Molecular distinction between true centric fission and pericentric duplication-fission

Centromere (centric) fission, also known as transverse or lateral centric misdivision, has been defined as the splitting of one functional centromere of a metacentric or submetacentric chromosome to produce two derivative centric chromosomes. It has been observed in a range of organisms and has been ascribed an important role in karyotype evolution; however, the underlying mechanisms remain unknown. We have investigated four cases of apparent centric fission in humans. Two cases show a missing chromosome 22 or 18 that is replaced by two centric ring products, a third case shows two chromosome-10-derived telocentric chromosomes, whereas a fourth case involves the formation of two chromosome-18-derived isochromosomes. In all four cases, results of gross cytogenetic and fluorescence in situ hybridisation analyses were consistent with a simple centric fission event. However, detailed molecular analyses provided evidence in support of centromere duplication as a predisposing mechanism for the observed chromosomal breakage in two of the cases. Results for the third case are consistent with direct centric fission not involving centromere pre-duplication as the likely mechanism. Insufficient material has precluded the further study of the fourth case. The data provide the first molecular evidence for centromere pre-duplication as a possible mechanism to explain the classically assumed simple centric fission events in clinical cytogenetics, karyotype evolution and speciation.     

When do trade‐offs occur? The roles of energy constraints and trait flexibility in bushcricket populations

In many animal species, the expression of sexually selected traits is negatively correlated with traits associated with survival such as immune function, a relationship termed a ‘trade‐off’. But an alternative in which sexually selected traits are positively correlated with survival traits is also widespread. We propose that the nature of intertrait relationships is largely determined by overall energy expenditure, energy availability and trait flexibility, with trade‐offs expected when individuals are subject to energy constraints. We tested this hypothesis in Ephippiger diurnus, a European bushcricket in which males are distinguished by two prominent sexually selected traits, acoustic calls and a large spermatophore transferred to the female at mating, and where immune function may be critical in survival. Ephippiger diurnus are distributed as small, isolated populations that are differentiated genetically and behaviourally. We analysed songs, spermatophores and the immune function in male individuals from eight populations spanning a range of song types. As predicted, we only found trade‐offs in those populations that expended more energy on song and were less flexible in their ability to adjust that expenditure. Ultimately, energy constraints and resulting trade‐offs may limit the evolution of song exaggeration in E. diurnus populations broadcasting long calls comprised of multiple ‘syllables’.     

Replication Stress Shapes a Protective Chromatin Environment across Fragile Genomic Regions

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The indirect effects of multiplicity of infection on baculovirus expressed proteins in insect cells: secreted and non-secreted products

The baculovirus expression vector system was employed to produce human apolipoprotein E and β-galactosidase in order to study the effect of multiplicity of infection on secreted and non-secreted recombinant protein production. Prior knowledge of the influence of other cell culture and infection parameters, such as the cell density at time of infection and the time of harvest, allowed determination of the direct and indirect influences of multiplicity of infection on recombinant protein synthesis and degradation in insect cells. Under non-limited, controlled conditions, the direct effect of multiplicity of infection (10⁻¹−10 pfu/cell) on specific recombinant product yields of non-secreted β-galactosidase was found to be insignificant. Instead, the observed increased in accumulated product was directly correlated to the total number of infected cells during the production period and therefore ultimately dependent on an adequate supply of nutrients. Only the timing of recombinant virus and protein production was influenced by, and dependent on the multiplicity of infection. Evidence is presented in this study that indicates the extremely limited predictability of post-infection cell growth at very low multiplicities of infection of less than 0.1 pfu/cell. Due to the inaccuracy of the current virus quantification techniques, combined with the sensitivity of post-infection cell growth at low MOI, the possibility of excessive post-infection cell growth and subsequent nutrient limitation was found to be significantly increased. Finally, as an example, the degree of product stability and cellular and viral protein contamination at low multiplicity of infection is investigated for a secreted recombinant form of human apolipoprotein E. Comparison of human apolipoprotein E production and secretion at multiplicities of infection of 10⁻⁴−10 pfu/cell revealed increased product degradation and contamination with intracellular proteins at low multiplicities of infection. This revised version was published online in July 2006 with corrections to the Cover Date.     

