Determinants of reproductive success in female adders,Vipera berus

Summary Female lifetime reproductive success in a small population of individually-marked adders in southern Sweden was studied over a period of seven years. Reproductive characteristics varied little from year to year and were consistent through time in individual females. Most females mature at four years of age and reproduce every two years. The total number of offspring produced by a female depends on her adult body size (and thus, litter size) and longevity (and thus, number of litters per lifetime). Adult body size in females is influenced mainly by subadult growth rates. Offspring size depends on maternal body size and a tradeoff between offspring size and offspring number. Maternal age does not affect litter sizes and offspring sizes except through ontogenetic changes in maternal body size.Survival of females after parturition is low because of the high energy costs of reproduction, compounded by low feeding rates of gravid females because of their sedentary behaviour at this time. About one-half of females produce only a single litter during their lifetimes, although some females live to produce four or five litters. On a proximate basis, rates of energy accumulation for growth (in subadults) and reproduction (in adults) may be the most important determinants of fitness in female adders.     

The growth of the freshwater crayfish A ustropotamobius pallipes in Northumbria

SUMMARY. Growth increments, moult frequency and growth rates of individuals in a population of the freshwater crayfish Austropotamobius pallipes were followed for a period of 3 years during a mark-recapture study. There was an inverse relationship between body size and the growth increment relative to body size. The absolute increment increased from the juvenile to the young adult stage and thereafter declined with increasing body size.
Differences between the adult male, reproductive female, non-reproductive female and juvenile subpopulations in the size of growth increments are reported and growth increments during the two major moult periods of each year are compared. The effect of the endoparasite Thelohania contejeani and of chela regeneration was to reduce slightly the growth increments.
Instantaneous growth rates declined throughout life in both sexes, but adult males maintained higher growth rates than adult females, particularly in the largest size class studied. The effect of reproduction on growth appeared to be most severe in the smallest breeding females. Males maintained the tendency to moult twice annually to a larger size than females. A simplified construction of the relationship between size and age in the population is presented for each sex. The oldest animals were estimated to be at least 11 years old.     

Body size, age and reproduction in the Smooth newt, Triturus vulgaris

Data on the relationships between individual body size, age and reproduction were obtained for a sample of Smooth newts collected from several sites in southern England. Age was determined by counting lines of arrested growth in histological sections of humerus. In males and females, body size increases with age, but only in the former sex is the correlation statistically significant. In both sexes, there is great inter-individual variability in body size within a year class. Measures of fecundity (testis size, ovary size, clutch size and oocyte size) are positively correlated with body size, but not age. The timing of first reproduction does not seem to depend on the attainment of a fixed body size; the earliest age at first reproduction is two or three years. Together with information obtained during previous studies, the data we present support the hypothesis that the Smooth newt may be an r -selected, colonizing species.     

Growth patterns,and age and size at maturity in femaleCottus hangiongensis,with special reference to their life-history variation

Growth patterns of the 1982 year-class, individual growth patterns, age and size at sexual maturity and longevity in females of the river-sculpin,Cottus hangiongensis (Cottidae), were examined along the course of the Daitobetsu River of southern Hokkaido, Japan. Growth of females slightly varied both along the river course and among individual fishes: slow growth occurs in females from the lower reaches, while more rapid growth occurs in females from upstream areas. Body size and age at the first sexual maturity of females slightly increased towards the upstream, from 52 mm SL and 2 years in the most downstream area to 72 mm SL and 2–3 years in the uppermost site. Longevity was estimated to be 7 years in the downstream areas and 8–9 years in the upstream sites. These results suggest that female life history varies along the course of the river and thus allow us to consider the following alternative reproductive tactics: when females stay in the lower reaches, they attain sexual maturity at a smaller body size and younger age, and have a small clutch size, but when females migrate into the upper reaches, their maturity is delayed until they reach a larger body size and older age, and have a greater clutch size.     

Estimation of age structure by skeletochronology of a population of Hynobius nebulosus in a breeding season (Amphibia,Urodela)

Using skeletochronology, we determined the age structure of adult Hynobius nebulosus from Kyoto in the breeding season of 1998. From previously marked individuals, the lines of arrested growth proved to be formed once per year, indicating the number of winters each salamander experienced. The age at first reproduction was estimated to be 2.8-2.9 yrs of age in males and 3.8-3.9 yrs in females. The oldest males and females were 9.8-9.9 and 5.8-5.9 yrs of age, respectively, and, therefore the longevity in this species was estimated to be more than 9 yrs for males and 5 yrs for females. The growth curve of male's body size estimated indicated that the growth rate much decreases after males attained sexual maturity. Because body sizes of adults greatly vary even within an age class, it is dangerous to estimate individual age from the size frequency data at least in adults. We discussed age properties in Hynobius by comparing lentic and lotic breeders.     

