Prestalk-like positioning of de-differentiated cells in the social amoeba Dictyostelium discoideum

The social amoeba Dictyostelium discoideum switches between solitary growth and social fruitification depending on nutrient availability. Under starvation, cells aggregate and form fruiting bodies consisting of spores and altruistic stalk cells. Once cells socially committed, they complete fruitification, even if a new source of nutrients becomes available. This social commitment is puzzling because it hinders individual cells from resuming solitary growth quickly. One idea posits that traits that facilitate premature de-commitment are hindered from being selected. We studied outcomes of the premature de-commitment through forced refeeding. Our results show that when refed cells interacted with non-refed cells, some of them became solitary, whereas a fraction was redirected to the altruistic stalk, regardless of their original fate. The refed cells exhibited reduced cohesiveness and were sorted out during morphogenesis. Our findings provide an insight into a division of labor of the social amoeba, in which less cohesive individuals become altruists.

Stability in gene expression and body-plan development leads to evolutionary conservation

BACKGROUND

Phenotypic evolution is mainly explained by selection for phenotypic variation arising from factors including mutation and environmental noise. Recent theoretical and experimental studies have suggested that phenotypes with greater developmental stability tend to have a constant phenotype and gene expression level within a particular genetic and environmental condition, and this positively correlates with stronger evolutionary conservation, even after the accumulation of genetic changes. This could reflect a novel mechanism that contributes to evolutionary conservation; however, it remains unclear whether developmental stability is the cause, or whether at least it contributes to their evolutionary conservation. Here, using Japanese medaka lines, we tested experimentally whether developmental stages and gene expression levels with greater stability led to their evolutionary conservation.

RESULTS

We first measured the stability of each gene expression level and developmental stage (defined here as the whole embryonic transcriptome) in the inbred F0 medaka population. We then measured their evolutionary conservation in the F3 generation by crossing the F0 line with the distantly related Japanese medaka line (Teradomori), followed by two rounds of intra-generational crossings. The results indicated that the genes and developmental stages that had smaller variations in the F0 generation showed lower diversity in the hybrid F3 generation, which implies a causal relationship between stability and evolutionary conservation.

CONCLUSIONS

These findings suggest that the stability in phenotypes, including the developmental stages and gene expression levels, leads to their evolutionary conservation; this most likely occurs due to their low potential to generate phenotypic variation. In addition, since the highly stable developmental stages match with the body-plan-establishment stage, it also implies that the developmental stability potentially contributed to the strict conservation of animal body plan.

Are there correlations between the levels of fluctuating asymmetry in Pelophylax ridibundus (Anura: Ranidae) meristic morphological traits and morphological parameters used for assessing their physical fitness (health status)?

The degree of developmental stability of individuals and populations is most often estimated by their level of fluctuating asymmetry (FA) - the random deviations from perfect symmetry. In our previous work, we recorded high levels of FA (FAMI index: frequency of asymmetric manifestation of an individual) in Pelophylax ridibundus populations that inhabit biotopes at Sazliyka River, south Bulgaria with high levels of anthropogenic pollution (domestic sewage pollution). At the same time, in the biotopes located in the upper reaches of the river (less disrupted habitats), the populations showed low levels of FA. Currently, we present the results of the study of the values of several morphological parameters: snout-vent length (SVL), body weight (BW), and body condition factor (CF) in the same populations of P. ridibundus. In addition, we evaluate the correlation between the values of these morphological parameters and the values of fluctuating asymmetry (the FAMI index), using the Kendall rank correlation analysis. The analysis of the relationships between the parameters characterizing the physical fitness of frogs and the indicator of developmental stability - the FAMI index - did not establish statistically significant correlations in the analyses in the whole groups of P. ridibundus from each site and in the correlations between sexes. We believe that the approaches to the study of developmental stability (analysis of fluctuating asymmetry levels) and those related to the assessment of physical fitness (health status) of frogs should be applied independently of each other.

