Evolution of the zygomasseteric construction in Rodentia,as revealed by a geometric morphometric analysis of the mandible of Graphiurus (Rodentia,Gliridae)

Graphiurus is a peculiar taxon among the monophyletic Gliridae (order Rodentia) in showing hystricomorphy of the zygomasseteric architecture of the skull [large infraorbital foramen (IOF), and correlative muscular arrangements). We analysed 34 extant genera taken from two groups of sciurognath rodents that share a large IOF (hystricomorph and myomorph) using elliptical Fourier transform in order to appraise whether this feature of cranial morphology was also accompanied by similar changes in mandible shape. The mandible of Graphiurus is distinct from those of all other hystricomorph sciurognath rodents in showing a more elongated coronoid process and a shorter angular process. Thus, two distinct zygomasseteric organizations (i.e. myomorphy and hystricomorphy of graphiurines) are associated with a similar mandible shape characterized by a well‐developed coronoid process. Results show that hystricomorphy of graphiurines was achieved convergently with other hystricomorph rodents. Protrogomorphy is the plesiomorphic condition in Gliridae and hystricomorphy is an autapomorphic feature of Graphiurus. © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society, 2008, 154 , 807–821.     

Genetic variation and structure in native populations of the fire ant Solenopsis invicta: evolutionary and demographic implications

We studied population genetic variation and structure in the fire ant Solenopsis invicta using nuclear genotypic and mitochondrial DNA (mtDNA) sequence data obtained from samples collected throughout its native range. Geographic populations are strongly differentiated at both genomes, with such structure more pronounced in Brazil than in Argentina. Higher-level regional structure is evident from the occurrence of isolation-by-distance patterns among populations, the recognition of clusters of genetically similar, geographically adjacent populations by ordination analysis, and the detection of an mtDNA discontinuity between Argentina and Brazil coinciding with a previously identified landform of biogeographical relevance. Multiple lines of evidence from both genomes suggest that the ancestors of the ants we studied resembled extant northern Argentine S. invicta , and that existing Brazilian populations were established more recently by serial long-distance colonizations and/or range expansions. The most compelling evidence for this is the corresponding increase in F _K (a measure of divergence from a hypothetical ancestor) and decrease in genetic diversity with distance from the Corrientes population in northern Argentina. Relatively deep sequence divergence among several mtDNA clades, coupled with geographical partitioning of many of them, suggests prolonged occupation of South America by S. invicta in more-or-less isolated regional populations. Such populations appear, in some cases, to have come into secondary contact without regaining the capacity to freely interbreed. We conclude that nominal S. invicta in its native range comprises multiple entities that are sufficiently genetically isolated and diverged to have embarked on independent evolutionary paths.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 541–560.     

Asymmetrical introgression in a freshwater fish hybrid zone as revealed by a morphological index of hybridization

Two cyprinid species, Barbus barbus and Barbus meridionalis , form a hybrid zone in the River Lergue (southern France). Hybrids were distinguished morphologically by discriminant function analysis based on samples from the two parental taxa using only three measurements. This morphological hybridization index showed a strong asymmetry in introgression between the two taxa. B. meridionalis can live in the habitats typical of B. barbus and also in habitats where the latter cannot (small upstream tributaries), while remaining essentially unaffected by the hybridization process. By contrast, B. barbus is strongly introgressed because its habitat is invaded at least sporadically by B. meridionalis migrants. There is no behavioral barrier to hybridization, suggesting that an asymmetrical gene flow is probably partly responsible for the asymmetry in introgression.     

The bryophyte Physcomitrella patens replicates extrachromosomal transgenic elements

Physcomitrella patens , recently renamed Aphanoregma patens , has been transformed with the plasmid, pBI426. On selective medium approx. 30% of regenerants expressed the transformed phenotype transiently (transients). The remaining 70% (transformants) retained their transformed phenotype (GUS-positive and resistant to G418) indefinitely when subcultured repeatedly on selective medium. However, most lost this phenotype after one or two passages through nonselective medium (unstable transformants). Approximately 0.2% of transformants retained their transformed phenotype after numerous passages through nonselective medium (stable transformants). Using PCR methodology, it has been shown that loss of the transformed phenotype by unstable transformants is invariably accompanied by disappearance of the transgenic DNA. Southern blot analysis data argue strongly that unstable transformants cultured under selective conditions contain unintegrated pBI426 as circular concatenates consisting of 3–40 copies of the plasmid. Under selective conditions, it appears that replication and/or partitioning of these extrachromosomal concatemers might be growth rate-limiting. This is the first report of a transgenic, autonomously replicating extrachromosomal element in a photosynthetic plant. A single copy of pBI426 has been inserted into the moss genome in each of three stable transformants analysed.     

