Relationships between locomotor activity, oxidative damage and life span in males and females of the linden bug, Pyrrhocoris apterus (Heteroptera: Pyrrhocoridae)

In this study we addressed a question of whether experimental manipulations that increase life span also reduce physical activity and molecular oxidative damage. We used three phenotypes of male and female Pyrrhocoris apterus that survive for different lengths of time, diapausing insects, reproductive insects and insects from which the corpus allatum, the source of juvenile hormone, was surgically removed. Protein carbonyl content of the thoracic muscles was used as an index of molecular oxidative modification. Diapause or ablation of the corpus allatum (allatectomy) was associated with an extended life span of both sexes, but only those individuals that were in diapause were less active. The carbonyl content, both relative (per protein unit) and absolute (per thorax) increased with age in reproductive insects of both sexes. However, the associations between the carbonyl content and diapause and allatectomy differed in males and females. In males, the carbonyl content was not associated with either diapause or allatectomy. There was no age-related increase in the relative and absolute carbonyl levels in diapausing females, while only the increase in the relative carbonyl level was absent in allectomized females. Overall, the results indicate that both allatectomy and diapause prolonged life span, but had different and sex-specific effects on locomotor activity and carbonyl content. Only the extension of the life span of diapausing females was correlated with both reduced locomotor activity and reduced carbonyl content. 443 * Corresponding author; e-mail: [email protected] long life span. Insects kept in long days (LD) conditions are reproductive and short-lived. The effect of photoperiod on life span is partly mediated through the corpus allatum (CA), an endocrine gland producing juvenile hormone (JH). Ablation of the CA (allatectomy) prolongs the life span of LD-insects, although allatectomized insects do not live as long as insects that undergo diapause (Hodkova, 2008; Blazkova et al., 2011). Allatectomized females are non-reproductive. However, ablation of the ovary has no effect on life span of LD-females (Hodkova, 2008). Consequently, the prolongation of life span by allatectomy is not because they do not produce eggs. The difference between the life spans of allatectomized insects and those that undergo diapause is associated with the differential activity of the neurosecretory cells in the pars intercerebralis (PI) (Hodkova, 2008). There seems to be no causal relationship between life span and the resting metabolic rate. Basal levels of oxygen consumption are similar in diapausing, reproductive and allatectomized males of P. apterus (Slama, 1964a). Reproductive females of P. apterus consume much more oxygen than allatectomized and diapausing females (Slama, 1964b). This indicates a negative correlation between metabolic rate and life span. However, ablation of the ovary decreases oxygen consumption to the level found in allatectomized females (Slama, 1964b), and yet, this operation does not prolong life span (Hodkova, 2008). We hypothesized that the endocrine regulation of life span in P. apterus might be mediated through the molecular oxidative damage caused by the metabolic processes related to physical activity. If this hypothesis is valid, then the experimental manipulations increasing life span should decrease both locomotor activity and molecular oxidative damage. The objective of the current study was to test these predictions. Life span was manipulated by changing the photoperiod and ablation of the CA. Protein carbonyl level in thoracic muscles (likely targets of oxidative damage caused by locomotion) was used as an index of molecular oxidative modification. MATERIAL AND METHODS