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While numerous studies have demonstrated that mitochondrial genetic variation can shape organismal phenotype, the level of contribution the mitochondrial genotype makes to life‐history phenotype across the life course remains unknown. Furthermore, a clear technical bias has emerged in studies of mitochondrial effects on reproduction, with many studies conducted on males, but few on females. Here, we apply a classic prediction of the evolutionary theory of aging to the mitochondrial genome, predicting the declining force of natural selection with age will have facilitated the accumulation of mtDNA mutations that confer late‐life effects on female reproductive performance. This should lead to increased levels of mitochondrial genetic variation on reproduction at later‐life stages. We tested this hypothesis using thirteen strains of Drosophila melanogaster that each possessed a different mitochondrial haplotype in an otherwise standard nuclear genetic background. We measured fecundity and egg‐to‐adult viability of females over five different age classes ranging from early to late life and quantified the survival of females throughout this time period. We found no significant variation across mitochondrial haplotypes for the reproductive traits, and no mitochondrial effect on the slope of decline in these traits with increasing age. However, we observed that flies that died earlier in the experiment experienced steeper declines in the reproductive traits prior to death, and we also identified maternal and grandparental age effects on the measured traits. These results suggest the mitochondrial variation does not make a key contribution to shaping the reproductive performance of females. In this study, we tested whether age‐related declines in female fruit fly fecundity and egg‐to‐adult viability varied based on mitochondrial DNA genotype. Using 13 strains of fruit flies with different mitochondrial DNA genotypes expressed alongside a common nuclear genetic "background," we measured fecundity and egg‐to‐adult viability in females across five age classes. We found that mitochondrial genotype did not affect the rate of physiological decline with increasing age in female fruit flies. [ABSTRACT FROM AUTHOR]

An evolutionary theory of adaptive behavior dynamics was tested by studying the behavior of artificial organisms (AOs) animated by the theory, working on concurrent ratio schedules with unequal and equal ratios in the components. The evolutionary theory implements Darwinian rules of selection, reproduction, and mutation in the form of a genetic algorithm that causes a population of potential behaviors to evolve under the selection pressure of consequences from the environment. On concurrent ratio schedules with unequal ratios in the components, the AOs tended to respond exclusively on the component with the smaller ratio, provided that ratio was not too large and the difference between the ratios was not too small. On concurrent ratio schedules with equal ratios in the components, the AOs tended to respond exclusively on one component, provided the equal ratios were not too large. In addition, the AOs' preference on the latter schedules adjusted rapidly when the equal ratios were changed between conditions, but their steady‐state preference was a continuous function of the value of the equal ratios. Most of these outcomes are consistent with the results of experiments with live organisms, and consequently support the evolutionary theory. [ABSTRACT FROM AUTHOR]

Abstract: Maternal effects, where the performance of offspring is determined by the condition of their mother, are widespread and may in some cases be adaptive. The crustacean Daphnia magna shows strong maternal effects: offspring size at birth and other proxies for fitness are altered when their mothers are older or when mothers have experienced dietary restriction. The mechanisms for this transgenerational transmission of maternal experience are unknown, but could include changes in epigenetic patterning. MicroRNAs (miRNAs) are regulators of gene expression that have been shown to play roles in intergenerational information transfer, and here, we test whether miRNAs are involved in D. magna maternal effects. We found that miRNAs were differentially expressed in mothers of different ages or nutritional state. We then examined miRNA expression in their eggs, their adult daughters and great granddaughters, which did not experience any treatments. The maternal (treatment) generation exhibited differential expression of miRNAs, as did their eggs, but this was reduced in adult daughters and lost by great granddaughters. Thus, miRNAs are a component of maternal provisioning, but do not appear to be the cause of transgenerational responses under these experimental conditions. MicroRNAs may act in tandem with egg provisioning (e.g., with carbohydrates or fats), and possibly other small RNAs or epigenetic modifications. [ABSTRACT FROM AUTHOR]

