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1.
Clonal and solitary anemones (Anthopleura) of western North America: population genetics and systematics 总被引:2,自引:0,他引:2
Francis (1979) proposed that clonal and solitary forms of the anemone Anthopleura elegantissima are actually two species. In 1984 and 1985, samples from two to six California populations of all known forms and species of California Anthopleura were analyzed electrophoretically to determine their taxonomic relationships. Data from 14 enzymes and 18 loci, 17 of them polymorphic, show that the two forms of A. elegantissima are virtually identical electrophoretically, and there is no evidence of reduced gene flow between them. We conclude there are three species of Anthopleura in California: A. elegantissima (Brandt, 1835), A. xanthogrammica (Brandt, 1835) and A. artemisia (Dana, 1848). Genetic variation in the two species capable of asexual reproduction, A. elegantissima and A. artemisia, is extremely high, approximately 2.5 times that of the strictly sexual A. xanthogrammica. 相似文献
2.
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
3.
Throughout its geographic range, the temperate-zone anemone Anthopleura elegantissima is the host of one or both of two distinctively different symbiotic microalgae: a dinoflagellate Symbiodinium (zooxanthellae, ZX) and a chlorophyte (zoochlorellae, ZC). Given the broad vertical intertidal and latitudinal range of this
anemone, we investigated the role of temperature in determining whether A. elegantissima supports one algal symbiont over the other and whether temperature regulates the observed distributions of natural populations
of ZX and ZC. Temperature appears to be a key factor in regulating both the photophysiology and metabolism of this algal–cnidarian
association. In anemones containing ZX, neither algal densities nor chlorophyll content varied with temperature (6–24 °C);
in contrast, anemones with ZC displayed reduced densities and chlorophyll content at the highest temperature treatment (24 °C).
Both ZX and ZC photosynthetic rates were directly related to temperature, as were anemone respiration rates. The higher photosynthetic
rates, maintenance of a stable algal density and chlorophyll content, and higher potential contribution of algal carbon toward
animal respiration (CZAR) suggest that the ZX are the more viable symbiont as temperature increases, but we suggest alternative
reasons why ZC are preserved in this symbiotic association. Elevated temperatures reduce ZC densities and chlorophyll, suggesting
that higher temperatures affect this relationship in a negative fashion, presumably due to a higher cost of maintaining ZC
by the association; alternatively, these costs may be affiliated with the deterioration of the ZC themselves. These results
suggest that temperature may be one of the most significant environmental parameters that sets the intertidal microhabitat
and latitudinal distribution patterns of the two algal taxa observed in the field.
Received: 2 November 1998 / Accepted: 25 October 2000 相似文献
4.
The temperate sea anemone Anthopleura elegantissima is facultatively symbiotic with unicellular algae. Symbiotic A. elegantissima can supplement heterotrophic feeding with excess photosynthate from their algal partners, while asymbiotic individuals must
rely solely on heterotrophy. A. elegantissima individuals were collected from Swirl Rocks, Washington (48°25′6″ N, 122°50′58″ W) in July 2010, and prey capture and feeding
characteristics were measured to determine whether asymbiotic individuals are more efficient predators. Feeding abilities
were then measured again after a 3-week exposure to full sunlight or shaded conditions. Freshly collected asymbiotic anemones
had larger nematocysts, but symbiotic individuals showed greater nematocyte sensitivity. Sunlight enhanced digestion and reduced
cnida density in all anemones regardless of symbiotic state. Results suggest that the phototropic potential of A. elegantissima, as influenced by symbiotic condition, has little effect on heterotrophic capacity. The anemones appear to maximize heterotrophic
energy input independent of the presence or identity of their algal symbionts. 相似文献
5.
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
6.
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
7.
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
8.
Genetic differentiation among populations of a broadcast spawning soft coral, Sinularia flexibilis, on the Great Barrier Reef 总被引:2,自引:0,他引:2
The genetic structure of 12 reef populations of the soft coral Sinularia flexibilis (Octocorallia, Alcyoniidae) was studied along the Great Barrier Reef (GBR) at a maximum separation of 1,300 km to investigate
the relative importance of sexual and asexual reproduction, genetic differentiation and gene flow among these populations.
