Attainment Of Sexual Maturity Research Articles

Social relations in family-groups of wood miceApodemus sylvaticus under laboratory and enclosure conditions

Two family-groups of wood miceApodemus sylvaticus (Linnaeus, 1758) were observed: one in the laboratory (terrarium 100 × 60 × 60 cm) and the other under enclosure conditions (outdoor enclosure 200 × 100 × 100 cm). Three consecutive periods in the social relations of the family-groups were described: the linear hierarchy, the multidirectional social relations, and the variable dominance-subordination relations. The linear social hierarchy was reflected in the subordination behaviour of family members in relation to the dominant male, the father of the family. During the period of coexistence of a pair of parents with two litters of juveniles, both in the laboratory and under enclosure conditions, amicable relations between individuals occurred. Advanced forms of social care (paternal care, allomaternal lactation, transportation and licking by relatives) were also observed. In the laboratory, agonistic interactions were lacking during the linear hierarchy period, but the attainment of sexual maturity by individuals of the first two litters, accompanied by an increase in the number of mice, resulted in aggression between mature males and competition for dominance. Further, under increasingly crowded conditions, agonistic behaviour prevailed over other types of social interaction, and the survival rate of juveniles decreased. Under enclosure conditions a seasonal variation in agonistic interaction between mature individuals was recorded, similar to that observed in the wild. Despite the systematic increase in population density, no attacks by mature males on juveniles were observed.

Relationship between body size and population growth rate in two opportunistic polychaetes

The relationship between body size and population growth rate λ has been studied in two species of opportunistic polychaetes, Dinophilus gyrociliatus and Ophryotrocha labronica, which colonize harbour environments. These species exhibit a semi-continuous iteroparous reproductive strategy, are phylogenetically closely-related but differ in body size and in some aspects of their sexuality. Ophryotrocha labronica is about 4 mm in body length, displays only slight sexual dimorphism and its sex ratio is biased towards the female sex in the ratio 2:1. Dinophilus gyrociliatus is about 1 mm in length, the males are extremely small and the sex ratio is strongly biased (3:1) in favour of the females. In spite of the considerable differences in all traits of their life histories and in many demographic parameters, the growth rates of the two populations are very similar. The analyses carried out have shown that the rapid attainment of sexual maturity of D. gyrociliatus gives it an advantage that offsets the greater fecundity of O. labronica. It is very likely that the reproductive peculiarities of D. gyrociliatus help to raise the population growth rates. The ‘saving’ on the male sex achieved both by the shift of the sex ratio in favour of the females and by the reduction in the males' body size would appear to enable D. gyrociliatus to grow at the same rate as O. labronica, a larger and more fecund species.

SOURCES OF COLOUR PATTERN VARIATION IN MEDITERRANEAN PSAMMODROMUS ALGIRUS

Colour pattern and its relation to sex, size and season were investigated in three coastal populations of Psammodromus algirus from NE Spain. Eight pattern variables, as well as body size and reproductive parameters, were recorded for 430 specimens. Results show that yellow head pattern was present in both males and females and depended on body size and locality. Furthermore, its seasonal variation was associated with reproductive activity in males. Orange infralabials appear almost exclusively in adult males. Blue ocelli constitute a potential size signal in intraspecific interactions, especially in males. The attainment of sexual maturity modified tail colour (antipredatory) and dorsolateral stripes (cryptic). Bright spots on hindlimbs varied between sites. Colour pattern is interpreted as a trade-off between different selective pressures including crypsis and intraspecific interactions. Most pattern variation is due to body size differences and only secondarily to sexual dimorphism. A hypothesis invoking differences in social system is proposed to explain the striking differences between these populations and those from Central Spain.

Effect of age of release from light or food restriction on age at sexual maturity and egg production of laying pullets

