Michael S. Eackles

Intraspecific phylogeography of Lasmigona subviridis (Bivalvia: Unionidae): conservation implications of range discontinuity

A nucleotide sequence analysis of the first internal transcribed spacer region (ITS‐1) between the 5.8S and 18S ribosomal DNA genes (640 bp) and cytochrome c oxidase subunit I (COI) of mitochondrial DNA (mtDNA) (576 bp) was conducted for the freshwater bivalve Lasmigona subviridis and three congeners to determine the utility of these regions in identifying phylogeographic and phylogenetic structure. Sequence analysis of the ITS‐1 region indicated a zone of discontinuity in the genetic population structure between a group of L. subviridis populations inhabiting the Susquehanna and Potomac Rivers and more southern populations. Moreover, haplotype patterns resulting from variation in the COI region suggested an absence of gene exchange between tributaries within two different river drainages, as well as between adjacent rivers systems. The authors recommend that the northern and southern populations, which are reproductively isolated and constitute evolutionarily significant lineages, be managed as separate conservation units. Results from the COI region suggest that, in some cases, unionid relocations should be avoided between tributaries of the same drainage because these populations may have been reproductively isolated for thousands of generations. Therefore, unionid bivalves distributed among discontinuous habitats (e.g. Atlantic slope drainages) potentially should be considered evolutionarily distinct. The DNA sequence divergences observed in the nuclear and mtDNA regions among the Lasmigona species were congruent, although the level of divergence in the COI region was up to three times greater. The genus Lasmigona, as represented by the four species surveyed in this study, may not be monophyletic.

Regional Differentiation and Sex-Biased Dispersal among Populations of the Horseshoe Crab Limulus polyphemus

Abstract Fourteen microsatellite DNA loci were surveyed in 892 horseshoe crabs Limulus polyphemus collected from 21 sites ranging from Franklin, Maine, to the Yucatan Peninsula, Mexico. This rangewide survey revealed a high degree of genetic diversity (up to 50 alleles per locus) and heterozygosity (up to 97.2%). There appears to be substantial gene flow between each population and its nearest neighbors. The correlation of genetic distance and geographic distance supports isolation by distance as a mechanism underlying the structure of L. polyphemus along the Atlantic coast of North America. Two statistical descriptors, mean assignment percentage and assignment variance, suggested the presence of male-biased dispersal throughout the study area. Within the continuum of isolation by distance and in the presence of male-biased dispersal, the clustering of specific collections on a tree of genetic distances and hierarchical gene diversity analyses demonstrate discrete regional units. These results suggest def...

Comprehensive genetic analyses reveal evolutionary distinction of a mouse ( Zapus hudsonius preblei ) proposed for delisting from the US Endangered Species Act

Zapus hudsonius preblei, listed as threatened under the US Endangered Species Act (ESA), is one of 12 recognized subspecies of meadow jumping mice found in North America. Recent morphometric and phylogenetic comparisons among Z. h. preblei and neighbouring conspecifics questioned the taxonomic status of selected subspecies, resulting in a proposal to delist the Z. h. preblei from the ESA. We present additional analyses of the phylogeographic structure within Z. hudsonius that calls into question previously published data (and conclusions) and confirms the original taxonomic designations. A survey of 21 microsatellite DNA loci and 1380 base pairs from two mitochondrial DNA (mtDNA) regions (control region and cytochrome b) revealed that each Z. hudsonius subspecies is genetically distinct. These data do not support the null hypothesis of a homogeneous gene pool among the five subspecies found within the southwestern portion of the species’ range. The magnitude of the observed differentiation was considerable and supported by significant findings for nearly every statistical comparison made, regardless of the genome or the taxa under consideration. Structuring of nuclear multilocus genotypes and subspecies‐specific mtDNA haplotypes corresponded directly with the disjunct distributions of the subspecies investigated. Given the level of correspondence between the observed genetic population structure and previously proposed taxonomic classification of subspecies (based on the geographic separation and surveys of morphological variation), we conclude that the nominal subspecies surveyed in this study do not warrant synonymy, as has been proposed for Z. h. preblei, Z. h. campestris, and Z. h. intermedius.

