Structural characterization of beta-cardiac myosin subfragment 1 in solution

beta-cardiac myosin subfragment 1 (betaS1) tertiary structure and dynamics were characterized with proteolytic digestion, nucleotide analogue trapping kinetics, and intrinsic fluorescence changes accompanying nucleotide binding. Proteolysis of betaS1 produces the 25, 50, and 20 kDa fragments and a new cut within the 50-kDa fragment at Arg369. F-actin inhibits cleavage of the 50-kDa fragment and fails to inhibit cleavage at the 50/20 kDa junction, suggesting betaS1 presents an actoS1 conformation fundamentally different from skeletal S1. Time-dependent changes in Mg(2+)-ATPase accompanying proteolysis identifies cleavage points that lie within the energy transduction pathway. The nucleotide analogue trapping kinetics reveal the presence of a reversible weakly actin attached state. Comparison of nucleotide analogue induced betaS1 structures with the transient structures occurring during ATPase indicates analogue induced and transient structures are in a one-to-one correspondence. Tryptophan fluorescence enhancement accompanies the binding or trapping of nucleotide or nucleotide analogues. Isolation of Trp508 fluorescence shows it is an ATP-sensitive tryptophan and that its vicinity changes conformation sequentially with the transient intermediates accompanying ATPase. These studies elucidate energy transduction and suggest how mutations of betaS1 implicated in disease might undermine function, stability, or efficiency.     

Song post exposure, song features, and predation risk

Male birds use song to attract mates and deter other males,but in doing so, they also attract the attention of predatorsand parasites. Such viability costs are inherent in reliablesignals, potentially causing females to prefer mates that displayfrom the most exposed sites. However, viability costs of sexualsignals may be ameliorated by affecting the choice of microhabitat,which in turn may affect the design of song features that aremost efficiently transmitted in this microhabitat. We estimatedthe exposure of song posts (microsites used by males when singing)used by passerine birds in relation to prey selection by thesparrowhawk Accipiter nisus, by calculating the proportion ofmales that sang from song posts that were at the maximum levelof the vegetation, in an attempt to quantify the costs of sexualselection. We quantified prey susceptibility to predation asthe difference between the log-transformed observed number ofprey minus the log-transformed expected number of prey in theenvironment. This prey susceptibility index increased with increasingsong post exposure similarly in sexually dichromatic and monochromaticspecies, although the prey susceptibility index was relatedto sexual dichromatism. Song post exposure was dependent onhabitat, but comparative models controlling for the potentiallyconfounding effects of habitat, sexual dichromatism, hole nesting,coloniality, body mass, cognitive capacities, and flying abilitiesindicated that the relationship between the prey susceptibilityindex and song post exposure is strong. Path analyses of therelationship between song post exposure, sexual dichromatism,and prey susceptibility index revealed that selection actingon sexual dichromatism and song post exposure has secondaryimpact on prey susceptibility index. The opposite causal mechanismsby which predation affects sexual traits are less likely. Thesemodels suggest that female preference for high song posts ordichromatic plumage increases predation risk on an evolutionarytime scale.     

Parasite-mediated evolution of the functional part of the MHC in primates

The major histocompatibility complex (MHC) is a key model of genetic polymorphism, but the mechanisms underlying its extreme variability are debated. Most hypotheses for MHC diversity focus on pathogen-driven selection and predict that MHC polymorphism evolves under the pressure of a diverse parasite fauna. Several studies reported that certain alleles offer protection against certain parasites, yet it remains unclear whether variation in parasite pressure more generally covaries with allelic diversity and rates of molecular evolution of MHC across species. We tested this prediction in a comparative study of 41 primate species. We characterized polymorphism of the exon 2 of DRB region of the MHC class II. Our phylogenetic analyses controlled for the potential effects of neutral mutation rate, population size, geographic origin and body mass and revealed that nematode species richness associates positively with nonsynonymous nucleotide substitution rate at the functional part of the molecule. We failed to find evidence for allelic diversity being strongly related to parasite species richness. Continental distribution was a strong predictor of both allelic diversity and substitution rate, with higher values in Malagasy and Neotropical primates. These results indicate that parasite pressure can influence the different estimates of MHC polymorphism, whereas geography plays an independent role in the natural history of MHC.     

