Allozyme and mitochondrial DNA variation in Cuban populations of the shrimp Farfantepenaeus notialis (Crustacea: Decapoda)

We investigated the genetic diversity among populations of the shrimp Farfantepenaeus notialis, the most abundant penaeid species around Cuba. A total of 25 allozyme loci were analyzed in samples of shrimps from seven localities at the south central platform of the island (Ana María Gulf). Samples from three of these localities and from Batabanó Gulf and Guacanayabo Gulf at the south west and south east platforms of the island, respectively, were also characterized at the mtDNA level through sequence variation of a 2027 bp segment including part of the COI and COIII genes. Of the 25 allozyme loci studied 9 were polymorphic: Akp2, Akp3, AmyB, Est3, Gdh, GP7, and Per1, 2 and 3. In contrast to mtDNA, the pattern of allozyme variation among localities revealed strong population structuring at Ana María Gulf, with significant F _st in all pairwise comparisons. The magnitude of F _st estimates as well as the grouping pattern obtained by a UPGMA analysis based on a distance matrix indicated that the level of differentiation was concordant with the geographical position of the localities and the hydrographic regime. Homogeneity of mtDNA suggested that differentiation of allozyme loci might be due to more recent events rather than historical isolation of the sampled populations. Ana María and Guacanayabo Gulf populations were differentiated by mtDNA from Batabanó Gulf, at the southwestern end of the island. The analysis showed three restriction site differences among them, suggesting genetic isolation of the two regions. The present results also suggest that an artificial introduction of larvae from Tunas de Zaza into Batabanó Gulf, in an effort to repopulate this fishing region, may have been ineffective. Received: 13 December 1999 / Accepted: 2 October 2000     

Spatial autocorrelation analysis of small-scale genetic structure in a clonal soft coral with limited larval dispersal

The philopatric larval dispesal and small effective population sizes characteristic of many clonal species should promote the development of significant small-scale genetic structure within populations as a result of isolation-by-distance. We used spatial autocorrelation statistics to detect genetic structure, arising from both clonal reproduction and philopatric dispersal of sexual propagules, for five allozyme loci within populations of the soft coral Alcyonium sp. In a population on Tatoosh Island, Washington, USA, sampled in 1991/1992, we found significant positive spatial autocorrelation at all loci among individuals separated by <40 cm, reflecting the presence of significant smallscale genetic structure due to associations among clonemates. For 4 of 5 loci, however, we detected no significant spatial autocorrelation among the different clones within this population over distances of 1 to 40 m. Analysis of soft-coral populations from six additional, topographically diverse sites in the north-east Pacific also did not reveal significant spatial autocorrelation among clones at any loci. This general lack of spatial autocorrelation of genotypes among clones suggests that significant small-scale genetic structure has not arisen in populations of Alcyonium sp. as a consequence of isolation-by-distance.     

Genetic structure of local populations and divergence between growth forms in a clonal invertebrate,the Caribbean octocoral Briareum asbestinum

Although the genetic structure of many populations of marine organisms show little deviation from panmixia, in those marine species with limited larval dispersal, patterns of microgeographic genetic differentiation may be common. The octocoral Briareum asbestinum should show local population differentiation because colonies reproduce asexually by fragmentation, most matings occur between colonies in very close proximity, and the sexually produced larvae and sperm appear to disperse only short distances. Variability in secondary chemistry of individual B. asbestinum colonies from different populations in close proximity also suggests local population differentiation. We determined the genetic composition of local populations by surveying allozyme variation of three shallow and two deep populations within a 300 m² area at San Salvador Island, Bahamas and at a site 161 km away on Little San Salvador, Bahamas in July 1990. As B. asbestinum occurs as either an erect branching form or an encrusting mat often at the same sites, we sampled both morphs to examine the extent of genetic exchange between them. Five of 21 loci were polymorphic and most populations showed a deficit of heterozygotes. Allele frequencies differed significantly between morphs at each site where they occurred together. The mean genetic distance (D=0.065) between morphs is consistent with the interpretation that the two morphs are genetically isolated. Despite the close spatial proximity of the San Salvador populations, both the branching and encrusting morphs showed significant genetic heterogeneity among neighboring populations. Similarly, pooled allelic frequencies for samples collected from the islands of San Salvador and Little San Salvador differed significantly at 1 locus for the branching morph and at 3 out of 5 loci for the encrusting morph.     

