Extensive local‐scale gene flow and long‐term population stability in the intertidal mollusc Katharina tunicata (Mollusca: Polyplacophora)

The dispersal capabilities of intertidal organisms may represent a key factor to their survival in the face of global warming, as species that cannot adapt to the various effects of climate change will have to migrate to track suitable habitat. Although species with pelagic larval phases might be expected to have a greater capacity for dispersal than those with benthic larvae, interspecies comparisons have shown that this is not always the case. Consequently, population genetic approaches are being increasingly used to gain insights into dispersal through studying patterns of gene flow. In the present study, we used nuclear single‐nucleotide polymorphisms (SNPs) and mitochondrial DNA (mtDNA) sequencing to elucidate fine‐scale patterns of genetic variation between populations of the Black Katy Chiton, Katharina tunicata, separated by 15–150 km in south‐west Vancouver Island. Both the nuclear and mitochondrial data sets revealed no genetic differentiation between the populations studied, and an isolation‐with‐migration analysis indicated extensive local‐scale gene flow, suggesting an absence of barriers to dispersal. Population demographic analysis also revealed long‐term population stability through previous periods of climate change associated with the Pleistocene glaciations. Together, the findings of the present study suggest that this high potential for dispersal may allow K. tunicata to respond to current global warming by tracking suitable habitat, consistent with its long‐term demographic stability through previous changes in the Earth's climate. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 589–597.     

The loss of submerged plants with eutrophication III. Potential role of organochlorine pesticides: a palaeoecological study

SUMMARY. 1 Mechanisms which might have caused a switch from submerged plant dominance to phytoplankton dominance in a series of shallow lakes, the Norfolk Broads, during the 1950s and 1960s, are reviewed. It is argued that a likely mechanism was a poisoning of the community of Cladocera which graze on algae and are associated with the plants. This allowed phytoplankton to take advantage of the increased nutrient loadings and to increase. The 1950s and 1960s were periods of liberal organochlorine pesticide use. Cladocera are particularly susceptible to organochlorine toxicity.
2. Sediment cores were taken from Hoveton Great Broad, in which the switch to phytoplankton has occurred, and from two Broads (Upton and Martham South Broads) in which submerged plants are still dominant. Analyses were made for cladoceran remains, diatoms and molluscs. Cross dating with previously taken dated cores allowed time-scales to be applied.
3. In Hoveton Great Broad, a switch from clear-water-associated chydorids to turbid-water forms was found to coincide with the loss of aquatic plants in the 1950s. No Daphnia remains were found. In the other two Broads, clear-water chydorids, mostly plant-associated, were found throughout the cores.
4. Residues of dieldrin (HEOD), DDD and TDE were found in the Hoveton Great Broad cores, with the DDT derivatives particularly associated with the end of the phase of submerged plant dominance and the beginning of that of phytoplankton dominance. Bosmina remains became more abundant after this point. Pesticide residues were scarce in the cores from the other two Broads and did not form any particular pattern. Residues of polychlorinated biphenyls were widespread in all cores.
5. Calculation of DDT concentration in the water at the time the sediments with greatest concentrations of residue were laid down suggests that concentrations above typical LC₅₀ values for Daphnia species could have been present.     

Gene and Enhancer Trap Transposable Elements Reveal Oxygen Deprivation-regulated Genes and their Complex Patterns of Expression in Arabidopsis

