RESUMEN

Evolution of unicellular to multicellular organisms must resolve conflicts in reproductive interests between individual cells and the group. The social amoeba Dictyostelium discoideum is a soil-living eukaryote with facultative sociality. While cells grow in the presence of nutrients, cells aggregate under starvation to form fruiting bodies containing spores and altruistic stalk cells. Once cells socially committed, they complete formation of fruiting bodies, even if a new source of nutrients becomes available. The persistence of this social commitment raises questions as it inhibits individual cells from swiftly returning to solitary growth. I hypothesize that traits enabling premature de-commitment are hindered from being selected. Recent work has revealed outcomes of the premature de-commitment through forced refeeding; The de-committed cells take an altruistic prestalk-like position due to their reduced cohesiveness through interactions with socially committed cells. I constructed an evolutionary model assuming their division of labor. The results revealed a valley in the fitness landscape that prevented invasion of de-committing mutants, indicating evolutionary stability of the social commitment. The findings provide a general scheme that maintains multicellularity by evolving a specific division of labor, in which less cohesive individuals become altruists.

Asunto(s)

RESUMEN

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.

Asunto(s)

RESUMEN

Progress in evolutionary developmental biology (evo-devo) has deepened our understanding of how intrinsic properties of embryogenesis, along with natural selection and population genetics, shape phenotypic diversity. A focal point of recent empirical and theoretical research is the idea that highly developmentally stable phenotypes are more conserved in evolution. Previously, we demonstrated that in Japanese medaka (Oryzias latipes), embryonic stages and genes with high stability, estimated through whole-embryo RNA-seq, are highly conserved in subsequent generations. However, the precise origin of the stability of gene expression levels evaluated at the whole-embryo level remained unclear. Such stability could be attributed to two distinct sources: stable intracellular expression levels or spatially stable expression patterns. Here we demonstrate that stability observed in whole-embryo RNA-seq can be attributed to stability at the cellular level (low variability in gene expression at the cellular levels). We quantified the intercellular variations in expression levels and spatial gene expression patterns for seven key genes involved in patterning dorsoventral and rostrocaudal regions during early development in medaka. We evaluated intracellular variability by counting transcripts and found its significant correlation with variation observed in whole-embryo RNA-seq data. Conversely, variation in spatial gene expression patterns, assessed through intraindividual left-right asymmetry, showed no correlation. Given the previously reported correlation between stability and conservation of expression levels throughout embryogenesis, our findings suggest a potential general trend: the stability or instability of developmental systems-and the consequent evolutionary diversity-may be primarily anchored in intrinsic fundamental elements such as the variability of intracellular states.

Asunto(s)

RESUMEN

The BBAA subgenomes of hexaploid common wheat can be 'extracted' to constitute a viable and self-reproducing novel tetraploid wheat, termed extracted tetraploid wheat (ETW). Prior studies have shown ETW manifesting phenotypic abnormalities and alteration in gene expression and epigenetic modifications. No population level investigation has been conducted, leaving the issue unclear regarding whether developmental stability, an essential property evolved in all natural organisms, might have been undermined in ETW. Here, we measured variations in five morphological traits and somatic chromosomal stability in populations of ETW and of its hexaploid donor, a resynthesized hexaploid and a natural tetraploid wheat. We observed phenotypic defects in ETW. Meanwhile, we documented much greater within-population variations in ETW than in the other wheat genotypes, most probably due to disrupted developmental stability in ETW. Also, somatic structural chromosome variations were detected only in ETW. Comparative transcriptome analyses indicated that the disrupted developmental stability of ETW is likely linked to massive dysregulation of genome-wide gene expression rather than to genetic mutations. Population network analysis of gene expression implicated intrinsic connectivity among the variable traits, while gene set enrichment analysis provided possible links between dysregulated gene expression and interlaced trait variation.

