Differential timing of larval starvation effects on filtration rate and growth in juvenile Crepidula onyx

This study demonstrates that the timing of larval starvation did not only determine the larval quality (shell length, lipid content, and RNA:DNA ratio) and the juvenile performance (growth and filtration rates), but also determine how the latent effects of larval starvation were mediated in Crepidula onyx. The juveniles developed from larvae that had experienced starvation in the first two days of larval life had reduced growth and lower filtration rates than those developed from larvae that had not been starved. Lower filtration rates explained the observed latent effects of early larval starvation on reduced juvenile growth. Starvation late in larval life caused a reduction in shell length, lipid content, and RNA:DNA ratio of larvae at metamorphosis; juveniles developed from these larvae performed poorly in terms of growth in shell length and total organic carbon content because of “depletion of energy reserves” at metamorphosis. Results of this study indicate that even exposure to the same kind of larval stress (starvation) for the same period of time (2 days) can cause different juvenile responses through different mechanisms if larvae are exposed to the stress at different stages of the larval life.     

Genetics of growth in blue mussels: family and enzyme-heterozygosity effects

Shell length and electrophoretic heterozygosity at six enzyme loci were scored in juveniles of 30 hatchery-grown families and in adults of 10 field-grown families of the blue mussel Mytilus edulis. A total of 4 809 offspring were scored. We found no consistent pattern in the correlations between shell length and enzyme heterozygosity among sibs within families. However, a significant family effect on shell length was observed, suggesting an influence of background genotype on this character. A family effect on viability was also observed. When the environment and family effects were accounted for, a small positive correlation between heterozygosity and shell length at the juvenile stage remained. This correlation was significant in one of the three experiments. No such correlation was evident at the adult stage. Our interpretation of these results is that electrophoretic alleles appear to have no direct of independent effect of their own on growth. We suggest that the negative correlation of homozygosity with these characters, seen in natural populations, results from homozygosity for hidden recessive deleterious genes with which the electromorphs are in a steady state of quasilinkage disequilibrium.     

Comparative effects of two antifouling paints on the oyster Crassostrea gigas

The effects of two antifouling paints, one containing organotin compounds, the other copper oxide, were studied from September 1983 to October 1984 on Crassostrea gigas (Thunberg) grown under natural field conditions in the Bay of Arcachon, France. The organotin paint reduced growth rate expressed as weight, length and width, but did not affect shell height; it drastically decreased the dry condition factor and shell density, but did not affect the viability of embryos and larvae from exposed oysters. However, some decrease in larval growth rate was observed. The copper paint had no effect on oyster growth, but lowered the condition factor compared to controls. Neither viability of embryos or larvae nor larval growth were affected by this paint.     

Growth and mortality in young larval herring (Clupea harengus); effects of repetitive changes in food availability

Following yolk resorption, laboratory-reared larval Baltic herring (Clupea harengus L.) were exposed to two sequences of food restriction for 5 d and re-alimentation for 10 d. Comparisons regarding larval growth (standard length and content of water-soluble protein), mortality and content of the sum of trypsin and trypsinogen were made with larvae at a continuous high ration. Larvae exposed to varying prey abundance grew less in length than the control, and during the second high-ration period (Day 22 to 32) growth in length ceased. From the first low-ration period onwards, the content of water-soluble protein in these larvae was lower than that of the control larvae, and the survival rate of the low-high ration group was 59% compared to 77% in the larvae at a continuous high ration. In contrast, the effects of varying food availability were minor on larval content of trypsin and trypsinogen. Results are compared with previous findings in larval Clyde herring, and the effects of larval stock and timing and duration of food restriction on larval growth performance are discussed.     

