Evolution & Development最新文献

A new phenotypic variant may appear first in organisms through plasticity, that is, as a response to an environmental signal or other nongenetic perturbation. If such trait is beneficial, selection may increase the frequency of alleles that enable and facilitate its development. Thus, genes may take control of such traits, decreasing dependence on nongenetic disturbances, in a process called genetic assimilation. Despite an increasing amount of empirical studies supporting genetic assimilation, its significance is still controversial. Whether genetic assimilation is widespread depends, to a great extent, on how easily mutation and recombination reduce the trait's dependence on nongenetic perturbations. Previous research suggests that this is the case for mutations. Here we use simulations of gene regulatory network dynamics to address this issue with respect to recombination. We find that recombinant offspring of parents that produce a new phenotype through plasticity are more likely to produce the same phenotype without requiring any perturbation. They are also prone to preserve the ability to produce that phenotype after genetic and nongenetic perturbations. Our work also suggests that ancestral plasticity can play an important role for setting the course that evolution takes. In sum, our results indicate that the manner in which phenotypic variation maps unto genetic variation facilitates evolution through genetic assimilation in gene regulatory networks. Thus, we contend that the importance of this evolutionary mechanism should not be easily neglected.

Ladybird homeobox (Lbx) transcription factors have crucial functions in muscle and nervous system development in many animals. Amniotes have two Lbx genes, but only Lbx1 is expressed in spinal cord. In contrast, teleosts have three lbx genes and we show here that zebrafish lbx1a, lbx1b, and lbx2 are expressed by distinct spinal cell types, and that lbx1a is expressed in dI4, dI5, and dI6 interneurons, as in amniotes. Our data examining lbx expression in Scyliorhinus canicula and Xenopus tropicalis suggest that the spinal interneuron expression of zebrafish lbx1a is ancestral, whereas lbx1b has acquired a new expression pattern in spinal cord progenitor cells. lbx2 spinal expression was probably acquired in the ray-finned lineage, as this gene is not expressed in the spinal cords of either amniotes or S. canicula. We also show that the spinal function of zebrafish lbx1a is conserved with mouse Lbx1. In zebrafish lbx1a mutants, there is a reduction in the number of inhibitory spinal interneurons and an increase in the number of excitatory spinal interneurons, similar to mouse Lbx1 mutants. Interestingly, the number of inhibitory spinal interneurons is also reduced in lbx1b mutants, although in this case the number of excitatory interneurons is not increased. lbx1a;lbx1b double mutants have a similar spinal interneuron phenotype to lbx1a single mutants. Taken together these data suggest that lbx1b and lbx1a may be required in succession for correct specification of dI4 and dI6 spinal interneurons, although only lbx1a is required for suppression of excitatory fates in these cells.

The capacity to respond to environmental challenges ultimately relies on phenotypic variation which manifests from complex interactions of genetic and nongenetic mechanisms through development. While we know something about genetic variation and structure of many species of conservation importance, we know very little about the nongenetic contributions to variation. Rhizophora mangle is a foundation species that occurs in coastal estuarine habitats throughout the neotropics where it provides critical ecosystem functions and is potentially threatened by anthropogenic environmental changes. Several studies have documented landscape-level patterns of genetic variation in this species, but we know virtually nothing about the inheritance of nongenetic variation. To assess one type of nongenetic variation, we examined the patterns of DNA sequence and DNA methylation in maternal plants and offspring from natural populations of R. mangle from the Gulf Coast of Florida. We used a reduced representation bisulfite sequencing approach (epi-genotyping by sequencing; epiGBS) to address the following questions: (a) What are the levels of genetic and epigenetic diversity in natural populations of R. mangle? (b) How are genetic and epigenetic variation structured within and among populations? (c) How faithfully is epigenetic variation inherited? We found low genetic diversity but high epigenetic diversity from natural populations of maternal plants in the field. In addition, a large portion (up to ~25%) of epigenetic differences among offspring grown in common garden was explained by maternal family. Therefore, epigenetic variation could be an important source of response to challenging environments in the genetically depauperate populations of this foundation species.

Organismal miniaturization is defined by a reduction in body size relative to a large ancestor. In vertebrate animals, miniaturization is achieved by suppressing the energetics of growth. However, this might interfere with reproductive strategies in egg-laying species with limited energy budgets for embryo growth and differentiation. In general, the extent to which miniaturization coincides with alterations in animal development remains obscure. To address the interplay among body size, life history, and ontogeny, miniaturization in chelydroid turtles was examined. The analyses corroborated that miniaturization in the Chelydroidea clade is underlain by a dampening of the ancestral growth trajectory. There were no associated shifts in the early sequence of developmental transformations, though the relative duration of organogenesis was shortened in miniaturized embryos. The size of eggs, hatchlings, and adults was positively correlated within Chelydroidea. A phylogenetically broader exploration revealed an alternative miniaturization mode wherein exceptionally large hatchlings grow minimally and thus attain diminutive adult sizes. Lastly, it is shown that miniaturized Chelydroidea turtles undergo accelerated ossification coupled with a ~10% reduction in shell bones. As in other vertebrates, the effects of miniaturization were not systemic, possibly owing to opposing functional demands and tissue geometric constraints. This underscores the integrated and hierarchical nature of developmental systems.

