Early Life History Traits Research Articles

Strong gene flow and lack of stable population structure in the face of rapid adaptation to local temperature in a spring-spawning salmonid, the European grayling (Thymallus thymallus).

Gene flow has the potential to both constrain and facilitate adaptation to local environmental conditions. The early stages of population divergence can be unstable because of fluctuating levels of gene flow. Investigating temporal variation in gene flow during the initial stages of population divergence can therefore provide insights to the role of gene flow in adaptive evolution. Since the recent colonization of Lake Lesjaskogsvatnet in Norway by European grayling (Thymallus thymallus), local populations have been established in over 20 tributaries. Multiple founder events appear to have resulted in reduced neutral variation. Nevertheless, there is evidence for local adaptation in early life-history traits to different temperature regimes. In this study, microsatellite data from almost a decade of sampling were assessed to infer population structuring and its temporal stability. Several alternative analyses indicated that spatial variation explained 2-3 times more of the divergence in the system than temporal variation. Over all samples and years, there was a significant correlation between genetic and geographic distance. However, decomposed pairwise regression analysis revealed differing patterns of genetic structure among local populations and indicated that migration outweighs genetic drift in the majority of populations. In addition, isolation by distance was observable in only three of the six years, and signals of population bottlenecks were observed in the majority of samples. Combined, the results suggest that habitat-specific adaptation in this system has preceded the development of consistent population substructuring in the face of high levels of gene flow from divergent environments.

Variability in water temperature affects trait-mediated survival of a newly settled coral reef fish

As animals with complex life cycles metamorphose from one stage to the next, carry-over effects from earlier stages can affect future mortality. To examine the relationship between early life history traits and survival, seven monthly cohorts of newly-settled bluehead wrasse Thalassoma bifasciatum were collected immediately after settlement and over sequential 3-day periods. Otolith analysis was used to quantify mean larval and juvenile growth rates, pelagic larval duration (PLD), and settlement size and condition of different age classes to identify the traits most important for survival. Overall, survivors tended to have shorter PLDs, to settle at smaller sizes and higher condition levels, and to exhibit faster early juvenile growth. Water temperature contributed to among-cohort variability in traits as warmer water led to faster larval and juvenile growth and shorter PLDs. Trait-specific fitness functions demonstrated that temperature can influence fitness by changing the nature of selection on each trait. Estimates of selection intensity revealed that settlement condition contributed the most to variation in fitness across cohorts, followed by juvenile growth. Frequent loss of low settlement condition individuals and occasional loss of the very highest condition fish suggest that particularly high settlement condition during the warmest temperatures may be detrimental. Not only does the quality of settlers vary over time, but selective loss of individuals with particular phenotypic traits is not pervasive and can vary with environmental conditions such as temperature.

Temporal variability of larval growth, size, stage duration and recruitment of a wrasse, <i>Coris julis</i> (Pisces: Labridae), from the Azores

SUMMARY: Temporal variability in the size at settlement (SAS), age at settlement (PLD), larval growth and recruitment patterns of a temperate wrasse, Coris julis, were examined over two recruitment seasons for a single island site from the Azores archipelago in the northeastern Atlantic. Relationships between these early life-history traits and recruitment variability over time were also investigated. Average PLD and SAS varied significantly among sampling dates over the settlement season, increasing consistently over time. This pattern was persistent over two consecutive summers. Larval growth was not a good predictor for PLD or SAS, which were in turn positively correlated with each other. Differences in recruitment magnitude over time were not related to SAS, PLD or larval growth. Instead, we found that recruits whose early pelagic stage (first 30 d) overlapped part of a period of enhanced growth (above average and independent of larval age), tended to result in the largest recruitment events; these tended to occur in the mid season. Larvae from earlier and later settlement events, overlapping periods of depressed growth, were linked to more modest recruitment events. We hypothesize that short PLD, with resulting small SAS is favoured early in the season, when post-settlement density is lowest. Over the course of the settlement season, as recruits accumulate competition may increase, and larger SAS (associated with longer PLD), may provide a competitive/survival advantage.