The existing different modes of reproduction in monotremes, marsupials and placentals are the main source for our current understanding of the origin and evolution of the mammalian reproduction. The reproductive strategies and, in particular, the maturity states of the neonates differ remarkably between the three groups. Monotremes, for example, are the only extant mammals that lay eggs and incubate them for the last third of their embryonic development. In contrast, marsupials and placentals are viviparous and rely on intra-uterine development of the neonates via choriovitelline (mainly marsupials) and chorioallantoic (mainly placentals) placentae. The maturity of a newborn is closely linked to the parental care strategy once the neonate is born. The varying developmental degrees of neonates are the main focus of this study. Monotremes and marsupials produce highly altricial and nearly embryonic offspring. Placental mammals always give birth to more developed newborns with the widest range from altricial to precocial. The ability of a newborn to survive and grow in the environment it was born in depends highly on the degree of maturation of vital organs at the time of birth. Here, the anatomy of four neonates of the three major extant mammalian groups is compared. The basis for this study is histological and ultrastructural serial sections of a hatchling of Ornithorhynchus anatinus (Monotremata), and neonates of Monodelphis domestica (Marsupialia), Mesocricetus auratus (altricial Placentalia) and Macroscelides proboscideus (precocial Placentalia). Special attention was given to the developmental stages of the organs skin, lung, liver and kidney, which are considered crucial for the maintenance of vital functions. The state of the organs of newborn monotremes and marsupials are found to be able to support a minimum of vital functions outside the uterus. They are sufficient to survive, but without capacities for additional energetic challenges. The organs of the altricial placental neonate are further developed, able to support the maintenance of vital functions and short-term metabolic increase. The precocial placental newborn shows the most advanced state of organ development, to allow the maintenance of vital functions, stable thermoregulation and high energetic performance. The ancestral condition of a mammalian neonate is interpreted to be similar to the state of organ development found in the newborns of marsupials and monotremes. In comparison, the newborns of altricial and precocial placentals are derived from the ancestral state to a more mature developmental degree associated with advanced organ systems. [ABSTRACT FROM AUTHOR]

What makes a theory ‘anthropological’ beyond it being a theory that anthropologists use? Assuming a framework that understands anthropology in its broadest sense, this article invites us to remind ourselves what theories are actually supposed to do. Distinguishing theories in terms of the scale of presumption in their claims, it argues for a pyramid of nested levels of explanation. As we move from the base to the tip of the pyramid, so our explanations and interpretation of data must become increasingly simple to accommodate the forms of measurement that each level demands. Given this model, how can evolutionary theories based on individual behaviour geared to immediate survival and reproduction be reconciled with theories that best explain the uncertainties of ‘emergent systems’, or that consider how individual actions are in turn constrained by the systems of which they are part? It is concluded that anthropology has always acquired its vitality by being critically ‘conjunctural’, and must be ultimately and necessarily a strategic cross-disciplinary theoretical compromise. Résumé Qu’est-ce qui rend une théorie « anthropologique », en dehors du fait que les anthropologues l’utilisent ? En posant une acception aussi large que possible de l’anthropologie, l’article invite à se rappeler à quoi servent en réalité les théories. En distinguant les théories par le niveau de conjecture de leurs affirmations, l’auteur propose une pyramide de niveaux d’explication imbriqués. En progressant de la base au sommet de la pyramide, les attentes et l’interprétation des données doivent devenir de plus en plus simples, afin de prendre en compte les formes de mesure exigées à chaque niveau. Sur la base de ce modèle, comment les théories évolutionnistes, basées sur des comportements individuels visant la survie et la reproduction immédiates, peuvent-elles être conciliées avec celles qui expliquent, au mieux, les incertitudes des « systèmes émergents » ou qui examinent la façon dont les actions individuelles sont contraintes par les systèmes dans lesquels elles s’inscrivent ? L’auteur conclut que l’anthropologie a toujours acquis sa vitalité par une approche « conjoncturelle » critique et qu’elle doit être en fin de compte, par nécessité, un compromis théorique stratégique transdisciplinaire. [ABSTRACT FROM AUTHOR]

