Browsing by Author "Niemeyer, HM"

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    Behavioural thermoregulation in Acyrthosiphon pisum (Homoptera: Aphididae)
    (2001) Lagos, NA; Fuentes-Contreras, E; Bozinovic, F; Niemeyer, HM
    The effects of parasitisation by Aphidius ervi on the thermoregulatory behaviour of the pea aphid Acyrtosiphon pisum were studied in alfalfa fields and in an experimental thermal gradient. In the field, mummies were found exclusively on the adaxial surface of the upper leaves, and aphids in the mid canopy. The adaxial surface of the upper leaves was ca, 2 degreesC hotter that the mid-canopy, In the thermal gradient, the thermal effect (selected minus exposure temperature) was higher in magnitude in non-parasitised than in parasitised aphids; the thermal effects of both types of aphids were linearly and negatively correlated with exposure temperature (i.e. aphids showed negative thermal sensitivity), The thermal sensitivity of parasitised aphids was lower than that of non-parasitised aphids. The results are discussed in relation to hypotheses on factors governing the host-parasite relationship. (C) 2001 Elsevier Science Ltd. All rights reserved.
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    Chemical exploratory behavior in the lizard Liolaemus bellii
    (2001) Labra, A; Beltrán, S; Niemeyer, HM
    An experimental study was carried out to determine whether self and conspecific chemical recognition occurs in Liolaemus bellii, a Tropidurid lizard from Central Chile. Experiments were performed during the autumn and the spring. Using the number of tongue flicks as an indicator of discrimination, it was found that L. bellii showed both self and conspecific chemical recognition. Lizards recognized their own territories, and conspecific chemical recognition showed seasonal changes. During autumn, lizards showed higher exploratory behavior (higher numbers of tongue flicks and motion time) than in spring, and female enclosures elicited in males higher numbers of tongue nicks. Similar results were previously found in other Liolaemus species from a different habitat The information available at present for Liolaemus suggests that recognition of own territory is more important than recognition of conspecifics, and the latter seems to be associated mainly to the reproductive season. Therefore, conspecific and self-chemical recognition seem to be independent of the habitat used by the species, although habitat could modulate the use of chemical signals.
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    Sources of pheromones in the lizard Liolaemus tenuis
    (2002) Labra, A; Escobar, CA; Ar, A; Niemeyer, HM
    Experimental tests were conducted with the lizard Liolaemus tenuis (Tropiduridae), to determine the potential sources of pheromones used in its chemical communication, centered in the phenomenon of self-recognition. During the post-reproductive season, feces of both sexes and secretions of precloacal pores (present only in males) were tested. Stimuli were presented to lizards spread on rocks, and the number of tongue-flicks (TF) to the rocks was used as a bioassay to determine pheromone recognition. Feces contained pheromones involved in self-recognition, since lizards showed less TF confronted to rocks with suspensions of their own feces than with suspensions of feces of conspecifics or with water (control). In order to assess the chemical nature of self-recognition pheromones, feces were submitted to a sequential extraction with three solvents of increasing polarity, thereby obtaining three feces fractions. There were no differences in TF towards rocks with different fractions with own feces. Additionally, lizards showed similar TF to rocks with fractions of own and conspecific feces, suggesting that the separation procedure broke up a complex stimulus into parts that were not active individually as pheromones. Finally, males did not discriminate between precloacal secretions from themselves and from another male. It is possible that these secretions convey information relevant to or detectable by females only.