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Title: The evolutionary genetics and developmental basis of eyespot morphology in butterfly wings
Author: Monteiro, Antonia A. T. F.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1996
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The wings of the Nymphalid butterfly, Bicyclus anynana, have a series of eyespot colour patterns, each composed of a white pupil, a black centre and a gold other ring. An eyespot pattern is organised around a group of signalling cells, the focus, that is active during the first hours of pupal development. Positional information, given to the cells around the focus, is translated into rings of differently pigmented scales. One hypothesis for the underlying mechanism is a concentration gradient of a diffusible morphogen produced by the focal cells, and interpreted in a threshold manner by the responding epidermis. If the diffusion gradient model is correct, when two foci are close together, the signals would summate and this effect would be apparent in the detailed shape of the pigment pattern formed. The morphogen gradient hypothesis was tested by measuring areas of fused eyespot patterns in Bicyclus anynana, by grafting focal cells close together, and also by using a mutation (Spotty) that produces adjacent fused eyespots. The results indicate that, in the region between two foci, there is nearly always an extra area of cells differentiating into part of the pattern. The same qualitative results were obtained using a computer model of two sources that, via diffusion, establish two overlapping concentration gradients. I investigated the potential for evolutionary change in the developmental mechanism of eyespot formation by applying artificial selection for various aspects of eyespot phenotype. Selection for color composition of the large dorsal eyespot on the forewing, produced a line of butterflies with a narrow or no gold ring (BLACK) and another line with a reduced black centre and a broad ring (GOLD). Heritabilities were high, giving a rapid response to selection, and other eyespots suffered a correlated change in the proportion of their color rings. Surgical experiments were then performed on pupal wings from the different lines at the time of eyespot pattern determination. Grafting foci between BLACK and GOLD line pupae, and inducing ectopic eyespots by damage, both showed that the additive genetic variance for eyespot composition was at the level of the response component of the developmental mechanism.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available