Genotypic differences in embryonic life history traits of Folsomia quadrioculata (Collembola: Isotomidae) across a wide geographical range
Sagnik Sengupta, Torbjørn H. Ergon and Hans Petter Leinaas
1. Life history traits play a central role in adaptation to specific environmental conditions. Egg development time, hatchling, and egg batch size in 10 populations of the soil-dwelling collembolan species Folsomia quadrioculata (Tullberg, 1871) from diverse habitats across arctic and temperate regions, ranging in latitude from 43 to 81°N were studied.
2. For all traits, 15 °C was used as the reference temperature. Phenotypic plasticity was studied by changing temperature to 10 and 20 °C in hatchling size, and to 20 °C in egg development time. The effect of latitude, climatic zone, and summer temperature at their sites of sampling was tested to address the hypotheses that populations from cooler areas would have (i) a faster temperature-dependent egg development, (ii) a larger hatchling size, (iii) smaller egg batches and (iv) higher phenotypic plasticity
3. The first and fourth hypothesis were not supported, whereas the second and third were partly supported when including the whole latitudinal gradient, but not within regions. Plasticity showed a complex pattern, including large differences between populations from similar macroclimates and considerable similarity between some populations from contrasting climates. Small effects of latitude and macroclimatic variables emphasised that local climate and microhabitat should be taken into account when evaluating thermal conditions as possible drivers of population-specific differences in soil-dwelling ectotherms.
4. There was a trade-off between egg batch and hatchling sizes. A weak correlation between the population mean egg development time and the mean hatchling size suggested that the populations are, or have been, exposed to differential selection.