Effects of host nutritional status and seasonality on the nitrogen status of zooxanthellae in the temperate coral Plesiastrea versipora (Lamarck)

The nitrogen status of endosymbiotic dinoflagellates (zooxanthellae) in the temperate coral Plesiastrea versipora (Lamarck) was determined by measuring the extent to which ammonium (40 μM NH₄⁺) enhanced the rate of zooxanthellar dark carbon fixation above that seen in filtered seawater (FSW) alone; the enhancement ratio was expressed as [dark NH₄⁺ rate/dark FSW rate]. V_D′/V_L, a further index of nitrogen status, was also calculated where V_D′ = [dark NH₄⁺ rate − dark FSW rate] and V_L = rate of carbon fixation in the light. When corals were starved for 2-8 weeks, zooxanthellar nitrogen deficiency became apparent at ≥ 4 weeks, with NH₄⁺/FSW and V_D′/V_L averaging up to 2.08 and 0.0061, respectively. A decrease in light-saturated photosynthesis per zooxanthella also occurred, with the photosynthetic rate after 4-6 weeks being just 81% of that seen prior to starvation. In comparison, when corals were fed 5 times per week for 8 weeks the addition of ammonium had little effect, indicating nitrogen sufficiency; NH₄⁺/FSW and V_D′/V_L were 1.03 and 0.0003, respectively. Photosynthetic rates of zooxanthellae from well-fed corals were up to 1.7 times greater than those of zooxanthellae from starved corals. The nitrogen status of zooxanthellae from corals in the field exhibited seasonal differences. Autumn samples were nitrogen sufficient, with NH₄⁺/FSW = 1.003 and V_D′/V_L = 0.0001. In contrast, a small degree of nitrogen deficiency was seen in winter and spring, when NH₄⁺/FSW averaged 1.075 and 1.249, and V_D′/V_L averaged 0.0013 and 0.0014, respectively. The greatest degree of nitrogen deficiency was observed in summer, when NH₄⁺/FSW averaged 1.318 and V_D′/V_L averaged 0.0036. Given the clear links between food supply and nitrogen status seen under experimental conditions, and the likelihood that the zooxanthellae are also able to take up nutrients directly from the seawater, the fluctuations in nitrogen status may reflect temporal fluctuations in seawater nutrient concentrations and plankton abundance. The nutrient status of these temperate zooxanthellae in the field is in contrast to the marked nitrogen deficiency seen in zooxanthellae from nutrient-poor coral reef waters, and raises the possibility that temperate zooxanthellae can store nitrogen for use when exogenous nutrients and food are less readily available. This, in turn, may contribute to the considerable stability of temperate zooxanthellar populations under highly variable environmental conditions.     

Functional consequence of positive selection revealed through rational mutagenesis of human myeloperoxidase

Myeloperoxidase (MPO) is a member of the mammalian heme peroxidase (MHP) multigene family. Whereas all MHPs oxidize specific halides to generate the corresponding hypohalous acid, MPO is unique in its capacity to oxidize chloride at physiologic pH to produce hypochlorous acid (HOCl), a potent microbicide that contributes to neutrophil-mediated host defense against infection. We have previously resolved the evolutionary relationships in this functionally diverse multigene family and predicted in silico that positive Darwinian selection played a major role in the observed functional diversities (Loughran NB, O'Connor B, O'Fagain C, O'Connell MJ. 2008. The phylogeny of the mammalian heme peroxidases and the evolution of their diverse functions. BMC Evol Biol. 8:101). In this work, we have replaced positively selected residues asparagine 496 (N496), tyrosine 500 (Y500), and leucine 504 (L504) with the amino acids present in the ancestral MHP and have examined the effects on the structure, biosynthesis, and activity of MPO. Analysis in silico predicted that N496F, Y500F, or L504T would perturb hydrogen bonding in the heme pocket of MPO and thus disrupt the structural integrity of the enzyme. Biosynthesis of the mutants stably expressed in human embryonic kidney 293 cells yielded apoproMPO, the heme-free, enzymatically inactive precursor of MPO, that failed to undergo normal maturation or proteolytic processing. As a consequence of the maturational arrest at the apoproMPO stage of development, cells expressing MPO with mutations N496F, Y500F, L504T, individually or in combination, lacked normal peroxidase or chlorinating activity. Taken together, our data provide further support for the in silico predictions of positive selection and highlight the correlation between positive selection and functional divergence. Our data demonstrate that directly probing the functional importance of positive selection can provide important insights into understanding protein evolution.     

