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  • Author or Editor: Rudolph J. Miller x
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Rudolph J. Miller and Darrell D. Hall

Abstract

An ethological study of courtship and reproductive behavior of the anabantoid fish, Trichogaster leeri (Bleeker), was conducted on 6 breeding pairs in aquaria. Sexual behavior in this species is characterized by stereotyped behaviors and a distinct temporal pattern of activities that presumably aids in species isolation. Data were taken on form and structural features of bubble-nests, colors of male and female, and behaviors occurring during daily or twice-daily 15-minute observation periods over a period of approximately one year. Spawning sequences usually last 2 to 5 hours in this species and are characterized by several different bout types (interactions between male and female), which may be initiated by either male or female. The major phases observed were: (1) prespawning preparatory phase (2) courtship phase (3) clasp (4) swimming inhibition (5) postspawning aggression and (6) interval between bouts. The prespawning phase in males is generally characterized by establishment of a nest-territory, development of breeding color, and elongation of dorsal and anal fin soft-rays. This phase in females is usually marked by increased abdominal plumpness and changes in color and body-markings. Strictly speaking, only the latter parts of this phase occur during spawnings. Spawning bouts (stages 2, 3, and 4 of the ethogram) comprise approximately 7% of all bouts and many of these do not follow an "ideal" pattern. Spawning bouts usually last 50-55 seconds with courtship requiring 12-15 seconds, the clasp about 25 seconds, swimming inhibition 2-5 seconds, and postspawning aggression 3-6 seconds. Female courtship butting precedes almost all spawnings and appears to release leading-to-the-nest, lateral spread display, and curving in sexually responsive males. Spawning bouts generally contain fewer female courtship butts than most other sexual bouts and a conspicuous difference exists between female courtship butting means in spawning and pseudospawning bouts. Although reproductive behavior in T. leeri is stereotyped, variation in form, sequence, and duration of components is evident. Flexibility and adaptability are common so that variation within certain limits may be tolerated and/or compensated for. Hyperaggressiveness, physiological condition, low sexual motivation, mechanical problems, and previous experience appear to be important factors in determining the success of sexual bouts in T. leeri. Reproductive color changes, body-marking changes, and sexual dimorphism provide visual stimuli that may aid in the synchronization of reproductive behavior.

