Negative effects of elevated testosterone on female fecundity in zebra finches

Although factors influencing androgen deposition in the avian egg and its effects on nestling fitness are recently receiving considerable attention, little is known about the potential costs of high testosterone levels in the females. Our study aimed at determining the effect of injections of testosterone (T) in female zebra finches (Taeniopygia guttata), on clutch size, egg mass, yolk mass, and yolk androgen content. Females were given a single bolus injection of T in a range of doses after laying the first egg. Results show that administration of T negatively affected clutch size; the strength of this effect increased with increasing doses of T. Females injected with the highest testosterone dose showed suppressed oviposition of the third and the fourth eggs. Interestingly, testosterone administration made females produce eggs with relatively large yolks, suggesting that T may mediate the trade-off between number and size of eggs. Testosterone injection resulted in elevated levels of androgen in the eggs, in contrast to control clutches, which showed a decreasing pattern of androgen concentration along the laying sequence. We conclude that high androgen investment in eggs may be limited by physiological requirements of the ovulatory process.     

Genomic inference accurately predicts the timing and severity of a recent bottleneck in a nonmodel insect population

The analysis of molecular data from natural populations has allowed researchers to answer diverse ecological questions that were previously intractable. In particular, ecologists are often interested in the demographic history of populations, information that is rarely available from historical records. Methods have been developed to infer demographic parameters from genomic data, but it is not well understood how inferred parameters compare to true population history or depend on aspects of experimental design. Here, we present and evaluate a method of SNP discovery using RNA sequencing and demographic inference using the program δaδi, which uses a diffusion approximation to the allele frequency spectrum to fit demographic models. We test these methods in a population of the checkerspot butterfly Euphydryas gillettii. This population was intentionally introduced to Gothic, Colorado in 1977 and has as experienced extreme fluctuations including bottlenecks of fewer than 25 adults, as documented by nearly annual field surveys. Using RNA sequencing of eight individuals from Colorado and eight individuals from a native population in Wyoming, we generate the first genomic resources for this system. While demographic inference is commonly used to examine ancient demography, our study demonstrates that our inexpensive, all‐in‐one approach to marker discovery and genotyping provides sufficient data to accurately infer the timing of a recent bottleneck. This demographic scenario is relevant for many species of conservation concern, few of which have sequenced genomes. Our results are remarkably insensitive to sample size or number of genomic markers, which has important implications for applying this method to other nonmodel systems.     

Assessing the degree of stratification between closely related Holstein-Friesian populations

Genomic information is an important part of the routine evaluation of dairy cattle and provides the wide availability of animals genotyped using single nucleotide polymorphism (SNP) microarrays. We analyzed 2243 Polish and 2294 German Holstein-Friesian bulls genotyped using the Illumina BovineSNP50 BeadChip. For each bull, estimated breeding values (EBVs) calculated from national routine genetic evaluation were available for production traits and for somatic cell score (SCS). Separately for each population, we estimated SNP haplotypes, pairwise linkage disequilibrium (LD), and SNP effects. The SNP genetic covariance between both populations was estimated using a bivariate mixed model. The average LD was lower in the Polish than in the German population and, with increasing genomic distance, LD decays 1.7 times more rapidly in German than in Polish cattle. The comparison of SNP allele frequencies for base populations estimated separately using Polish and German data revealed a very good agreement. The comparison of genetic effects corresponding to various window lengths defined in bp emerged a systematic pattern: regardless of the length of the compared region, few significant differences were found for production traits, while many were observed for SCS. For each trait, the German population had much higher SNP variances than the Polish population and the genetic covariance estimates were all positive. Depending on traits’ inheritance mode, the additive genetic variation can be stored in many genes following the infinitesimal model (like for SCS) or distributed between genes with high effects and the polygenic “background” (like for production traits). Accounting for those differences has implications on the prospective international genomic evaluation.     

Glycoprotein hypersecretion alters the cell wall in Trichoderma reesei strains expressing the Saccharomyces cerevisiae dolichylphosphate mannose synthase gene

Expression of the Saccharomyces cerevisiae DPM1 gene (coding for dolichylphosphate mannose synthase) in Trichoderma reesei (Hypocrea jecorina) increases the intensity of protein glycosylation and secretion and causes ultrastructural changes in the fungal cell wall. In the present work, we undertook further biochemical and morphological characterization of the DPM1-expressing T. reesei strains. We established that the carbohydrate composition of the fungal cell wall was altered with an increased amount of N-acetylglucosamine, suggesting an increase in chitin content. Calcofluor white staining followed by fluorescence microscopy indicated changes in chitin distribution. Moreover, we also observed a decreased concentration of mannose and alkali-soluble beta-(1,6) glucan. A comparison of protein secretion from protoplasts with that from mycelia showed that the cell wall created a barrier for secretion in the DPM1 transformants. We also discuss the relationships between the observed changes in the cell wall, increased protein glycosylation, and the greater secretory capacity of T. reesei strains expressing the yeast DPM1 gene.     

