Patterns of larval dispersal and their effect on the maintenance of a blue mussel hybrid zone in southwestern England

Abstract The blue mussels Mytilus edulis and M. galloprovincialis hybridize in southwestern England. Within this hybrid zone environmentally based directional selection favors individuals with alleles specific to M. galloprovincialis . What forces are countering this directional selection and allowing for the maintenance of a stable hybrid population are unknown. We used both the genetics of recently settled larvae and a fine-scale model of the physical oceanography of the region to determine the patterns of larval dispersal throughout the hybrid zone and the bordering parental populations. Evidence from both the model and the genetics suggests that the hybrid zone lies between two barriers to dispersal. Start Point separates the M. edulis population from the hybrid zone and allows minimal dispersal from the hybrid zone into the M. edulis population, but none in the other direction. Likewise, the M. galloprovincialis populations along the northern coast of Cornwall regularly receive immigrating larvae from the hybrid zone, but larvae from the M. galloprovincialis population do not enter the hybrid zone. However, larvae settling at hybrid zone sites have high frequencies of alleles specific to M. edulis , suggesting that reproductive barriers, selection in the larval stage, or gene flow from an undetermined source is effectively balancing the directional selection observed in the adults.     

Isolation of ten tetranucleotide microsatellite loci in the Northern Wheatear (Oenanthe oenanthe)

We isolated 10 polymorphic microsatellite DNA loci from the Northern Wheatear (Oenanthe oenanthe) and optimized these for future studies in population genetics and behavioural ecology. The loci were screened for polymorphism using 107 individuals from one population in Germany. The primers amplified loci with high numbers of alleles ranging from two to 20 alleles per locus.     

Population bottleneck and effective size in Bonamia ostreae-resistant populations of Ostrea edulis as inferred by microsatellite markers

Genetic variability at five microsatellite loci was analysed in three hatchery-propagated populations of the flat oyster, Ostrea edulis. These populations were part of a selection programme for resistance to the protozoan parasite Bonamia ostreae and were produced by mass spawns, without control of the genealogy. Evidence for population bottlenecks and inbreeding was sought. A reduction in the number of alleles, mainly due to the loss of rare alleles, was observed in all selected populations, relative to the natural population from which they were derived. Heterozygote excesses were observed in two populations, and were attributed to substructuring of the population into a small number of families. Pedigree reconstruction showed that these two populations were produced by at most two spawning events involving a limited number of parents. Most individuals within these populations are half or full-sib, as shown by relatedness coefficients. The occurrence of population bottlenecks was supported by estimates of effective number of breeders derived by three methods: temporal variance in allelic frequencies, heterozygote excess, and a new method based on reduction in the number of alleles. The estimates from the different methods were consistent. The evidence for bottleneck and small effective number of breeders are expected to lead to increasing inbreeding, and have important consequences for the future management of the three O. edulis selected populations.     

Isolation and characterization of microsatellite loci in Schizolobium parahyba (Leguminosae)

Primer sequences for 16 microsatellite loci were developed from Schizolobium parahyba, a tropical tree species. Twelve loci were found to be polymorphic after screening diversity in individuals from Belize. A total of 39 alleles were found at nine loci. The markers are invaluable tools for studying the population genetics and mating system of the species.     

Fifteen new polymorphic microsatellite loci for the meadow brown butterfly,Maniola jurtina

We characterized fifteen microsatellite markers for the butterfly Maniola jurtina. For the six studied populations (96 samples) the total number of alleles per locus ranged from 3 to 55 and mean overall expected heterozygosity across all loci was 0.74. In spite of a high frequency of null alleles detected in part of the loci, a recurrent phenomenon in Lepidopteron, the estimation of pairwise F_ST seems rather insensitive to the presence of these null alleles as shown by the high correlation between F_ST calculated after correction for the presence of null alleles and non-corrected F_ST, indicating that the loci may be usable in population genetics, more specifically for the study of populations genetics structure.     

Population differences of aspartate aminotransferase and peptidase in the bay mussel Mytilus edulis

This investigation has demonstrated considerable heterogeneity among populations and some heterogeneity within populations in the distribution of alleles at two variant loci of Mytilus edulis. Although the causes of this variation remain obscure, some speculations have been made on the basis of available data. A cline for aspartate aminotransferase (AAT) alleles has been observed on the Pacific Coast. An immigration model has been proposed to explain the atypical ecological and genetic characteristics of large mussels found on Amchitka Island, Alaska. Marked differences were found in the distribution of peptidase alleles among collections from Southern California, the North Pacific Ocean, and New Jersey. Deviations from random distribution of phenotypes observed in comparisons made between large and small mussels from the New Jersey collection may reflect selection operating on these loci in this population.     

Inheritance of null alleles for microsatellites in the white pine weevil (Pissodes strobi [Peck] [Coleoptera: Curculionidae])

Four families of the white pine weevil (Pissodes strobi) produced by controlled breeding were used to study the mode of inheritance at four microsatellite loci. The results confirmed the Mendelian segregation of all loci. Three of the four loci showed the presence of null alleles. The observed high polymorphism of P. strobi microsatellites increased their usefulness for paternity determination. The presence of null alleles predicates the need to redesign primers before using them in population genetics studies where pedigree is unknown.     

