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1.
Thuy Yen Duong Kim T. Scribner Patrick S. Forsythe James A. Crossman Edward A. Baker 《Molecular ecology》2013,22(5):1282-1294
Quantifying interannual variation in effective adult breeding number (Nb) and relationships between Nb, effective population size (Ne), adult census size (N) and population demographic characteristics are important to predict genetic changes in populations of conservation concern. Such relationships are rarely available for long‐lived iteroparous species like lake sturgeon (Acipenser fulvescens). We estimated annual Nb and generational Ne using genotypes from 12 microsatellite loci for lake sturgeon adults (n = 796) captured during ten spawning seasons and offspring (n = 3925) collected during larval dispersal in a closed population over 8 years. Inbreeding and variance Nb estimated using mean and variance in individual reproductive success derived from genetically identified parentage and using linkage disequilibrium (LD) were similar within and among years (interannual range of Nb across estimators: 41–205). Variance in reproductive success and unequal sex ratios reduced Nb relative to N on average 36.8% and 16.3%, respectively. Interannual variation in Nb/N ratios (0.27–0.86) resulted from stable N and low standardized variance in reproductive success due to high proportions of adults breeding and the species' polygamous mating system, despite a 40‐fold difference in annual larval production across years (437–16 417). Results indicated environmental conditions and features of the species' reproductive ecology interact to affect demographic parameters and Nb/N. Estimates of Ne based on three single‐sample estimators, including LD, approximate Bayesian computation and sibship assignment, were similar to annual estimates of Nb. Findings have important implications concerning applications of genetic monitoring in conservation planning for lake sturgeon and other species with similar life histories and mating systems. 相似文献
2.
Sexual selection has minimal impact on effective population sizes in species with high rates of random offspring mortality: An empirical demonstration using fitness distributions
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Alison Pischedda Urban Friberg Andrew D. Stewart Paige M. Miller William R. Rice 《Evolution; international journal of organic evolution》2015,69(10):2638-2647
The effective population size (Ne) is a fundamental parameter in population genetics that influences the rate of loss of genetic diversity. Sexual selection has the potential to reduce Ne by causing the sex‐specific distributions of individuals that successfully reproduce to diverge. To empirically estimate the effect of sexual selection on Ne, we obtained fitness distributions for males and females from an outbred, laboratory‐adapted population of Drosophila melanogaster. We observed strong sexual selection in this population (the variance in male reproductive success was ~14 times higher than that for females), but found that sexual selection had only a modest effect on Ne, which was 75% of the census size. This occurs because the substantial random offspring mortality in this population diminishes the effects of sexual selection on Ne, a result that necessarily applies to other high fecundity species. The inclusion of this random offspring mortality creates a scaling effect that reduces the variance/mean ratios for male and female reproductive success and causes them to converge. Our results demonstrate that measuring reproductive success without considering offspring mortality can underestimate Ne and overestimate the genetic consequences of sexual selection. Similarly, comparing genetic diversity among different genomic components may fail to detect strong sexual selection. 相似文献
3.
Effective population size (N e) quantifies the effects of micro-evolutionary processes and the rate of loss of genetic diversity in a population. Several demographic and mating parameters reduce N e. Theoretical studies elucidate the impacts of various demographic and mating system parameters on N e, while empirical studies illustrate realized N e for species with differing life histories and mating systems. However, effect of intra-specific variation in mating system on effective size remains largely unexplored. In this paper we investigated the effect of promiscuous and polygynous mating on N e in two wild populations of the short-nosed fruit bat, Cynopterus sphinx. N e/N (ratio of effective population size to census size) was lower than unity in both populations, and much lower for the polygynous population compared to promiscuous population. Elasticity analyses reveal that N e/N was sensitive to deviations in the sex ratio. Variance in female reproductive success had a higher impact on N e compared to variance in male reproductive success in the promiscuous population. However, for the polygynous population, impact of variance in male reproductive success on N e was higher than that of variance in female reproductive success. Our results suggest that depending on mating system, different populations of the same species could have alternate evolutionary trajectories. The rate of loss of genetic diversity would be lower for the promiscuous population compared to the polygynous population. Our study is the first to highlight which parameters would most significantly impact population specific N e under different mating systems. 相似文献
4.
