Somatic mutations in mitochondria: the chicken or the egg?

Somatic mutations of mitochondrial DNA have been detected in various pathologies such as cancer, neurodegenerative diseases, cardiac disorders and aging in general. Now it has been found that patients with rheumatoid arthritis also have a higher incidence of mitochondrial mutations in synoviocytes and synovial tissue compared with patients with osteoarthritis. Furthermore, it has been shown that these mutations possibly result in changed peptides that are presented by major histocompatibility complex II and thus might be recognized as non-self by the immune system. Further studies will show whether these mutations are actually able to trigger autoimmune inflammation in rheumatoid arthritis or whether they must be considered epiphenomena of cellular damage in chronic inflammation.     

Mating for convenience or genetic diversity? Mating patterns in the polygynous ant Plagiolepis pygmaea

Several genetic and nongenetic benefits have been proposed toexplain multiple mating (polyandry) in animals, to compensatefor costs associated with obtaining additional mates. The mostprominent hypotheses stress the benefits of increased geneticdiversity. In social insects, queens of most species mate onlyonce or have effective mating frequencies close to one. Yet,in a few species of ants, bees, and wasps, polyandry is therule. In these species, colonies are usually headed by a singlequeen, whereas multiple queening adds diversity in several ofthe remaining species, especially in ants. Here we investigatedmating frequency, inbreeding and relatedness between the queensand their mates in the polygynous ant Plagiolepis pygmaea, andthe effect of polyandry on the genetic diversity as a functionof the effective population size of individual colonies. Ourresults show that polyandry occurs frequently in the species.However, queens are frequently inseminated by close relatives,and additional sires add little genetic diversity among offspringof individual queens. In addition, the increase in diversityat the colony level is only marginal. Hence, contrary to establishednotions, polyandry in P. pygmaea seems not to be driven by substantialbenefits of genetic diversity. Nonetheless, very small or asyet unidentified genetic benefits to one party (males, workers,queens) in conjunction with low costs of mating may favor polyandry.Alternatively, nongenetic factors, such as convenience polyandry,may be more important than genetic factors in promoting polyandryin P. pygmaea.     

Exosomes and retroviruses: the chicken or the egg?

Retroviruses appropriate pre‐existing cellular machineries to propagate. In the last decade, impressive similarities have been observed in the generation and dissemination in the host cells of retroviruses and small cellular vesicles known as exosomes. These cellular vesicles are thought to facilitate intercellular communication processes and mediate immune functions. However, their link to the retroviral life cycle has given rise to distinct hypotheses and puzzling dilemmas. Are exosomes the antecessors of retroviruses or do retroviruses merely exploit the same cellular machinery designated for exosome biosynthesis? Here, we address these fascinating evolutionary questions by reviewing recent discoveries and analysing the controversies surrounding them.     

Kasha or state selective behavior in the photochemistry of ortho-nitrobenzaldehyde?

The photochemistry of ortho-nitrobenzaldehyde dissolved in tetrahydrofuran was studied by means of femtosecond UV/Vis and IR spectroscopy. Comparison was made of the spectral and temporal signatures for ~400 nm and ~260 nm excitation. The 400 nm excitation promotes NBA to its lowest excited singlet state of nπ* character whereas for 260 nm an upper excited state of ππ* character is addressed. On the picosecond time scale, the molecule undergoes hydrogen transfer, yielding a ketene intermediate, internal conversion recovering the starting material, and intersystem crossing. Time constants and yields of these processes are virtually not affected by the excitation wavelength. For 400 nm excitation a ~100 fs decay component seen in the 260 nm experiment is absent, indicating that this component is due to a ππ* → nπ* internal conversion. In contrast to its formation, the decay of the ketene intermediate is influenced by the excitation wavelength. This can be attributed to different amounts of vibrational excitation.     

Mammalian development: Axes in the egg?

An enduring but erroneous belief is that the post-fertilisation period is irrelevant for axis development in mammals. Two recent studies further undermine this belief. Is information for axial developmental encoded in the egg cortex?     