Darrell D. Hall and Rudolph J. Miller

Abstract

This paper provides a detailed quantitative description and analysis of the courtship and reproductive actions of Trichogaster leeri. Principal objectives are to present a description which will be useful in future comparative (and phylogenetic) studies, to determine how well detailed quantitative analysis provides insights into motivational mechanisms in these fish, and to see how well such data can be interpreted in terms of conventional ethological theories. Five pairs of mature fish provided complete records of fifteen spawnings (referred to below as sequences) ranging in duration from 2.7 to 5.5 hours. Reproductive and courtship activities in captive T. leeri and other anabantoid fishes occur in bouts of varying length which may be categorized on the basis of behavioral components present. While most bouts contain behaviors involving both fish, some bouts occur in which one fish (usually the female) shows no visible response to the action of the other. Examination of the organization of these bouts in the spawning sequence, the nature of activities in the different types of bouts, and the relationships between completeness of the bout, sex of the fish initiating the bout, and duration of intervals between bouts provide information about some of the factors influencing courtship and spawning. Bouts that are initiated by females are much more likely to be successful (proceed to clasping or spawning) than those initiated by males. Although males initiated over half of the bouts, spawning occurred in 88 female-initiated bouts and in only 10 male-initiated bouts. Thus we suggest that while male overt activity is often prominent several days to weeks before and after spawning, it is actually less critical in determining the outcome of sexual bouts than are female activities. Highly motivated males had little success in stimulating refractory females to successful spawning, whereas the converse appeared commonplace. Data on duration of intervals between bouts shows that females generally remained away from the nest and male longer after more complete bouts than after less complete (and typically shorter) bouts. Thus it seems unlikely that sexual and agonistic interplay during the bouts stimulated the female directly (arousal function). Furthermore, male-initiated bouts were found to be more successful the greater the duration of the interval preceding his approach. Although part of this apparent refractoriness is undoubtedly attributable to muscle fatigue or a similar phenomenon, performance of more complex actions in the more complete bouts may have some kind of central satiating (or drive-reducing) function. In the next section, variations in the frequency and duration of female approach, male leading-to-the-nest, male lateral spread, male circling, female courtship butting, male clasp, swimming inhibition, male butting and biting, male chasing, female appeasement, and total bout durations are presented in tables as they occurred in the 15 different types of bouts. Possible causes for these variations are discussed and the use of bout statistics in evaluating motivation levels is examined. For example, detailed examination of data on male butting and biting and male chasing suggest that male aggression only bouts may actually represent a rather lower degree of absolute aggressiveness in males than that which occurs in many bouts that succeed to more complex levels. Female sexual signals or responses may enhance aggression as part of a general increase in excitement, or partial female responses may lead to thwarting and resultant increased aggression. Much data is presented to support the contention that male courtship only bouts are least associated with aggressive motivation and are a good indicator of sexual motivation in the male. Furthermore, we suggest that the frequency of these two types of bouts in a sequence may be a fairly accurate reflection (if such is actually possible) of the relative strengths of sexual vs. aggressive motivation in a given sequence, because these two bout types occur in the absence of any measurable female responses, thus eliminating that critical variable from the list of factors which might influence male behavior. Evidence also is cited to support the contentions that female flight tendency is lower in female-initiated bouts and that male aggressiveness tends to be slightly higher in many (if not most) male-initiated bouts than in female-initiated bouts. There is also an indication that the nature of actions occurring in bouts have less influence on the activities of males in subsequent bouts than on those of females. In the next section, data on 10 of 11 activities discussed above in terms of their appearance in all bouts of a certain type (across the 15 sequences) are presented as they occur in each sequence, regardless of the bout type in which they occurred. The sequences are ranked (Table 18) from those in which the males were judged most aggressive (measured by frequency of male butts and bites) to those judged least aggressive. Aggression analysis shows that another potential measure of aggressiveness, male chasing frequency and duration, shows no direct correlation wih butting frequency, except perhaps a slightly negative one. The reasons for this are discussed in detail. The choice of male butting rate as the most nearly accurate indicator of male aggressiveness is justified on the basis of its agreement with other parameters such as female appeasement duration and circling duration (previously and subsequently shown to be associated with several indicators of aggression). High-aggression sequences tend to be those in which female responsiveness (or sexual initiative) is minimal. If male aggressiveness is determined exclusively internally, it is likely that female self-protection butting would occur more commonly than it apparently does in such sequences. It seems probable, therefore, that female behaviors may markedly effect motivation levels in the male. Since highly-aggressive males also seem to exhibit much leading-to-the-nest and other indicators of sexual motivation we suggest that factors causing increased approach tendency, aggression, and courtship in males are not entirely independent of one another. In the sexual motivation analysis, data are discussed which indicate that high clasp frequency and low clasp durations in a sequence are indicative of high female sexual motivation. Such sequences also have a high percentage of female-initiated bouts. Conventional analysis of male leading-to-nest, lateral spread display, and circling can be interpreted to support the hypothesis that the three behaviors represent three conflict levels between aggressive and sexual systems, with leading dominated by sexual factors, lateral spread indicating near equilibrium, and long-duration circling dominated by aggressive factors. Female butting is a sexual signal indicating readiness for further sexual activity and there is a strong indication that it is used also as a self-protection device in the absence of female readiness to spawn. Examination of spawnings of the same pairs in a temporal sequence shows that female butting rate increased in later sequences in all cases, suggesting the importance of experiential factors in the ultimate regulation of this activity. In the section on organization of motivating mechanisms, one pattern, the lateral spread display, was selected for more detailed analysis in order to evaluate the utility of generally-accepted ideas on conflict theory and attack-escape motivation. We are forced to reject the theory that lateral spread can be strictly interpreted in terms of a certain A/F ratio. Rather, the idea that fin spreading need not be under the direct control of motivational systems (at least initially) is expanded to encompass the possibility that learning processes may be intimately involved in the development of the lateral spread. The senior author presently is testing this typothesis in Trichogaster trichopterus and Macropodus opercularis. Our final conclusion is that alternate hypotheses appear to be as useful as conventional attack-escape theory in interpreting this extremely common behavior. In the final section we have tried to see whether or not our data can provide some insight into the nature of phenomena such as positive or negative arousal in T. leeri. Although we have shown in an earlier section that longer, more successful bouts were followed by longer inactivity in females, other data indicate that female-initiated bouts are generally followed by female-initiated bouts which are as complex or more complex than the initial bout. The latter pattern (in females) might be interpreted as an indication of arousal. If so, it is possible that performance of courtship and sexual behaviors has both positive and negative effects on arousal. Interestingly, some degree of success in male-initiated bouts tends to increase the probability of further male courtship in subsequent bouts. It thus appears that performance and success in actions initiated by fish of each sex has reinforcing properties only on fish of that sex. Although virtually no clues exist as to the nature of the factors that terminate spawning in the female, some of the factors affecting the male apparently are accessible. Data on male approach, aggressiveness, and courting actions throughout a spawning cycle suggest that males are more prone to courtship activity after the terminal spawning bout than at any other time. Since there is no clear evidence of enhanced male courting tendency after other spawnings, the effect must be due to some cumulative process. Failure of the female to respond to male courting gradually leads to increased male aggressiveness, which a few hours after spawning is greater than at any other time.

