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1.
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
2.
Vermilion snapper (Rhomboplites aurorubens) were collected from four sites off the Atlantic coast of the USA and one site in the Gulf of Mexico to evaluate effective
population size and genetic stock structure. Previous studies had suggested geographic variation in the ratio of males to
females, so this population characteristic was explored in conjunction with the genetic analysis. Sex ratio varied greatly
among the five sample sites; males comprised 57% of samples in the Gulf of Mexico, while within the South Atlantic Bight they
comprised between 36% (Morehead City, North Carolina) and 53% (Carolina Beach, North Carolina) of samples. No clear geographic
trends in the sex ratio emerged; instead, it was found to vary with fish length, the percentage of males decreasing with increasing
size. Allelic variation assessed at seven dinucleotide microsatellite loci was large; gene diversities ranged from 0.43 to
0.95 and allelic counts from 7 to 39. Estimates of the effective population size ranged from 24 500 (based on the infinite-alleles
model) to 150 500 (based on the stepwise-mutation model). There was evidence for excess homozygosity within samples: estimates
of F
IS
(the correlation of alleles within individuals) ranged from 0.01 to 0.03 among the seven loci, and three estimates were significantly
greater than zero. Differentiation among localities was very weak, as estimates of F
ST
(the correlation of alleles within populations) were on the order of 0.001 to 0.002 and genetic distance estimates between
localities were not related to geographic distances. This suggested that vermilion snapper in the South Atlantic Bight (Cape
Hatteras, North Carolina to Cape Canaveral, Florida) and Gulf of Mexico are likely to consist of one genetic stock. Despite
the overall homogeneity, there were indications of a temporally dynamic local structure that would bear further examination.
Received: 6 July 1998 / Accepted: 9 February 1999 相似文献
3.
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
4.
Steve W. Ross Tara L. Casazza Andrea M. Quattrini Kenneth J. Sulak 《Marine Biology》2007,150(4):681-695
The distinctive larval stage of eels (leptocephalus) facilitates dispersal through prolonged life in the open ocean. Leptocephali are abundant and diverse off North Carolina, yet data on distributions and biology are lacking. The water column (from surface to 1,293 m) was sampled in or near the Gulf Stream off Cape Hatteras, Cape Lookout, and Cape Fear, North Carolina during summer through fall of 1999–2005, and leptocephali were collected by neuston net, plankton net, Tucker trawl, and dip net. Additional samples were collected nearly monthly from a transect across southern Onslow Bay, North Carolina (from surface to 91 m) from April 2000 to December 2001 by bongo and neuston nets, Methot frame trawl, and Tucker trawl. Overall, 584 tows were completed, and 224 of these yielded larval eels. The 1,295 eel leptocephali collected (combining all methods and areas) represented at least 63 species (nine families). Thirteen species were not known previously from the area. Dominant families for all areas were Congridae (44% of individuals, 11 species), Ophichthidae (30% of individuals, 27 species), and Muraenidae (22% of individuals, ten species). Nine taxa accounted for 70% of the overall leptocephalus catches (in order of decreasing abundance): Paraconger caudilimbatus (Poey), Gymnothorax ocellatus Agassiz complex, Ariosoma balearicum (Delaroche), Ophichthus gomesii (Castelnau), Callechelys muraena Jordan and Evermann, Letharchus aliculatus McCosker, Rhynchoconger flavus (Goode and Bean), Ophichthus cruentifer (Goode and Bean), Rhynchoconger gracilior (Ginsburg). The top three species represented 52% of the total eel larvae collected. Most leptocephali were collected at night (79%) and at depths > 45 m. Eighty percent of the eels collected in discrete depth Tucker trawls at night ranged from mean depths of 59–353 m. A substantial number (38% of discrete depth sample total) of larval eels were also collected at the surface (neuston net) at night. Daytime leptocephalus distributions were less clear partly due to low catches and lower Tucker trawl sampling effort. While net avoidance may account for some of the low daytime catches, an alternative explanation is that many species of larval eels occur during the day at depths > 350 m. Larvae of 21 taxa of typically shallow water eels were collected at depths > 350 m, but additional discrete depth diel sampling is needed to resolve leptocephalus vertical distributions. The North Carolina adult eel fauna (estuary to at least 2,000 m) consists of 51 species, 41% of which were represented in these collections. Many species of leptocephali collected are not yet known to have juveniles or adults established in the South Atlantic Bight or north of Cape Hatteras. Despite Gulf Stream transport and a prolonged larval stage, many of these eel leptocephali may not contribute to their respective populations. 相似文献
5.
