Larval growth strategies in the genus Erebia Dalman, 1816 as analyzed by the size increment of the head capsule: different strategies – same goal (Lepidoptera: Nymphalidae)

Larval growth strategies and trajectories were analyzed in the genus Erebia Dalman 1816 in order to understand the interspecies variability in growth increments in connection with Dyar’s rule. For this, the number of larval moults and the size increments per moult were comparatively analyzed for the first time in a large number of phylogenetically closely related species, in this case within a single genus. Growth increments and trajectories were determined by measuring head capsule widths of each instar and the subsequent calculation of Dyar’s constant as well as by mathematical modeling, applying exponential, logarithmic and second order polynomial functions. Calculated parameters of the exponential and log functions were well suited for inter-species comparison. The frequency distributions of the growth increment parameters derived from 34 data sets are discontinuous, exhibiting four clear cut groups which can be attributed to the number of larval instars. Accordingly, variability of growth increments, expressed as Dyar’s constant, and of parameters derived from mathematical functions can be explained by the different number of moults. Developmental polymorphism has been shown for some species. In these cases, the different number of required instars, 4 or 5 of the same species, is associated to an altered growth increment, ultimately leading, however, to the same size in the last instar. The number of moults in an Erebia species is related to its life history, namely, to the number of hibernations in the larval stage. There is no association between instar numbers and phylogenetically defined species clusters.