The genetics of adaptation to novel environments: selection on germination timing in Arabidopsis thaliana

When studying selection during adaptation to novel environments, researchers have often paid little attention to an organism's earliest developmental stages. Despite this lack of attention, early life history traits may be under strong selection during colonization, as the expression of adaptive phenotypes at later points is contingent upon early survival. Moreover, the timing of early developmental transitions can constrain the timing of later transitions, with potentially large effects on fitness. In this issue, Huang et al. (2010) underscore the importance of early life history traits in the adaptation of Arabidopsis thaliana to old-field sites in North America. Using a new population of mapped recombinant inbred lines, the authors examined germination timing and total lifetime fitness of A. thaliana while varying site latitude, dispersal season, and maternal photoperiod. Huang et al. (2010) discovered several Quantitative Trait Loci (QTL) with large effects on fitness that colocalized with QTL for field germination timing and seed dormancy-demonstrating that fitness is genetically associated with these early life history traits, and that these loci are likely under strong selection during adaptation to novel environments. In the epistatic interactions of some loci, recombinant genotypes outperformed parental genotypes, supporting the potentially adaptive role of recombination. This study provides elegant evidence that traits expressed early in an organism's development can play an important role during adaptive evolution.

Early Life History Variation among Hatchery‐ and Wild‐Origin Lake Trout Reared in a Hatchery Environment

AbstractHatcheries play a key role in augmenting populations for conservation, harvest, or both, although rapid domestication and adaptation to hatchery conditions may lead to fish that are maladapted to natural environments. Three processes may lead to domestication: (1) negative selection against fish adapted to wild environments, (2) positive selection for fish that thrive in artificial conditions, or (3) relaxation of selection pressures. In this study, early life history traits and survival were contrasted among wild‐ and hatchery‐origin lake trout Salvelinus namaycush reared in a common hatchery environment to address the hypotheses of processes leading to domestication. Examination of egg size, egg survival, fry deformity, and early growth rate found no evidence of negative selection against wild‐origin lake trout or positive selection for hatchery‐origin lake trout when reared in a hatchery environment. Wild‐origin lake trout outperformed hatchery‐origin fish in all life history traits examined, suggesting that relaxation of natural selective pressures may be occurring in the hatchery environment. Furthermore, the hatchery‐origin strains failed to show maternal effects on egg size and exhibited limited variability in egg size and hatching time, as well as no significant differences in early growth rate, suggesting potential homogenization of life history traits as a result of the hatchery environment.

Discovery and application of insertion-deletion (INDEL) polymorphisms for QTL mapping of early life-history traits in Atlantic salmon

BackgroundFor decades, linkage mapping has been one of the most powerful and widely used approaches for elucidating the genetic architecture of phenotypic traits of medical, agricultural and evolutionary importance. However, successful mapping of Mendelian and quantitative phenotypic traits depends critically on the availability of fast and preferably high-throughput genotyping platforms. Several array-based single nucleotide polymorphism (SNP) genotyping platforms have been developed for genetic model organisms during recent years but most of these methods become prohibitively expensive for screening large numbers of individuals. Therefore, inexpensive, simple and flexible genotyping solutions that enable rapid screening of intermediate numbers of loci (~75-300) in hundreds to thousands of individuals are still needed for QTL mapping applications in a broad range of organisms.ResultsHere we describe the discovery of and application of insertion-deletion (INDEL) polymorphisms for cost-efficient medium throughput genotyping that enables analysis of >75 loci in a single automated sequencer electrophoresis column with standard laboratory equipment. Genotyping of INDELs requires low start-up costs, includes few standard sample handling steps and is applicable to a broad range of species for which expressed sequence tag (EST) collections are available. As a proof of principle, we generated a partial INDEL linkage map in Atlantic salmon (Salmo salar) and rapidly identified a number of quantitative trait loci (QTLs) affecting early life-history traits that are expected to have important fitness consequences in the natural environment.ConclusionsThe INDEL genotyping enabled fast coarse-mapping of chromosomal regions containing QTL, thus providing an efficient means for characterization of genetic architecture in multiple crosses and large pedigrees. This enables not only the discovery of larger number of QTLs with relatively smaller phenotypic effect but also provides a cost-effective means for evaluation of the frequency of segregating QTLs in outbred populations which is important for further understanding how genetic variation underlying phenotypic traits is maintained in the wild.

