The behaviour of leaf traps of carnivorous herb Drosera rotundifolia  L. (Droseraceae).

Volkova P.A., Shipunov  A.B.

Volkova P.A., Shipunov A.B. The behaviour of leaf traps of carnivorous herb Drosera  rotundifolia  L. (Droseraceae) // The materials of the White Sea Expedition of Moscow South-West High School. Vol. 1 [Electronic resourse]. 2001. Mode of access: http://herba.msu.ru/shipunov/belomor/english/non-stop.htm

[Russian text]

Introduction

The behaviour of leaf traps of the carnivorous herb Drosera  rotundifolia was studied by mean of laboratory experiments more then a century ago [1], [3]. More detailed information on this phenomenon can be found in the modern publications [2], [4]. However, the knowledge about carnivorous behaviour of D.  rotundifolia wasn't confirmed with systematic field observations.

Materials and methods.

We made continous field observations for 72 hours on two D. rotundifolia plants in Loukhskii region (the republic of Karelia) from 25 to 27 July, 2000. Once in 40 minutes the condition of the leaf blade and the number of caught insects fot each of 9 investigated leaves was registred. The changes of the investigated leaves characteristics during the observations were analyzed, taking into account the number of the caught insects.

Resultes and their discussion.

The rithmic changes of the moisture degree of tentacles and the shape of leaf blade (from flat to curved) were marked for the majority of D. rotundifolia leaves (70-80 % from the total number of the investigated leaves). These changes had 8-hour period and didn't depend on the presence of insects on the leaf blade. There weren't marked any changes of the leaf blade condition during one hour after catching the insect. This fact contradicts the published data [2] about quick reaction of the leaf on the caught insect; we observed only slow (in 2-4 hours) reaction.

We often have noticed the leaf behaviour, which had significant differencies from early described. For example, the margin tentacles on a half of the investigated leaves weren't curved, when there was an insect on the leaf blade. The tentacles of all the investigated leaves periodically became dry, when there was a fresh insect on the leaf blade. We noticed on the majority of the investigated leaves the frequent changes of the leaf blade form, the condition of the margin tentacles and the degree of their moisture, while the number of caught insects was constant. We can suppose that such a behaviour is necessory for changing the position of the insect being disgested. This behaviour may be analogous to animal's peristaltic movements.

Summary.

Our observations show that the D. rotundifolia leaf traps behaviour submits to the 8-hours rithms and may be only corrected by environmental factors, one of which can be the number of caught insects. Insects are probably retained on the leaf blade not with sticky tentacles tops but with sticky substances, situated on the leaf blade between the bases of the tentacles. The margin tentacles cover the caught insects, creating the close space for more effective insect disgesting, not for the retaining the insect. The resultes of the current investigations don't confirm the published data on the behavior of the leaf traps of D. rotundifolia [1-4].

References.

1. Darwin C., 1875. -- Insectivorous Plants. Murray, London.

2. Bopp M., Weber I. Studies on hormonal regulation of leaf blade movement or Drosera  capensis L. // Physiologia Plantarum. 1981, 53. P. 491-496.

3. Busgen M. Die Bedeutung des Insektenfangs fur Drosera rotundifolia L. // Botanische Zeitung. 1883. Vol. 41. N 35. P. 569-577.

4. Chandler G.E., Anderson J.W. Studies on the nutrition and growth of Drosera species with reference to the carnivorous habit // New Phytologist. 1976. Vol. 76. P. 129-141.

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