Ophthalmology

Comparative Physiology and Evolution of Vision in by H. Autrum, M. F. Bennet, B. Diehn, K. Hamdorf, M.

By H. Autrum, M. F. Bennet, B. Diehn, K. Hamdorf, M. Heisenberg, M. Järviletho, P. Kunze, R. Menzel, W. H. Miller, A. W. Snyder, D. G. Stavenga, M. Yoshida

In the comparative body structure of photoreception by means of the Protista and the invertebrates elements are emphasised: (1) the range of visible tactics in those teams and (2) their bearing upon normal mechanisms of photoreception. Invertebrates have developed a much higher number of variations than vertebrates­ transformations supporting survival within the remarkably varied biotopes they occupy. The variety of species in itself indicates this multiformity; every one of them has peculiarities of its personal, in morphology in addition to in body structure and behaviour. yet those specified diversifications are diversifications on a number of nice issues. even if of invertebrate species is giant, the literature relating them approximately opponents it in extent-even if one considers purely that fraction facing visible body structure. Taxonomy proceeds by means of grouping the species, categorizing them in genera, households, orders, and steadily greater devices. equally, comparative body structure goals at the same, kind of compre­ hensive, category. This half A of quantity VII/6, like half B that follows it, emphasizes the vast questions that hindrance teams better than the person species; often times those questions have basic applicability. the center path among methods which are too really good and those who are too common is frequently elusive, yet right here we try to stick with it. The giant variety of exact adaptations-probably, as we've got stated, as huge because the variety of species-is past the diversity even of a handbook.

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Extra resources for Comparative Physiology and Evolution of Vision in Invertebrates: A: Invertebrate Photoreceptors

Sample text

An example of a negative klinophobic response is found in the step-up chemoresponse of Escherichia coli (BERG and BROWN, 1972). y) Stropho-: rate of turning or rotation. The phobic response of Euglena gracilis (DIEHN, 1969a) upon a change in light intensity is an example of a positive strophophobic response. <5) Morpho-: rate of change of body shape or outline. A good example of a morphokinesis is exhibited by mechanically stimulated Euglena upon an increase in illumination (MIKOLAJCZYK and DIEHN, 1975).

At first glance, this appears reasonable since there seems to be no possibility of photophobic trapping in the cuvette. However, the actinic light intensity is not really uniform in the cuvette; because of absorption and scattering of the stimulating light by the cells, the cells nearest the light source are more strongly illuminated than the cells in the· rear. This is a potential problem, especially with dense suspensions. Later in this chapter (see E,I2) some experimental results suggesting a phobic accumulation mechanism in this apparatus will be discussed.

In practice, this also requires that one makes sure to measure a primary response of the cell and not a possible mixture of responses. The dual requirement for the absence of screening and a clearly characterized response limits the utility of mass-movement methods. On the other hand, single-cell observations are not only extremely tedious if statistical accuracy is desired, but also show poor resolution because eye-and-stopwatchquantification of behavioral responses is not very accurate. An automated cell-tracking technique would appear to be the method of choice, but in the only instance to date in which a tracking method has been used for determining an action spectrum (in Gymnodinium, FORWARD, 1974), the tracks were evaluated manually and the percentage of cells responding near threshold was determined rather than a dose-response curve.

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