Juveniles of the planehead filefish Stephano-lepishispidus (Pisces: Monacanthidae) (Linnaeus, 1766) are a major component of the Sargassum spp. community, yet little is known of their ecology. In this study, the otolith record of age, growth, and ontogeny in S.
hispidus was examined. Juveniles caught off Beaufort Inlet, North Carolina (USA) on 30 June 1996 were marked with alizarin complexone
and reared in a flow-through, outdoor tank for up to 19 days. Examination of marked otoliths at several time intervals showed
that increment formation was not significantly different than one increment per day, and thus, increment number was used to
estimate age. Depth-distribution, morphology, and meristics of larvae and juveniles collected (1990–1992) between Cape Romain,
South Carolina, and Cape Hatteras, North Carolina, were examined to identify the timing of the larval to juvenile transition.
All indicators suggested the transition occurred between 17 and 20 days. Mean otolith increment widths exhibited a marked
change at about 20 days, coinciding with the timing of the larval to juvenile transition and a change in the depth distribution
from bottom to surface waters. Increment width of individual juveniles, however, did not exhibit the same pattern; only 40%
conformed to the pattern identified for all fish. Thus, the record of the larval to juvenile transition is clear at the population
level, but unresolved at the individual level.
Received: 1 November 1999 / Accepted: 18 December 2000 相似文献
6.
Satellite tracking reveals a dichotomy in migration strategies among juvenile loggerhead turtles in the Northwest Atlantic 总被引:2,自引:2,他引:0
Katherine L. Mansfield Vincent S. Saba John A. Keinath John A. Musick 《Marine Biology》2009,156(12):2555-2570
Few data are available on the movements and behavior of immature Atlantic loggerhead sea turtles (Caretta caretta) from their seasonal neritic foraging grounds within the western north Atlantic. These waters provide developmental habitat
for loggerheads originating from several western Atlantic nesting stocks. We examined the long-term movements of 23 immature
loggerheads (16 wild-caught and seven headstart turtles) characterizing their seasonal distribution, habitat use, site fidelity,
and the oceanographic conditions encountered during their migrations. We identified two movement strategies: (1) a seasonal
shelf-constrained north–south migratory pattern; and (2) a year-round oceanic dispersal strategy where turtles travel in the
Gulf Stream to the North Atlantic and their northern dispersal is limited by the 10–15°C isotherm. When sea surface temperatures
dropped below 20°C, neritic turtles began a migration south of Cape Hatteras, North Carolina (USA) where they established
fidelity to the waters between North Carolina’s Outer Banks and the western edge of the Gulf Stream along outer continental
shelf. Two turtles traveled as far south as Florida. Several turtles returned to their seasonal foraging grounds during subsequent
summers. Northern movements were associated with both increased sea surface temperature (>21°C) and increased primary productivity.
Our results indicate strong seasonal and interannual philopatry to the waters of Virginia (summer foraging habitat) and North
Carolina (winter habitat). We suggest that the waters of Virginia and North Carolina provide important seasonal habitat and
serve as a seasonal migratory pathway for immature loggerhead sea turtles. North Carolina’s Cape Hatteras acts as a seasonal
“migratory bottleneck” for this species; special management consideration should be given to this region. Six turtles spent
time farther from the continental shelf. Three entered the Gulf Stream near Cape Hatteras, traveling in the current to the
northwest Atlantic. Two of these turtles remained within an oceanic habitat from 1 to 3 years and were associated with mesoscale
features and frontal systems. The ability of large benthic subadults to resume an oceanic lifestyle for extended periods indicates
plasticity in habitat use and migratory strategies. Therefore, traditional life history models for loggerhead sea turtles
should be reevaluated. 相似文献
7.