Transposon tagging with modified maize Ds–GUS constructswas used to isolate genes induced by oxygen deprivation in Arabidopsisthaliana. Seedlings of 800 gene-trap (DsG) and 600 enhancer-trap(DsE) lines were grown on vertically positioned plates for 1 week,oxygen deprived for up to 24 h and stained for GUS activity.Oxygen deprivation induced intricate patterns of gene expressionin seedlings of 65 lines. The insertion site and phenotypesof 15 lines were examined. Surprisingly, none of the insertionswere into genes that encode known anaerobic polypeptides. Insertionswere identified within or adjacent to genes encoding proteinsof regulatory, enzymatic, mitochondrial protein import and unknownfunction, as well as adjacent to genes encoding a putative receptor-likekinase and putative sensor-histidine kinase. Four lines hadsignificantly lower ADH activity after 24 h of oxygen deprivationand three of these showed reduced stress tolerance. Two lineswith wild-type levels of ADH were low-oxygen intolerant. Paradoxically,several lines had significantly higher ADH activity after 12 hof oxygen deprivation but reduced stress tolerance. Caffeinetreatment, which increased ADH specific activity in wild-typeseedlings under aerobic conditions, was sufficient to increaseGUS staining in seven of the 15 lines, providing evidence thatthese genes may be regulated by cytosolic calcium levels. Theseresults demonstrate the effectiveness of the Ds–GUS taggingsystem in the identification of genes that are regulated inresponse to oxygen deprivation and a calcium second messenger.     

A phylogenetic analysis of the genera of Lejeuneaceae (Hepaticae)

The Lejeuneaceae are the largest family of the liverworts (Hepaticae), with almost a thousand species in 91 currently accepted genera. We analysed phylogenetic relationships of 69 genera, representing all major subfamilies and tribes recognized in the family, by using 49 informative morphological characters (31 gametophytic, 18 sporophytic), one chemical character, and applying equal and successive weighting of characters and parsimony analysis. In all trees recovered, the Lejeuneaceae were monophyletic with Nipponolejeunea (subfam. Nipponolejeuneoideae) forming the basalmost lineage. The remaining genera clustered in two major groups, the monophyletic Lejeuneoideae (52 genera) and the paraphyletic Ptychanthoideae (16 genera). Within each, several multigeneric lineages corresponding in part to previously described taxa were recovered: the Acrolejeuneinae and Ptychanthinae clades in the Ptychanthoideae, and the Brachiolejeuneinae, Lejeuneeae and Tuyamaella–Cololejeunea clades in the Lejeuneoideae. Bryopteris , a genus sometimes treated as a separate family, was nested in the Ptychanthinae clade. The Tuyamaella–Cololejeunea lineage corresponded with three previously recognized subfamilies (Cololejeuneoideae, Myriocoleoideae and Tuyamaelloideae) and contained genera with neotenic features, in two subclades. These features seemed to have originated by multiple heterochronic events: single origins were detected for 'protonemal neoteny' and 'primary neoteny', whereas 'secondary neoteny' probably evolved twice. Relationships within the large Lejeuneeae clade (43 genera) remained largely unresolved, although several putative lineages were detected in majority rule trees. Additional characters such as DNA sequences may provide better phylogenetic resolution in this group.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 143 , 391–410.     

Mitochondrial DNA distributions indicate colony propagation by single matri-lineages in the social spider Stegodyphus dumicola (Eresidae)

Colony-dwelling social spiders of the genus Stegodyphus are characterized by high colony turnover, within-colony mating, inbreeding and skewed sex ratios. These phenomena may purge genetic variation from the entire species gene pool. Social Stegodyphus have previously been discussed as ecologically unstable and evolutionary dead ends. We investigated the distribution and age (sequence divergence) of mitochondrial DNA variation for inferences of colony propagation, colony discreteness and maintenance of genetic variation in the social spider S. dumicola . In contrast to our expectations, we found abundant mtDNA variation, consisting of 15 haplotypes belonging to four haplotype lineages. Lineage divergence ranged between 2.75 and 6% for the gene ND1. Nearly all colonies (86%) were monomorphic and even neighbour colonies showed fixed differences. Simulations show that genetic drift in multifounder colonies cannot alone explain monomorphism within colonies. Haplotypes in polymorphic colonies and from neighbouring colonies were always genealogically similar. Monomorphism and the genealogical pattern among colonies suggest 'clonal' colony propagation involving single matrilineages. The divergence of haplotype lineages and distribution of haplotypes imply that colony turnover is not high enough to purge genetic variation in the species gene pool, and that S. dumicola as a species is old enough to question the instability (in ecological time) of a social spider.  © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 76 , 591–600.