1. Lohmann Brown pullets, in one trial, and Hyline Brown pullets in another, were reared from day 2 on short daylengths, and from week 8 in trial 1 (week 16 in trial 2) on food restriction. These restrictions were lifted at various times during the rearing period as a means of determining the relative importance of the day length and food restriction stimuli on the attainment of sexual maturity and subsequent laying performance. 2. A total of 2304 pullets were used in each trial. The birds were reared in light proof rooms, and subjected to 8L:16D until they were moved to a laying facility where a light stimulus of 16L:8D was applied. In trial 1 the six ages at which light stimulation was applied were 115, 122, 129, 136, 143 and 171 d. Within each light treatment, food restriction of pullets, which consisted of feeding 72 g of food/bird d, was lifted at six different ages, namely, 115, 129, 143, 157, 171 and 185 d. In trial 2 both the light stimulation and the lifting of food restriction occured at 111, 125, 139, 153, 167 and 181 d of age, producing 6 × 6=36 treatments in both trials. 3. The first trial was terminated when the pullets were 28 weeks old, soon after all the birds had commenced laying, because of an outbreak of Egg Drop Syndrome. However, because age at maturity was the variable of major interest, data from this experiment could be used in the analysis. The second trial ended when the birds reached 40 weeks of age. Variables measured were age at maturity, food intake and body weight gain subsequent to the lifting of restrictions and, in the second experiment, rate of lay, peak rate of lay and egg weight at various ages. 4. The mean age at sexual maturity was influenced by the date of release from light restriction ( P <0001) and from food restriction ( P <0.001) in both trials. In addition, the interaction between the age at release from light and from food restriction was significant. Regression equations were produced for each trial to describe the relationships between the age at sexual maturity and the age at release from light restriction and food restriction. 5. There was an effect of both light restriction ( P <0.001) and of food restriction ( P <0.001) on the increase in food intake (g/bird d) in the week following release from food restriction in both experiments. These effects were not independent: the effect of the interaction of light and food restriction on this increase in food intake was also highly significant. The longer the birds were subjected to light restriction, the less dramatic the increase in food intake when food restriction was lifted. The more sustained the period of food restriction, the higher the increase in food intake in the week following release from the restriction. 6. Mean egg weight was 4 g heavier at 22 weeks of age in birds released from food restriction at 16 and 18 weeks, than from those released at 24 and 26 weeks of age. However, by 30 weeks of age, birds restricted for longer produced heavier eggs than their earlier-maturing counterparts. This effect continued to the end of the trial at 40 weeks of age, at which time there was a 2.3 g difference in egg weight between these treatments. 7. Both light and food restriction have an effect on the age of maturity in laying hens. The length of time between the release from light or from food restriction to the onset of laying depended on the age of the pullets when the release occurred. Egg weight at a given age was significantly affected by the age at release from food restriction, but not from light restriction.

Pregnancy in female house mice exposed to urinary chemosignals from other females.

Seven experiments were performed to investigate pregnancy termination, urinary chemosignals, and litter sex ratio variation in female house mice. Experiments tested the effects of urine from adult and prepubertal females, housed individually or in groups, on successful insemination and litter production by females treated at different times and for different periods during the 3 weeks before mating and during gestation. Treatment of females with urine from adult females housed eight per cage or with urine pooled from eight adult females housed individually for 2 or 3 weeks before mating resulted in fewer successful pregnancies and significantly more female-biased litters. Treatment with urine from adult or prepubertal females housed eight per cage or with urine pooled from eight mice housed individually for the first 6 days of gestation or throughout pregnancy resulted in a significant increase in the rate of pregnancy termination. These treatments resulted in lower body weights at birth and slower growth rates in all males and in some females. Puberty was delayed in female progeny from urine-treated dams in five of seven experiments, and these young females attained first oestrus at greater mean body weights than mice in other treatments. These findings indicate that, in mice, at high population density, communication via a urinary chemosignal can alter reproduction in recipient females. Availability of, and competition for, resources such as food would be greater at higher densities, possibly lowering the probability of reproductive success. Pregnancy termination and delays in reproduction and attainment of sexual maturity might lead to greater successful reproduction at a later time.

Bone growth from 11 to 17 years: relationship to growth, gender and changes with pubertal status including timing of menarche

The tempo and change in bone growth during puberty in relation to physical growth is described in a cohort of 56 boys and 52 girls. Distal forearm bone width, mineral content and volumetric density, anthropometry and pubertal status were measured at ages 11, 13, 15 and 17 y, and bone age at 17 y. Bone width and mineral content increased independently with age for each pubertal stage. Volumetric density fell during early puberty and then increased rapidly. Maximal increase of all bone variables occurred earlier in girls than in boys and earliest for bone width, then mineral content, then density. In girls most change occurred in the 12 mo before and after menarche. The degree of tracking was similar to that for height. Bone growth followed physical growth but at a slower tempo. By age 17 y boys had attained 86% of the reference adult bone mineral content and volumetric density; girls had attained 93% of the reference adult bone mineral content and 94% of volumetric density. Those skeletally mature at 17 y had greater mineral content and volumetric density. To maximize peak bone mass, modifiable environmental factors should be optimized before the onset of puberty and be maintained throughout this period of rapid growth and beyond attainment of sexual maturity.

