Life-history strategies of Acrossocheilus fasciatus (Barbinae, Cyprinidae) in the Huishui Stream of the Qingyi watershed, China

Life-history traits of Acrossocheilus fasciatus were examined using 384 specimens collected monthly during May 2009 and April 2010 in the Huishui Stream of the Qingyi watershed, China. Using scales for age determination, female and male fish comprised five and four age groups, respectively. The monthly changes in marginal increment ratio suggested that annuli on scales were formed during March through May. Total lengths back-calculated significantly increased with age for both sexes and varied significantly between the two sexes at each age. The fact that females had larger body size and grew faster than males indicated the sexual size dimorphism for this species. Both sexes got their 50% maturity at age 3, when females and males were 105.3 and 112.1?mm total length, respectively. Based on the monthly changes in the gonado-somatic index and egg-development process, fish spawned from April through August. Absolute fecundity ranged from 295 to 3,573 eggs per fish and increased significantly with age. But relative fecundity, ranging from 11.77 to 69.96?eggs/g, was not significantly different among age groups. Compared with the life-history traits of an upstream population in the Puxi Stream (a headwater stream within this study watershed), the downstream population of A. fasciatus in the Huishui Stream (a 4th-order stream) exhibits larger body size, faster somatic growth, later sexual maturity, and lower reproductive investment. These variations in life-history strategies between the two populations could perhaps be explained by the spatial heterogeneity in habitat environment along the upstream–downstream gradient in this watershed.     

A Review for Life-history Traits Variation in Frogs Especially for Anurans in China

Environmental variation can promote differentiation in life-history traits in species of anurans. Increased environmental stress usually results in larger age at sexual maturity, older mean age, longer longevity, slower growth, larger body size, and a shift in reproductive allocation from offspring quantity to quality, and a stronger trade-off between offspring size and number. However, previous studies have suggested that there are inconsistent geographical variations in life-history traits among anuran species in China. Hence, we here review the intraspecific patterns and differences in life-history traits(i.e., egg size, clutch size, testes size, sperm length, age at sexual maturity, longevity, body size and sexual size dimorphism) among different populations within species along geographical gradients for anurans in China in recent years. We also provide future directions for studying difference in sperm performance between longer and shorter sperm within a species through transplant experiments and the relationships between metabolic rate and brain size and life-history.     

Adaptive life-history evolution in the livebearing fish Brachyrhaphis rhabdophora: genetic basis for parallel divergence in age and size at maturity and a test of predator-induced plasticity

I document a genetic basis for parallel evolution of life-history phenotypes in the livebearing fish Brachyrhaphis rhabdophora from northwestern Costa Rica. In previous work, I showed that populations of B. rhabdophora that co-occur with predators attain maturity at smaller sizes than populations that live in predator-free environments. I also demonstrated that this pattern of phenotypic divergence in life histories was independently repeated in at least five isolated drainages. However, life-history phenotypes measured from wild-caught fish could be attributed to environmental effects rather than to genetic differences among populations. In the present study, I reared male fish from four populations (two that co-occur with predators and two from predator-free environments) under four sets of environmental conditions. The pattern of phenotypic divergence in maturation size documented in the field between populations collected from different predation environments persisted after two generations in the laboratory. I also found a genetic basis for differences between populations in the age at which males attain maturity and in growth rates. By rearing fish in four different common environments, I tested for phenotypic plasticity in male life-history traits in response to nonlethal exposure to predators. There was a significant delay in the onset of sexual maturity in fish exposed to predators relative to those in the control, but no differences among treatments in size at maturity or growth rates. These results, coupled with previous work on B. rhabdophora, demonstrate a repeated pattern of parallel evolutionary divergence among genetically isolated populations that is strongly associated with predation.     

