Contemporary egg size divergence among sympatric grayling demes with common ancestors

Abstract  This study documents divergence in egg size that has occurred over less than 25 generations among sympatric demes of European grayling ( Thymallus thymallus ) from Lake Lesjaskogsvatnet in Norway. A cluster analysis identified two clusters of tributaries: one of small, warm tributaries (SW) and the other of large, cold tributaries (LC). Spawning occurs more regularly and up to 4 weeks earlier in SW tributaries compared with that in LC ones. We explored numerous mixed models predicting egg size from year (random effect), basin and tributary (fixed effects), and female length. The most supported model estimated length-adjusted egg size to be larger in SW tributaries compared with that in LC tributaries. Combinations of density-dependent (competition for food/space) and density-independent (temperature) factors along with phenotypic plasticity and maternal effects are discussed as potential differentiation sources. We suggest high temperatures (increased metabolism) to reinforce the selective advantage of large eggs under conditions with highly density-dependent fry interactions.     

Seasonal and interannual components of intrapopulation variation in clutch size and egg size of a darter

Abstract –  Previous studies have offered suggestive but sometimes conflicting glimpses at the range and patterns of seasonal and interannual variation in female darter life-history traits. The present study examined clutch-size and egg-size variation from a single Mississippi population of brighteye darters (Etheostoma lynceum ), collected at regular intervals over four sequential spawning seasons. Both life-history traits were significantly correlated with body size, and they both showed significant variation within and among breeding seasons. The overall intraseasonal trends in these traits involved an increase in clutch size (CS) and a decrease in egg size from early to late periods of the spawning season. Clutch size and egg size showed a weak but significant negative correlation, which was indicative of a trade-off between the two clutch parameters. Seasonal changes in temperature appear to be related to differing patterns of seasonal variation in egg size reported in the literature for darters. Inverse seasonal shifts in egg size and CS in the brighteye darter may represent adaptive phenotypic plasticity that allows females to produce larger, competitively superior offspring early in the reproductive season when there is low supply of food for them (parental investment hypothesis) or to produce larger eggs early in the reproductive season to ensure that each egg is adequately provisioned in the face of uncertainty (bet-hedging hypothesis) if the food available for the young is unpredictable early in the season. Consistent with theoretical predictions, egg size showed less phenotypic variability than CS.     

Density-dependent growth of young-of-the-year Atlantic salmon (Salmo salar) revisited

Imre I, Grant JWA, Cunjak RA. Density-dependent growth of young-of-the-year Atlantic salmon ( Salmo salar ) revisited. Ecology of Freshwater Fish 2010: 19: 1–6. © 2009 John Wiley & Sons A/S
Abstract –  The length of individual young-of-the-year (YOY) Atlantic salmon ( Salmo salar ) in Catamaran Brook decreases with increasing population density following a negative power curve. Because most of this decrease in growth rate occurs at low densities (<1 fish·m⁻²), ( Imre et al. 2005 ; Journal of Animal Ecology, 74: 508–516) suggested that exploitation competition for drifting prey rather than space limitation might be responsible for this pattern. Recently, ( Ward et al. 2007 ; Journal of Animal Ecology, 76: 135–138) showed that the negative power curve of growth rate versus density can be caused by other mechanisms and suggested that Imre et al.'s evidence for density-dependent growth would have been stronger if we had analysed final size versus initial density rather than final density. We examined (i) whether the negative power curve of size versus density was also apparent in an analysis of final size versus initial density and tested two predictions that emerge from Ward et al.'s model, (ii) the variance in body size increases with population density, and (iii) the maximum fish size at a site is density-independent. The final size of YOY salmon decreased with increasing initial density following a negative power curve. Our data did not provide strong support for the above predictions emerging from Ward et al.'s model. Our analyses of different years, sites and seasons were consistent with the hypothesis of density-dependent growth of YOY salmon.     