Intergenomic epistasis causes asynchronous hatch times in whitefish hybrids, but only when parental ecotypes differ

Support for the theory of ecological speciation requires evidence for ecological divergence between species which directly or indirectly causes reproductive isolation. This study investigates effects of ecological vs. genetic disparity of parental species on the presence of endogenous selection (deformation and mortality rates) and potential sources of exogenous selection (growth rates and hatch timing) on hybrids. Hybrid embryonic development is analysed in a common-garden full-sib cross of three species belonging to two different ecotypes within the Coregonus lavaretus species flock in the central Alpine region of Europe. Although hatch timing was similar across the three species, embryonic growth rates and egg sizes differed between ecotypes. This led to a mismatch between embryonic growth rate and egg size in hybrid crosses that reveals epistasis between the maternal and embryonic genomes and transgressive hatch times that were asynchronous with control crosses. A strong constraint of egg size to embryo size at late development was also evident. We argue that this demonstrates potential for coadaptation of a maternal trait (egg size) with offspring growth rate to be an important source of selection against hybridization between ecotypes with different egg sizes. Implications for the measurement and quantification of early life-history traits affected by this additive relationship, such as hatch day and larval size, are also discussed.

Early ontogeny shows the same interspecific variation as natural history parameters in the crested newt (Triturus cristatus superspecies) (Caudata, Salamandridae)

When the phenotypic divergence within a monophyletic group is characterised by parallel variation of different phenotypic traits, it is very likely that the environment through constraints and/or selection has affected the developmental pathways simultaneously. Such patterns of phenotypic divergence characterise the phenotypic evolution of the crested newts (Triturus cristatus superspecies). In this study, we have examined interspecific variations in the embryonic development of four crested newt species. The species are similar with respect to some basic developmental traits, some morphologically defined developmental stages and the survival rate during early embryogenesis. However, there is significant variation in the developmental rate, as well as differences in the pattern of correlation amongst analysed life-history and developmental traits. Consistent with previous studies, T. dobrogicus appears to be an outlier species, with the longest embryonic period and a significantly different correlation pattern for early life-history and developmental traits. We suggest that the invasion of a novel aquatic environment by T. dobrogicus resulted in large-scale directional changes in development, which could explain parallel change in numerous phenotypic and life-history traits with a high rate of evolution.

Clues to the location of the spawning area and larval migration characteristics of Anguilla mossambica as inferred from otolith microstructural analyses

The spawning area location and the larval migration characteristics of Anguilla mossambica were studied through the examination of early life-history traits (ELHT) inferred from otolith microstructural analyses of 122 glass A. mossambica collected along the eastern coast of Madagascar, in the south-western Indian Ocean. Backcalculated hatching dates of leptocephali that recruited between November 2005 and February 2006 suggested that spawning was continuous from June to November 2005, although individual migration duration periods were variable. Larvae that exhibited the highest daily otolith growth rates had the shortest leptocephalus durations and total length (L(T)) at recruitment, possibly because they reached the competence to metamorphose more rapidly and to recruit to fresh waters. Migration durations and L(T) increased from north to south on the Malagasy eastern coast, supporting earlier suggestions that A. mossambica spawns north-east of Madagascar, west of the Mascarene Ridge in the Indian Ocean.

Egg trait variation in anchoveta Engraulis ringens: a maternal response to changing environmental conditions in contrasting spawning habitats

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 381:237-248 (2009) - DOI: https://doi.org/10.3354/meps07922 Egg trait variation in anchoveta Engraulis ringens: a maternal response to changing environmental conditions in contrasting spawning habitats L. R. Castro1,2,*, G. Claramunt3, M. C. Krautz1,4, A. Llanos-Rivera1,5, P. Moreno3 1Laboratorio de Oceanografía Pesquera y Ecología Larval, Departamento de Oceanografía, 2Centro FONDAP-COPAS, and 4Programa de Doctorado en Oceanografía, Universidad de Concepción, PO Box 160-C, Concepción, Chile 3Departamento de Ciencias del Mar, Universidad Arturo Prat, Casilla 121, Iquique, Chile 5Present address: Unidad de Biotecnología Marina, Faculdad de Ciencias Naturales e Oceanográficas, Universidad de Concepción, PO Box 160-C, Concepcíon, Chile *Email: lecastro@udec.cl ABSTRACT: The Engraulis ringens distribution (4 to 42°S) covers a wide variety of environmental conditions. We assessed the coping mechanisms used by this anchoveta in different spawning habitats, reporting differences in egg traits between populations off northern (Iquique, 20°S) and southern Chile (Talcahuano, 36°S) and throughout the spawning season. Eggs were smaller off Iquique, declined in size during the reproductive season (both populations), and inter-population differences persisted throughout the spawning season. Batch fecundity (eggs per batch per female) and relative fecundity (eggs per female weight) were lower off Talcahuano during the peak spawning months. Thus, larger eggs spawned in the southern population seem to be produced at the cost of a reduction in fecundity. The eggs also differed biochemically between the 2 populations; total lipids and triacylglycerides were much higher off Talcahuano. The biochemical composition (both populations) also changed throughout the spawning season, with higher lipids early in the spawning season (July to August) off Talcahuano. Hatching success decreased during the spawning season, and correlated positively with egg size and lipid contents. Environmental conditions differed markedly between spawning areas and from mid-winter to late spring. Off Talcahuano, the temperature and winter-time water column productivity are lower and turbulence is higher, while eggs are larger, lipid contents higher, and batch fecundity lower. This mechanism seems to facilitate survival of young offspring in the more adverse winter conditions off Talcahuano. These egg characteristics are determined by the adult female reproductive system, representing a maternal influence on the early life-history traits of anchoveta that might enable rapid changes in population densities in some years of improved habitat conditions. KEY WORDS: Anchoveta · Engraulis ringens · Upwelling · Reproductive strategy · Egg quality · Lipids · Humboldt Current · Small pelagic fishes Full text in pdf format PreviousNextCite this article as: Castro LR, Claramunt G, Krautz MC, Llanos-Rivera A, Moreno P (2009) Egg trait variation in anchoveta Engraulis ringens: a maternal response to changing environmental conditions in contrasting spawning habitats. Mar Ecol Prog Ser 381:237-248. https://doi.org/10.3354/meps07922 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 381. Online publication date: April 17, 2009 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2009 Inter-Research.

