亚洲玉米螟体重和体型的地理变异

为探明亚洲玉米螟Ostrinia furnacalis体重和体型地理变异,我们详细比较了来自4个不同地理种群（海南乐东18.8°N, 109.2°E),广西阳朔24.8°N, 110.5°E),江西南昌28.8°N, 115.9°E)和河北廊坊39.5°N, 116.7°E)）亚洲玉米螟的体重、体型大小及其与采集地纬度的关系。结果表明：不同地理种群的亚洲玉米螟卵重随纬度的升高而逐渐增大,符合贝格曼法则(Bergmann’s law), 而雌雄蛹重及成虫体长、后足腿节长和前翅长均随纬度的升高而逐渐减小, 符合反贝格曼法则(Converse Bergmann’s law)。雌虫的前翅显著长于雄虫, 其性体型二型性符合任希法则(Rensch’s rule),即在雌虫体型较大的种群中,雄虫前翅比雌虫前翅增长幅度相对较大。本文结果进一步揭示了即使在同一种类昆虫中,其各个虫态体重和体型的地理变异也可能不同。     

Body size variation and caste ratios in geographically distinct populations of the invasive big‐headed ant,Pheidole megacephala (Hymenoptera: Formicidae)

Body size is an important life history trait that can evolve rapidly as a result of how species interact with each other and their environment. Invasive species often encounter vastly different ecological conditions throughout their introduced range that can influence relative investment in growth, reproduction and defence among populations. In this study, we quantified variation in worker size, morphology and proportion of majors among five populations of a worldwide invasive species, the big‐headed ant, Pheidole megacephala (Fabricius). The sampled populations differed in ant community composition, allowing us to examine if P. megacephala invests differently in the size and number of majors based on the local ant fauna. We also used genetic data to determine if these populations of P. megacephala represented cryptic species or if morphological differences could be attributed to change following introduction. We found significant variation in worker mass among the populations. Both major and minor workers were largest in Australia, where the ant fauna was most diverse, and minor workers were smallest in Hawaii and Mauritius, where P. megacephala interacted with few to no other ants. We also found differences in major and minor worker morphology among populations. Majors from Mauritius had significantly larger heads (width and length) relative to whole body size than those from Hawaii and Florida. Minors had longer heads and hind tibias in South Africa compared with populations from Australia, Hawaii and Florida. The proportion of majors did not differ among populations, suggesting that these populations may not be subject to trade‐offs in investment in major size versus number. Our molecular data place all samples within the same clade, supporting that these morphologically different populations represent the same species. These results suggest that the variation in shape and morphology of major and minor workers may therefore be the result of rapid adaptation or plastic responses to local conditions. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 423–438.     

Morphological differences between extranidal and intranidal workers in the ant Temnothorax rugatulus,but no effect of body size on foraging distance

Most ant genera are thought to have monomorphic workers, indicating perhaps a high degree of flexibility in task allocation, and the well-studied genus Temnothorax is an example of this. However, considerable size variation may exist between individuals. In addition, though workers can show flexible behavior, it has been shown that individuals may consistently differ in their task profiles. Here we test whether body size variation among workers affects foraging behavior. Two main hypotheses were tested: first, whether larger ants forage at greater distance from the nest, and second, whether larger individuals show a higher propensity to work outside of the nest. Our results showed that ant body size does not significantly affect foraging distance. However, larger ants were more likely to be found outside the nest. Though Temnothorax ants are a common model system, this is the first study demonstrating task allocation based on body size, which is fixed in adults. Our study suggests that particularly small species may have to be examined carefully for body size variation before concluding that body size is uniform and therefore irrelevant for task allocation.     

Habitat-related microgeographic variation of worker size and colony size in the ant Cataglyphis cursor

In social insects, colony size is a crucial life-history trait thought to have major implications for the evolution of social complexity, especially in relation to worker size polymorphism. Yet, little is known about how ecological factors can affect and constrain colony. Here, we explored the pattern of colony-size and worker-size variation in the Mediterranean ant Cataglyphis cursor, in relation to the type of habitats colonized (seaside vs. vineyard). The high level of the water table in the seaside habitat could constrain the depth of C. cursor underground nests and directly constrain its colony size. If worker size increases with colony size, as observed in other ant species, larger colony size and larger workers should be found in the vineyard populations. By comparing worker size among 16 populations, we verified that workers were significantly larger in the vineyard populations. We further determined that the morphological similarities detected among populations from the same habitat type were not due to geographic or genetic proximity. In two populations from each habitat type, the depth of nests was positively correlated with colony size and colony size with worker size. Using a type II regression approach, we further showed that the difference between the two populations in the depth of nest was sufficient to explain the difference in colony size, and similarly, variation in colony size was sufficient to explain variation in worker size. Our results suggest that a single proximate ecological factor could lead to significant variation in major life-history parameters.     