Streamflow environment predicts divergent life history phenotypes among populations of the Blacktail Shiner Cyprinella venusta: Temporal stability of a large‐scale pattern

Egg size variation among 16 Gulf Coast populations of Cyprinella venusta, the Blacktail Shiner, previously was shown to be significantly correlated with annual stream runoff. In this study, we examined egg size across multiple years and seasons in a subset of the original populations, focusing on three streams that differed widely in annual stream runoff. These populations appear to have been derived independently, possibly nearly synchronously in geological time, from an ancestral form. Thus, they can be considered statistically independent. Most of the variation in egg size was attributable to differences across the three populations. Although annual and seasonal variation was present, the three populations shifted similarly on both of these time scales. The results support an earlier hypothesis that streamflow, quantified using mean annual runoff, is a strong selective influence on egg size, hence offspring size, favouring larger egg size in populations inhabiting streams with greater levels of runoff.     

Life-history variation in perch (Perca fluviatilis L.) in five neighbouring Norwegian lakes

Abstract – We have studied the population dynamics and reproductive biology of perch ( Perca fluviatilis L.) from five neighbouring lakes in Norway. The lakes vary in water quality, varying from strongly acidified (pH≤5.0) to not acidified (pH≥6.0). Estimated annual survival rates did not differ among populations. There was no strong relationship between age at maturity in female perch and acidification. However, age at maturity was lower for female perch from the most acidic lake ( c . 2 years) compared with perch in the four other lakes (2.5–3.5 years). There was no relationship between acidification level and size-adjusted egg size, fecundity or reproductive investment (Gonadosomatic index – GSI). Perch in the most acidified lake showed large variation in egg size, the lowest length-specific fecundity, the highest GSI, and the lowest age at maturity. Environmental stress, such as acidification, induces a number of changes to a lake community. It is therefore difficult to predict how acidification will influence the population dynamics and reproductive biology of a perch population.     

Foraging specialisms, prey size and life-history patterns: a test of predictions using sympatric polymorphic Arctic charr (Salvelinus alpinus)

Abstract –  We use arguments based on optimal foraging theory to predict body size constraints and the consequences of these on a range of life-history traits in three trophic specialist morphs of Arctic charr, Salvelinus alpinus , living in sympatry in Loch Rannoch, Scotland. As predicted, foraging specialists feeding on small prey items with a narrow size range showed evidence of deterministic growth; the ultimate body size of macrobenthos feeders being larger ( L _∞ = 238 mm) than that of planktivores ( L _∞ = 216 mm). In contrast, the piscivorous morph showed no evidence of reaching a maximal body size.
The two size-constrained morphs (benthivores and planktivores) matured earlier and died younger (living for up to 11 and 7 years, respectively, in this study) than did the piscivorous charr which showed continuous growth up to at least 17 years.
The pattern of annual reproductive investment in maturing individuals was complex. Planktivores invested in larger eggs than the other two forms, but benthivores produced a greater number of eggs than planktivores, which in turn produced more than piscivores. Planktivorous males had a greater investment in mean testis weight than the other two forms.
Lifetime reproductive output was the greatest in the benthivorous charr, intermediate in planktivorous and the lowest in the piscivorous charr when measured either as fecundity or as gonadal weight. We conclude that constraints imposed upon foraging specialists by foraging efficiency is a significant driver of body size and ultimately reproductive investment in gape-limited foraging salmonids.     

Bigger is not always better: egg size influences survival throughout incubation in brown trout (Salmo trutta)

Classical optimality models for the evolution of egg size predict a single optimal investment for females inferior to the optimal investment for offspring because of the egg size–fecundity trade‐off and the assumption that ‘bigger is better’ for offspring fitness. Such models do not satisfactorily represent observed within‐population variation in egg size. We measured the influence of maternal investment in egg size on offspring survival in brown trout. Individual measures of egg size, metabolism and survival at different temperatures throughout ontogeny were carried out. We then developed a survival model with regard to egg size, incubation temperature and observed metabolic rate. Small eggs were found to survive at higher rates than large eggs, and the egg size–survival relationship was found to differ among females in accordance with average metabolic rate measured at hatching. These results provide insights for the understanding of the evolutionary significance of egg size variations within a population.     

