Journal Article

Do Agonistic Interactions Underlie the Segregation and Relative Abundances Between Two <i>Loxosceles</i> Species (Araneae: Sicariidae)?

in Journal of Medical Entomology

Published on behalf of Entomological Society of America

Volume 51, issue 3, pages 547-559
Published in print May 2014 | ISSN: 0022-2585
Published online December 2014 | e-ISSN: 1938-2928 | DOI: http://dx.doi.org/10.1603/ME13064
Do Agonistic Interactions Underlie the Segregation and Relative Abundances Between Two Loxosceles Species (Araneae: Sicariidae)?

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The medically important spiders Loxosceles intermedia Mello-Leitão and Loxosceles laeta (Nicolet) are segregated in Curitiba, southern Brazil, where L. intermedia is more abundant and widespread than L. laeta. Because they share similar microhabitat preferences and wander in search of web sites, agonistic encounters are likely to occur. The purposes of this study were to describe agonistic interactions and interpret their consequences for the relative abundances and spatial segregation of L. intermedia and L. laeta. Experimental contests were performed between residents and intruders. Asymmetries between contestants included sex, age, species, weight, and residence status. Nine behavioral categories were defined. Through discriminant analyses, it was possible to differentiate spider sex, species, and residence based on their agonistic behaviors. Intruders, juveniles, and L. intermedia individuals were better characterized by exploratory behaviors, whereas L. laeta females were differentiated by aggressiveness. By performing a multiple logistic regression, with winning or defeat as a dependent variable of sex, age, species, size, weight, and residence, it was possible to say that residents and L. intermedia individuals had the highest winning odds in contests, whereas juveniles had lower winning odds than adults. Advantages of the prior residence may help to explain the predominance of L. laeta in old colonization sites, whereas the higher winning odds of L. intermedia and less aggressive behavior toward conspecifics may lead to a successful establishment of dense populations in new sites. A better understanding of agonistic interactions as a mechanism of spacing, segregation, and species replacement among spiders may be helpful for control purposes.

Keywords: agonistic behavior; Loxosceles; prior residence; species segregation

Journal Article.  5987 words.  Illustrated.

Subjects: Disease Ecology and Epidemiology ; Entomology

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