Population structure, multiple paternity, and long-distance transport of spermatozoa in the freshwater mussel Lampsilis cardium (Bivalvia:Unionidae)

Abstract. Freshwater mussels (Bivalvia:Unionidae) are among the most imperiled organisms in North America. Information on the spatial scale of reproduction and population connectivity will better enable mussel conservation programs to sustain long-term population viability, particularly restocking and recovery programs. Here we used genetic methods to characterize population structure, dispersal potential, and reproductive strategies in the freshwater mussel Lampsilis cardium from Twin Creek and Big Darby Creek (Ohio, USA). We genotyped adults and individual glochidia at 12 microsatellite loci to assess local population structure relative to within-population patterns of relatedness and parentage. Local populations within watersheds were weakly structured, and within-population estimates of relatedness identified probable full- and half-siblings several kilometers apart. Parent–offspring comparisons provided evidence of multiple paternity in single broods and identified the likely father of 3 glochidia from 1 females brood 16.2 km upstream of the mother, indicating that long-distance transport of spermatozoa can promote population connectivity within watersheds. Given that lampsilines and other unionoids exhibit similar reproductive strategies, it is possible that other species are capable of long-distance fertilization. If so, fertilization in populations of many freshwater mussels might not be limited by local density of breeding adults. Therefore, the prospects for recovery of imperiled freshwater mussels might be better than what is now expected.

Characterization of 13 microsatellite loci for the deep-sea coral, Lophelia pertusa (Linnaeus 1758), from the western North Atlantic Ocean and Gulf of Mexico

A suite of 13 polymorphic tri‐ and tetranucleotide microsatellite loci were isolated from the ahermatypic deep‐sea coral, Lophelia pertusa. Among 51 individuals collected from three disjunct oceanic regions, allelic diversity ranged from six to 38 alleles and averaged 9.1 alleles per locus. Observed heterozygosity ranged from 9.1 to 96.8% and averaged 62.3% in the Gulf of Mexico population. For some loci, amplification success varied among collections, suggesting regional variation in priming site sequences. Four loci showed departures from Hardy–Weinberg equilibrium in certain collections which may reflect nonrandom mating.

Conservation Genetics of the American Horseshoe Crab (Limulus polyphemus): Allelic Diversity, Zones of Genetic Discontinuity, and Regional Differentiation

Extensive studies of genetic variation of Atlantic horseshoe crab Limulus polyphemus populations have revealed the presence of considerable allelic diversity and population structuring that appear to reflect the actions of various evolutionary processes. We have expanded on our previous efforts to gain a more refined understanding of L. polyphemus population structure by surveying 792 additional animals distributed among 12 additional spawning aggregations. Here we report on variation at 13 microsatellite DNA markers for 1,684 horseshoe crabs sampled from 33 spawning assemblages from northern Maine to the Yucatan Peninsula, Mexico. Average unbiased heterozygosity (uH E ) was high (0.74 ± 0.01), the number of private alleles was low (0.06 ± 0.04), effective population size (Ne) ranged from 22 to 187, inbreeding (F) ranged from −0.07 to 0.07, and tests for genic differentiation among populations indicated shallow but statistically significant differentiation within regions and highly significant differences among regions (P < 0.005). Current findings are consistent with previous research by this group in suggesting a series of genetic discontinuities across the species’ range that could indicate regional adaptive significance or reflect vicariant geographic events. Additional collections allowed improved delineation of structuring (as reflected by two new zones of genetic discontinuity) along the southeast Atlantic coast as well as identification of previously undetected shallow but significant structuring along the Florida Gulf coast. Regional groupings may warrant management unit recognition based on the patterns observed among multiple genetic metrics. The integration of this information with previously identified genetic variation and ecological data is essential to developing an ecologically and evolutionarily sound conservation management strategy.