Many mammals have brains substantially larger than expected for their body size, but the reasons for this remain ambiguous. Enlarged brains are metabolically expensive and require elongated developmental periods, and so natural selection should have favoured their evolution only if they provide counterbalancing advantages. One possible advantage is facilitating the construction of behavioural responses to unusual, novel or complex socio-ecological challenges. This buffer effect should increase survival rates and favour a longer reproductive life, thereby compensating for the costs of delayed reproduction. Here, using a global database of 493 species, we provide evidence showing that mammals with enlarged brains (relative to their body size) live longer and have a longer reproductive lifespan. Our analysis supports and extends previous findings, accounting for the possible confounding effects of other life history traits, ecological and dietary factors, and phylogenetic autocorrelation. Thus, these findings provide support for the hypothesis that mammals counterbalance the costs of affording large brains with a longer reproductive life. [ABSTRACT FROM AUTHOR]

1. Sexual selection is a powerful evolutionary force that is hypothesised to play an important role in the evolution of lifespan. Here we test for the potential contribution of sexual selection to the rapid evolution of male lifespan in replicated laboratory populations of the seed beetle, Callosobruchus maculatus. 2. For 35 generations, newly hatched virgin male beetles from eight different populations were allowed to mate for 24 h and then discarded. Sexual selection was removed in half of these populations by enforcing random monogamy. 3. Classic theory predicts that because of sexual competition, males from sexually selected lines would have higher age-specific mortality rates and shorter lifespan than males from monogamous lines. 4. Alternatively, condition-dependent sexual selection may also favour genes that have positive pleiotropic effects on lifespan and ageing. 5. Males from all eight populations evolved shorter lifespans compared with the source population. However, there was no difference in lifespan between males from populations with or without sexual selection. Thus, sexual selection did not contribute to the evolution of male lifespan despite the fact that such evolution did occur in our study populations. [ABSTRACT FROM AUTHOR]

The origin and evolution of the perianth remains enigmatic. While it seems likely that an undifferentiated perianth consisting of tepals arose early in angiosperm evolution, it is unclear when and how differentiated periauths consisting of distinct organs, such as petals and sepals, arose. Phylogenetic reconstructions of ancestral perianth states across angiosperms have traditionally relied on morphological data from extant species, but these analyses often produce equivocal results. Here we describe the use of developmental genetic data as an additional strategy to infer the ancestral perianth character state for different angiosperm clades. By assessing functional data in combination-with expression data in a maximum likelihood framework, we provide a novel approach for investigating the evolutionary history of the perianth. Results of this analysis provide new insights into perianth evolution and provide a proof of concept for using this strategy to explore the incorporation of developmental genetic data in character state re-constructions. As the assumptions outlined here are tested and more genetic data are generated, we hope that ancestral stale rcconstructions based on multiple lines of evidence will converge. [ABSTRACT FROM AUTHOR]

Although oxidative stress is a central topic in biochemical and medical research, the number of reports on its relevance in life-history studies of non-human animals is still low. Information about oxidative stress in wild birds may help describe functional interactions among the components of life-history traits. Currently available evidence suggests that oxidative stress may impart an important physiological cost on longevity, reproduction, immune response or intense physical activity. Given the gaps in our present knowledge, it is still premature to attempt to draw definitive conclusions and basic questions (e.g. how is oxidative stress generated and how do organisms cope with it?) have yet to be fully explored under natural conditions. Therefore, caution is needed in developing hypotheses or drawing general conclusions until additional data become available to perform more rigorous comparative analyses. [ABSTRACT FROM AUTHOR]

The article examines the "mother" hypothesis that senescence of reproduction may explain adaptive human menopause. Fertility functions that maximize fitness are assembled into a model. The results are then given according to difference situations of increase age of maternal mortality risk and risk of stillbirth and birth defects. Finally, a population genetics framework is used to estimate selection on optimal fertility function.