The Effect of Food Intake from 2 to 24 Weeks of Age on LHRH-I Content in the Median Eminence and Gonadotrophin Levels in Pituitary and Plasma in Female Broiler Breeder Chickens

The present study describes the effect of long-term food restriction on hypothalamopituitary function in the broiler breeder hen during the period prior to sexual maturity. From 1 week of age onward, chickens were divided into 3 groups: one group received foodad libitum(Ad lib); a second group was fed a restricted quantity of food (Res); and a third group was restricted to obtain an intermediate body weight (Int) in between groups one and two. The effects of these feeding regimes on hypothalamopituitary function were assessed by measuring the amounts of cLHRH-I stored in the median eminence (ME) and the pituitary content and plasma levels of gonadotrophins. The Res group had significantly lower levels of cLHRH-I in the ME compared to the Ad lib animals. In all groups, there was a major increase in cLHRH-I in the median eminence about 3 weeks before onset of lay. The age of first oviposition was delayed by 2 and 6 weeks in the Int and Res groups, respectively, compared to the Ad lib animals, indicating that body weight gain patterns are not directly related to the appearance of the first egg. The attainment of sexual maturity may be associated with a threshold value of cLHRH-I stored in the ME in the Ad lib and Int birds. The pituitary LH and FSH contents (after week 16) were positively related to the amount of cLHRH-I in the ME. Plasma FSH concentrations in Ad lib and Int chickens peaked about 3 weeks before the first oviposition and this prepubertal peak was associated with increased pituitary FSH and ME cLHRH-I. There were however no relationships between plasma LH concentrations and pituitary LH content and between plasma LH and cLHRH-I amounts in the ME. The present study demonstrates that the delayed sexual maturation, caused by a chronic food restriction, may be associated with (1) delayed ovarian and oviductal growth, (2) decreased cLHRH-I storage in the ME, and (3) lower levels of LH and FSH in the pituitary. These hormones were however not directly related to levels of food restriction.

Evaluation of a technique to obtain development-stage-synchronised earthworms ( Eisenia fetida )

The aim of this experiment was to investigate whether Eisenia fetida hatchlings of different ages, kept initially without food, could be used to obtain worms of a comparable development stage (measured as growth) with similar maturation properties (measured as clitellum development). Seven groups of hatchlings, each differing in age by 7 days (range: 0–42 days) were collected as follows. Cocoons were kept in water in multicell containers and individuals that hatched during a 24-h period were placed on moist vermiculite with no food, at weekly intervals. The longest period that hatchlings were fasted was 42 days, after which food was added and growth monitored for 50 days. No differences in weight gain between the different batches were observed. Analysis of the growth curves and attainment of sexual maturity (clitellum development) indicated no effect of age or stage of development at the onset of feeding. It was concluded that this technique allows the production of cohorts of E. fetida, synchronised with respect to development stage, for use in toxicological and biological investigations that require control of factors such as development stage, age and size, and in particular for use in toxicological experiments complying with OECD regulatory procedures.

Biology, spatial distribution and population dynamics of Lepidotrigla cavillone (Pisces: Triglidae) in the Central Tyrrhenian Sea

Specimens of Lepidotrigla cavillone (the large-scaled gurnard) were collected in the Central Tyrrhenian Sea during trawl surveys carried out in April–May and September 1985, 1986, 1987, 1994, and in October 1995. The species was fished between 30 and 200 m depth. A significant size-depth relationship ( p < 0.001), was observed for juveniles (S.L. < 7 cm) and adults: the former migrated deeper from the coastal nursery, at the end of the first year of life; the latter moved shallower toward the spawning grounds at 60–100 m depth. Principal Component Analysis, indicated gonadal development as the main factor affecting L. cavillone depth-size relationships. Mature females were observed with significantly higher abundance ( p < 0.001) at depth of 80–100 m. Large-scaled gurnards accomplished more than half of their growth during the first two years. Reduction of growth coincided with attainment of sexual maturity. An increase of the mesh size towards the legal size may bring the age at first capture from 1.5 years up to the age of first maturity (second year) improving current Y/R.