Long-term familiarity promotes joining in neighbour nest defence

Familiarity plays an important role in the evolution of sociality and cooperation. Familiar individuals may gain a reputation for participating in, or defecting from, cooperative tasks. Previous research suggests that long-term familiarity with territorial neighbours benefits breeders. We tested the hypothesis that great tits (Parus major) are more likely to join in neighbours' nest defence if those neighbours are familiar from the previous year. We show that neighbours that shared a territory boundary the previous year are more likely to join their neighbours' nest defence than neighbours that did not share a boundary before. Closer neighbours did not differ from distant neighbours in their latency to join. For familiar neighbours that joined, there was no difference in call rate in relation to whether one or both members of the focal pair were familiar. First-time breeders (by definition unfamiliar) did not join each other's nest defence. This is the first evidence of a relationship between familiarity and joining in nest defence. Such direct benefits of familiarity may have important implications in the evolution of sociality.     

Respiratory epithelial cells convert inactive vitamin D to its active form: potential effects on host defense

The role of vitamin D in innate immunity is increasingly recognized. Recent work has identified a number of tissues that express the enzyme 1alpha-hydroxylase and are able to activate vitamin D. This locally produced vitamin D is believed to have important immunomodulatory effects. In this paper, we show that primary lung epithelial cells express high baseline levels of activating 1alpha-hydroxylase and low levels of inactivating 24-hydroxylase. The result of this enzyme expression is that airway epithelial cells constitutively convert inactive 25-dihydroxyvitamin D(3) to the active 1,25-dihydroxyvitamin D(3). Active vitamin D that is generated by lung epithelium leads to increased expression of vitamin D-regulated genes with important innate immune functions. These include the cathelicidin antimicrobial peptide gene and the TLR coreceptor CD14. dsRNA increases the expression of 1alpha-hydroxylase, augments the production of active vitamin D, and synergizes with vitamin D to increase expression of cathelicidin. In contrast to induction of the antimicrobial peptide, vitamin D attenuates dsRNA-induced expression of the NF-kappaB-driven gene IL-8. We conclude that primary epithelial cells generate active vitamin D, which then influences the expression of vitamin D-driven genes that play a major role in host defense. Furthermore, the presence of vitamin D alters induction of antimicrobial peptides and inflammatory cytokines in response to viruses. These observations suggest a novel mechanism by which local conversion of inactive to active vitamin D alters immune function in the lung.     

The conservation of the belted beauty Lycia zonaria britannica (Lepidoptera, Geometridae) in the United Kingdom

Recent surveys have established that the belted beauty moth Lycia zonaria britannica, which is an endemic subspecies found only in the British Isles, now occurs at just three sites in England and Wales. Populations at all three sites are small, with annual peak counts of usually less than 50 females. At Morfa Conwy in Wales and Meols Common in England, habitat quality has been declining for more than a decade as open, herb-rich, early successional dune grassland is replaced by fixed, rank grassland. Uniquely at Sunderland Point in England, the moth is primarily associated with areas of saltmarsh, but distribution is constrained by surrounding farmland and man-made structures. Attempts are now being made to restore areas of open grassland and to return the moth to its former distribution. Since the winter of 2000-2001, small plots of rank grassland on Meols Common have been excavated annually, with all vegetation removed, together with any humic layer present. The exposed bare sand has then been allowed to re-vegetate naturally. Within 18 months, the plots have developed into open, herb-rich habitats suitable for the moth. Adults were recorded on the plots for the first time in spring 2003 and may have been the product of the small numbers of eggs and larvae introduced to the plots in spring 2002. Similar excavations have been initiated at Morfa Conwy, which is in the process of being notified as a Site of Special Scientific Interest (SSSI). A 3-year programme to establish a second Welsh population is underway and, to date, more than 2000 captive-reared larvae have been released on the receptor site which lies 21 km to the east of Morfa Conwy.