Analysis of the effects of inbreeding on the morphological integration of the skull of the guppy (Poecilia reticulata)



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Texas Tech University


Morphological integration can be conceptualized as the relationship of parts to the whole in an organism. The parts are interrelated wherein change in one will affect the other. The levels of integration can be observed through the phenotypic relationships among the different parts. However, phenotypic relationships are determined by the organism's genotype. Therefore, the levels of genetic variation should ultimately affect the levels of phenotypic variation and consequently the amount of morphological integration.

Inbreeding is the most common form of non-random mating and is a violation of the assumption of random mating of the Hardy-Weinburg equilibrium principle. While inbreeding does not directly result in evolution, it does ultimately lead to reductions in genetic variation. In this study, the effects of inbreeding on the levels of morphological integration amongst characters in the skull of the guppy, Poeciiia reticulata, were examined using a wild-type guppy strain and two iso-female lines of inbred Yellow Cobra guppies.

Three females per strain were bred repetitively. Offspring were sampled throughout development. Both dorsal and lateral characters, and distances among characters were measured for 430 specimens. Levels of integration were estimated for distances under the hypothesis that distances between characters and morphological integration have an inverse relationship. Morphological integration also was estimated for characters and character suites representing functional or developmental groups. This was done for both size-dependent and size-free levels of integration. Probabilities of significant differences between integration indices were estimated subsequently.

I found that there was statistically significant morphological integration within the guppy skull based on size-dependent and size-free analyses. The character suites had significant levels of integration when analyzed both size-dependent and size-free. Therefore, character suites in the guppy skull are developmentally and functionally integrated. Levels of integration were unrelated to distances among characters. Inbreeding neither systematically increases nor decreases morphological integration. In contrast, significantly different integration indices among females within strains may have masked any differences among strains