GEOGRAPHIC VARIATION IN LIFE-HISTORY TRAITS OF THE ANT LION,MYRMELEON IMMACULATUS: EVOLUTIONARY IMPLICATIONS OF BERGMANN'S RULE

In eastern North America, body size of the larval ant lion Myrmeleon immaculatus increases from south to north, following Bergmann's rule. We used a common-garden experiment and a reciprocal-transplant experiment to evaluate the effects of food and temperature on ant lion growth, body size, and survivorship. In the laboratory common-garden experiment, first-instar larvae from two southern (Georgia, South Carolina) and two northern (Connecticut, Rhode Island) populations were reared in incubators under high- and low-food and high- and low-temperature regimes. For all populations, high food increased final body mass and growth rate and decreased development time. Growth rates were higher at low temperatures, but temperature did not affect larval or adult body mass. Survivorship was highest in high-food and low-temperature treatments. Across all food and temperature treatments, northern populations exhibited a larger final body mass, shorter development time, faster growth rate, and greater survivorship than did southern populations. Results were similar for a field reciprocal-transplant experiment of third-instar larvae between populations in Connecticut and Oklahoma: Connecticut larvae grew faster than Oklahoma larvae, regardless of transplant site. Conversely, larvae transplanted to Oklahoma grew faster than larvae transplanted to Connecticut, regardless of population source. These results suggest that variation in food availability, not temperature, may account for differences in growth and body size of northern and southern ant lions. Although northern larvae grew faster and reached a larger body size in both experiments, northern environments should suppress growth because of reduced food availability and a limited growing season. This study provides the first example of countergradient selection causing Bergmann's rule in an ectotherm.     

Water balance in the Argentine ant (Linepithema humile) compared with five common native ant species from southern California

Abstract.  Little attention has been given to the effect of physiological limitations on the ability of introduced species to invade ecological communities. In the present study, the water balance of the invasive Argentine ant ( Linepithema humile ) is compared with five common ant species native to southern California. Total and critical water contents are measured, as well as rates of water loss and survival times. The results show that the body size of ant species has a strong effect on water balance, explaining between 99% of total and 90% of critical water content (i.e. the amount of water remaining when the ant becomes moribund). The measured survival times at 40 °C and approximately 0% relative humidity are shorter for L. humile than for the other five native ant species. The area-independent water-loss rate is higher for L. humile than for the other native ant species studied. This finding is corroborated by independent data using two different methods (i.e. gravimetric measurement and open-flow respirometry). Somewhat surprisingly, significant differences in the water-loss rates of different sizes of Solenopsis xyloni workers are found, even after adjusting for surface area. The area-independent water-loss rate is significantly lower for larger than for smaller workers. Consistent with circumstantial evidence from the field, the results suggest that the physiological constraints of invasive species, such as water-loss rates and critical water content, can limit their distribution and abundance not only at regional scales, but also at fine scales.     

Bergmann's rule in larval ant lions: testing the starvation resistance hypothesis

Abstract.  1. Body size of the ant lion Myrmeleon immaculatus follows Bergmann's rule – an increase in body size towards higher latitudes. The hypothesis that ant lion body size is larger in the north as an adaptation for starvation resistance was tested.
2. In a laboratory experiment testing starvation resistance, survivorship curves differed among 10 ant lion populations for both a starved and a fed treatment.
3. The average number of months survived by each population was correlated positively with latitude for both treatments. Across both treatments and all populations, large individuals survived longer than small individuals; however individuals from high latitudes had higher survivorship, even after factoring out variation due to initial body size.
4. These results suggest that starvation resistance may be an adaptation for coping with reduced prey availability in high latitudes. Starvation resistance may contribute to latitudinal gradients in body size of ant lions and other ectotherms.     

