Reproductive Morphometric Plasticity in Gregarina polymorpha Infecting Tenebrio molitor Larvae

Morphological variability remains one of the principal challenges in the taxonomy and species delimitation of gregarines (Apicomplexa: Gregarinomorphea). In the present study, we investigated morphometric variability in gametocysts and syzygies of Gregarina polymorpha infecting Tenebrio molitor larvae through quantitative morphometric and molecular analyses. A total of 100 gametocysts and 100 independent syzygies were examined using light microscopy and digital morphometry. Gametocyst size exhibited extensive variability, with estimated areas ranging from 4850 to 30,844 μm² and coefficients of variation exceeding 30%. Size distributions significantly departed from normality and displayed marked heterogeneity associated with the presence of unusually small gametocysts. However, Hartigan's dip test did not detect statistically significant deviation from unimodality. Within syzygies, primite and satellite areas were strongly positively correlated (Pearson's r = 0.726, p < 0.001), and standard major axis regression indicated growth patterns consistent with approximate isometry despite substantial dispersion among larger associations. Molecular characterization of small and large gametocyst pools recovered identical SSU rRNA sequences, indicating that the observed variability occurs within the same species. These results reveal substantial reproductive morphometric plasticity in G. polymorpha and highlight limitations of morphology alone for species delimitation in gregarines.