Impact of fluctuating developmental temperatures on phenotypic traits in reptiles: a meta-analysis

During the vulnerable stages of early life, most ectothermic animals experience hourly and diel fluctuations in temperature as air temperatures change. While we know a great deal about how different constant temperatures impact the phenotypes of developing ectotherms, we know remarkably little about the impacts of temperature fluctuations on the development of ectotherms. In this study, we used a meta-analytic approach to compare the mean and variance of phenotypic outcomes from constant and fluctuating incubation temperatures across reptile species. We found that fluctuating temperatures provided a small benefit (higher hatching success and shorter incubation durations) at cool mean temperatures compared with constant temperatures, but had a negative effect at warm mean temperatures. In addition, more extreme temperature fluctuations led to greater reductions in embryonic survival compared with moderate temperature fluctuations. Within the limited data available from species with temperature-dependent sex determination, embryos had a higher chance of developing as female when developing in fluctuating temperatures compared with those developing in constant temperatures. With our meta-analytic approach, we identified average mean nest temperatures across all taxa where reptiles switch from receiving benefits to incurring costs when incubation temperatures fluctuate. More broadly, our study indicates that the impact of fluctuating developmental temperature on some phenotypes in ectothermic taxa are likely to be predictable via integration of developmental temperature profiles with thermal performance curves.

Nonadditive genetic effects induce novel phenotypic distributions in male mating traits of F1 hybrids

Hybridization is a source of phenotypic novelty and variation because of increased additive genetic variation. Yet, the roles of nonadditive allelic interactions in shaping phenotypic mean and variance of hybrids have been underappreciated. Here, we examine the distributions of male-mating traits in F1 hybrids via a meta-analysis of 3208 effect sizes from 39 animal species pairs. Although additivity sets phenotypic distributions of F1s to be intermediate, F1s also showed recessivity and resemblance to maternal species. F1s expressed novel phenotypes (beyond the range of both parents) in 65% of species pairs, often associated with increased phenotypic variability. Overall, however, F1s expressed smaller variation than parents in 51% of traits. Although genetic divergence between parents did not impact phenotypic novelty, it increased phenotypic variability of F1s. By creating novel phenotypes with increased variability, nonadditivity of heterozygotic genome may play key roles in determining mating success of F1s, and their subsequent extinction or speciation.

Genetic and morphological variation of metacercariae of Microphallus piriformes (Trematoda, Microphallidae): Effects of paraxenia and geographic location

Host organism offers an environment for a parasite, and this environment is heterogenous within the host, variable among individual as well as between the hosts, and changing during the host's lifetime. This heterogeneity may act as a prerequisite for parasite species divergence. Intraspecific variability related to a certain type of heterogeneity may indicate an initial stage of speciation, and thus poses an evolutionary importance. Here we analyzed genetic and morphologic variation of trematode metacercariae of Microphallus piriformes (Trematoda, Microphallidae). Genetic variability of trematodes was assessed from sequences of cytochrome c oxidase subunit 1 (COI) and internal transcribed spacer region (ITS-1). Morphological variation of metacercarial body shape was for the first time analyzed using geometric morphometrics. Parasites from the White Sea and the Barents Sea coasts demonstrated partial genetic divergence (according to COI sequence analysis) and had significantly different body shape. Neither genetic nor morphological variation of metacercariae was related to intermediate host species. We discuss possible causes of the observed genetic divergence of parasite populations in different geographic regions.

Fathers' and Mothers' Early Mind-Mindedness Predicts Social Competence and Behavior Problems in Childhood

Parental mind-mindedness, the parent's propensity to treat the child as an intentional agent, has repeatedly shown to promote children's development of social understanding and secure attachment. Less is known about whether the impact of maternal and paternal mind-mindedness extends to children's social and behavior problems. We investigated the combined effect of mothers' and fathers' (N = 104) mind-mindedness at 4, 12, and 30 months on children's social competence and externalizing and internalizing behavior problems at 4.5 years. Besides, we examined the stability, continuity, parental concordance, and inter-parental differences in the use of mind-related comments. Appropriate mind-mindedness (i.e., correct interpretations of the child's mental states) and nonattuned mind-mindedness (i.e., misinterpretations of the child's mental states) were observed during parent-child free-play interactions. Social competence, internalizing and externalizing behavior problems were assessed using both parents' reports. Hierarchical multiple regression analyses showed that, at 12 months, infrequent use of appropriate mind-related comments of both parents predicted children's externalizing problems, while their frequent use of nonattuned comments predicted children's low social competence. Furthermore, mothers' frequent use of nonattuned comments at 12 and 30 months and fathers' nonattuned comments at 30 months predicted children's externalizing behavior. The findings suggest that both parents' low use of mind-related comments, and frequent misinterpretations of their child's mind, may act as risk factors for later social and behavior problems of their child.

