Physiological correlates to courtship, mating, ovarian development and maternal behaviour in the ring‐legged earwig

Abstract

The involvement of the endocrine system in courtship, mating, maternal behaviour and the gonadotrophic cycle was studied in the earwig, Eubnrellia annulipes, after application of JH 111 and, alternatively, precocene 11.Topical application of 35 or 122 pg of JH 111 to newly eclosed females advanced the onset of courtship behaviour from 6.6 f 1.3 days in acetone-treated controls to 1.4 f 2.8 and 0.5 k 2.5 days, respectively. Application of 6 pg of JH I11 had no effect on the onset of courtship behaviour. Applications of Juvenile Hormone had no significant effect on the age at first mating nor on the duration of mating, though the trend is towards advanced onset. The age at first oviposition was advanced by hormone treatment; clutch size and the proportion of offspring hatching was reduced by hormone treatment. The interclutch interval, size and proportion hatching of the second clutch were not affected by hormone treatment. Topical application of 50 pg of JH I11 to females on the day of oviposition shortened the total duration of maternal care from 15.4 f 0.5 to 5.3 f 1.7 days; whereas in acetone-treated and precocene 11-treated groups maternal care lasted 16.1 f 1.9 and 13.8 f 1.6 days, respectively. The duration of maternal care was positively correlated with number of offspring hatching and fledging.In a corollary experiment, topical application of JH 111 significantly enhanced the onset of the second gonadotrophic cycle as assessed by basal follicle length; application of 20 pg of precocene 11, either singly or in repeated doses, did not delay growth of basal follicles. Finally, repeated application of as much as 80 pg of precocene I1 had no effect on basal follicle length, nor on ovary wet weights.These results are consistent with the hypothesis that intermediate to high titres of JH are associated with oocyte growth, mating, and the cessation of maternal care; low titres of JH appear to be associated with the period of maternal behaviour and slow ovarian follicle development.

Juvenile hormone in earwigs: Roles in oogenesis, mating, and maternal behaviors

“…As shown in Table 3, the second gonadotropic cycle was unaffected: there were no differences between groups in interclutch interval, size of the second clutch, or in the proportion hatching in the second clutch (Rankin et al, 1995a). This finding suggests that the JH had been inactivated, most likely by specific hemolymph esterases.…”

“…riparia-e.g., see Juberthie and Caussanel, 1980). Interestingly, despite differences in courtship behavior neither the age at which first mating occurred nor duration of copulation was significantly affected, though the trend is toward advanced onset (Table 2; Rankin et al, 1995a). This suggests that to advance mating might require a longer duration of elevated JH levels, or that some other factors might be required, possibly from the ovaries or neurosecretory sources.…”

“…Instead, these earwigs appear similar to the cockroach Blattella germanica (Liang and Schal, 1994;Schal and Chiang, 1995). Table 2 shows that application of 35 and 122 µg JH III decreased the age at first oviposition compared with the other three groups, and in a dosage-dependent way (Rankin et al, 1995a). This suggests that application of JH enhanced vitellogenesis, as does application of the JH precursor, farnesol, to pre-reproductive L. riparia (Rouland et al, 1980(Rouland et al, , 1981a(Rouland et al, , 1981b.…”

“…) (Caussanel, 1973b), and release of material at the neurohemal aorta accompanied egg-laying (Juberthie and Caussanel, 1980). JH III application also elicited a reduction in clutch size (Table 2; Rankin et al, 1995a), implying that fewer follicles were present or, alternatively, fewer follicles responded to JH application. This observation awaits empirical confirmation (by sacrificing females and assessing follicular development in the vitellarium).…”

“…Mating behavior was similar to that described for other earwig species (e.g., see Knabke and Grigarick, 1971;Moore and Wilson, 1993), including forceps-to-forceps alignment, male twisting of the abdomen 180°, and insertion of copulatory organs. Table 1 shows that treatment with 35 or 122 µg JH III significantly advanced the onset of courtship behavior in the females; neither treatment with 6 µg JH III nor acetone affected the age at first courtship (Rankin et al, 1995a). Since high dosages affected the behavioral response within hours of treatment, this behavior may be directly linked to elevated levels of JH or to factors readily released by this treatment, such as neurosecretory material from the brain, corpora cardiaca, or aorta (the aorta has been shown to be neurohemal in the earwig L.…”