We used microsatellite genetic markers to investigate adult population structure and the formation of a new year-class in
Sebastes mystinus (blue rockfish). Since S. mystinus may live as long as 45 years and reach reproductive age at approximately 5 years, the adult population may contain as many
as eight generations of reproductive adults. We investigated whether the juveniles of the 2000 year-class and the adult population
were genetically homogeneous along the California coast. We sampled approximately 100 juveniles from three sites, two sites
along the Monterey Peninsula (Carmel and Monterey) in central California and one at Fort Ross in northern California, and
approximately 50 adult S. mystinus from five sites throughout the population center. The adult sampling spanned approximately 700 km from the northern Channel
Islands to Fort Bragg. The juveniles showed significant heterogeneity in allele frequencies among distant locations and genetic
homogeneity among adjacent locations. In contrast, the adults showed genetic homogeneity over large distances (San Miguel
Island to Fort Bragg), indicating little limitation of gene flow in this region. Allele frequencies of juveniles differed
from adult samples and in some cases reduced genetic diversity indicative of sweepstakes recruitment (small sample of the
adult reproductive potential). The genetic structure of the 2000 year-class suggests that despite a genetically homogenous
adult population, settled juveniles can be genetically heterogeneous along the California coast. The results also suggest
that the adults, with several year-classes, are capable of maintaining a panmictic population despite the genetic distinctiveness
of individual year-classes. 相似文献
8.
Juveniles of Leiognathus nuchalis were raised from fertilized eggs for up to 60 d and examined for luminescence activity. Almost all juveniles raised separately
from adults failed to produce detectable light. In contrast, a significant percentage (33 to 100%) of the juveniles became
luminescent in less than 48 h when they were either kept with adults or inoculated with a homogenate of the adult light organs.
The luminescence tended to increase with time after the treatments. These findings suggest that: (1) most of L. nuchalis offspring typically hatch and develop apo-symbiotically and (2) at least 45 d after hatching, juveniles can be infected with
symbiotic luminous bacteria from the light organ of adult fish, and thereby gain the ability to produce light.
Received: 16 February 1999 / Accepted: 21 September 1999 相似文献
9.
M. Thiel 《Marine Biology》2000,137(4):661-674
The population dynamics and reproductive biology of an ascidian- and a sponge-dwelling amphipod were examined. The two undescribed
amphipod species, Leucothoe“ascidicola” and L.“spongicola”, are closely related to each other, and occur in ascidians and sponges, respectively, along the Florida Atlantic coast.
L. “ascidicola” was abundant in solitary ascidians during fall 1997, disappeared during spring/early summer, and became abundant again in
September 1998. During the time when L. “ascidicola” were absent from their hosts, a copepod became a frequent inhabitant of the ascidians but disappeared again when L.“ascidicola” returned to the ascidians in September 1998. The numbers of L.“spongicola” in sponges increased substantially during spring, when high reproductive activity was observed. Following this reproductive
peak, both adult and juvenile amphipods apparently left the sponges, and during the summer amphipod numbers in the sponges
were very low. Another small amphipod species, which often co-occurred with L.“spongicola”, showed less seasonal variation and was found in sponges throughout the whole study period. The percentage of ovigerous
females per host unit was usually lower in the ascidian-dwelling than in the sponge-dwelling amphipods. In solitary ascidians,
L.“ascidicola” amphipods usually occurred in groups of several adults, yet there never was more than one ovigerous female per ascidian.
In contrast, several ovigerous L.“spongicola” females were found to cohabit in the same spongocoel. This suggests that intrasexual aggression may be stronger among reproductive
amphipod females in the ascidians than in sponges. The size distributions of juvenile cohorts indicate that juvenile L.“ascidicola” remain for relatively long time periods in the parental ascidian, where they may reach sexual maturity. In contrast, in
L.“spongicola”, only cohorts of very small juveniles could be identified, indicating that juveniles disperse shortly after emerging from
the female's brood pouch. It is concluded that extended parental care is of very short duration or does not occur in the sponge-dwelling
amphipod L. “spongicola”, possibly because fast-growing sponges with a highly branched spongocoel system do not allow long-lasting coexistence of
parent-offspring groups. In contrast, the discrete character of the solitary ascidians may enhance the potential for exclusion
of other species, resource monopolization by reproductive females, and furthermore for long-lasting extended parental care
in the ascidian-dwelling amphipod. Groups of single parents together with cohorts of large juveniles are reported in the literature
for amphipods and isopods from brachiopods, bivalves and ascidians, suggesting that these discrete biotic microhabitats may
favor the evolution of extended parental care in peracarid crustaceans.
Received: 30 July 1999 / Accepted: 8 May 2000 相似文献
10.
