Early Maturing Males Research Articles

Side effects of sexual maturation on heritability estimates in rainbow trout (Oncorhynchus mykiss)

In ¢sh, sexual maturation is often considered to be a problem because it perturbs growth and product quality. Therefore, it is common to select against early-maturing males in commercial breeding programmes (Gjedrem 2000). Genetic determinism of age at sexual maturation has been extensively studied in many species, and even some QTLs have been found (e.g. Gjerde 1986; Hankin, Nicholas & Downey 1993; Longalong, Eknath & Bentsen 1999; Kause, Ritola, Paananen, Mantysaari & Eskelinen 2003; Haidle, Janssen, Gharbi, Moghadam, Ferguson & Danzmann 2008). However, the eiect of sexual maturation on heritability estimates for other traits is not documented. In this paper, we present data collected during the beginningof sexualmaturationof a group of rainbow trout and showhow it biases heritability estimations. The ¢sh studied were issued froma full-factorial mating between two dams and 45 sires. Fish were all reared in the same tank since the eyed stage under a natural photoperiod and pedigrees were redrawn using10 microsatellites. Fishwere harvested in April at 17 months of age. They were killed on ice and several growth and quality traits were determined. Body weight was the main trait studied in this paper. The sex of the ¢sh was recorded by visual inspection of the gonads. For females, none of the individuals showed signs of maturation. For males, observers attempted to diierentiate non-maturing and maturing males but it turned out to be di⁄cult because we were at the very beginning of the maturation (this rainbow trout strain usually spawns in November^ December). However, we recorded gonads weight to enable calculation of the gonado-somatic index (GSI5100 gonads weight/body weight), which was used to determine which males were maturing or not.We studied several GSI thresholds: 0.1, 0.2, 0.3, 0.4 and 0.5. For each threshold, males with GSI above the threshold were considered to be maturing males. We studied sex eiect and heritability estimates for each threshold. Heritability was estimated using VCE5 (Groeneveld & Kovac 1990) with a sire model and sex and dam as ¢xed eiects. Dam was set as a ¢xed eiect because there were only two dams in our mating design, and therefore between-dams variance is of no interest. Two dams were used instead of one in order to avoid confusion of dominance eiects with additive genetic eiects in the between-sires variance. Moreover, this design was demonstrated to be e⁄cient for estimating heritabilities when the total number of oispring analysed is ¢xed (Dupont-Nivet, Vandeputte & Chevassus 2002). First, we analysed all the datasets with a sex eiect comprising three levels (female, male and maturing male). Second, maturing males were removed from the dataset and the sex effect was set to two levels (male and female). Using ‘FAP’ software (Taggart 2007), 87% of ¢sh could be attributed to their parents. Oispring from two sires with less than three oispring were removed from the data set. Four hundred and thirty-three animals were ¢nally analysed. The sex ratio was well equilibrated with 217 females, i.e., 50.1%. In Table 1, Aquaculture Research, 2010, 41, e878^e880 doi:10.1111/j.1365-2109.2009.02448.x

Fitness And Cardiovascular Risk Factors In Males Of Contrasting Maturity Status.

During adolescence, the associations between biological maturation, fitness, and cardiovascular risk factors have been studied to some extent. Little is known, however, about the later outcomes of the maturation process. PURPOSE: To document the differences in fitness and risk factors between adult males of contrasting maturity status during adolescence. METHODS: In the Leuven Longitudinal Study on Lifestyle, Fitness and Health, 133 males were followed from 1969, when they were 12 to 13 years, until 2002-2004 when they were 47 years. Anthropometric variables, (height, weight, waist circumference, skinfolds, bioelectrical impedance, Dual X-ray absorptiometry) were measured, the adult Eurofit tests and Biodex strength measurements were administered, and risk factors ( blood pressure, glucose level, and blood lipids) were examined. Age at peak height velocity (APHV), derived from individual curve fitting using non-smoothed polynomials, was used to classify the adolescent boys into three maturity groups: (1) early maturing males: APHV -1 SD before mean APHV of the total sample, late maturing males: APHV +1 SD after mean APHV of the total sample, and average: APHV between 0.5 SD before and 0.5 SD after the mean APHV of the total sample. After normalization of the phenotypes, ANOVA's and post-hoc tests were used to verify the mean differences between the contrasting maturity groups. RESULTS: At 47 years, early maturing males had higher systolic blood pressure and biceps and subscapular skinfolds, whereas late maturing males had better strength (handgrip & isokinetic knee-extension torque at 60°/sec (borderline significant)), and power (standing long jump and counter movement jump). CONCLUSION: For some fitness components the adolescent advantage of early maturation reverses in adulthood whereas for some risk factors early maturing males are more at risk.

