
the Diptera,
Hymenoptera, and
Acari, orders with a
high proportion of
parasitic species.
57) Tachinid fly, parasitoid of
Pandora moth larvae.
58) Parasitized larvae and
host pupae of 57.
59) Braconid wasp, parasite of
bark beetles.
60) Jewel wasp, parasitoid of
ground-nesting bees.
61) Velvet ant, parasitoid of
ground nesting wasps.
62) Soft tick, parasite of gulls.
Diverse Parasite
Relationships to Host
Louse
(PHTHIRAPTERA):
Some Factors:
• Host specificity
• Duration on Host
• Life cycle dependency on Host
• Alternate hosts
• Number of host individuals
Mosquito (DIPTERA):
All stages, permanent
adult only, intermittent,
on host
Flea (SIPHONAPTERA):
many host indiv’s
adult only, intermittent,
usually same host individual
Environment & Host Relations in Parasites
For most parasites, the environment is patchy (very “coarse
grain”) in terms of host-finding.
> Much time & energy are expended to find a new host and
there is serious exposure to predation and physical harm.
> Once a host is found, however, the parasite and possibly
is offspring can live on their unlimited food source,
depending on their relationship to the host.
Host Relationships
1) Long-term host (many generations; host as “island”)
a) Continuous host residence, e.g. lice (PHTHIRAPTERA)
b) Intermittant host residence (usually “rest” near same
host), e.g. bed bugs (HEMIPTERA)
both:Advantage: limited or no host-finding
Disadvantage: host may die!
2) New Host with Each Generation
a)
Larva searches
• Frequently the adult selects a likely host-encounter area.
• Active early instar larvae, often with hypermetamorphosis. E.g.
“triungulins” or “planidia” of some DIPTERA, COLEOPTERA,
STREPSIPTERA, HYMENOPTERA
• Phoresy, “hitchhiking”
• Adult can broadcast eggs; no host-search required (eggs usually small)
• High egg mortality if broadcast; often time-expensive for larva, hazards in
hitchhiking, host defenses
b) Adult searches
• Highly developed sensory abilities:
Substrate vibrations, e.g. fruit fly parasite
Visual/olfactory: syphid flies/lady beetles laying eggs near aphid colonies
Chemical cues, pheromones => kairomones; sources incl. frass,
host CO2, bark beetle and cavity-nesting bee parasitoids
• Host Acceptance, Manipulation
• Faster development: larva can specialize in feeding
• All offspring dependent on search success of adult
Two Different Parasitoid
Host-Finding Strategies
Parasitoid wasps:
Adult search, larvae
deposited inside host
Bee Fly: Larval hostsearching; eggs laid near host
burrow, active larvae find host.
Host Specificity & Evolution
Farenholz’s Rule: phylogeny of parasite mirrors phylogeny of
host. Implications, one parasite per host, one host per parasite,
with corresponding evolution. This is now considered more
theoretical than real.
Reality: dynamic evolution of hosts & parasites influenced by:
• Irregularities in host distribution,
• Sudden host declines or extinctions
• Differential vagility of parasites vs. hosts
• Differential host defenses.
• Length of association
Generalizations
Monoxenous (single host species)
Usually full-time parasites (permanent host-residence)
Oligoxenous (narrow host range, e.g. within one genus)
Many parasitoids, cleptoparasites
from Borror, DeLong, & Triplehorn 1981
Hymenopterous parasitoids of potential importance in biocontrol.
A. Habrocytus (Pteromalidae); B. H. feeding from oviposition puncture; C. Zarhopalus
inquisitor (Encyrtidae); D. Aphelinus jucundus (Eulophidae); E. Euplectrus (Eulophidae).
Variations in Parasitism
Hyperparasitism, parasite of a parasite (of a….up to 7 levels!)
Superparasitism, mulitple eggs from one or more individuals of
the same parasitoid species in a single host.
Multiparasitism, eggs from more than one species. Many
parasites have been shown to protect themselves from
competition with larvae of other parasitic species. It is relatively
rare to find more than one species of parasitoid in a single host
individual.
Hyperparasitism Complex,
part of a dynamic food web
from Evans, 1984
Inquilines & Social Parasites
• Taking advantage of
COLEOPTERA THYSANURA
ACARI
social insect colonies as a
special concentrated
resource.
• Requires highly
specialized means of
overcoming colony
defenses.
• Most are non-lethal to
the colony.
from Holdobler & Wilson
Complex
behavioral/physiological
ruse of an inquiline
staphylinid beetle.
Ant-simulating behavior
(as perceived by attending ant)
3 glands:
adoption gland
defensive gland
apeasement gland
from Holdobler & Wilson
Adoption strategy of a predaceous, socially parasitic predatory caterpillar.
Worker ant bringing home a Lycaenid caterpillar.
2 glands are used to:
pacify an ant and
encourage “adoption”.
Once in the ant nest, the
caterpillar commences to
feed on the ant larvae.
from Holldobler & Wilson 1986
Cleptoparasitic bumbe bee, Bombus (Psithyrus) vestalis.
Females are all queens that aggressively take over mature colonies of
host bumble bees. The host queen is killed and the worker bees raise
the (all-queen) larvae of the parasite.
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