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1.
The orange roughy Hoplostethus atlanticus is a well-known commercial species with a global distribution. There is no consensus about levels of connectivity among populations
despite a range of techniques having been applied. We used cytochrome c oxidase subunit I (COI) and cytochrome b sequences to study genetic connectivity at a global scale. Pairwise ΦST analyses revealed a lack of significant differentiation among samples from New Zealand, Australia, Namibia, and Chile. However,
low but significant differentiation (ΦST = 0.02–0.13, P < 0.05) was found between two Northeast Atlantic sites and all the other sites with COI. AMOVA and the haplotype genealogy
confirmed these results. The prevalent lack of genetic differentiation is probably due to active adult dispersal under the
stepping-stone model. Demographic analyses suggested the occurrence of two expansion events during the Pleistocene period. 相似文献
2.
Spatial and temporal genetic homogeneity in the Arctic surfclam (<Emphasis Type="Italic">Mactromeris polynyma</Emphasis>) 总被引:1,自引:0,他引:1
Commercially harvested marine bivalve populations show a broad range of population-genetic patterns that may be driven by
planktonic larval dispersal (gene flow) or by historical (genetic drift) and ecological processes (selection). We characterized
microsatellite genetic variation among populations and year classes of the commercially harvested Arctic surfclam, Mactromeris polynyma, in order to test the relative significance of gene flow and drift on three spatial scales: within commercially harvested
populations in the northwest Atlantic; among Atlantic populations; and between the Atlantic and Pacific oceans. We found small
nonsignificant genetic subdivision among eight populations from the northwest Atlantic (F
ST = 0.002). All of these Atlantic populations were highly significantly differentiated from a northeast Pacific population
(F
ST = 0.087); all populations showed high inbreeding coefficients (F
IS = 0.432). We tested one likely source of heterozygote deficits by aging individual clams and exploring genetic variation
among age classes within populations (a temporal Wahlund effect). Populations showed strikingly different patterns of age
structure, but we found little differentiation among age classes. In one case, we were able to analyze genetic diversity between
age classes older or younger than the advent of intensive commercial harvesting. The results generally suggest spatially broad
and temporally persistent genetic homogeneity of these bivalves. We discuss the implications of the results for the biology
and management of surfclam populations.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
3.
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
4.
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
5.
Jennifer K. Schultz Richard L. Pyle Edward DeMartini Brian W. Bowen 《Marine Biology》2007,151(1):167-175
Color variation is used in taxonomic classification of reef fishes, but it may not reliably indicate evolutionary divergence.
In the central Pacific, there are three color morphs of the flame angelfish, Centropyge loriculus: a red morph that occurs primarily in the Hawaiian archipelago, the endemic Marquesan color morph with reduced black markings,
and an orange morph that occurs throughout the rest of Oceania. The red and orange morphs co-occur at Johnston Atoll (1,300 km
south of Hawai’i), but intermediate forms have not been reported. To determine whether the three color morphs represent distinct
evolutionary lineages, we compared 641 base pairs of mitochondrial cytochrome b. Forty-one closely related haplotypes were observed in 116 individuals. Analysis of molecular variance (AMOVA) indicated
no significant genetic structure among color morphs (ΦST = 0.011, P = 0.147). Likewise, there was no significant pairwise structure between sampling locations, separated by up to 5,700 km,
after a Bonferroni correction (ΦST = 0.000–0.080, P = 0.0130–0.999). Genetic studies in conjunction with larval distribution data indicate that Centropyge species are highly dispersive. While there is a strong geographic component to the distribution of color morphs in C. loriculus, we find no evidence for corresponding genetic partitioning. We do not rule out an adaptive role for color differentiation,
but our data do not support emerging species. 相似文献
6.
