Phylogeographic analysis reveals a deep lineage split within North Atlantic Littorina saxatilis

Phylogeographic studies provide critical insight into the evolutionary histories of model organisms; yet, to date, range-wide data are lacking for the rough periwinkle Littorina saxatilis, a classic example of marine sympatric speciation. Here, we use mitochondrial DNA (mtDNA) sequence data to demonstrate that L. saxatilis is not monophyletic for this marker, but is composed of two distinct mtDNA lineages (I and II) that are shared with sister species Littorina arcana and Littorina compressa. Bayesian coalescent dating and phylogeographic patterns indicate that both L. saxatilis lineages originated in the eastern North Atlantic, around the British Isles, at approximately 0.64 Ma. Both lineages are now distributed broadly across the eastern, central and western North Atlantic, and show strong phylogeographic structure among regions. The Iberian Peninsula is genetically distinct, suggesting prolonged isolation from northeastern North Atlantic populations. Western North Atlantic populations of L. saxatilis lineages I and II predate the last glacial maximum and have been isolated from eastern North Atlantic populations since that time. This identification of two distinct, broadly distributed mtDNA lineages further complicates observed patterns of repeated incipient ecological speciation in L. saxatilis, because the sympatric origins of distinct ecotype pairs on eastern North Atlantic shores may be confounded by admixture of divergent lineages.     

Synthesis of Some 2-Alkylated-5-Aminoimidazoles Related to Intermediates in Purine Nucleotide de novo and Thiamine Biosynthesis

Abstract

Routes to 2-alkylated-5-aminoimidazole nucleosides have been investigated in which the 2-substituent has up to 3 carbon atoms and capable of being interconverted into suitable oxy and 0x0 alkyl derivatives for use in enzyme inhibition and biochemical incorporation studies involving both purine nucleotide de novo and thiamine biosynthesis.     

Extradural Corticosteroid Injection in Management of Lumbar Nerve Root Compression

The effect of extradural corticosteroid injection in patients with nerve root compression syndromes associated with degenerative disease of the lumbar intervertebral discs was assessed in a double-blind controlled trial on 100 consecutive inpatients assigned by random allocation to treatment and control groups. Assessment during admission and at three months revealed statistically highly significant differences in respect of relief of pain and resumption of normal occupation in favour of the group treated by extradural injection. This treatment seems to be a valuable adjunct to the management of lumbar nerve root compression syndromes associated with degenerative disc disease.     

Ontogeny of shell morphology and shell strength of the marine snails Littorina obtusata and Littorina mariae: different defence strategies in a pair of sympatric, sibling species

The sibling marine snails Littorina obtusata (L.) and Littorina mariae Sacchi & Rastelli are sympatrically distributed and the shells of both species are subject to similar breaking forces by predatory crabs. Nevertheless, the two species exhibit rather different growth and defence strategies. To determine growth patterns, we measured changes in five morphological variables with increasing shell length: body whorl thickness at the point of crushing force application, shell height (related to globosity), shell mass, body mass, and apertural lip thickness. We also measured ontogenetic changes in the ability to withstand shell crushing. For most morphological variables, L. mariae showed uniformly allometric growth of juveniles into adults. In contrast, L. obtusata usually exhibited a distinct change in growth pattern upon reaching maturity. As adults, L. mariae showed a more sustained increase in overall shell mass and in body whorl thickness (defence against crushing attacks) and also had proportionally thicker apertural lips (defence against peeling attacks). Littorina obtusata , however, grew to a larger size and their shells could accommodate larger bodies at all sizes. Furthermore, the strength of L. obtusata shells increased faster than could be accounted for by either overall shell mass or thickness at the point of force application, suggesting strengthening by other means such as changes in shell microstructure or shape (other than globosity). These results illustrate the viability of two contrasting antipredator strategies, despite a highly similar phylogenetic history and selective regime.     