Reduction of sexual maturation in male Dicentrarchus labrax by continuous light both before and during gametogenesis

The objective of this study was to investigate the effect of exposure to continuous light (LL) during the pregametogenesis (4-month duration) and gametogenesis (6-month duration) periods on early male sexual maturation in the sea bass. A simulated natural photoperiod group (SNP) and a long-term exposure group to LL during 12 months were kept as controls. Somatic growth, gonadal development, plasma testosterone (T) and 11-ketotestosterone (11-KT) and the expression of the follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in the pituitary were analysed as indicators of maturation. Growth in all treatments was independent of photoperiod. Nevertheless, all LL treatments were effective in reducing the number of early maturing males (<3% with <0.2% GSI versus 22% with 0.8% GSI in SNP). This inhibition was not complete but the effect was comparable among all LL treatments thus suggesting that a potential photo-labile period might exist in the sea bass. In the SNP group, the T and 11-KT plasma levels as well as the gene expression values of the three gonadotropin subunits (i.e., LHβ, FSHβ and glycoprotein (GP) α) peaked in February concomitantly with the increase of the GSI (≥0.51%) and the accumulation of LH protein in the pituitary (≥14.6 μg) and declined at post-spermiation stage (GSI≤0.12% and LH protein≤10.2 μg/pit). Exposure to different LL treatments induced a differential response particularly on the 11-KT levels and the gene expression of the FSHβ subunit. We suggest that the unbalanced production of this androgen regulated by FSHβ might be limiting the stimulation of germ cell proliferation at the testicular level and thus arresting early puberty male sea bass.

Combining ability and heterosis for earliness characters in line×tester population of Gossypium hirsutum L.

The objective of this study was to estimate the general combining ability of the parents and specific combining ability of hybrids for earliness traits for line selection. Inheritance and interrelationships of earliness characters were evaluated in a line x tester design. Three intermediate-early-maturing female (lines) which are grown regionally and four early-maturing males (testers) cotton varieties were crossed in 2003. The twelve F(1) and seven parents were planted randomized block design with three replications in 2004. For each earliness trait, general combining ability (GCA) and specific combining ability and gene effects were estimated using the line x tester method of analysis and also were determined heterosis and narrow sense heritability. Parents and their hybrids (except the monopodial branch) were significant for all the earliness traits studied. Estimates of variance due to GCA and SCA and their ratio revealed predominantly non-additive gene effects for date of first square, date of first flowers and harvested rate of first picking. Among the lines, Ersan 92 and Maras 92 and among the testers Acala Royal was found to be the best general combiners for most of the earliness characters. Four out of twelve crosses namely Ersan 92 x Chirpan 603, Ersan 92 x Acala Maxa, Maras 92 x Acala Royal and Nazilli 87 x Acala Royal were found to be the best crosses for investigated earliness characters.

State-dependent life history plasticity in Sacramento River winter-run chinook salmon (Oncorhynchus tshawytscha): interactions among photoperiod and growth modulate smolting and early male maturation

An experiment was performed to determine the relative effects of photoperiod at emergence and growth rate on smolting pattern and early male maturation rate in Sacramento River (California, USA) winter-run chinook salmon (Oncorhynchus tshawytscha) (listed as endangered under the US Endangered Species Act). Fry were ponded on the same day but at three different points in the seasonal photoperiod cycle (using artificial lighting) spanning the natural range of emergence timing in this population. Significant increases in gill Na+,K+-ATPase activity and seawater survival were found during March and April in all treatments, similar to yearling smolting patterns found in many salmonids. Fish that emerged early and grew at a relatively high rate also demonstrated signs of smolting in August–November. Male maturation was growth dependent, with HiFeed groups maturing at a rate double that found in LoFeed groups. Male maturation was also photoperiod dependent with a linear relation found between emergence date and rate of male maturation. These results demonstrate that individual life history pattern was variable and dependent on emergence timing and growth rate.