A new view of avian life-history evolution tested on an incubation paradox

Viewing life-history evolution in birds based on an age-specific mortality framework can explain broad life-history patterns, including the long incubation periods in southern latitudes documented here. I show that incubation periods of species that are matched phylogenetically and ecologically between Argentina and Arizona are longer in Argentina. Long incubation periods have mystified scientists because they increase the accumulated risk of time-dependent mortality to young without providing a clear benefit. I hypothesize that parents of species with low adult mortality accept increased risk of mortality to their young from longer incubation if this allows reduced risk of mortality to themselves. During incubation, songbird parents can reduce risk of mortality to themselves by reducing nest attentiveness (percentage of time on the nest). Here I show that parents of species with lower adult mortality exhibit reduced nest attentiveness and that lower attentiveness is associated with longer incubation periods. However, the incubation period is also modified by juvenile mortality. Clutch size variation is also strongly correlated with age-specific mortality. Ultimately, adult and juvenile mortality explain variation in incubation and other life-history traits better than the historical paradigm.     

Within‐season variation in sexual selection in a fish with dynamic sex roles

The strength of sexual selection may vary between species, among populations and within populations over time. While there is growing evidence that sexual selection may vary between years, less is known about variation in sexual selection within a season. Here, we investigate within‐season variation in sexual selection in male two‐spotted gobies (Gobiusculus flavescens). This marine fish experiences a seasonal change in the operational sex ratio from male‐ to female‐biased, resulting in a dramatic decrease in male mating competition over the breeding season. We therefore expected stronger sexual selection on males early in the season. We sampled nests and nest‐holding males early and late in the breeding season and used microsatellite markers to determine male mating and reproductive success. We first analysed sexual selection associated with the acquisition of nests by comparing nest‐holding males to population samples. Among nest‐holders, we calculated the potential strength of sexual selection and selection on phenotypic traits. We found remarkable within‐season variation in sexual selection. Selection on male body size related to nest acquisition changed from positive to negative over the season. The opportunity for sexual selection among nest‐holders was significantly greater early in the season rather than late in the season, partly due to more unmated males. Overall, our study documents a within‐season change in sexual selection that corresponds with a predictable change in the operational sex ratio. We suggest that many species may experience within‐season changes in sexual selection and that such dynamics are important for understanding how sexual selection operates in the wild.     

Phenotypic plasticity of life history traits in relation to reproductive strategies in <Emphasis Type="Italic">Boa constrictor occidentalis</Emphasis>

The close connection between reproductive ecology and life history in snakes leads to trade-offs between reproductive and other life-history traits. Optimal energy allocation to growth and reproduction is a key factor to determine life history structure. Therefore, elucidating the relationship between body size variations and reproductive characters is essential for a better understanding of life-history plasticity. The aim of this work was to determine to what extent life-history differs among populations of Boa constrictor occidentalis and to identify possible life-history trade-offs between morphological and reproductive traits. We compared two populations from areas that are separated latitudinally, with different climatic conditions and vegetation landscape structure. Reproductive and morphological data of specimens were recorded. Although populations had a similar mean length of mature snakes, the frequency of some size classes tended to be different. Size at sexual maturity differed between populations for females, generating variations in the proportion of mature individuals. Reproductive threshold and follicular size also varied, but female reproductive frequency was similar between populations. Reproductive frequency of males varied between populations although their body condition was similar. We discussed two major issues: (1) implications of size at sexual maturity for body size and fecundity; (2) trade-offs in reproductive characters.     

Growth differences in males of the river-sculpin Cottus hangiongensis along a river course,a correlate of life-history variation

Synopsis Growth patterns of the 1982 year-class, individual growth patterns, age at sexual maturity and longevity in the river-sculpin, Cottus hangiongensis (Cottidae), were investigated along the course of the Daitobetsu River of southern Hokkaido, Japan. Slow growth occurred in males from the lower reaches, while more rapid growth was found in males from upstream areas. Age at first sexual maturity in males generally increased from 2 or 3 years in downstream areas to 4–6 years in upstream sites. Longevity was estimated as 7 years throughout the river course except in the uppermost site where it was 6 years. The growth differences evident in male C. hangiongensis are likely a result of differences in sculpin population density and/or food abundance along the river course, and are apparently reflected in variation in their life-history as well.     