Genetic Diversity in a Threatened Wetland Species, Helonias bullata (Liliaceae)

Genetic variation was examined in Helonias bullata , a threatened perennial plant species that occurs in isolated wetland habitats. Fifteen populations representing the species' geographic range were sampled. Genetic diversity was low for the species ( H _es = 0.053) as well as within populations ( H _ep = 0.029). Of the 33 allozyme loci examined, 11 (33%) were polymorphic, while on average only 12.8% (4) of the loci were polymorphic within populations. The number of alleles per polymorphic locus was 2.36 for the species and averaged 2.09 across populations. For every genetic parameter calculated, variation in H. bullata was lower than that typically found for narrowly distributed plant species. The lowest levels of genetic diversity were found in northern areas that were colonized following the last glacial epoch. The number of genotypes detected per population ranged from three to 21, with a mean of 13 for this clonally reproducing species. We found a relatively high proportion of total genetic diversity (30.6%) among populations and a significant correlation (p < 0.002) between genetic distance and geographic distance. Genetic drift phenomena appear to play a major role in the population genetics of this species. Anomalously, several populations that appeared most limited in size and vigor were genetically most variable, perhaps because they represent older, relictual populations. Life-history characteristics of H. bullata coupled with low levels of genetic diversity and the degradation and disappearance of wetlands threaten the existence of this species.     

Fitness in the Endangered Gila Topminnow

The Gila topminnow (Poeciliopsis o. occidentalis) is a small, live-bearing, endangered fish extant in a maximum of nine locales in four separate watersheds in the United States. To determine if these populations differed in their fitness, we obtained samples from the four watersheds and examined them for four fitness correlates: survival, growth rate, fecundity, and bilateral asymmetry. Earlier research found that one population, Sharp Spring, had higher allozyme heterozygosity than the other three and had higher survival, growth rate, and fecundity and lower bilateral asymmetry than a sample from one of the other populations with no polymorphic allozyme loci, Monkey Spring. We also verified that Sharp Spring fish were polymorphic for the same allozyme loci whereas the Monkey Spring population was not. We did not, however, find positive associations of allozyme heterozygosity with the four fitness correlates for the four samples. Because the earlier study had much lower survival, it is likely that the differences resulted from differential response of the two populations to a stressful laboratory environment. Whether this unknown stress occurs in natural environments or its effect is predictive of other stresses remains unresolved. As a result, we concur with suggestions in the draft recovery plan that topminnows from nearby sources be used for reintroductions and that the Sharp Spring stock not be used outside the upper Santa Cruz River drainage.     

Interspecific variation in thermal denaturation of proteins in the congeneric musselsMytilus trossulus andM. galloprovincialis: evidence from the heat-shock response and protein ubiquitination

