Modelling copepod development: current limitations and a new realistic approach

Gentleman, W. C., Neuheimer, A. B., and Campbell, R. G. 2008. Modelling copepod development: current limitations and a new realistic approach. – ICES Journal of Marine Science, 65: 399–413. To predict the influence of environmental variability on copepod dynamics and production, models must account for the effects of temperature and food on stage-dependent time-scales. Here, data for development-time means and variance of Calanus finmarchicus are used to quantify the limitations of existing models. Weight-based individual models are sensitive to uncertain parameters, such as moulting weights, assimilation efficiency, and environmental dependencies, making them highly difficult to calibrate. The accuracy of stage-based population models using ordinary differential equations depends on model structure, with some predicted generation times being incorrect by months. Even when large numbers of age classes are used to reduce modelled variability, it is not possible to make variability consistent with the data. Accuracy of mean times for stage-based population models using difference equations requires a small time-step, which results in large numbers of age classes and modelled variability that is underestimated by orders of magnitude, unless a probabilistic moult fraction is used. We present a new stage-based individual model that avoids the limitations of other models and successfully represents C. finmarchicus mean development timing and associated variability. This approach can be adapted easily for other species, as well as dynamic environmental conditions.

Copepod development rates in relation to genome size and 18S rDNA copy number

It is known that body sizes and temperature-independent developmental durations within two genera of calanoid Copepoda (Crustacea) are positively related to nuclear DNA contents of their somatic nuclei. Evidently because of the constraint of similar cell numbers among the species, (nucleotypic) effects of nucleus size on cell size and on cell-level processes are expressed at the whole-organism level. Here, we show that developmental durations of eight species of five genera are also negatively related to their greatly differing numbers of 18S rRNA genes per unit DNA. We propose that levels of rDNA iteration among copepods have been controlled by natural selection to regulate ribosome concentrations, therefore protein production and development rates, independently of the large variations in genome sizes, which are in turn adapted to regulating cell and therefore body sizes.Key words: Copepoda, rDNA repeats, development rate, iteration, nucleotype.

Empirical analysis of the effect of temperature on marine harpacticoid copepod development time

Predictive equations to estimate development time from environmental temperature for marine harpacticoid copepods were developed from data extracted from the literature. Separate equations were constructed for egg, nauplius, copepodite, and total juvenile development, as well as for generation time. Power curves adequately described the data and each regression was significant (P < 0.001). Approximately 50% of the variance in each data set was explained by regression on temperature. Predictions of development time generally were precise, with the upper 95% confidence limit 39–65% greater than the prediction at low temperatures (4–5 °C), 7–13% greater at mean temperatures (17.6–19.3 °C), and 13–31% greater at high temperatures (28–40 °C). Application of these predictive equations will facilitate analysis of the population dynamics and production of marine harpacticoid copepods.