The control of Myrmica rubra workers by queens of their own and other Myrmica species and the interaction between queenless groups of workers

ABSTRACT. Queens of two species of the ant genus Myrmica bonded to workers of the species M. rubra L. as the latter emerge from the pupal skin can use these workers nearly 6 months later to arrest gyne formation in sex-competent larvae of the same species. Queens of M. ruginodis Nylander var. microgyria (Brian & Brian, 1949) are as good at this as the natural M. rubra , but those of M. sabuleti Meinert (of a race close to M. scabrinodis) are not. Though the M. sabuleti queens induce normal aggression against sexualizing larvae, they are unable to prevent some or all of the workers feeding larvae as though they were queenless. However, queens from different colonies of M. rubra adopted by queenless populations of workers in spring, control their brood-rearing behaviour perfectly. M. rubra workers from different colonies bring gynes to maturity from female sexual larvae at different average sizes. When workers from two such sources are mixed in equal proportions, the size of gyne larva produced after a week's culture corresponds with that of one of the worker populations; it is not intermediate in size. Also, large workers can rear larger gyne-larvae than small workers of the same age. This is only true if the workers have been living with queens all the time from emergence as an imago to the moment the experiment was set. Size mixtures only achieve the same size larvae as a pure culture of small workers would. A possible reason for this is that small workers exclude the larger ones from the nursery areas of the nest.     

Shear adhesive performance of leaf‐cutting ant workers (Atta cephalotes)

Wingless arboreal ants must resist the force of gravity while traversing substrates in their environment. For leaf‐cutting ants like Atta cephalotes, foraging may also include a ca. 30 m vertical descent while carrying a load 1–6 times their body mass. We hypothesized that heavier and larger ants would carry heavier and larger loads and that adhesive performance would positively correlate with load mass. We found no relationship between ant mass, body length, head width, or adhesive performance, and the load size an ant carried. In addition to workers carrying vegetative loads (most often leaves), workers in an active foraging trail also include smaller workers riding on the leaves carried by larger workers, and large major workers, providing protection from aerial and ground attacks (Soldiers), respectively. Despite varying functional roles, all foraging ants require secure attachment to the substrate. We measured shear adhesive performance of each foraging role and found that Soldiers produced the highest shear adhesive forces. However, when controlling for tarsal pad area, we found that ants carrying loads have higher shear adhesive performance per unit area than those riding on leaves, and that Soldiers have the lowest shear adhesive performance per unit area. This suggests that while leaf choice does not appear to be dictated by size, mass, or shear adhesive performance of individual ants, overall, ants who carry leaves adhere more strongly given their pad size than those who do not. Abstract in Spanish is available with online material.     

Geographic variation in jungle cat (Felis chaus Schreber, 1777) (Mammalia,Carnivora, Felidae) body size: is competition responsible?

There is a striking difference in body size of jungle cats ( Felis chaus ) in the west and the east of their distribution, with Israeli cats being 43% heavier than Indian cats. We tested the hypothesis that increasing competition from other small felids towards the east is responsible for the difference in body size. We measured jungle cat skulls for eight cranial and dental variables and related these to independent variables such as species richness (local and regional), latitude, longitude, temperature, and precipitation. Data from a narrow band between latitudes 24.0°N and 33.9°N, where Bergmann's rule was largely not observed, showed that the western population (≤ 50.0°E longitude) of jungle cats is larger than the eastern (> 60.0°E longitude) population with the size difference being most evident in the upper carnassials (P⁴L). Species richness at the regional level showed a significant negative relation to P⁴L. An even spacing in condylobasal length for a small-cat guild from India through null model analysis indicated the occurrence of character displacement. The results support the hypothesis that competition is responsible for geographical variation in jungle cat body size in the region where Bergmann's rule does not apply. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 163–172.     

Studies on the relationship between the ant ectoparasite Antennophorus grandis (Acarina: Antennophoridae) and its host Lasius flavus (Hymenoptera: Formicidae)

The mite Antennophorus grandis (Berlese, 1903) is a large obligate ectoparasite of workers of the ant Lasius flavus(Fabricius). It rides under the head of the ants and uses its long front legs to communicate with its hosts and stimulate them to give it food. We present allometric and morphometric data showing that L. flavus workers can occur in two size classes. We also present the first quantitative ethograms of mite-bearing and mite-free L. flavus workers of the two size categories. The mites tend to occur on the smaller nurse workers and receive food from them at an extremely high frequency. Antennophorus grandis also frequently gain food when one ant is donating food to the one they are riding upon. The mites seem to inhibit the ability of their host worker to show most social behaviours such as tending ant larvae. The mites frequently move from one host worker to another. For these reasons the mites may have a larger impact upon their host colony than their relative rarity first suggests. The ants do not seem to have any specific defence against these parasites. The mites live in small populations and show female-biased sex ratios consistent with local mate competition. Preliminary evidence suggests that the mites have haplodiploid sex determination which may explain how they are able to adapt their sex allocation to their population size.     