The genetic population structure of the precominant zooplankter, the copepod Calanus finmarchicus (Gunnerus), was examined to determine whether genetically distinct populations exist in the Gulf of Maine. C. finmarchicus was sampled in three regions of the Gulf of Maine (Great South Channel, spring 1989; northern Gulf of Maine, winter 1990; Great South Channel and Georges Bank, spring 1990). Copepods from seven locations in the Great South Channel, five in the northern Gulf of Maine and four on or near Georges Bank were assayed for allozyme variation and mitochondrial DNA variation of amplified 16S rRNA and cytochrome b genes. Restriction fragment length polymorphism (RFLP) analyses of both mitochondrial DNA genes revealed no variation among any of the individuals assayed. Analysis of five polymorphic allozyme loci revealed that genetic variation among the three geographic regions was low, and genetic identities were high between all locations (I>0.97). Most of the genetic variation was among locations regardless of region. Chi-square tests were used to examine genetic similarity between specific pairs of locations within and between regions. In the northern Gulf of Maine, genetic homogeneity occurred over larger spatial scales (hundreds of km) than in either the Great South Channel or Georges Bank (tens of km). Only copepods from the Bay of Fundy and Nova Scotian Shelf locations were genetically distinct from Wilkinson Basin copepods at two loci. Copepod populations from the northern locations may have been partially isolated or they may represent immigrant populations (e.g., from the Gulf of St. Lawrence). Several pairs of locations were genetically distinct at one or more loci in the two southern regions. Differences between locations in these regions may represent distinct populations advected into the areas at different times or from different sources (e.g., genetic variation may represent a mixture of genetically distinct northern and southern copepod populations). These results suggest extensive gene flow among populations of C. finmarchicus in the Gulf of Maine with some evidence of genetic population subdivision near the Gulf's northeastern and southern boundaries.     

Extensive gene flow among mytilid (Bathymodiolus thermophilus) populations from hydrothermal vents of the eastern Pacific

Prior studies of the hydrothermal vent mussel Bathymodiolus thermophilus (Bivalvia: Mytilidae), provided conflicting predictions about the dispersal ability and population structure of this highly specialized species. Analyses of morphological features associated with its larval shells revealed a feeding larval stage that might facilitate dispersal between ephemeral vent habitats. In contrast, an allozyme study revealed substantial genetic differentiation between samples taken from populations 2370 km apart on Galápagos Rift (Latitude 0°N) and the East Pacific Rise (13°N). To resolve the discrepancy between these studies, we examined allozyme and mitochondrial (mt) DNA variation in new samples from the same localities plus more recently discovered sites (9° and 11°N) along the East Pacific Rise. Although analysis of 26 enzyme-determining loci revealed relatively low levels of genetic variation within the five populations, no evidence existed for significant barriers to dispersal among populations. We estimated an average effective rate of gege flow (Nm) of 8 migrants per population per generation. Two common mtDNA variants predominated at relatively even frequencies in each population, and similarly provided no evidence for barriers to gene flow or isolation-by-distance across this species' known range. Larvae of this species appear to be capable of dispersing hundreds of kilometers along a continuous ridge system and across gaps separating non-contiguous spreading centers.     

Use of Congeneric Assessment to Reveal the Linked Genetic Histories of Two Threatened Fishes in the Murray‐Darling Basin,Australia

Abstract: The intensely regulated Murray‐Darling Basin in southeastern Australia is the nation's most extensive and economically important river system, and it contains fragmented populations of numerous fish species. Among these is the Murray hardyhead (Craterocephalus fluviatilis), a species listed as endangered (International Union for Conservation of Nature Red List) in the mid‐1990s prior to its acute decline with the progression of a severe drought that began in 1997. We compared the genetic structure of Murray hardyhead with 4 congeneric species (Darling hardyhead[C. amniculus], Finke hardyhead[C. centralis], Lake Eyre hardyhead[C. eyresii], and unspecked hardyhead[C. stercusmuscarum]), selected on the basis of their taxonomic or biological similarity to Murray hardyhead, in order to affirm species boundaries and test for instances of introgressive hybridization, which may influence species ecology and conservation prospects. We used allozyme (52 loci) and mtDNA markers (1999 bp of ATPase and cytochrome b) to provide a comparative genetic assessment of 139 Murray hardyhead, which represented all extant and some recently extirpated populations, and 71 congeneric specimens from 12 populations. We confirmed that Murray hardyhead and Darling hardyhead are taxonomically distinct and identified a number of potential conservation units, defined with genetic criteria, in both species. We also found allozyme and mtDNA evidence of historic genetic exchange between these 2 allopatric species, apparently involving one population of each species at the geographic edge of the species’ ranges, not in the most proximate populations sampled. Our results provide information on species boundaries and offer insight into the likely causes of high genetic diversity in certain populations, results which are already being used to guide national recovery planning and local action. Given the prevalence of incorrect taxonomies and introgression in many organismal groups, we believe these data point to the need to commence genetic investigations of any threatened species from an initially broad taxonomic focus.     