Isolation and characterization of 18 polymorphic microsatellite markers in Chinese mandarin fish Siniperca chuatsi (Basilewsky)

Eighteen microsatellite markers were isolated and characterized using an enrichment protocol in the Chinese mandarin fish Siniperca chuatsi (Basilewsky), a commercially important piscivorous fish in China. Out of 48 pairs of primers designed, 18 loci exhibited polymorphism with three to six alleles (mean 4.4 alleles/locus) and average observed heterozygosity ranged from 0.633 to 0.833 (mean 0.748) in a test population from Dongting Lake of China. Except for two loci, all other 16 loci were in the Hardy–Weinberg equilibrium. These markers would be useful for such studies as population genetics, ecology and selective breeding of the Chinese mandarin fish in future.     

Polymorphic microsatellite markers for studies of Aedes aegypti (Diptera: Culicidae), the vector of dengue and yellow fever

A significant challenge to population genetic studies of the dengue vector, Aedes aegypti, has been the lack of polymorphic microsatellite loci. In an effort to develop useful markers, we evaluated the genetic variation at 17 microsatellite loci identified in the A. aegypti genome. Nine loci with at least five alleles were identified in field‐collected specimens from Thailand. An additional two loci carried five alleles if samples from an A. aegypti laboratory colony were included. Our results greatly increase the number of highly variable markers available for the study of the genetics and the population structure of this medically important species.     

Population differences of aspartate aminotransferase and peptidase in the bay mussel Mytilus edulis.

This investigation has demonstrated considerable heterogeneity among populations and some heterogeneity within populations in the distribution of alleles at two variant loci of Mytilus edulis. Although the causes of this variation remain obscure, some speculations have been made on the basis of available data. A cline for aspartate aminotransferase (AAT) alleles has been observed on the Pacific Coast. An immigration model has been proposed to explain the atypical ecological and genetic characteristics of large mussels found on Amchitka Island, Alaska. Marked differences were found in the distribution of peptidase alleles among collections from Southern California, the North Pacific Ocean, and New Jersey. Deviations from random distribution of phenotypes observed in comparisons made between large and small mussels from the New Jersey collection may reflect selection operating on these loci in this population.     

Isolation of microsatellites from Girella tricuspidata

Microsatellites were isolated from Girella tricuspidata (Girellidae) and screened for 64 individuals collected from coastal reefs in New South Wales, Australia. All seven loci tested were highly polymorphic, having seven to 42 alleles with average heterozygosities between 0.44 and 1.0. One locus (GT1N8) had a significant excess of homozygotes, probably due to the presence of null alleles. These microsatellite loci should be informative for examining population genetics of this species.     

Development of polymorphic microsatellite markers for the zebra finch (Taeniopygia guttata)

To study the population genetics as well as the mating system of captive zebra finch (Taeniopygia guttata) populations, we developed primers for 12 microsatellite loci and screened them in 529 individuals from two successive generations of a single captive population. All markers were polymorphic with five to 14 alleles per locus. We checked all markers for Mendelian inheritance in 307 offspring whose parents were known for sure. Four markers showed evidence for the presence of null alleles. Once allowing for null alleles, we found no mismatches between offspring and parents, suggesting a very low rate of mutation. Average observed and expected heterozygosities across the eight loci showing no evidence for null‐alleles was 0.819 and 0.812, respectively.     

Isolation of polymorphic microsatellite markers in the tree sparrow (Passer montanus)

To enable the study of the population genetics of the tree sparrow (Passer montanus), which is distributed in many islands of Japan, nine polymorphic microsatellite loci were isolated from 32 individuals. The number of alleles per locus ranged from 2 to 17, and observed heterozygosities ranged from 0.1250 to 0.9375. In eight of the nine loci, the heterozygosities were not significantly different from those expected from Hardy-Weinberg equilibrium. Cross-species amplification in the russet sparrow (P. rutilans) was successful with all primer sets, which were highly polymorphic, suggesting these markers are useful for the population genetics of genus Passer.     

Isolation and validation of eight microsatellite loci in a damselfly Ischnura senegalensis (Odonata: Coenagrionidae) by pyrosequencing a bead-enriched library

Eight microsatellite markers for the population genetics and evolutionary ecology of Ischnura senegalensis (Rambur 1842), which shows body color polymorphism in females, were developed using a streptavidin-bead enrichment library and pyrosequence by a next generation sequencer. The number of alleles per locus and effective number of alleles ranged from 3 to 11 and from 1.24 to 5.51, respectively. Observed and expected heterozygosities were 0.18–0.75 and 0.19–0.77, respectively. No linkage disequilibrium between loci was detected. One locus, IsenAC75, deviated significantly from the Hardy–Weinberg equilibrium, and the locus and additional two loci, IsenAC40 and IsenAC8, were suspected for the presence of null alleles. Altogether, these eight microsatellite loci are considered to be useful for population genetic analyses because of the high polymorphic status and independency.     