Molecular resolution of marine turtle stock composition in fishery bycatch: a case study in the Mediterranean

Based on an extensive sampling regime from both nesting populations and bycatch, frequency analyses of mitochondrial (mt) DNA control region haplotypes in the Mediterranean were used to assess the genetic structure and stock composition of the loggerhead sea turtle, Caretta caretta, in different marine fisheries. The analyses show the following. (i) In drifting longline fisheries working in Mediterranean pelagic habitats 53–55% of turtles caught originated from the Mediterranean stock; (ii) In bottom-trawl fisheries all turtle bycatch is derived from this regional stock; (iii) This regional stock contribution to fishery bycatch suggests that the population size of the Mediterranean loggerhead nesting population is significantly larger than previously thought. This is consistent with a recent holistic estimate based on the discovery of a large rookery in Libya. (iv) Present impact of fishery-related mortality on the Mediterranean nesting population is probably incompatible with its long-term conservation. Sea turtle conservation regulations are urgently needed for the Mediterranean fisheries. (v) The significant divergence of mtDNA haplotype frequencies of the Turkish loggerhead colonies define this nesting population as a particularly important management unit. Large immature and adult stages from this management unit seem to be harvested predominantly by Egyptian fisheries. (vi) Combined with other data, our findings suggest that all the nesting populations in the Mediterranean should be considered as management units sharing immature pelagic habitats throughout the Mediterranean (and possibly the eastern Atlantic), with distinct and more localized benthic feeding habitats in the eastern basin used by large immatures and adults. (vii) Between the strict oceanic pelagic and the benthic stages, immature turtles appear to live through an intermediate neritic stage, in which they switch between pelagic and benthic foods.     

atz gene expressions during atrazine degradation in the soil drilosphere

One of the various ecosystemic services sustained by soil is pollutant degradation mediated by adapted soil bacteria. The pathways of atrazine biodegradation have been elucidated but in situ expression of the genes involved in atrazine degradation has yet to be demonstrated in soil. Expression of the atzA and atzD genes involved in atrazine dechlorination and s‐triazine ring cleavage, respectively, was investigated during in situ degradation of atrazine in the soil drilosphere and bulked samples from two agricultural soils that differed in their ability to mineralize atrazine. Interestingly, expression of the atzA gene, although present in both soils, was not detected. Atrazine mineralization was greatest in Epoisses soil, where a larger pool of atzD mRNA was consistently measured 7 days after atrazine treatment, compared with Vezin soil (146 vs. 49 mRNA per 10 ⁶ 16S rRNA, respectively). Expression of the atzD gene varied along the degradation time course and was profoundly modified in soil bioturbated by earthworms. The atzD mRNA pool was the highest in the soil drilosphere (casts and burrow‐linings) and it was significantly different in burrow‐linings compared with bulk soil (e.g. 363 vs. 146 mRNA per 10 ⁶ 16S rRNA, 7 days after atrazine treatment in Epoisses soil). Thus, consistent differences in atrazine mineralization were demonstrated between the soil drilosphere and bulk soil. However, the impact of bioturbation on atrazine mineralization depended on soil type. Mineralization was enhanced in casts, compared with bulk soil, from Epoisses soil but in burrow‐linings from Vezin soil. This study is the first to report the effects of soil bioturbation by earthworms on s‐triazine ring cleavage and its spatial variability in soil.     

Differential response of phytoplankton to additions of nitrogen, phosphorus and iron in Lake Tanganyika

1. In order to evaluate limitation of different phytoplankton groups by inorganic nutrients, multiple nutrient enrichment bioassays using the addition of iron (Fe) and the combined addition of nitrogen and phosphorus (NP) were carried out in the north and the south of Lake Tanganyika during the rainy and dry seasons in 2003 and 2004. 2. Nutrient additions resulted in an increase in phytoplankton growth rate relative to control treatments in all experiments. HPLC pigment data and epifluorescence microscopy counts indicated differential stimulation of the dominant phytoplankton groups. Iron additions mainly stimulated prokaryotic picophytoplankton, while enrichments with nitrogen and phosphorus stimulated green algae and in some cases diatoms. Extended incubation (3 days) indicated co‐limitation of Fe and NP, in particular for picocyanobacteria.