RESUMEN

OBJECTIVES: The level of fluctuating asymmetry is suggested as a putative signal of developmental stability, thus according to this theoretical framework more symmetric individuals should be in better biological condition and have greater reproductive potential. Here we hypothesize that women with more symmetric faces have more successful reproduction. METHODS: Data were collected from 164 postmenopausal Polish women. Facial photographs were taken and the overall facial asymmetry (OFA) was calculated. The associations between the OFA and reproductive parameters were analyzed using multiple regression models. Furthermore, the mediation analysis was conducted to test for the indirect effects of the OFA on reproductive success. RESULTS: There was a statistically significant relationship between the OFA and the number of children born, which was mediated by the age at first reproduction (p = 0.03), however, the size of the effect was rather low. Women with more symmetric faces had an earlier age at first reproduction and, in consequence, a greater number of children. DISCUSSION: As fluctuating asymmetry is suggested to be established in utero, these findings shed light on the possible life-long importance of developmental conditions in shaping women's reproductive potential and performance.

Asunto(s)

RESUMEN

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.

RESUMEN

Size and shape are important determinants of fitness in most living beings. Accordingly, the capacity of the organism to regulate size and shape during growth, containing the effects of developmental disturbances of different origin, is considered a key feature of the developmental system. In a recent study, through a geometric morphometric analysis on a laboratory-reared sample of the lepidopteran Pieris brassicae, we found evidence of regulatory mechanisms able to restrain size and shape variation, including bilateral fluctuating asymmetry, during larval development. However, the efficacy of the regulatory mechanism under greater environmental variation remains to be explored. Here, based on a field-reared sample of the same species, by adopting identical measurements of size and shape variation, we found that the regulatory mechanisms for containing the effects of developmental disturbances during larval growth in P. brassicae are also effective under more natural environmental conditions. This study may contribute to better characterization of the mechanisms of developmental stability and canalization and their combined effects in the developmental interactions between the organism and its environment.

RESUMEN

Developmental instability (DI) is an individual's inability to produce a specific developmental outcome under a given set of conditions, generally thought to result from random perturbations experienced during development. Fluctuating asymmetry (FA) - asymmetry on bilateral features that, on average, are symmetrical (or asymmetry deviating from that arising from design) - has been used to measure DI. Dating to half a century ago, and accelerating in the past three decades, psychological researchers have examined associations between FA (typically measured on bodily or facial features) and a host of outcomes of interest, including psychological disorders, cognitive ability, attractiveness, and sexual behavior. A decade ago, a meta-analysis on findings from nearly 100 studies extracted several conclusions. On average, small but statistically reliable associations between FA and traits of interest exist. Though modest, these associations are expected to greatly underestimate the strength of associations with underlying DI. Despite the massive sample size across studies, we still lack a good handle on which traits are most strongly affected by DI. A major methodological implication of the meta-analysis is that most studies have been, individually, woefully underpowered to detect associations. Though offering some intriguing findings, much research is the past decade too has been underpowered; hence, the newer literature is also likely noisy. Several large-scale studies are exceptions. Future progress depends on additional large-scale studies and researchers' sensitivity to power issues. As well, theoretical assumptions and conceptualizations of DI and FA driving psychological research may need revision to explain empirical patterns.

Asunto(s)

RESUMEN

Fluctuating asymmetry as a special kind of asymmetry can be defined as deviations from a known predetermined ratio of the parts of morphological structure under study. As a special type of phenotypic variability fluctuating asymmetry is a manifestation of ontogenetic noise or developmental variability. This type of variability is ubiquitous and plays a significant role in the observed phenotypic diversity. The level of fluctuating asymmetry turns out to be an indicator of optimal developmental conditions and genetic coadaptation. It is also considered as a parameter of fitness. Thus, fluctuating asymmetry acts as a measure of developmental stability in developmental biology and as a measure of population condition in population biology.

