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Bladderwort (Utricularia vulgaris): Utricularia’s trap

Real size of the animated area: length ca. 5 mm (ca. original size:   )

In reality the suction process occurs 500 times faster.


"The following questions and statements posed by Nachtwey in 1959 concerning the origin of Utricularia’s trap still have not been answered satisfactorily at the beginning of the twenty-first century and may illustrate some of the principal problems of the origin of carnivory in plants. After a careful description of the structures and functions of the trap, Nachtwey raised the question of how the origin from a leaf tip should be envisioned and went on to ask (pp. 99/100):

‘Which nondirectional mutation should have occurred first in a normal leaf tip and subsequently displayed any selective advantage? Without an advantage it would have been lost as trivial. The modern synthesis strongly emphasizes that mutation and selection have to cooperate to generate new structures. So, by which blind mutations should the suction trap have originated?’

And regarding the problem of further evolutionary stages the writer continues:

‘Even a perfect suction trap displaying the astonishing ability to rapidly catch animals would have no advantage in the struggle for life because the prey would not be digested. Conversely, the production of highly effective digestive juices would be of no avail for the tip of a leaf as long as it could not capture the prey, which is absolutely necessary. But even if suction trap and digestive juices cooperated, nothing would be gained in the struggle for life. The dissolved proteins must also be absorbed and metabolized to species-specific proteins. The formation of the suction trap requires the perfect cooperation of many different genes and developmental factors. Only at the end a benefit is reached in the struggle for life, but not by any evolutionary stage.’ Nachtwey concluded that none of the contemporary evolutionary theories was able to answer these questions, proposing that the answer might lie outside the present scientific paradigms."

From Lönnig and Becker 2004 : Nature Encyclopaedia of Life Sciences.

"Highly specialized suction traps as depicted in Utricularia are also adapted to water as surrounding medium. The trap is set by negative hydrostatic pressure. Glandular structures outside and inside the bladder were shown to be involved in water transport from the lumen to the surrounding medium. When a potential prey (e.g. acopepod, cladoceran, ostracod) stimulates the antennae of the trapdoor, the latter is opened and the trap walls, being under negative pressure, expand rapidly sucking in water through the door opening. The prey is sucked in concomitantly and the door quickly returns to its former state. The opening process is estimated to take less than 2 ms and the entirefiring process - stimulation, door opening, and closing – lasts about 30 ms and is thus one of the fastest movements in the plant kingdom.

In addition to the main characteristics of the physical trapping mechanisms, the traps of most carnivorous plants exibit accessory features suitable for attracting small animals. Different trap types increase their efficiency by colours, olfactoric stimuli and further anatomical devices (windows, detaining hairs, slippery material). Moreover, apart from the trapping devices there are some additional deviations from the general angiosperm design principle: Utricularia does not develop any roots, and Genlisea has ‘root-leaves’, so that genuine roots are missing here, too.

Nutrition and Digestion

The basic question which has been debated for more than a century is whether the insects and other small invertebrates, as well as some fish fry, are really essential for normal development of carnivorous plants or whether they can also persist and flourish without prey. Regarding the observation of many authors that the species investigated can normally grow and flower under laboratory conditions, it has been objected that such environments do not reflect their special natural habitats and thus cannot provide the solution to this problem.

The conventional view is that carnivorous plants are clearly benefiting from digestion of small invertebrates and fish fry. This, however, could not be corroborated by recent painstaking investigations in Utricularia purpurea. The return of nitrogen and phosphorus from an overall investment of 25 - 50% in bladder formation proved to be less than 1% in the cases investigated. One hypothesis is that Utricularia plants benefit more from living communities of microorganisms and associated detritus, i.e. by mutualism, than from carnivory. The open questionis, however, to what extent the results can be generalized for other Utricularia species or for other carnivorous plant genera. Conversely, writers like Schnell (2002, p.20) are convinced ‘that carnivorous plants do indeed benefit from their unique adaptations by exhibiting more rapid and enhanced growth, more prolific flowering and seed set, and a better ability to maintain and even improve their competitive edge within their habitats’.

Carnivorous plants digest their prey by means of enzymes such as acid phosphatase, proteases, peptidases, esterases and chitinase. Also, ribonuclease and deoxyribonuclease and still other shave beendetected. An amylase is found in Aldrovanda. For several carnivorous plant species more investigations are necessary to corroborate and enlarge earlier findings.

Usually the same glands producing the enzymes are also responsible for the absorption of the digested materials."

NATURE ENCYCLOPEDIA OF LIFE SCIENCES / © 2004 Nature Publishing Group / www.els.net and http://onlinelibrary.wiley.com/

See also http://www.weloennig.de/Utricularia.html or Polypompholyx.pdf


Quelle: http://upload.wikimedia.org/wikipedia/commons/e/e7/Uk_pond_bladderwort.jpg
Utricularia, Wasserschlauch
Letzte Aktualisierung 24. September 2010
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