Model System

Analysis of focused scientific questions require a model organism that is useful for testing hypotheses through experimentation. The work in our laboratory uses a teleost fish as a model for two reasons: First, it offers the opportunity to manipulate aspects of the social system and measure the consequences of these manipulations at the behavioral, physiological and molecular levels; second, for work on visual system development, teleost fish continue to grow, adding new neurons throughout life. The animal we use is an African cichlid fish, Haplochromis (Astatotilapia) burtoni (Günther).

The social system of H. burtoni centers on adult males of two types: those with and those without territories. Territorial (T) males are brightly colored, with blue or yellow basic body coloration, a dark black stripe through the eye (lachrymal), vertical black bars on the body from the opercula to the tail, a black spot on the tip of the gill cover and a large red humeral patch just behind it. In contrast, nonterritorial (NT) males are cryptically colored, making them difficult to distinguish from the background and from females that are similarly camouflaged (Figure HERE). Social communication among these fish appears to depend primarily on visual signals since we have been unable to identify such chemical signals in H. burtoni. An analysis of them in their natural habitat, the shallow shorepools and river estuaries of Lake Tanganyika showed that H. burtoni live in a social system in which territorial males vigorously defend contiguous territories.

H. burtoni territorial males are very active exhibitng 19 distinct behavioral patterns in social interactions. Territorial males dig a pit in their territory, exchange threat displays with neighboring territorial males, chase non-territorial animals from their territories and solicit and court females. When soliciting and courting females, territorial males display bright coloration patterns towards the female being courted. The male will lead a female toward his territory, typically using large movements of his tail and he courts by quivering his opened, brightly colored anal fin in front of the female. When a territorial male manages to lure a female into his territory, she will normally eat by sifting the substrate in the territory. Non-territorial males mimic female behavior sufficiently well so that the territorial males allows non-territorial males to enter the territories and feed before the deception is discovered. This non-territorial male behavior occurs because only sites defended as territories contain food so non-territorial males need to enter to eat. Normally, however, these non-territorial “female impersonators” are quickly chased off. If a female responds to male courtship, the territorial male will lead her to his pit and continue courtship movements. Males swim vigorously in front of the female, quivering their entire body with spread anal fins. If appropriately stimulated, the female will lay her eggs in the pit and collect them in her mouth immediately. After she has deposited several eggs, the male will swim in front of her displaying the egg-like spots on his anal fin (ocelli). T males display this fin because the spots may seem to the female like eggs not yet collected. Thus, while attempting to “collect” the egg-spots, the female ingests milt ejected near them by the male and ensures fertilization. The spawning male may repeatedly interrupt his courtship and mating to chase off intruders into his territory. After several bouts of egg laying and fertilization, the female departs with fertilized eggs which she broods in her mouth.

To see the fish in action, take a look at this:

⇐ Reproduction