Patterns of growth and sexual size dimorphism in two species of box turtles with environmental sex determination

An adaptive explanation for environmental sex determination is that it promotes sexual size dimorphism when larger size benefits one sex more than the other. That is, if growth rates are determined by environment during development, then it is beneficial to match developmental environment to the sex that benefits more from larger size. However, larger size may also be a consequence of larger size at hatching or growing for a longer time, i.e., delayed age at first reproduction. Therefore, the adaptive significance of sexual size dimorphism and environmental sex determination can only be interpreted within the context of both growth and maturation. In addition, in those animals that continue to grow after maturation, sexual size dimorphism at age of first reproduction could differ from sexual size dimorphism at later ages as growth competes for energy with reproduction and maintenance. I compared growth using annuli on carapace scales in two species of box turtles (Terrapene carolina and T. ornata) that have similar patterns of environmental sex determination but, reportedly, have different patterns of sexual size dimorphism. In the populations I studied, sexual size dimorphism was in the same direction in both species; adult females were, on average, larger than adult males. This was due in part to males maturing earlier and therefore at smaller sizes than females. In spite of similar patterns of environmental sex determination, patterns of growth differed between the species. In T. carolina, males grew faster than females as juveniles but females had the larger asymptotic size. In T. ornata, males and females grew at similar rates and had similar asymptotic sizes. Sexual size dimorphism was greatest at maturation because, although males matured younger and smaller, they grew more as adults. There was, therefore, no consistent pattern of faster growth for females that may be ascribed to developmental temperature. Received: 20 March 1996 / Accepted: 10 March 1998     

Growth and life history traits of Aegean chub,Squalius fellowesii (Günther, 1868) in streams in Muğla Province,Aegean coast,Turkey

To aid in species' conservation, the aim of this study was to provide initial findings on age, growth and reproduction of an endemic species, Aegean chub Squalius fellowesii (Günther, 1868) populations from streams in the Aegean region of Mu?la Province, Turkey. The species is relatively short‐lived (maximum 6 years), attaining a size of about 200 mm total length with a rapid growth to first maturity (≈60 mm TL), and relatively little growth thereafter. The male:female ratio was 1.0 : 0.6, males significantly outnumbering females in the majority of the streams. General condition values of individual fish varied between 2.9 and 3.4. Sexual maturity was usually achieved later and at larger sizes in females than in males. Sexual maturation in most populations was at the age of 2 years in females and 1 year in males. The species spawns between early April and late May. Mean absolute and relative fecundity were about 4440 eggs and 57 eggs·g^?1, respectively. Mean egg diameter was 1.00 ± 0.03 mm, ranging from 0.70 to 1.20 mm. Suggestions for the conservation of Aegean chub are discussed.     

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

To 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 (>55 years minimum age) reproduced more frequently than did younger females (minimum age <36 y).     

Food habits, growth rates, and reproductive biology of grass snakes, Natrix natrix (Colubridae) in the Italian Alps

A five-year mark-recapture study at Sella Nevea, a montane (1100 m a.s.1.) site in the Carnic Alps, provided information on diets, growth rates, and reproductive output in an Italian population of the wide-ranging grass snake, Natrix natrix. Our snakes resembled a previously-studied population in lowland Sweden in terms of body size at sexual maturation in females (70 cm) and mean adult female body length (82 cm). However, growth rates were lower in our population, and sexual maturation was delayed (6–8 years, versus 4–5 years in Sweden), perhaps because of the cool climate and relatively brief growing period each year. Females produced a single clutch of 4–24 eggs in late July each year. Larger females produced larger clutches, but clutch size relative to maternal size was lower than in Swedish grass snakes. Hatchling sizes and Relative Clutch Masses (RCMs) did not shift with increasing female size. RCMs may provide a useful index of 'costs of reproduction' in this population, because females with high RCMs were very emaciated after oviposition, and hence may experience a greater risk of mortality, as well as a high energy expenditure. Prolonged incubation gave rise to longer, thinner hatchlings, but the low environmental temperatures at the study site may favour early hatching (and hence, result in a shorter fatter hatchling emerging from the egg, with more of its energy stores unused). Compared to sympatric viviparous snakes ( Coronella austriaca and Vipera berus ), the oviparous grass snakes can achieve a much higher reproductive output owing to a larger clutch size and more frequent reproduction (annual, rather than biennial or triennial). The abundant prey resource used by grass snakes (amphibians) may also enable them to recoup energy more rapidly after reproduction; dietary composition shifts ontogenetically in both sexes, with the largest prey (mice and adult toads) taken primarily by large female snakes.     

