Variability in life-history and behavioural responses to toxicants across genetic backgrounds in Bacillus rossius (Phasmidae)

Biological variation, encompassing the diversity of structures, functions, and responses to external factors, is a fundamental feature of living systems. Nonetheless, it may hamper precise measurements of biological damage to environmental pollution, because it allows the expression of alternative phenotypic responses. This study investigates whether reduced genetic variability leads to reduced variation in phenotypic response in a non-model insect, the walking stick Bacillus rossius (Phasmidae), exposed to copper sulphate, a widely used agrochemical compound. Specifically, 135 adult females, representing four parthenogenetic clonal pedigree lines and one sexually reproducing line, were tested for two environmentally relevant concentrations of the selected pollutant. Third-generation clonal females were obtained in captivity by parthenogenetic females, while the sexual line consisted of second-generation females derived from a mixed-sex group collected in a region free from intensive farming and bred under the same laboratory conditions as the clonal lines to minimize environmental variability. We measured key life-history (body condition and fecundity) and behavioural traits (activity levels and mean movement speed), given that copper sulphate is known to have cytotoxic and neurotoxic effects on exposed animals. The results of this work will add novel knowledge on the sensitivity and predictability of clonal responses compared to the sexual ones to environmental pollutants. Furthermore, this study can highlight the critical role of genetic diversity in the resistance and resilience of wild populations in an increasingly polluted world.