Thanx so much.
The questions:
Is there anything I said in the review that seems unreasonable
Which species of CP have strong odors (not the flowers, the insect catching
parts)? How would you describe them?
Do these odors change in strength or character over the course of the
day/season?
Outside of the pitcher plants where there is prey data, has anyone noticed
any patterns in the prey that are caught, if you've seen them in the field?
Plants and fungi that lure prey. - A diverse assemblage of plants and fungi
trap, kill and digest animals (reviews in Lloyd 1942, Slack 1979, and
Givnish et al 1984; other refs. in Duddington and Wyborn 1972, Zuckerman
and Jansson 1984; Simons 1981 reviews unstudied, potentially carnivorous
plants). Many (perhaps most) of the species in this assemblage chemically
attract their prey. Unlike most of the animal predators mentioned below,
the majority of these plants and fungi 1) can survive without carnivory,
and 2) capture a significant percentage of their prey by chance. However,
various evidence suggests that the ability to lure prey is important to
these organisms.
Fungi that capture and digest nematodes are ubiquitous. Numerous studies
have demonstrated that the nematodes are attracted to the fungi, and can be
attracted to filtrates and other preparations of fungal material (review in
Zuckerman and Jansson 1984). Possibly the fungi mimic nematode feeding
cues. Different fungus species attract different sets of nematode species
(most attract fungal-feeding and plant parasitic nematodes). Attraction of
prey is also possible in a second, less-studied class of fungi which
capture rotifers after they bite specialized hyphal knobs (Lloyd 1942,
Duddington and Wyborn 1972).
Barber and Page (1976, review in Barber 1978) suggest that the mucilaginous
seeds of many plants (including many common crucifers such as Capsella
bursa-pastoris) 1) attract and entrap soil organisms such as nematodes, and
2) make use of nutrients from the captured animals. (Currently, the
evidence for this proposition is indirect.)
In many familiar carnivorous plants, chemical mimicry probably aids in the
capture of insects (Lloyd 1942, Slack 1979). Unfortunately, although
biologists and abundant enthusiasts outside academia have long been
fascinated by these plants, there have been remarkably few ecological
studies. For most species, even the common ones, descriptions of prey more
specific than "insects" or "small flies" are unavailable. Prey have been
recorded for the tank bromeliad Brocchinia reducta (Givnish et al 1984),
Dionaea muscipula (the Venus fly trap) (Lichtner and Williams 1977), and
some Sarracenia (pitcher plant) species (the "Sarracenia refs.": Wray and
Brimley 1943, Fish 1976, Rymal and Folkerts 1982, Folkerts 1982, D.
Folkerts in prep., and S. Hermann et al in prep.). S. Hermann et al's (in
prep.) study is the first long-term field experiment to demonstrate that
captured insects significantly increase carnivorous plant growth rates.
Nectar glands help position prey for capture in many carnivorous plants
including Dionaea, and the pitcher plants (all five genera in all three
families - Sarraceniaceae, Nepenthaceae, Cephalotaceae). Various
observations suggest that many species also attract prey from a distance
with odors (and visual cues). (However, experiments to test this
hypothesis have never been conducted.) Sweet 'nectar-like' scents are
produced by many pitcher plant species, and by the tank fluid in the
bromeliad Brocchinia reducta. The latter is the only species in its genus
known to be carnivorous. Tank fluid odor is unusual (possibly unique)
among tank bromeliads, and could be one of the more important adaptations
of the plant for carnivory (Givnish et al 1984). Sarracenia species with a
floral odor tend to capture larger numbers of flower-visiting insects than
species without a floral odor (Sarracenia refs.). Other trends in prey
capture might also be odor mediated (see Sarracenia refs.).
Almost nothing is known concerning the chemistry of carnivorous-plant
volatiles. In the only study that I know of, terpenes, amines and a large
number of other compounds were identified from extracts of Sarracenia flava
(Miles et al 1975, Mody et al 1976). The role of these compounds in
interactions with prey was not determined (contra the claims of Mody et al
1976).
Among those carnivorous plants that capture their prey with sticky
droplets, there is less indication of an important role for scent. The
possible attraction of some insects to the large droplets of Drosera and
other sundews may be purely visual. However, some Drosophyllum species
have a 'honey' odor (Lloyd 1942). Also many Pinguicula species give off a
'fungus' odor, and "small flies" are a major prey item (Lloyd 1942 pp. 2,
106, Slack 1979 p. 107; are some of these flies attracted fungus gnats?).