Zoë Anne Doubleday Jayson M. Semmens Adam J. Smolenski Paul W. Shaw 《Marine Biology》2009,156(6):1183-1192
Five polymorphic microsatellite loci were developed and then used to assess the population genetic structure of a commercially
harvested merobenthic octopus species (Octopus maorum) in south-east Australian and New Zealand (NZ) waters. Beak and stylet morphometrics were also used to assess population
differentiation in conjunction with the genetic data. Genetic variation across all loci and all sampled populations was very
high (mean number alleles = 15, mean expected heterozygosity = 0.85). Microsatellites revealed significant genetic structuring
(overall F
ST = 0.024, p < 0.001), which did not fit an isolation-by-distance model of population differentiation. Divergence was observed between
Australian and NZ populations, between South Australia and north-east Tasmania, and between two relatively proximate Tasmanian
sites. South Australian and southern Tasmanian populations were genetically homogeneous, indicating a level of connectivity
on a scale of 1,500 km. Morphometric data also indicated significant differences between Australian and NZ populations. The
patterns of population structuring identified can be explained largely in relation to regional oceanographic features. 相似文献
7.
M. B. McEachern John M. Eadie Dirk H. Van Vuren 《Behavioral ecology and sociobiology》2007,61(9):1459-1469
We used DNA microsatellites to investigate temporal and spatial patterns of local genetic differentiation and relatedness
in a solitary mammal, the dusky-footed woodrat (Neotoma fuscipes). Patterns of genetic variation were measured relative to spatial clusters, or neighborhoods, of woodrats. We detected significant genetic differentiation among woodrat neighborhoods in two populations spanning multiple
habitat types and densities. Estimates of θ
ST
among neighborhoods ranged 0.034–0.075 and were comparable to levels reported in social mammals. Genetic differentiation
at such a local scale is noteworthy because it occurred in the absence of any physical barriers to gene flow, suggesting that
the patterns observed are linked to the nonrandom patterns of mating and dispersal that characterize woodrat social structure.
Genetic differentiation and relatedness among neighborhoods were even higher when only resident females were analyzed. These
results are consistent with a pattern of female philopatry and male-biased dispersal in woodrats. Geographic distance and
relatedness were inversely correlated in adult females at intermediate densities, but not at low densities. Nonetheless, matrilineal
genetic structure was apparent even at low woodrat densities based on estimates of θ
ST
among neighborhoods of resident females that were significantly greater than zero and consistently greater than estimates
including all individuals. In summary, this study demonstrates a matrilineal genetic structure in dusky-footed woodrats. In
addition, our results support the idea that intermediate densities may be better at facilitating the formation of spatial
kin clusters than either extreme.
An erratum to this article can be found at 相似文献
8.
We used random amplified polymorphic DNA (RAPDs) to examine small-scale spatial genetic structure in the red alga Delisea pulchra (Greville) Montagne at two locations near Sydney, Australia. We examined genetic structure among plants at four spatial scales
ranging from 2 km apart down to <50 cm apart between locations, among sites within locations, among quadrats within sites,
and among plants within quadrats. Haploid stages of D. pulchra were absent from the populations studied, suggesting that they are maintained through asexual reproduction of diploid plants.
Consistent with this, we found that 19 RAPD phenotypes scored in this study had multiple individuals, indicating the presence
of clones in these populations. However, there were no RAPD phenotypes common to two locations separated by only 2 km. Analysis
of molecular variance revealed that strong genetic differences occurred between plants from these two locations, with 46.3%
of the total genetic variation occurring at this scale, most probably reflecting limited gene flow. Within each location,
<25% of the genetic variation was attributable to differences among sites or quadrats, indicating gene flow at those smaller
scales. Most of the variation within each location occurred at the smallest spatial scale, among plants within 0.25 m2 quadrats. Nonetheless, some pairwise genetic distances (φST) between sites or quadrats within locations were large, indicating some genetic divergence on smaller scales. Genetic distance
was independent of spatial distance within both locations, suggesting that fine-scale differences within locations were most
probably caused by variation in fine-scale patterns of water movement or fine-scale natural selection. We assessed the impact
of one potential selective agent, grazing sea urchins, on the fine-scale genetic structure of D. pulchra. There was no evidence that grazing by sea urchins affected the genetic structure of D. pulchra. In combination with demographic data, our results indicated that local populations of D. pulchra within locations were relatively open and that fine-scale genetic structure was probably constrained by gene flow. At the
larger scale however, strong genetic differentiation indicated little gene flow between locations and restricted dispersal
of spores.
Received: 22 April 1999 / Accepted: 29 November 1999 相似文献
9.