Analysis of mouse Rad54 expression and its implications for homologous recombination

Homologous recombination is one of the major pathways for repair of DNA double-strand breaks (DSBs). Important proteins in this pathway are Rad51 and Rad54. Rad51 forms a nucleoprotein filament on single-stranded DNA (ssDNA) that mediates pairing with and strand invasion of homologous duplex DNA with the assist of Rad54. We estimated that the nucleus of a mouse embryonic stem (ES) cells contains on average 4.7x10(5) Rad51 and 2.4x10(5) Rad54 molecules. Furthermore, we showed that the amount of Rad54 was subject to cell cycle regulation. We discuss our results with respect to two models that describe how Rad54 stimulates Rad51-mediated DNA strand invasion. The models differ in whether Rad54 functions locally or globally. In the first model, Rad54 acts in cis relative to the site of strand invasion. Rad54 coats the Rad51 nucleoprotein filament in stoichiometric amounts and binds to the target duplex DNA at the site that is homologous to the ssDNA in the Rad51 nucleoprotein filament. Subsequently, it promotes duplex DNA unwinding. In the second model, Rad54 acts in trans relative to the site of strand invasion. Rad54 binds duplex DNA distant from the site that will be unwound. Translocation of Rad54 along the duplex DNA increases superhelical stress thereby promoting duplex DNA unwinding.     

Kin recognition and adjustment of reproductive effort in zebra finches

The differential allocation theory predicts that females should invest more in offspring produced with attractive partners, and a number of studies support this prediction in birds. Females have been shown to increase reproductive investment when mated to males showing elaborated sexual traits. However, mate attractiveness might also depend on the interaction between male and female genotypes. Accordingly, females should invest more in offspring sired by individuals that are genetically dissimilar or carry superior alleles. Here, we show in zebra finches (Taeniopygia guttata) that pairs of unfamiliar genetic brothers and sisters are less likely to reproduce in comparison with randomly mated pairs. Among the brother–sister pairs, those that attempted to breed laid smaller clutches and of lower total clutch mass. Our results provide the first experimental evidence that females adjust their reproductive effort in response to the genetic similarity of their partners. Importantly, these results imply a female ability to assess relatedness of a social mate without prior association.     

Effects of the endosomal lipid bis(monoacylglycero)phosphate on the thermotropic properties of DPPC: A 2H NMR and spin label EPR study

Bis(monoacylglycero)phosphate (BMP) is an endosomal lipid with a unique structure that is implicated in the formation of intraendosomal vesicular bodies. Here we have characterized the effects of dioleoyl-BMP (BMP_18:1) at concentrations of 5, 10, 15 and 20 mol% on the thermotropic behavior of dipalmitoyl phosphatidylcholine (DPPC) vesicles, and compared them to those of equimolar concentrations of dioleoyl phosphatidylglycerol (DOPG), a structural isoform of BMP_18:1. Because BMP is found in the acidic environments of the late endosome and intralysosomal vesicles, samples were prepared at pH 4.2 to mimic the pH of the lysosome. Both ²H NMR of perdeuterated DPPC and spin-labeled EPR with 16-doxyl phosphatidylcholine were utilized in these investigations. NMR and EPR results show that BMP_18:1 induces a lowering in the main phase transition temperature of DPPC similar to that of DOPG. The EPR studies reveal that BMP_18:1 induced more disorder in the L_β phase when compared to equimolar concentrations of DOPG. Analysis from dePaked ²H NMR spectra in the L_α phase reveals that BMP_18:1 induces less disorder than equal concentrations of DOPG. Additionally, the results demonstrate that BMP mixes with other phospholipids as a phospholipid and not as a detergent molecule as once speculated.     

Reproductive Parameters and Maternal Investment in Mandrills (Mandrillus sphinx)

We report on 14 years of reproductive data for semifree-ranging mandrills (Mandrillus sphinx) in Gabon, and we explore relationships between female rank, age and parity, and reproductive strategies. Most births (61% of 132) occurred during the wet season in Gabon, between January and March. Female rank and parity were unrelated to the timing of parturition. Gestation lengths average 175 days (SE = ±1 day; N = 61) and were similar irrespective of female rank, parity, or sex of offspring. Birth sex ratio did not differ significantly from unity (52% male), and was unrelated to maternal rank or parity. Stillbirths and neonatal mortality tended to be more common among lower-ranking females than among either mid-ranking or dominant females. Median age at first birth is 4.71 years, at a median body mass of 7.6 kg, ca 5 years before females attain their adult body mass (median 12 kg). Age at first reproduction is significantly correlated with dominance rank, with dominant females giving birth on average 1.3 years earlier than lower-ranking females do. Interbirth intervals (IBI) average 405 days (range 184–1159 days, N = 103), and are independent of the sex of the offspring. Infant death within 6 months shortened IBI to 305 days. Increasing age and parity are also associated with short IBI, as is higher rank. Maternal rank and parity appear to influence reproductive success in female mandrills, but there is no apparent differential maternal investment by sex.