1. There is growing evidence that sexually mature but morphologically juvenile males of Atlantic salmon (precocious or mature male parr) actively participate in reproduction and, therefore, in the genetic composition of the populations of this species. The impact of mature male parr on the effective population size (Ne) of such populations has been previously studied under experimental settings, but no studies have been performed directly on natural populations. 2. Continuous monitoring and sampling of all sea returns is possible in the Lérez River (northwest of Spain). From demographic data on variances of reproductive success and genetic data from six microsatellite marker loci we carried out parentage assignment and assessed the impact of male parr on demographic and genetic estimates of Ne in two consecutive years. 3. Our results reveal that: (i) approximately 60% of the total sire paternity is attributable to mature parr; (ii) mature parr decrease the variance of reproductive success of males by a threefold factor and increase the effective population size of males by a 10‐fold factor; (iii) however, they do not substantially affect the variance of reproductive success and the effective size of females; (iv) mature parr increase two‐to threefold the overall effective size of the population but the ratio Ne/N, where N is the population size including or not mature parr in each case, is not affected. 相似文献
5.
John S. Hargrove Jesse McCane Curtis J. Roth Brett High Matthew R. Campbell 《Ecology and evolution》2021,11(16):11295
Mating systems and patterns of reproductive success in fishes play an important role in ecology and evolution. While information on the reproductive ecology of many anadromous salmonids (Oncorhynchus spp.) is well detailed, there is less information for nonanadromous species including the Yellowstone Cutthroat Trout (O. clarkii bouvieri), a subspecies of recreational angling importance and conservation concern. Using data from a parentage‐based tagging study, we described the genetic mating system of a migratory population of Yellowstone Cutthroat Trout, tested for evidence of sexual selection, and identified predictors of mating and reproductive success. The standardized variance in mating success (i.e., opportunity for sexual selection) was significantly greater for males relative to females, and while the relationship between mating success and reproductive success (i.e., Bateman gradient) was significantly positive for both sexes, a greater proportion of reproductive success was explained by mating success for males (r 2 = 0.80) than females (r 2 = 0.59). Overall, the population displayed a polygynandrous mating system, whereby both sexes experienced variation in mating success due to multiple mating, and sexual selection was variable across sexes. Tests for evidence of sexual selection indicated the interaction between mating success and total length best‐predicted relative reproductive success. We failed to detect a signal of inbreeding avoidance among breeding adults, but the group of parents that produced progeny were on average slightly less related than adults that did not produce progeny. Lastly, we estimated the effective number of breeders (N b) and effective population size (N e) and identified while N b was lower than N e, both are sufficiently high to suggest Yellowstone Cutthroat Trout in Burns Creek represent a genetically stable and diverse population. 相似文献
6.
Robin S. Waples Tiago Antao 《Evolution; international journal of organic evolution》2014,68(6):1722-1734
In iteroparous species, it is easier to estimate Nb (effective number of breeders in one reproductive cycle) than Ne (effective population size per generation). Nb can be used as a proxy for Ne and also can provide crucial insights into eco‐evolutionary processes that occur during reproduction. We used analytical and numerical methods to evaluate effects of intermittent breeding and litter/clutch size on inbreeding Nb and Ne. Fixed or random litter sizes ≥ 3 have little effect on either effective‐size parameter; however, in species (e.g., many large mammals) in which females can produce only one offspring per cycle, female Nb = ∞ and overall Nb = 4Nb(male). Intermittent breeding reduces the pool of female breeders, which reduces both female and overall Nb; reductions are larger in high‐fecundity species with high juvenile mortality and increase when multiple reproductive cycles are skipped. Simulated data for six model species showed that both intermittent breeding and litter‐size constraints increase Ne, but only slightly. We show how to quantitatively account for these effects, which are important to consider when (1) using Nb to estimate Ne, or (2) drawing inferences about male reproductive success based on estimates of female Nb. 相似文献
7.