Patterns of growth and physical maturity in the western Mediterranean striped dolphin, Stenella coeruleoalba (Cetacea: Odontoceti)

The growth and physical maturation of striped dolphins (Stenella coeruleoalba) of the northern section of the western Mediterranean Sea were studied. Fitted Gompertz growth curves indicate that females grow faster than males when they are young, but their growth ceases and the asymptotic length is attained earlier than in males. Asymptotic length was greater in males (200 cm) than in females (194 cm). Males reached vertebral physical maturity at 15–20 years old and females earlier, at 13–18 years old. Cranial maturity was apparently achieved at similar ages and body lengths. The radius and ulna, however, completed their ossification much earlier, again showing sexual dimorphism, with females maturing at a younger age (5–6 years) and smaller body length (160–175 cm) than males (8–9 years and 170–181 cm). Age-related parameters of physical maturation and growth determined for this population were similar to those estimated for the striped dolphins inhabiting Japanese waters, while length-related parameters differed markedly between the two conspecific populations. It is concluded that the only age- or length-related parameter associated with body growth or ossification of the skeleton that is liable to be affected by density-dependent forces is the body growth rate or, as a consequence, the age at attainment of sexual maturity.

The age of sexual maturity in Japanese giant flyin squirrels, Petaurista leucogenys.

I determined the age of sexual maturity in Japanese giant flying squirrels, Petaurista leucogenys. The degree of testicular development was estimated in 25 males 224 times during eight years. The scrotum began to extend at the age of 7.5-8.5 months, and was slightly swollen in males 8-13 months old. Testes of 1⁄2-3⁄4 size were observed in males from 14 months onward. By the mating season when they were 21-22 months old, the proportion with full-sized testes was 57% of the males. All five males of 27-28 months of age had full-sized testes. One 22 month-old male and one 27 month-old were observed copulating. Summer-born males had slightly faster developing testes than spring-born males. None of 19 young females were observed in estrus. The attainment of sexual maturity in males at 21-22 months of age seems very late as the intermediate-sized rodents. It is suggested that mothers allow their young to remain with them for 1-1.5 years until they become sexually mature in order to increase the survival rate of their young, thereby compensating for their small litter sizes of one or two.

Testis of Prepubertal Rhesus Monkeys Receives a Dual Catecholaminergic Input Provided by the Extrinsic Innervation and an Intragonadal Source of Catecholamines1

The mammalian testis is innervated by extrinsic catecholaminergic nerves and responds to catecholamines with steroid secretion. Although the primate testis has also been shown to be innervated, potential differences in the density of this innervation between immature and sexually developed individuals have not been described. A recent study demonstrated that the primate ovary contains a network of neuron-like cells and that some of these cells are catecholaminergic. It is thus possible that the male gonad is also endowed with a similar intragonadal source of catecholamines. The present study addresses these two issues. Catecholaminergic nerves were identified as such by their content of immunoreactive tyrosine hydroxylase (TH; the rate-limiting step in catecholamine biosynthesis), and in some cases by glyoxylic acid histochemistry. Fibers containing TH were abundant in testes from juvenile animals (1-2 yr of postnatal life), but the density of this innervation was not maintained in adult animals, whose testis showed only a few TH-positive fibers scattered in the interstitial tissue. Testicular norepinephrine (NE) concentration was much lower in adult than in juvenile animals, suggesting that the marked increase in testicular weight that occurs with the attainment of sexual maturity is not accompanied by corresponding changes in NE content. At the ultrastructural level, testicular nerve fibers contained pleiomorphic, dense-core and clear vesicles, suggesting the presence of catecholamines and other neurotransmitters. In addition to this extrinsic catecholaminergic innervation, prepubertal testes, but not adult gonads, contained an intrinsic population of TH-immunopositive neuron-like elements, identified as cells by confocal scanning laser microscopy. To determine whether the prepubertal monkey testis indeed expresses the TH gene, testicular RNA was subjected to reverse transcriptase polymerase chain reaction to amplify the 5' end of TH mRNA, which encodes the regulatory domain of the enzyme. The cDNA that was obtained predicts an amino acid sequence similar, but not identical, to that encoded by the alternatively spliced type 1 TH mRNA form present in the adrenal gland. These results indicate 1) that the primate testis receives a dual catecholaminergic input, one provided by the extrinsic innervation and the other by neuron-like cells located within the gonad itself, and 2) that the influence exerted by both sources on testicular function may be more prominent during the prepubertal period than in adulthood. The presence in the testis of a TH mRNA variant encoding amino acid substitutions in its 5' end suggests that regulation of testicular TH enzyme activity may include a gonad-specific component.

