A test of the general occurrence and predictive utility of isochronal, equiproportional, ‘variable proportional’, and ‘mixed’ development among arthropods

HighlightsWhether arthropod development is generally isochronal or equiproportional was testedDevelopmental proportions of most species’ stages varied with temperatureMany species had ‘mixed’ development between variable and equiproportional typesThe general occurrence of isochronal and equiproportional development was rejectedEquiproportional development did make reasonable predictions of stage durations ABSTRACTIn isochronal (ICD) and equiproportional development (EPD), the proportion of total immature development spent in each stage does not vary among temperatures or stages, respectively. ICD and EPD have mainly been reported in copepod crustaceans, and whether they occur in other arthropods is not known. If they did, then rearing studies could be simplified because the durations of later developmental stages could be predicted based on those of earlier ones. In this study, published data for 71 arthropods (arachnids, copepod and decapod crustaceans, and insects) were tested to objectively determine whether they had ICD, EPD, or an alternative form of development in which stage-specific proportions depend on temperature, termed ‘variable proportional’ development (VPD). How well ICD, EPD, and VPD could predict later-stage durations from earlier ones was also assessed. Most (85.9 %) species were concluded to have VPD, meaning that ICD and EPD do not occur generally among arthropods. However, EPD predicted later-stage durations comparably well to VPD (within 19-23 %), and thus may still be useful in arthropod development studies. Interestingly, some species showed a ‘mixed’ form of development, where some stages’ developmental proportions varied with temperature while those of others did not; these findings should be further investigated.