Jangoux, M.

Van den Spiegel, D.

Open Marine Archive

C O M P A R A T I V E  S T U D Y  O F  T H E  G R O W T H  R A T E  I N  T W O  P O P U L A T I O N S  
O F  T H E  C O M M O N  L I Z A R D  (LACERTA VIVIPARA)
by
F r a n k  SCHOETERS 
Department of Biology, University of Antwerp (U.I.A.)
Universiteitsplein 1, B-2610 Wilrijk 
Field Biological Station, University of Antwerp (U.I.A.)
Verbindingsweg, B-2180 Kalmthout
Phenotypic differences between populations have often been attributed to adap­
tation to local circumstances. Recent studies have, however, stressed tho importance 
of phenotypical plasticity. Studies of intraspecific variation in phenotypical traits, 
should therefore take in account the possibility of an immediate response to environ­
mental factors.
The basic goal of this comparative study was to explore the influence of genetical 
and environmental factors on the differences in body-size and growth rates in two popu­
lations of Common lizards, living 2.5 km apart at Kalmthout (51°25' N ; 4°25' E). I 
found that in all age-classes, the lizards in the first population were much larger and 
that this difference in body-size was due to a higher growth rate of the animals in this 
first population.
Tests with newborn lizards that were exchanged between the two populations or 
that were reared under identical standardized circumstances in the laboratory, showed 
that the difference in growth rate between the two populations was not the result of 
a difference in genetic constitution. Therefore, the observed difference should be attri­
buted to environmental factors.
Earlier studies of the food consumption of this lizard indicate that Lacerta vivipara 
is an alimentary opportunist, feeding especially on invertebrates that are 2 up to 10 mm 
large. Sampling with sticky traps and pitfalls revealed that such preys were more readily 
available in the first population.
In both populations, the lizards prefered places where sun as well as shade were 
available. I attribute this to the fact that such places allow these ectotherm reptiles 
to regulate their body temperature very economically. In the first population such 
« sun and shade » places remained much longer available throughout the day and conse­
quently allowed the animals to increase their daily activity period.
Hence, a longer activity period and a higher food abundance, are two possible envi­
ronmental factors that induce the observed difference in growth rates and consequently 
in body-size distribution between the two populations.
Instead of showing a strong genetical basis, this study underlines the importance 
of environmental factors as a source of phenotypical variation, a finding which, in the 
biological research into the aspects of life-history strategies of different populations, is 
endorsed by an increasing number of authors.
M É C A N I S M E  D ’É J E C T I O N  E T  S T R U C T U R E  F I N E  
D E S  T U B E S  D E  C U V I E R  C H E Z  L ’H O L O T H U R I E  : 
HOLOTHURIA FORSKALI
par
D i d i e r  VAN DEN SPIEGEL et M i c h e l  JANGOUX  
Laboratoire de Biologie Marine 
Université Libre de Bruxelles 
50, Avenue Roosevelt, B-1050 Bruxelles
L expulsion et l’extension des tubes de Cuvier se realise comme suit : on réponse 
à. une irritation, 1 holothurie se contracte. La surpression du liquide coelomique due 
cette contraction provoque une déchirure de la paroi du cloaque. Le liquide coelomique 
s échappant par la dechirure entraîne avec lui plusieurs tubes de Cuvier. L ’extension
des tubes a lieu en même temps qu’ils sont expulsés. Elle est due à l’action conjointe 
de deux mécanismes : l’injection d’eau sous pression (provenant de la cavité pulmonaire) 
dans la lumière des tubes, et la contraction des muscles circulaires des tubes.
La structure des tubes de Cuvier d 'Holothuria forslcali a été etudiée a la fois en 
microscopie photonique, en microscopie électronique à transmission et en microscopie 
électronique à balayage. Les tubes sont formés de trois couches tissulaires qui sont, 
de dehors en dedans, un mésothélium en continuité avec celui du coelome general, une 
couche conjontivo-musculaire, et un épithélium interne en continuité avec 1 epithelium 
interne des poumons.
Un tube non étendu possède la structure suivante : Le mésothélium est pseudo­
stratifié. Il comprend une assise de cellules adluminales relativement linéaire qui recouvre 
une assise de cellules granulaires qui s’invagine profondément dans l’assisse conjonctive. 
L’assise conjonctive est formée de très nombreuses übres de collagène disposées de façon 
hélicoïdales selon l’axe longitudinal du tube. Une assise musculaire double (muscles 
longitudinaux et circulaires) s’observe dans la partie externe de la couche conjonctive. 
La ^ musculature est, chez les tubes «adultes», séparée du mésothélium. L epithelium 
interne est formé de larges cellules à cytoplasme homogène et dense dans lequel se 
remarquent par endroits des accumulations de gros sphérules d’aspect muqueux. Les 
cellules épithéliales présentent des replis apicaux irréguliers et d’étroits prolongements 
basaux s’enfonçant dans la couche conjonctive. La lumière du tube est etroite.
La structure du tube étendu (il peut être 30 fois plus allongé que le tube in situ, 
tout en gardant un diamètre semblable) est assez différente. L ’assise de cellules mésothé­
liales adluminales a disparu et les cellules granulaires sont disposées de façon lineaire 
(disparition des indentations). Le contact du tube avec un objet quelconque rompt la 
membrane cellulaire, et entraîne la transformation des granules en une substance dotee 
de propriétés adhésives remarquables. La c o u c h e  conjonctive, d hélicoïdale devient 
cylindrique et s’amincit considérablement. L ’épithélium interne s amincit lui aussi et 
les prolongements basaux ne s’aperçoivent plus. La lumière est très large.
C L O N I N G  O F  A  B A C T E R I A L  I N S E C T I C I D E  
S P E C I F I C  A G A I N S T  D I P T E R A
by
Bart O. M. VANDERBORGHT  
Dienst Algemene Biologie 
Instituut voor Moleculaire Biologie 
Vrije Universiteit Brussel
Each year thousands of people die from diseases like malaria, onchoceriasis, yellow 
fever, and filariasis.
All those diseases need a Diptera as a vector to go from one host to another. Since 
years people try to fight against those diseases by killing the vector with classical agro­
chemicals. As Diptera have developed a high resistance against those insecticides and 
the persistance of those insecticides in the environment, one had to look for alternative 
pesticides, like bacterial pesticides.
One of the bacteria used for this purpose is Bacillus thuringiensis.
B. thuringiensis is a gram positive, sporulating, aerobic bacteria, that can produce 
a toxin specific against Diptera and Lopidoptera, also called the deltaendotoxin. Ihis 
toxin is produced as a cristal during sporulation, which is released in the environment 
with the spore after sporulation.
B. thuringiensis var. istaelensis (Bti) is a variety that can produce a toxin specific 
against Diptera. The toxic effect is likely caused by the synergistic effect of a 28 kDal 
and a 65 kDal protein. Both proteins are coded on a 75 MDal plasmid, which is one ot 
the 8 plasmids of Bti.
The 28 kDal protein probably has a toxic function while the 65 kDal protein has 
to recognise a specific phospholipid target in the Dipterian midgut epithelium. The
28 kDal protein is coded on a 9.7 kDal Hind III fragment.


Mécanismes d'éjection et structure fine des tubes de Cuvier chez de l'holothurie <i>Holothuria forskali</i>

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