. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. THRESHOLD SIZE FOR METAMORPHOSIS 221 8 E ~ 6 u> a. a 0 4 TJ O 0> I. Time FIGURE 7. Diagrammatic summary of the experiments described under results. The vertical dimensions of the boxes indicate the range of larval head capsule widths found in each group. Roman numerals indicate larvae growing under standard laboratory conditions. Arabic numerals indicate larval instars derived from 3rd and 4th instar larvae that had been temporarily starved (dashed lines). Larvae with head capsules smaller than threshold size ( mm)
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. THRESHOLD SIZE FOR METAMORPHOSIS 221 8 E ~ 6 u> a. a 0 4 TJ O 0> I. Time FIGURE 7. Diagrammatic summary of the experiments described under results. The vertical dimensions of the boxes indicate the range of larval head capsule widths found in each group. Roman numerals indicate larvae growing under standard laboratory conditions. Arabic numerals indicate larval instars derived from 3rd and 4th instar larvae that had been temporarily starved (dashed lines). Larvae with head capsules smaller than threshold size ( mm) molt to an additional larval instar. Those with head capsules larger than threshold size pupate (P). larval instars in this species is a determinate character and that the 5th instar is the final instar. When 3rd or 4th instar larvae were temporarily starved and allowed to molt at a subnormal weight, the resulting 5th instar larvae were proportionally smaller, as measured by their head capsule sizes (Figures 2 and 5). The subsequent fate of these individuals depended on their absolute size. Only larvae with a head capsule above a threshold size of mm pupated at the next molt. Smaller larvae underwent additional larval molts (Figures 4 and 6B). In a few instances the 6th instar larvae that resulted were also below threshold size for metamorphosis and formed a 7th instar (Table I). Larval-pupal intermediates were never formed in these experiments. These experiments are summarized in Figure 7. Except for size, supernumerary larval instars, as well as the pupae, that were obtained were normal and viable. The data presented in Table I and Figure 6B indicate that the threshold size for metamorphosis does not depend on the size of the preceding instars. Rather, it appears to be a pre-coded threshold of absolute size which is not affected by the developmental history of the individual. The number of larval instars is therefore an indeterminate character. A larva does not "coun
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