Genetic variation and covariation during larval and juvenile growth in Mercenaria mercenaria

Quantitative genetic variances and covariances were estimated for shell length of the hard clam Mercenaria mercenaria (L.) at three larval stages (prodissoconch I, 2 d and 10 d post-fertilization) in 1987 and in 1988 after ca. 9 mo of growth. At each sample interval additive genetic variance was a highly significant component of the total size variation. Narrow sense heritability estimates for shell length ranged between 0.58 (±0.10) for prodissoconch I and 1.08 (±0.29) for 2-d-old larvae. There was significant and positive genetic covariance in prodissoconch I and 2-d larval shell length which resulted in a highly significant genetic correlation (r _g=0.74) between these two traits. This covariance is not surprising since the prodissoconch I comprises the majority of the larval shell of a 2-d-old larvae. The genetic covariances between 2-d-old and 10-d-old larvae and between 10-d-old larvae and 9-mo-old juveniles were low and not significantly different from zero. These results indicate that there is substantial genetic variation for shell growth in M. mercenaria but this variation is not stable during development; the genetic variation in shell growth at one stage of development is not strongly related to the genetic variation in growth during other ontogenetic periods. In this study there were no evident constraints to natural selection for increased shell growth rate during development, which coupled with the high levels of genetic variation may suggest that in nature high rates of larval growth may not be normally subject to significant selective pressure.     

Spawning and larval development of the black turban snail Tegula funebralis (Prosobranchia: Trochidae)

An understanding of spawning and larval development can be fundamental to interpreting the abundance, distribution, and population structure of marine invertebrate taxa. Tegula funebralis (A. Adams, 1855), the black turban snail, has been the focus of numerous ecological studies on the Pacific coast of North America. To date, there are only conflicting and anecdotal reports of spawning, and there is no information on larval or juvenile development for this conspicuous and abundant species. On 19 September 1995, two individuals of T. funebralis were observed free-spawning gametes into seawater in tanks at the Oregon Institute of Marine Biology. Embryos and larvae were subsequently reared to metamorphosis and beyond. Development was pelagic and similar to development described for other trochids, and larvae were observed not to feed at any stage. Larvae began to metamorphose at 5.7 to 6.7 d and settled at 260 μm shell length. Juveniles grew ≃ 10 μm in shell length per day and appeared to feed on detritus. Juveniles lacked some adult diagnostic shell characters, including two columellar nodes and a closed umbilicus. In the field, small (<3 mm) juveniles occurred in the adult habitat on all sampling dates between October and March. Small juveniles were found only under rocks and were most abundant under rocks partially buried in coarse sand, suggesting that juveniles may utilize a specific microhabitat within the adult T. funebralis habitat. Received: 7 October 1996 / Accepted: 17 October 1996     

Larval period and its influence on post-larval life history: comparison of lecithotrophy and facultative planktotrophy in the aeolid nudibranch Phestilla sibogae

The variable duration of the pelagic phase of metamorphically competent larvae of benthic marine invertebrates is set by an interaction between environmental factors and larval traits that together influence the chance that a larva will encounter and respond to a suitable settlement site. In the Hawaiian aeolid nudibranch Phestilla sibogae Bergh, an extended competent larval phase resulted in a cascade of negative effects on larval and post-larval life-history traits. When raised as fed (i.e., facultatively planktotrophic) larvae, an extended larval period resulted in lower larval survival, slightly lower metamorphic success, and delayed reproduction. When raised as unfed (i.e., lecithotrophic) larvae, an extended larval period resulted in lower larval and post-larval weights, survival, metamorphic success, and reproductive output, and also resulted in a longer juvenile period and delayed reproduction. The chance nature of locating a settlement site generally spreads these negative effects over all larvae of a cohort, and so balances the relative fitness of the genetic lineages within a population.     