Glial Ensheathment of GnRH Neurons in Pubertal Female Rhesus Macaques

During the period of development, prior to full sexual maturity, gonadotropin hormone-releasing hormone (GnRH) neurons are fully capable of synthesizing and processing the GnRH decapeptide. Nonetheless, the secretion of the hormone is not adequate to stimulate adult patterns of gonadotropin release. The present study was undertaken to examine ultrastructural characteristics of the GnRH neuron and its relationship to its environment in early-midpubertal female rhesus monkey. The neurons bore all the ultrastructural immunocytochemical characteristics of those in mature animals, but quantitative morphometrics revealed that they were extensively apposed by glial processes. Such ensheathment was described earlier in ovariectomized adult animals and was found to be reversible by administration of gonadal steroids. The density of synaptic input to GnRH neurons in the pubertal animals did not differ significantly from that of adult intact or ovariectomized animals from a previous study. Chemical identification will be required to determine whether there are age or hormonal differences in the innervation of these neurons. These results provide anatomical evidence in support of indications from other studies that the ovarian steroidal milieu affects GnRH-glial relationships. Further testing will be required to determine whether the attainment of sexual maturity in the female rhesus macaque is dependent upon a reduction in glial ensheathment of GnRH neurons.

Growth-related changes in testicular mass and plasma testosterone concentrations in long-finned pilot whales, Globicephala melas.

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.

Anamorphosis in millipedes (Diplopoda)-the present state of knowledge with some developmental and phylogenetic considerations

Abstract A review of the postembryonic development of millipedes (Diplopoda) is given, based mainly on published information. Original observations are, however, also included. Millipedes hatching from the pupoid usually have three pairs of legs; during their postembryonic growth they acquire more segments and more legs. This process is known as anamorphosis. Three types of anamorphosis are recognized. In euanamorphosis , every moult is accompanied by addition of new segments, even after the attainment of sexual maturity. In hemianamorphosis , the addition of new segments goes on until a certain stadium, and further moults take place without addition of segments. In teloanamorphosis , the addition of segments stops at a certain stadium (the adult, and ultimate, stadium) after which no further moults occur. Available information on anamorphosis in each of the millipede orders is reviewed. General patterns are emphasized, but variations are also considered in detail. It is shown that the so-called 'law of anamorphosis' is valid only for the 'ring-forming' millipedes (Merocheta and Juliformia) in which tergites, pleurites, and sternites of each diplosegment are firmly fused into a complete 'ring', and for some other forms (Polyzoniida, Chordeumatida), where there is a constant relationship between rings and legs. The chapter on the order Julida is particularly detailed and includes discussions of patterns in the variation and a section on periodomorphosis. The general chapter on developmental patterns includes inter alia an interpretation of the variations in millipede anamorphosis in terms of the 'biometabolic modi' of Remane. The hypothetical ancestral millipede is shown to have developed by hemianamorphosis. Euanamorphosis was acquired by the ancestral species of Helminthomorpha. Within this clade, Chordeumatida and Merocheta have secondarily become teloanamorphic, whereas some Juliformia seem to have returned to hemianamorphosis. The contrasting principles of elongation and contraction, subject of much debate among diplopodologists, are shown both to have played a role in the course of millipede evolution.

Anamorphosis in millipedes (Diplopoda)— the present state of knowledge with some developmental and phylogenetic considerations