Relatively little overlap exists in faunal assemblages in the oceanic waters found north of, and over the reef-like structure south of, Cape Hatteras, North Carolina, USA. To better understand the mechanisms influencing the zoogeography of these animals, metabolic-temperature patterns have been characterized for both larvae and adults of animals collected in waters north and south of Cape Hatteras and from the Caribbean Sea. Southern affinity species from north of Cape Hatteras are the most metabolically labile of the groups, based on seasonal and laboratory-acclimated studies. Adults having a northern affinity found north of Cape Hatteras are metabolically depressed at high temperatures, whereas species from the reef area and the Caribbean are metabolically depressed at low temperatures. Metabolic rates of first stage zoea of crabs from the reef area are depressed at lower temperatures than larvae of the same stage of other species of crabs from the Cape Hatteras region or the Caribbean Sea.Supported by Grant NSF GB 7435 from the National Science Foundation. The authors thank Duke University Marine Laboratory and the Cooperative Program of Biological Oceanography for the use of the R.V. Eastward. The Co-operative Program is supported through the National Science Foundation Grant GB-8189. 相似文献
11.
Lane snappers (Lutjanus synagris), sampled from eight localities in the northern Gulf of Mexico (Gulf) and one locality along the Atlantic coast of Florida,
were assayed for allelic variation at 14 nuclear-encoded microsatellites and for sequence variation in a 590 base-pair fragment
of the mitochondrially encoded ND-4 gene (mtDNA). Significant heterogeneity among the nine localities in both microsatellite
allele and genotype distributions and mtDNA haplotype distributions was indicated by exact tests and by analysis of molecular
variance (AMOVA). Exact tests between pairs of localities and spatial analysis of molecular variance (SAMOVA) for both microsatellites
and mtDNA revealed two genetically distinct groups: a Western Group that included six localities from the northwestern and
northcentral Gulf and an Eastern Group that included three localities, one from the west coast of Florida, one from the Florida
Keys, and one from the east (Atlantic) coast of Florida. The between-groups component of molecular variance was significant
for both microsatellites (Φ
CT = 0.016, P = 0.009) and mtDNA (Φ
CT = 0.208, P = 0.010). Exact tests between pairs of localities within each group and spatial autocorrelation analysis did not reveal genetic
heterogeneity or an isolation-by-distance effect among localities within either group. MtDNA haplotype diversity was significantly
less (P < 0.0001) in the Western Group than in the Eastern Group; microsatellite allelic richness and gene diversity also were significantly
less in the Western Group (P = 0.015 and 0.013, respectively). The difference in genetic variability between the two groups may reflect reduced effective
population size in the Western Group and/or asymmetric rates of genetic migration. The relative difference in variability
between the two groups was substantially greater in mtDNA and may reflect one or more mtDNA selective sweeps; tests of neutrality
of the mtDNA data were consistent with this possibility. Bayesian analysis of genetic demography indicated that both groups
have experienced a historical decline in effective population size, with the decline being greater in the Western Group. Maximum-likelihood
analysis of microsatellite data indicated significant asymmetry in average, long-term migration rates between the two groups,
with roughly twofold greater migration from the Western Group to the Eastern Group. The difference in mtDNA variability and
the order-of-magnitude difference in genetic divergence between mtDNA and microsatellites may reflect different demographic
events affecting mtDNA disproportionately and/or a sexual and/or spatial bias in gene flow and dispersal. The spatial discontinuity
among lane snappers in the region corresponds to a known zone of vicariance in other marine species. The evidence of two genetically
distinct groupings (stocks) has implications for management of lane snapper resources in the northern Gulf. 相似文献
12.
