A Quantitative Study of Long-Term Courtship: II. a Comparative Study of the Dynamics of Courtship in Two New World Cichlid Fishes

i. The courtship behavior of two sympatric species of New World cichlid fish was quantitatively studied. The two species were Cichlasoma citrinellum (Gunther) and C. zaliosum Barlow. The species are closely related. 2. Data recording was based on heterosexual, homospecific dyads. Ten event categories, representing cichlid courtship behaviors, were recorded for each sex. 3. Both species showed long-term courtship behavior, the minimum time to spawning after first contact being 52 hrs. Data were recorded three times a day for each pair throughout the courtship period. 4. Four measures based on information theory were used to describe overall changes in behavior with the pair. These were H1, the first order diversity; D1, the first order redundancy (repetition); H2, the second order diversity; and D2, the second order redundancy (divergence from independence). 5. Courtship in these species has three distinct phases that can be characterized quantitatively by their patterns of behavioral diversity. There is an early phase of high activity, high first order diversity, and low first order redundancy. This appears to be the time of pair formation. The second, intermediate phase, is a period of relatively low activity and intermediate behavioral diversity and redundancy. This is the interval after pair formation, but prior to attachment to a spawning site. The third phase is characterized by high activity, primarily by the female, with low diversity and high redundancy. This phase is primarily one of spawning-site preparation and synchronization for the release of gametes. 6. The changes in the overall organization of behavior within the pair were primarily the result of frequency of occurrence (first order). There were no apparent overall changes in the level of dependency between events during courtship (second order). 7. Similar analysis of a species showing short-term courtship should reveal greater importance of second order effects due to reliance on releasers and chaining of events between the sexes. 8. The two species differ primarily in the frequency with which they performed various courtship behaviors. C. zaliosum did more agonistic behaviors such as Bite, Lateral, Frontal and Yield; C. citrinellum performed more behaviors typical of later stages of courtship, such as Quiver and Nip Off. 9. The frequencies with which the behaviors followed each other differed in the two species. 10. The species were least similar in their courtship behavior during the earliest stages of courtship, and showed the greatest resemblance during the parental period. II. Heterospecific pairs resembled C. citrinellum more in their overall behavior than they did C. zaliosum, but this may have been an artifact of the abnormal size ratios within those pairs. 12. The differences in behavior seem due mainly to a lower threshold of aggression in C. zaliosum, while C. citrinellum has a lower threshold for sexual behavior. 13. The differences in courtship are sufficient to explain the reproductive isolation of the two species, but the mechanism is effective only when a choice of mates from both species is available.