RESUMEN

BACKGROUND: Despite the morphological diversity of animals, their basic anatomical patterns-the body plans in each animal phylum-have remained highly conserved over hundreds of millions of evolutionary years. This is attributed to conservation of the body plan-establishing developmental period (the phylotypic period) in each lineage. However, the evolutionary mechanism behind this phylotypic period conservation remains under debate. A variety of hypotheses based on the concept of modern synthesis have been proposed, such as negative selection in the phylotypic period through its vulnerability to embryonic lethality. Here we tested a new hypothesis that the phylotypic period is developmentally stable; it has less potential to produce phenotypic variations than the other stages, and this has most likely led to the evolutionary conservation of body plans. RESULTS: By analyzing the embryos of inbred Japanese medaka embryos raised under the same laboratory conditions and measuring the whole embryonic transcriptome as a phenotype, we found that the phylotypic period has greater developmental stability than other stages. Comparison of phenotypic differences between two wild medaka populations indicated that the phylotypic period and its genes in this period remained less variational, even after environmental and mutational modifications accumulated during intraspecies evolution. Genes with stable expression levels were enriched with those involved in cell-cell signalling and morphological specification such as Wnt and Hox, implying possible involvement in body plan development of these genes. CONCLUSIONS: This study demonstrated the correspondence between the developmental stage with low potential to produce phenotypic variations and that with low diversity in micro- and macroevolution, namely the phylotypic period. Whereas modern synthesis explains evolution as a process of shaping of phenotypic variations caused by mutations, our results highlight the possibility that phenotypic variations are readily limited by the intrinsic nature of organisms, namely developmental stability, thus biasing evolutionary outcomes.

Asunto(s)

RESUMEN

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.

Asunto(s)

RESUMEN

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.

Asunto(s)

RESUMEN

Developmental monitoring and screening are recommended strategies for identifying children with sickle cell disease at high risk for cerebrovascular complications. Studies examining developmental screenings have provided little data on change over time. We examined screenings longitudinally in 43 children screened as two-year-olds and four-year-olds using the Ages and Stages Questionnaire, 2nd edition. Only two-thirds of children had stable screening outcomes. A new onset of cerebrovascular complications predicted the emergence of developmental delay (P = 0.017). Multivariate analysis suggested a benefit from formal developmental interventions. Regular developmental screening during the preschool period is important to identify systematic changes in developmental status.

Asunto(s)

RESUMEN

Understanding how environmental variation influences even cryptic traits is important to clarify the roles of selection and developmental constraints in past evolutionary divergence and to predict future adaptation under environmental change. Female yellow dung flies (Scathophaga stercoraria) typically have three sperm storage compartments (3S), but occasionally four (4S). More spermathecae are thought to be a female adaptation facilitating sperm sorting after mating, but the phenotype is very rare in nature. We manipulated the flies' developmental environment by food restriction, pesticides, and hot temperatures to investigate the nature and extent of developmental plasticity of this trait, and whether spermatheca expression correlates with measures of performance and developmental stability, as would be expected if 4S expression is a developmental aberration. The spermathecal polymorphism of yellow dung fly females is heritable, but also highly developmentally plastic, varying strongly with rearing conditions. 4S expression is tightly linked to growth rate, and weakly positively correlated with fluctuating asymmetry of wings and legs, suggesting that the production of a fourth spermatheca could be a nonadaptive developmental aberration. However, spermathecal plasticity is opposite in the closely related and ecologically similar Scathophaga suilla, demonstrating that overexpression of spermathecae under developmental stress is not universal. At the same time, we found overall mortality costs as well as benefits of 4S pheno- and genotypes (also affecting male siblings), suggesting that a life history trade-off may potentially moderate 4S expression. We conclude that the release of cryptic genetic variation in spermatheca number in the face of strong environmental variation may expose hidden traits (here reproductive morphology) to natural selection (here under climate warming or food augmentation). Once exposed, hidden traits can potentially undergo rapid genetic assimilation, even in cases when trait changes are first triggered by random errors that destabilize developmental processes.

Asunto(s)

RESUMEN

BACKGROUND: We compared skull shape and variation among genetically modified mice that exhibit different levels of connexin43 (Cx43) channel function, to determine whether Cx43 contributes to craniofacial phenotypic robustness. Specifically, we used two heterozygous mutant mouse models (G60S/+ and I130T/+) that, when compared to their wildtype counterparts, have an ~80% and ~50% reduction in Cx43 function, respectively. RESULTS: Both mutant strains showed significant differences in skull shape compared to wildtype littermates and while these differences were more severe in the G60S/+ mouse, shape differences were localized to similar regions of the skull in both mutants. However, increased skull shape variation was observed in G60S/+ mutants only. Additionally, covariation of skull structures was disrupted in the G60S/+ mutants only, indicating that while a 50% reduction in Cx43 function is sufficient to cause a shift in mean skull shape, the threshold for Cx43 function for disrupting craniofacial phenotypic robustness is lower. CONCLUSIONS: Collectively, our results indicate Cx43 can contribute to phenotypic robustness of the skull through a nonlinear relationship between Cx43 gap junctional function and phenotypic outcomes.