Using allometry with fish size to estimate production to biomass (P/B) ratios of salmonid populations

Abstract – The ratio of annual production rate to average biomass ( P / B ) is sometimes used as a shortcut method of estimating production if biomass is known. P / B ratios vary among salmonid populations in different areas depending on the species, fish size and growing conditions. The hypothesis that annual P / B ratios for salmonid populations can be predicted from the allometric equation: P / B  =  a W ^−0.35 was investigated in this study. The allometric coefficient (−0.35) was obtained from the literature, and W was the average weight (g) of fish in the population. Plots of P / B versus fish weight for three species of salmonids, Salvelinus fontinalis , Salmo trutta and Salmo salar , showed a declining trend, with a slope consistent with the hypothesis. The coefficient a of the allometric equation was species and habitat dependent. The efficacy of using the allometric formula to estimate the P / B ratio of specific salmonid populations is examined.     

Effects of dietary keto-carotenoids (canthaxanthin and astaxanthin) on the reproductive performance of female rainbow trout Oncorhynchus mykiss (Walbaum)

The aim of this study was to clarify further the relationship between dietary keto-carotenoids (canthaxanthin and astaxanthin) and reproductive performance in female rainbow trout. Three experiments were undertaken in three successive breeding seasons. In addition to a control diet, fish were fed a canthaxanthin-supplemented diet (200 mg canthaxanthin kg⁻¹ feed, designated as 6mC200) for 6 months prior to spawning (experiment A); the same diet as in A but for either 3 months (3mC200) or 6 months (6mC200) before spawning (experiment B); diets with one of two levels of astaxanthin supplementation, 50 mg (6mA50) or 100 mg (6mA100) kg⁻¹ feed, or a diet with 100 mg canthaxanthin kg⁻¹ feed (6mC100) fed for 6 months (experiment C).
There was no significant influence of carotenoid supplementation on either the frequency of maturing females or the date of maturation. The number of ova per kg of female body weight averaged 2700 and did not vary significantly among fish fed the different diets. Across experiments A, B and C there was no significant difference in egg and larval survival among fish fed carotenoid-supplemented and control diets. In experiment A, 6mC200 females produced smaller eggs than controls but this result was not confirmed in experiments B and C. In general, eyed egg yield appeared partly dependent upon egg size. Alevin weight was also correlated with egg weight. The growth test conducted on fingerlings from experiment B failed to provide any evidence of an effect of feeding carotenoid supplemented diets to the female parent. Pigment analyses conducted on alevins revealed that canthaxanthin fed to the female parent was transferred into the eggs and therefore to the larvae, although canthaxanthin was metabolized within a few weeks after hatching.     

Characterization of Small-size Egg-bearing Thai ss-strain Rotifers Brachionus rotundiformis and Their First Offspring

This study selected small (100–120 μm) egg-bearing females from a local Thai ss population and characterized their first offspring's life history in an attempt to produce small-size rotifers. Mean lorica length of selected small adult females was 120 ± 6 μm at the time of collection, and this mean length did not increase over their lifetime. While their first offspring life span was only 5.11 ± 0.35 d, the reference population longevity was higher, 9.65 ± 0.4 d. The length of reproductive period of offspring from the small-size egg-bearing female was 2.58 ± 0.38 d, shorter than that of reference population 6.83 ± 0.58 d. Although the rate of egg production was not different between small egg-bearing female and reference population, the total number of eggs produced by the small egg-bearing female's first offspring was lower (4.78 ± 0.60) compared to the reference population (11.83 ± 1.26). The small egg-bearing female's first offspring had a higher egg to lorica length ratio (76.1 ± 1.64%) than the reference population (56.6 ± 1.3%), indicating a relatively high investment in reproduction. The small egg-bearing female's first offspring reached only 125 ± 6 μm in 36 h, and further culture of their offspring over 35 d resulted in a mean offspring size, 163 ± 11 μm, similar to the reference population (159 ± 16 μm). This shows that population mean size reduction is not likely to result from selecting small egg-bearing females within a single generation. The unique reproductive characteristics of small egg-bearing female place it in its own category.     

