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1.
This paper reports data on 28 allozyme loci in wild and artificially reared sea bass (Dicentrarchus labrax) samples, originating from either coastal lagoon or marine sites in the Mediterranean Sea. F
ST analysis (θ estimator) indicated strong genetic structuring among populations; around 34% of the overall genetic variation
is due to interpopulation variation. Pairwise θ estimates showed that, on average, the degree of genetic structuring was much
higher between marine populations than between samples from lagoons. Six polymorphic loci showed differences in allele frequencies
between marine and lagoon samples. Multivariate analyses of individual allozymic profiles and of allele frequencies suggested
that different arrays of genotypes prevail in lagoons compared to marine samples, particularly at those loci that, on the
basis of previous acclimation experiments, had been implicated in adaptation to freshwater. On the other hand, variation at
“neutral” allozyme loci reflects to a greater extent the geographic location of populations. Allozyme differentiation was
also studied in a D. labrax population from the Portuguese coast. Average genetic distance between this population and the Mediterranean populations
was quite high (Nei's D = 0.236) and calls into question the taxonomic status of the Portuguese population. Finally, genetic relationships between
D. labrax and D. punctatus were evaluated. Average Nei's D was 0.648, revealing high genetic differentiation between the two species, even for two sympatric populations of these species
in Egypt; thus gene flow was not indicated between species.
Received: 24 October 1996 / Accepted: 27 November 1996 相似文献
2.
We surveyed patterns of allelic variation within twelve samples of the pipi Donax deltoides Lamarck from beaches separated by up to 1200 km but connected to varying degrees by the East Australian Current. We used
these data to test the prediction that the irregular patterns of water movement would cause genetic differentiation in pipis,
so that there would be more genetic variation within and among the more southern regions than the northern regions. We found
that six loci were at least moderately variable within all samples, and there were no clear geographic patterns in allelic
frequencies. In general, genotype frequencies within samples were consistent with predictions for an outcrossed, sexually
reproducing species, and we detected no evidence of population subdivision. Within samples, with the exception of the peptidase
loci, single-locus genotype frequencies were in close agreement with expectations for Hardy–Weinberg equilibrium. We observed
no significant linkage disequilibrium for any pairwise comparison of loci in any sample. Our hierarchical analysis of genetic
variation revealed little variation among all samples (F
st = 0.009). Loci showed consistently low levels of subdivision (F
st from 0.003 to 0.018). We found almost no variation among the four geographic regions sampled (F
rt = 0.001). All variation was therefore attributable to variation among samples within regions (F
sr = 0.010). These data imply that larvae are moving between regions and that levels of present or recent gene flow are high,
and support the conclusions of other studies which have inferred widespread gene flow for animals dispersing via planktonic,
outcrossed larvae in parts of this region. This implies that the East Australian Current is sufficient to produce strong larval
connections despite its intermittent nature. If existing levels of population subdivision reflect current levels of gene flow,
then these data imply that D. deltoides represents a single fishery on the east coast of Australia.
Received: 16 September 1996 / Accepted: 25 September 1996 相似文献
3.
Allozymes were examined in quantitative lunar monthly collections of larval recruits of the western rock lobster Panulirus cygnus George over three recruitment seasons at two sites nearly 350 km apart in Western Australia. At Alkimos, the southern site,
recruitment occurs in a relatively narrow peak early in the spring, whereas at the northern Houtman Abrolhos Islands, recruitment
extends into the summer months. In the 1995/1996 recruitment season, the frequency of the GPI
*
100 allele increased from early to late in the season, but the frequencies were indistinguishable at the two sites in each monthly
collection. The combination of this temporal variation in allelic frequencies with the contrasting patterns of recruitment
at the Abrolhos Islands and Alkimos resulted in genetically different cohorts at the two sites. This pattern was ephemeral,
as it was not repeated in the subsequent two years. Thus, ephemeral genetic patchiness in P. cygnus can be generated by the locally-specific genetic mix of recruits obtained from a common larval pool. This mechanism is the
probable explanation of previously observed temporal and possible spatial genetic variation in adult P. cygnus, and highlights the importance of studying recruitment in order to understand the genetic structure of marine species.
Received: 22 February 1999 / Accepted: 8 June 1999 相似文献
4.