Gregorio Sánchez‐Montes Jinliang Wang Arturo H. Ariño José Luis Vizmanos Iñigo Martínez‐Solano 《Ecology and evolution》2017,7(23):10301-10314
The ratio of the effective number of breeders (Nb) to the adult census size (Na), Nb/Na, approximates the departure from the standard capacity of a population to maintain genetic diversity in one reproductive season. This information is relevant for assessing population status, understanding evolutionary processes operating at local scales, and unraveling how life‐history traits affect these processes. However, our knowledge on Nb/Na ratios in nature is limited because estimation of both parameters is challenging. The sibship frequency (SF) method is adequate for reliable Nb estimation because it is based on sibship and parentage reconstruction from genetic marker data, thereby providing demographic inferences that can be compared with field‐based information. In addition, capture–mark–recapture (CMR) robust design methods are well suited for Na estimation in seasonal‐breeding species. We used tadpole genotypes of three pond‐breeding amphibian species (Epidalea calamita, Hyla molleri, and Pelophylax perezi, n = 73–96 single‐cohort tadpoles/species genotyped at 15–17 microsatellite loci) and candidate parental genotypes (n = 94–300 adults/species) to estimate Nb by the SF method. To assess the reliability of Nb estimates, we compared sibship and parentage inferences with field‐based information and checked for the convergence of results in replicated subsampled analyses. Finally, we used CMR data from a 6‐year monitoring program to estimate annual Na in the three species and calculate the Nb/Na ratio. Reliable ratios were obtained for E. calamita (Nb/Na = 0.18–0.28) and P. perezi (0.5), but in H. molleri, Na could not be estimated and genetic information proved insufficient for reliable Nb estimation. Integrative demographic studies taking full advantage of SF and CMR methods can provide accurate estimates of the Nb/Na ratio in seasonal‐breeding species. Importantly, the SF method provides results that can be readily evaluated for reliability. This represents a good opportunity for obtaining robust demographic inferences with wide applications for evolutionary and conservation research. 相似文献
8.
C. L. Pruett J. A. Johnson L. C. Larsson D. H. Wolfe M. A. Patten 《Conservation Genetics》2011,12(5):1205-1214
Assessments of census size (N
c) and effective population size (N
e) are necessary for the conservation of species exhibiting population declines. We examined two populations (Oklahoma and
New Mexico) of the lesser prairie-chicken (Tympanuchus pallidicinctus), a declining lek-breeding bird, in which one population (Oklahoma) has larger clutch size and more nesting attempts per
year but lower survival caused by human changes to the landscape. We estimated demographic and genetic estimates of N
e for each population and found that both populations have low N
e estimates with a risk of inbreeding depression. Although Oklahoma females produce a larger number of offspring, the proportion
of females successfully reproducing is not higher than in New Mexico. Higher reproductive effort has likely reached a physiological
limit in Oklahoma prairie-chickens but has not led to a higher N
e or even a larger N
c than New Mexico. We propose that future conservation efforts focus on maximizing survivorship and decreasing the variance
in reproductive success because these factors are more likely than increasing reproductive output alone to yield population
persistence in lek-breeding species. 相似文献
9.
In 1996 and 1997, the spawning behavior of fluvial white-spotted charr Salvelinus leucomaenis, was observed in the upstream area of an erosion control dam. A small number of males with relatively large body size mated successfully with females as a pair, while almost all satellite males did not sneak successfully, resulting in a non-random mating system. The low sneaking success of subordinate males, in addition to the monopolization of spawning opportunities by a few dominant males, is one of the most important causes of skewed reproductive success among males. The total number of adult fishes in the study area (N: approximately half of the whole tributary above a dam) was estimated as 148 and 102 in 1996 and 1997, respectively. Based on these findings and some further assumptions, the estimated effective population size (Ne) was low in both years. The Ne/N ratio ranged from 0.33 to 0.36 in both years. In addition to reduced population size by construction of an impassable dam, the above-dam population suffered low Ne due to skewed reproductive success among males. The low Ne may be one cause of extinction in above-dam populations of fluvial charr, especially just after the construction of impassable barriers. 相似文献
10.
Devon L. Johnstone Michael F. O'Connell Friso P. Palstra Daniel E. Ruzzante 《Molecular ecology》2013,22(9):2394-2407
We describe temporal changes in the genetic composition of a small anadromous Atlantic salmon (Salmo salar) population from South Newfoundland, an area where salmon populations are considered threatened (COSEWIC 2010). We examined the genetic variability (13 microsatellite loci) in 869 out‐migrating smolt and post‐spawning kelt samples, collected from 1985 to 2011 for a total of 22 annual collections and a 30 year span of assigned cohorts. We estimated the annual effective number of breeders (Nb) and the generational effective population size (Ne) through genetic methods and demographically using the adult sex ratio. Comparisons between genetic and demographic estimates show that the adult spawners inadequately explain the observed Ne estimates, suggesting that mature male parr are significantly increasing Nb and Ne over the study period. Spawning as parr appears to be a viable and important strategy in the near absence of adult males. 相似文献
11.