The article discusses a paper by G. Hunt, which reveals that there is relatively small directional change during lineage evolution. In line with this, the authors demonstrate that significant evolutionary information about the processes involved in the generation of species, can be derived by examining the directional changes within lineages and among clades.

In the course of evolution, mechanisms have evolved to anticipate the timing of regularly occurring events. These mechanisms are encompassed in a circadian timing system that include a master clock localized to the suprachiasmatic nucleus of the hypothalamus and “slave” oscillators distributed throughout the body. This system serves multiple functions so as to ensure that various physiological processes occur at optimal and nonoverlapping times, to synchronize our activities to local environmental time, and to permit changes required to respond to new environmental circumstances. We suggest that a generalized concept of arousal (which includes alterations in responsiveness to homeostatic pressures, sensory stimuli and emotional reactivity, and to changes in motor activity) serves as a rubric in which to explore the multiple ways in which the circadian system modulates behavior. [ABSTRACT FROM AUTHOR]

Individuals who reproduce asexually have a two-fold advantage over their sexually-reproducing counterparts as they are able to reproduce twice as fast. Explaining why sexual reproduction is favoured over asexual reproduction therefore remains an important challenge in evolutionary biology. Various mechanisms involving resistance to parasites, adaptation to novel environments and helping to purge the genome of deleterious mutations have all been proposed as potential mechanisms which could promote the evolution of sex. A recent article has suggested that spiteful males may help to reduce the two-fold advantage of asexual females. Here I discuss this idea, and further ask whether punishment of asexual females by sexual females could be one way in which sexual reproduction could be maintained in groups of animals; in light of recent research on the repression of competition, it could be possible that asexual females which reproduce faster than their sexual counterparts will be punished for using group resources. It may therefore be possible that the behaviour of sexual individuals towards asexual females could have fitness consequences which could potentially reduce the two-fold advantage they gain from reproducing parthenogenetically. [ABSTRACT FROM AUTHOR]

1. In many reptile species, females oviposit communally (i.e. many clutches are laid within the same nest). This behaviour might result from constraint (scarcity of nest-sites offering suitable incubation conditions) or adaptation (direct fitness benefits accruing from the proximity of other eggs). 2. To test between these alternatives, we gathered field and laboratory data on montane scincid lizards Bassiana duperreyi from south-eastern Australia. Our data support the adaptationist hypothesis. 3. In the field, communal vs. solitary clutches were laid in similar sites, and the relative frequency of communal nesting was not predictable from nest-site availability. Thermal regimes for incubation did not differ between communal vs. solitary nests, nor between eggs at the core vs. periphery of a communal nest. In the laboratory, females selectively oviposited beside existing eggs rather than in otherwise identical potential nesting sites. 4. From cycling-temperature incubation in the laboratory, eggs incubated within a cluster of other eggs took up less water, but produced hatchlings that were larger and faster-running than were hatchlings from eggs incubated alone. 5. Hydric modifications of incubation conditions within a cluster of tightly packed eggs thus may provide a direct fitness benefit to communal oviposition. [ABSTRACT FROM AUTHOR]

The article reports on transposable elements and domesticated sequences. The transposable elements are recruited by their host during evolution. Domesticated sequences, formed from the encoding of transposase, integrase and invertase by transposable element genes, are essential for the protection against infection, vital for reproduction, permit chromosonal reproduction and control cell proliferation and death.