Variation in life-history characteristics among populations of North American wood turtles: a view from the north

Life-history traits such as age at maturity, body size and clutch size tend to vary across a species' distribution. The purpose of our study was to describe the demography of a newly discovered population of North American wood turtles Glyptemys insculpta at the species' northern range limit, and to compare our findings to those of other studies to test hypotheses about adaptive life-history variation. Turtles were hand-captured from May to October 2005 and 2006 along a 4.5 km stretch of river located in the Sudbury District, ON, Canada (46°N). Fifty-five captured individuals provided a population density estimate of 1.3 turtles/100 m of river. Juveniles comprised 35% of wood turtles captured, and growth ring counts (i.e. age estimates) indicated recruitment in each of the past 11 years. Among populations, we found a nonlinear pattern in body size variation with the largest turtles in the north, smallest turtles in the centre of the range, and intermediate-sized turtles in the south. This nonlinear pattern in body size was reflected in clutch size variation. Selective pressures to overcome years of low recruitment may have resulted in larger body sizes and hence large clutch sizes at northern latitudes while conspecifics at southern latitudes can achieve larger body sizes because they live in a more productive environment. Population density decreased with latitude, likely as a result of a gradient in habitat productivity.     

Factors affecting river entry of adult Atlantic salmon in a small river

In this study, effects of stock origin, fish size, water flow and temperature on time of river ascent of adult Atlantic salmon Salmo salar were tested. Brood stocks were collected in eight Norwegian rivers situated between 59 and 69° N. The fish were reared to smolts, individually tagged and released in the River Imsa, south-west Norway (59° N). Adults from all stocks approached the Norwegian coast concurrently, but Atlantic salmon ≥70 cm in natural tip length entered coastal water slightly earlier during summer than smaller fish. Atlantic salmon <70 cm, however, ascended the river significantly earlier and at lower water flow and higher water temperature than larger fish. Although largest in size, the fish from the northern populations (62–69° N) ascended the River Imsa almost 1 month earlier than those from the south (59–60° N). They seemed less restricted by the environmental factors than the fish originating from the more southern rivers. There was no apparent trend among years in time of river ascent. Maximum ascent per day occurred at water discharges between 12·5 and 15 m³ s⁻¹ and at water temperatures between 10 and 12·5° C. There was a significant positive correlation between water flow and river ascent during the first part of the upstream run from July to September with best correlation for September, when multiple regression analysis indicated that water temperature had an additional positive effect. Stock origin, fish size and water discharge were important variables influencing the upstream migration of Atlantic salmon in small rivers.     

The Role of Wood Ants (Formica rufa group) in Carbon and Nutrient Dynamics of a Boreal Norway Spruce Forest Ecosystem

Wood ants (Formica rufa group) are regarded as keystone species in boreal and mountain forests of Europe and Asia by their effect on ecosystem carbon (C) and nutrient pools and fluxes. To quantify the impact of their activity on boreal forest ecosystems, C, nitrogen (N), phosphorus (P), potassium (K) and calcium (Ca) pools and fluxes in wood ant nests (WAN), and soil were assessed along a 5-, 30-, 60-, and 100-year-old Norway spruce (Picea abies L. Karsten) dominated successional gradient in eastern Finland. Amounts of C and nutrients in WAN increased with stand age, but contained less than 1% of total C and nutrient pools in these stands. The CO₂-efflux from nests was also insignificant, as compared to CO₂-efflux from the forest floor. Annually, the amount of C brought by wood ants into their nests as honeydew, prey and nest-building materials ranged from 2.7 to 49.3 kg ha^?1 C, but this is only 0.1–0.7% of the combined net primary production of trees and understorey in boreal forests. The difference between wood ant nest C inputs and outputs was very small in the younger-aged stands, and increased in the older stands. Carbon accumulation rates in nests over a 100 year period are estimated to be less than 10 kg ha^?1 a^?1. In contrast to C, annual inputs of N, P, and K are larger compared to wood ant nest nutrient pool size, ranging from 3 to 6% of the annual tree stand and understorey uptake. This indicates a more rapid turnover and transport of N, P, and K out of WAN, and suggests that wood ants increase the cycling rate of these nutrients in boreal forests.     

