Intra-genomic variation in Symbiodinium correlates negatively with photosynthetic efficiency and coral host performance

Coral Reefs - Reef-building corals are nutritionally dependent on the symbiotic alga Symbiodinium and may therefore select for high-performing symbiont lineages. However, the effects of fine-scale...     

Evolution of Cranial Shape in Caecilians (Amphibia: Gymnophiona)

Insights into morphological diversification can be obtained from the ways the species of a clade occupy morphospace. Projecting a phylogeny into morphospace provides estimates of evolutionary trajectories as lineages diversified information that can be used to infer the dynamics of evolutionary processes that produced patterns of morphospace occupation. We present here a large-scale investigation into evolution of morphological variation in the skull of caecilian amphibians, a major clade of vertebrates. Because caecilians are limbless, predominantly fossorial animals, diversification of their skull has occurred within a framework imposed by the functional demands of head-first burrowing. We examined cranial shape in 141 species, over half of known species, using X-ray computed tomography and geometric morphometrics. Mapping an existing phylogeny into the cranial morphospace to estimate the history of morphological change (phylomorphospace), we find a striking pattern: most species occupy distinct clusters in cranial morphospace that closely correspond to the main caecilian clades, and each cluster is separated by unoccupied morphospace. The empty spaces in shape space are unlikely to be caused entirely by extinction or incomplete sampling. The main caecilian clades have different amounts of morphological disparity, but neither clade age nor number of species account for this variation. Cranial shape variation is clearly linked to phyletic divergence, but there is also homoplasy, which is attributed to extrinsic factors associated with head-first digging: features of caecilian crania that have been previously argued to correlate with differential microhabitat use and burrowing ability, such as subterminal and terminal mouths, degree of temporal fenestration (stegokrotaphy/zygokrotaphy), and eyes covered by bone, have evolved and many combinations occur in modern species. We find evidence of morphological convergence in cranial shape, among species that have eyes covered by bone, resulting in a narrow bullet-shaped head. These results reveal a complex history, including early expansion of morphospace and both divergent and convergent evolution resulting in the diversity we observe today.     

Short and long term prognosis of acute myocardial infarction since introduction of thrombolysis.

OBJECTIVE--To record prognosis and determinants of outcome in patients with acute myocardial infarction since thrombolysis was introduced. DESIGN--Observational study. SETTING--London district general hospital. PATIENTS--608 consecutive patients admitted to the coronary care unit with acute myocardial infarction between 1 January 1988 and 31 December 1991. MAIN OUTCOME MEASURE--All cause mortality, non-fatal ischaemic events (myocardial infarction, unstable angina), and revascularisation. RESULTS--Of the 608 patients, 89 (14.6%) died in hospital. 507 [corrected] patients were followed up after discharge from hospital. Mortality (95% confidence interval) at 30 days, one year, and three years was 16.0% (13.4% to 19.2%), 21.7% (18.6% to 25.2%), and 29.4% (25.3% to 33.9%) respectively. Event free survival (survival without a non-fatal ischaemic event) was 80.4% (77.0% to 83.4%) at 30 days, 66.8% (62.8% to 70.5%) at one year, and 56.1% (51.3% to 60.6%) at three years. Survival in patients treated with thrombolysis was considerably higher than in those not given thrombolysis (three year survival: 76.7% v 54.3%), although the incidence of non-fatal ischaemic events was the same in the two groups. Multivariate determinants of six month survival were left ventricular failure, treatment with thrombolysis and aspirin, smoking history, bundle branch block, and age. For patients who survived six months, age was the only factor related to long term survival. CONCLUSIONS--Although patients treated by thrombolysis had a relatively good prognosis, long term mortality and the incidence of non-fatal recurrent ischaemic events remained high. Effective strategies for the identification and treatment of high risk patients need to be reassessed.     

