[Paleopsych] SW: On Social Parasitism
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Evolutionary Biology: On Social Parasitism
The following points are made by J.A. Thomas and J. Settele (Nature
1) Ants are such formidable predators that perhaps 100,000 other
species of insect have evolved mechanisms to coexist with them.
Adaptations include armor to resist attack, mimicry to avoid
detection, and secretions such as honeydew to feed or appease them.
In general, both partners benefit: in return for honeydew, the ants
protect aphids from enemies. But natural selection can also favor
cheats. It is a short evolutionary step from possessing the attributes
to live safely among ants to deploying them against a colony.
2) Thus, among insects as diverse as butterflies, crickets, beetles
and flies are specialist "social parasites", perhaps 10,000 species in
all, equipped to penetrate the highly protected chambers inside ant
nests and feed, isolated from enemies, on the rich resources
concentrated there. New work has provided the first
molecular-genetic reconstruction of one such evolutionary pathway,
that of large blue butterflies (genus Maculinea), including the
pathway's divergence into two remarkable strategies for exploiting
3) The large blues form a small genus that has become an icon for
conservation across Europe and Asia. The adults fly in summer, laying
eggs on specific plants. After two to three weeks of eating flowers,
the caterpillar settles beneath its food plant to await discovery by
red ants (Myrmica). By secreting hydrocarbons that mimic those made by
Myrmica, the caterpillar tricks a foraging worker into taking it
into the nest, where it is placed among the ant grubs. In most species
-- the "predatory" large blues -- the caterpillar then moves to safer
chambers, returning periodically to binge-feed on ant grubs. But in
two "cuckoo" species, the caterpillars remain among the brood and
become increasingly integrated with their society. Nurse ants feed
them directly, neglecting their own brood, which may be cut up and
recycled to feed the parasites.
4) Cuckoo-feeding is an efficient way to exploit Myrmica, resulting in
six times more butterflies per nest than is achieved by the predatory
species. The downside is that social acceptance is won only through
secreting chemicals that so closely match the recognition codes of one
host species that survival with any other ant is unlikely. Thus, a
typical population of a cuckoo Maculinea species depends exclusively
on a single Myrmica species -- which, however, differs in different
regions of Europe. Predatory Maculinea are more generalist;
nevertheless, each species survives three to five times better with a
single (and different) species of Myrmica.
1. Elmes, G. W. in Biodiversity Research and its Perspectives in East
Asia (eds Lee, B. H., Kim, T. H. & Sun, B. Y.) 33-48 (Chonbuk Natl
Univ., Korea, 1996)
2. Hoelldobler, B. & Wilson, E. O. The Ants (Springer, Berlin, 1990)
3. Als, T. D. et al. Nature 432, 386-390 (2004)
4. Akino, T., Knapp, J. J., Thomas, J. A. & Elmes, G. W. Proc. R. Soc.
Lond. B 266, 1419-1426 (1999)
5. Elmes, G. W., Wardlaw, J. C., Schoenrogge, K. & Thomas, J. A. Ent.
Exp. Appl. 110, 53-63 (2004)
AN INTERESTING CASE OF ANT-PLANT MUTUALISM
Notes by ScienceWeek:
In biology, symbiosis is an intimate and protracted association of
individuals of different species, and mutualism is a type of symbiosis
in which both participants receive benefits from the association. An
intriguing mutualism is that between ants and Acacia trees. In East
Africa, one finds Acacia trees that are "ant-guarded": the ants live
on the trees inside modified thorns (pseudogalls), patrol the
branches, and attack any insect or vertebrate herbivore, thus
protecting the plant, but also preserving the plant for the use of the
ant. But this plant requires cross-pollination by visiting insects in
order to reproduce, and what one observes is that during the
pollination periods the ant-guards essentially remain in the
guard-house and cross-pollination by visiting insects proceeds without
difficulty. Which of course provokes the question of what are the
signals involved in this delicate bit of cooperative maneuvering?
P.G. Willmer and G.N. Stone ((Nature 1997 388:165) report that during
the pollination period, the young Acacia flowers apparently release a
volatile chemical that deters the ant-guards. The ants thus patrol
before and after pollination, but not during the pollination period
ANTAGONISTIC SYMBIOSIS: ABDUCTION OF ONE SPECIES BY ANOTHER
The following points are made by McClintock and Baker (American
Scientist May/Jun 1998):
1) Many interactions between species occur on a covert level and are
difficult to perceive. These interactions are chemical, not physical,
and rely on substances such as pheromones that attract mates, as well
as toxins that repel or kill predators, competitors, and other
enemies. Chemical interactions can profoundly alter the conventional
scenarios posited by ecologists studying predators and their prey.
2) The research of the authors has focused on secondary metabolites,
chemicals that do not seem to be required for any of the primary
metabolic processes such as energy production, respiration, or
photosynthesis. They have found that sessile and sluggish organisms on
the Antarctic ocean floor are much threatened by invertebrate
predators and competitors, and the threatened organisms have developed
chemical defenses to ward off their enemies.
3) In one unusual adaptation, the amphipod crustacean Hyperiella
dilatata captures the sea butterfly Clione antarctica (a snail without
a shell). The sea butterfly is held alive in a sustained forced
attachment on the back of the crustacean, and experiments and analysis
reveal that the sea butterfly secretes a previously undescribed
beta-hydroxyketone that turns away fish that are normally predators of
the crustacean. The authors suggest this unique association -- the
abduction of one species by another --is unprecedented in the annals
of behavioral and chemical ecology.
American Scientist http://www.americanscientist.org
INITIAL CHEMICAL SIGNAL IN INSECT-PLANT-INSECT TROPHIC TRIANGLES
Notes by ScienceWeek:
Both corn and cotton plants, when attacked by plant-eating insects,
release a volatile substance that specifically attracts other insects
that are the natural predators of the plant-eating insects.
The following points are made by J. H. Tumlinson et al (Science 1997
1) The authors studied the trophic triangle of the beet armyworm
caterpillar (Spodoptera exigua Hubner), corn seedlings (Zea mays L.),
and the parasitic wasp (Cotesia marginiventris).
2) The authors have isolated and synthesized the chemical substance
responsible for the initial signal. They have named the substance
volicitin. It is present in the oral secretions of the caterpillar,
and it induces the damaged corn seedlings to release a volatile blend
of terpenoids and indole, which calls in the parasitic female wasps
that are the natural enemies of the caterpillars. The wasps lay eggs
in the caterpillars, and the hatched larvae destroy the caterpillars
by eating them.
3) Mechanically damaged plants exposed to synthetic volicitin, in the
absence of caterpillar attack, release the usual volatiles that
attract the wasps. Plants mechanically damaged but not exposed to
volicitin do not release the volatiles.
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