Heterozygosity,growth, and survival of the hard clam,Mercenaria mercenaria,in seagrass vs sandflat habitats

Populations of the hard clam,Mercenaria mercenaria L., sampled from dissimilar, adjacent habitats (October and November 1987), were used to assess environmental effects on associations among multi-locus heterozygosity, growth, and survival. Individuals were collected from three widely separated localities along the east coast of North America with each consisting of a seagrass bed and an adjacent, unvegetated sandflat. Demographic differences between adjacent populations were attributed to habitat type. Samples from intertidal sandflats at two of the localities were dominated by younger individuals than those from seagrass beds. Differential growth between adjacent populations was detected at only one locality wherein seagrass individuals grew faster than those from the sandflat. Allelic frequencies revealed adjacent populations that were genetically homogeneous. Nearly all of the genetic variance (98%) was within populations, yet a small (1.7%), but significant, portion occurred between localities. Observed and expected heterozygosities revealed a deficiency of heterozygotes in all six samples. Inbreeding and small-scale population subdivision were discounted as causative factors because deficiencies were heterogeneous across loci. Multi-locus heterozygosity was not correlated with growth rate in samples from any locality. Using a consensus test, multilocus heterozygosity was positively associated with ageclass in sandflat, but not seagrass, samples. We suggest that heterozygosity-fitness trait associations in marine bivalves are more likely to occur in populations inhabiting more stressful, fluctuating environments     

Genetic structure of crown-of-thorns starfish (Acanthaster planci ) on the Great Barrier Reef, Australia: comparison of two sets of outbreak populations occurring ten years apart

Six populations of the crown-of-thorns starfish, Acanthaster planci, showing large increases in population size in 1994 to 1995, were examined by allozyme electrophoresis of 100 to 300 individuals collected from each population in November 1995 to February 1996. Analysis of nine loci, used to determine the structure of outbreak populations in the early-mid-1980s, demonstrated no significant differentiation among the 1996 outbreak populations in any age class (2 to 6 yr old). No significant variation was detected between age classes in any of the six populations. These data are consistent with the recent outbreak populations having been derived from one genetic source, and suggest no change in the source of recruits to these reefs between 1989/1990 to 1994/1995. In a multi-dimensional scaling analysis, the 1996 samples clustered with the eight 1986 outbreak populations in a small part of the genetic space spanned by the 1986 non-outbreak populations, suggesting that the outbreak populations were derived from the same genetic source in both 1986 and 1996. Statistically significant, but small, differences in gene frequencies detected between the 1986 and 1996 outbreak populations are thought to result from genetic drift, but are unlikely to provide a means of distinguishing sets of outbreak populations because of the large sample sizes required to detect the small shifts in gene frequency. Received: 21 March 1997 / Accepted: 2 April 1997     

Lack of genetically-subdivided population structure in Bullia digitalis, a southern African marine gastropod with lecithotrophic development

Larval shell morphology in fossil and present-day gastropods is often used to infer modes of larval development and levels of dispersal. Dispersal ability influences not only genetic population structure, but also is thought to influence a species' geographical range and evolutionary duration. We tested these predictions in Bullia digitalis, a sandy-beach whelk, by examining genetic variability at 33 protein-coding loci in nine samples (N=739) taken in 1984 to 1985 at localities extending over about three-quarters of the geographical range of this species in southern Africa. Females of this species deposit eggs into benthic or brooded capsules in which larvae develop through the trochophore and veliger stages to emerge as crawling juveniles. Scanning electron micrographs confirmed a protoconch morphology typical for gastropods with lecithotrophic larval development. Contrary to expectations, subpopulations of B.␣digitalis had high levels of variability (H=0.102) and lacked a genetically-fragmented structure (=0.013). The lack of a genetically-subdivided population structure would not have been correctly inferred, if this species were known only from well-preserved fossil shells. Indirect estimates of migration between populations based on and the island model of migration, which assumes drift-mutation equilibrium, ranged between 19 and 23 individuals per generation. Either an undescribed mechanism of dispersal facilitates gene flow between populations, or the geographical range of this species has recently expanded to produce the appearance of high levels of gene flow. Gene-frequency distributions showed that relative to four other species of Bullia, populations of B. digitalis were in mutation-drift disequilibrium, with a significant excess of low-frequency alleles that is consistent with a recent rapid expansion from a small population. Also contrary to expectations, this species has a large geographical range (2 400 km) and an apparently long evolutionary history extending 5 to 20 million years, as estimated from an allozyme phylogeny with four other species of Bullia. Received: 15 January 1997 / Accepted: 28 January 1997     

