Blood samples and testes were collected from long-finned pilot whales (Globicephala melas) off the Faroe Islands at irregular intervals over a period of 3 years (July 1986–December 1989). Changes in testis mass (n = 674) and plasma testosterone concentrations (n = 214), measured by radioimmunoassay, were examined with respect to age, bodylength and bodymass of the animals. Corresponding to a rapid testicular growth (from 0.25 kg up to 1.9 kg), puberty occurred in male pilot whales of 4.6–5.7 m in bodylength, 1.2–1.9 tonnes in bodymass and 11–22 years of age. Changes in plasma testosterone concentrations confirmed this result, with very low values (< 2 ng ml⁻¹) in immature animals (testis mass < 0.2 kg), followed by a sharp increase (from 2 to 29 ng ml⁻¹) during the pubertal period, and the maintenance of high concentrations with large variability (> 1.5 ng ml⁻¹ to 14 ng ml⁻¹) in mature males. Testosterone concentrations were significantly correlated with testis mass (P < 0.001), but not with bodylength or age, and very large individual variations were observed in mature males. The average age, length and mass at the attainment of sexual maturity were estimated at 16.99 ± 0.30 years, 5.162 ± 0.013 m and 1.403 ± 0.005 tonnes, respectively.

The role of photoperiod in the entrainment and synchronization of the reproductive cycle of male hedgehogs, seasonal breeders and hibernating mammals, was investigated. Groups of adult hedgehogs were either maintained outdoors (controls, n = 6) or submitted to accelerated 6-month artificial light regimens under constant ambient temperatures (20 ± 2°C versus 5 ± 1°C) in light-proofed rooms. The daily duration of light was varied sinusoidally to produce an amplitude change from 8 h (winter solstice) to 16 h (summer solstice) during the 6-month light cycle. Animals were transferred from outdoors to a high ambient temperature (20 ± 2°C) and submitted to accelerated 6-month light regimens at two times of the year: from winter solstice (Group 1, n= 14) with increasing daylengths (from 8 to 16 h) and from summer solstice (Group 2, n = 8) with decreasing daylengths (from 16 to 8 h). The light regimens were then reversed for Groups 1 and 2. After the first 6-month cycle, the animals in Group 1 were allocated to two groups and maintained under the same initial light regimen but submitted to two ambient temperatures: Group 1 (n = 7) was maintained at 20 ± 2°C and Group 3 (n = 7) was transferred to a cold environment (5 ± 1°C). In control and experimental animals, testicular volume was estimated and blood samples were obtained twice a month to measure plasma testosterone and LH concentrations by radioimmunoassay. In all groups, all the parameters of the reproductive activity studied (testicular volume, testosterone and LH concentrations) were entrained and synchronized by the 6-month light rhythm and two cycles were observed in a year. Reproductive activity was maximum during the long days (light > 12 h) and minimum during the short days (light < 12 h). In the experimental animals and in the controls, the amplitude of variations in the parameters studied were similar. The recrudescence of reproductive activity took place just before the artificial spring equinox (short and increasing daylengths), whereas regression always occurred near the autumn equinox (12 h light:12 h dark), as in the controls kept in a natural environment. The regular incidence of involution at the autumn equinox indicates that there is a period of photosensitivity to decreasing daylengths in summer. In the experimental animals, the resting season was usually 2 months. A comparison of Groups 1 and 2 that had undergone reversed light regimens also showed that the reproductive parameters were driven in opposition. In Groups 1 and 3, no significant effect of ambient temperature (high or low) on the entrainment of the reproductive cycle by the photoperiodic rhythm was observed. These results clearly indicate that photoperiod is of prime importance among the environmental factors controlling reproduction in hedgehogs and can entrain and synchronize the seasonal changes of the reproductive cycle.

Summary. A double-antibody heterologous radioimmunoassay (RIA) was developed to measure plasma LH values in hedgehogs. This RIA system used anti-rat LH serum and rabbit LH (AFP-559B) for radioiodination and as standard. The accuracy of the method was evaluated and indicated the ability to detect various relative concentrations of LH in plasma. The minimum detectable dose was 0·2 ng/ml. The intra- and inter-assay coefficients of variation were 4·2 and 7·9% respectively. Biological tests, e.g. effect of castration, effect of castration + testosterone implant and GnRH administration, confirmed that this method was suitable to determine subsequent changes in pituitary gonadotrophic activity in the hedgehog. LH concentrations were determined in blood samples obtained during 1 year: (a) each month, at 4-h intervals during 24 h, from different groups of unanaesthetized animals fitted with a catheter and (b) twice a month, under a light anaesthesia, from the same group of 6 animals. During the year: (1) the range of LH change was narrow (minimum values ≃0·25 ng/ml and maximum values ≃2·00 ng/ml); (2) the 24-h LH patterns did not exhibit any daily rhythm; (3) a clear annual rhythm was observed with the highest values from February to April and the lowest values in October and November. LH decreased rapidly at the end of summer and increased progressively from December to February, during hibernation. In these experiments, it was not possible to determine the characteristics of LH release patterns in the hedgehog but individual profiles indicated clearly the episodic secretion of LH, particularly during the highest pituitary activity period. During the year, a close relationship between the seasonal cycles of plasma LH and testosterone was observed.

Keywords: hedgehog; LH; testosterone; daily variations; seasonal cycle