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Body Proportions of Mainland and Island Lizards

Gustav Kramer
Evolution
Vol. 5, No. 3 (Sep., 1951), pp. 193-206
DOI: 10.2307/2405459
Stable URL: http://www.jstor.org/stable/2405459
Page Count: 14
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Body Proportions of Mainland and Island Lizards
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Abstract

In two separate areas (Tyrrhenian area, Southwestern Italy, and Western Istria, North Adriatic), island populations of the lizard species Lacerta serpa (= sicula) show a relative shortening of hind legs at hatching stage. In the case of adult island lizards the same shortening is demonstrable with populations inhabiting flat islands. Equally, the hind legs of the latter are more markedly shortened at hatching stage than those of the inhabitants of steep cliffs. The shortening of hind legs is accounted for as a regressive change in adaptation to the reduced demands on locomotion in insular environment (no predators). On steep cliffs, the regression appears to be less marked owing to an increased demand on climbing ability. All island populations examined have shorter tails than continental ones, a fact that is equally accounted for as a locomotor regression. Lizards hatched at different temperatures behave the same with regard to relative hind leg and tail measurements. The number of tail vertebrae (measured by the number of verticils, two verticils each associated to one vertebra) is higher with continental lizards than with insular ones. The determination of the number of vertebrae is independent of the quantity of yolk material available. The length of tail with newly-hatched lizards, however, clearly depends on the quantity of reserve substance. The tails of such populations as lay big eggs (island populations) therefore require less growth in post-embryonic stages than the tails of populations laying small eggs. (An exception to this rule is formed by one of the two Istrian island populations.) In inter-specific comparison, relative length of tail and length of legs are correlated. Such a correlation cannot be established in intra-specific comparison. There is no indication that the intrapopulation variability of the features examined is restricted by the effect of small population numbers. The relative growth of hind legs and tail makes possible a distinction between allometric changes in early and later ontogenetic stages. Presumably the latter only can be considered indicative in a sense of evolutionary allomorphosis.

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