Laboratory-based reproduction success of ruffe, Gymnocephalus cernuus (L.), in brackish water is determined by maternal properties

Abstract – Body length, age, egg size, embryo salinity tolerance and length at hatching of the freshwater (salinity <0.1 ppt, Lake Peipsi) and brackish-water (salinity 2–6 ppt, Pärnu and Matsalu Bay) ruffe, Gymnocephalus cernuus (L.), were examined to reveal their reproductive success in moderate salinity. Eggs of females originating from brackish water were significantly larger than eggs of freshwater females. No correlation between egg size and female size and age was found in brackish-water populations. In the freshwater population there was a small negative correlation between egg size and female size, but no correlation with female age. Fertilisation by sperm of males of different origin (brackish water or freshwater) produced no significant differences at any critical developmental stage (fertilisation, gastrulation, hatching) in the development of eggs from brackish-water or freshwater females at 3.3, 5.5, 7.7 and 9.9 ppt salinity. Survival rates in different salinity depended only on female origin; embryonic salinity tolerance was higher in ruffe inhabiting brackish water. Obviously, embryo salinity tolerance in ruffe is determined by egg qualities.     

Microgeographical variation in ovum size of the blacktail shiner, Cyprinella venusta Girard, in relation to streamflow

Abstract – There is a strong, positive correlation between egg size and the discharge variable mean annual runoff among populations of Cyprinella venusta Girard from streams in different drainages ranging across the Gulf Coastal Plain of the southern United States. This variation may have resulted from selection for larger egg size, hence larger offspring size, because of greater environmental fluctuation or a greater number of floods in streams with higher runoff. In the present study, we examined C. venusta from populations inhabiting streams varying in mean annual runoff within a single drainage and found a similar correlation between ovum size and runoff. Therefore, the egg size–runoff relationship exists at a much smaller (i.e., intra-drainage) spatial scale than previous research (based on widespread inter-drainage variation) has shown. We also attempted to establish a link between mean annual runoff and streamflow-mediated disturbance as indicated by predictability of streamflow, monthly coefficients of variation in discharge and number of days with extreme low and high flows. Although the overall predictability of discharge did not differ among streams, the streams with high mean annual runoff were characterized by smaller coefficients of variation in winter, fewer days of extremely low flows and a trend toward higher flows in late summer and early fall. At the intra-drainage scale, higher coefficients of variation did not accurately reflect the numbers of extreme flows. These results call into question the use of coefficients of variation in discharge as indicators of disturbance. Given that eggs, larvae and small juveniles of C. venusta are present in late summer and early fall, when flows in high runoff streams tend to be high relative to low runoff streams, we conclude that these high flows may act as a selective force causing the evolution of larger egg size.     

The effect of ploidy and incubation temperature on survival and the prevalence of aplasia of the septum transversum in Atlantic salmon,Salmo salar L

Heart deformities are a concern in aquaculture and are linked to egg incubation temperature. Diploid and triploid Atlantic salmon, Salmo salar L., were incubated at 6, 8 and 10 °C and analysed for aplasia of the septum transversum (n = 150 ploidy^?1 incubation temperature^?1). Heart morphology (size and shape) was assessed in fish incubated at 6 °C and in fish with and without aplasia of the septum transversum (n = 9 group^?1) incubated at 10 °C. Egg mortality was significantly higher in triploids than in diploids at all incubation temperatures, and increased egg incubation temperatures increased mortality in both ploidy. Triploids grew quicker than diploids after egg incubation at 10 °C, but not at 6 °C. Aplasia of the septum transversum occurred only in triploid fish after incubation at 6 °C and 8 °C (0.7% and 3.3%, respectively) and was significantly greater (P ≤ 0.05) in triploids after incubation at 10 °C compared with diploids (30% and 18%, respectively). Aplasia of the septum transversum significantly increased heart mass and resulted in a long flat ventricle compared with fish displaying a septum transversum. The results suggest triploid salmon should be incubated below 8 °C.     

Sex-specific growth pattern during early life history in masu salmon, Oncorhynchus masou

Abstract –  To examine whether or not sex-specific growth occurs in fry of masu salmon Oncorhynchus masou , 90 half-sibling fry chosen from three different classes of egg size (small, medium and large) and emergence time (period from fertilisation to first feeding; early, middle and late) were raised in a tank for 60 days. In all four replications, male fry grew faster than females. The difference in growth between sexes was greater among siblings hatched from larger eggs. Fast-growing, young male masu salmon show a precocious form that tends to mature without migrating to sea. Slower growing males tend to show the anadromous form, which is only shown in females. Sex-specific life histories may influence the sex-specific growth patterns during early life history.     