Prey attraction has been suggested for some of the carnivorous plants that
capture prey underwater (Lloyd 1942, Slack 1979). The closely related
genera Utricularia and Polypompholyx grow in aquatic, moist-soil, or rain
forest epiphyte environments. They capture prey that trigger their small,
underwater (or water-film) suction traps (review in Wallace 1978). Very
little is known about the prey of most species, particularly those that
live in highly specialized habitats. In at least one species, filaments
probably guide prey to the trap; many of the prey (particularly chydorid
crustaceans) normally travel along algal filaments eating epiphytes (Meyers
and Strickler 1979). However, many workers have suggested that 'odors' may
also attract prey to the traps, which bear secretory trichomes (refs. in
Lloyd 1942 and in Wallace 1978, Wallace pers. comm.). Chemical lures would
not be surprising in two unrelated aquatic genera, Genlisea and Aldrovanda;
to be captured, prey must pull themselves through narrow slits. In
Genlisea these slits are associated with mucilage-secreting glands (refs.
in Lloyd 1942).
Barber, J. T. 1978. Capsella bursa-pastoris seeds. Are they carnivorous?
Carnivorous Plant Newsletter. 7:(2)39-42.
Barber, J. T., and Page, C. R. 1976. Mucilaginous seed pellicles. What's
New in Plant Physiology. 8:(6)1-5.
Duddington, C. L., and Wyborn, C. H. E. 1972. Recent research on the
nematophagous hyphomycetes. Bot. Rev. 38:545-65.
Fish, D. 1976. Insect-plant relationships of the insectivorous pitcher
plant Sarracenia minor. Fla. Entomol. 59:199-203.
Folkerts, G. W. 1982. The Gulf Coast pitcher plant bogs. Amer. Sci. 70:260-7.
Givnish, T. J., Burkhardt, E. L., Happel, R. E., and Weintraub, J. D. 1984.
Carnivory in the bromeliad Brocchinia reducta, with a cost/benefit model
for the general restriction of carnivorous plants to sunny, moist,
nutrient-poor habitats. American Naturalist. 124:479-97.
Lichtner, F. T., and Williams, S. E. 1977. Prey capture and factors
controlling trap narrowing in Dionaea (Droseraceae). Am. J. Bot. 64:881-6.
Lloyd, F. E. 1942. The Carnivorous Plants. Chronica Botanica Co.
(republished in 1976 by Dover Publications, Inc., NYC.), Waltham, MA.
Meyers, D. G. and Strickler, J. D. 1979. Capture enhancement in a
carnivorous plant: function of antennae and bristles in Utricularia
vulgaris. Science. 203:1022-5.
Miles, D. H., Kokpol, U., Mody, N. V., and Hedin, P. A. 1975. Volatiles in
Sarracenia flava. Phytochemical Reports. 14:845-6.
Mody, N. V., Henson, R., Hedin, P. A., Kokpol, U., and Miles, D. H. 1976.
Isolation of the insect paralyzing agent coniine from Sarracenia flava.
Experientia. 32:829-30.
Rymal, D. E. and Folkerts, G. W. 1982. Insects associated with pitcher
plants (Sarracenia: Sarraceniaceae), and their relationship to pitcher
plant conservation: a review. J. Ala. Acad. Sci. 53:131-51.
Simons, P. 1981. How exclusive are carnivorous plants? Carnivorous Plant
Newsletter. 10:65-80.
Slack, A. 1979. Carnivorous Plants. The MIT Press, Cambridge, MA.
Wallace, R. L. 1978. Substrate selection by larvae of the sessile rotifer
Ptygura beauchampi. Ecology. 59:(2)221-7.
Wray, D. L., and Brimley, C. S. 1943. The insect inquilines and victims of
pitcher plants in North Carolina. Ann. Ent. Soc. Amer. 36:128-37.
Zuckerman, B. M. and Jansson, H. 1984. Nematode chemotaxis and possible
mechanisms of host/prey recognition. Ann. Rev. Phytopathol. 22:95-113.
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Mark Stowe c/o Jon Reiskind
Department of Zoology
University of Florida
Gainesville, FL 32611 USA
E-mail: MKS@ZOO.UFL.EDU
phone: 904 373 3202, 904 392 1187
fax: 904 392 3704