Life-history phenotypes in populations of Brachyrhaphis episcopi (Poeciliidae) with different predator communities

Variation among populations in extrinsic mortality schedules selects for different patterns of investment in key life-history traits. We compared life-history phenotypes among 12 populations of the live-bearing fish Brachyrhaphis episcopi. Five populations co-occurred with predatory fish large enough to prey upon adults, while the other seven populations lacked these predators. At sites with large predatory fish, both sexes reached maturity at a smaller size. Females of small to average length that co-occurred with predators had higher fecundity and greater reproductive allotment than those from populations that lacked predators, but the fecundity and reproductive allotment of females one standard deviation larger than mean body length did not differ among sites. In populations with large predatory fish, offspring mass was significantly reduced. In each population, fecundity, offspring size and reproductive allotment increased with female body size. When controlling for maternal size, offspring mass and number were significantly negatively correlated, indicating a phenotypic trade-off. This trade-off was non-linear, however, because reproductive allotment still increased with brood size after controlling for maternal size. Similar differences in life-history phenotypes among populations with and without large aquatic predators have been reported for Brachyrhaphis rhabdophora in Costa Rica and Poecilia reticulata (a guppy) in Trinidad. This may represent a convergent adaptation in life-history strategies attributable to predator-mediated effects or environmental correlates of predator presence.     

Mixed-stock aging analysis reveals variable sea turtle maturity rates in a recovering population

Quantifying demographic parameters and variable vital rates, such as somatic growth rates, time to maturity, and reproductive longevity, is important for effective management of threatened and endangered populations such as sea turtles (Cheloniidae). To address these knowledge gaps, we applied skeletochronology to analyze and compare somatic growth rates and variation in life-history traits such as age and size at sexual maturity for 65 green turtles (Chelonia mydas) in the eastern Pacific Ocean (EP), along the west coast of the United States; turtles belonged to ≥2 nesting subpopulations that differed in body size (mean nesting size). Green turtles in the EP spend approximately 5 years in the oceanic stage before recruiting to nearshore habitats, males may be smaller and younger than females at maturation (x̅ = 17.7 ± 5.5 yr vs. 28.0 ± 8.2 yr), and younger age at sexual maturity was associated with smaller size at sexual maturity, suggesting that mean nesting body size may be reflective of maturation timing for subpopulations. Smaller body sizes for females nesting at Michoacán, Mexico (continental) rookeries, yielded a younger predicted age at sexual maturity (x̅ = ~17 yr) compared to females from Revillagigedo Islands, Mexico rookeries, which displayed larger body sizes and older age at sexual maturity (x̅ = ~30 yr). We consider possible mechanisms driving the observed divergence in life-history traits, including the possibility that earlier maturation (reduced generation length) for turtles in the Michoacán nesting subpopulation may be a response to intense harvesting in the past 50 years, and consideration of such anthropogenic impacts is warranted by population managers. Finally, our results indicate green turtles moved into nearshore neritic habitats at a young age (4–6 yr), emphasize the importance of protecting neritic habitats along the southwestern United States and northwestern Mexican coasts, and encourage the incorporation of variable maturation time in population recovery assessments.     

Life-history phenotypes in a live-bearing fish Brachyrhaphis episcopi living under different predator regimes: seasonal effects?

Several key life-history attributes in a tropical live-bearing fish, Brachyrhaphis episcopi, have previously been shown to differ between populations that co-occur with large predatory fish (Characin sites) and those that do not (Rivulus sites). Here we show that differences between Characin and Rivulus localities are also repeatable over time; patterns observed in the wet season also persisted during the dry. Both sexes reached maturity at a smaller size at Characin sites. Although there was no difference in fecundity between larger females living in different predator communities, smaller females at Characin sites produced more offspring. Females also produced smaller offspring at Characin localities. These differences are remarkably similar to those reported in two other species of live-bearing fish, B. rhabdophora and Poecilia reticulata suggesting possible convergent adaptation in life-history strategies due to predator-mediated effects or correlates thereof. We also found seasonal changes in life-history traits that were independent of predator community. In the wet season, mature males were larger, females allocated more to reproduction, and offspring mass was also greater. The results of our study generate testable predictions using B. episcopi to further our understanding of life-history evolution.     