Sources of phenotypic variance in egg and larval traits in a marine invertebrate

Contrary to many separate sex systems, the evolutionary ecology of polyandry in simultaneous hermaphrodites, and in particular in those with internal fertilization, has received little attention. Recent studies on the promiscuous gastropod Chelidonura sandrana showed that offspring size, an important determinant of offspring performance in many marine invertebrates, varies with the number of different mating partners. However, the source of this differential allocation by mothers remained unclear. Using a quantitative genetic model, we here tested for parental effects on offspring size and the importance of ‘good gene’ effects on early life history traits. Our analysis revealed no significant sire but strong dam effects for all investigated traits. Moreover, embryo viability tended to increase with egg capsule volume, thus linking offspring size with offspring performance. Our findings suggest that in C. sandrana (1) differential allocation is a maternal effect in response to the number of different partners, and that (2) additive genetic variance is of negligible importance in early life history traits.

Fast versus Slow Larval Growth in an Invasive Marine Mollusc: Does Paternity Matter?

Reproductive strategies and parental effects play a major role in shaping early life-history traits. Although polyandry is a common reproductive strategy, its role is still poorly documented in relation to paternal effects. Here, we used as a case study the invasive sessile marine gastropod Crepidula fornicata, a mollusc with polyandry and extreme larval growth variation among sibling larvae. Based on paternity analyses, the relationships between paternal identity and the variations in a major early life-history trait in marine organisms, that is, larval growth, were investigated. Using microsatellite markers, paternities of 437 fast- and slow-growing larvae from 6 broods were reliably assigned to a set of 20 fathers. No particular fathers were found responsible for the specific growth performances of their offspring. However, the range of larval growth rates within a brood was significantly correlated to 1) an index of sire diversity and 2) the degree of larvae relatedness within broods. Multiple paternity could thus play an important role in determining the extent of pelagic larval duration and consequently the range of dispersal distances achieved during larval life. This study also highlighted the usefulness of using indices based on fathers' relative contribution to the progeny in paternity studies.

Impact of salinity on early life history traits of three estuarine fish species in Senegal

The adaptive mechanisms on the early life stages of fishes to hypersaline stress are still poorly understood and probably determine the resistance of a population to disruption, compared with other less plastic species. The Casamance River in Senegal is an ideal location to test the adaptation to salinity as a dam was built in 1998 to exclude saline water intrusion. This lowered the salinity from 70 to 5 upstream and 60 downstream. The salinity influence on the growth in the early life of three West African fish species ( Ethmalosa fimbriata, Sarotherodon melanotheron, and Tilapia guineensis) was studied using the width of microstructures in the otoliths and the individual migratory behaviour analysed from strontium (Sr) to calcium (Ca) ratios in the otoliths. The Sr:Ca ratio was quantified along individual transects measured from the posterior edge of the otolith to the core. The fishes were sampled on both sides of the dam that separated water with low salinity upstream from metahaline and hyperhaline water downstream. The results showed that salinity has different influence on the growth of each species. Ethmalosa fimbriata has the highest growth during the first 180 days in the freshwaters, indicating growth inhibition in the hyperhaline areas. For the two other species no growth difference were found. The Sr/Ca ratio varied widely, in Tilapia and Sarotherodon from below the dam. Individual life histories were more heterogeneous than upstream and showed a crossing of the dam for some individuals which could reach half of the fishes analysed. On the contrary in E. fimbriata, despite the large range of salinity, identical Sr/Ca profiles were found both upstream and downstream. This indicated that Sr/Ca ratio was not appropriate to evaluate life history patterns linked to salinity for this specie.