Rudolph J. Miller and Dennis F. Frey

Abstract

I. Hierarchical relationships in the blue gourami, T. trichopterus, are characterized by two distinct temporal phases — an ephemeral period of dominance establishment and a period of hierarchical maintenance. Variable behavior patterns are shown in the mutual fighting during dominance establishment between pairs of fish, but the initial outcome is always a discrete event, i.e., one fish dominates the other. The influence of several parameters on this period of dominance establishment has heen investigated in this study, and the probable relationships between these parameters and patterns of behavior characteristic of ultimate winners and losers has been discussed. 2. Prior residency per se does not increase the "dominance potential" of this species. Residency was not found to act as a positive input for increased aggressiveness; rather it was concluded that the "fright" component due to moving a fish into unfamiliar surroundings acts to inhibit the "normal" expression of aggressive behavior. The residency factor interacts both with prior dominance experience and with time since that experience. 3. Prior experience as a dominant increases the probability that a fish will win a subsequent encounter, while fish previously dominated within the last 24 hr seldom win subsequent encounters. Forty-three behavior measures recorded during these subsequent encounters did not indicate an arousal phenomenon due to dominating a partner for 24 hr, but a highly significant inhibitory effect on all agonistic behaviors was observed for those fish which had been dominated for 24 hr. These inhibitory effects wane during the next 24 hr, provided the dominating partner is removed. It is conceivable that short-term arousal input due to winning per se may temporarily lower aggressive thresholds, but whether these lowered levels would be "transferred" into a new fighting context is questionable. 4. The inhibitory effects of "non-residency" are in part dependent upon the "dominance state" of a fish. Dominant-experienced fish are only slightly inhibited by non-residency, while subordinate-experienced fish are strongly inhibited by this factor. A s the prior experience effect wanes, the fright due to unfamiliarity with surroundings is less inhibiting. 5. Initially, the decrement in responses due to prior experience is greater than the decrement due to non-residency. 6. Two measures of intra-individual sequence uncertainty (entropy) were calculated. The first included the uncertainty associated with all the elements defined for the system, i.e., [L, O, BS, F,, S, and P], while the second entropy values were based on only the agonistic set [L, O, BS, and F]. The prior experience factor influenced both entropy values more strongly than it did any other single variable. 7. The relative sizes of opponents seem paramount in deciding bout outcome when standard length differences (Δ S.L.) are beyond the range tested here, i.e., where Δ S.L. > 5 mm. As the time since the last dominance experience increases, the influence of Δ S.L. also increases. The length of time that two fish fight was shown to depend upon Δ S.L., while the only behavior correlated with relative size was BS rate. Smaller fish bit more frequently than did their counterparts. Finally, entropy measures were found to be functions of Δ S.L. Since entropy values increase as Δ S.L. approaches zero, entropy may contribute more to the "dominance vector" when fish are of nearly equal size. Other variables, such as biting intensity, may be more important as "dominance vector" components when one fish is considerably larger than its partner. 8. A "dominance vector" was defined in this study as that complex of variables which contribute to the defeat of one fish by another. Such a complex, highly integrated variable remains hypothetical. Some possible components of this vector indicated by this study include: variables associated with fin tugging rate or duration, biting intensity, unpredictability, and redundancy of certain inter-individual or intra-individual dyads such as [B1-Bw] or [LW-B1] where their conditional probabilities may be important. 9. A simple descriptive model relating environmental, experiential, size, temporal or other parameters to the dominance vector was presented. A mechanism describing how such a vector might operate in determining bout outcome was also postulated.