Latitudinal clines in life-history variables of anadromous brown trout in Europe

Based on published data, we reviewed clinal variations in life-history characteristics of anadromous brown trout Salmo trutta from 102 European rivers at latitudes between 54 and 70° N. Growth rate in fresh water, mean smolt age, mean sea age at first sexual maturity, proportion of repeal spawners among adults, longevity, and length of adult life span exhibited latitudinal clines. Brown trout grew faster in fresh water, smolted and matured younger, lived fewer years but spawned more times in the south than in the north. The life-history traits studied were often correlated. Longevity, smolt age and sea age at maturity were negatively and smolt length and proportion of repeat spawners among adults were positively correlated with growth rate in fresh water. Longevity was positively correlated with smolt age and sea age at maturity. The latter also increased with increasing smolt age. None of these significant correlations among life history variables, except for those between smolt age and parr growth and proportion of repeat spawners and parr growth, are latitudinal effects. We do not know to what extent the latitudinal variation in life–history traits reflects phenotypic plasticity and to what extent it is caused by inherited differences among populations.     

Salmon lice increase the age of returning Atlantic salmon

The global increase in the production of domestic farmed fish in open net pens has created concerns about the resilience of wild populations owing to shifts in host–parasite systems in coastal ecosystems. However, little is known about the effects of increased parasite abundance on life-history traits in wild fish populations. Here, we report the results of two separate studies in which 379 779 hatchery-reared Atlantic salmon smolts were treated (or not) against salmon lice, marked and released. Adults were later recaptured, and we specifically tested whether the age distribution of the returning spawners was affected by the treatment. The estimates of parasite-induced mortality were 31.9% and 0.6% in the River Vosso and River Dale stock experiments, respectively. Age of returning salmon was on average higher in treated versus untreated fish. The percentages of fish returning after one winter at sea were 37.5% and 29.9% for the treated and untreated groups, respectively. We conclude that salmon lice increase the age of returning salmon, either by affecting their age at maturity or by disproportionately increasing mortality in fish that mature early.     

Reaction norms of size and age at maturity of Pomacea canaliculata (Gastropoda: Ampullariidae) under a gradient of food deprivation

Pomacea canaliculata, an apple snail native to South America,has become a serious pest of aquatic crops and a promoter ofecosystem changes in natural wetlands worldwide. Its successas an invader has been attributed to its great phenotypic plasticityin life-history traits. Our aims were to determine the reactionnorms of size and age at maturity under a gradient of food deprivation.Full sibling experimental snails were reared in isolation fromhatching and maintained until maturity under seven differentlevels of relative food deprivation based on size-specific ingestionrates. To detect the onset of sexual activity of experimentalsnails, fully mature virgin snails reared in the laboratorywere used as consorts. The reaction norms for age and size atmaturity of P. canaliculata showed marked sexual dimorphism.Shell length was the main component of variation in the malereaction norms for both copulation and egg-laying by femaleconsorts, whereas age was the main component of variation forfemales. Irrespective of the intensity of food deprivation,males mature at the same age at the expense of size, since sizeis apparently irrelevant in the access to females and male fitnesscan be maximized through fast maturation. In contrast, a minimumsize is required for females to reach maturity, perhaps as aresult of their higher reproductive costs. The highly dimorphicreaction norms lead to an increasing lag between male and femalematurity as deprivation increases; in temperate regions, malesborn early in the reproductive season would mature in the sameseason irrespective of food availability, while most femaleswould have to overwinter before attaining sexual maturity inunproductive habitats or those dominated by unpalatable macrophytes.The great life-history plasticity reported in invaded areascould be a heritage from populations in the native range. (Received 10 August 2007; accepted 30 July 2008)     

Genetic correlations do not constrain the evolution of sexual dimorphism in the moss Ceratodon purpureus

The trajectory of phenotypic evolution is constrained in the short term by genetic correlations among traits. However, the extent to which genetic correlations impose a lasting constraint is generally unknown. Here, I examine the genetic architecture of life-history variation in male and female gametophytes from two populations of the moss Ceratodon purpureus, focusing on genetic correlations within and between the sexes. A significant negative correlation between allocation to vegetative and reproductive tissue was evident in males of both populations, but not females. All traits showed between-sex correlations of significantly less than one, indicating additive genetic variance for sexual dimorphism. The degree of dimorphism for traits was significantly negatively associated with the strength of the between-sex correlation. The structure of genetic correlations among life-history traits was more divergent between the two populations in females than in males. Collectively, these results suggest that genetic correlations do not impose a lasting constraint on the evolution of life-history variation in the species.     

