Michael H. Figler's research while affiliated with Towson University and other places

The consequences of an intruder size advantage on the territorial prior residence effect were investigated using resident-intruder pairs in which the intruder was 10%-20%, 25%-35%, or 40%-50% larger than the resident fish. Regardless of the magnitude of the size advantage, intruders established dominance in every pair in which any aggression occurred and delivered significantly more attacks (bites) than did residents. Apparently, an intruder size advantage (fighting ability asymmetry) can overwhelm the territorial prior residence effect (uncorrelated asymmetry) relatively easily.

Experiment I investigated the 24-h retention of chlordiazepoxide (Librium) -induced attenuation and facilitation of habituation of species-specific threat behavior in male Siamese fighting fish. In Session 1, subjects, in a drug solution or plain water, were exposed to an undrugged conspecific stimulus fish for 40 min. After 24 h back in their home jars, all fish were retested in plain water with the same stimulus fish. Chlordiazepoxide showed similar threat behavior attenuation in Sessions 1 and 2 as compared to the control situation. In Experiment II, subjects were immersed in one of the two treatments for the same time period with no stimulus fish present. After 24 h in their home environment, all fish were tested in plain water with a stimulus fish present. Chlordiazepoxide attenuated threat behavior and facilitated its habituation 24 h after initial exposure to the drug. Therefore, the results of Experiment I are due to sustained drug activity rather than transfer of drug-induced behavior from a drugged to a nondrugged state. Suggestions for further research, based upon this sustained drug activity, are discussed.

Group-size preference in circadian hiding behavior by female B. Germanica was investigated by providing first-instar nymphs and adults with numerous similar hiding shelters. The cockroaches were given the opportunity to aggregate, space, or distribute themselves among the shelters in any fashion. Results indicated that both nymphs and adults preferred to hide either alone or in small groups of six or less. However, nymphs chose smaller groups than adults. The results are discussed in terms of circadian vs. escape hiding. It is also suggested that group-size preference may partially depend on population density, since cockroaches aggregate rather than space themselves as population density increases.

Investigating the effects of initial proximity to territorial markers on experimentally produced prior residence effects, 16 pairs of male convict cichlids were randomly assigned to two treatment conditions: a nonreversal condition where the natural resident was closest to the territorial markers at the onset of the encounter, or a reversal condition where the intruder had initially closer proximity to these cues. Results showed that the proximity variable did not change the relative frequency of dominance by the natural resident. The relative frequency of natural residents biting first was also not affected by the proximity variable. As in past studies, the natural residents significantly dominated over intruders, and bit first more frequently, with biting first being a reliable predictor of eventual dominance.

The shelter defense dynamics of reproductively active (Form I) male red swamp crayfish Procambarus clarkii (Girard) were investigated by staging serial intrusions by male, maternal or non-maternal female conspecifics after one day of residence. The male residents showed a direct contest advantage only against non-maternal females, and won a significantly higher proportion of the encounters against non-maternal females than against either male or maternal female intruders. However, there was no significant difference in success against male or maternal female intruders. Further experiments against male intruders showed that increasing male prior residence to either 2 or 4 days did not significantly improve the residents’ proportion of successful encounters. A final experiment revealed extremely low shelter fidelity in male P. clarkii, the most likely reason why male shelter defense against conspecific males and maternal females is not successful. These results, combined with those of past research, suggest that non-maternal females, juveniles and recently molted conspecifics are most vulnerable to predation and cannibalism, since males and maternal females easily out-compete non-maternal females for shelter, and adults out-compete juveniles. These findings may have implications for P. clarkii aquaculture and general management.

