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  • Author or Editor: David Chiszar x
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Abstract

Male pumpkinseed sunfish (Lepomis gibbosus) readily attacked plywood models placed into their nests. Models containing red features (iris, opercular flap) received more attacks and aggressive displays than models lacking these features or than models which had these features painted black. This indicates that in the pattern of the male pumpkinseed, the red portion of the opercular flap and the red iris are social releasers for aggressive behavior. These features fade in subordinate pumpkinseeds in the laboratory and also in female pumpkinseeds before they enter the male's nest during reproduction. This pattern change would therefore function to decrease aggressive behavior directed at these individuals. A conspicuous feature of the female pumpkinseed is the presence of lateral bars. When bars were added to models, reductions in aggressive behavior were consistently observed. Hence, bars appear to inhibit male aggression. Bluegill sunfish (L. macrochirus) nest sympatrically with pumpkinseeds and interspecific nest defense was commonly seen. A conspicuous feature of male bluegills is a dark spot in the area of the dorsal fin rays. When such a spot is added to models, increases in aggressive behavior were observed in male pumpkinseeds. Hence, this feature may provide a basis for interspecific recognition and reproductive isolation. Finally, pumpkinseeds responded more vigorously to models than did bluegills. This may imply that the former are more attuned to morphological features than the latter. Bluegills, on the other hand, may be more attuned to the behavior of nest intruders. This hypothesis agrees with differences in the nesting ecology of these species.

In: Behaviour

Abstract

Several parameters of predatory and aggressive behaviors were measured in bluegill sunfish (Lepomis macrochirus) as a function of the social condition of the fish. Subjects were observed as 1) isolated individuals, 2) maintained pairs with complete dominance but no prior residency, and 3) temporary pairs equivalent to a resident-intruder relationship. Aggressive interactions weer also recorded during feeding sessions and during non-feeding control periods. An almost complete inhibition of feeding occurred for intruders in the temporary pairs with little or no deficit seen for submissive fish in the maintained pairs when compared to individual controls. No predatory differences were found among the dominant fish of the three groups. Aggressive behavior showed little reliable change between types of session, although all forms of aggression were much higher in the temporary pairs than in maintained pairs. In a second experiment, performed to determine the effects of the transfer procedure independent of social interaction, fish were transferred from their home tank to either an empty tank or one containing a resident conspecific. A significant decrement in predatory behavior occurred when compared to measurements taken in the home tank only when subjects were transferred to aquaria containing resident fish. The data indicated that the behavioral suppression seen in intruding subjects was due entirely to an inability to respond to both prey and aggression with the latter taking precedence. No evidence was obtained to indicate any form of motivational interdependence between the behaviors studied.

In: Behaviour

Abstract

We tested the roles of prey odor and other habitat cues in the pre-strike movement patterns of two, ecologically distinct sub-species of the western rattlesnake in naturalistic arenas. In the first experiment, rattlesnakes preferred habitat containing prey odor and cover comprised of rocks, sticks and plants. While searching, rattlesnakes methodically investigated the edges and crevices within rock, areas rodents might frequent in nature. In the second experiment, rattlesnakes investigated sticks more than rocks arranged topographically similar to sticks. In the third experiment, rattlesnakes preferred habitat that included brush foliage and used chemical prey trails in pre-strike behavior via (i) trail-following, (ii) casting search patterns and (iii) scanning search patterns. Several snakes coiled in stereotyped ambush postures that allowed them to face chemical trails while resting against rocks and foliage. These results suggest that rattlesnake foraging exhibits qualities advantageous for hunting rodent prey in addition to providing protection from predators and perhaps promoting thermoregulation. Sub-species did not exhibit geographic variation in foraging behavior despite differences in natural history and morphology. Hence, the microevolutionary pattern suggests that generalized foraging repertoires are successful in numerous environments when coupled with locally specialized body patterns.

In: Behaviour

Abstract

Three experiments studied predation upon neonatal rodents by brown tree snakes (Boiga irregularis). Experiment 1 showed that chemical cues arising from prey were used in foraging tests that could not be completed on the basis of vision alone. Experiment 2 provided only airborne chemical cues, and snakes performed at chance levels in selecting among odoriferous (baited) and non-odoriferous (unbaited) nests. Snakes performed above chance, however, when a chemical trail led to the baited nest (Experiment 3), suggesting that non-volatile chemicals are most important in guiding choice behaviour.

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In: Amphibia-Reptilia

Abstract

Bidder's organs in both male and female bufonids are hypothesized to represent a transitory state in an evolutionary transformation from extensive, hyperfecund ovaries to smaller, less fecund ones-a transformation that other families of anurans experienced in forms now long extinct. Some members of the genus Bufo retain considerable hyperfecundity, but in derived species of Bufo and genera of Bufonidae a spectrum of ovarian reduction exists. In those groups, Bidder's organs normally persist, always in males and often in females, as an undifferentiated ovaroid or ovary in a non-functional transition between the ancestral state and modification as part of the fat body. The organs are gynomorphs in males and highly variable as vestigial structures, but may well have endocrinogenic functions in both sexes although gametogenic functions in nature have been lost in males. Presence of Bidder's organs is a derived condition in the context of anurans as a whole, but primitive within the family Bufonidae.

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In: Amphibia-Reptilia