Thermal preferences of hatchling saltwater crocodiles (Crocodylus porosus) in response to time of day,social aggregation and feeding

Three month old hatchling Crocodylus porosus with data loggers in their stomachs were placed in thermal gradients, in isolation (N=16) and in groups of 4 (N=8 groups; 32 individuals). Mean T_b and variation in T_b (SD) was not different whether individual crocodiles in isolation were fasted or fed, or if individuals were housed in isolation (I) or in groups (G). However, individuals in isolation (N=16) maintained slightly lower T_bs than those in groups (N=32) during the early morning (06:00–11:00 h). The overall mean T_b recorded for fasted individuals in the isolated and group treatments (N=48) was 30.9±2.3 °C SD, with 50% of T_bs (T_set) between 29.4 °C and 32.6 °C, and a voluntary maximum and minimum of 37.6 °C and 23.2 °C respectively. During the day (11:00–17:00 h), individuals in isolation and in groups selected the warmer parts of the gradient on land, where they moved little. Outside of this quiescent period (QP), activity levels were much higher and they used the water more. There was a strong diurnal cycle for fasted individuals in isolation and in groups, with T_b during the QP (31.9±2.09 °C; N=48) significantly higher than during the non-quiescent period (NQP: 30.6±2.31 °C). Thermal variation (SD) in T_b was relatively stable throughout the day, with the highest variation at around dusk and early evening (18:00–20:00 h), which coincided with a period of highest activity. The diurnal activity cycle appears innate, and may reflect the need to engage in feeding activity at the water's edge in the early evening, despite ambient temperatures being cooler, with reduced activity and basking during the day. If so, preferred T_b may be more accurately defined as the mean T_b during the QP rather than the NQP. Implications for the thermal environment best suited for captive C. porosus hatchlings are discussed.     

A neural protection racket: AMPK and the GABA(B) receptor

The cellular energy-sensing kinase AMPK is known to be activated in neurons in response to metabolic insults, but the downstream consequences have been unclear. A study by Kuramoto and colleagues in this issue of Neuron favors the idea that AMPK activation is neuroprotective, and suggests a potential mechanism for this effect involving phosphorylation of the GABA(B) receptor.     

Aging-associated reductions in AMP-activated protein kinase activity and mitochondrial biogenesis

Recent studies have demonstrated a strong relationship between aging-associated reductions in mitochondrial function, dysregulated intracellular lipid metabolism, and insulin resistance. Given the important role of the AMP-activated protein kinase (AMPK) in the regulation of fat oxidation and mitochondrial biogenesis, we examined AMPK activity in young and old rats and found that acute stimulation of AMPK-alpha(2) activity by 5'-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR) and exercise was blunted in skeletal muscle of old rats. Furthermore, mitochondrial biogenesis in response to chronic activation of AMPK with beta-guanidinopropionic acid (beta-GPA) feeding was also diminished in old rats. These results suggest that aging-associated reductions in AMPK activity may be an important contributing factor in the reduced mitochondrial function and dysregulated intracellular lipid metabolism associated with aging.     

Nuclear DNA restriction site polymorphisms and the phylogeny and population structure of an intertidal snail species complex (Littorina)

Primers for amplification of four novel, unlinked nuclear DNA loci, the first reported for the rough periwinkles of the genus Littorina, are described. Patterns of restriction site polymorphism for these loci are detailed within the rough periwinkles. RFLPs are not found to be diagnostic for any of the currently accepted species within this group, nor for any of the contentious subspecies, or forms, whose taxonomic status is uncertain. However, there are important differences in allele frequencies between these taxa and certain of these mirror differences detected in a previous study of the mitochondrial DNA. These allele frequency data are used to construct a phylogeny in which groupings of the three recognised species are obvious when either Nei's genetic distances or Reynold's distances are clustered. Contentious forms (L. neglecta, L. saxatilis 'b' and L. tenebrosa) do not cluster as distinct taxa, although populations of L. neglecta have important allele frequency differences from L. saxatilis. These four loci have confirmed the consensus view of Littorina phylogeny and provided important information on population structure-however four loci is insufficient for reaching definitive conclusions. Since analysis of nuclear DNA polymorphisms such as these is invaluable for analysis of phylogeny, population structure and phylogeography, identification of additional loci is considered imperative.