The advantage of sexual reproduction remains a puzzle for evolutionary biologists. Everything else being equal, asexual populations are expected to have twice the number of offspring produced by similar sexual populations. Yet, asexual species are uncommon among higher eukaryotes. In models assuming small populations, high mutation rates, or frequent environmental changes, sexual reproduction seems to have at least a two-fold advantage over asexuality. But the advantage of sex for large populations, low mutation rates, and rare or mild environmental changes remains a conundrum. Here we show that without recombination, rare advantageous mutations can result in increased accumulation of deleterious mutations (‘evolutionary traction’), which explains the long-term advantage of sex under a wide parameter range. [ABSTRACT FROM AUTHOR]

SUMMARY Natural populations of sexually reproducing Drosophila mercatorum are capable of a very low rate of parthenogenesis, but this mode of reproduction has apparently never characterized an entirely asexual population in this species. The high abortion rate observed in laboratory parthenogenetic lines suggests that developmental constraints may cause the failure of this trait to spread in nature. To investigate the basis of this developmental instability and how it may affect the evolution of parthenogenesis in natural populations, early embryonic development was compared between one sexual and four parthenogenetic laboratory strains of D. mercatorum . There is a large amount of variation within a given parthenogenetic strain, suggesting that parthenogenesis is associated with a general breakdown of developmental stability. There is relatively little variation among different parthenogenetic strains, suggesting that most abortions are due to a feature inherent to parthenogenetic reproduction rather than a feature of a particular genome. Likewise, there is little variation between parthenogenetic and sexual strains in the causes of abortions, suggesting that the developmental problems encountered by parthenogenetic lineages are not unique to parthenogens. Thus, the failure of parthenogenesis to spread within D. mercatorum can be attributed to no particular developmental constraint per se operating after the initiation of embryogenesis. However, the overall increase in all developmental problems that occurs with the transition from sexual to parthenogenetic development suggests that the high degree of developmental instability associated with parthenogenesis may be considered a developmental constraint in its own right. [ABSTRACT FROM AUTHOR]

SUMMARY Developmental instability is particularly pronounced in parthenogenetic strains of Drosophila mercatorum . All parthenogenetically produced eggs in a given strain have the same genotype, but even when reared in the same environment, only approximately 5% of the eggs initiating development ever reach adulthood. A sexual analogue of a parthenogenetic strain was created to investigate the basis of this developmental instability. The two strains have identical genotypes (except for the Y chromosome in males of the sexual strain) and differ only in mode of reproduction. The sexual strain had a much lower rate of developmental instability than the parthenogenetic strain, suggesting that the instability is caused by the mode of reproduction per se and is not due to homozygosity, disruption of coadapted gene complexes, or any other feature of the parthenogenetic genome. The increased rate of abortion with parthenogenetic reproduction is caused by a proportional increase in the normal panoply of errors that occur in sexual reproduction but at a much lower rate. Attempts to establish other sexual analogues of laboratory parthenogenetic strains revealed different male sterility factors within several parthenogenetic genomes that could potentially act to prevent hybridization with sexually reproducing ancestors during the incipient stages in the evolution of an entirely parthenogenetic lineage. [ABSTRACT FROM AUTHOR]

The parental investment in angiosperms comprises the endosperm, a nutrient reserve that is used during seed development. The endosperm contains genes from both parents. The most common endosperm form is the 3n Polygonum -type with more maternal genetic influence than paternal, i.e. with two maternal nuclei and one paternal nucleus. The evolutionary original state is thought to be a diploid endosperm with equal influence of the parents. We focus on the evolution of the triploid endosperm and show that a gene for triploid endosperm would have an initial advantage in a population of diploid endosperm type plants, and increase to fixation. We assume that endosperm amount is controlled by endosperm genes. Then a gene causing triploid endosperm will increase the influence of the mother plant on parental investment. The production of endosperm with two copies of the maternal genes will modify the inheritance of endosperm amount and cause an increased production of seeds. [ABSTRACT FROM AUTHOR]