Recruitment and population structure of Perna perna in low shore mussel beds were investigated over 15 months at six sites along the south coast of South Africa. Initial, subjective
classification of sites as wave exposed or wave sheltered (three of each) was confirmed using the dissolution of cement blocks
to measure average water flux and dynamometers for maximum wave force. Recruitment occurred throughout the year, but recruit
(1–5 mm) densities were significantly higher from January to April 1996 on both shore types. Recruit densities were positively
correlated with adult (>15 mm) densities for both shore types (P < 0.05) but the correlations were extremely weak (r
2 < 0.06 in each case). In areas with 100% cover, adult size (mean and maximum lengths) was greater on exposed sites, but density
showed the reverse and was negatively correlated with maximum wave strength (r = −0.84). Despite differences in adult densities and sizes, biomass, which is a product of the two, showed no significant
difference between the two shore types (ANOVA P > 0.05). Thus wave exposure dramatically affects density, recruitment and mussel size, but not recruitment timing or biomass
where there is 100% cover, and mediates a three-way interaction among food supply, larval supply and intraspecific competition
for space. In contrast to shores with saturation recruitment, mussel biomass here appears to be limited by recruit supply
and constraints of food, especially on sheltered shores, while density is regulated through intraspecific competition for
space primarily on exposed shores and at small spatial scales. 相似文献
10.
The finless porpoise (Neophocaena phocaenoides) inhabits a wide range of tropical and temperate waters of the Indo-Pacific region. Genetic structure of finless porpoises
in Chinese waters in three regions (Yangtze River, Yellow Sea, and South China Sea) was analyzed, including the Yangtze finless
porpoise which is widely known because of its highly endangered status and unusual adaptation to freshwater. To assist in
conservation and management of this species, ten microsatellite loci were used to genotype 125 individuals from the three
regions. Contrary to the low genetic diversity revealed in previous mtDNA control region sequence analyses, relatively high
levels of genetic variation in microsatellite profiles (H
E = 0.732–0.795) were found. Bayesian clustering analysis suggested that finless porpoises in Chinese waters could be described
as three distinct genetic groups, which corresponded well to population “units” (populations, subspecies, or species) delimited
in earlier studies, based on morphological variation, distribution, and genetic analyses. Genetic differentiation between
regions was significant, with F
ST values ranging from 0.07 to 0.137. Immigration rates estimated using a Bayesian method and population ancestry analyses suggested
no or very limited gene flow among regional types, even in the area of overlap between types. These results strongly support
the classification of porpoises in these regions into distinct evolutionarily significant units, including at least two separate
species, and therefore they should be treated as different management units in the design and implementation of conservation
programmes. 相似文献
11.
Despite high potential for dispersal, the purple sea urchin Strongylocentrotus purpuratus was found to have significant genetic subdivision among locations. Ten geographic locations along the coast of California and Baja California were sampled between 1994 and 1995. Samples from some locations included both adult and recruit urchins. Allozyme analyses revealed a genetic mosaic, where differentiation over short geographic distances could exceed differentiation over much larger distances. Significant allozyme differentiation was found among subpopulations of adults (standardized variance, F
ST
=0.033), among subpopulations of recruits (F
ST
=0.037), and between adults and recruits from the same location. DNA-sequence data for the mitochondrial cytochrome oxidase I gene also showed significant heterogeneity among locations, with a mild break in haplotype frequencies observed 300 km south of Point Conception. California. Repeated sampling over time is necessary to determine whether these patterns of differentiation are stable and to begin to understand what forces produce them. 相似文献
12.
Megan E. Mach Elizabeth J. Sbrocco Lyndie A. Hice Tara A. Duffy David O. Conover Paul H. Barber 《Marine Biology》2011,158(3):515-530
The coastal marine environment of the Northwest Atlantic contains strong environmental gradients that create distinct marine
biogeographic provinces by limiting dispersal, recruitment, and survival. This region has also been subjected to numerous
Pleistocene glacial cycles, resulting in repeated extirpations and recolonizations in northern populations of marine organisms.