Environmental conditions can impact the development of phenotypes and in turn the performance of individuals. Climate change, therefore, provides a pressing need to extend our understanding of how temperature will influence phenotypic variation. To address this, we assessed the impact of increased temperatures on ecologically significant phenotypic traits in Arctic charr (Salvelinus alpinus). We raised Arctic charr at 5°C and 9°C to simulate a predicted climate change scenario and examined temperature-induced variation in ossification, bone metabolism, skeletal morphology, and escape response. Fish reared at 9°C exhibited less cartilage and bone development at the same developmental stage, but also higher bone metabolism in localized regions. The higher temperature treatment also resulted in significant differences in craniofacial morphology, changes in the degree of variation, and fewer vertebrae. Both temperature regime and vertebral number affected escape response performance, with higher temperature leading to decreased latency. These findings demonstrate that climate change has the potential to impact development through multiple routes with the potential for plasticity and the release of cryptic genetic variation to have strong impacts on function through ecological performance and survival.

Humans are changing and challenging nature in many ways. Conservation Biology seeks to limit human impacts on nature and preserve biological diversity. Traditionally, Developmental Biology and Conservation Biology have had nonoverlapping objectives, operating in distinct spheres of biological science. However, this chasm can and should be filled to help combat the emerging challenges of the 21st century. The means by which to accomplish this goal were already established within the conceptual framework of evo- and eco-devo and can be further expanded to address the ways that anthropogenic disturbance affect embryonic development. Herein, I describe ways that these approaches can be used to advance the study of reptilian embryos. More specifically, I explore the ways that a developmental perspective can advance ongoing studies of embryonic physiology in the context of global warming and chemical pollution, both of which are known stressors of reptilian embryos. I emphasize ways that these developmental perspectives can inform conservation biologists trying to develop management practices that will address the complexity of challenges facing reptilian embryos.

One of the most defining moments in history was the colonization of land by plants approximately 470 million years ago. The transition from water to land was accompanied by significant changes in the plant body plan, from those than resembled filamentous representatives of the charophytes, the sister group to land plants, to those that were morphologically complex and capable of colonizing harsher habitats. The moss Physcomitrium patens (also known as Physcomitrella patens) is an extant representative of the bryophytes, the earliest land plant lineage. The protonema of P. patens emerges from spores from a chloronemal initial cell, which can divide to self-renew to produce filaments of chloronemal cells. A chloronemal initial cell can differentiate into a caulonemal initial cell, which can divide and self-renew to produce filaments of caulonemal cells, which branch extensively and give rise to three-dimensional shoots. The process by which a chloronemal initial cell differentiates into a caulonemal initial cell is tightly regulated by auxin-induced remodeling of the actin cytoskeleton. Studies have revealed that the genetic mechanisms underpinning this transition also regulate tip growth and differentiation in diverse plant taxa. This review summarizes the known cellular and molecular mechanisms underpinning the chloronema to caulonema transition in P. patens.

The MADS-box genes constitute a large transcription factor family that appear to have evolved by duplication and diversification of function. Two types of MADS-box genes are distinguished throughout eukaryotes, types I and II. Type II classic MADS-box genes, also known as MIKC-type, are key developmental regulators in flowering plants and are particularly well-studied for their role in floral organ specification. However, very little is known about the role that these genes might play outside of the flowering plants. We investigated the evolution of type II classic MADS-box genes across land plants by performing a maximum likelihood analysis with a particular focus on lycophytes. Here, we present the expression patterns of all three type II classic MADS-box homologs throughout plant development in the lycophyte Selaginella moellendorffii: SmMADS1, SmMADS3, and SmMADS6. We used scanning electron microscopy and histological analyses to define stages of sporangia development in S. moellendorffii. We performed phylogenetic analyses of this gene lineage across land plants and found that lycophyte sequences appeared before the multiple duplication events that gave rise to the major MADS-box gene lineages in seed plants. Our expression analyses by in situ hybridization show that all type II classic MADS-box genes in S. moellendorffii have broad but distinct patterns of expression in vegetative and reproductive tissues, where SmMADS1 and SmMADS6 only differ during late sporangia development. The broad expression during S. moellendorffii development suggests that MADS-box genes have undergone neofunctionalization and subfunctionalization after duplication events in seed plants.