Triploidy Induction in Jundiá, Rhamdia quelen, Through Hydrostatic Pressure Shock

ABSTRACT Jundiá, Rhamdia quelen, is considered to be a fish with great farming potential in South and Southeast Brazil. For this species, early male sexual maturation has a negative influence on the growth rate. Thus, the possibility of using sterile jundió triploids becomes an interesting option in fish farming. This study assessed the effect of pressure shock on the production of Jundió triploid larvae and their yield at the end of yolk absorption. Exposure for 5 minutes at 3.4473950 X107 Pa after 2 or 5 minutes post-fertilization was enough to induce 100% triploidy in R. quelen, showing 29.1% and 20.5%, respectively, of larval yield at the end of the endogenous feeding period.

Longitudinal gradients in threshold sizes for alternative male life history tactics in a population of Atlantic salmon (Salmo salar)

Atlantic salmon (Salmo salar) males may mature early in life in freshwater, rather than maturing after a migration to sea, if their size is above a threshold value. We analyzed the spatiotemporal variation in size and incidence of the early maturity tactic among males over an 8-year period in six subpopulations on two branches of a river and collected environmental data on each site and across the river scape. A positive longitudinal trend in the frequency of early maturing males that was stable over the 8-year period occurred from the mouth to the head of the river. Threshold sizes for early maturation varied among subpopulations; size thresholds for male parr to mature were higher in downstream habitats and lowest upstream. This pattern was consistent in both river branches over the 8-year period and was not related to either the density of parr or site-specific abiotic habitat characteristics. However, the cumulative incidence of habitat features that could impede migration of large individuals increased with increasing upstream distance. Migration costs may contribute to the observed variation in threshold sizes.

Growth Modulation Alters the Incidence of Early Male Maturation and Physiological Development of Hatchery‐Reared Spring Chinook Salmon: A Comparison with Wild Fish

AbstractPrevious studies conducted at the Cle Elum Spring Chinook Salmon Supplementation Hatchery in Washington State demonstrated that 37–49% of the male Chinook salmon Oncorhynchus tshawytscha released from this facility in its first years of operation precociously matured at age 2 rather than the more typical age 4. We examined the effects of altering seasonal growth rate on the incidence of age‐2 male maturation in an experimental subset of that population and compared their physiological development (size, growth rate, condition factor, whole‐body lipid, gill Na+,K+‐ATPase activity, and plasma insulin‐like growth factor‐I [IGF‐I]) with that of both hatchery (production) and wild fish. Altering summer and autumn rations resulted in four growth trajectories with the following size and precocious male maturation rates: The high summer—high autumn growth trajectory produced fish averaging 25 g and 69% precocious maturation; the high summer—low autumn trajectory yielded fish that averaged 18 g and exhibited 58% precocious maturation; the low summer—high autumn trajectory produced 18‐g fish with 51% precocious maturation; and the low summer—low autumn trajectory yielded fish averaging 16 g and 42% precocious maturation. Production fish averaged 22 g and exhibited a 53% precocious maturation rate. The high summer growth treatments and production fish were largest among all groups and had higher plasma IGF‐I, adiposity levels, and precocious male maturation rates than did the low summer growth treatments. Wild fish were significantly smaller and leaner and had much lower plasma IGF‐I levels than all other groups. Gill Na+,K+‐ATPase activity was not different between groups, suggesting that there was no differential effect on smoltification. Growth modulation reduced the precocious male maturation rate by 39% among experimental treatments and by 21% between production fish and the low—low treatment. However, the maturation rate and adiposity of hatchery fish differed markedly from those of wild fish, suggesting that more dramatic alterations of rearing regime may be required to further reduce the prevalence of this phenotype in cultured fish.

Comparative analysis of growth performance and sperm motility between precocious and non-precocious males in the European sea bass ( Dicentrarchus labrax, L.)