Effects of contrasting modes of larval development on the genetic structures of populations of three species of prosobranch gastropods 总被引:1,自引:0,他引:1
M. G. Hoskin 《Marine Biology》1997,127(4):647-656
In south-eastern Australia, the prosobranch gastropods Morula marginalba (Blainville), Cominella lineolata (Lamarck) and Bedeva hanleyi (Angas) have similar fine-scale distributions, but appear to possess very different dispersal capabilities due to contrasting
modes of larval development. M.marginalba produce planktonic larvae, whereas C. lineolata and B. hanleyi undergo direct development in benthic egg capsules and emerge as crawling juveniles. To test for possible effects of contrasting
life histories on levels of genetic variation within and among populations, a survey was conducted of allozyme variation at
six polymorphic loci in 8 to 9 local populations of each species. Collections of snails were made between June 1992 and November
1993. Sampling ranges spanned between 162 and 180 km of coast. Regardless of larval type, proportions of single-locus genotypes
in each collection were consistent with the recruitment of offspring which had been generated through random mating. However,
genotypic diversity was lower in those species that undergo direct development. Loci surveyed in C. lineolata and B. hanleyi were polymorphic (i.e. frequency of most common allele <95%) in fewer populations than those examined for M.␣marginalba (P <0.001) and, where polymorphisms occurred, also possessed significantly fewer alleles (P <0.001). Consequently, average levels of expected heterozygosity were greater in populations of M. marginalba than in those of either of the other species (P <0.001). Genetic variation among populations, expressed as the standardised variance in allele frequencies (F
ST
), was inversely related to expected larval dispersal capability. The nine collections of M. marginalba showed little overall differentiation (F
ST
= 0.017; P <0.001), reflecting the ability of planktonic larvae to interconnect local populations, and so limit divergence due to drift
and natural selection. In contrast, there were high levels of allelic heterogeneity among the nine collections of C. lineolata (F
ST
= 0.523; P <0.001) and eight collections of B. hanleyi (F
ST
= 0.140; P <0.001). These data imply that for species which undergo direct development, local populations are effectively closed and
evolve largely independent of one another.
Received: 3 May 1996 / Accepted: 12 July 1996 相似文献
5.
E. A. Perry G. B. Stenson S. E. Bartlett W. S. Davidson S. M. Carr 《Marine Biology》2000,137(1):53-58
Harp seals (Pagophilus groenlandicus Erxleben, 1777) comprise three populations based upon whelping areas in the Greenland Sea, White Sea, and Northwest Atlantic.
The last comprises two subpopulations, one whelping in the Gulf of St. Lawrence (“Gulf ”) and one on the pack ice of the southern
Labrador/northern Newfoundland coastal shelf (“Front”). A total of 40 female seals from the four whelping areas were collected
during the 1990 and 1992 whelping seasons. DNA sequence variation was examined in a 307 bp region of the mitochondrial cytochrome
b gene. Eleven variable nucleotide positions defined 13 genotypes: a significant fraction of the genotypic variance (F
ST=0.12, or 0.09 as measured by Weir's coancestry coefficient θ) is attributable to differentiation between Northwest and Northeast
Atlantic populations. There was no significant differentiation between the two whelping areas in the Northwest Atlantic, or
between the Greenland Sea and White Sea. These findings suggest significant reproductive isolation exists between trans-Atlantic
breeding populations.
Received: 18 January 1999 / Accepted: 22 February 2000 相似文献
6.
As part of a “European Sardine/Anchovy Recruitment Program” (SARP), sardine larvae (Sardina pilchardus) were sampled off the Atlantic coast of Spain through the spawning season from March to June. The larvae were analysed for
carbon and nitrogen content as a measure of nutritional condition and survival potential. There was no significant diel variation
in larval carbon content, but there was a small significant diel variation in nitrogen; the absence of a strong diel signal
in elemental composition was ascribed to the overnight retention of the gut contents. There was an increase in carbon content
with increase in body length which reached an asymptote at ∼40% carbon content at a larval length of 20 mm. It is argued that
larvae with a carbon content of <25% of body weight were nutritionally stressed, with the smaller larvae (<10 mm in length)
appearing to be more vulnerable to food limitation. Although larvae with the lowest age-specific carbon content (poorest condition)
occurred on the cruise with the lowest food availability, there was no consistent relationship between carbon content and
food availability. While the successive monthly estimates of carbon content revealed differences in potential recruitment
between months, these were not related to the birth-date distribution of the surviving juveniles.
Received: 23 November 1998 / Accepted: 3 March 1999 相似文献
7.