Sex‐specific differences in gonopore and gonadal growth trajectories in the brooding sea urchin,Abatus cavernosus (Spatangoida)

The heart urchin Abatus cavernosus shows sexual dimorphism characterized by the development of external brood pouches and the enlargement of gonopores in brooding females. Relationships between body size, gonopore size, and gonadal maturation in each sex were examined for inflection points using piecewise regression models (PRM). Opening of the gonopore occurred at 15.5 mm test length. Inflection points in the gonadal growth and gonopore diameter trajectories were clustered at smaller sizes in males (23 and 24.2 mm, respectively) than in females (25.1 and 25.9 mm), indicating sex‐specific differences in sexual maturation. Gonopore growth showed positive allometry at pre‐adult stages of development in both sexes, but isometry and negative allometry in adult females and males, respectively. Gonadal growth was initiated at smaller sizes and proceeded at a higher rate with increasing body size in males than in females. Identification of inflection points in gonopore and gonadal growth trajectories, using objective PRM, allows the determination of life stages and sexual maturation for individuals, thus providing a complementary tool for population studies.     

Interpopulation variation in growth and life-history traits of the introduced sunfish, pumpkinseed Lepomis gibbosus, in southern England

We examined attributes of growth and reproduction in 19 populations of pumpkinseed (Lepomis gibbosus) introduced into southern England in order to: (i) assess variability of these traits in a northern European climate; (ii) assess inter‐relationships among these variables; and (iii) compare these attributes with populations from other parts of Europe where pumpkinseeds have been introduced. Growth rates varied considerably among populations, but juvenile growth rates and adult body sizes were generally among the lowest in Europe. Mean age at maturity ranged from 2.0 to 3.9, and was strongly predicted by the juvenile growth rate (earlier maturity with faster juvenile growth). Other population parameters that also displayed significant negative associations with mean age at maturity were gonadosomatic index, body condition, and adult body size (total length, TL at age 5). Mean TL at maturity and the adult growth increment showed no significant associations with any of the other growth or life‐history variables. Pumpkinseed populations in England matured significantly later than those introduced into warmer, more southerly areas of the continental Europe. All of these data suggest that a combination of cool summer temperatures and resource limitation is the cause of slow growth, small adult body size and delayed maturity relative to introduced populations on the European mainland.     

Measuring temporal variation in reproductive output reveals optimal resource allocation to reproduction in the northern grass lizard, Takydromus septentrionalis

We measured the reproductive output of Takydromus septentrionalis collected over 5 years between 1997 and 2005 to test the hypothesis that reproductive females should allocate an optimal fraction of accessible resources in a particular clutch and to individual eggs. Females laid 1–7 clutches per breeding season, with large females producing more, as well as larger clutches, than did small females. Clutch size, clutch mass, annual fecundity, and annual reproductive output were all positively related to female size (snout–vent length). Females switched from producing more, but smaller eggs in the first clutch to fewer, but larger eggs in the subsequent clutches. The mass-specific clutch mass was greater in the first clutch than in the subsequent clutches, but it did not differ among the subsequent clutches. Post-oviposition body mass, clutch size, and egg size showed differing degrees of annual variation, but clutch mass of either the first or the second clutch remained unchanged across the sampling years. The regression line describing the size–number trade-off was higher in the subsequent clutch than in the first clutch, but neither the line for first clutch, nor the line for the second clutch varied among years. Reproduction retarded growth more markedly in small females than in large ones. Our data show that: (1) trade-offs between size and number of eggs and between reproduction and growth (and thus, future reproduction) are evident in T. septentrionalis ; (2) females allocate an optimal fraction of accessible resources in current reproduction and to individual eggs; and (3) seasonal shifts in reproductive output and egg size are determined ultimately by natural selection.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 315–324.     