Effect of temperature and social environment on worker size in the ant Temnothorax nylanderi

Warm temperatures decrease insect developmental time and body size. Social life could buffer external environmental variations, especially in large social groups, either through behavioral regulation and compensation or through specific nest architecture. Mean worker size and distribution of worker sizes within colonies are important parameters affecting colony productivity as worker size is linked to division of labor in insect societies. In this paper, we investigate the effect of stressful warm temperatures and the role of social environment (colony size and size of nestmate workers) on the mean size and size variation of laboratory-born workers in the small European ant Temnothorax nylanderi. To do so, we reared field-collected colonies under medium or warm temperature treatments after having marked the field-born workers and removed the brood except for 30 first instar larvae. Warm temperature resulted in the production of fewer workers and a higher adult mortality, confirming that this regime was stressful for the ants. T. nylanderi ants followed the temperature size rule observed in insects, with a decreased developmental time and mean size under warm condition. Social environment appeared to play an important role as we observed that (i) larger colonies buffered the effect of temperature better than smaller ones (ii) colonies with larger workers produced larger workers whatever the rearing temperature and (iii) the coefficient of variation of worker size was similar in the field and under medium laboratory temperature. This suggests that worker size variation is not primarily due to seasonal environmental fluctuations in the field. Finally, we observed a higher coefficient of variation of worker size under warm temperature. We propose that this results from a disruption of social regulation, i.e. the control of nestmate workers over developing larvae and adult worker size, under stressful conditions.     

Geographical variation in body weight and sexual size-dimorphism of Norwegian moose (Alces alces)

Geographical variation in male carcass weight, and sexual dimorphism in size was studied in 19 populations of Norwegian moose ( Alces alces (L.)).
Significant age-specific variation in male carcass weight was found for all the populations studied up to the age of 4 1/2 years, but in some populations maximum weight was not reached until at least 5 1/2 years. Increase in the mean weight of females after the age of 2 1/2 years was not significant. Only a weak relationship existed between mean yearling and adult bull weights in a population. However, within both the southern (< 62°N) and northern (> 62°N) parts of the country, yearling carcass weight was a good predictor of adult bull weight in a region.
Adult bull weight in a region was best predicted from the increment in mean carcass weight observed between 1 1/2 and 3 1/2 years of age. Within a region, variation in age-specific carcass weight between cohorts of bulls from different years was also well predicted from annual variation in growth increment.
Those patterns reveal a sexual difference in strategy of body growth. The adult weight of females is probably strongly determined by the weight gained by the time of onset of reproduction. The males have available a longer period for growth in body weight. They are therefore able to compensate for low weights early in life by increased gain of weight in later years, that provide good conditions for growth.
Geographical variation in the degree of sexual dimorphism in size correlated only poorly with adult male size. We suggest that the sexual size-dimorphism is a result of reproductive constraints of the female, i.e. in populations living in poor conditions and having small body size, the onset of reproduction prevents further gain in body weight.     

Body size but not colony size increases with altitude in the holarctic ant,Leptothorax acervorum

1. Bergmann's rule states that organisms inhabiting colder environments show an increase in body size or mass in comparison to their conspecifics living in warmer climates. Although originally proposed for homoeothermic vertebrates, this rule was later extended to ectotherms. In social insects, only a few studies have tested this rule and the results were ambiguous. Here, ‘body size’ can be considered at two different levels (the size of the individual workers or the size of the colony). 2. In this study, data from 53 nests collected along altitudinal gradients in the Alps were used to test the hypotheses that the worker body size and colony size of the ant Leptothorax acervorum increase with increasing altitude and therefore follow Bergmann's rule. 3. The results show that the body size of workers but not the colony size increases with altitude. Whether this pattern is driven by starvation resistance or other mechanisms remains to be investigated.     