Genetic variability in reaction norms between farmed and wild backcrosses of Atlantic salmon (Salmo salar)

Adaptive responses to environmental heterogeneity may vary among populations. Genetic variability in reaction norms might account for population differences in the ability to respond to environmental change and may reflect local adaptation. Reaction norms for early life history traits were compared among three population crosses of Atlantic salmon ( Salmo salar ). Two comprised second-generation backcrosses introgressed with either farmed or wild genes; the third comprised individuals from a second-generation, pure wild cross. Using a common-garden experimental protocol, each cross was exposed to three temperature regimes. Plasticity in embryonic development, growth, survival, and body size was measured from fertilization up to 24 weeks of exogenous feeding. Reaction norms differed markedly among crosses, irrespective of whether individuals interbred with those whose genes originated from another wild population or from a cultured population. We find that introgression involving individuals with comparatively few genetic differences can change reaction norms. If plasticity represents an adaptive response to local environments, then changes to reaction norms resulting from interbreeding between populations are unlikely to have a beneficial effect on fitness.

Local adaptation in brown trout early life-history traits: implications for climate change adaptability

Knowledge of local adaptation and adaptive potential of natural populations is becoming increasingly relevant due to anthropogenic changes in the environment, such as climate change. The concern is that populations will be negatively affected by increasing temperatures without the capacity to adapt. Temperature-related adaptability in traits related to phenology and early life history are expected to be particularly important in salmonid fishes. We focused on the latter and investigated whether four populations of brown trout (Salmo trutta) are locally adapted in early life-history traits. These populations spawn in rivers that experience different temperature conditions during the time of incubation of eggs and embryos. They were reared in a common-garden experiment at three different temperatures. Quantitative genetic differentiation (QST) exceeded neutral molecular differentiation (FST) for two traits, indicating local adaptation. A temperature effect was observed for three traits. However, this effect varied among populations due to locally adapted reaction norms, corresponding to the temperature regimes experienced by the populations in their native environments. Additive genetic variance and heritable variation in phenotypic plasticity suggest that although increasing temperatures are likely to affect some populations negatively, they may have the potential to adapt to changing temperature regimes.

A genetic assessment of polyandry and breeding‐site fidelity in lemon sharks

We here employ 11 microsatellite markers and recently developed litter reconstruction methods to infer mating system parameters (i.e. polyandry and breeding-site fidelity) at a lemon shark nursery site in Marquesas Key, Florida. Four hundred and eight juvenile or subadult sharks were genotyped over eight complete breeding seasons. Using this information, we were able to infer family structure, as well as fully or partially reconstruct genotypes of 46 mothers and 163 fathers. Multiple litter reconstruction methods were used, and novel simulations helped define apparent bias and precision of at least some mating system parameters. For Marquesas Key, we find that adult female lemon sharks display high levels of polyandry (81% of all litters sampled) and stronger fidelity to the nursery site than do males. Indeed, few male sharks sired offspring from more than one litter during the course of the study. These findings were quite similar to previous results from another lemon shark nursery site (Bimini, Bahamas), suggesting conserved mating system parameters despite significant variation in early life-history traits (i.e. body size and growth) among sites. The finding of at least some site fidelity in females also supports the need for careful conservation of each nursery.

Postsettlement survival linked to larval life in a marine fish.

There is a growing realization that the scale and degree of population connectivity are crucial to the dynamics and persistence of spatially structured populations. For marine organisms with complex life cycles, experiences during larval life may influence phenotypic traits, performance, and the probability of postsettlement survival. For a Caribbean reef fish (Thalassoma bifasciatum) on an oceanic island, we used otolith (ear stone) elemental profiles of lead (Pb) to assign recent settlers to a group that developed in waters elevated in Pb concentrations throughout larval life (i.e., nearshore signature) and a group that developed in waters depleted in Pb (i.e., offshore signature), potentially dispersing from upstream sources across oceanic waters. Larval history influenced early life history traits: offshore developers initially grew slowly but compensated with fast growth upon entering nearshore waters and metamorphosed in better condition with higher energy reserves. As shown in previous studies, local production contributed heavily to settlement: at least 45% of settlers developed nearshore. However, only 23% of survivors after the first month displayed a nearshore otolith profile. Therefore, settlers with different larval histories suffered differential mortality. Importantly, selective mortality was mediated by larval history, in that the postsettlement intensity of selection was much greater for fish that developed nearshore, potentially because they had developed in a less selectively intense larval environment. Given the potential for asymmetrical postsettlement source-based survival, successful spatial management of marine populations may require knowledge of "realized connectivity" on ecological scales, which takes into account the postsettlement fitness of individuals from different sources.