Costs of reproduction are traditionally defined as reductions in thepotential for future fitness contributions, induced by current reproductive investments, i.e. postbreeding costs. However, preparation for breeding and parental care may expose parents to survival costs already before offspring independence. Such prebreeding survival costs have only rarely been considered in the context of life history evolution. Theoretical analyses show that pre and postbreeding costs have differential effects on fitness, and a distinction between these two systems of costs may therefore be of crucial importance in analyses ofoptimal parental investment. With prebreeding costs, optimal parental investment is lower than with postbreeding costs, ceteris paribus. We illustrate this in a simple analysis of optimal clutch size, and provide general conditions for optimal clutch size with prebreeding and postbreeding costs, respectively. Through their differential effects on fitness, systems of costs may also influence and direct the evolution of behavioural and physiological patterns associated with parental investments. The distinction between pre and postbreeding costs provides new perspectives on costs of reproduction that may prove fruitful in the future development of life history theory. It also allowsanalyses of optimal life histories under reproductive costs in semelparous organisms. As predation may be an important mechanism behind prebreeding survival costs, we emphasize the role of predation and antipredatory behaviour in the evolution of life histories and breeding behaviour. [ABSTRACT FROM AUTHOR]

Fluctuations in essential resources cause a strong selection pressure on the ability to adjust parental investment accordingly. In the dog family, Canidae, variance in female prebirth investment is adjustedby litter size. The arctic fox, Alopex lagopus , is a small canid living on the northern tundras of the world. It has the largest known litter size in the order Carnivora, up to 18 young, and litter size ishighly variable. We have analysed data from arctic fox populations throughout the species circumpolar range. In some areas, arctic foxes feed on strongly fluctuating populations of small rodents. In contrast, they have more stable food resources at bird cliffs and along coast lines. Food availability determines arctic fox litter and population sizes. A comparison between fluctuating and stable arctic fox populations showed that fluctuations are associated with large litter sizes. There were significant differences in litter size means, maxima and variances, as well as in placental scar count means. We have discussed five hypotheses on the determination of variation in litter size:one energetic, one genetic (based on density variation), one diet-determined, one based on reproductive allocation and one based on differences in reaction norms. Our findings suggest that litter size in the arctic fox is determined by the combined effect of immediate resource levels and the degree of resource predictability. We describe reaction norms that suggest how litter sizes result from adaptive plasticity within each of two genetic strategies where, according to the jackpot hypothesis, populations with unpredictable food resources generally have larger litter sizes. Within each genetic strategy, or reaction norm, litter sizes are adjusted through a number of plastic traits. These traits are influenced by nutritional limitations and include reduced ovulation rates, prenatal losses, and litter size reduction during the lactation period. [ABSTRACT FROM AUTHOR]

The concept of a cost of reproduction has associations with a variety of other ideas in population biology, among them trade-offs and antagonistic pleiotropy. Within the concept of a cost of reproduction, avariety of components can be distinguished, such as physiological and ecological costs of reproduction. This article concentrates on the former type of cost. Empirically, a variety of approaches can be, andhave been, used to analyze the cost of reproduction. Three are distinguished: genetic, environmental, and physiological. These are discussed first in general terms and second with specific reference to research on laboratory evolution in Drosophila. The latter discussion serves to focus and to instantiate the general analysis of the field. Emerging themes from this area of research include the environmental plasticity of costs of reproduction, the difficulties facing simple trade-off theories, and the critical role of physiological integration in determining costs at the organismal level. [ABSTRACT FROM AUTHOR]

Recent advances in understanding mammalian reproductive patterns mirror general developments in phylogenetic, physiological, and ecological research. We provide an overview of the diverse approaches used instudying mammalian litter size and discuss recent advances in evolutionary ecological theory and experimental data concerning reproductive patterns. Extensively documented natural history studies and breeding data from work in applied zoology and animal husbandry constitute a rich source of information for comparative studies. Such studies have helped identify fundamental differences in reproductive 'strategies' depending on whether taxa produce altricial or precocial young andwhether a given reproductive effort results in a single offspring ora litter. On the other hand, research on ecological and physiological correlates of litter size is providing new insights about reproductive energetics, the relationship between resource availability and litter size, and optimality in varying environments in general. Continuing experimental approaches are broadening our understanding of the mechanistic bases of patterns of mammalian litter size, but such studies, especially those involving manipulation of litter size, must carefully consider the potential biases introduced by experimentally induced non-congruence between pre- and postnatal litter sizes. For example, without accounting for the effects of placental hormones on mammogenesis and lactation, postnatal manipulations of litter size might be based on faulty assumptions implicit in such manipulations. To conclude, despite substantial advances in these diverse approaches, our degree of understanding of optimal litter size in mammals remains unclear because of inconsistencies in data often used in comparative studies and because of physiological and ecological constraints on littersize adjustments that hinder or bias experimental approaches. These areas should be addressed in future studies. [ABSTRACT FROM AUTHOR]

