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POLYETHISM IN FORAGING IN A POLYMORPHIC PREDATOR, ENOPLOGNATHA OVATA (ARANEAE: THERIDIIDAE): A CASE FOR BALANCE

Published online by Cambridge University Press:  31 May 2012

Carlos F. Greco  and
Peter G. Kevan
Carlos F. Greco
Affiliation:
Department of Environmental Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1
Peter G. Kevan*
Affiliation:
Department of Environmental Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1
*
2Author to whom all correspondence should be addressed.
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Abstract

Two colour morphs of Enoplognatha ovata (Clerck), “redimita” and “lineata” the abdomens of which are whitish with two pink stripes and greyish-yellow, respectively, differ in their foraging strategies. When placed in artificial arenas with flowering stems to ascend, we noted that both morphs had a strong tendency to wander over the ground rather than ascend a stem [unlike the crab spider, Misumena vatia Clerck (Araneae: Thomisidae)], but that lineata was significantly more prone to wander than was redimita. Neither morph showed choice for the type of stem or colour of flower. Nevertheless, redimita showed a greater preference for choosing white artificial flowers (discs) atop 30-cm wooden rods than did lineata. We propose that the relative abundances of the two colour morphs in the natural population represents a balanced polymorphism which is maintained in part by polyethism in hunting strategies, with redimita being more fastidious in its selection of cryptic hunting sites in flowers than is lineata, and the latter being more cryptic and more errant on the ground.

Résumé

Deux formes de colorations différentes d’Enoplognatha ovata (Clerck), «redimita» et «lineata», la première à l’abdomen blanc portant deux rayures roses, la seconde à l’abdomen jaune grisâtre, diffèrent aussi par leur stratégie de quête de nourriture. En présence de tiges à inflorescences pour grimper, dans des arènes artificielles, nous avons constaté que les deux formes ont fortement tendance à errer sur le sol plutôt qu’à grimper [contrairement à l’araignée crabe Misumena vatia Clerck (Araneae : Thomisidae)], et que lineata est significativement plus encline à errer que redimita. Ni l’une ni l’autre forme n’ont manifesté de préférence pour une couleur de fleur ou un type de tige en particulier. Cependant, les araignées de la forme redimita ont montré une préférence plus grande à choisir des fleurs artificielles blanches (disques) au bout de tiges de bois de 30 cm que celles de la forme lineata. Nous croyons que les abondances relatives des deux formes dans la population naturelle représentent un polymorphisme d’équilibre maintenu en partie par le polyéthisme des stratégies de chasse : redimita est un chasseur plus pointilleux dans son choix de sites de chasse dissimulés dans les fleurs, alors que la forme lineata a plus tendance à se cacher et est plus encline à errer sur le sol.

[Traduit par la Rédaction]

Type
Articles
Information
The Canadian Entomologist , Volume 131 , Issue 2 , April 1999 , pp. 259 - 268
Copyright
Copyright © Entomological Society of Canada 1999

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