Asunto(s)

RESUMEN

Gynandromorphs, i.e., individuals with a mix of male and female traits, are common in the wild bees of the genus Megachile (Hymenoptera, Apoidea). We described new transverse gynandromorphs in Megachile pilidens Alfkeen, 1924 and analyze the spatial distribution of body parts with male vs. female phenotype hitherto recorded in the transverse gynandromorphs of the genus Megachile. We identified 10 different arrangements, nine of which are minor variants of a very general pattern, with a combination of male and female traits largely shared by the gynandromorphs recorded in 20 out of 21 Megachile species in our dataset. Based on the recurrence of the same gynandromorph pattern, the current knowledge on sex determination and sex differentiation in the honey bee, and the results of recent gene-knockdown experiments in these insects, we suggest that these composite phenotypes are possibly epigenetic, rather than genetic, mosaics, with individual body parts of either male or female phenotype according to the locally expressed product of the alternative splicing of sex-determining gene transcripts.

RESUMEN

Pathways through which phenotypic variation among individuals arise can be complex. One assumption often made in relation to intraspecific diversity is that the stability or predictability of the environment will interact with expression of the underlying phenotypic variation. To address biological complexity below the species level, we investigated variability across years in morphology and annual growth increments between and within two sympatric lake charr Salvelinus namaycush ecotypes in Rush Lake, USA. A rapid phenotypic shift in body and head shape was found within a decade. The magnitude and direction of the observed phenotypic change were consistent in both ecotypes, which suggests similar pathways caused the variation over time. Over the same time period, annual growth increments declined for both lake charr ecotypes and corresponded with a consistent phenotypic shift of each ecotype. Despite ecotype-specific annual growth changes in response to winter conditions, the observed annual growth shift for both ecotypes was linked, to some degree, with variation in the environment. Particularly, a declining trend in regional cloud cover was associated with an increase of early-stage (ages 1-3) annual growth for lake charr of Rush Lake. Underlying mechanisms causing changes in growth rates and constrained morphological modulation are not fully understood. An improved knowledge of the biology hidden within the expression of phenotypic variation promises to clarify our understanding of temporal morphological diversity and instability.

RESUMEN

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.

Asunto(s)

RESUMEN

The Hippo signaling pathway is a major regulator of organ growth, which controls the activity of the transcription coactivator Yorkie (Yki) in Drosophila and its homolog YAP in mammals. Both Yki and YAP proteins exist as alternatively spliced isoforms containing either one or two WW domains. The biological importance of this conserved alternative splicing event is unknown. Here, we identify the splicing factor B52 as a regulator of yki alternative splicing in Drosophila and show that B52 modulates growth in part through modulation of yki alternative splicing. Yki isoforms differ by their transcriptional activity as well as their ability to bind and bridge PPxY motifs-containing partners, and can compete in vivo. Strikingly, flies in which yki alternative splicing has been abrogated, thus expressing only Yki2 isoform, exhibit fluctuating wing asymmetry, a signal of developmental instability. Our results identify yki alternative splicing as a new level of modulation of the Hippo pathway, that is required for growth equilibration during development. This study provides the first demonstration that the process of alternative splicing contributes to developmental robustness.

Asunto(s)

RESUMEN

By adopting a longitudinal study design and through geometric morphometrics methods, we investigated size and shape regulation in the head capsule during the larval development of the cabbage butterfly Pieris brassicae under laboratory conditions. We found evidence of size regulation by compensatory growth, although not equally effective in all larval stages. Size compensation is not attained through the regulation of developmental timing, but rather through the modulation of per-time growth rate. As for the shape, neither the variance of the symmetric component of shape, nor the level of fluctuating asymmetry show any evidence of increase across stages, either at the population or individual level, which is interpreted as a mark of ontogenetic shape regulation. In addition, also the geometry of individual asymmetry is basically conserved across stages. While providing specific documentation on the ontogeny of size and shape variation in this insect, this study may contribute to a more general understanding of developmental regulation and its influence on phenotypic evolution.

Asunto(s)