S. flexibilis is a widely distributed Indo-Pacific species and a gamete broadcaster that can form large aggregations of colonies on near-shore
reefs of the GBR. Up to 60 individuals per reef were collected at a minimum sampling scale of 5 m at two sites per reef, from
December 1998 to February 2000. Electrophoretic analyses of nine polymorphic allozymes indicated that genotypic frequencies
in most populations and loci did not differ significantly from those expected from Hardy–Weinberg predictions. Analysis of
multi-locus genotypes indicated a high number of unique genotypes (N
go) relative to the number of individuals sampled (N) in each reef population (range of 0.69–0.95). The maximum number of individuals likely to have been produced sexually (N*) was similar to the number of individuals sampled (i.e. N*:N ˜ 1), suggesting that even repeated genotypes may have been produced sexually. These results demonstrated a dominant role
of sexual reproduction in these populations at the scale sampled. Significant genetic differentiation between some populations
indicated that gene flow is restricted between some reefs (F
ST=0.026, 95% CI= 0.011 − 0.045) and even between sites within reefs (F
ST=0.041, 95% CI=0.027 − 0.055). Nevertheless, there was no relationship between geographic separation and genetic differentiation.
Analyses comparing groups of populations showed no significant differentiation on a north-south gradient in the GBR. The pattern
in the number of significant differences in gene frequencies in pairwise population comparisons, however, suggested that gene
flow may be more restricted among inner-shelf reef populations near to the coast than among mid/outer-shelf populations further
from the coast.
Received: 10 July 2000 / Accepted: 5 October 2000 相似文献
9.
Starch-gel electrophoresis of allozymes was used to differentiate the two red mullet species (Mullus barbatus L. and M. surmuletus L.) in the Mediterranean Sea and, further, to investigate the genetic stock structure of M. barbatus in the eastern Mediterranean area. Twenty putative enzyme-coding loci were examined in eight M. barbatus samples caught in the Aegean and Ionian Seas (Greece) and in the Gulf of Lion (France), and two M. surmuletus samples caught in the Aegean and Gulf of Lion. A high degree of genetic polymorphism was found in both species. Species-specific
electrophoretic patterns were found in PGI* and PGM*. Estimates of variance of allele frequencies among samples (F
ST) and 2 analyses both revealed significant differences (P < 0.05) among the M. barbatus samples. Most of the genetic variation was among samples regardless of region. The mean value of Nei's genetic distance between
the two species was 0.329. Genetic distance among M. barbatus samples was low (maximum Nei's D = 0.012), with the sample from Platania differing most from other M. barbatus samples. This is probably be due to founder effects existing at this area. These results suggest that allozyme analysis may
provide important information on the genetic structure of the red mullet to ensure sustainable management of this species.
Received: 7 May 1997 / Accepted: 13 October 1997 相似文献
10.
The sea anemone Anthopleura elegantissima hosts two phylogenetically different symbiotic microalgae, a dinoflagellate Symbiodinium (zooxanthellae, ZX) and a chlorophyte (zoochlorellae, ZC). The photosynthetic productivity (P), respiration (R), and contribution
of algal carbon translocated to the host (CZAR) in response to a year’s seasonal ambient changes of natural light and temperature
are documented for both ZX- and ZC-bearing anemones. Light and temperature both affect photosynthesis, respiration, and CZAR,
as well as various algal parameters; while there are evident seasonal differences, for the most part the relative effects
on P, R, and CZAR by the two environmental variables cannot be determined. Net photosynthesis (Pn) of both ZX and ZC was significantly higher during spring and summer. During these seasons, the Pn of ZX was always greater than that of ZC. Regardless of algal symbiont, anemone respiration (R) was significantly higher
during the spring and summer. The annual net carbon fixation rate of anemones with ZX and ZC was 325 and 276 mg C anemone−1 year−1, respectively, which translates to annual net community productivity rates of 92 and 60 g C m−1 year−1 for anemones with ZX or ZC, respectively. CZAR did not show a clear relationship with season; however the CZAR for ZX was
always significantly greater than for ZC. Lower ZX growth rates, coupled with higher photosynthetic rates and higher CZAR
estimates, compared to ZC, suggest that if A. elegantissima is simply carbon limited, ZX-bearing anemones should be the dominant symbiont in the field. However ZC-bearing anemones persist
in low light and reduced temperature microhabitats, therefore more than the translocation of carbon from ZC must be involved.
Given that global climate change will increase water temperatures, the potential for latitudinal range shifts of both ZC and
ZX (S. californium and muscatinei) might be used as biological indicators of thermal shifts in the littoral zone of the Pacific Northwest. 相似文献
11.
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
12.
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
13.
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
14.