Early puberty affects a considerable amount of males in commercially farmed fish species. It results in additional annual production costs for aquaculture that need to be reduced. The present study is focused in the sea bass ( Dicentrarchus labrax L.), an important marine teleost fish in European aquaculture that exhibits 25–30% of precocious males under farming conditions. Thus, the effects of early sexual maturation on growth performance and sperm quality between the early-maturing males (1-year-old precocious fish) and their counterparts, the normal maturing fish which mature 1 year later, were compared in this species. Sea bass males were judged to be precociously mature on the basis of their capacity to release sperm after abdominal massage at 12–14-month-old, during their first annual cycle of life. Those individuals that did not release sperm were considered as normal-maturing males. Fish, with a similar size (127.67 ± 1.2 g; 21.01 ± 0.05 cm) at the beginning of the experiment, were monthly sampled from 14 to 24 months of age for comparative growth performance between both types of males. Results evidenced that precocious fish grew up to 18% less in weight and 5% less in fork length than their counterparts during their second annual cycle of life. A computerized analysis of sperm motility was carried out to estimate sperm quality and animal reproduction performance between both types of males in the sea bass. During the first annual cycle of life, significant differences were observed in sperm volume and concentration and several motility parameters (i.e., curvilinear, straight line and average path velocity and beat cross frequency) between the 1-year-old early-maturing males and adult fish that were used for comparison at this time. Nevertheless, sperm motility was comparable between the early-maturing males and the normal-maturing ones during the second annual cycle of life of the animals, suggesting similar reproductive success of both types of males around 2 years of age.

Genetic trends in growth, sexual maturity and skeletal deformations, and rate of inbreeding in a breeding programme for rainbow trout ( Oncorhynchus mykiss)

Progress in the Finnish breeding programme for rainbow trout was assessed by estimating genetic trends in growth, maturity age and skeletal deformations and by calculating rates of inbreeding and additive genetic relationships. The analysis included two pedigreed populations with three generations and over 117,000 individuals recorded for skeletal deformations, growth and age at maturity. Because the breeding station is located in fresh water but sea is the main production environment, each family was split into subgroups to be tested for performance either in fresh or sea water. Estimation of breeding values across the generations showed that multitrait selection has produced an average of 7% genetic gain per generation in fresh and sea water growth of market-sized fish. In the population with high frequency of early maturing males, phenotypic culling of early maturing males has prevented an increase in the frequency of early maturing fish. In the other population, the frequency of early maturing females has increased, the genetic change being unfavourable. Weak favourable or no correlated genetic changes were observed in the frequency of deformations in response to selection for the production traits. Rate of inbreeding has remained low, the maximum value being 0.7% per generation. Because mating of close relatives has been avoided, an increase in coefficient of additive genetic relationships describes the risk of the programme more realistically than rate of inbreeding. The average increase in relationship was 0.7% per generation, a value below the suggested precaution level.

Sexual selection for increased male body size and protandry in a spider

Female-biased sexual size dimorphism (SSD) is found in many organisms yet is poorly understood. Spiders in general, and web-building species in particular, typically have strongly female-biased SSD. We investigated the causes of SSD in the web-building spider Stegodyphus lineatus. Females are slightly, but significantly, larger than males. Large females are more fecund but the selection pressures on male body size are not clear. Males were introduced on to the webs of virgin and mated females and we also conducted competition experiments between males. Large males did not have longer copulations, nor did they mate more successfully with virgin females than small males did; however, they were more successful with previously mated females and remated more often. They also won more fights, and were more successful at obtaining prey from the female's web. Indiscriminate mating by virgin females, however, conferred a fitness advantage on early maturing males. We suggest that the female's mating strategy selects for protandry, which results in female-biased SSD, despite the selection for large body size in males. Indiscriminate mating by females and a trade-off between time to maturation and male body size may be important in understanding the evolution of female-biased SSD.

Raffles, roles, and the outcome of sperm competition in sockeye salmon

In species with male alternative reproductive phenotypes, one phenotype is usually disadvantaged in mating competition. In salmonid fishes, large late-maturing males pair with nesting females and maintain close contact before and during spawning. Small early-maturing males have little contact with nesting females and, during spawning, begin to release sperm after the paired male. The effects of male phenotype and timing of ejaculation on success in sperm competition are not known. In this study, we determined paternity of offspring resulting from in vitro competitive fertilizations to examine these two aspects of sperm competition in sockeye salmon, Oncorhynchus nerka (Walbaum, 1792). When we fertilized eggs with mixtures of equal numbers of sperm from each of two male age classes, we found that success in sperm competition did not depend on male age. However, success in these competitive fertilizations did not conform to the fair raffle model of sperm competition, since paternity in most of the clutches was biased in favour of one male. When we added milt from two males sequentially to a batch of eggs, we found that sperm from the second male fertilized fewer eggs than sperm from the first male, but the difference was less than expected. In addition, a male's success when his milt was added first was not correlated with his success when his milt was added second.