Indicators of physiological stress and the elaboration of sexual traits in the collared flycatcher

Stress may have consequences for the evolution of condition-dependentsexual traits. For example, stress may be related to sexualtraits through immune function, and sexual traits can reflecthow individuals bear the costs of stress-mediated immunosuppression.However, male traits may be directly associated with stress,and such traits would then indicate stress tolerance. Here,we present initial results for the relationship between physiologicalstress estimated by the levels of heat shock proteins (HSP60and HSP70) and heterophil/lymphocyte ratio and the elaborationof sexual traits, such as forehead and wing patch size and songfeatures in the collared flycatcher Ficedula albicollis. Malesproducing longer and more versatile songs had significantlyhigher levels of HSP70, but other traits were unrelated to stress.In general, effect sizes for the relationship between stressand sexual traits had broad confidence intervals and variedbetween being small and medium effects. Immunoglobulin levels,leukocyte abundance, haemoparasite prevalence, male age, anddate and time effects did not affect the relationship betweenstress and sexual traits. These preliminary results, servinga basis for further experimental studies indicate that the relationshipbetween sexual traits and stress does not seem to be strong,but stress may partially constrain the expression of some sexualtraits.     

A comparative study of the function of heterospecific vocal mimicry in European passerines

Although heterospecific vocal imitation is well documented inpasserines, the evolutionary correlates of this phenomenon arepoorly known. Here, we studied interspecific variation in vocalmimicry in a comparative study of 241 European songbirds. Wetested whether vocal mimicry is a mode of repertoire acquisitionor whether it resulted from imperfect song learning. We alsoinvestigated the effect of the degree of contact with the vocalenvironment (with species having larger ranges, abundance, orbeing long lived having a higher degree of mimicry) and a possiblelink with cognitive capacity (an overall larger brain in specieswith mimicry). Finally, we determined the potential evolutionaryrole of vocal mimicry in different interspecific contexts, predictingthat mimicry may affect the intensity of brood parasitism, predation,or degree of hybridization. While controlling for research effortand phylogenetic relationships among taxa, we found that effectsizes for intersong interval, brain size, breeding dispersal,abundance, age-dependent expression of repertoires, and predationrisk reached a level that may indicate evolutionary importance.Vocal mimicry seems to be a consequence of song continuity ratherthan song complexity, may partially have some cognitive componentbut may also be dependent on the vocal environment, and mayattract the attention of predators. However, estimates of sexualselection and interspecific contacts due to brood parasitismand hybridization varied independently of vocal mimicry. Therefore,mimicry may have no function in female choice for complex songsand may be weakly selected via interspecific associations. Thesefindings provide little evidence for vocal mimicry having evolvedto serve important functions in most birds.     

Migratory divides and their consequences for dispersal, population size and parasite-host interactions

Populations of migratory birds differ in their direction of migration with neighbouring populations often migrating in divergent directions separated by migratory divides. A total of 26% of 103 passerine bird species in Europe had migratory divides that were located disproportionately often along a longitudinal gradient in Central Europe, consistent with the assumption of a Quaternary glacial origin of such divides in the Iberian and Balkan peninsulas followed by recolonization. Given that studies have shown significant genetic differentiation and reduced gene flow across migratory divides, we hypothesized that an absence of migratory divides would result in elevated rates of gene flow and hence a reduced level of local adaptation. In a comparative study, species with migratory divides had larger population sizes and population densities and longer dispersal distances than species without migratory divides. Species with migratory divides tended to be habitat generalists. Bird species with migratory divides had higher richness of blood parasites and higher growth rates of Staphylococcus on their eggs during the incubation period. There was weaker cell-mediated immunity in adults and stronger cell lysis in species with migratory divides. These findings may suggest that migratory divides constitute barriers to dispersal with consequences for ecology and evolution of distributions, population sizes, habitats and parasite-host interactions. They also suggest that migratory divides may play a role in local adaptation in host-parasite interactions.