In this study, we examined patterns of genetic structure and historical demography in the Atlantic silverside, Menidia menidia, an annual marine fish with high dispersal potential but with well-documented patterns of clinal phenotypic adaptation along
the environmental gradients of the Northwest Atlantic. Contrary to previous studies indicating genetic homogeneity that should
preclude regional adaptation, results demonstrate subtle but significant (F
ST = 0.07; P < 0.0001) genetic structure among three phylogeographic regions that partially correspond with biogeographic provinces, suggesting
regional limits to gene flow. Tests for non-equilibrium population dynamics and latitudinal patterns in genetic diversity
indicate northward population expansion from a single southern refugium following the last glacial maximum, suggesting that
phylogeographic and phenotypic patterns have relatively recent origins. The recovery of phylogeographic structure and the
partial correspondence of these regions to recognized biogeographic provinces suggest that the environmental gradients that
shape biogeographic patterns in the Northwest Atlantic may also limit gene flow in M. menidia, creating phylogeographic structure and contributing to the creation of latitudinal phenotypic clines in this species. 相似文献
13.
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
14.
Coupled bio-physical models of larval dispersal predict that the Costa Rica–Panama (CR–PAN) reefs should constitute a demographically
isolated region in the western Caribbean. We tested the hypothesis that CR–PAN coral reef fish populations would be isolated
from Mesoamerican Barrier Reef System (MBRS) populations. To test that, we assessed population genetic structure in bicolor
damselfish (Stegastes partitus) from both regions. Adult fish were genotyped from five reefs in CR–PAN and from four reefs along the MBRS at 12 microsatellite
loci. Between-region F
ST (F
ST = 0.0030, P < 0.005) and exact test (x
2 = 74.34, df = 18, P < 0.0001) results indicated that there is weak but significant genetic differentiation between regions, suggesting some restriction
in connectivity along the Central American coastline, as predicted by bio-oceanographic models. Additionally, there is among-site
genetic structure in the CR–PAN region, relative to the MBRS and between regions, suggesting higher self-recruitment within
CR–PAN. This finding may be explained by differences in habitat characteristics. 相似文献
15.
Variations at 22 enzyme coding loci were surveyed in 11 populations of the oyster Ostrea edulis L., which were sampled between 1988 and 1990 along the Atlantic and Mediterranean coasts of Europe. Atlantic oyster beds suffered a steady decline during the last century, and restocking of beds with oysters of foreign origin has probably resulted in a high degree of interbreeding of natural oyster stocks from all Atlantic Europe. Our study confirms the low levels of genetic variability previously reported for the oyster populations from the Atlantic coasts, and extends it to the Mediterranean coasts. The locus arginine-kinase (ARK
*) exhibited a high degree of interpopulation differentiation (F
ST=0.289), resulting from extensive variation in gene frequencies along a geographical cline. However, the overall genetic differentiation between populations was slight, and similar to that reported for other local populations of bivalves (mean genetic distance between populations is 0.010, mean F
ST=0.062). A general pattern of increasing differentiation along the coastline in an Atlantic-mediterranean direction emerged; but genetic differentiation among the Atlantic populations was not significantly lower than that observed among the Mediterranean populations. This and other results suggest that the effects of extensive transplantation of oysters among various areas in Europe are detectable only in some particular localities. The geographical distribution of low-frequency alleles suggests a restriction to gene flow outwards from the Mediterranean Sea, across the Straits of Gibraltar. 相似文献
16.
Endemism and dispersal: comparative phylogeography of three surgeonfishes across the Hawaiian Archipelago 总被引:1,自引:0,他引:1
To evaluate the hypothesis that a general correlation exists between species range size and dispersal ability, we surveyed
mitochondrial cytochrome b sequence variation in three surgeonfish species with vastly different ranges: Ctenochaetus strigosus, Hawaiian endemic, N = 531; Zebrasoma flavescens, North Pacific, N = 560; Acanthurus nigrofuscus, Indo-Pacific, N = 305. Collections were made throughout the 2,500 km expanse of the Hawaiian Archipelago and adjacent Johnston Atoll. Analyses
of molecular variance demonstrate that all three species are capable of maintaining population connectivity on a scale of
thousands of km (all species global ΦST = NS). However, rank order comparison of pairwise ΦST results and Exact test P-values revealed modest but significantly different patterns of gene flow among the three species surveyed, with the degree
of genetic structure increasing as range size decreases (P = 0.001). These results are consistent with mtDNA surveys of four additional Hawaiian reef fauna in which a wide-spread Indo-Pacific
species exhibited genetic homogeneity across the archipelago, while three endemics had significant population subdivision
over the same range. Taken together, these seven cases invoke the hypothesis that Hawaii’s endemic reef fishes evolved from
species with reduced dispersal ability that, after initial colonization, could not maintain contact with parent populations.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
17.