Modeling the cuckoo’s brood parasitic behavior in the presence of egg polymorphism

The common cuckoo Cuculus canorus is a brood parasite that utilizes many host species. These have evolved defense against parasitism to reject cuckoo eggs that look unlike their own and some cuckoos have evolved egg mimicry to counter this defense. Egg phenotype indeed plays a key role for both the cuckoo and its hosts to successfully reproduce. It has been argued that cuckoos should parasitize host nests where egg phenotype matches because this makes parasitism more successful. Details of the cuckoo’s parasitic behavior, however, largely remains unknown if they really parasitize hosts depending on “egg matching”. In this paper, we model a time sequence of parasitic events in which a cuckoo finds host nests and decides to parasitize them or not in the presence of egg polymorphism. We evaluate which strategy is optimal: (1) opportunistic parasitism where cuckoos parasitize hosts irrespective of the phenotype, or (2) non-opportunistic parasitism where cuckoos parasitize hosts where egg phenotype matches. The analysis showed that either of the two strategies can be optimal. Factors not considered in the model, e.g., ecological and evolutionary changes both in the cuckoo and the host side, are discussed to explain apparent contrasts observed in some cuckoo–host interactions.     

Panic attacks and supraventricular tachycardias: the chicken or the egg?

Panic attacks occur in about 2 % of the population. Symptoms include a racing or pounding heart beat, chest pain, dizziness, light-headedness, nausea, difficulty in breathing, tingling or numbness in the hands, flushes or chills, dreamlike sensations or perceptual distortions. The symptoms of paroxysmal supraventricular tachycardia (PSVT) may be similar. A PSVT is often difficult to document on the ECG since it has often ceased before the patient comes to medical attention. Besides, a tachycardia may still be present and even be documented but interpreted as a phenomenon secondary to the panic attack. In addition, ECG abnormalities between episodes can often not be identified. The evidence that in some patients paroxysmal SVT is the cause, but not the consequence of a panic attack, is based on observations that catheter ablation was able to cure patients presenting with panic disorders. To better establish the prevalence of SVT as the underlying mechanism of a panic attack, there is a need for prospective studies and/or registries. Whereas gastric ulcer has in some patients changed from a psychosomatic disorder to an infectious disease, we may hypothesise that a certain proportion of panic disorders may mutate into an underlying arrhythmia rather than a primary psychiatric disorder.     

Is the black robin in genetic peril?

In 1980 the entire black robin species Petroica traversi comprised only five birds, and the current population of ≊ 200 individuals is known to be derived from a single breeding pair. We show here that levels of minisatellite DNA variation in the black robin are among the lowest reported for any avian species in the wild. Surprisingly, similarly bottlenecked control populations of a closely related species ( P. australis australis ) exhibit significantly higher levels of genetic variation. This suggests that the black robin's persistence in a single small population for the last 100 years, rather than the recent bottleneck itself, accounts for the low genetic variation observed. Despite apparent genetic impoverishment, survival and reproductive performance indicate that the black robin is viable under existing conditions. This example illustrates that significant levels of genetic variation are not a necessary prerequisite for endangered species' survival.     

Tau phosphorylation, tangles, and neurodegeneration: the chicken or the egg?

Pathological aggregation of the microtubule-associated protein tau is a common feature of many neurodegenerative diseases. Although tau aggregation is associated with abnormal tau phosphorylation, the role of phosphorylation in the initiation of neurodegeneration has been unclear. Now, several animal models and data from human patients provide converging evidence that aberrant tau phosphorylation can cause a neurodegenerative phenotype similar to that seen in human neurodegenerative diseases.     

The chicken or the egg? Plastome evolution and an independent loss of the inverted repeat in papilionoid legumes

The plastid genome (plastome), while surprisingly constant in gene order and content across most photosynthetic angiosperms, exhibits variability in several unrelated lineages. During the diversification history of the legume family Fabaceae, plastomes have undergone many rearrangements, including inversions, expansion, contraction and loss of the typical inverted repeat (IR), gene loss and repeat accumulation in both shared and independent events. While legume plastomes have been the subject of study for some time, most work has focused on agricultural species in the IR-lacking clade (IRLC) and the plant model Medicago truncatula. The subfamily Papilionoideae, which contains virtually all of the agricultural legume species, also comprises most of the plastome variation detected thus far in the family. In this study three non-papilioniods were included among 34 newly sequenced legume plastomes, along with 33 publicly available sequences, to assess plastome structural evolution in the subfamily. In an effort to examine plastome variation across the subfamily, approximately 20% of the sampling represents the IRLC with the remainder selected to represent the early-branching papilionoid clades. A number of IR-related and repeat-mediated changes were identified and examined in a phylogenetic context. Recombination between direct repeats associated with ycf2 resulted in intraindividual plastome heteroplasmy. Although loss of the IR has not been reported in legumes outside of the IRLC, one genistoid taxon was found to completely lack the typical plastome IR. The role of the IR and non-IR repeats in the progression of plastome change is discussed.     

Sex differences in scent‐marking in sifaka: Mating conflict or male services?