Parental effects on fertilization and hatching success and development of Atlantic halibut (Hippoglossus hippoglossus L.) embryos and larvae

The parental effects on fertilization and early life history traits were studied in Atlantic halibut, Hippoglossus hippoglossus L. Sperm from 12 different males were used to fertilize eggs of two females in separate crosses. The fertilization success were generally high, above 80% of developing embryos at 16-cell stage in 20 of 24 crosses with an average of 85.9+/-17.6% and 87.2+/-16.5% for female A and female B, respectively. Corresponding hatching success was 74.8+/-17.7% and 41.6+/-20.1%, respectively. The relationship between fertilization success and hatching success was positive. The parental influence on hatching was dominated by a strong and significant (p<0.001) maternal effect; however, the paternal effect was also significant (p<0.001). Furthermore, there was no relationship between fertilization success, hatching success and larvae viability as a high number of larvae developed locked jaws (i.e., were not functional). There was a significant (p<0.01) difference in yield of functional larvae of female A (43%) and female B (56%), and also between crosses sired by different males. The standard length of offspring of female A (12.4+/-0.5 mm) and B (12.6+/-0.6 mm) were significantly (p<0.001) different, and also significantly influenced by both the female (p<0.001) and the male (p<0.001). The present paper provides strong indications that not only the female, but also the male parent influences quantitative features of early development of their offspring.

Maternal effects vary between source populations in the Atlantic tomcod Microgadus tomcod

Identifying the sources of variation in traits of larvae is one of the first steps in interpreting the role of phenotypic variation in recruitment. We examined the contributions of geographic source and parentage to phenotypic variation in offspring traits in a gadid, Microgadus tomcod, from 2 contrasting yet nearby locations. Adults were collected from the Hudson River (HR), a polluted riverine estuary with strong freshwater and tidal fluxes, and Shinnecock Bay (SB), a relatively clean barrier beach and lagoon system with minimal freshwater inflows. Eggs were stripped from fish in the laboratory and incubated in a common environment. Female and offspring traits varied substantially between populations. Females from SB had a higher ovary weight and gonado-somatic index (GSI) relative to body length, and produced larger eggs. Contrary to expectation, higher female condition did not result in larvae of better condition. SB offspring had smaller yolk reserves at hatch and were less resistant to starvation than offspring from HR, though size at hatching did not differ between the 2 populations. SB offspring took 25% longer to hatch, thereby increasing dependence on yolk reserves as embryos. This may represent a trade-off in time to hatching versus quality at hatching in tomcod from different environments. Geographic source accounted for more variance than maternal effects in time to hatch (90%) and yolk volume at hatch (42%). Maternal influence accounted for more variance in egg diameter (90%), length at hatch (33%) and starvation resistance (30%), though none of these measures was correlated to female size or age. These results emphasize differences in early life history traits across a small geographic scale and the extent to which offspring differences due to maternal effects depend on the local environment.

Temperature-induced shifts in selective pressure at a critical developmental transition

Selective mortality within a population, based on the phenotype of individuals, is the foundation of the theory of natural selection. We examined temperature-induced shifts in the relationships among early life history traits and survivorship over the embryonic and larval stages of a tropical damselfish, Pomacentrus amboinensis. Our experiments show that temperature determines the intensity of selective mortality, and that this changes with ontogeny. The size of energy stores determined survival through to hatching, after which egg size became a good indicator of fitness as predicted by theoretical models. Yet, the benefits associated with egg size were not uniform among test temperatures. Initial egg size positively influenced larval survival at control temperature (29 degrees C). However, this embryonic trait had no effect on post-hatching longevity of individuals reared at the higher (31 degrees C) and lower (25 degrees C) end of the temperature range. Overall, our findings indicate that the outcome of selective mortality is strongly dependent on the interaction between environment conditions and intrinsic developmental schedules.