Life-history traits and secondary sexual characters often demonstrate condition-dependence, and reproductive success thus ultimately appears to be determined by condition. Here we test the hypothesis that anti-parasite defense is condition-dependent and thus ultimately limits fitness. Animal hosts defend themselves against parasites by an efficient immune system that changes its activity level depending on level of infection. Since immune function is costly, as demonstrated by several field studies, we predicted that large immune defence organs should be maintained when the costs of an elevated immune response were reduced, or when the benefits were increased. Hence, the size of immune defence organs was predicted to increase in response to diseasedue to increased benefits of investment in immune function, and the size was predicted to increase in response to high body condition because of reduced costs of investment in immune function. A comparativestudy of birds demonstrated that the size of the spleen was significantly increased among individuals suffering from parasitic infectionsand signs of disease as compared to healthy individuals. Furthermore, we found evidence for a positive association between spleen size and body condition. These findings are consistent with the hypothesisedcost of immune function and hence a cost of anti-parasite defence. [ABSTRACT FROM AUTHOR]

Seed dormancy is hypothesized to be a risk-spreading strategy that maximizes plant fitness. By spreading germination time of offspring among years, plants may not only vary the environment to which their offspring are exposed, but may also reduce potential fitness losses dueto sib competition. The sibling competition hypothesis predicts thatlarge families whose offspring are more likely to experience siblingcompetition should stagger germination over several seasons (i.e. have greater dormancy) to a greater extent than small families. This should be observed as a lower initial probability of germination for seeds from large families than those from small families. We examined the relationship between family size and germination behavior in the desert mustard Lesquerella fendleri. In a single population in centralNew Mexico, USA, we estimated family size and germination fraction of 189 randomly selected maternal plants. Although a median test was not supportive, the randomization test showed marginal support for thesibling competition hypothesis. An additional study of twelve large and twelve small families in each of three other populations also showed a trend (significant in one population) for larger families to have lower germination fractions than small families. These results suggest a degree of support for the hypothesis, given that so many selective forces interact to generate patterns of seed dormancy. Thus, we have not ruled out the hypothesis that large families reduce the likelihood of sib competition in good years by producing seed crops with initially low germination. Sibling competition as well as environmental heterogeneity may have influenced the evolution of seed dormancy in this system. [ABSTRACT FROM AUTHOR]

One of the most promising hypotheses for the evolution of sex is that sexual reproduction is adventageous because it increases the rate of adaptive evolution in response to parasites. To investigate this advantage of sex, we compared genetic variation of gemini-virsuses infecting sexual and asexual populations of Eupatorium (Asteraceae). The infection frequency was 37.5% in the sexual population and 87.8% in the asexual population. The lower infection frequency in the sexual population might be the result of higher genetic diversity of host plants. If geminiviruses have diverged to counter defence systems of genetically variable hosts, genetic diversity of viruses is expected to be higher in sexual host populations than in asexual host populations. To test this expectation, we used single-strand conformation polymorphism (SSCP) analysis to examine genetic diversity of the geminiviruses in a DNA region containing the open-reading frame (ORF) C4 gene, which is known to function as a host range determinant. As predicted, higher genetic diversity of viruses was observed in the sexual population: three SSCP types were found in the asexual population while six types were found in the sexual population. Sequencing of the polymerase chain reaction (PCR) products revealed further genetic diversity. Phylogenetic analysis of the sequences showed that the SSCP types belonged to four different clades. Several SSCP types from the same clade were found in the sexual population, whereas the asexual population included only one SSCP type from each clade. Amino acid replacements of ORF C4 suggested to be accelerated in the sexual population. This evidence supports the hypothesis that sexual reproduction is advantageous as a defence against epidemic disease. [ABSTRACT FROM AUTHOR]