Population structure of the giant tiger prawn Penaeus monodon in Australian waters, determined using microsatellite markers 总被引:3,自引:0,他引:3
We describe three highly polymorphic microsatellite loci which have been isolated from the giant tiger prawn Penaeus monodon. The number of alleles present among 312 samples at the loci Pmo9, Pmo25 and Pmo27 were 84, 34 and 35, respectively, with
heterozygosities all >90%. Analyses of the distribution of length variation at three microsatellite loci among five Australian
P. monodon populations revealed strong differentiation between populations from the west and those from the northern and eastern coasts.
Tests for population differentiation (F
st) values and an analogous measure for microsatellite loci (R
st) all demonstrated that Western Australian P. monodon are a separate genetic stock which exhibits reduced genetic variation relative to the other populations. Reduced variability
is consistent with a recent population bottleneck or colonization by a small founding population from the east when sea links
between Indonesia, New Guinea and Australia were re-established following the last ice age. The results of this study are
in agreement with previous surveys of P. monodon conducted with allozymes and mtDNA.
Received: 18 December 1998 / Accepted: 27 August 1999 相似文献
18.
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
19.
Andrew J. Pemberton Lars J. Hansson Sean F. Craig Roger N. Hughes John D. D. Bishop 《Marine Biology》2007,153(1):71-82
Microscale genetic differentiation of sessile organisms can arise from restricted dispersal of sexual propagules, leading
to isolation by distance, or from localised cloning. Cyclostome bryozoans offer a possible combination of both: the localised
transfer of spermatozoa between mates with limited dispersal of the resulting larvae, in association with the splitting of
each sexually produced embryo into many clonal copies (polyembryony). We spatially sampled 157 colonies of Crisia denticulata from subtidal rock overhangs from one shore in Devon, England at a geographic scale of ca. 0.05 to 130 m plus a further 21
colonies from Pembrokeshire, Wales as an outgroup. Analysis of molecular variance (AMOVA) revealed that the majority (67%)
of genetic variation was distributed among individuals within single rock overhangs, with only 16% of variation among different
overhangs within each shore and 17% of variation between the ingroup and outgroup shores. Despite local genetic variation,
pairwise genetic similarity analysed by spatial autocorrelation was greatest at the smallest inter-individual distance we
tested (5 cm) and remained significant and positive across generally within-overhang comparisons (<4 m). Spatial autocorrelation
and AMOVA analyses both indicated that patches of C. denticulata located on different rock overhangs tended to be genetically distinct, with the switch from positive to negative autocorrelation,
which is often considered to be the distance within which individuals reproduce with their close relatives or the radius of
a patch, occurring at the 4–8 m distance class. Rerunning analyses with twenty data sets that only included one individual
of each multilocus genotype (n = 97) or the single data set that contained just the unique genotypes (n = 67) revealed that the presence of repeat genotypes had an impact on genetic structuring (PhiPT values were reduced when
shared genotypes were removed from the dataset) but that it was not great and only statistically evident at distances between
individuals of 1–2 m. Comparisons to a further 20 randomisations of the data set that were performed irrespective of genotype
(n = 97) suggested that this conclusion is not an artefact of reduced sample size. A resampling procedure using kinship coefficients,
implemented by the software package GENCLONE gave broadly similar results but the greater statistical power allowed small
but significant impacts of repeat genotypes on genetic structure to be also detected at 0.125–0.5 and 4–16 m. Although we
predict that a proportion of the repeat multilocus genotypes are shared by chance, such generally within-overhang distances
may represent a common distance of cloned larval dispersal. These results suggests that closely situated potential mates include
a significant proportion of the available genetic diversity within a population, making it unlikely that, as previously hypothesised,
the potential disadvantage of producing clonal broods through polyembryony is offset by genetic uniformity within the mating
neighbourhood. We also report an error in the published primer note of Craig et al. (Mol Ecol Notes 1:281–282, 2001): loci Cd5 and Cd6 appear to be the same microsatellite.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
20.
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