Synopsis A sweepstakes–mismatch process whereby reproduction is poorly coordinated with appropriate resources for larval development and recruitment can result in large variance in reproductive success among individuals and spawning aggregations. This process has been proposed to explain low ratio of genetic effective population size (Ne) to adult census size (N) ratios in marine species with high fecundity, pelagic spawning, and extensive mortality in early life stages. This process is also hypothesized to also account for very low Ne/N (≈ 0.001) observed in the federally endangered Rio Grande silvery minnow, Hybognathus amarus. This species is a freshwater fish that shares life-history features with marine pelagic spawners. We tested two key predictions of the sweepstakes–mismatch hypothesis using molecular data: (i) that temporally distinct samples of eggs differ in genetic composition and, (ii) that egg samples do not comprise a random subset of potential adult breeders. We present genetic data that supports both predictions and that are consistent with the hypothesis that high variance in reproductive success among adult breeders is an important factor that lowers Ne/N in H. amarus. This study highlights the importance of understanding the interaction of early life history and fragmentation in devising conservation plans for endangered aquatic organisms. 相似文献
12.
Isabel Castro Karen M. Mason Doug P. Armstrong David M. Lambert 《Conservation Genetics》2004,5(3):381-393
We collected genetic and behavioural data on hihi (Notiomysts cincta, an endangered New Zealand bird) after reintroduction to Mokoia Island to assess the effect of extrapair copulation on effective population size (N
e), and investigate the potential for increasing N
e through behavioural management. DNA fingerprinting revealed that 46% of chicks (n = 188) resulted from extra-pair paternity, and 82% of broods (n = 56) had at least one extra-pair chick. Of the extra-pair young, 34%(n = 89) were from unpaired males, and the remainder were from paired males. Variance in reproductive success (VRS) among individuals changed between years, and the relative variance among males and females depended on the sex ratio. VRS increased when measured over longer time scales, the variance in recruits being three times higher than the variance in the number of hatchlings. Extra-pair copulation increased VRS by 150% in 1 year and decreased it by 30% in another year, but this only caused a 4% decrease and 8% increase, respectively, to N
e/N. Although there is potential to manage VRS in this species through behavioural management, a more important factor is adult lifespan, which is the main correlate of lifetime reproductive success as well as the determinant of generation time. The high annual mortality rate in Mokoia hihi (females = 64%, males = 52%) has prevented the population from growing, so the key factors limiting N and N
e/N are the same. 相似文献
13.
Multiple estimates of effective population size for monitoring a long‐lived vertebrate: an application to Yellowstone grizzly bears
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Pauline L. Kamath Mark A. Haroldson Gordon Luikart David Paetkau Craig Whitman Frank T. van Manen 《Molecular ecology》2015,24(22):5507-5521
Effective population size (Ne) is a key parameter for monitoring the genetic health of threatened populations because it reflects a population's evolutionary potential and risk of extinction due to genetic stochasticity. However, its application to wildlife monitoring has been limited because it is difficult to measure in natural populations. The isolated and well‐studied population of grizzly bears (Ursus arctos) in the Greater Yellowstone Ecosystem provides a rare opportunity to examine the usefulness of different Ne estimators for monitoring. We genotyped 729 Yellowstone grizzly bears using 20 microsatellites and applied three single‐sample estimators to examine contemporary trends in generation interval (GI), effective number of breeders (Nb) and Ne during 1982–2007. We also used multisample methods to estimate variance (NeV) and inbreeding Ne (NeI). Single‐sample estimates revealed positive trajectories, with over a fourfold increase in Ne (≈100 to 450) and near doubling of the GI (≈8 to 14) from the 1980s to 2000s. NeV (240–319) and NeI (256) were comparable with the harmonic mean single‐sample Ne (213) over the time period. Reanalysing historical data, we found NeV increased from ≈80 in the 1910s–1960s to ≈280 in the contemporary population. The estimated ratio of effective to total census size (Ne/Nc) was stable and high (0.42–0.66) compared to previous brown bear studies. These results support independent demographic evidence for Yellowstone grizzly bear population growth since the 1980s. They further demonstrate how genetic monitoring of Ne can complement demographic‐based monitoring of Nc and vital rates, providing a valuable tool for wildlife managers. 相似文献
14.
