Stochastic exits from dormancy give rise to heavy‐tailed distributions of descendants in bacterial populations

Variance in reproductive success is a major determinant of the degree of genetic drift in a population. While many plants and animals exhibit high variance in their number of progeny, far less is known about these distributions for microorganisms. Here, we used a strain barcoding approach to quantify variability in offspring number among replicate bacterial populations and developed a Bayesian method to infer the distribution of descendants from this variability. We applied our approach to measure the offspring distributions for five strains of bacteria from the genus Streptomyces after germination and growth in a homogenous laboratory environment. The distributions of descendants were heavy‐tailed, with a few cells effectively ‘winning the jackpot’ to become a disproportionately large fraction of the population. This extreme variability in reproductive success largely traced back to initial populations of spores stochastically exiting dormancy, which provided early‐germinating spores with an exponential advantage. In simulations with multiple dormancy cycles, heavy‐tailed distributions of descendants decreased the effective population size by many orders of magnitude and led to allele dynamics differing substantially from classical population genetics models with matching effective population size. Collectively, these results demonstrate that extreme variability in reproductive success can occur even in growth conditions that are far more homogeneous than the natural environment. Thus, extreme variability in reproductive success might be an important factor shaping microbial population dynamics with implications for predicting the fate of beneficial mutations, interpreting sequence variability within populations and explaining variability in infection outcomes across patients.     

Evolutionary perspectives on human height variation

Human height is a highly variable trait, both within and between populations, has a high heritability, and influences the manner in which people behave and are treated in society. Although we know much about human height, this information has rarely been brought together in a comprehensive, systematic fashion. Here, we present a synthetic review of the literature on human height from an explicit evolutionary perspective, addressing its phylogenetic history, development, and environmental and genetic influences on growth and stature. In addition to presenting evidence to suggest the past action of natural selection on human height, we also assess the evidence that natural and sexual selection continues to act on height in contemporary populations. Although there is clear evidence to suggest that selection acts on height, mainly through life‐history processes but perhaps also directly, it is also apparent that methodological factors reduce the confidence with which such inferences can be drawn, and there remain surprising gaps in our knowledge. The inability to draw firm conclusions about the adaptiveness of such a highly visible and easily measured trait suggests we should show an appropriate degree of caution when dealing with other human traits in evolutionary perspective.     

No evidence that polyandry benefits females in Drosophila melanogaster

Understanding the evolution of polyandry (mating with multiple males) is a major issue in the study of animal breeding systems. We examined the adaptive significance of polyandry in Drosophila melanogaster, a species with well-documented costs of mating in which males generally cannot force copulations. We found no direct fitness advantages of polyandry. Females that mated with multiple males had no greater mean fitness and no different variance in fitness than females that mated repeatedly with the same male. Subcomponents of reproductive success, including fecundity, egg hatch rate, larval viability, and larval development time, also did not differ between polyandrous and monogamous females. Polyandry had no affect on progeny sex ratios, suggesting that polyandry does not function against costly sex-ratio distorters. We also found no evidence that polyandry functions to favor the paternity of males successful in precopulatory sexual selection. Experimentally controlled opportunities for precopulatory sexual selection had no effect on postcopulatory sperm precedence. Although these results were generally negative, they are supported with substantial statistical power and they help narrow the list of evolutionary explanations for polyandry in an important model species.     

Fragmentation of riverine systems: the genetic effects of dams on bull trout (Salvelinus confluentus) in the Clark Fork River system

Migratory bull trout (Salvelinus confluentus) historically spawned in tributaries of the Clark Fork River, Montana and inhabited Lake Pend Oreille as subadult and adult fish. However, in 1952 Cabinet Gorge Dam was constructed without fish passage facilities disrupting the connectivity of this system. Since the construction of this dam, bull trout populations in upstream tributaries have been in decline. Each year adult bull trout return to the base of Cabinet Gorge Dam when most migratory bull trout begin their spawning migration. However, the origin of these fish is uncertain. We used eight microsatellite loci to compare bull trout collected at the base of Cabinet Gorge Dam to fish sampled from both above and further downstream from the dam. Our data indicate that Cabinet Gorge bull trout are most likely individuals that hatched in above-dam tributaries, reared in Lake Pend Oreille, and could not return to their natal tributaries to spawn. This suggests that the risk of outbreeding depression associated with passing adults over dams in the Clark Fork system is minimal compared to the potential genetic and demographic benefits to populations located above the dams.     

