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Open Access Publications from the University of California


The International Journal of Comparative Psychology is sponsored by the International Society for Comparative Psychology. It is a peer-reviewed open-access digital journal that publishes studies on the evolution and development of behavior in all animal species. It accepts research articles and reviews, letters and audiovisual submissions.

Volume 4, Issue 3, 1990


Wavelength Categorization by Goldfish (Carassius auratus)

Goldfish pressed a paddle

for intermittent food reinforcement in the presence of one of seven different monochromatic wavelengths. Wavelengths in 20nm steps from 430 to 690 nm, matched for "brightness," were then presented for 20 days during which food maintained responding to the training stimulus. Generalization gradients calculated from the final four days were asymmetric. A long wavelength gradient showed maintained responding above 630 nm; at short wavelengths responding generalized below 490 nm; four middle wavelength gradients could indicate two groupings having maximum responses at around 510 and 570 nm. 


Dominance Behavior in Asexual Gecko, Lepidodac lugubris, and its Possible Relationship to Calcium

Investigations of dominance behavior and its relationship to  calcium gland size were conducted in the asexual gecko, Lepidodactylus lugubris. In an initial study, geckos,immediately after laying eggs, were randomly assigned to one of six groups where time of social contact (2 vs. 7 days) and type of social contact (direct experience with a gravid or non-gravid gecko or indirect experience) were varied in a 2 X 3 factorial design. Behaviors displayed by geckos in social contact were system atically recorded. Dominance hierarchies were readily formed between gecko  dyads that received 7 days of social contact with each other. Dominance was not related to gecko size or reproductive state. A second study examined the relationship between dominance, calcium gland size and egg development. Geckos were housed in groups of 4 for 28 days and were subsequently transferred into either dyads or housed individually for an additional 28 days. During the final 28 days, half of the geckos received extra calcium. Dominance, size of calcium glands and egg development were recorded. Dominant geckos developed a greater number of eggs and had larger initial  calcium glands than subordinates, but extra calcium was not related o gland size. The function of dominance in L. lugubris populations may be two-fold: it may act as a spacing mechanism in low density environments and may facilitate the development and laying of eggs by more nutritionally fit individuals in high density environments.

Boxing in Red Kangaroos, Macropos Rufus: Aggression or Play?

Fighting in a boxing style is the most spectacular behaviour of red kangaroos,  Macropus rufus, yet its structure and function have not been analysed in detail. Patterns of sparring, kicking and wrestling occur between mothers and young (especially males), in formalized contests between males, and in escalated conflicts over resources (shelter, water, oestrous females). Observations were made of fighting behaviour in free-living and captive individuals. The frequency of fighting between various age/sex classes in the field was determined and the structure of fighting over a water resource was analysed from a 12 h videotape record. These results were compared with an analysis of 85 videotaped plus 35 other fights observed in a captive group of eight males (age 1 - 7 year). These fights were formalized contests  which did not involve or resolve any immediate conflict over a resource. Such fights share many of the properties ascribed to play-fighting. They are initiated with invitational behaviour that does not include characteristic threat behaviour seen in fights over a resource. They involve self-handicapping, some lack of dominance distinctions, and usually several bouts occur interrupted by mutual pauses. The structure of the fight suggests that the main goal is to push or wrestle the opponent off balance and down to the ground rather than inflict potentially injurious kicks as seen in resource conflicts. Furthermore larger opponents often adopt an inferior flat-footed stance and dominants and/or winners kick significantly less than losers. The  context, goals and structure of these non-resource based fights suggest that they are a form of play-fighting. Selection of play partners on the basis of size/dominance or kinship indicate that such play-fighting in red kangaroos is neither truly cooperative nor disruptive and selfish. The behaviour most likely functions as a form of non-damaging assessment of opponents with benefits in skill development in younger individuals.