Genotype-dependent fecundity and temporal variation of spawning in hybrid mussel (Mytilus) populations

Mussel samples were collected at 4 to 6 wk intervals throughout 1987 from two hybridMytilus edulis/M. galloprovincialis populations, at Croyde Bay and Whitsand Bay, in southwest England. These were analyzed at two polymorphic loci which are diagnostic for allozyme differences which typifyM. edulis andM. galloprovincialis. Dry mantle weight as a function of shell length was determined for all individuals of each sample. Size-frequency data for the two populations was obtained in September 1987 and March 1988. For all genotypes at both sites, fecundity was a function of shell length, and in both populations the frequency ofM. galloprovincialis alleles was positively correlated with shell length. At both sites, allozyme genotype explained a significant amount of variation in mantle weight either when assessed as a main effect or when assessed as an interaction with shell length or time of collection. At Croyde,M. galloprovincialis mussels had greater estimated fecundity per unit length than theM. edulis mussels. Differences in the timing of spawning activity between theM. edulis and theM. galloprovincialis mussels were inferred, and these differences might act to reduce the amount of interbreeding at Croyde. At Whitsand, a reduced level of variability in the timing of spawning activity and fecundity between the genotypes was observed and explained by a higher degree of genetic mixing. Because theM. galloprovincialis mussels had (1) a greater estimated fecundity at any length, and (2) a greater mean length than theM. edulis mussels, the mean genotypic annual fecundity perM. galloprovincialis mussel was 2.8 times greater than an individualM. edulis mussel at Croyde, and 2.2 times greater than an individualM. edulis mussel at Whitsand. This evidence thatM. galloprovincialis mussels have an advantage in fecundity, and thus perhaps in fertility, taken together with the evidence thatM. galloprovincialis also has a higher viability, indicates directional selection in favour of theM. galloprovincialis phenotype. Because of the observed temporal stability of the population it seems likely that this selection is counterbalanced by a massive imigration ofM. edulis spat from neighbouring populations.     

Genetic consequences of long larval life in the starfish Linckia laevigata (Echinodermata: Asteroidea) on the Great Barrier Reef

Gene flow between populations of the asteroid Linckia laevigata (Linnaeus) was investigated by examining over 1000 individuals collected from ten reefs throughout the Great Barrier Reef (GBR), Australia, for genetic variation at seven polymorphic enzyme loci. Despite geographic separations in excess of 1000 km, Nei's unbiased genetic distance (0 to 0.003) and standardised genetic variation between populations (F _ST) values (mean 0.0011) were small and not significant. Genetic homogeneity among L. laevigata populations is consistent with the long-distance dispersal capability of its 28 d planktonic larval phase, and is greater than that observed for other asteroid species, including another high-dispersal species, Acanthaster planci, which has a 14 d larval phase. Variation within populations was also higher than previously recorded for asteroids (mean heterozygosity=0.384; number of alleles per locus ranged from 5.1 to 6.0 in each population). Among asteroids, dispersal ability is positively correlated with gene flow and levels of variation, and negatively correlated with levels of differentiation.     

Quantitative genetic analysis of growth in larval scallops (Placopecten magellanicus)

We estimated the broad-sense heritability of larval size in 20 full-sib families of the giant scallop, Placopecten magellanicus (Gmelin, 1791) grown in laboratory culture in August and September 1991. The goal was to compare scallops with other bivalves which have been shown to have significant heritabilities for larval growth. Secondly, we estimated the lipid content of occytes from female parents, since this is hypothesized to affect larval growth and survival. Finally, we estimated the among-family variation in mortality from 4 to 21 d as a test of possible genetic variation for viability among larval scallops. Significant genetic variation (h²=1.10 to 1.24) was estimated for larval shell length at 4, 14, and 21 d. There was a significant correlation (r=0.66) between larval size at 4 d and lipid content of oocytes, but only when two females with high levels of lipid oocyte^–1 were excluded as outliers. There was no correlation between larval size at 14 and 21 d and lipid content of oocytes. Mortality among families from 4 to 21 d was high (69 to 97%), and was significantly different among families. These results indicate that there is significant heritability for larval growth which is largely independent of the lipid content of the oocytes. A high heritability for larval growth may indicate that this trait is only weakly correlated with fitness.     