Temperature and herbivory, but not pollution, affect fluctuating asymmetry of mountain birch leaves: Results of 25-year monitoring around the copper‑nickel smelter in Monchegorsk, northwestern Russia

Fluctuating asymmetry (FA), which is defined as the magnitude of the random deviations from a symmetrical shape, reflects developmental instability and is commonly assumed to increase under environmental and genetic stress. We monitored the leaf FA of mountain birch, Betula pubescens subsp. czerepanovii, from 1993 to 2017 in individually marked trees at 21 sites around the copper‑nickel smelter at Monchegorsk, and we then analysed the results with respect to spatial and temporal variation in pollution, climate and background insect herbivory. Responses of leaf FA to different stressors were stressor specific: FA did not correlate with pollution load, it decreased significantly with an increase in June air temperature and it increased slightly but significantly with an increase in the previous-year leaf damage due to defoliating and leafmining insects. Our findings suggest that climate warming is unlikely to impose stress on the explored mountain birch populations, but even small increases in insect herbivory may adversely affect birch trees. However, these conclusions, since they are based on an observational study, should be viewed as tentative until confirmed by controlled experiments. We also demonstrated that the use of non-blinded measurements, which are prone to confirmation bias, was the primary reason for the earlier report of an increase in birch leaf FA near the Monchegorsk smelter. We hope that our findings will promote a wide use of blinded methods in ecological research and that they will contribute to debunking the myth that plant leaf FA consistently increases with increases in environmental pollution.

Temperature-induced phenotypic plasticity in the ovipositor of the invasive species Drosophila suzukii

Drosophila suzukii (Matsumura, 1931) is a highly successful invasive dipteran which represents a serious threat for global fruit industry. Among other adaptive traits, D. suzukii owes its success to the derived morphological features of its ovipositor, which allows the insect to exploit the exclusive ecological niche of fresh fruit, thus avoiding competition with other closely related species. With the aim of investigating temperature-induced phenotypic plasticity of D. suzukii ovipositor, we reared this insect in four different laboratory conditions, represented by the combination of two developmental temperatures and two diet regimes for the larvae. We recorded the effects of these two factors on ovipositor size and shape and overall body size through a combination of distance-based and geometric morphometric analyses. Results showed that insects attain the largest body sizes at lower temperature, whereas the diet does not determine significant difference in size. However, the effect on size of the two factors is less pronounced in the ovipositor, which shows a negative allometry with respect to body size in all treatments. At higher temperature, ovipositor shape tends also to co-vary with its own size. Neither temperature nor diet have significant effect on ovipositor bilateral fluctuating asymmetry. These results confirm the hypothesis that in D. suzukii the toughened valve of the ovipositor are subjected to effective morpho-functional constraints, while probably being under strong selection by reason of their mechanical role.

Developmental stability, age at onset of foraging and longevity of Africanized honey bees (Apis mellifera L.) under heat stress (Hymenoptera: Apidae)

Beekeeping with the western honey bee (Apis mellifera) is important in tropical regions but scant information is available on the possible consequences of global warming for tropical beekeeping. We evaluated the effect of heat stress on developmental stability, the age at onset of foraging (AOF) and longevity in Africanized honey bees (AHBs) in the Yucatan Peninsula of Mexico, one of the main honey producing areas in the Neotropics, where high temperatures occur in spring and summer. To do so, we reared worker AHB pupae under a fluctuating temperature regime, simulating current tropical heatwaves, with a high temperature peak of 40.0 °C for 1 h daily across six days, and compared them to control pupae reared at stable temperatures of 34.0-35.5 °C. Heat stress did not markedly affect overall body size, though the forewing of heat-stressed bees was slightly shorter than controls. However, bees reared under heat stress showed significantly greater fluctuating asymmetry (FA) in forewing shape. Heat stress also decreased AOF and reduced longevity. Our results show that changes occur in the phenotype and behavior of honey bees under heat stress, with potential consequences for colony fitness.

