Effects of food, kinship, and density on the longevity of spiderlings.

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From: Canadian Journal of Zoology(Vol. 99, Issue 9)
Publisher: NRC Research Press
Document Type: Report
Length: 9,145 words
Lexile Measure: 1560L

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Abstract :

Cannibalism is a behavioral characteristic found in a wide variety of animal groups. Although the rates of cannibalism can vary from one group to another, studies indicate that the main factors contributing to an increase in the frequency of such behavior are the availability of food, population density, the behavior and availability of victims, and environmental stress. We carried out different laboratory experiments to assess whether different factors such as the presence or absence of food among siblings and non-siblings, and at different densities among conspecific and heterospecific individuals, affect longevity of recently emerged Brazilian brown recluse (Loxosceles intermedia Mello-Leitao, 1934) and Chilean recluse (Loxosceles laeta (Nicolet, 1849)) spiderlings during periods of starvation. The results revealed that the survivorship of L. laeta during starvation was significantly higher than that of L. intermedia and that the addition of conspecific individuals increased survival rates by 1.5- and 1.6-fold, respectively. The tolerance of conspecifics differed between the two species, and generally, cannibalism was not observed, probably due to the risk of predation and limited consumption by weakened spiders, which coincided with the continued availability of endogenous vitelline reserves, thus indicating that the use of these spiderlings as a food resource may act to regulate starvation in more resistant spiders. The greater longevity and conspecific tolerance of L. laeta may be important factors contributing to the establishment of large populations of this spider in restricted areas, whereas for L. intermedia, hunger probably functions as a trigger for dispersal. Key words: brown spider, Chilean recluse, Loxosceles laeta, Brazilian brown recluse, Loxosceles intermedia, cannibalism, competition, niche partitioning, starvation. Le cannibalisme est une caracteristique comportementale observee dans des groupes d'animaux tres varies. Bien que les taux de cannibalisme puissent varier d'un groupe a l'autre, des etudes indiquent que les principaux facteurs qui contribuent a accroître la frequence de tels comportements sont la disponibilite de nourriture, la densite de la population, le comportement et la disponibilite de victimes et le stress environnemental. Nous avons realise differentes experiences en laboratoire pour evaluer si differents facteurs comme la presence ou l'absence de nourriture chez des specimens de la meme fratrie ou non et a differentes densites d'individus conspecifiques et heterospecifiques ont une incidence sur la longevite de jeunes recemment emerges de la recluse bresilienne (Loxosceles intermedia Mello-Leitão, 1934) et de la recluse chilienne (Loxosceles laeta (Nicolet, 1849)) durant des periodes de privation de nourriture. Les resultats revelent que la survie de L. laeta durant la privation de nourriture etait significativement plus grande que celle de L. intermedia et que l'ajout d'individus conspecifiques multipliait leurs taux de survie par 1,5 et 1,6, respectivement. La tolerance aux conspecifiques etait differente entre les deux especes et, en general, le cannibalisme n'a pas ete observe, probablement en raison du risque de predation et de la consommation limitee par des araignees affaiblies, qui coincidait avec la disponibilite continue de reserves vitellines endogenes, indiquant que l'utilisation de ces jeunes araignees comme ressource alimentaire pourrait servir a reguler la privation de nourriture chez les araignees plus resistantes. La plus grande longevite et la plus grande tolerance aux conspecifiques de L. laeta pourraient jouer un rôle important dans l'etablissement de grandes populations de cette espece en zones restreintes, alors que, pour L. intermedia, la faim agit probablement comme un declencheur de dispersion. [Traduit par la Redaction] Mots-cles : araignee brune, recluse chilienne, Loxosceles laeta, recluse bresilienne, Loxosceles intermedia, cannibalisme, concurrence, partage des niches, privation de nourriture.

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Gale Document Number: GALE|A675222800