Population structure of the wreckfish Polyprion americanus determined with microsatellite genetic markers 总被引:1,自引:0,他引:1
A. O. Ball G. R. Sedberry M. S. Zatcoff R. W. Chapman J. L. Carlin 《Marine Biology》2000,137(5-6):1077-1090
We examined population structure in the wreckfish, Polyprion americanus, by assaying six microsatellite loci in 422 individuals collected throughout the geographic range. Eighteen hapuku, P. oxygeneios, were assayed at the same loci for use as an outgroup. Expected heterozygosities ranged from 0.49 to 0.88 and averaged 0.66.
Allele-frequency distributions at those loci indicated that samples from the eastern North Atlantic, western North Atlantic
and the Mediterranean were genetically similar, confirming the pattern seen in a previous analysis of mitochondrial DNA (mtDNA)
restriction fragment length polymorphisms (RFLPs). Both mtDNA and microsatellite studies differentiated northern and southern
wreckfish stocks. However, in contrast to the mtDNA studies, allelic variation at microsatellite loci clearly differentiated
wreckfish from two Southern Hemisphere locations, Brazil and the South Pacific. Far more genetic variation was observed at
microsatellite loci than with mtDNA RFLPs (haplotype diversity averaged 0.01), and we saw more evidence of population structure
with the microsatellite loci. The differentiation between southern and northern wreckfish supports the distribution records,
which indicate that wreckfish do not occur in the tropics. Temperature profiles and current patterns throughout the southern
oceans apparently also prevent significant gene flow between the South Pacific and Brazilian samples.
Received: 29 January 2000 / Accepted: 27 June 2000 相似文献
8.
Results of isozyme electrophoresis were used to explore the genetic relationships between several Mediterranean morphs of
Cerithium (Gastropoda: Prosobranchia), for which taxonomy is currently uncertain because of high intraspecific variability and low
interspecific differentiation. The large species, classically known as C. vulgatum Bruguière, 1789 was identified at four sites (two in the French Mediterranean and two in southern Spain). Two different larval
types were found in the French sites, but poecilogony could not be demonstrated. Individuals collected from harbours were
not genetically distinct from open-sea populations of classic C. vulgatum. However, a population in the Embiez lagoon (French Mediterranean) which morphologically resembles C. vulgatum did display distinct genetic traits, supporting its status as a separate species. Of the small Cerithium species usually known as C. rupestre, two sympatric species (C.“rupestre” Risso, 1826 and C. lividulum Risso, 1826) were distinguished. Genotype frequencies within the analysed populations revealed much heterozygote deficiency.
F
ST
values (fixation index measuring the effects of population subdivision) suggest a higher genetic differentiation for C. lividulum populations than for C. vulgatum populations. We assume that a high larval dispersal capability (via planktotrophy) allows a high gene flow between populations
of C. vulgatum.
Received: 24 November 1998 / Accepted: 24 September 1999 相似文献
9.
Jeffrey N. Schinske Giacomo Bernardi David K. Jacobs Eric J. Routman 《Marine Biology》2010,157(1):123-134
We compared morphology and sequenced nuclear and mitochondrial genes from 11 populations of a previously genetically unstudied
“Baja California disjunct” species, the diamond turbot (Hypsopsetta guttulata). This species exhibits very limited adult movement and restriction to soft-bottom habitats but has a moderately long pelagic
larval duration. Therefore, if pelagic larval duration is correlated with gene flow between Gulf of California and Pacific
populations, we expect a reduced level of genetic and morphological differentiation. However, if adult habitat and ecology
have more effect on gene flow, we expect the populations in the two bodies of water to be more highly differentiated. We used
logistic regression to compare morphological features and phylogenetic and population genetic analyses to compare nucleotide
sequence data. Gulf of California H. guttulata are different from Pacific populations in morphology and both mitochondrial and nuclear gene sequences. MtDNA shows reciprocal
monophyly, and nuclear sequences from the Gulf of California formed a monophyletic group. Population genetic analyses also
suggest further population subdivision within the Pacific and within the Gulf of California. We argue that adult ecology has
a significant effect on migration rates among populations in the Pacific Ocean and the Gulf of California. 相似文献
10.