Geographical variation in the breeding biology of the Purple Sandpiper Calidris maritima

Studies in Iceland (66°N) and Svalbard (78°N), combined with the results of previous work, allowed geographical comparisons of different aspects of the breeding biology of the Purple Sandpiper Calidris maritima , testing predictions that they may be related to latitude and altitude (here taken as surrogates for climatic severity). The breeding density was lowest in the polar deserts of Franz Josef Land (82°N) and highest in coastal Arctic Tern Sterna paradisaea colonies in Iceland where the terns perhaps afforded protection from predators. There was no difference in the percentages of 1-year-old (first-year) birds in the breeding populations in Svalbard and Iceland. Time of breeding was related to both latitude and altitude, being later at higher latitudes and altitudes. In Iceland, larger males and males over 1 year old nested earlier than small males and 1-year-old males, respectively. Relaying occurred in Iceland but it was not observed in Svalbard. There were no geographical differences in clutch size. Egg size was related to female size in Svalbard. There were also geographical differences in egg size associated with female size (wing length), with the largest eggs in Iceland and smallest in south Norway. Males usually attended broods and the rates at which females deserted their broods were similar in Iceland and Svalbard. Chick growth rates were similar for Iceland and Franz Josef Land. Thus, in breeding biology, Purple Sandpipers varied geographically only in breeding density, time of nesting and egg size, which was associated with female size.     

Forager polymorphism, size-matching, and load delivery in the leaf-cutting ant, Atta cephalotes

Abstract.

• 1 This study examined the importance of forager polymorphism and division of labour among foragers of different size for the economics of load delivery in a leaf-cutting ant, Atta cephalotes (L.). I collected A.cephalotes foragers coming down trees carrying leaf fragments to evaluate the degree of match between forager mass and the density (mass per unit area) of leaves being cut, and to quantify how this match affects whether the mass of leaf fragments cut by the ants are within the range which maximizes the rate and efficiency of load delivery.
• 2 Foragers ranged 23-fold in mass (1.4–32.1 mg). On average, larger workers cut at denser leaf sources. Leaf fragment area increased with ant mass, but relative area (fragment area/ant mass) decreased with ant mass. The density of a leaf type had little or no effect on the area cut by ants of a given size. As a result, ants of a given mass cut heavier fragments from the denser leaves. The effect of leaf density, however, was partly counteracted at the colony level by recruitment of larger ants, which cut smaller area fragments relative to their body mass, to cut at denser leaf sources.
• 3 Despite a fairly high variance in the relationship between ant mass and fragment mass, overall 87% of the laden ants (74–100% for different trees) carried leaf fragments in the 1.5–6 times body mass range. Earlier studies indicate that loads in this range yield the highest biomass transport rate and transport efficiency. Thus, the variance falls within bounds such that it has little effect on load transport efficiency. Having a broad range in optimal load mass may be considered an adaptation to the expected variability in load masses.
• 4 If there were no correlation between ant mass and leaf density, mismatches between ant mass and load mass would be more common than observed. Thus, size-matching of larger workers to cut denser leaves increases the rate and ergonomic efficiency of load delivery.

     

Trade-off between egg mass and egg number in brown trout

Individual egg mass and fecundity increased with somatic mass in first time and repeat spawning wild anadromous and freshwater resident brown trout Salmo trutta . The egg mass was larger for similar-sized trout in south (58° N) than mid Norway (63° N), whereas fecundity was higher in mid- than in south Norway, making total gonadal investment similar in the two areas. Repeat spawners had heavier eggs than similar-sized first time spawners. The egg mass of residents was c. 10% larger than that of similar-sized first time spawning anadromous trout. Common garden experiments with offspring of wild anadromous trout showed no significant correlation between egg and somatic mass in first time spawners in two of the three populations studied. In the third population, a slight positive correlation was found. Similar results were found for repeat spawners. In the three populations, fecundity increased significantly with somatic mass in both first time and repeat spawners. Wild and hatchery-reared trout showed negative correlation between egg mass and fecundity when the effect of body size was excluded, indicating a trade-off between the two parameters. In wild trout, this was caused by variation among populations, whereas in hatchery fish, within population variation was observed in egg mass over fecundity. Furthermore, the egg mass of first time and repeat spawners were positively correlated, when adjusted for fish size. Size-specific gonadal investment was significantly higher in wild anadromous than resident trout. There was no significant difference in gonadal investment between first time and repeat spawners in wild anadromous trout. However, in the hatchery-reared trout, gonadal investment was significantly higher at repeat than first time maturation. The hatchery trout did not spawn naturally, but were artificially stripped. Among populations, a part of the variation in egg mass and fecundity is phenotypically plastic, a part appears genetically determined.