The relative contribution of dissolved nitrogen (ammonium and dissolved free amino acids DFAAs) to the nitrogen budget of
the reef-building coral Pocillopora damicornis was assessed for colonies growing on control and ammonium-enriched reefs at One Tree Island (southern Great Barrier Reef)
during the ENCORE (Enrichment of Nutrient on Coral Reef; 1993 to 1996) project. P. damicornis acquired ammonium at rates of between 5.1 and 91.8 nmol N cm−2 h−1 which were not affected by nutrient treatment except in the case of one morph. In this case, uptake rates decreased from
80.5 to 42.8 nmol cm−2 h−1 (P < 0.05) on exposure to elevated ammonium over 12 mo. The presence or absence of light during measurement did not influence
the uptake of ammonium ions. Nitrogen budgets revealed that the uptake of ammonium from concentrations of 0.11 to 0.13 μM could completely satisfy the demand of growing P. damicornis for new nitrogen. P. damicornis also took up DFAAs at rates ranging from 4.9 to 9.8 nmol N cm−2 h−1. These rates were higher in the dark than in the light (9.0 vs 5.1 nmol m−2 h−1, P < 0.001). Uptake rates were highest for the amino acids serine, arginine and alanine, and lowest for tyrosine. DFAA concentrations
within the ENCORE microatolls that received ammonium were undetectable, whereas they ranged up to 100 nM within the control microatolls. The contribution of DFAAs to the nitrogen budget of P. damicornis constituted only a small fraction of the nitrogen potentially contributed by ammonium under field conditions. Even at the
highest field concentrations measured during this study, DFAAs could contribute only ≃11.3% of the nitrogen demand of P.␣damicornis. This contribution, however, may be an important source of nitrogen when other sources such as ammonium are scarce or during
periods when high concentrations of DFAAs become sporadically available (e.g. cell breakage during fish-grazing).
Received: 22 April 1998 / Accepted: 3 November 1998 相似文献
15.
Littoraria cingulata (Philippi, 1846) is a Western Australian, mangrove littorine snail, represented by two morphologically distinct subspecies,
whose distributions are separated by >300 km. The southern subspecies, L. cingulata pristissini, is distinguished from the northern subspecies, L. cingulata cingulata, by having a thinner, keelless shell with more primary grooves, and lower and much more numerous ribs. In contrast with these
striking differences, L. cingulata cingulata is morphologically very similar to another species, L. sulculosa, with which it also shares a nearly coincident geographic range. Allozyme comparisons at 22 presumptive loci confirmed a
large genetic distance between L. cingulata and L. sulculosa, and the apparent conspecificity of the morphologically divergent subspecies of L. cingulata. Based on geological evidence, the geographical separation of the morphologically divergent forms of L. cingulata has developed within the past 5000 to 10 000 yr. The extensive continuous distribution of the northern subspecies, L. cingulatacingulata, and the large geographic disjunction between the northern and Shark Bay subspecies, L. cingulata pristissini, allowed a test of the genetic importance of this relatively recent disjunction. Within the continuous distribution of the
two subspecies, a pattern of isolation by distance was visible up to distances of 300 km. Beyond 300 km, genetic subdivision,
measured by pairwise G
ST
(the proportion of genetic diversity due to differences between populations), averaged 0.028, whereas subdivision between
Shark Bay and northern populations averaged 0.055 over the same range of distances. Although the relative paucity of barriers
to gene flow tends to limit genetic subdivision in marine species with planktotrophic larvae, the results for L. cingulata suggest that subdivision can occur within a continuous distribution, but that special events leading to major disjunctions
can substantially increase divergence, even over a relatively short period of time.
Received: 16 February 1998 / Accepted: 23 April 1998 相似文献
16.
C. A. Fredericks 《Marine Biology》1976,38(1):25-28
Phototaxis in Anthopleura elegantissima, a sea anemone symbiotic with zooxanthellae, was investigated with special reference to oxygen as a possible controlling factor. Under high oxygen concentrations in seawater, movement towards light was not observed for symbiotic anamones as it was under normal oxygen concentrations. Both aposymbiotic and symbiotic anemones demonstrated movement towards high oxygen concentrations in seawater. Oxygen is, therefore, implicated as a controlling factor in phototaxis. Under laboratory conditions, increased intraclonal spacing occurred with low oxygen concentrations in seawater. In the field, individuals in symbiotic clones were spaced significantly closer than in aposymbiotic clones. Since intraclonal spacing is controlled by oxygen in the laboratory, spacing may also be affected in the field by oxygen; symbiotic clones may be spaced closer because they have better oxygen availability than do aposymbiotic clones. 相似文献
17.