Influence of Fragmentation and Bottlenecks on Genetic Divergence of Wild Turkey Populations

Abstract: There are few empirical studies of the effects of human-induced fragmentation and bottlenecks on the genetic structure of field populations. Assessment of these effects is necessary to evaluate the relevance of predictions obtained from simulation and theoretical models to the management of wild populations. The genetic structure of populations of the Wild Turkey (Meleagris gallopavo), which have been heavily influenced by human activities, was examined using allozyme electrophoresis Allele frequencies at four polymorphic loci were estimated for 27 localities using 461 turkeys The estimated proportion of genetic variation resulting from differences among populations (F_st= 0.102) was one of the highest reported for any avian species and was also much higher than that observed between turkey populations that had not passed through known bottlenecks Almost all of the variation (89%) among populations was accounted for by differences between groups of populations with different histories of manipulation Fragmented distributions and population bottlenecks due to human activities appear to have increased genetic differentiation among populations of wild turkeys. This observation agrees with theoretical predictions concerning the effects of isolation and bottlenecks on the genetic structure of field populations.     

Genetic structure and allozyme variation of sea bass (Dicentrarchus labrax and D. punctatus) in the Mediterranean Sea

This paper reports data on 28 allozyme loci in wild and artificially reared sea bass (Dicentrarchus labrax) samples, originating from either coastal lagoon or marine sites in the Mediterranean Sea. F _ST analysis (θ estimator) indicated strong genetic structuring among populations; around 34% of the overall genetic variation is due to interpopulation variation. Pairwise θ estimates showed that, on average, the degree of genetic structuring was much higher between marine populations than between samples from lagoons. Six polymorphic loci showed differences in allele frequencies between marine and lagoon samples. Multivariate analyses of individual allozymic profiles and of allele frequencies suggested that different arrays of genotypes prevail in lagoons compared to marine samples, particularly at those loci that, on the basis of previous acclimation experiments, had been implicated in adaptation to freshwater. On the other hand, variation at “neutral” allozyme loci reflects to a greater extent the geographic location of populations. Allozyme differentiation was also studied in a D. labrax population from the Portuguese coast. Average genetic distance between this population and the Mediterranean populations was quite high (Nei's D = 0.236) and calls into question the taxonomic status of the Portuguese population. Finally, genetic relationships between D. labrax and D. punctatus were evaluated. Average Nei's D was 0.648, revealing high genetic differentiation between the two species, even for two sympatric populations of these species in Egypt; thus gene flow was not indicated between species. Received: 24 October 1996 / Accepted: 27 November 1996     

Genetic differentiation and reproductive incompatibility among Baja California populations of the copepod Tigriopus californicus

Populations of the harpacticoid copepod Tigriopus californicus were sampled from five sites from San Diego, California, to Playa Altamira, Baja California, Mexico. Allozyme analyses revealed that all the study populations are sharply differentiated genetically. At the extreme, two populations, Punta Baja and Playa Altamira, have no alleles in common at the seven allozyme loci studied. All pairwise interpopulation crosses successfully produced F₂ hybrids except those involving the Playa Altamira population. All crosses using Playa Altamira females failed to produce F₁ hybrids, while Playa Altamira males successfully produced F₁ progeny with females from all other sites. These F₁ offspring, however, were completely sterile (with San Diego and Punta Banda females) or only occasionally produced F₂ offspring (with Punta Morro and Punta Baja females). These results suggest that allopatric differentiation among Baja populations has resulted in exceptionally high levels of genetic divergence and nearly complete reproductive isolation of the Playa Altamira population, which should now be recognized at the semispecies (or perhaps sibling species) level.     