Morphometric and electrophoretic analysis of 13 populations of Anatolian black pine in Turkey

The genetic variation in populations of Anatolian black pine (Pinus nigra Arn. subsp. pallasiana (L.) Holmboe.), one of the species covering large areas in Turkey, was investigated. Open pollinated seeds were collected from 13 populations in a natural distribution range. Six characters of seeds (length, width, ratio of length to width, weight/1000 seeds) and seedling characters (cotyledon number and hypocotyls height) and two enzyme systems viz. leucine aminopeptidase (LAP) and glutamate oxaloacetate transaminase, (GOT) were investigated. Significant differences were detected among the populations for the morphological characters. In addition, isozyme patterns of two enzyme systems revealed that LAP has two loci (one with 2 alleles and the other with 3), while GOT has three loci (two with 3 alleles and the third one with 2 alleles). Polymorphic loci were 74% on the average. The mean number of alleles per loci was 1.94 and expected heterozygosity was 19%. The mean total genetic diversity was calculated as 0.203; the mean gene diversity within populations was determined as 0.188, and the average between subpopulations diversity was 0.016. The relative magnitude of genetic differentiation among subpopulations was measured as 0.074 indicating that only 7.4% of the total genetic diversity was there between populations. Average genetic distance was 0.093 according to Gregorius. Nei's genetic distance was 0.022.     

Inbreeding and Outbreeding Depression in Natural Populations of Chamaecrista fasciculata (Fabaceae)

Abstract: The deleterious consequences of inbreeding have been well documented. There are, however, few empirical studies that have examined the consequences of restoring heterozygosity and hence the fitness of inbred populations by conducting interpopulation crosses and measuring the performance of later-generation hybrids under field conditions. We conducted interpopulation crosses of 100 m to 2000 km, which spans the range of Chamaecrista fasciculata ( Fabaceae) in eastern North America. We then contrasted the performance of the F1 and later-segregating F3 hybrids with the parental generation. We found almost universal F1 superiority over the parents. The F3 hybrids suffered a loss of fitness compared to the F1 hybrids. The drop off in fitness of the F3 reflects both the loss of heterozygosity and the disruption of coadapted gene complexes. The F3 performance, however, was still often equal to that of the parents, suggesting that heterosis can outweigh the loss of coadaptation except for the longest-distance crosses. In a subset of environments, the F3 performance of long-distance (≥1000 km) interpopulation crosses was less than that of both parents and indicated true outbreeding depression. For C. fasciculata , it appears that crossing populations of up to intermediate distances of hundreds of kilometers has a short-term beneficial effect on progeny performance through F1, and that longer-term effects are not necessarily disruptive of fitness, at least relative to parental performance. The degree of F1 heterosis and F3 outbreeding depression varied between site and year, however, indicating an important role for the environment in the expression of these effects.     

Use of Linkage Disequilibrium Data to Estimate Effective Size of Hatchery and Natural Fish Populations

A primary parameter in the assessment of the viability of a population is its effective population size ( Ne ). Allozyme analysis of four groups of fishes provided data on linkage disequilibrium, which were then used to estimate Ne . The groups included hatchery samples of juvenile white seabass, Atractoscion nobilis , juvenile rainbow trout, Oncorhynchus mykiss , from the Shasta Hatchery, and juvenile chinook salmon, O. tshawytscha , from the Coleman National Fish Hatchery. The fourth sample consisted of juvenile chinook salmon from the threatened winter run in the upper Sacramento River. The groups of fish were chosen to represent different applications of the methodology to conservation of fishes. For a variety of reasons. Ne may be considerably lower than census counts of fish present in the parental populations. The Ne of the hatchery broodstock that produced the sample of juvenile white seabass was estimated to be approximately 10, although 25 adult white seabass were present in a mass spawning tank. Ne estimates for the parental populations of the Shasta and Coleman Hatchery samples were 35.8 and 132.5, respectively. The actual number of fish spawned at the Shasta Hatchery was approximately 40, whereas nearly 10,000 salmon were spawned at the Coleman Hatchery. The threatened winter run of chinook salmon had an estimated Ne of 85.5 and an approximate run size of 2000 salmon. The method of estimating effective population size from linkage disequilibrium data appears to result in realistic estimates of effective population size when adequate sample size and a sufficient number of polymorphic loci are available.     