The genetic structure of Mycedium elephantotus (Pallas, 1766) populations from three regions around Taiwan was examined using allozyme electrophoresis. Eight loci were
scored from seven enzyme systems. Seven loci were polymorphic under the 95% criterion. The high ratio of observed to expected
genotypic diversities at the collection sites (G
O:G
E=0.8 to 1.0) indicate that M. elephantotus propagates predominantly by sexual reproduction. Allele frequencies of M. elephantotus differed significantly among regions (D=0.024 to 0.256, F
ST=0.032 to 0.218, p < 0.001), while populations among collection sites within each region were homogeneous (D=0.000 to 0.015, F
ST=0.010 to 0.022, p > 0.05). Genetic differentiation between populations from southern Taiwan and the Penghu Islands is greater than that between
southern and northern Taiwan populations, although the former two regions are much closer geographically. The UPGMA dendrogram
based on Nei's unbiased genetic distance showed a clear subdivision of populations into two groupings, northern Taiwan/Penghu
Islands and southern Taiwan. A higher level of gene flow was found between M. elephantotus populations in northern Taiwan and the Penghu Islands (N
m=7.56) than that between populations in southern Taiwan and other regions (N
m=0.90 to 1.72). The pattern of genetic subdivision among regions is consistent with the pattern of ocean currents, indicating
that genetic differentiation is likely driven by surface circulation vicariance.
Received: 2 December 1997 / Accepted: 15 September 1998 相似文献
11.
Detailed inventories of the benthos and field studies of the settlement and recruitment processes of marine benthic invertebrates
require accurate identification of newly settled larvae and early juvenile stages. We provide morphological criteria, visible
under a good quality dissecting stereomicroscope, by which to discriminate between species of the settling larval and early
postlarval stages (∼250 to 700 μm shell length) of mussels of the genus Mytilus on the west coast of Vancouver Island and Southern California. Compared to the bay mussel (M. trossulus), the sea mussel (M. californianus) has: (i) a shallower and flatter umbo, the latter corresponding to a significantly less pronounced prodissoconch I (PI)
curvature and (ii) a greater PI length; as well as (iii) a wider separation between the provincular lateral teeth (PLT). The
PLT distance is a new term denoting the separation between the midpoint of two reddish pigment spots of the provinculum (larval
hinge apparatus) region of settling larvae and early postlarvae of Mytilus spp. from the East Pacific Coast. These spots mark the larger provincular lateral teeth, situated at either end of the provinculum.
We confirmed the validity of morphological criteria by comparing PCR products of genomic DNA of provisionally identified postlarvae.
Furthermore, measurements of PI lengths and PLT distance from well-preserved postlarvae of sea mussels (M. californianus) and of bay mussels (M. galloprovincialis) from Southern California indicate that the PI morphology and morphometry, and PLT distance criterion apply for that region
as well. The criteria presented here can also apply to the advanced (competent) veliger stages, as the latter may settle (i.e.
become the “settling” stage) upon encountering a suitable substrate. Our present and previously published work provide economical
and effective identification methods that can be used to discriminate among early life history stages (∼250 μm to 5.0 mm shell
length) of Mytilus spp. along the west coast of North America.
Received: 10 November 1999 / Accepted: 6 September 2000 相似文献
12.
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. 相似文献
13.
Samples of the scleractinian coral Pocillopora damicornis were collected from six sites located around four islands in the Ryukyu Archipelago, southern Japan, and subjected to allozyme
electrophoresis. Seven polymorphic loci were examined for their allelic patterns. The ratio of observed to expected genotypic
diversity (0.30 < G
o
:G
e
< 0.64), the ratio of the observed number of genotypes to the number of individuals (0.47 < N
g
:N
i
< 0.75), and deviations from Hardy–Weinberg equilibrium indicated that asexual reproduction plays a major role in the maintenance
of established populations. However, populations were not completely dominated by a single or a few clones, and most clones
were represented by only a few individual samples. The high frequency of typhoons in the region suggests that, in P. damicornis, fragmentation caused through occasional exposure to powerful waves is a major mode of asexual reproduction, but asexual
production of planulae may also be contributing to the maintenance of populations. A significant genetic differentiation (F
ST) was found between the six populations examined (0.027 < F
ST < 0.092, average F
ST = 0.056). The moderate gene flow is discussed according to characteristics of the larval stage of the species, and to circulation
patterns in the region.
Received: 7 August 1998 / Accepted: 18 May 1999 相似文献
14.