Consequences of multiple mating‐system shifts for population and range‐wide genetic structure in a coastal dune plant
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Evolutionary transitions from outcrossing to selfing can strongly affect the genetic diversity and structure of species at multiple spatial scales. We investigated the genetic consequences of mating‐system shifts in the North American, Pacific coast dune endemic plant Camissoniopsis cheiranthifolia (Onagraceae) by assaying variation at 13 nuclear (n) and six chloroplast (cp) microsatellite (SSR) loci for 38 populations across the species range. As predicted from the expected reduction in effective population size (Ne) caused by selfing, small‐flowered, predominantly selfing (SF) populations had much lower nSSR diversity (but not cpSSR) than large‐flowered, predominantly outcrossing (LF) populations. The reduction in nSSR diversity was greater than expected from the effects of selfing on Ne alone, but could not be accounted for by indirect effects of selfing on population density. Although selfing should reduce gene flow, SF populations were not more genetically differentiated than LF populations. We detected five clusters of nSSR genotypes and three groups of cpSSR haplotypes across the species range consisting of parapatric groups of populations that usually (but not always) differed in mating system, suggesting that selfing may often initiate ecogeographic isolation. However, lineage‐wide genetic variation was not lower for selfing clusters, failing to support the hypothesis that selection for reproductive assurance spurred the evolution of selfing in this species. Within three populations where LF and SF plants coexist, we detected genetic differentiation among diverged floral phenotypes suggesting that reproductive isolation (probably postzygotic) may help maintain the striking mating‐system differentiation observed across the range of this species. 相似文献
15.
MEGAN J. OSBORNE STEPHEN R. DAVENPORT CHRISTOPHER W. HOAGSTROM THOMAS F. TURNER 《Molecular ecology》2010,19(14):2832-2844
Genetic monitoring tracks changes in measures of diversity including allelic richness, heterozygosity and genetic effective size over time, and has emerged as an important tool for understanding evolutionary consequences of population management. One proposed application of genetic monitoring has been to estimate abundance and its trajectory through time. Here, genetic monitoring was conducted across five consecutive year for the Pecos bluntnose shiner, a federally threatened minnow. Temporal changes in allele frequencies at seven microsatellite DNA loci were used to estimate variance effective size (NeV) across adjacent years in the time series. Likewise, effective size was computed using the linkage disequilibrium method (NeD) for each sample. Estimates of Ne were then compared to estimates of adult fish density obtained from traditional demographic monitoring. For Pecos bluntnose shiner, density (catch‐per‐unit‐effort), NeV and NeD were positively associated across this time series. Results for Pecos bluntnose shiner were compared to a related and ecologically similar species, the Rio Grande silvery minnow. In this species, density and NeV were negatively associated, which suggested decoupling of abundance and effective size trajectories. Conversely, density and NeD were positively associated. For Rio Grande silvery minnow, discrepancies among estimates of Ne and their relationships with adult fish density could be related to effects of high variance in reproductive success in the wild and/or effects of supplementation of the wild population with captive‐bred and reared fish. The efficacy of Ne as a predictor of density and abundance may depend on intrinsic population dynamics of the species and how these dynamics are influenced by the landscape features, management protocols and other factors. 相似文献
16.
Density dependence in vital rates is a key feature affecting temporal fluctuations of natural populations. This has important implications for the rate of random genetic drift. Mating systems also greatly affect effective population sizes, but knowledge of how mating system and density regulation interact to affect random genetic drift is poor. Using theoretical models and simulations, we compare Ne in short‐lived, density‐dependent animal populations with different mating systems. We study the impact of a fluctuating, density‐dependent sex ratio and consider both a stable and a fluctuating environment. We find a negative relationship between annual Ne/N and adult population size N due to density dependence, suggesting that loss of genetic variation is reduced at small densities. The magnitude of this decrease was affected by mating system and life history. A male‐biased, density‐dependent sex ratio reduces the rate of genetic drift compared to an equal, density‐independent sex ratio, but a stochastic change towards male bias reduces the Ne/N ratio. Environmental stochasticity amplifies temporal fluctuations in population size and is thus vital to consider in estimation of effective population sizes over longer time periods. Our results on the reduced loss of genetic variation at small densities, particularly in polygamous populations, indicate that density regulation may facilitate adaptive evolution at small population sizes. 相似文献
17.