Genetic structure and phylogeography of the lined shore crab, Pachygrapsus crassipes, along the northeastern and western Pacific coasts 总被引:1,自引:0,他引:1
Marine invertebrates with high larval dispersal capacity typically exhibit low degrees of population differentiation, which reflects both contemporary and historical processes. We sampled 346 individuals from seven populations of the lined shore crab, Pachygrapsus crassipes Randall, along the northeastern Pacific Coast and Korea during summer 2003. DNA sequence analysis of 613 bp of the mitochondrial COI gene showed that overall gene diversity (h) was high (0.92±0.01), whereas overall nucleotide diversity (π) was low (0.009±0.005). A total of 154 mtDNA haplotypes were identified; however, 114 were present in only one individual. Analysis of molecular variance revealed significant genetic structuring at Point Conception, CA, USA, that is likely due to the oceanographic circulation patterns, which result in asymmetrical migration of haplotypes. However, genetic variation among eastern Pacific populations was generally low, probably because of high contemporary gene flow and recent common ancestry of haplotypes. Mismatch analysis and nested clade analysis suggested that the population history of this region is characterized by two contiguous northwards range expansions, which are congruent with Late Pleistocene glacial cycles. Highly significant genetic differentiation was detected between eastern Pacific populations and Korea, indicating transpacific gene flow is restricted. Time of divergence between the two transpacific lineages was estimated between 0.8 and 1.2 Myrs ago. The small, recently founded population of P. crassipes at Bamfield, BC, Canada, did not appear to have undergone a founder effect. 相似文献
13.
The degree of population subdivision among collections of young-of-the-year (YOY) Spanish mackerel Scomberomorus maculatus sampled from along the Atlantic coast of the United States (Atlantic) and Gulf of Mexico (Gulf) was examined. Young-of-the-year
were collected from spawning areas to minimize possible mixing among putative spawning stocks that may occur at later life
history stages along migratory pathways or at over-wintering grounds. Restriction fragment length polymorphism (RFLP) analysis
of the mitochondrial DNA (mtDNA) ND4 region and a nuclear actin intron was conducted. Collections in each of two years were
analyzed to minimize bias associated with sampling at a single point in space or time. Substantial variation was detected
at ND4 (haplotype diversity=0.81) and at the actin intron locus (gene diversity=0.21). Significant differences in gene diversity
or allele frequencies were not detected among temporal samples at any of three locations. A homogeneous distribution of genetic
variance among samples from widely spaced geographic regions was consistent with the hypothesis that Spanish mackerel comprise
a single intermingling genetic stock. Power analysis showed that the mitochondrial analysis from this study was much more
likely to detect population subdivision than analysis of the nuclear actin locus, despite lower mtDNA sample size.
Received: 3 January 2000 / Accepted: 28 August 2000 相似文献
14.
Restriction-site variation in mitochondrial (mt) DNA was assayed among 1675 red drum (Sciaenops ocellatus Linnaeus) sampled from 20 localities along the southeastern coast of the USA (western Atlantic) and the Gulf of Mexico (Gulf).
Up to four consecutive year-classes (cohorts) were sampled at most localities. Nucleotide-sequence divergence among 170 mtDNA
haplotypes identified ranged (in percentage) from 0.184 to 1.913, with a mean (±SD) of 0.887 ± 0.300. Comparisons of mtDNA
haplotype frequencies across year-classes within localities were non-significant, indicating temporal stability of breeding
components within localities. Significant heterogeneity in mtDNA haplotype frequencies was found across all localities, between
(pooled) samples from the western Atlantic and the Gulf, and among geographically spaced, regional groupings in the Gulf.
Genetic divergence between subpopulations of red drum in the western Atlantic and Gulf follows a pattern exhibited in other
marine fishes, and probably stems from physical (historical environmental heterogeneity, absence of suitable habitat, and
current patterns) and, perhaps, behavioral factors. Genetic differences among red drum in the Gulf appear to be due largely
to an isolation-by-distance effect that is attributable to behavioral factors. The latter may include female philopatry to
natal bays or estuaries, limited offshore (coastwise) movement of females relative to their natal bay or estuary, or both.
Genetic divergence among red drum in the Gulf occurs despite high gene flow (estimated as the number of genetic effective
migrants in an island mode). Conservation and management of red drum should be based on the premise that strategies for a
given bay or estuary will impact geographically proximal bays or estuaries more than distal ones. Trajectories of correlograms
in spatial autocorrelation analysis suggest a geographic neighborhood size, relative to genetic migration of red drum from
a bay or estuary, of roughly 500 to 600 km.
Received: 22 July 1998 / Accepted: 19 November 1998 相似文献
15.