A genetic analysis of the pea crabs (Decapoda: Pinnotheridae) of New Zealand

Seven populations of the pea crabPinnotheres atrinicola Page were sampled from around the North Island of New Zealand from February to October 1987, and individuals were scored at 23 presumptive enzymatic loci. For a brachyuran crab,P. atrinicola revealed high levels of polymorphism and heterozygosity. Of the loci scored, phosphoglucose isomerase (Gpi) and phosphoglucomutase (Pgm) were distinguished by high variability ( =0.602 and 0.526, respectively). A clinal variation in electromorph frequency was evident at several loci, and atGpi in particular. Statistical analyses revealed that, despite relatively small genetic distance separation, a high degree of structuring was present between the geographic populations. The degree of population subdivision observed in this study is atypical of brachyuran crabs. It is suggested that the genetic differentiation observed between pea crab populations is maintained by life-history attributes and current movements which restrict gene flow between populations and, to some extent, by random genetic drift.Publication No. 41 from the Evolutionary Genetics Laboratory, University of Auckland     

Genetic Structure of Fragmented Populations of the Endangered Daisy Rutidosis leptorrhynchoides

Abstract: The endangered grassland daisy Rutidosis leptorrhynchoides has been subject to severe habitat destruction and fragmentation over the past century. Using allozyme markers, we examined the genetic diversity and structure of 16 fragmented populations. The species had high genetic variation compared to other plant species, and both polymorphism and allelic richness showed strong positive relationships with log reproductive population size, reflecting a loss of rare alleles (frequency of q < 0.1) in smaller populations. Fixation coefficients were positively related to size, due either to a lack of rare homozygotes in small populations or to Wahlund effects (owing to spatial genetic structure) in large ones. Neither gene diversity nor heterozygosity was related to population size, and other population parameters such as density, spatial contagion, and isolation had no apparent effect on genetic variation. Genetic divergence among populations was low , despite a large north-to-south break in the species' current distribution. To preserve maximum genetic variation, conservation strategies should aim to maintain the five populations larger than 5000 reproductive plants, all of which occur in the north of the range, as well as the largest southern population of 626 plants at Truganina. Only one of these is currently under formal protection. High heterozygosity in smaller populations suggests that they are unlikely to be suffering from inbreeding depression and so are also valuable for conservation. Erosion of allelic richness at self-incompatibility loci, however, may limit the reproductive capacity of populations numbering less than 20 flowering plants.     

Genetic Diversity and Tests of the Hybrid Origin of the Endangered Yellow Larkspur

Abstract: Delphinium luteum ( Ranunculaceae), an endangered larkspur, is restricted to two wild populations near Bodega Bay, California. The total number of individuals in these two populations is estimated to be <100. We used allozyme and random amplified polymorphic DNA ( RAPD) markers to (1) assess levels and patterns of genetic diversity in one wild population and two cultivated populations and (2) test the hypothesis that D. luteum is of hybrid origin between D. decorum and D. nudicaule . These data will be used to aid in developing a management plan to conserve the species. The wild population maintains high levels of genetic diversity. Genetic data indicate that both cultivated populations, especially the north Sonoma population, have several allozymes and RAPD markers not found in the wild population and could be used to establish new populations of D. luteum or to enhance the diversity and size of the wild population. The allozyme data did not reveal any fixed differences between D. decorum and D. nudicaule , although allele frequencies of the putative parental populations differed. At these loci, D. luteum resembled D. nudicaule more than D. decorum  . Many unique RAPD markers distinguish each of the three species. The diagnostic markers from populations of D. nudicaule and D. decorum were not additive in the putative hybrid, and these data indicate that D. luteum is not of recent hybrid origin. Conservation of the yellow larkspur should include strategies that use the cultivated populations of D. luteum , but hybridizing D. decorum and D. nudicaule to "recreate" D. luteum is not recommended.     