Molecular cytogenetic characterization of three familial cases of satellited Y chromosomes

Three families in which a satellited Y chromosome (Yqs) was segregating without apparent phenotypic effect were re-investigated with non-isotopic in situ hybridization methods. Active nucleolus organizer regions were seen in the distal long arm region of all Yqs chromosomes studied and in situ hybridization with the probe D15Z1 showed that, in all three families, the Yqs was the result of a 15p;Yq translocation. In one case, an additional focus of D15Z1 hybridization was seen on 21p.     

The fission yeast gene pmt1+ encodes a DNA methyltransferase homologue.

DNA methylation of cytosine residues is a widespread phenomenon and has been implicated in a number of biological processes in both prokaryotes and eukaryotes. This methylation occurs at the 5-position of cytosine and is catalyzed by a distinct family of conserved enzymes, the cytosine-5 methyltransferases (m5C-MTases). We have cloned a fission yeast gene pmt1+ (pombe methyltransferase) which encodes a protein that shares significant homology with both prokaryotic and eukaryotic m5C-MTases. All 10 conserved domains found in these enzymes are present in the pmt1 protein. This is the first m5C-MTase homologue cloned from a fungal species. Its presence is surprising, given the inability to detect DNA methylation in yeasts. Haploid cells lacking the pmt1+ gene are viable, indicating that pmt1+ is not an essential gene. Purified, bacterially produced pmt1 protein does not possess obvious methyltransferase activity in vitro. Thus the biological significance of the m5C-MTase homologue in fission yeast is currently unclear.     

Relative distribution of blood flow in rats during surface and submerged swimming

The relative distribution of blood flow was investigated in conscious rats with a radiological imaging technique that utilizes technetium-99m ethyl cysteinate dimer (99mTc-ECD). The objective of the study was to determine the effects of locomotory activity on the distribution of blood flow during a dive response. We compared the relative distribution of systemic flow in rats at rest, surface swimming and during periods of voluntarily initiated underwater swimming. The pattern of blood flow differed considerably between the three groups of rats. In resting controls, blood flow was widely distributed throughout the whole body with the thoraco-abdominal region receiving the largest fraction of cardiac output. During surface swimming blood shifted towards the exercising limbs, while during underwater swimming systemic blood flow was largely restricted to the head and thorax. However, the active front and hind limbs were not rendered totally ischemic. This suggests that the demands of exercising skeletal muscle partially over-ride the peripheral vasoconstriction during asphyxic diving in conscious rats. Furthermore, relative blood flow to the head increased during underwater swimming, which supports the view that there is a preferential maintenance of blood flow to the brain.     

Evolution of female mating preferences in stalk-eyed flies

Sensory exploitation predicts that female mate preferences existbefore the evolution of exaggerated male ornaments. We testedthis prediction by estimating female preference functions, rematingintervals, and copulation durations for three species of stalk-eyedflies. Two species, Cyrtodiopsis whitei and C dalmanni, exhibitextreme sexual dimorphism in eye span, with eye stalks exceedingbody length in large males. In contrast, C quinqucguttata ofboth sexes possess short eye stalks. Maximum parsimony analysisof 437 basepairs of the 16S mitochondrial ribosomal RNA genefrom 6 Malaysian diopsids reveals that short, sexually monomorphiceye stalks are plesiomorphic in Cyrtodiopsis. Observations ofmultiple copulations by females in paired-choice mating chambersindicated that female C whitei and C. dalmanni exhibit relativepreferences for longer eye stalks such that preference intensityincreases linearly with the difference in eye stalk length betweenmales. Females from the sexually monomorphic species showedno detectable preference for male eye stalk length. Female matingpreferences of bodi sexually dimorphic species exhibited significantrepeatability, as expected if genetic variation underlies thepreference. In addition, female C whitei and C. dalmanni exhibitedshorter copulations, mated more frequently, and rejected fewermating attempts than female C quinqueguttata. Thus, opportunitiesfor sperm competition have increased with acquisition of femalepreferences. We conclude that female sensory bias for maleswith long eye span did not exist in a common ancestor to thesespecies. Instead, female preference and remating propensityeither coevolved with eye span dimorphism or evolved after maleeye stalks elongated.