Alternative male life‐history tactics as potential vehicles for speeding introgression of farm salmon traits into wild populations

AbstractReleases of cultured organisms, such as farm Atlantic salmon (Salmo salar L.), threaten native biodiversity and the integrity of natural communities. Salmon escaping from sea farms, however, have relatively poor reproductive success, suggesting that the rate of spread of domesticated traits may be reduced. We now compare the relative reproductive success of males that mature precociously in freshwater (parr) and find that those of farm origin have higher breeding and fertilization success than wild and hybrid individuals. Specifically, hybrid parr had 57% and wild parr 25% the success of farm parr. Early maturing males could thus be important vehicles promoting introgression of domesticated and/or non‐native traits into wild populations and ultimately have long‐term impact on the genetic integrity of native populations.

The effects of long-term testosterone, gonadotropin-releasing hormone agonist and pimozide treatments on testicular development and luteinizing hormone levels in juvenile and early maturing striped bass, Morone saxatilis

The present study was conducted to test the responsiveness of the juvenile male reproductive axis to hormonal stimulation and to compare it to that of early maturing males. Long-term treatments with various combinations of T, GnRHa and pimozide did not result in an increased incidence of early maturing males, but did stimulate spermatogenesis slightly in juvenile fish. In early maturing males, the treatments appeared to be inhibitory since they resulted in a reduction of the GSI and a lower incidence of spermiating males. In early maturing males, pituitary LH content was elevated by GnRHa treatments alone while in juvenile males a combination of T and GnRHa was needed to increase the levels of LH in the pituitary. Thus, T may play an important role during puberty by potentiating the effects of GnRH on LH synthesis. In both juvenile and early maturing males, plasma LH levels could be increased only by high doses of GnRHa (in combination with T). Therefore, LH synthesis and release probably require different levels of GnRH stimulation. A GnRH challenge (single injection of 50 μg GnRHa/kg) at the end of the experiment resulted in a dramatic elevation of plasma LH levels in almost all animals. This finding demonstrates that pituitaries from juvenile and early maturing males were responsive to GnRHa stimulation, even after long-term hormonal treatments. The addition of pimozide did not affect the T- and GnRHa-induced increase in pituitary LH content but inhibited the release of LH in response to a GnRHa challenge. In conclusion, high doses of GnRHa in combination with T can increase plasma LH levels in juvenile males but do not induce complete testicular maturation. Factors other than T, GnRHa or LH are probably involved in the induction and completion of spermatogenesis.

Effects of continuous additional light on growth and sexual maturity in Atlantic salmon, Salmo salar, reared in sea cages

Individually tagged Atlantic salmon postsmolts (body weight 243±0.9 g [mean±SE], n=1800) were distributed randomly among four sea cages, two cages received continuous additional light (AL) from November to July, and two received natural light (NL) only (controls). Equal numbers of fish (150 from each cage) were moved between the AL and NL cages in December and January, creating a total of six experimental groups. The fish were fed to excess during the hours of NL. Compared with the control group, exposure to AL from November, December or January until July (Nov–Jul, Dec–Jul and Jan–Jul groups, respectively) resulted in a 48–52% reduction in specific growth rate (SGR) during the subsequent 6 weeks, followed by a higher SGR during the next 4 to 5 months. A similar growth response as in the Nov–Jul group occurred in the groups receiving only 6 or 12 weeks of AL from November (Nov–Dec and Nov–Jan groups, respectively). The SGR of the Nov–Jul group was higher than in the Nov–Jan and Nov–Dec groups at the end of the experiment. Between May and July, groups exposed to AL from November (Nov–Jul, Nov–Jan and Nov–Dec) grew significantly less than the groups initially receiving NL (Control, Jan–Jul and Dec–Jul). In July, the body weight (mean±SE) of the fish depended on the duration and timing of AL exposure; Nov–Jul: 1072±26 g, Dec–Jul: 995±23 g, Jan–Jul: 977±20 g, Nov–Dec: 930±23 g, Nov–Jan: 870±22 g and Control: 815±17 g. The proportion of sexually maturing males increased with early exposure and duration of AL; Control: 6.5%, Jan–Jul: 8.0%, Dec–Jul: 14.7%, Nov–Dec: 15.5%, Nov–Jan: 21.7% and Nov–Jul: 37.6%. The study provides evidence that AL superimposed on NL enhances growth of Atlantic salmon in sea cages during winter and spring, with timing and duration of the exposure affecting growth and the proportion of early maturing males.