Effects of salinity and temperature conditions on the reproductive success of turbot (Scophthalmus maximus) in the Baltic Sea

In the Baltic Sea, a large brackish water area, turbot (Scophthalmus maximus) occurs at the border of its distribution with respect to salinity. Using turbot caught in ICES subdivision (SD) 28 (mid-Baltic), salinity requirements for successful egg development were evaluated by assessment of spermatozoa mobility, fertilisation and egg survival at different salinities. Further, to evaluate potential effects of temperatures, egg survival at different temperatures was assessed. Spermatozoa activity and fertilisation rate decreased with decreasing salinity with a significant drop at <7 psu. The viable hatch was significantly lower at <7 psu compared to at 7–15 psu. Hence, due to decreasing salinity this implies lower egg survival in SD 29 and 30 compared to in SD 24–28, and that salinity conditions in SD 31 are insufficient for egg development. Further, following a long period without major inflows of saline water into the Baltic Sea, salinity has decreased. From 1995 onwards salinities <7 psu prevail in SD 27–28 suggesting decreased reproductive success and potentially weaker year-classes in this area. Egg survival was high at 12–18 °C and considerably lower at 9 and 21 °C. Comparing the results with environmental data suggested that spawning time of turbot is adapted to optimum temperatures for egg development, but that occasions with temperatures involving increased egg mortality may occur, e.g. during upwelling situations.     

Effect of temperature on resting egg formation of the tropical SS-type rotifer Brachionus rotundiformis Tschugunoff

ABSTRACT:   Tropical minute rotifer strains (SS-type) induce mixis at 30–35°C but sexual reproduction and resting egg formation do not proceed well due to rapid environmental change. The present study examined the effect of temperature regulation on rotifer Brachionus rotundiformis (Langkawi strain, SS-type) resting egg formation in small (500 mL in culture volume)- and large-scale (500 L in culture volume) experiments. Rotifers were cultured at 30°C in 15–17 p.p.t. seawater with an initial density of 1 individual (ind.)/mL. After 4 days, when cultures were in exponential growth stage with active mixis induction, the culture temperature of the experimental rotifers was changed to 25°C. Control rotifers were cultured at 30°C throughout the experiment. Fresh or frozen Nannochloropsis oculata and condensed freshwater Chlorella vulgaris were used as the rotifer diets in the small- and large-scale experiments, respectively. Significantly higher resting egg production was observed with the experimental rotifers (30→ 25°C) versus the control rotifers. In the large-scale trial, experimental rotifers produced 2.6 × 10⁶ resting eggs during a 9-day experiment, which was 1.6-fold more than the control rotifers. Moreover, the efficiency of resting egg formation was found to increase by a factor of 1.8. The present study indicates that decreasing culture temperature from 30 to 25°C after active mixis increased resting egg formation in B. rotundiformis (SS-type).     

Application of high‐throughput single nucleotide polymorphism genotyping for assessing the origin of Engraulis encrasicolus eggs

1. Single nucleotide polymorphism (SNP) markers in anchovy (Engraulis encrasicolus) egg samples were analysed to detect their origin on a small spatial scale (200 km) by assigning genotypes to adult anchovy stocks. The novelty of this work is the application of a rapid high‐throughput method for genotyping each single anchovy egg, in a single execution, using a set of 96 genome‐wide SNPs in a dynamic array system with microfluidic technology (Fluidigm 96.96).
2. The existence of two ecotypes in E. encrasicolus had already been identified based on SNP polymorphism in the Atlantic Ocean and in the Mediterranean Sea, showing that habitat type (offshore versus coastal/estuarine) is the most important component of genetic differentiation among populations of anchovy.
3. In this work, anchovy egg genotypes from areas of the Western Mediterranean were assigned to adult populations. Only two localities in which adult anchovies were sampled represented donor populations for the coastal/estuarine egg genotypes. Although some degree of mixing among the hauls could exist, the assignment of egg groups to adult populations led to distinguishing the contributions of distinct ecotypes to new wild generations. We can conclude that the high rate of egg dispersion caused by marine currents and the different degrees of local retention could explain the genetic heterogeneity observed in the adult populations, where eggs from neighbouring spawning sites tend to mix.
4. The results highlight that this technique represents a new and useful tool for addressing evolutionary questions, breed recognition, assignment, and connectivity assessment of individual eggs, and anchovy population dynamics, for the management of stocks.