Quantitative and Molecular Genetic Variation in Captive Cotton-Top Tamarins (Saguinus oedipus)

Most genetic surveys of captive and endangered populations are carried out with single gene characters bearing no direct relationship to life history or other features for which genetic variation needs to be maintained. Quantitative genetic estimates of heritable variation for life-history traits may be a more direct and appropriate measure of genetic variation for some conservation purposes. Furthermore, recent theoretical and empirical results indicate that genetic variation measured on these two levels may not be concordant. We analyzed heterozygosity at 41 allozyme loci and heritability for body weight in captive cotton-top tamarins ( Saguinus oedipus ) from the Marmoset Research Center of the Oak Ridge Associated Universities in order to compare these two levels of genetic variation. Cotton-top tamarins are a highly endangered species native to Colombia. Many animals currently reside in research facilities and zoological parks. A total of 106 animals were used in the isozyme survey, while data on 364 animals contributed to the quantitative genetic study of body weight. We found a very low average heterozygosity ( H = 1%) for this colony. Body weight was moderately and significantly heritable ( h ² = 35%). This heritability is within the normal range for natural animal populations. The finding of biologically significant levels of heritability in a population with abnormally low allozyme heterozygosity illustrates the point that low levels of allozyme heterozygosity should not be taken as an indication of overall lack of genetic variation in important quantitative characters such as life-history traits. Genetic variation required for adaptation of species to future environmental challenges can exist despite low levels of enzyme heterozygosity.     

Genetic uniformity of widely separated populations of the coral reef starfishLinckia laevigata from the East Indian and West Pacific Oceans,revealed by allozyme electrophoresis

Gene flow among 18 widely separated populations of the starfishLinckia laevigata was investigated using allozyme electrophoresis at seven polymorphic enzyme loci. Little genetic differentiation was observed among East Indian-West Pacific populations separated by thousands of kilometres. Gene flow was estimated to be of the same order of magnitude as that found in the highly connected Great Barrier Reef region. The absence of genetic structure over such a broad geographic range is consistent with any of three conclusions: (1) there is extensive dispersal among widely separated populations across the range examined, (2) there has been a rapid expansion of the East Indian-West Pacific populations in the recent past, or (3) the loci surveyed are under the influence of balancing selection. The first two conclusions are not totally exclusive, since a recent expansion over several thousand generations would also require rapid dispersal at some stage, although present-day levels of dispersal need not be of the same order. With the available data, it is not possible to distinguish which of these mechanisms is the most likely. The most parsimonious conclusion is that extremely low levels of population differentiation are consistent with the existence of a large, homogeneous, panmictic population, with extensive dispersal occurring throughout the East Indian-West Pacific.     

Conservation Genetics of the Endangered Isle Royale Gray Wolf

Abstract. The small group of wolves on Isle Royale has been studied for over three decades as a model of the relationship between large carnivores and their prey. During the last ten years the population declined from 50 individuals to as few as 12 individuals. The causes of this decline may be food shortages, disease, or reduced genetic variability. We address the issues of genetic variability and relationships of Isle Royale wolves using allozyme electrophoresis, mtDNA restriction-site analysis, and multilocus hypervariable minisatellite DNA analysis (genetic fingerprinting). Our results indicate that approximately 50% of the allozyme heterozygosity has been lost in the island population, a decline similar to that expected if no immigration had occurred from the mainland. The genetic fingerprinting data indicate that the seven sampled Isle Royale wolves are as similar as captive populations of siblings. Surprisingly, the Isle Royale wolves have an mDNA genotype that is very rare on the mainland, being found in only one of 144 mainland wolves ThFF suggests that the remaining Isle Royale wolves areprobably derived from a single female founder