Paternal age and offspring growth: separating the intrinsic quality of young from rearing effects

Younger individuals are often less successful in reproduction than older ones. This might be because of improving breeding skills with age or because the genetic quality of young or early maternal effects on them vary with parental age. However, no attempt has been made to experimentally separate these processes in vertebrates. We conducted a cross-fostering experiment in collared flycatchers (Ficedula albicollis) in three breeding seasons to disentangle origin- and rearing-related effects of paternal age on chick growth, while controlling for date-specific environmental conditions as well as differences in clutch and brood size. The age of the male at the nest of origin, but not that of the rearing male, had a year-dependent effect on nestling body mass and tarsus length. In two seasons, young of subadult males grew slower in the early linear phase of growth than young of adult males. There was no compensatory growth in the final asymptotic phase, so both body mass and tarsus length before fledging reflected the differential early development. In the remaining year, the age of the male at the nest of origin had no significant effect on chick growth. The environment-dependent origin effect we detected was unexplained by incubation times, hatching asynchrony, chick masses at swapping or previously described age-dependent egg quality patterns. Our results therefore suggest a genotype × environment interaction on the relative development of offspring sired by subadult and adult males. Our results also raise the possibility that female birds may gain genetic benefits by mating with older males. Further studies should identify general patterns of male age-dependent female mate choice and offspring quality in different environmental conditions.     

Spatio-temporal patterns in the genetic structure of recently settled blue mussels (<Emphasis Type="Italic">Mytilus</Emphasis> spp.) across a hybrid zone

Previous studies of a hybrid zone between the mussels Mytilus edulis Linnaeus and M. galloprovincialis Lamarck have not resolved the relative importance of the genetic composition of settling larval cohorts versus post-settlement selection in determining the distribution of the parental species and their hybrids. In the present study, recently settled mussels (spat) were collected from 20 sites in southwest England throughout the summer and fall (May–October) in 1998 and 1999. This study investigated the spatio-temporal patterns of settlement and genetics of mussel spat by genetically identifying M. edulis, M. galloprovincialis and their hybrids using the diagnostic PCR marker Glu-5. Settlement was observed earlier in populations of M. edulis than in populations of M. galloprovincialis. Settlement occurred in hybrid populations at times intermediate to and overlapping with both of the parental populations. Temporal genetic variation within years was rare at most sites, while there was some variation between the two years. Spatial genetic variation, however, was common among spat settling within the hybrid populations and matched that observed in small, sub-adults at the same sites. No consistent directional changes in allele frequency were observed over the course of several weeks after settlement. These data suggest that the observed spatial variation in the adult populations is the result of spatial variation in settling larval cohorts and not of either temporal genetic variation or of selection soon after settlement.Communicated by J.P. Grassle, New Brunswick     

Mutation and Conservation

Mutation can critically affect the viability of small populations by causing inbreeding depression, by maintaining potentially adaptive genetic variation in quantitative characters, and through the erosion of fitness by accumulation of mildly detrimental mutations. I review and integrate recent empirical and theoretical work on spontaneous mutation and its role in population viability and conservation planning. I analyze both the maintenance of potentially adaptive genetic variation in quantitative characters and the role of detrimental mutations in increasing the extinction risk of small populations. Recent experiments indicate that the rate of production of quasineutral, potentially adaptive genetic variance in quantitative characters is an order of magnitude smaller than the total mutational variance because mutations with large phenotypic effects tend to be strongly detrimental. This implies that, to maintain normal adaptive potential in quantitative characters under a balance between mutation and random genetic drift (or among mutation, drift, and stabilizing natural selection), the effective population size should be about 5000 rather than 500 (the Franklin-Soulé number). Recent theoretical results suggest that the risk of extinction due to the fixation of mildly detrimental mutations may be comparable in importance to environmental stochasticity and could substantially decrease the long-term viability of populations with effective sizes as large as a few thousand. These findings suggest that current recovery goals for many threatened and endangered species are inadequate to ensure long-term population viability.     