Genetic stock structure of the swordfish (Xiphias gladius ) inferred by PCR-RFLP analysis of the mitochondrial DNA control region 总被引:2,自引:0,他引:2
Restriction fragment length polymorphism (RFLP) analysis was performed on PCR amplified DNA fragments containing the control
region of the swordfish (Xiphias gladius Linnaeus, 1758) mitochondrial DNA. A total of 456 individuals comprising 13 local samples (six Pacific, three Atlantic, the
Mediterranean Sea, two Indian Ocean and the Cape of Good Hope) were surveyed with four endonucleases (Alu I, Dde I, Hha I and Rsa I), yielding a total of 52 composite genotypes. Within-sample genotypic diversity (H) was high ranging from 0.702 to 0.962 with a value of 0.922 for the pooled sample. Significant geographic variation in the
frequencies of genotypes and restriction patterns was revealed. The Mediterranean sample was highly distinct from all other
samples. Further, Rsa I digestion revealed high levels of polymorphism in all but the Mediterranean samples, indicating that exogenous swordfishes
rarely enter that body of water. Heterogeneity between the North and South Atlantic samples was significant, both of which
differed from those of the Pacific. In contrast, the Indian Ocean samples were not significantly different from the samples
of South Atlantic and Pacific. Genetic differentiation among the Pacific samples was low. The results indicate that the world-wide
swordfish population is genetically structured not only among, but also within ocean basins and suggest that gene flow is
restricted despite the absence of geographic barriers.
Received: 28 August 1996 / Accepted: 2 October 1996 相似文献
16.
The relative roles of kinship and familiarity in affecting an individual’s growth and fitness are not easy to disentangle.
Not only is an individual more likely to have prior behavioral interactions with conspecifics in close proximity, it may also
be related (in terms of kinship) to those nearby conspecifics. While some studies have inferred that kin discrimination affects
fitness correlates, other studies found that familiarity alone can reduce aggressive interactions, thus increasing fitness.
These studies have all focused on intra-age class pairs or groups. However, many animals interact with conspecifics from different
cohorts. In many populations, adults of Plethodon cinereus territorially defend rocks and logs that retain moisture and food resources. We investigated whether juveniles of P. cinereus grew more in the presence of adults that were relatives or familiar. We collected pairs of juveniles and adults found under
the same cover objects in the forest (familiar) and pairs of juveniles and adults found under different cover objects, approximately
10 m apart (unfamiliar). We determined parentage and relatedness of the adult–juvenile pairs and then placed these pairs in
semi-natural mesocosms for 17 days. We found that juveniles housed with familiar adults had significantly greater increases
in mass and snout–vent length than juveniles housed with unfamiliar adults in 2006 but not in 2007. Relatedness had no effect
on growth. In addition, juveniles cohabitating with adults were not more likely to be their offspring. At least under certain
environmental conditions, familiarity with adults, independent of relatedness or parentage, increased the growth of juvenile
salamanders. 相似文献
17.
Demersal 0-group Atlantic cod (Gadus morhua L.) were collected in Trinity Bay, Newfoundland, Canada, between August 1993 and January 1994. Diet composition and simple
indices of condition (hepato-somatic index, condition factors and body ash content) were determined. Laboratory experiments
were also conducted to determine whether simple indices of condition reflect differences in energy intake (ration level) and
to determine minimum index of condition values, assessed from 0-group cod that died due to exhaustion of their energy reserves.
Determination of lower critical indices of condition provided a meaningful interpretation of field data on feeding, condition
and survival of 0-group cod. In the wild, indices of condition reflecting variation in liver and muscle energy reserves of
cod increased rapidly with the consumption of Calanus finmarchicus, which exhibited a high incidence of oil sacs, and declined abruptly when this lipid-rich prey was no longer consumed. Liver
and muscle condition of 0-group cod from the field varied seasonally, but their condition was consistently above that of cod
that died in the laboratory. Laboratory studies, using three ration levels, revealed that condition indices differed over
time and among ration levels. Indices of condition representing variation in muscle energy reserves exhibited a steady decline
once the hepato-somatic index fell below about 2.0. We interpret this as evidence for depletion of lipids first and then proteins,
a pattern similar to that of larger juveniles and adults. We conclude that as long as 0-group cod are above a “safe” level
of condition their body length can still increase even when condition is declining.
Received: 2 September 1997 / Accepted: 8 December 1998 相似文献
18.