The effect of whole body lipid on early sexual maturation of 1+ age male chinook salmon ( Oncorhynchus tshawytscha)

Early sexual maturation of male chinook salmon (maturation 1 to 4 years prior to females in the same age class) results in reduced effectiveness of stock enhancement programs and a financial loss to the salmon farming industry. Previous studies in Atlantic salmon have shown that the age of maturity in males is affected by growth and/or body energy stores, but the relative roles of these two factors are not well understood. Therefore, an experiment was designed to determine when spermatogenesis was initiated, to characterize the endocrine changes during the onset of puberty in male salmon, and to determine if the level of whole-body lipid affects the incidence of early male maturation in a wild stock (Yakima River) of 1+ spring chinook salmon. Fry were fed a commercial diet from February until August and were then divided into groups of 320 fish (mean weight, 5.6 g) and fed one of five experimental diets (two replicate groups/diet) containing 4%, 9%, 14%, 18% or 22% lipid and 82%, 77%, 73%, 69%, or 65% protein for 13 months. Fish were reared on natural photoperiod and ambient temperature (6°C to 16°C), and pair-fed to a level based on the tank with the lowest feed consumption. Fish were weighed monthly and sampled to determine body composition, pituitary follicle-stimulating hormone (FSH) and luteinizing hormone (LH) levels, plasma insulin-like growth factor I (IGF-I) levels, and stage of gonadal development. Throughout the experimental period the mean fish weight was similar among treatment groups. However, from December through the end of the experiment in the following September, maturing males were significantly larger than nonmaturing fish. Initial lipid levels in 0-age experimental fish were near 6%, which is similar to wild fish of the same stock and age captured in the Yakima River during August. Fish fed diets containing more than 4% lipid increased in whole-body lipid content during the first 2 months of feeding and then maintained at relatively constant levels during the course of the experiment. Whole-body lipid levels for the dietary treatment groups averaged 5.6%, 7.1%, 8.2%, 9.4%, and 9.6% from October through the following September. Based on histological examination of the testes of experimental fish, type B spermatogonia and primary spermatocytes were first observed in some of the yearling males during November. These were designated maturing males. Pituitary FSH levels were significantly higher in maturing than nonmaturing males at this time and for the remainder of the study. Pituitary FSH levels increased as spermatogenesis proceeded in maturing fish, whereas pituitary LH levels increased in maturing 1+ males only during July and August, when testes were in late stages of spermatogenesis and in September during spermiation. Plasma IGF-I levels were significantly higher in maturing males than nonmaturing fish from December through the end of experiment. Since maturing males were significantly larger than nonmaturing fish of both sexes from December through September, the difference in IGF-I levels could be due to differences in growth or due to maturation. The percentage of maturing males was significantly influenced by whole-body lipid, increasing from 34% in fish fed the 4% lipid diet to 45% in fish fed the 22% lipid diet. These data suggest that whole-body lipid levels influenced the incidence of maturation of male spring chinook salmon. In addition, both endocrine and histological indicators suggest that maturation was initiated in males approximately a full year prior to the time the fish will spawn.

Factors affecting the occurrence of early maturing males in the protandrous pandalid shrimp Pandalus latirostris