Precedence effects and the evolution of chorusing

The structured choruses produced by rhythmically signalling males in many species of acoustic animals have long-captured the imagination of evolutionary biologists. Though various hypotheses have been forwarded to explain the adaptive significance of such chorusing, none have withstood empirical scrutiny. We suggest instead that alternating and synchronous choruses represent collective epiphenomena resulting from individual males competing to jam each other''s signals. These competitions originate in psychoacoustic precedence effects wherein females only orient toward the first call of a sequence, thus selectively favouring males who produce leading calls. Given this perceptual bias, our modelling confirms that a resetting of signal rhythm by neighbours'' signals, which generates either alternation or synchrony, is evolutionarily stable provided that resetting includes a relativity adjustment for the velocity of signal transmission and selective attention toward only a subset of signalling neighbours. Signalling strategies in chorusing insects and anurans are consistent with these predicted features.     

Assortative mating by size: A meta-analysis of mating patterns in water striders

Summary Assortative mating by size is a common mating pattern that can be generated by several different behavioural mechanisms, with different evolutionary implications. Assortative mating is typically associated with sexual selection and has been regarded as an attribute of populations, species, mating systems or even higher order taxa. In most animal groups, however, appropriate analyses of assortative mating at these different levels are lacking and the causes and forms of assortative mating are poorly understood. Here, we analyse 45 different population level estimates of assortative mating and non-random mating by size in seven confamiliar species of water striders that share a common mating system. A hierarchical comparative analysis shows that virtually all the variance within the clade occurs among samples within species. We then employ meta-analysis to estimate the overall strength of assortative mating, to determine the form of assortative mating and to further assess potential differences among species as well as the probable causes of assortative mating in this group of insects. We found overall weak but highly significant positive assortative mating. We show that analyses of the degree of heteroscedasticity in plots of male versus female size are critical, since the evolutionary implications of true and apparent assortative mating differ widely and conclude that the positive assortative mating observed in water striders was of the true rather than the apparent form. Further, within samples, mating individuals were significantly larger than non-mating individuals in both males and females. All of these non-random mating patterns were consistent among species and we conclude that weak positive assortative mating by size is a general characteristic of those water strider species that share this mating system. We use our results to illustrate the importance of distinguishing between different forms of assortative mating, to discriminate between various behavioural causes of assortative mating and to assess potential sources of interpopulational variance in estimates of assortative mating. Finally, we discuss the value of using meta-analytic techniques for detecting overall patterns in multiple studies of non-random mating.     

The Sexual Behaviour of the Great Crested Newt,Triturus cristatus (Amphibia: Salamandridae)

The sexual behaviour of Triturus cristatus is described. The first stage of sexual behaviour consists of an orientation phase in which the male approaches the female, sniffs her and moves in front of and perpendicular to her. The second stage is a prolonged period of static display with two different tail movements, called Fan and Lash, in 13.8 ± 1.3 bouts (x? ± SE) with intervals of 10.5 ± 0.3 s between bouts. Each bout contains 6.7 ± 0.3 regular Fan beats at a frequency of 0.5–0.8 Hz. This Fanning provides olfactory and mechanical stimulation to the female. 15% of bouts also contain a violent Lash, in which the male rapidly slaps the female's flank. Some Lashes are used to stop the female when she tries to move away. In the third stage of the sexual sequence, the male turns away, Creeps for 6.7 ± 0.3 s (x? ± SE) and then Quivers his tail. A receptive female follows and touches his tail, and the male deposits a spermatophore and then turns to one side with his tail folded along his flank in a position called Brake. The female now approaches again and the male steps away sideways in a movement called Rebrake. After several Rebrakes the male stops, the female touches his tail and the spermatophore may now be picked up in her cloaca. This sequence can be repeated several times during one encounter. This behaviour is discussed in relation to previous studies of courtship in this genus.     

Genetic Mapping of the BRCA1 Region on Chromosome 17q21

Chromosome 17q21 harbors a gene (BRCA1) associated with a hereditary form of breast cancer. As a step toward identification of this gene itself we developed a number of simple-sequence-repeat (SSR) markers for chromosome 17 and constructed a high-resolution genetic map of a 40-cM region around 17q21. As part of this effort we captured genotypes from five of the markers by using an ABI sequencing instrument and stored them in a locally developed database, as a step toward automated genotyping. In addition, YACs that physically link some of the SSR markers were identified. The results provided by this study should facilitate physical mapping of the BRCA1 region and isolation of the BRCA1 gene.