DEVELOPMENTAL STABILITY, FITNESS, AND TRAIT SIZE IN LABORATORY HYBRIDS BETWEEN EUROPEAN SUBSPECIES OF THE HOUSE MOUSE

The effects of hybridization on developmental stability and size of tooth characters were investigated in intersubspecific crosses between random-bred wild strains of the house mouse (Mus musculus domesticus and M. m. musculus). Fluctuating asymmetry (FA) and trait size were compared within and between parental, F₁ , backcross, and F₂ hybrid groups. The relationship between FA and reproductive fitness within the F₁ hybrids was also studied. The results indicated that both FA and character size levels differed significantly between the two subspecies. The F₁ hybrids and the recombined groups (backcrosses and F₂ hybrids) showed heterosis for both parameters. No significant differences in the FA of fertile and sterile F₁ hybrid individuals were found. Comparison of the FA levels obtained in this study with those found in wild populations from the hybrid zone in Denmark showed that the levels of FA were lower in laboratory-bred samples than in the wild populations. This study provides further evidence that, in hybrids, the developmental processes underlying most of the morphological traits we studied benefit from a heterotic effect, despite the genomic incompatibilities between the two European house mice revealed by previous genetical and parasitological studies.

Development and evolution of segmentation assessed by geometric morphometrics: The centipede Strigamia maritima as a case study

Using the centipede model species Strigamia maritima as a subject of study, we illustrate the potential of geometric morphometrics for investigating the development and evolution of segmentation, with a specific focus on post-embryonic segmental patterning. We show how these techniques can contribute detailed descriptive data for comparative purposes, but also precious information on some features of the developmental system that are considered relevant for the evolvability of a segmented body architecture, such as developmental stability and canalization. Morphometric analyses allow to separately investigate several sources of phenotypic variation along a segmented body axis, like constitutive and random segment heteronomy, both within and among individuals. Specifically, in S. maritima, the segmental pattern of ventral sclerite shapes mirrors that of their bilateral fluctuating asymmetry and among-individual variation in associating the most anterior and most posterior segments in diverging from the central ones. Also, among segments, there seems to be a correlation between fluctuating asymmetry and shape variation among individuals, suggesting that canalization and developmental stability are somehow associated. Overall, these associations might stem from a joint influence of the segmental position on the two processes of developmental buffering.

One-year developmental stability and covariance among oddball, novelty, go/no-go, and flanker event-related potentials in adolescence: A monozygotic twin study

ERP measures may index genetic risk for psychopathology before disorder onset in adolescence, but little is known about their developmental rank-order stability during this period of significant brain maturation. We studied ERP stability in 48 pairs of identical twins (age 14-16 years) tested 1 year apart. Trial-averaged voltage waveforms were extracted from electroencephalographic recordings from oddball/novelty, go/no-go, and flanker tasks, and 16 amplitude measures were examined. Members of twin pairs were highly similar, whether based on ERP amplitude measures (intraclass correlation [ICC] median = .64, range = .44-.86) or three factor scores (all ICCs ≥ .69) derived from them. Stability was high overall, with 69% of the 16 individual measures generating stability coefficients exceeding .70 and all factor scores showing stability above .75. Measures from 10 difference waveforms calculated from paired conditions within tasks were also examined, and were associated with lower twin similarity (ICC median = .52, .38-.64) and developmental stability (only 30% exceeding .70). In a supplemental analysis, we found significant developmental stability for error-related negativity (range = .45-.55) and positivity (.56-.70) measures when average waveforms were based on one or more trials, and that these values were equivalent to those derived from averages using the current field recommendation, which requires six or more trials. Overall, we conclude that the studied brain measures are largely stable over 1 year of mid- to late adolescence, likely reflecting familial etiologic influences on brain functions pertaining to cognitive control and salience recognition.