Global population structure of albacore (Thunnus alalunga) inferred by RFLP analysis of the mitochondrial ATPase gene 总被引:1,自引:0,他引:1
The genetic population structure of the highly migratory albacore (Thunnus alalunga) was investigated using restriction fragment length polymorphism (RFLP) analysis of the mitochondrial ATPase gene amplified by the polymerase chain reaction (PCR). 620 individuals comprising 13 geographically distant samples (ten Pacific, two Atlantic and the Cape of Good Hope) were surveyed between 1991 and 1994 with two restriction endonucleases (Mse I and Rsa I), resulting in seven haplotypes. No heterogeneity was observed in the distribution of haplotypes among the ten samples from the North and South Pacific, nor among the samples from North and South Atlantic and Cape of Good Hope. However, highly significant heterogeneity was evident among Atlantic and Pacific samples. Higher haplotypic diversity (h) was observed in the Pacific samples (0.59 to 0.69) than in the Atlantic and Cape samples (0.22 to 0.43). These results suggest greater gene flow between albacore of the northern and southern hemispheres (within oceans) than between the Atlantic and Pacific Oceans. 相似文献
19.
New information on the brooding reproduction of Amphiura carchara, and previous studies of several deep-sea congeners, contradict the prevailing notion that direct development is exceptional
among deep-sea echinoderms. Over 500 specimens of A. carchara from 2,850 to 4,100-m depths off the coast of California, USA, were studied. The species was found to be gonochoric, although
most brooding species of ophiuroids are hermaphroditic. Females each brooded up to 72 embryos at a time, with up to 10 in
a single bursa. The embryos of individual adults were often at different stages of development, but those brooded in a single
bursa tended to be at the same stage. Thus, the species has characteristics that breach the distinctions between sequential
and simultaneous brooding exhibited by shallow-water ophiuroids. The embryos developed from yolky eggs that are large for
an ophiuroid, with the mean largest oocytes 0.45 mm, and ranging to 1.28 mm in diameter. Almost all late-stage embryos were
positioned with their mouth and arms pressed against the wall of the bursa, possibly to facilitate the uptake of nutrients
from the parent. Thus, A. carchara may be matrotrophic. The largest embryos examined had a rudimentary disk skeleton, and arms with four joints and a terminal
plate. Emerging juveniles probably differ in disk diameter. The species appears to brood year round, although differences
in gonad size, the incidence of brooding, and the relative numbers of early developmental stages in summer and winter samples
indicated that there are seasonal trends in reproduction.
Received: 14 February 2000 / Accepted: 3 July 2000 相似文献
20.
Genetic structure of the flounders Platichthys flesus and P. stellatus at different geographic scales 总被引:1,自引:0,他引:1
The genetic structure of the flounders Platichthys flesus L. and P. stellatus Pallas was investigated on different spatial scales through analysis of allozyme variation at 7 to 24 polymorphic loci in
samples collected from different regions (Baltic Sea, North Sea, Brittany, Portugal, western Mediterranean, Adriatic Sea,
Aegean Sea and Japan) in 1984 to 1987. No geographic variation was evident within a region. Some pattern of differentiation
by distance was inferred within the Atlantic, while the Mediterranean comprised three geographically isolated populations
and was itself geographically isolated from the Atlantic (fixed allele differences at up to three loci were found among P. flesus populations from the Atlantic, the western Mediterranean, the Adriatic Sea, the Aegean Sea and also P. stellatus from the coast of Japan). Sea temperature during the reproductive period probably acts as a barrier to gene flow between
populations. Genetic distances among European flounder populations (P. flesus) were higher than, or of the same magnitude as, the genetic distance between Pacific (P. stellatus) and European flounder populations, suggesting that P. flesus is paraphyletic and/or there is no phylogenetic basis to recognising P. stellatus as a different species. The divergence between P. flesus and P. stellatus was thus inferred to be more recent than the divergence between the present P. flesus populations from the NE Atlantic and eastern Mediterranean. The eastern Mediterranean populations are thought to originate
from the colonisation of the Mediterranean by a proto-P. flesus/P. stellatus ancestor, whereas the present western Mediterranean population has undergone a more recent colonisation event by P. flesus. Patterns of mitochondrial DNA variation, established on a smaller array of P. flesus samples, were in accordance with the geographic patterns inferred from the allozyme survey. In addition, they supported the
hypothesis of a two-step colonisation of the western Mediterranean. These results contribute to our understanding of the biogeography
of the Mediterranean marine fauna, especially the group of boreal remnants to which P. flesus belongs.
Received: 7 February 1997 / Accepted: 26 March 1997 相似文献