Wendy L. Hill

Correlates of male mating success in the ruff Philomachus pugnax, a lekking shorebird

SummaryMale ruffs (Philomachus pugnax), a lekking shorebird, can generally be divided into two morphs according to behavior and plumage coloration. Predominantly dark-colored, “independent” male ruffs defend small territories on a lek, whereas lighter colored “satellite” males are non-territorial and less site-faithful to a particular lek. The traits associated with the mating success of independent male ruffs were studied at two leks during two seasons on the island of Öland, Sweden in May and June of 1985 and 1987. Using multivariate analyses, three characteristics were found to be significantly related to mating success: high frequency of visits by satellites to an independent males residence, consistency of lek attendance, and low rates of aggressive behavior. In contrast, mating success was unrelated to the degree of darkness of the independent male nuptial plumage, territory location on the lek, or rate of courtship displays. The use of multivariate analyses helped to resolve conflicting conclusions from previous studies which employed simple statistical analyses, or none at all. Experimental manipulations are suggested which will help to further determine the influence of female mate choice in this lekking system.

Acute effects of aspartame on aggression and neurochemistry of rats.

The inverse relationship between serotonin and aggression was investigated in rats treated with aspartame, a sweetener thought to interfere with the synthesis of this neurotransmitter. Eleven adult, male Long-Evans rats received either aspartame (200-800 mg/kg, IP) or the vehicle prior to testing in a standard resident-intruder paradigm. Contrary to our hypothesis, aspartame significantly decreased aggression as shown by increased latencies to the first attack and decreased number of bites per session. Corresponding with the effects on aggression, aspartame significantly increased striatal levels of serotonin. It was concluded that high doses of aspartame reduced aggressive attack via a serotonergic mechanism while the lower dose was without effect on either variable.

Time-dependent effects of PCPA on social aggression in chicks

We investigated the effects of para-chlorophenylalanine (PCPA), a serotonin (5-HT) antagonist, on social aggression and brain neurochemistry in young domestic chickens (Gallus domesticus). In Experiment 1, the effects of four different doses of PCPA (0, 100, 200, and 400 mg/kg) were examined for 3 days after injection. Immediately after PCPA injection, aggressive pecking was low and then increased over the 3-day test period. PCPA significantly decreased 5-HT, 5-hydroxyindoleacetic acid (5-HIAA), and 5-HT turnover. In addition, the frequency of aggression was negatively correlated with levels of 5-HIAA. In Experiment 2, the time-dependent effects of a single 400-mg/kg dose of PCPA were examined for 5 and 7 days after drug exposure. PCPA-treated chicks observed for 5 days after injection had significantly greater frequencies of aggression 4 days following drug exposure and significantly reduced 5-HT levels when measured on the next day. Similarly, chicks observed for 7 days exhibited significantly elevated aggression 5 days after injection, after which their pecking decreased to control levels on days 6 and 7. Coinciding with this behavioral pattern, 5-HT levels from these PCPA-treated chicks when assessed 7 days after drug exposure were the same as those for control birds. We concluded that PCPA increased social aggression in birds, an effect that diminished as brain 5-HT levels recovered over a 1-week period.

Nest distance mediates the costs of coloniality in Eared Grebes

-We examined the behaviors and reproductive characteristics of 4 Eared Grebe (Podiceps nigricollis) colonies located at the Malheur National Wildlife Refuge in eastern Oregon that varied in nesting density. In 1993, we studied 2 colonies found on 2 different lakes, whereas in 1994 we conducted a within-lake comparison of 2 subcolonies. During both years, nearest neighbor distances differed significantly between the colonies investigated. Breeding pairs were significantly more aggressive at those colonies with smaller distances among nests. Within each year, there was a greater rate of intraspecific brood parasitism and egg loss at the higher density colony. Infanticide occurred at high rates when nests were very densely packed, whereas a relatively high rate of predation by American Coots (Fulica americana) resulted when nests were quite dispersed. Thus, in spite of the distinct breeding characteristics of Eared Grebes, many disadvantages associated with nesting density in seabirds also have an impact on these colonially breeding waterbirds. Received 30 May 1997, accepted 19 August 1997, final version received 11 September 1997.

Performance of Zucker rats in two consummatory contrast paradigms

Zucker obese rats showed larger successive negative contrast (degree of reduction in licking when shifted from 32% to 4% sucrose) and larger anticipatory contrast (depressed intake of 4% sucrose when 4% sucrose preceded 32% sucrose in once-per-day pairings) than Zucker lean rats. However, the difference between the lines was small and the performance of the obese rats was similar to that of commercially available Sprague-Dawley rats. The lean and obese rats did not differ in their intake of 32% or 4% sucrose in noncontrast conditions, but they did differ in open-field activity—the obese rats were considerably less active than the lean rats. These data indicate that Zucker obese rats show normal incentive relativity functions in the consumption of sucrose.