The mutational dynamics of the SARS-CoV-2 virus in serial passages in vitro

Since its outbreak in 2019, Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) keeps surprising the medical community by evolving diverse immune escape mutations in a rapid and effective manner. To gain deeper insight into mutation frequency and dynamics, we isolated ten ancestral strains of SARS-CoV-2 and performed consecutive serial incubation in ten replications in a suitable and common cell line and subsequently analysed them using RT-qPCR and whole genome sequencing. Along those lines we hoped to gain fundamental insights into the evolutionary capacity of SARS-CoV-2 in vitro. Our results identified a series of adaptive genetic changes, ranging from unique convergent substitutional mutations and hitherto undescribed insertions. The region coding for spike proved to be a mutational hotspot, evolving a number of mutational changes including the already known substitutions at positions S:484 and S:501. We discussed the evolution of all specific adaptations as well as possible reasons for the seemingly inhomogeneous potential of SARS-CoV-2 in the adaptation to cell culture. The combination of serial passage in vitro with whole genome sequencing uncovers the immense mutational potential of some SARS-CoV-2 strains. The observed genetic changes of SARS-CoV-2 in vitro could not be explained solely by selectively neutral mutations but possibly resulted from the action of directional selection accumulating favourable genetic changes in the evolving variants, along the path of increasing potency of the strain. Competition among a high number of quasi-species in the SARS-CoV-2 in vitro population gene pool may reinforce directional selection and boost the speed of evolutionary change.     

Pollination efficiency and reproductive patterns in relation to local plant density,population size,and floral display in the rewarding Listera ovata (Orchidaceae)

Pollination efficiency and reproductive success vary strongly among populations of most animal‐pollinated plant species, depending on their size and local density, whereas individual plants within populations experience varying levels of reproductive output as a result of differences in floral display. Although most orchid species have been shown to be severely pollination limited, few studies have investigated the impact of the above‐mentioned factors on pollination success and reproduction, especially in rewarding species. In this study, the impact of population size, local density of flowering plants, and floral display on the rates of pollinia export and fruit production was investigated in 13 natural populations of the rewarding terrestrial orchid Listera ovata. In addition, an emasculation experiment was set up to examine how floral display and local density of flowering plants affected the relative importance of cross‐ vs. geitonogamous pollination in determining fruit set. In the studied populations, pollination efficiency, pollen removal, and fruit set increased with increasing population size until a threshold value of 30–40 flowering plants was reached, above which pollination efficiency and reproductive output decreased again. On average, plants with large floral displays showed higher proportional pollinia removal and fruit set compared with smaller plants. Fruit production was also significantly and positively related to local plant density, whereas emasculation did not affect the relationship between local plant density and fruit set, suggesting that geitonogamous pollination did not affect the outcome of female function. The results of this study are discussed in the light of the flowering mechanism of the species and its generalized pollination system. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 157 , 713–721.     

The role of environmental factors and genetic diversity on colonization success of a non-native fish,Lepomis gibbosus from western part of Turkey

Non-native freshwater fishes may become one of the dominant species in still and slow running waters and may impact whole ecosystem. One such species is the pumpkinseed Lepomis gibbosus, which has become widely distributed throughout Western Europe occurring primarily lakes and reservoirs. Although the species is known to have existed at least for four decades and expanded its distribution range in Turkish waters widely, virtually there is no study on the factors behind the species' establishment success. We hypothesized high environmental tolerance as well as high population structuring result in more successful establishment of pumpkinseed in new environments. We sampled three reservoirs, one canal and one stream located longitudinally along western part of Turkey to test this hypothesis. Optima (uk) and tolerance (tk) levels of the species were calculated with weighted averaging values for several measured environmental factors. Invasiveness of pumpkinseed populations was determined with the model proposed earlier examining the relationship between juvenile growth and age at maturity. The phylogenetic network of mitochondrial haplotypes was constructed for Turkish populations and other populations of pumpkinseed from native (North America) and introduced range (Europe). Potential invasiveness of pumpkinseed populations in Turkey was categorized as invasive in one location (Sarıçay stream) and transitional in other locations. Environmental tolerance values were higher in southern populations. Likewise phylogenetic network showed that the Turkish populations have unique haplotypes, which were originated from native North American populations suggesting a high differentiation in haplotypes. Results clearly demonstrate the effect of environmental factors on genetic structure and the establishment success of pumpkinseed.     

