The Causes and Evolutionary Consequences of Mixed Singing in Two Hybridizing Songbird Species (Luscinia spp.)

Bird song plays an important role in the establishment and maintenance of prezygotic reproductive barriers. When two closely related species come into secondary contact, song convergence caused by acquisition of heterospecific songs into the birds’ repertoires is often observed. The proximate mechanisms responsible for such mixed singing, and its effect on the speciation process, are poorly understood. We used a combination of genetic and bioacoustic analyses to test whether mixed singing observed in the secondary contact zone of two passerine birds, the Thrush Nightingale (Luscinia luscinia) and the Common Nightingale (L. megarhynchos), is caused by introgressive hybridization. We analysed song recordings of both species from allopatric and sympatric populations together with genotype data from one mitochondrial and seven nuclear loci. Semi-automated comparisons of our recordings with an extensive catalogue of Common Nightingale song types confirmed that most of the analysed sympatric Thrush Nightingale males were ‘mixed singers’ that use heterospecific song types in their repertoires. None of these ‘mixed singers’ possessed any alleles introgressed from the Common Nightingale, suggesting that they were not backcross hybrids. We also analysed songs of five individuals with intermediate phenotype, which were identified as F₁ hybrids between the Thrush Nightingale female and the Common Nightingale male by genetic analysis. Songs of three of these hybrids corresponded to the paternal species (Common Nightingale) but the remaining two sung a mixed song. Our results suggest that although hybridization might increase the tendency for learning songs from both parental species, interspecific cultural transmission is the major proximate mechanism explaining the occurrence of mixed singers among the sympatric Thrush Nightingales. We also provide evidence that mixed singing does not substantially increase the rate of interspecific hybridization and discuss the possible adaptive value of this phenomenon in nightingales.     

Localisation of RFLPs of the medium chain acyl-CoA dehydrogenase gene

Summary Six restriction fragment length polymorphisms (RFLPs) of the gene are described. Three of these are in linkage disequilibrium. Hybridisation with sub-probes allowed localisation of the RFLPs to different regions of the gene.     

Modulation of Malaria Phenotypes by Pyruvate Kinase (PKLR) Variants in a Thai Population

Pyruvate kinase (PKLR) is a critical erythrocyte enzyme that is required for glycolysis and production of ATP. We have shown that Pklr deficiency in mice reduces the severity (reduced parasitemia, increased survival) of blood stage malaria induced by infection with Plasmodium chabaudi AS. Likewise, studies in human erythrocytes infected ex vivo with P. falciparum show that presence of host PK-deficiency alleles reduces infection phenotypes. We have characterized the genetic diversity of the PKLR gene, including haplotype structure and presence of rare coding variants in two populations from malaria endemic areas of Thailand and Senegal. We investigated the effect of PKLR genotypes on rich longitudinal datasets including haematological and malaria-associated phenotypes. A coding and possibly damaging variant (R41Q) was identified in the Thai population with a minor allele frequency of ~4.7%. Arginine 41 (R41) is highly conserved in the pyruvate kinase family and its substitution to Glutamine (R41Q) affects protein stability. Heterozygosity for R41Q is shown to be associated with a significant reduction in the number of attacks with Plasmodium falciparum, while correlating with an increased number of Plasmodium vivax infections. These results strongly suggest that PKLR protein variants may affect the frequency, and the intensity of malaria episodes induced by different Plasmodium parasites in humans living in areas of endemic malaria.     

Selection of the conodont Idiognathodus simulator (Ellison) as the event marker for the base of the global Gzhelian Stage (Upper Pennsylvanian, Carboniferous)

Studies carried out for more than 10 years by the Task Group to establish GSSPs at the base of the Moscovian–Kasimovian and Kasimovian–Gzhelian boundaries have resulted in the proposal that the level at which the conodont species Idiognathodus simulator (Ellison, 1941) first appears be selected to mark the base of the Gzhelian Stage. This expands this eastern European chronostratigraphic unit to a global scale.I. simulator (sensu Barrick et al., 2008) has been identified so far in Midcontinent and eastern North America, the Moscow and Donets basins and southern Urals of eastern Europe, and in south-central China. Correlation of this level based on this species and other conodont species can be reinforced in some areas by ammonoid and fusulinid data.     

Effects of food supplementation on a tropical bird

Tropical birds typically exhibit a ‘slow pace of life’ relative to higher latitude species. This is often manifested as slow development, low fecundity, and high survival. Following from this, it is predicted that tropical birds may be more likely to trade current reproductive effort to favor self-maintenance, thus supporting survival and future reproduction. To test this idea, we conducted two food supplementation experiments on tropical rufous-collared sparrows (Zonotrichia capensis) in the eastern Andes of Ecuador. In the first experiment, we food-supplemented pairs during the non-breeding life-history stage, and in the second experiment, we food-supplemented pairs that were provisioning fledglings. In both experiments, a larger proportion of food-supplemented birds exhibited pre-basic molt (replacement of feathers) than in a control group. To our knowledge, this is the first study to experimentally demonstrate that a food-supplemented bird invests extra resources into molt, a form of self-maintenance, and contrasts with the majority of food supplementation studies in high latitude birds that show they typically advance the initiation of, or extend the period of, reproduction. Our results are consistent with the syndrome of the slow pace of life in the tropics and support the concept of fundamental differences between temperate-zone and tropical birds.     

Reproducibility and Consistency of Proteomic Experiments on Natural Populations of a Non-Model Aquatic Insect

Population proteomics has a great potential to address evolutionary and ecological questions, but its use in wild populations of non-model organisms is hampered by uncontrolled sources of variation. Here we compare the response to temperature extremes of two geographically distant populations of a diving beetle species (Agabus ramblae) using 2-D DIGE. After one week of acclimation in the laboratory under standard conditions, a third of the specimens of each population were placed at either 4 or 27°C for 12 h, with another third left as a control. We then compared the protein expression level of three replicated samples of 2–3 specimens for each treatment. Within each population, variation between replicated samples of the same treatment was always lower than variation between treatments, except for some control samples that retained a wider range of expression levels. The two populations had a similar response, without significant differences in the number of protein spots over- or under-expressed in the pairwise comparisons between treatments. We identified exemplary proteins among those differently expressed between treatments, which proved to be proteins known to be related to thermal response or stress. Overall, our results indicate that specimens collected in the wild are suitable for proteomic analyses, as the additional sources of variation were not enough to mask the consistency and reproducibility of the response to the temperature treatments.