Microsatellite primers for Halophila ovalis and cross-amplification in H. minor (Hydrocharitaceae)

?Premise of the study: Polymorphic microsatellite primers were developed in the seagrass Halophila ovalis to investigate genetic variation. ?Methods and Results: Ten polymorphic microsatellite loci were developed in Halophila ovalis. The number of alleles per locus ranged from 2 to 12 across 80 H. ovalis individuals. These loci were successfully amplified in H. minor, and four were monomorphic across 30 individuals. ?Conclusions: These results from four H. ovalis populations and one H. minor population show the broad utility of microsatellite loci in future studies of population genetics. Four distinct alleles were present in H. minor but absent in H. ovalis, indicating potential divergence between them.     

Isolation and characterization of microsatellite loci in Pseudoplatystoma corruscans (Siluriformes: Pimelodidae) and cross‐species amplification

A total of five polymorphic microsatellites loci from Pseudoplatystoma corruscans were isolated and characterized. A population survey involving 43 specimens resolved a large number of alleles (range seven to eight among loci) and high observed heterozygosity (0.500–0.615), indicating its usefulness in population genetics studies. Cross‐species amplification was successful in four other Pimelodidae species.     

PERMANENT GENETIC RESOURCES: Isolation and characterization of polymorphic trinucleotide and dinucleotide microsatellite loci for the ice goby, Leucopsarison petersii

Eleven microsatellite markers were isolated and characterized for the ice goby, Leucopsarion petersii, from genomic libraries enriched for (ATG)(9) and (CA)(16) . Twenty individuals from a single population were used to screen polymorphism in these loci. The number of alleles per locus and observed heterozygosity ranged from four to 22 and from 0.35 to 1.00, respectively. All loci did not significantly deviated from Hardy-Weinberg equilibrium, and there was no evidence of linkage disequilibrium between all loci-pairs. These loci showed Mendelian inheritance in a full-sib family. The high level of polymorphism of these loci will be useful for studies of population genetics.     

Clonal diversity and genetic differentiation revealed by SSR markers in wild Vaccinium macrocarpon and Vaccinium oxycoccos

American cranberry (Vaccinium macrocarpon) is a perennial, woody plant species, native to North American bogs and wetlands. Cranberries represent one of the few agriculturally important native plants in which wild gene pools are still readily available within the undeveloped wetlands of the northern US and Canada. Earlier studies have reported low genetic variation in V. macrocarpon at the species and population level. However, in this study, we characterised 229 individuals of wild V. macrocarpon and V. oxycoccos (small cranberry) from Wisconsin and 22 accessions using microsatellite markers and observed substantial genetic variation and differentiation within and among populations and species. While V. macrocarpon was analysed using 108 alleles from 11 microsatellite loci revealing 42 unique genotypes, V. oxycoccos was analysed using 156 alleles from eight loci revealing 28 unique genotypes. There were a total of 182 alleles found in both species combined with 156 of those alleles present in V. oxycoccos and 84 alleles found in V. macrocarpon. All eight loci possessed species‐specific alleles with V. oxycoccos possessing 98 private alleles versus 26 private alleles found V. macrocarpon, and 58 alleles were found in common between both species. Our data will be valuable not only for future wild cranberry diversity and population genetics research, but for other cranberry breeding and genetics studies.     

Genetic diversity and recruitment of the tropical palm, Euterpe edulis Mart., in a natural population from the Brazilian Atlantic Forest

The genetic diversity and recruitment of plants of heart-of-palm tree (Euterpe edulis Mart.) were investigated in a natural population located in Southern Brazil. Five categories of plants, from seedlings to adults, were analysed using 16 allozymic loci. The results showed an average population level of genetic diversity (He=0.278) greater than the average of plant species already studied. The recruitment process of E. edulis is related to its genetic characteristics. A significant increase in the heterozygote frequency towards the adult stages was observed at three loci (Pgdh-2, G6pdh-1 and Mdh-1). This suggests the possible action of natural selection in promoting such heterozygote increase. In the same way, a linear increase in allele frequencies was observed at four loci (Prx-3, Prx-4, Pgdh-2 and G6pdh-1), indicating that recruitment is also related to a greater survival of individuals that are carriers of certain alleles. The maintenance of high diversity levels, as well as the increase in the heterozygote frequency, are positive aspects for in situ conservation. Furthermore, an increase in heterozygote frequency is favourable to the management of the species, since the maintenance of a stock of reproductive individuals with high heterozygosity levels favours the maintenance of the population dynamic and structure.     

Isolation and characterization of microsatellite loci from Corydalis ambigua (Papaveraceae)

Primers for seven unlinked and highly polymorphic microsatellite loci were developed for Corydalis ambigua to investigate its mating system and population genetics. This species can be used to explore the impact of an alien bumblebee on plant reproduction. Genetic diversity and other population genetic parameters were estimated in two populations with and without the alien bumblebee. The number of alleles per locus ranged from 4 to 20, and observed heterozygosities ranged from 0.355 to 0.969. These markers can be applied to study mating systems and population genetics in C. ambigua.