Strong maternal effects and extreme heterogeneity of progeny development in the caridean shrimp Sclerocrangon boreas (Crangonidae)

Sclerocrangon boreas is uncommon among marine coastal carideans in having a non-dispersing, abbreviated (2-stage) larval phase. We investigated the implications of this strategy in terms of fecundity, offspring provisioning and brood care in S. boreas from the St. Lawrence Gulf and Estuary in 2009–2010. Fecundity scaled positively to female body size but was low due to the production of large, lipid-rich eggs. Offspring size at all stages of development was positively related to female size. Larval traits and lipid dynamics indicate obligatory lecithotrophic development from hatching to juvenile. The larva becomes a juvenile on the mother and remains associated with her for sometime after. The co-occurrence of early egg stages among many juveniles in some clutches raises the possibility that maternal care of juveniles includes the provisioning of trophic eggs or eggs reclaimed from other females.     

Genetic differentiation of Texas Gulf Coast populations of the blue crab Callinectes sapidus

Allelic frequencies at three polymorphic, enzyme-encoding gene loci (GOT-2, EST-1, EST-2) were determined for Callinectes sapidus (Rathbun) megalopae and adults sampled along the Texas coast of the Gulf of Mexico. Significant temporal and spatial variation was observed at all three loci. Primary findings included: (1) megalopal allelic frequencies often differed significantly from those observed among neighboring adult populations; (2) larval allelic frequencies appeared to vary seasonally, with populations showing sharp differences in the summer months but tending to be more homogeneous in winter; (3) allelic frequencies among adult populations were significantly heterogeneous, but only one locus (EST-2) showed significant temporal variation; (4) juvenile and adult crabs sampled within one bay showed no size-specific differences in allelic frequencies. The spatial heterogeneity in allelic frequencies suggests that interpopulation gene flow is not sufficient to overcome population differentiation resulting from genetic drift and/or natural selection. Temporal variation in larval allelic frequencies suggests seasonal changes in larval source populations which may result from population differences in spawning season or developmental times or from seasonal changes in coastal current patterns.     

Interaction of genotype and salinity in larvae of the oyster Crassostrea virginica

Adult Crassostrea virginica were obtained from 4 populations and spawned in the laboratory. The larvae from the within-population crosses and the hybrid crosses were raised at 4 salinities. There were no significant differences in survival of the larvae between the populations. However, one set of hybrids did show overdominance in survival. There were genetic differences between the populations in growth rate, but the expression of the differences depended upon the salinity, i.e, there was significant genotype-environment interaction. There were expressions of nonadditive genetic effects in the hybrid crosses, but the direction and magnitude was dependent upon the salinity. There was as much difference between populations from the same estuary as there was between populations from geographically isolated populations.     

Translocations and the Preservation of Allelic Diversity

Translocation is a tool commonly used for the conservation of threatened and endangered fish species. Despite extensive use, the biological implications of translocation remain poorly understood. Of particular interest is the effect of translocation on genetic variability. Maintenance of genetic variability in these "refuge" populations is assumed to be important for both short- and long-term success. We examined allozyme variability at 16 loci for western mosquitofish ( Gambusia affinis ) populations with known histories of introduction. Refuge populations had significantly lower levels of heterozygosity. Refuge populations also had considerably lower levels of allelic diversity than parental populations. All losses were of relatively rare alleles (frequency less than 0.1 in parental population). These losses were probably due to an undocumented bottleneck early in the introduction history. These results were surprising because the initial transplant involved 900 fish and because mosquitofish have numerous reproductive traits that should minimize the effects of bottlenecks on genetic diversity. A literature review revealed that genetic variability is often reduced in refuge populations and that such reductions typically involve the loss of alleles. We suggest that translocated populations be examined periodically for losses of genetic variability.