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Because fish heads are densely packed with muscles, ligaments, skeletal elements and other structures, transformations in one structure may influence surrounding structures. Transformations occur during phylogeny, ontogeny and as environmentally induced alterations, i.e. phenotypic plasticity. We describe differences in intra- and interspecific transformations of the pharyngeal jaw apparatus of haplochromine cichlids. Using multivariate clustering techniques we trace possible correlations in transformations of anatomical characters of the pharyngeal jaws and surrounding structures. The intraspecific transformation analysis is based on two environmentally induced morphs of Astatoreochromis alluaudi : a molluscivorous morph with a hypertrophied pharyngeal jaw apparatus and an insectivorous one with a non-hypertrophied apparatus. For the interspecific analysis five other haplochromine species from Lake Victoria with diets ranging from insects to molluscs were investigated. Although range in diet are the same, the anatomical ranges differ between A. alluaudi and the species cline. Besides similarities in anatomical changes of the pharyngeal jaw apparatus in the intra- and interspecific cline, differences were also observed. Apparently there are among haplochromines multiple pathways to achieve similar performance. In A. alluaudi architectonic and intrinsic plasticity constraints limit the adaptability of the pharyngeal jaw apparatus. In the species cline, these constraints have been overcome by genetical adaptation.

Organisms are tightly packed with structures so architectonic interdependency of structures is an obvious aspect of integration. This aspect of functional morphology, however, has received remarkably little attention. The present paper presents an example of the spatial relations among several apparatuses in the head of the cichlid fish, Astatoreochromis alluaudi . It investigates the transformations of these apparatuses and their functions due to a change in the pharyngeal jaw apparatus resulting from a functional shift (insect eating to snail crushing or vice versa ). The volume of the pharyngeal jaw apparatus differs 55% between the insect eating- and the snail eating morph. The increase in volume of the pharyngeal jaw apparatus has an impressive number of spatial effects, both direct and indirect, on other structures. Reallocation of space within the pharyngeal jaw apparatus occurs. Total head volume increases 31% but a reallocation of space is still necessary as the increase of the opercular compartment where the pharyngeal jaw apparatus is situated compensates for only 59% of the volume increase of that. Not all spatial effects do impose constraints. Spatial constraints are avoided when one of the apparatuses can use a topographically different volume of space. The respiratory apparatus shows internal reallocations of space without loss of total volume. The same solution occurs for elements of the expansion apparatus and the buccal cavity. The eyes are not influenced. Finally spatial effects can have positive repercussions. The muscles of the oral jaw apparatus increase in size. This may be an example of an epiphenomenon.

Phenotypic differences of the pharyngeal jaw apparatus between morphs of Astatoreochromis alluaudi are well known. But only a limited number of elements have been described in detail. In this study an anatomical description of elements markedly differing between the two extremes of the phenotypic range - the snail-eating and the non-snail-eating morph - is provided, and compared with the anatomy of a generalized Haplochromis species, H. elegans. Many skeletal elements and muscles of the pharyngeal jaw apparatus show hypertrophy in the snail-eating (hypertrophied) morph. However, the elements of the pharyngeal jaw apparatus of the non-snail-eating (non-hypertrophied) morph, which mainly feeds on insects, are generally more hypertrophied than the elements in the obligate insectivorous species H. elegans. Many of the differences between the two morphs can be interpreted functionally as adaptations to the increased crushing force of the hypertrophied morph. Differences between the morphs were compared with literature data of differences between non-durophagous and durophagous trophic types in other labroid taxa and in the Centrarchidae. Comparable differences are found for the pharyngeal jaw bones and the two largest pharyngeal muscles. The functional demands of crushing hard prey types appear to be very similar for the different groups. The small muscles show only slight similarity. Demands of other functions may co-determine their shape.

The conversion factor for the calculation of bacterial production from rates of [ 3 H]thymidine incorporation was examined with diluted batch cultures of freshwater bacteria. Natural bacterial assemblages were grown in aged, normal, and enriched media at 10 to 20°C. The generation time during 101 growth cycles covered a range from 4 to >200 h. The average conversion factor was 2.15 × 10 18 cells mol -1 of thymidine incorporated into the trichloroacetic acid (TCA) precipitate (standard error = 0.29 × 10 18 ; n = 54), when the generation time exceeded 20 h. At generation times of 18 cells mol -1 of thymidine incorporated into TCA precipitate (standard error = 1.72 × 10 18 ; n = 47). The amount of radioactivity in purified DNA increased with decreasing generation time and increasing conversion factor (calculated from the TCA precipitate), corresponding to a decrease in the percentage in protein. The conversion factors calculated from purified DNA or from the TCA precipitate gave the same variability. Conversion factors did not change significantly with the medium, but were significantly higher at 20°C than at 15 and 10°C. A detailed examination of the [ 3 H]thymidine concentrations that were needed to achieve maximum labeling in DNA was carried out 6 times during a complete growth cycle. During periods with low generation times and high conversion factors, 15 nM [ 3 H]thymidine was enough for the maximum labeling of the TCA precipitate. This suggests that incorporation of [ 3 H]thymidine into DNA is probably limited by uptake during periods with generation times of 18 cells mol -1 of thymidine incorporated is used.