Life-history traits of the endangered river blenny Salaria fluviatilis (Asso) and their implications for conservation

The life-history characteristics of the river blenny Salaria fluviatilis in a Mediterranean stream in north-east Spain have been studied. The maximum age observed was 4+ years in both sexes, although only age groups 0+ and 1+ years were well represented. For both sexes, growth was rapid between April and June (before the summer drought) and in October. The instantaneous rate of monthly growth (April to October) was positively correlated with water depth. All fish attained sexual maturity during their first year of life. Females spawned multiple times. Spawning occurred mainly from June to August, although older females (2+ years old) began in May. The relationship between fecundity and total length recorded for older females in the spring was not significantly different from that obtained for 1 year-old females in the summer. The mean diameter of ripe oocytes, however, was greater in older females. Larger eggs that were laid during a period of good food supply (spring) might have a higher probability of survival. The results suggest that female fecundity is affected by environmental conditions. The species is characterized by fast growth, early maturity, multiple spawning and limited longevity. This may be a good life-history strategy for small fish species in unstable environments, where adult mortality is high, variable or unpredictable. Some life-history traits of the river blenny suggest that this species might be vulnerable to more severe drought conditions than those associated with the Mediterranean climate.     

Sexual isolation promotes divergence between parapatric lake and stream stickleback

Speciation can be initiated by adaptive divergence between populations in ecologically different habitats, but how sexually based reproductive barriers contribute to this process is less well understood. We here test for sexual isolation between ecotypes of threespine stickleback fish residing in adjacent lake and stream habitats in the Lake Constance basin, Central Europe. Mating trials exposing females to pairings of territorial lake and stream males in outdoor mesocosms allowing for natural reproductive behaviour reveal that mating occurs preferentially between partners of the same ecotype. Compared to random mating, this sexual barrier reduces gene flow between the ecotypes by some 36%. This relatively modest strength of sexual isolation is surprising because comparing the males between the two ecotypes shows striking differentiation in traits generally considered relevant to reproductive behaviour (body size, breeding coloration, nest size). Analysing size differences among the individuals in the mating trials further indicates that assortative mating is not related to ecotype differences in body size. Overall, we demonstrate that sexually based reproductive isolation promotes divergence in lake–stream stickleback along with other known reproductive barriers, but we also caution against inferring strong sexual isolation from the observation of strong population divergence in sexually relevant traits.     

Consistency in the life history traits of four invasive pseudorasbora parva populations in Southern England

Life history plasticity can be a strong predictor of the establishment and invasion success of introduced fishes. Here, the life-history traits of four P. parva populations in adjacent ponds in Southern England were measured throughout 2013 to determine the timing and length of their reproductive season and the extent of trait plasticity. The relative abundance of the populations (as catch per unit effort) was similar, with low variability in their traits relating to reproductive effort and somatic growth. All the populations were male dominated. Both sexes matured at small body sizes, with fish as small as 30 mm being mature in both sexes, with the age at maturity for both sexes being age 1+ years. The peak spawning period, characterised by female fish investing heavily in reproduction when their gonado-somatic index (GSI) values were highest and declined thereafter, occurred in May and June, and after a mean of 212 ± 24 degree-days >12°C, and with water temperatures being 13.2–14.6°C. There were no further peaks in GSI, despite the species being considered to have prolonged spawning periods across spring and summer. These results also suggest that whilst the expression of life-history traits of invasive fishes often vary with density, they can be highly consistent between populations at similar abundances and locations.     