The blue mussels Mytilus edulis L. and M. galloprovincialis Lmk. hybridize in western Europe. Within hybrid populations nuclear alleles specific to M. galloprovincialis increase in frequency with age and size. This relationship changes with tidal height; alleles from M. galloprovincialis occur more frequently high in the intertidal zone, while M. edulis alleles predominate in the low intertidal zone. We tested the hypotheses that larvae with M. galloprovincialis alleles tend to settle higher in the intertidal zone, or that mussels redistribute themselves with respect to tidal height
after initial larval settlement. We sampled recently metamorphosed mussels every 2 weeks in a hybrid mussel population at
Whitsand Bay in southwest England throughout the summer of 1996. We observed four cohorts of newly settled mussels. There
was no evidence of differential settlement of mussels with different genotypes in connection with tidal height, or into shaded
versus unshaded microsites. Therefore, we rejected the preferential settlement hypothesis. There was substantial movement
of juvenile mussels in the first 4 weeks following initial settlement, but this “secondary settlement” did not result in genetic
differentiation with respect to tidal height. Further, significant differences in allele frequencies were found between primary
and secondary spat. This allele frequency change was in the opposite direction of that seen in the adult population, suggesting
newly settled larvae may be experiencing different selective pressures than adults. We propose that the genetic structure
of hybrid mussel populations with respect to tidal height is the consequence of differences in selection intensity.
Received: 30 April 1999 / Accepted: 5 May 2000 相似文献
15.
It has been hypothesized that marine fish larvae in the advanced stages of starvation would show increased density (ρ = mass
volume−1) from water loss due to osmoregulation failure. Changes in larval buoyancy are currently attributed to swim bladder regulation
and protein synthesis or catabolism. Osmoregulation-related changes in density is an alternative mechanism, the importance
of which remains untested in the laboratory and the influence of which on vertical distributions is unknown. We provide evidence
that loss of osmotic control is a plausible mechanism for increased density of larval cod (Gadus morhua L.). Furthermore, our results show that this mechanism is not restricted to larvae in the advanced stages of starvation.
“Relative” larval densities are estimated using a modified density gradient. We use a gravimetric method to separate the effects
of nutrition from osmoregulation failure. We assessed the importance of sampling strata on estimates of larval density. Proportional
sampling within three depth strata (stratified sample) produced the least biased method for determining the “average” density
of a population of larvae in laboratory culture. Larvae sampled from the bottom third of the culture tank were significantly
more dense then those sampled from the surface. This was true for larvae of all ages. The average change in density from hatching
till death from starvation for larvae sampled in the surface stratum was nominal (Δρ = 5.0 × 10−4 g cm−3), while the change for those sampled from the bottom stratum was large (Δρ = 3.8 × 10−3 g cm−3). These large density differences suggest that larvae sampled from the bottom stratum were either osmotically stressed or
were facultatively changing their density via regulatory pathways. Preliminary observations suggest that vitality is lower
amongst those larvae which are sampled near the bottom. The small change in average density of larvae sampled from the surface
stratum was due to starvation. The density differences we observed between “osmotically stressed” and “starving” larvae could
readily have been misconstrued as differences in feeding and growth experienced by individual larvae. The potential bias of
increased density from osmoregulation failure must be considered as a factor in experimental designs developed to assess the
effect of fed and starved treatments on buoyancy for larvae of all ages. The simple bioassay we describe may prove useful
both as a means of assessing larval condition and as a mechanism for evaluating factors affecting larval vertical distributions
in the field.
Received: 13 January 1997 / Accepted: 3 February 1997 相似文献
16.
Life history of Gonatus onyx (Cephalopoda: Teuthoidea): deep-sea spawning and post-spawning egg care
A reproductive strategy consisting of deep- water spawning and egg-care was inferred for the midwater squid Gonatus onyx Young, 1972. Brooding females and associated eggs and hatchlings, captured between 1250 and 1750 m depth off southern California,
are described. Brooding females appear to be senescent and lack tentacles. Large eggs of this species (3 mm) at cold temperatures
(3 °C at capture depth) may require as long as 9 mo to develop. The high lipid content of the digestive gland in adult females
of this species may provide fuel to support such an extended “brooding” period.
Received: 22 February 1999 / Accepted: 25 May 2000 相似文献
17.
Genetic structure of populations of two species of Chthamalus (Crustacea: Cirripedia) in the north-east Atlantic and Mediterranean 总被引:2,自引:0,他引:2
Protein electrophoresis on starch gels was used to investigate population genetic structure of the barnacles Chthamalus
montagui
Southward and C. stellatus (Poli) over their north-east Atlantic and Mediterranean ranges. In each species, a single locus exhibited marked differentiation
of allele frequencies between Atlantic and Mediterranean localities; in C. stellatus, genetic differentiation between the two basins had not previously been noted. In both species, mean heterozygosity per locus
appeared higher in the Mediterranean samples than in the Atlantic, and Mediterranean populations had more alleles at the loci
studied. Possible explanations for the differentiation between the Atlantic and the Mediterranean populations are discussed.
