[Paleopsych] SW: On Social Parasitism

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Evolutionary Biology: On Social Parasitism
http://scienceweek.com/2005/sa050114-1.htm

    The following points are made by J.A. Thomas and J. Settele (Nature
    2004 432:283):
    1) Ants are such formidable predators that perhaps 100,000 other
    species of insect have evolved mechanisms to coexist with them[1].
    Adaptations include armor to resist attack, mimicry to avoid
    detection, and secretions such as honeydew to feed or appease them[2].
    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[3] 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
    ants.
    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[4], 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[5].
    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.
    References (abridged):
    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)
    Nature http://www.nature.com/nature
    --------------------------------
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