Parental investment, sexual selection and sex ratios

Conventional sex roles imply caring females and competitive males. The evolution of sex role divergence is widely attributed to anisogamy initiating a self‐reinforcing process. The initial asymmetry in pre‐mating parental investment (eggs vs. sperm) is assumed to promote even greater divergence in post‐mating parental investment (parental care). But do we really understand the process? Trivers [Sexual Selection and the Descent of Man 1871–1971 (1972), Aldine Press, Chicago] introduced two arguments with a female and male perspective on whether to care for offspring that try to link pre‐mating and post‐mating investment. Here we review their merits and subsequent theoretical developments. The first argument is that females are more committed than males to providing care because they stand to lose a greater initial investment. This, however, commits the ‘Concorde Fallacy’ as optimal decisions should depend on future pay‐offs not past costs. Although the argument can be rephrased in terms of residual reproductive value when past investment affects future pay‐offs, it remains weak. The factors likely to change future pay‐offs seem to work against females providing more care than males. The second argument takes the reasonable premise that anisogamy produces a male‐biased operational sex ratio (OSR) leading to males competing for mates. Male care is then predicted to be less likely to evolve as it consumes resources that could otherwise be used to increase competitiveness. However, given each offspring has precisely two genetic parents (the Fisher condition), a biased OSR generates frequency‐dependent selection, analogous to Fisherian sex ratio selection, that favours increased parental investment by whichever sex faces more intense competition. Sex role divergence is therefore still an evolutionary conundrum. Here we review some possible solutions. Factors that promote conventional sex roles are sexual selection on males (but non‐random variance in male mating success must be high to override the Fisher condition), loss of paternity because of female multiple mating or group spawning and patterns of mortality that generate female‐biased adult sex ratios (ASR). We present an integrative model that shows how these factors interact to generate sex roles. We emphasize the need to distinguish between the ASR and the operational sex ratio (OSR). If mortality is higher when caring than competing this diminishes the likelihood of sex role divergence because this strongly limits the mating success of the earlier deserting sex. We illustrate this in a model where a change in relative mortality rates while caring and competing generates a shift from a mammalian type breeding system (female‐only care, male‐biased OSR and female‐biased ASR) to an avian type system (biparental care and a male‐biased OSR and ASR).     

Female sperm use and storage between fertilization events drive sperm competition and male ejaculate allocation

Sperm competition theory has traditionally focused on how male allocation responds to female promiscuity, when males compete to fertilize a single clutch of eggs. Here, we develop a model to ask how female sperm use and storage across consecutive reproductive events affect male ejaculate allocation and patterns of mating and paternity. In our model, sperm use (a single parameter under female control) is the main determinant of sperm competition, which alters the effect of female promiscuity on male success and, ultimately, male reproductive allocation. Our theory reproduces the general pattern predicted by existing theory that increased sperm competition favors increased allocation to ejaculates. However, our model predicts a negative correlation between male ejaculate allocation and female promiscuity, challenging the generality of a prevailing expectation of sperm competition theory. Early models assumed that the energetic costs of precopulatory competition and the level of sperm competition are both determined by female promiscuity, which leads to an assumed covariation between these two processes. By modeling precopulatory costs and sperm competition independently, our theoretical framework allows us to examine how male allocation should respond independently to variation in sperm competition and energetic trade‐offs in mating systems that have been overlooked in the past.     

Foraging for mates in the hyperparasitic wasp, Dendrocerus carpenteri: impact of unfavourable weather conditions and parasitoid age

Males of the aphid hyperparasitoid Dendrocerus carpenteri (Curtis) were attracted by a sex pheromone released by conspecific females. The intensity of this cue, and thus female attractiveness, depended both on the female's mating status and her age. Only virgin females younger than 2 h were consistently recognized as mates by foraging males. Male age did not influence foraging and mating success. Empty mummies, from which females had emerged within the previous 10 min were attractive to males and examined intensively. Rain reduced the searching success of males, although the host plant Vicia faba provided sheltered places. Wind did not reduce mating success but prevented both sexes from leaving the host plant. Since the time of female attractiveness seems to be very limited, wind may have an enormous effect on the mating success of D. carpenteri in the field and thus on the population dynamics of this species. Received: 5 October 1998 / Accepted: 16 December 1998