Occurrence and predictive utility of isochronal, equiproportional, and other types of development among arthropods

Abstract

In isochronal (ICD) and equiproportional development (EPD), the proportion of total immature (egg, larval, and/or juvenile) development spent in each stage (developmental proportion) does not vary among stages or temperatures, respectively. ICD and EPD have mainly been reported in copepods, 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. The goal of this study was to test whether different taxa have ICD, EPD, or an alternative development type in which stage-specific proportions depend on temperature, termed ‘variable proportional’ development (VPD), and also how well each development type allowed later-stage durations to be predicted from earlier ones. Data for 71 arthropods (arachnids, copepod and decapod crustaceans, and insects) were tested, and most (85.9 %) species were concluded to have VPD, meaning that ICD and EPD do not occur generally. However, EPD predicted later-stage durations comparably well to VPD (within 19-23 %), and thus may still be useful. Interestingly, some species showed a ‘mixed’ form of development, where some stages’ developmental proportions varied with temperature while those of others did not, which should be further investigated.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

Stagewise resolution of temperature-dependent embryonic and postembryonic development in the cowpea seed beetle Callosobruchus maculatus (F.)

“…The question of whether each consecutive developmental stage takes the same proportion of total development time, regardless of temperature, has a long history in the literature on copepods and terrestrial arthropods. In the former, the constancy of the fraction of a stage in total development is termed equiproportional development [ 12 ]; in the latter, the same phenomenon is referred to as developmental rate isomorphy [ 26 , 27 , 69 ], and both groups include species that violate this pattern [ 5 , 39 , 52 ]. All of these studies mostly focus on postembryonic development while embryos, if considered at all, are never separated into stages.…”

“…There are two approaches to testing whether development scales proportionately with temperature. The first one is, obviously, to check whether relative durations of any stages (i.e., proportions of total development) vary with temperature in any regular manner [ 26 , 52 ]. However, proportions sum up to unity and as such do not represent independent observations: proportion of one stage can only increase with temperature at the expense of proportion(s) of the other stage(s).…”

Stagewise Resolution of Temperature-Dependent Embryonic and Postembryonic Development in the Cowpea Seed Beetle Callosobruchus Maculatus (F.)

“…There are two approaches to testing whether development scales proportionately with temperature. The rst one is, obviously, to check whether relative durations of any stages (i.e., proportions of total development) vary with temperature in any regular manner [26,52]. However, proportions sum up to unity and as such do not represent independent observations: proportion of one stage can only increase with temperature at the expense of proportion(s) of the other stage(s).…”