     

Body shape variation within and among three species of darters (Perciformes: Percidae)

Abstract –  Using geometric morphometric (GM) techniques, we quantified intra and interspecific variation in female body shape using five collections each of Etheostoma caeruleum Storer, Etheostoma nigrum Rafinesque, and Etheostoma stigmaeum (Jordan). Nested multivariate analysis of variance showed significant variation in body shape among populations (Wilks' Λ = 0.0687, F _144,7585.1 = 19.35, P  < 0.0001), as well as among species (Wilks' Λ = 8.7 × 10⁻⁶, F _24,2 = 28.18, P  = 0.0348). Etheostoma caeruleum displayed greater body depth relative to both E. nigrum and E. stigmaeum , whereas E. nigrum displayed a compressed arrangement of mid-body landmarks relative to both E. stigmaeum and E. caeruleum . The broader implications of these findings highlight the value of geometric morphometrics as both an exploratory and analytical approach. Conclusions drawn from comparisons among moderately differentiated darter species in future studies of body size and shape are likely robust to intraspecific variation within species, and will permit more rigorous investigations into the ecomorphology of these benthic stream fishes.     

Effects of egg stocking density on egg hatchability,larval quality and water quality for pinfish,Lagodon rhomboides,and pigfish,Orthopristis chrysoptera

Pinfish (Lagodon rhomboides Linnaeus) and pigfish (Orthopristis chrysoptera L.) are relatively new, cultured species commonly used as marine baitfish in the south‐eastern United States and currently have no defined protocols for egg incubation. Thus, experiments were conducted to determine efficient egg stocking densities during static and flow‐through incubation that yielded higher quality larvae. Eggs of each species were incubated statically at 250, 500, 1000 and 2000 eggs L^?1, and after incubation, egg hatching success, larval survival to first feeding, larval morphometrics and water quality were assessed. Stocking densities above 250 eggs L^?1 led to significant reductions in pinfish hatching success and water quality degradation, evident from decreased dissolved oxygen and pH levels and increased nitrogenous wastes. Increased stocking densities for pigfish also resulted in significant water quality degradation, although hatching success was unaffected up to a density of 1000 eggs L^?1. A high flow‐through water exchange rate of 2000% daily resulted in significant reductions in nitrogenous wastes and greater stability in dissolved oxygen and pH levels during incubation when compared to static treatments of the same egg density. Additionally, the high exchange rate of 2000% was critical in maintaining high hatching success and larval survival to first feeding at stocking densities of 1000 eggs L^?1 for pinfish and up to 4000 eggs L^?1 for pigfish. No clear patterns in larval morphometrics were observed among stocking densities. Static incubation densities of 250 and 1000 eggs L^?1 are recommended for pinfish and pigfish, respectively.     

Ecological and genetic differentiation among the Arctic charr of Lake Aigneau, Northern Québec

Abstract –  Two modal size groups of sexually mature Arctic charr ( Salvelinus alpinus ) differing in shape and found at different depths in Lake Aigneau in the Canadian sub-Arctic are described and tested for genetic and ecological differentiation. Forms consisted of a small littoral resident, mean size 21.7 cm, and a large profundal resident, mean size 53.9 cm. Mitochondrial DNA analysis indicated that seven of eight haplotypes were diagnostic for either the littoral or profundal fish, with 66.6% of the variation being found within form groupings. Pairwise tests of microsatellite data indicated significant differences in nine of 12 loci and a significant difference between the forms across all tested loci. Molecular variation was partitioned to 84.1% within and 15.9% between forms and suggestive of either restricted interbreeding over time or different allopatric origins. Stable isotope signatures were also significantly different, with the profundal fish having higher δ¹³C and δ¹⁵N values than the littoral fish. Overlap and separation, respectively, in the range of form δ¹³C and δ¹⁵N signatures indicated that carbon was obtained from similar sources, but that forms fed at different trophic levels. Littoral fish relied on aquatic insects, predominantly chironomids. Profundal fish were largely piscivorous, including cannibalism. Predominantly empty stomachs and low per cent nitrogen muscle-tissue composition among profundal fish further indicated that the feeding activity was limited to the winter when ice-cover increases the density of available prey at depth. Results provide evidence of significant differences between the modal groups, with origins in both genetics and ecology.