Male and female interests can either be in conflict or serve as a basis for exchange. Communication is thus an important aspect of intersexual relationships. Verreaux's sifaka (Propithecus verreauxi verreauxi), like many prosimians, uses chemical signals as one form of communication. The goals of this study were to determine 1) if males and females exhibit sex differences in their scent-marking behavior, and 2) if scent-marking is an example of mating conflict or cooperation. All occurrences of scent-marks, scent-mark context, and scent-mark style were collected on 23 sifaka in the Kirindy Forest of western Madagascar for 7 months (September 2001-March 2002). Scent-mark rates were collected using continuous focal animal sampling from November 2000-March 2002. Home-range data were collected using monthly censuses and instantaneous focal sampling throughout those 17 months. The pressures of behavioral ecology seem to have shaped scent-marking in sifaka: the sexes exhibited significantly different scent-marking behavior. Results from this study are consistent with the hypotheses that 1) females scent-mark to advertise their presence and mark their resources, 2) clean-chested males use scent-marks as between-group communication to advertise their presence, and 3) stained-chested males use scent-marks as a form of olfactory mate-guarding. Scent-marking does not appear to be a "service" that males provide to females, because overmarking limits female communication rather than adding to the overall number of scent-marks. Scent-marking behavior is a crucial aspect of the mating conflict and for understanding intersexual relationships in sifaka.     

Mating in the rain? Climatic variance for polyandry in the honeybee (Apis mellifera jemenitica)

We tested the impact of colony density and climatic conditions on the level of queen polyandry in different wild populations of the honeybee (Apis mellifera jemenitica). We identified the mating frequency of queens by genotyping worker offspring (n = 672) of 28 wild colonies with microsatellite DNA markers. The populations sampled in different climatic regions in Sudan showed a high variance for the queen mating frequency ranging from 9 to 23 estimated matings with an average of 14.00 ± 3.94 (13.16 ± 4.87 effective matings). The degree of polyandry was highly significantly correlated with the rainfall in the various regions. In general, more rainfall resulted in lower mating frequencies. Polyandry did not correlate with colony density or with genetic diversity of the local sample populations. This suggests that variation in polyandry in wild honeybee populations of Sudan is primarily driven by climatic differences among ecosystem variation rather than by the absolute or effective local honeybee population size.     

Nest desertion by a cowbird host: an antiparasite behavior or a response to egg loss?

Natural selection can favor songbirds that desert nests containingeggs of the parasitic brown-headed cowbird (Molothrus ater).However, the high variability in desertion of parasitized nestswithin species is perplexing in light of the typically highcosts of parasitism. Because nest desertion can also be a responseto partial clutch predation, we first asked if Bell's vireos(Vireo bellii) deserted nests in response to the presence ofcowbird eggs (antiparasite response hypothesis) or to egg removalby predators and female cowbirds (egg predation hypothesis).Second, we asked whether variation in nest desertion was dueto intrinsic differences among individuals or to variation innest contents. We monitored a large number of nests (n = 494)and performed a clutch manipulation experiment to test thesehypotheses. The number of vireo eggs that remained in a nestwas a strong predictor of desertion both within and among pairs.Neither the presence of a single cowbird egg, which leads tonest failure for this host, nor the number of cowbird eggs receivedin a vireo nest influenced nest desertion. Furthermore, vireosdid not desert experimental nests when we immediately exchangedcowbird eggs for vireo eggs but deserted if we removed vireoeggs and replaced them with cowbird eggs the following morning.Desertion of parasitized nests by Bell's vireos can be almostentirely explained as a response to partial or complete clutchloss and does not appear to have been altered by selection frombrood parasitism.     

Mating behavior as an indicator of quality of Drosophila subobscura males?

According to current theoretical predictions, any deleterious mutations that reduce nonsexual fitness may have a negative influence on mating success. This means that sexual selection may remove deleterious mutations from the populations. Males of good genetic quality should be more successful in mating, compared to the males of lower genetic quality. As mating success is a condition dependent trait, large fractions of the genome may be a target of sexual selection and many behavioral traits are likely to be condition dependent. We manipulated the genetic quality of Drosophila subobscura males by inducing mutations with ionizing radiation and observed the effects of the obtained heterozygous mutations on male mating behavior: courtship occurrence, courtship latency, mating occurrence, latency to mating and duration of mating. We found possible effects of mutations. Females mated more frequently with male progeny of nonirradiated males and that these males courted females faster compared to the male progeny of irradiated males. Our findings indicate a possible important role of sexual selection in purging deleterious mutations.