Although the genetic structure of many populations of marine organisms show little deviation from panmixia, in those marine species with limited larval dispersal, patterns of microgeographic genetic differentiation may be common. The octocoral Briareum asbestinum should show local population differentiation because colonies reproduce asexually by fragmentation, most matings occur between colonies in very close proximity, and the sexually produced larvae and sperm appear to disperse only short distances. Variability in secondary chemistry of individual B. asbestinum colonies from different populations in close proximity also suggests local population differentiation. We determined the genetic composition of local populations by surveying allozyme variation of three shallow and two deep populations within a 300 m2 area at San Salvador Island, Bahamas and at a site 161 km away on Little San Salvador, Bahamas in July 1990. As B. asbestinum occurs as either an erect branching form or an encrusting mat often at the same sites, we sampled both morphs to examine the extent of genetic exchange between them. Five of 21 loci were polymorphic and most populations showed a deficit of heterozygotes. Allele frequencies differed significantly between morphs at each site where they occurred together. The mean genetic distance (D=0.065) between morphs is consistent with the interpretation that the two morphs are genetically isolated. Despite the close spatial proximity of the San Salvador populations, both the branching and encrusting morphs showed significant genetic heterogeneity among neighboring populations. Similarly, pooled allelic frequencies for samples collected from the islands of San Salvador and Little San Salvador differed significantly at 1 locus for the branching morph and at 3 out of 5 loci for the encrusting morph. 相似文献
18.
Genetic divergence among ten populations of small- and large-egg forms of the brackish-water polychaete Hediste japonica complex was investigated on 14 isozyme loci by electrophoretic analysis. The two forms were distinguishable by complete allele
substitutions at five loci, resulting in high genetic differentiation (Nei's D: 0.533 to 0.662). No genetic evidence of hybridization between the two forms was detected in sympatric populations in three
rivers. These results indicate that the two forms are reproductively isolated, clearly showing that the two forms are distinct
species. The genetic differentiation among populations was higher in the large-egg form (D: 0.005 to 0.111, G
ST: 0.435) than that in the small-egg form (D: 0.000 to 0.001, G
ST: 0.020). This genetic difference between the two forms seems to be attributable to a difference in their life histories.
The average expected heterozygosity was low in populations of both the large-egg form (0.005 to 0.068) and the small-egg form
(0.014 to 0.038) in comparison with other marine invertebrates.
Received: 11 April 1997 / Accepted: 8 September 1997 相似文献
19.
Genetic heterogeneity among adult and recruit red sea urchins, Strongylocentrotus franciscanus 总被引:1,自引:1,他引:0
Allozyme electrophoresis was used to characterize genetic variation within and among natural populations of the red sea urchin
Strongylocentrotus franciscanus. In 1995 to 1996, adult urchins were sampled from twelve geographically separated populations, seven from northern California
and five from southern California (including Santa Rosa Island). Significant population heterogeneity in allelic frequencies
was observed at five of six polymorphic loci. No geographic pattern of differentiation was evident; neighboring populations
were often more genetically differentiated than distant populations. Northern and southern populations were not consistently
distinguishable at any of the six loci. In order to assess within-population genetic variation and patterns of recruitment,
large samples were collected from several northern California populations in 1996 and 1997, and were divided into three size
classes, roughly representing large adults (>60 mm), medium-sized individuals (31 to 60 mm, “subadults”) and individuals <2 yr
of age (≤30 mm test diam, referred to as “recruits”). Comparisons of allelic counts revealed significant spatial and temporal
differentiation among size-stratified population samples. Recruit samples differed significantly from adult samples collected
at the same locale, and showed extensive between-year variation. Genetic differentiation among recruit samples was much higher
in 1997 than in 1996. Between-year differences within populations were always greater for recruits than for adults. Potential
explanations for the differentiation of recruit samples include pre- and post-settlement natural selection and high interfamily
variance in reproductive success or “sweepstakes” recruitment. Unless recruit differentiation can be attributed to an improbable
combination of strong and spatially diverse selection, such differentiation across northern California populations indicates
that the larval pool is not well mixed geographically (even on spatial scales <20 km), despite long planktonic larval duration.
Received: 6 July 1999 / Accepted: 25 January 2000 相似文献
20.
Microgeographic genetic differentiation in a colonial ascidian (Botryllus schlosseri) population 总被引:3,自引:0,他引:3
Limited gene flow via the restricted dispersal of larvae and gametes is expected to result in the genetic differentiation
of populations of clonal invertebrates on small spatial scales. However, occasional dispersal events over greater distances
may generate sufficient gene flow to maintain genetic homogeneity. We applied a spatial autocorrelation approach that does
not require a priori definitions of subdivision boundaries to examine genetic differentiation within a continuous population
of the colonial ascidian Botryllus schlosseri (Pallas) at two allozyme and five polychromatism loci. Colonies were sampled in July 1992, on a 12 by 18 m grid superimposed
on a shallow subtidal (1 to 3 m) population in the Damariscotta River estuary in Maine, USA. Low but significant levels of
positive autocorrelation were detected over very small spatial scales (<5 m), with negative autocorrelation occurring on larger
scales (>8 m). This pattern indicates significant genetic differentiation over distances of 8 to 21 m, and is consistent with
genetic drift and inbreeding creating small scale genetic structure.
Received: 18 October 1999 / Accepted: 11 July 2000 相似文献