Synchrony among reproductive or other states is a widespread phenomenon of significance in evolutionary theory. A model is presented for use in the measurement of the degree of synchrony in any set of behavioral or biological states, such as menstrual cycling, pregnancy, or lactation. At a given time, maximum group synchrony occurs when all members of a group are in a single state, minimum synchrony occurs when equal numbers are in all states, and intermediate values of synchrony occur for other proportional representations of the states. The model yields group synchrony scores ranging from 0 to 100 by standardizing the average of the absolute deviations among frequencies of occurrence in pairs of states. In addition, individual synchrony is characterized by the proportion of others who share an individual's state at a specified set of times. Properties of the model are discussed, simplified calculation procedures are presented, and the method's usefulness for comparative purposes is illustrated. [ABSTRACT FROM AUTHOR]

The biogeography of speciation remains a controversial issue and the process of allopatric speciation reigns. Sympatric speciation differs from allopatric speciation in terms of geographic setting and the role of selection in bringing about reproductive isolating mechanisms, making it a particularly fascinating and controversial subject for evolutionary biologists. Mayr (1947) explained the difference eloquently: for allopatric speciation, populations spatially diverge and then become reproductively isolated; for sympatric speciation, populations first become reproductively isolated and then diverge. Because of this, sympatric speciation is difficult to show empirically and most evolutionary biologists agree that strict ecological, evolutionary, and geographic criteria must be met ( Coyne & Orr 2004 ). In this issue, Crow et al. (2010) challenge us to expand the definition of sympatric speciation by studying species of marine fishes that they propose have arisen by sympatric speciation in a setting that does not appear to conform to the usual geographical criteria. [ABSTRACT FROM AUTHOR]

Ever since Ernst Mayr (1942) called ring species the ‘perfect demonstration of speciation’, they have attracted much interest from researchers examining how two species evolve from one. In a ring species, two sympatric and reproductively isolated forms are connected by a long chain of intermediate populations that encircle a geographic barrier. Ring species have the potential to demonstrate that speciation can occur without complete geographic isolation, in contrast to the classic model of allopatric speciation. They also allow researchers to examine the causes of reproductive isolation in the contact zone and to use spatial variation to infer the steps by which speciation occurs. According to the classical definition, a ring species must have (i) gradual variation through a chain of populations connecting two divergent and sympatric forms, and (ii) complete or nearly complete reproductive isolation between the terminal forms. But evolutionary biologists now recognize that the process of speciation might often occur with some periods of geographic contact and hybridization between diverging forms; during these phases, even partial reproductive isolation can limit gene flow and permit further divergence to occur. In this issue Bensch et  al. (2009) make an exciting and important contribution by extending the ring species concept to a case in which the divergence is much younger and not yet advanced to full reproductive isolation. Their study of geographic variation in willow warblers ( Phylloscopus trochilus; Fig. 1 ) provides a beautiful example of gradual variation through a ring of populations connecting two forms that are partially reproductively isolated where they meet, possibly due to divergent migratory behaviours of the terminal forms. [ABSTRACT FROM AUTHOR]

The article focuses on the study on nature and evolution of Pseudomyrmex pallidus. The Nearctic ant species inhabit primarily in dead stalks and culms of herbaceous plants from southern U.S. to Central America. They are usually grouped in colonies consisting of 1 to 15 queens and 20 to 200 workers. The species are observed through an experimental system to identify the effects of connection on social organization, behavior and division of reproduction. Information regarding the use of microsatellites for discerning genetic aspects of sociality is also discussed.