Some Age-0 males of the protandrous pandalid shrimp Pandalus latirostris Rathbun mature in their first year, and the proportion of these early maturing males (EMMs) in a population varies both locally and annually. Two laboratory experiments and 2 field observations were con- ducted to clarify the factors affecting the occurrence of EMMs. The first experiment showed that EMMs needed to grow fast until the breeding season and began producing sperm at about 14 mm carapace length. Individuals with an AMP (length of the endopod/length of the appendix masculina) value above 40 were defined as EMMs. In the second experiment, the effects of food amount, hatch- ing date and maternal size on growth at Age-0 were examined. Food amount strongly affected the early growth. A difference in hatching date of >2 wk caused a large difference in body size of juve- niles; this difference was maintained until the breeding season 3 mo later. Large females spawned larger larvae than small females, but the size difference between larvae from large females and those from small females decreased with time. Field observations showed that at one site in Saroma Lagoon, Hokkaido, Japan, hatching occurred over a 1 mo period. In 1996/1997, we found no obvious differences of size distribution of Age-0 individuals and the occurrence of EMM as a function of loca- tion in the lagoon or year. These results may have been caused by slow growth, because water tem- peratures in the lagoon were much colder in 1996/1997 than during 1987 to 1995. We conclude that the occurrence of EMMs is closely related to various environmental factors in shallow waters. There- fore, the proportion of EMMs may fluctuate both locally and annually. This study shows that a small difference in juvenile growth over a short period can alter the subsequent life history of P. latirostris.

The effect of sexual maturation on the spatial distribution of Baltic salmon

This study examines the migratory habits of tagged mature and immature Atlantic salmon parr Salmo salar released from the Norrfors hatchery on the River Umeälven, Sweden from 1975 to 1977 and 1988 to 1990. Tags were recaptured in the Baltic Main Basin, the Gulf of Bothnia, and in the Umeälven. Ninety‐three per cent of previously mature males were recovered in the Umeälven compared with 23% of the previously immature smolts during the calendar year of release. In the second year after release (grilse year), the proportion of early maturing males recovered in the Umeälven was significantly greater than the proportion of previously immature smolts recovered in the Umeälven. Likewise, the proportion of previously mature males recovered in the Main Basin was significantly less than the proportion of previously immature smolts recovered in the Main Basin in the second calendar year after release. Previously mature males rematured after fewer years at sea, on average, than the previously immature smolts. Following the second calendar year after release, the proportions of previously mature males and previously immature smolts were not significantly different throughout the Baltic Sea.

The effect of sexual maturation on the spatial distribution of Baltic salmon

This study examines the migratory habits of tagged mature and immature Atlantic salmon parr Salmo salar released from the Norrfors hatchery on the River Umeälven, Sweden from 1975 to 1977 and 1988 to 1990. Tags were recaptured in the Baltic Main Basin, the Gulf of Bothnia, and in the Umeälven. Ninety-three per cent of previously mature males were recovered in the Umeälven compared with 23% of the previously immature smolts during the calendar year of release. In the second year after release (grilse year), the proportion of early maturing males recovered in the Umeälven was significantly greater than the proportion of previously immature smolts recovered in the Umeälven. Likewise, the proportion of previously mature males recovered in the Main Basin was significantly less than the proportion of previously immature smolts recovered in the Main Basin in the second calendar year after release. Previously mature males rematured after fewer years at sea, on average, than the previously immature smolts. Following the second calendar year after release, the proportions of previously mature males and previously immature smolts were not significantly different throughout the Baltic Sea.

Comparative Perspectives on Bimaturism, Ontogeny, and Dimorphism in Lemurid Primates

We address questions regarding the general absence of dimorphism in lemurid primates (Hapalemur, Eulemur, and Varecia) through comparative analyses of ontogeny. We described and analyzed body mass growth data for 9 lemurid taxa and compared them to similar data for anthropoid primates. Lemurids tend to grow rapidly over a short period of time when compared to anthropoid primates of similar body sizes. Size variation among lemurid taxa arises primarily as a consequence of differences in rates of growth. Comparative analyses of body mass growth data suggest that natural selection has produced ontogenetic adaptations in lemurids that center on relatively short periods of growth. Reduced growth periods preclude the evolution of sexual dimorphism through bimaturism—a sex difference in the length of the growth period—despite high levels of intermale competition. Selective factors related to seasonal variability of lemurid habitats play important roles in limiting the potential for the evolution of bimaturism. Other selective factors that limit bimaturism are related to female reproductive synchrony. In combination, they favor relatively early male maturation, precluding sexual selection that would otherwise promote the evolution of dimorphism through bimaturism. Natural selection on growth rates may preclude somatic responses to sexual selection that involve elevated male growth rates. In general, existing ontogenetic or life history adaptations appear to restrict responses to sexual selection in male lemurids.