In many disparate taxa, including crayfish, a freshwater decapod crustacean, the presence of one’s offspring has been shown to be an important variable in the level of maternal aggression. Ovigerous American lobsters (Homarus americanus) show a territorial advantage against nonmaternal females, even though no posthatch care is provided. The eggs are attached to the pleopods (swimmerets) throughout embryogenesis. We evaluated the effect of stripping ovigerous H. americanus females of their eggs on maternal territoriality. In one treatment group, maternal females were stripped of all eggs. Twelve days later, including being individually isolated for an additional 48 h in a test tank, each resident was serially intruded upon by 4 non-maternal conspecific females. An identically treated control group of ovigerous female residents was left intact prior to the serial intrusions. Various biochemical parameters of the stripped and unstripped animals were measured before and after the experimental treatment (or control). The behavioral modulators measured were the biogenic amines, octopamine and serotonin, and the stress indicators were a heat-shock protein (HSP70), methyl farnesoate, and crustacean hyperglycemic hormone. The intact ovigerous residents showed a significant territorial advantage over the intruders, whereas the contest outcomes of stripped residents were reduced to chance. The presence of eggs in maternal H. americanus is therefore necessary for the maintenance of the shelter-related territorial advantage. However, no significant differences in any of the biochemical parameters were observed between or within treatment conditions. It appears that these amines are not prominently involved in the mechanism of maternal aggression, and that these changes in territorial defense are not simply due to changes in general stress as a result of stripping the females of their eggs.

The offspring-defense hypothesis of maternal territoriality in solitary and semisocial mammals [Wolff JO and Peterson JA. 1998. Ethol Ecol Evol 10:227–239] was evaluated in another taxon using maternal and nonmaternal female red swamp crayfish (Procambarus clarkii), a freshwater decapod crustacean that shows pronounced shelter-related maternal aggression. The maternal females were of three different categories: (1) ovigerous, (2) carrying primarily stage 1 offspring, or (3) tending offspring that were primarily stage 2. Each female was in residence in an individual aquarium containing only a gravel substrate for 24 hr prior to serial intrusions by male conspecifics. Virtually all of the residents, maternal and nonmaternal, excavated a depression (shelter) in the substrate prior to the first intrusion. The results showed that residents in each of the maternal categories won a significantly higher proportion of their encounters than did the nonmaternal residents, which showed only negligible defense and lost every encounter. However, there were no significant differences in encounter outcomes between the maternal resident categories. There was clear defense of the shelter by maternal females, with virtually all fighting being in or around it, thus demonstrating stable, heightened territorial defense throughout these maternal phases of reproduction. This support of the offspring-defense hypothesis of maternal territoriality is the first such evidence for a freshwater crustacean and is very similar to that recently reported in a related marine decapod, the American lobster (H. americanus). Aggr. Behav. 27:391–403, 2001. © 2001 Wiley-Liss, Inc.

Three experiments were conducted to determine (1) the pharmacodynamics of 5-hydroxytryptamine in juvenile lobsters; (2) the effects of 5-hydroxytryptamine, using a range of dosages, on a motor behavior used to escape an aversive situation; and (3) the effect of doses that did and did not inhibit this motor behavior on measures of dominance and shelter competition. The fate of 5-hydroxytryptamine in hemolymph over a 60-min post-injection period showed that the concentration fell rapidly to a low plateau that was maintained for at least 1 h. Low doses of 5-hydroxytryptamine did not affect locomotor behavior, but higher doses inhibited it. Dominance and subsequent possession of a shelter were unaffected by a low dose of 5-hydroxytryptamine but a higher dose that inhibited locomotion resulted in lobsters that lost fights and did not secure or retain possession of the shelter. In the context of dominance and shelter competition, we were unable to demonstrate any advantage of the low dose of exogenous 5-hydroxytryptamine and a severe disadvantage with the higher dose. Previous reports of transient increases in aggression in 5-hydroxytryptamine-treated subordinate lobsters did not take into account motor inhibition as a possible critical variable in aggression.

Using a resident–intruder model, 24-h resident juvenile male and female red swamp crayfish, Procambarus clarkii, were intruded upon by same or opposite sex juvenile conspecifics that were the same size or larger than the residents. Relative size was significantly related to contest outcomes. Residents that were the same size as the intruders won a significantly higher proportion of their encounters than residents that were smaller than the intruders. Overall, neither sex nor prior residence was significantly related to contest outcome. There was clear shelter-related territorial defense in both male and female juveniles, and is very similar to that shown in adult conspecifics. The provision of shelter for juveniles in the aquaculture of P. clarkii is especially important because of the shelter competition advantage of adults. This indirectly increases juvenile vulnerability to heterospecific predation and cannibalism by conspecific adults and juveniles.