Proximate causes of sexual size dimorphism in Colorado pikeminnow, a long‐lived cyprinid

Evidence for sexual size dimorphism (SSD) and its possible causes were examined in the endangered Colorado pikeminnow Ptychocheilus lucius, a large, piscivorous, cyprinid endemic to the Colorado River system of North America. Individuals representing 18–24% of the upper Colorado River population were captured, measured, sexed and released in 1999 and 2000. Differing male and female total length‐(L_T) frequency distributions revealed SSD with females having greater mean and maximum sizes than males. Although both sexes exhibit indeterminate post‐maturity growth, growth trajectories differed. The point of trajectory divergence was not established, but slowed male growth might coincide with the onset of maturation. Differing growth rate was the dominant proximate cause of SSD, accounting for an estimated 61% of the observed difference in mean adult L_T. The degree of SSD in adults, however, was also related to two other factors. Evidence suggests males become sexually active at a smaller size and earlier age than females; a 2 year difference, suggested here, accounted for an estimated 12% of the between‐sex difference in mean adult L_T. Temporal shifts in gender‐specific survival accounted for an additional 27% of the observed between‐sex difference in mean adult L_T. Estimated age distributions indicated a higher number of older females than older males and more younger males than younger females in the population during the period of sampling. Dissimilarity of age distributions was an unexpected result because the male : female population sex ratio was 1 : 1 and estimates of long‐term annual survival for adult males and females were equal (88%). Future assessments of SSD in this population are apt to vary depending on the prior history of short‐term gender‐specific survival. Without recognizing SSD, non‐gender‐specific growth curves overestimate mean age of adult females and underestimate mean age of adult males of given L_T. Assuming age 8 years for first reproduction in males and age 10 years for females, the adult male : female ratio was estimated as 1·1 : 1 and mean adult age, or generation time, was estimated as 16·4 years for males and 18·4 years for females.     

Geographic variation as a result of evolution of the traits with broad and narrow norms of reaction in the moor frog (Rana arvalis)

Females reproductive, size, and age characteristics were studied in isolated local populations of Rana arvalis in the southern and northern parts of its range. The yearlings of the southern populations used to get larger by their first overwintering due to earlier beginning of the breeding season, as compared with the yearlings of the northern population. As a result, "southern" females become sexually mature at the age of two years while the "northern" ones become mature at the age of three years. This causes geographic differences in age composition among two populations, the "southern" reproductive females being younger on average than the "northern" ones. The earlier female maturation in the first case is not compensated by respective rise of the growth rate; to the contrary, the "southern" females grow more slowly during the first two years of their life and appear to be smaller than the "norhern" ones. These reproduction and growth patterns arise supposedly due to paedomorphosis, which causes specific reproductive characteristics, namely decrease in the egg size, increase in the reproductive effort and more strong correlation between female fertility and body size. Local and geographic differences are expressed not in the extent but in the structure of reproductive pattern, as no negative correlation was revealed between female reproductive age and body size in the southern populations. Southern habitats cannot be considered as "unfavourable with respect to body size", so the geographic differences under consideration cannot be explained by optimization of the reproductive strategies at population level. Paedomorphosis appears as a result of the female maturation rate possessing a wider norm of reaction than the growth rate. At the same time, fixation of the specific growth rate narrows norm of reaction of some other characters important for the phenotype reproductive fitness thus predetermining their subsequent evolution.     

Body size, age and reproduction in the leopard toad, Bufo pardalis

Data on the relationships between body size and age were obtained for a sample of leopard toads Bufo pardalis from a breeding population of this species from the Cape Peninsula, South Africa. Age was determined by counting the number of lines of arrested growth in histological sections of a digit clipped from each individual. In males there was a positive, but weak, correlation (explaining only 18% of the variance) between body size and age, and in females no correlation at all existed between these two variables. Males which were successful in obtaining matings were not older than unsuccessful males. Age of males at the breeding site ranged from one to three years, whereas females ranged from two to six years old. This represents both the earliest age of reproduction, as well as the greatest difference in longevity between the sexes, documented for an anuran species.     