Received: 30 May 1996 / Accepted: 17 September 1996 相似文献
18.
The bay scallop, Argopecten irradians, exhibits extensive variation in morphology among geographically separated populations, resulting in the recognition of three
major subspecies (A. i. irradians, A. i. concentricus, A. i. amplicostatus). The extent to which morphological variation results from differing environmental conditions is unknown. In the present
study, bay scallops from Massachusetts, North Carolina, Florida, and Texas were collected, spawned and the offspring reared
in a common garden experiment to determine if scallops cultured under similar environmental conditions exhibited the morphology
expected given the geographic origin of their parents. Significant differences among populations were indicated by ANOVA in
both the wild-caught (13/14 morphological characters) and cultured (11/14 characters) scallops. Principal components analysis
clustered wild-caught scallops according to geographic origin and cultured scallops according to geographic ancestry. The
morphological characters most influential in resolving groups were plical width, plical spacing, number of plicae and valve
convexity. Geographic variation in morphology apparently has a strong genetic basis, and reflects significant differentiation
among disjunct populations of bay scallops.
Received: 12 September 1996 / Accepted: 15 October 1996 相似文献
19.
In situ and in vitro observations indicate that brooding colonial ascidians commonly display limited larval dispersal, whilst
the larvae of most solitary species are assumed to be widely dispersed. We used allozyme data to determine the population
genetic consequences of reproduction and dispersal in a broadcast-spawning solitary ascidian and two brooding colonial species
along the central and southern coast of New South Wales, Australia. We surveyed genetic variation at 2 to 9 variable loci
for samples collected from 6 to 8 local populations of each of the stalked solitary species Pyura gibbosa gibbosa Heller, 1878; the social Stolonica australis Michaelsen, 1927 and the compound Botrylloides magnicoecum Hartmeyer, 1912. Samples from each local population displayed levels and patterns of genotypic diversity that were consistent
with expectations for sexually-derived recruitment of both solitary zooids and separate colonies. However, we found clear
differences in the structure of the populations of solitary and colonial species. Genotype frequencies within all nine samples
of P. gibbosa gibbosa conformed to expectations for random mating (i.e. Hardy–Weinberg equilibria). Moreover, allele frequencies showed little
variation among samples [mean standardised genetic variance (F
S
T
) =0.002], which implies that local populations are strongly connected by larval dispersal. We estimate (via Wright's “island
model”) that gene flow (N
e
m) within this set of local populations is 125 effective migrants per generation, which is very similar to estimates obtained
for other broadcast-spawning taxa in this region. In contrast, genotype frequencies within samples of both colonial species
were characterised by large and statistically significant deficits of heterozygotes, consistent with expectations for highly
limited dispersal of larvae or sperm. Moreover, local populations were highly differentiated (F
S
T
=0.201 and 0.202 for S. australis and B. magnicoecum, respectively) and N
e
m was estimated to be ∼1.0 in each case. These values of F
S
T
and subsequent estimates of N
e
m lie within the range of values reported for other New South Wales taxa with direct larval development, and imply that local
populations are effectively closed to immigration.
Received: 13 February 1997 / Accepted 18 July 1997 相似文献
20.
Growth trajectories of individual larvae of Japanese sardine, Sardinops melanostictus, caught in the coastal waters off western Japan were back-calculated from the first feeding stage up to date of capture (approximate
size of 20 to 35 mm total length; TL) based on individually determined allometric relationships between otolith daily ring
radii and fish total lengths. The larvae in January-, February-, and March-hatched cohorts in the coastal waters grew faster
and more uniformly than those in the oceanic waters offshore of the Kuroshio current. Growth trajectories of the three hatch-month
cohorts were similar and could be expressed by the Gompertz model. The inflection points of the growth curves were reached
at 9 to 11 d after hatching, when larvae were 10.8 to 11.8 mm TL. Maximum growth rates at these points were 0.80 to 0.85 mm
d−1. Growth rates gradually declined after the inflection points, and larval TLs converged into the infinite length of 29 to
32 mm, the sizes at which metamorphosis from larvae to juveniles is initiated. This asymptotic growth pattern in the larval
stage resulted in the narrow ranges in TLs in spite of the wide range of ages of the larvae caught by boat seiners in the
coastal waters. Slow growth and therefore long duration of the metamorphosing stage could be influential in determining the
cumulative total mortality in the early life stages of the Japanese sardine.
Received: 14 July 1996 / Accepted: 20 August 1996 相似文献