The female and male mitochondrial genomes of Unio delphinus and the phylogeny of freshwater mussels (Bivalvia: Unionida)

Abstract We have sequenced the female and male mtDNA of Unio delphinus and inferred the Unionidae phylogeny using 41 complete mtDNA sequences. Additionally, we compared the concatenated mtDNA trees with those using single or combination of two mtDNA genes to identify the best genes to use in the absence of complete mitogenomes. The gender-specific mtDNAs of U. delphinus contain all Unionida mtDNA specific features. The mtDNA phylogeny supports the reciprocal monophyly of the gender-specific clades but it was inconclusive regarding Unionidae subfamilies relationships. The gene trees topologies using ND5 or 16S-rRNA with ND1 were the closest trees to the mtDNA trees.

Development of tri- and tetra- nucleotide polysomic microsatellite markers for characterization of American ginseng (Panax quinquefolius L.) genetic diversity and population structuring

American ginseng (Panax quinquefolius L., syn. Panax quinquefolium) is an herbaceous perennial plant native to eastern North America that is both harvested from the wild and cultivated in farm and woodlot settings to supply the international market. We describe the development of microsatellite markers to better characterize Panax quinquefolius population structure and phylogeography. We developed and tested 12 microsattelite loci, scored as 106 psuedo-dominant alleles due to the tetraploid nature of P. quinquefolius. We employed the newly developed markers to characterize population structure of field sampled populations from 13 states in comparison with commercially cultivated samples. Results reveal distinct phylogeographic and population structuring as well as a high degree of selfing in this CITES protected species.

The Pleurobemini (Bivalvia: Unionida) revisited: Molecular species delineation using a mitochondrial DNA gene reveals multiple conspecifics and undescribed species

Abstract. The Pleurobemini (Bivalvia: Unionida) represent approximately one-third of freshwater mussel diversity in North America. Species identification within this group is challenging due to morphological convergence and phenotypic plasticity. Accurate species identification, including characterisation of currently unrecognised taxa, is required to develop effective conservation strategies because many species in the group are imperiled. We examined 575 cox1 sequences from 110 currently recognised species (including 13 Fusconaia and 21 Pleurobema species) to understand phylogenetic relationships among pleurobemine species (mainly Fusconaia and Pleurobema) and to delineate species boundaries. The results of phylogenetic analyses showed no geographic structure within widespread species and illustrated a close relationship between Elliptio lanceolata and Parvaspina collina. Constraint tests supported monophyly of the genera Fusconaia and Pleurobema, including the subgenus P. (Sintoxia). Furthermore, results revealed multiple conspecifics, including P. hanleyianum and P. troschelianum, P. chattanoogaense and P. decisum, P. clava and P. oviforme, P. rubrum and P. sintoxia, F. askewi and F. lananensis, and F. cerina and F. flava. Species delimitation analyses identified three currently unrecognised taxa (two in Fusconaia and one in Pleurobema). Further investigation using additional genetic markers and other lines of evidence (e.g. morphology, life history, ecology) are necessary before any taxonomic changes are formalised.

The complete maternal mitochondrial genome sequences of two imperiled North American freshwater mussels: Alasmidonta heterodon and Alasmidonta varicosa (Bivalvia: Unionoida: Unionidae)

Abstract The freshwater mussels Alasmidonta heterodon and A. varicosa historically inhabited rivers along the North American Atlantic coast from the Carolinas, U.S.A., to New Brunswick, CA. However, many populations have been extirpated, and A. heterodon is now federally listed in the U.S.A. as endangered, and both A. heterodon and A. varicosa are listed as vulnerable on the IUCN Red List. To facilitate genetic study of these species, we sequenced the complete female mitochondrial genomes of A. heterodon (15,909 bp; GenBank accession no. MG905826), and A. varicosa (15,693 bp; GenBank accession no. MG938673). Both mitogenomes contained 14 protein coding genes, 2 rRNA genes, and 22 tRNAs with the same gene order as reported for other members of the subfamily Anodontinae. When these two genomes were put into a phylogenetic context with other members of the Unionidae, they clustered together with other species in the subfamily Anodontinae, Tribe Anodontini.