A test of the reproductive cost hypothesis for sexual size dimorphism in Yarrow's spiny lizard Sceloporus jarrovii

1. Trade-offs between reproduction and growth are central assumptions of life-history theory, but their implications for sexual size dimorphism (SSD) are poorly understood. 2. Adult male Yarrow's spiny lizards Sceloporus jarrovii average 10% larger than adult females. In a low-altitude (1700 m) population, this SSD develops because males grow more quickly than females during the first year of life, particularly during the first female reproductive season. This study tests the hypothesis that SSD develops because female growth is constrained by energetic costs of reproduction. 3. To test for a growth cost of reproduction, I compared growth rates of free-living females that differed, either naturally or experimentally, in reproductive status. Females that naturally delayed reproduction until their second year grew more quickly than females that reproduced as yearlings, and ovariectomized yearlings grew more quickly and to larger sizes than reproductive controls. 4. To determine whether SSD develops in the absence of this inferred reproductive cost, I also studied a high-altitude (2500 m) population in which all females delay reproduction until their second year. Sex differences in growth trajectories were similar to those observed at low altitude, such that males averaged 10% larger than females even prior to female reproduction. 5. Although female growth may be constrained by reproduction, multiple lines of evidence indicate that this cost is insufficient to explain the full magnitude of SSD in S. jarrovii. First, differences in growth of reproductive and nonreproductive females are not observed until the final month of gestation, by which time SSD is already well developed. Second, the growth benefit accruing from experimental inhibition of reproduction accounts for only 32% of the natural sex difference in body size. Finally, SSD develops well in advance of female reproduction in a high-altitude population with delayed maturation.     

Short and chubby or long and slim? Food intake,growth and body condition in free‐ranging pythons

Abstract An animal's sex and body size can influence not only its rate of food consumption, but also the way in which it allocates the resultant energy among the competing demands of maintenance, growth, reproduction and storage. A 13‐year mark–recapture study of pythons (Liasis fuscus) in tropical Australia provides extensive data on these topics. Rates of food intake and growth were highest in small pythons, and decreased more rapidly with body size in males than in females. Allocation to storage (as measured by the snake's mass relative to its body length) showed a more complex pattern. Body condition was high at hatching, but dropped rapidly as energy was allocated to growth rather than storage. Condition then increased through juvenile life, was at a maximum close to maturation, and was higher in females than in conspecific males. Body condition thereafter decreased with increasing body length. These allocation ‘decisions’ reflect the relative advantages of growth versus energy storage at different body sizes. Hatchling snakes grow rapidly (and hence become thin) because greater body size enables the snake to ingest larger prey items. Adult females amass larger energy reserves than males, because they need reserves to produce the clutch. Large snakes become thinner because their feeding rates are low, and they cannot compensate with increased prey size because large‐bodied mammalian prey are rare in our study area.     

Optimal individual growth and reproduction in perennial species with indeterminate growth

Summary A model predicting optimal timing of growth and reproduction in perennial species with indeterminate growth living in a seasonal environment, is presented. According to the model, the optimal fraction of growing season devoted to growth decreases with increasing individual age and size, which leads to S-shaped growth curves. Winter mortality seems to be a crucial factor affecting the timing of growth and reproduction, under the same function describing the dependence of growth rate and reproductive rate on body size. When winter mortality is heavy, it is often optimal to start reproducing in the first year, and to devote a large proportion of the subsequent years to reproduction, thus leading to small adult body sizes.The model has been applied to two species of mollusc and one species of fish. The model predictions fit well to the field data for these three species.     

The effects of size, age and a cost of early breeding on reproduction in female mountain hares

Both age and size may influence female reproductive performance in mammals, and successful early reproduction may lead to reduced success at later attempts. The effects of age, size and early reproduction on distribution of reproductive effort throughout a single breeding season was examined in female mountains hares Lepus timidus L. Hind foot length was used as an index of body size, because, unlike body weight, it did not fluctuate with reproductive status. Fifty-six female carcasses were collected from March to October 1984, and their litters were assigned to one of three chronologically equal'litter periods'(1–3) of equal length. Whereas number of ova shed was always independent of age, large females shed more ova than did smaller females in litter periods 1 and 2. Prenatal mortality of ova and embryos was highest during litter period 1, when it was independent of age and size. Although prenatal mortality remained high in first year females in litter period 2, there was an overall decline through to the final litter period when it was negligible. Total number of young produced through the season increased with skeletal size in old females (age > 1), but not significantly in first year females. It is concluded that large size, rather than age, favours early reproduction in mountain hares. Every additional offspring produced in litter periods 1 and 2 reduced that female's production in period 3. After correcting for this cost of early reproduction the number of young produced in the final litter period also increased with maternal size.