PSMC analysis of effective population sizes in molecular ecology and its application to black‐and‐white Ficedula flycatchers
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Krystyna Nadachowska‐Brzyska Reto Burri Linnéa Smeds Hans Ellegren 《Molecular ecology》2016,25(5):1058-1072
Climatic fluctuations during the Quaternary period governed the demography of species and contributed to population differentiation and ultimately speciation. Studies of these past processes have previously been hindered by a lack of means and genetic data to model changes in effective population size (Ne) through time. However, based on diploid genome sequences of high quality, the recently developed pairwise sequentially Markovian coalescent (PSMC) can estimate trajectories of changes in Ne over considerable time periods. We applied this approach to resequencing data from nearly 200 genomes of four species and several populations of the Ficedula species complex of black‐and‐white flycatchers. Ne curves of Atlas, collared, pied and semicollared flycatcher converged 1–2 million years ago (Ma) at an Ne of ≈ 200 000, likely reflecting the time when all four species last shared a common ancestor. Subsequent separate Ne trajectories are consistent with lineage splitting and speciation. All species showed evidence of population growth up until 100–200 thousand years ago (kya), followed by decline and then start of a new phase of population expansion. However, timing and amplitude of changes in Ne differed among species, and for pied flycatcher, the temporal dynamics of Ne differed between Spanish birds and central/northern European populations. This cautions against extrapolation of demographic inference between lineages and calls for adequate sampling to provide representative pictures of the coalescence process in different species or populations. We also empirically evaluate criteria for proper inference of demographic histories using PSMC and arrive at recommendations of using sequencing data with a mean genome coverage of ≥18X, a per‐site filter of ≥10 reads and no more than 25% of missing data. 相似文献
18.
We used genetic methods to estimate the effective number of breeders (N
b) in a population of Rana
pretiosa, an imperiled amphibian in western North America. Microsatellite data was gathered from large samples of adults, eggs, and
juveniles collected in 2006. We wished to determine where in the life cycle the greatest reductions in N
b occur, and to compare genetic estimates of N
b to an egg mass count estimate of the number of breeding adults. We predicted that N
b estimated at the metamorph stage would be reduced by increased variance in family size due to egg mass mortality. Contrary
to our prediction, estimates of N
b at the egg and metamorph stages were similar. Thus, we found no evidence of inflated variance in family size between the
two stages. If our results for this population are typical for R. pretiosa, then increased variance in family size during the egg to metamorph stage may not be a strong factor in reducing the effective
population sizes (N
e) relative to the census sizes (N) in this species. 相似文献
19.
We studied genetic drift of mitochondrial DNA (mtDNA) haplotype frequencies in a natural population of red drum (Sciaenops ocellatus) from the northern Gulf of Mexico (Gulf). The amount of genetic drift observed across temporally adjacent year classes (1986–89) was used to estimate variance effective (female) population size (Nef). Nef was estimated to be 14 308 and the ratio of female effective size to adult female census size was approximately 0.004, which is among the lowest value reported for vertebrate animals. Low effective size relative to census size among red drum in the northern Gulf may result from yearly fluctuations in the number of breeding females, high variance in female reproductive success, or both. Despite low genetic effective size relative to census size, the genetic effective population size of red drum in the northern Gulf appears sufficiently large to preclude potentially deleterious effects of inbreeding. 相似文献
20.
David S. Portnoy Jan R. McDowell Camilla T. McCandless John A. Musick John E. Graves 《Conservation Genetics》2009,10(6):1697-1705
The sandbar shark, Carcharhinus plumbeus, is a long-lived species with low lifetime fecundity that is heavily fished in the western North Atlantic. Inshore nursery
grounds increase survivorship of sandbar shark pups and the principal nurseries are in the mid-Atlantic region. We calculated
effective number of breeders (Nb) and effective population size (Ne) for adults utilizing the nursery grounds of the Delaware Bay and the Eastern Shore of Virginia by genotyping 902 animals
across five cohorts at eight microsatellite loci. Estimates of Nb and Ne were compared to estimates of census size (Nc) of cohorts obtained from Delaware Bay. The estimated Ne/Nc and Nb/Nc ratios were 0.45 or higher whether the Delaware Bay cohorts were considered as distinct year classes or combined. This is
in contrast to estimated Ne/Nc ratios in other exploited marine fishes, which are several orders of magnitude smaller. Instead, the Ne/Nc ratio of sandbar sharks is similar to that found in marine and terrestrial mammals. 相似文献