MODE OF SEXUAL SELECTION DETERMINED BY RESOURCE ABUNDANCE IN TWO SAND GOBY POPULATIONS

We used field observations and experiments to show that sexual selection in two populations of sand gobies, Pomatoschistus minutus (Pisces, Gobiidae), was affected by differences in resource availability. Male sand gobies rely on empty mussel shells for nest building and spawning. The two populations differed considerably in nest-site abundance and sexual-selection regimes. In one population nest sites were scarce, leading to stronger male-male competition over nests, a higher nest site colonization rate and reduced potential for female choice compared with the other population that had a surplus of nests. In the high-competition population, males were larger than females, perhaps as a response to selection, whereas the other population was not sexually size dimorphic. The results from the field were confirmed in a pool experiment that demonstrated the effect of nest abundance on nest occupancy and male reproductive success. Larger males were more successful in obtaining nest sites in both high and low nest availability treatments. Larger males were also favored by females as mating partners, but only in the treatment with surplus nest sites. Nest shortage was associated with an increased potential for intrasexual selection (measured as the coefficient of variation), whereas the potential for intersexual selection was increased when nests were common. In conclusion, nest-site abundance can influence the relative contribution of intrasexual competition and mate choice in a population. Hence, resource availability can contribute to within-species variation in mating patterns.     

LABORATORY EVOLUTION OF LIFE-HISTORY TRAITS IN THE BEAN WEEVIL (ACANTHOSCELIDES OBTECTUS): THE EFFECTS OF DENSITY-DEPENDENT AND AGE-SPECIFIC SELECTION

Four types of laboratory populations of the bean weevil (Acanthoscelides obtectus) have been developed to study the effects of density-dependent and age-specific selection. These populations have been selected at high (K) and low larval densities (r) as well as for reproduction early (Y) and late (O) in life. The results presented here suggest that the r- and K-populations (density-dependent selection regimes) have differentiated from each other with respect to the following life-history traits: egg-to-adult viability at high larval density (K > r), preadult developmental time (r > K), body weight (r > K), late fecundity (K > r), total realized fecundity (r > K), and longevity of males (r > K). It was also found that the following traits responded in statistically significant manner in populations subjected to different age-specific selection regimes: egg-to-adult viability (O > Y), body weight (O > Y), early fecundity (Y > O), late fecundity (O > Y), and longevity of females and males (O > Y). Although several life-history traits (viability, body weight, late fecundity) responded in similar manner to both density-dependent and age-specific selection regimes, it appears that underlying genetic and physiological mechanisms responsible for differentiation of the r/K and Y/O populations are different. We have also tested quantitative genetic basis of the bean weevil life-history traits in the populations experiencing density-dependent and age-specific selection. Among the traits traded-off within age-specific selection regimes, only early fecundity showed directional dominance, whereas late fecundity and longevity data indicated additive inheritance. In contrast to age-specific selecton regimes, three life-history traits (developmental time, body size, total fecundity) in the density-sependent regimes exhibited significant dominance effects. Lastly, we have tested the congruence between short-term and long-term effects of larval densities. The comparisons of the outcomes of the r/K selection regimes and those obtained from the low- and high-larval densities revealed that there is no congruence between the selection results and phenotypic plasticity for the analyzed life-history traits in the bean weevil.     

Early growth trajectories affect sexual responsiveness

The trajectory of an animal''s growth in early development has been shown to have long-term effects on a range of life-history traits. Although it is known that individual differences in behaviour may also be related to certain life-history traits, the linkage between early growth or development and individual variation in behaviour has received little attention. We used brief temperature manipulations, independent of food availability, to stimulate compensatory growth in juvenile three-spined sticklebacks Gasterosteus aculeatus. Here, we examine how these manipulated growth trajectories affected the sexual responsiveness of the male fish at the time of sexual maturation, explore associations between reproductive behaviour and investment and lifespan and test whether the perceived time stress (until the onset of the breeding season) influenced such trade-offs. We found a negative impact of growth rate on sexual responsiveness: fish induced (by temperature manipulation) to grow slowest prior to the breeding season were consistently quickest to respond to the presence of a gravid female. This speed of sexual responsiveness was also positively correlated with the rate of development of sexual ornaments and time taken to build a nest. However, after controlling for effects of growth rate, those males that had the greatest sexual responsiveness to females had the shortest lifespan. Moreover, the time available to compensate in size before the onset of the breeding season (time stress) affected the magnitude of these effects. Our results demonstrate that developmental perturbations in early life can influence mating behaviour, with long-term effects on longevity.