A review of the postembryonic development of millipedes (Diplopoda) is given, based mainly on published information. Original observations are, however, also included. Millipedes hatching from the pupoid usually have three pairs of legs; during their postembryonic growth they acquire more segments and more legs. This process is known as anamorphosis. Three types of anamorphosis are recognized. In euanamorphosis, every moult is accompanied by addition of new segments, even after the attainment of sexual maturity. In hemianamorphosis , the addition of new segments goes on until a certain stadium, and further moults take place without addition of segments. In teloanamorphosis , the addition of segments stops at a certain stadium (the adult, and ultimate, stadium) after which no further moults occur. Available information on anamorphosis in each of the millipede orders is reviewed. General patterns are emphasized, but variations are also considered in detail. It is shown that the so-called 'law of anamorphosis' is valid only for the 'ring-forming' millipedes (Merocheta and Juliformia) in which tergites, pleurites, and sternites of each diplosegment are firmly fused into a complete 'ring', and for some other forms (Polyzoniida, Chordeumatida), where there is a constant relationship between rings and legs. The chapter on the order Julida is particularly detailed and includes discussions of patterns in the variation and a section on periodomorphosis. The general chapter on developmental patterns includes inter alia an interpretation of the variations in millipede anamorphosis in terms of the 'biometabolic modi' of Remane. The hypothetical ancestral millipede is shown to have developed by hemianamorphosis. Euanamorphosis was acquired by the ancestral species of Helminthomorpha. Within this clade, Chordeumatida and Merocheta have secondarily become teloanamorphic, whereas some Juliformia seem to have returned to hemianamorphosis. The contrasting principles of elongation and contraction, subject of much debate among diplopodologists, are shown both to have played a role in the course of millipede evolution.

Relationships of reproductive traits and body size with attainment of sexual maturity and age in Blanding's turtles (Emydoidea blandingi)

AbstractTo place associations among body size, age at maturity, age, and reproductive traits of a long‐lived organism in the context of current life history models based on the concept of norms of reaction, we examined data from a mark‐recapture study of Blanding's turtles (Emydoidea blandingi) in southeastern Michigan during 24 of the years between 1953 and 1988. Females matured between 14 and 20 years of age. Both the smallest and largest adult females in the population were reproducing for the first time in their lives. This result suggests that a combination of differences in juvenile growth rates and ages at maturity, and not indeterminate growth, are the primary cause of variation in body size among adults. Body size variation among individuals was not related to age at sexual maturity. Females that had slower growth rates as juveniles matured later at similar mean body size compared to those with more rapid growth that matured at an earlier age. As a result, a linear model of age at sexual maturity with growth rates of primiparous females between hatching and maturity was significant and negative (R2 = 0.76). Frequency of reproduction of the largest and smallest females was not significantly different. Clutch size did not vary significantly with age among either primiparous or multiparous females. Clutch sizes of primiparous females and multiparous females were not significantly different. However, older females (&gt;55 years minimum age) reproduced more frequently than did younger females (minimum age &lt;36 y).

Life history and male intertroop mobility among Japanese macaques (Macaca fuscata)

Male intertroop transfer among Japanese macaques (Macaca fuscata) often coincides with the mating season. However, no necessary connection exists between mating by newly arrived males and whether they join a troop—visitors often mate, and males that join troops may show little mating success. On the other hand, intertroop transfer often coincides with major events in the developmental and social life history of males, such as the attainment of sexual maturity and full adult body size or rise in dominance rank. Thus, intertroop transfer may reflect age-specific behavioral patterns in which males maintain a position in the age-rank structure of troops, where the rank acquired in a new troop is partially determined by age.

Age at attainment of sexual maturity in humpback whales, Megaptera novaeangliae

Twelve female humpback whales (Megaptera novaeangliae) in the southern Gulf of Maine produced first-observed calves at ages ranging from 5 to 7 years. These data confirm that most females of this species attain sexual maturity at an average age of approximately 5 years. Observations in the West Indies of two males, aged 6 and 7 years, engaged in breeding-related behavior that is characteristic of mature animals suggests that males attain sexual maturity within a similar range of ages to females, although they may not be able to successfully engage in intrasexual competition until later in life. These data imply that the examination of ear plugs to determine the age of dead humpback whales should be based upon an assumed annual growth rate of two growth layer groups, not one.

The reproductive biology of the harbour seal,Phoca vitulinaL., in Norwegian waters

Abstract This study is aimed at establishing the mean age at attainment of sexual maturity and birth rates of harbour seals at the Norwegian coast, using information from 172 female and 184 male harbour seals sampled between 62 and 66° N during the period 1977–1982. Based on the occurrence of first time ovulation, the mean age at attainment of female sexual maturity was 3.75 years. The mass of ovaries showed maximum rate of increase between three and five years of age. Testicular growth indicates that males matured between five and seven years of age. The birth rate increased from 0.2 in four-year-old females to 0.5 in six-year-olds and to 0.9 in females eight years of age and older.