Keith Nelson

The Temporal Patterning of Courtship Behaviour in the Glandulocaudine Fishes (Ostariophysi, Characidae)

1. The glandulocaudine fishes are a tribe of small South American characids, most of which are internally fertilizing. The courtship behavior of four species is described, and their temporal patterns analysed. 2. In Corynopoma riisei, a sequence of male courtship was defined as a series of statistically dependent actions, separated from other such series by intervals separating statistically independent actions. Sequences thus occurred randomly in time. In general, a sequence of male courtship could be descrihed as a first-order semi-Markov process, in which different classes of action were regarded as having different lengths, and in which the probability of occurrence of an action was dependent upon the nature of the immediately preceding action, and upon no other. Sequences were thus found to end randomly in time. 3. When fertilization occurred, however, it was preceded by a more determinate series of female and male actions. Female responses were rare and sporadic in occurrence, and appeared to depend upon the cumumative effect of male courtship activities. When they occurred they altered the probabilities of occurrence of the next male act. These probabilities were altered in the direction of the series leading to fertilization when the female Nipped at the males Twitching opercular extension. 4. A darkening of the belly spot of the male Corynopoma was found to accompany courtship sequences. This and other evidence suggested that the random beginning of a sequence depended on different factors from those governing its continuation. In particular, the performance of a courtship action by the male appeared to facilitate his further courtship, but in this species the effect was not cumulative. 5. During courtship sequences in Pseudocorynopoma doriae, the males courtship activity rose to a peak and then abruptly terminated, to slowly rise again. Although direct evidence was not available, it was concluded that the pattern was most likely a result of cumulative facilitatory effects of male courtship upon his own performance. Female responses were found to alter the male behavior pattern in the direction of the putative spawning act. 6. In Coelurichthys and Glandulocauda a courtship encounter consisted of alternating aggressive and courtship sequences, with the former gradually becoming shorter and less frequent. In C. tenuis, analysis indicated that the male pattern within a courtship sequence was semi-Markovian, with the probability of occurrence of an act dependent upon one or at most several preceding acts. The transition probabilities were not stationary from sequence to sequence; rather, the probability of Chasing fell during an encounter in a stepwise fashion, apparently as a result of the cumulative effect of male activity upon the female. In Glandulocauda inequalis, a pattern of rhythmic Gulping of air by the male was superimposed upon a courtship pattern which was in general quite similar to that in Coelurichthys. Gulping was essential for the production of a sound, Croaking, by the male during courtship. 7. The patterns of courtship in the internally fertilizing species can be regarded as adaptations to the temporal dissociation of mating and spawning which has accompanied the development of internal fertilization. In these forms, a continuously active male courts an unresponsive female; his efforts raise in a cumulative fashion the probability of successful fertilization. This dependence upon male activity may be a substitute for the dependence of female courtship upon the physiological events underlying egg maturation, which dependence has been lost in the evolution of the temporal separation of mating and spawning. The absence of appetitive and consummatory phases in the male courtship patterns of these species may be attributed to the advantages the male gains in being continuously sexually active. 8. It appears that the externally fertilizing Pseudocorynopoma doriae has reverted to a pattern similar to that in the externally fertilizing ancestors of the Glandulocaudines in that the performance of courtship in this species lowers the probability of is own recurrence. This pattern has not, however, arisen de novo, but rather shows traces of the temporal organization in the internally fertilizing species. Thus it is clear that the particular pattern which is found, and its physiological bases, will be adaptive, but will bear a relation to the evolutionary history of the species.

Size-dependence of growth inhibition among juvenile lobsters (Homarus)

Abstract Growth inhibition of post-larval lobsters ( Homarus ) in compartments immediately downstream from older individuals was found to depend upon size relative to the upstream animals, but not upon species or age combination per se at least within the species, age, and size combinations used in this experiment. The growth of juveniles downstream from smaller individuals was greater than that downstream from juveniles their own size, confirming previous indications of disinhibition of growth by smaller upstream individuals.

On the nature of short-range growth inhibition in juvenile lobsters (Homarus)

Abstract By means of compartmental analysis of two experiments manipulating flow rate, short-range density-dependent growth inhibition in juvenile lobsters ( Homarus ) was shown to implicate a rapidlydecaying or ephemeral substance. Pulsed production of a long-lived inhibitor was ruled out as a sole explanation of the effect. Behavioral observations eliminated the hypothesis that reduced growth of inhibited animals was causally related to their increased locomotory activity. Implications for chemical ecology of the effects of ephemeral agents upon growth and behavior are discussed.