Article Database

The Global Precipitation Measurement Mission

Abstract:

Precipitation affects many aspects of our everyday life. It is the primary source of freshwater and has significant socioeconomic impacts resulting from natural hazards such as hurricanes, floods, droughts, and landslides. Fundamentally, precipitation is a critical component of the global water and energy cycle that governs the weather, climate, and ecological systems. Accurate and timely knowledge of when, where, and how much it rains or snows is essential for understanding how the Earth system functions and for improving the prediction of weather, climate, freshwater resources, and natural hazard events.

Repeated Loss of Variation in Insect Ovary Morphology Highlights the Role of Developmental Constraint in Life-History Evolution

Abstract:

The number of offspring an organism can produce is a key component of its evolutionary fitness and lifehistory. Here we perform a test of the hypothesized trade off between the number and size of offspring using thousands of descriptions of the number of egg-producing compartments in the insect ovary (ovarioles), a common proxy for potential offspring number in insects. In contrast to prior claims, we find that ovariole number is not generally negatively correlated with the size of insect eggs, and we highlight several factors that may have contributed to this size-number trade off being strongly asserted in previous studies. We reconstruct the evolutionary history of the nurse cell arrangement within the ovariole, and show that the diversification of ovariole number and egg size have both been largely independent of nurse cell presence or position within the ovariole. Instead we show that ovariole number evolution has been shaped by a series of transitions between variable and invariant states, with multiple independent lineages evolving to have almost no variation in ovariole number. We highlight the implications of these invariant lineages on our understanding of the specification of ovariole number during development, as well as the importance of considering developmental processes in theories of life-history evolution.

Cricket Genomes: the Genomes of Future Food

Abstract:

Crickets are currently in focus as a possible source of animal protein for human consumption as an alternative to protein from vertebrate livestock. This practice could ease some of the challenges both of a worldwide growing population and of environmental issues. The two-spotted Mediterranean field cricket Gryllus bimaculatus has traditionally been consumed by humans in different parts of the world. Not only is this considered generally safe for human consumption, several studies also suggest that introducing crickets into one’s diet may confer multiple health benefits. Moreover, G. bimaculatus has been widely used as a laboratory research model for decades in multiple scientific fields including evolution, developmental biology, neurobiology, and regeneration. Here we report the sequencing, assembly and annotation of the G. bimaculatus genome, and the annotation of the genome of the Hawaiian cricket Laupala kohalensis. The comparison of these two cricket genomes with those of 14 additional insects supports the hypothesis that a relatively small ancestral insect genome expanded to large sizes in many hemimetabolous lineages due to transposable element activity. Based on the ratio of observed versus expected CpG sites (CpG_o/e), we find higher conservation and stronger purifying selection of typically methylated genes than of non-methylated genes. Finally, our gene family expansion analysis reveals an expansion of the pickpocket class V gene family in the lineage leading to crickets, which we speculate might play a relevant role in cricket courtship behavior, including their characteristic chirping.

Adaptation of Codon and Amino Acid Use for Translational Functions in Highly Expressed Cricket Genes

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Competing Interest Statement

The authors have declared no competing interest.

Sex-biased Genes Expressed in the Cricket Brain Evolve Rapidly

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Bacterial Contribution to Genesis of the Novel Germ Line Determinant Oskar

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New cellular functions and developmental processes can evolve by modifying existing genes or creating novel genes. Novel genes can arise not only via duplication or mutation but also by acquiring foreign DNA, also called horizontal gene transfer (HGT). Here we show that HGT likely contributed to the creation of a novel gene indispensable for reproduction in some insects. Long considered a novel gene with unknown origin, oskar has evolved to fulfil a crucial role in insect germ cell formation. Our analysis of over 100 insect Oskar sequences suggests that oskar arose de novo via fusion of eukaryotic and prokaryotic sequences. This work shows that highly unusual gene origin processes can give rise to novel genes that may facilitate evolution of novel developmental mechanisms.

Absence of a Faster-X Effect in Beetles (Tribolium, Coleoptera)

Abstract:

The faster-X effect, namely the rapid evolution of protein-coding genes on the X chromosome, has been widely reported in metazoans. However, the prevalence of this phenomenon across diverse systems and its potential causes remain largely unresolved. Analysis of sex-biased genes may elucidate its possible mechanisms: for example, in systems with X/Y males a more pronounced faster-X effect in male-biased genes than in female-biased or unbiased genes may suggest fixation of recessive beneficial mutations rather than genetic drift. Further, theory predicts that the faster-X effect should be promoted by X chromosome dosage compensation. Here, we asked whether we could detect a faster-X effect in genes of the beetle Tribolium castaneum (and T. freemani orthologs), which has X/Y sex-determination and heterogametic males. Our comparison of protein sequence divergence (dN/dS) on the X chromosome vs. autosomes indicated a rarely observed absence of a faster-X effect in this organism. Further, analyses of sex-biased gene expression revealed that the X chromosome was particularly highly enriched for ovary-biased genes, which evolved slowly. In addition, an evaluation of male X chromosome dosage compensation in the gonads and in non-gonadal somatic tissues indicated a striking lack of compensation in the testis. This under-expression in testis may limit fixation of recessive beneficial X-linked mutations in genes transcribed in these male sex organs. Taken together, these beetles provide an example of the absence of a faster-X effect on protein evolution in a metazoan, that may result from two plausible factors, strong constraint on abundant X-linked ovary-biased genes and a lack of gonadal dosage compensation.

Traveling Without a Destination: Primordial Germ Cell Migration in a Hemipteran Insect

Abstract:

In many animal species, the first line of restricted germ cells (Primordial Germ Cells) are formed in a location independent from the site of gonad development. In these species, the germ cells must migrate to the future gonad location before they are incorporated into the developing gonads. In some animals, such as Drosophila melanogaster, the tissue where PGCs will end up has already been specified when the PGCs begin migrating. However, in other animals, including the hemipteran insect, Oncopeltus fasciatus, PGCs begin migrating before the cells of their final resting place have been formed or been given an identity. In this insect, the mechanisms used by PGCs to find their location while the abdominal segments are growing and being specified around them remain unknown. Similarly, during this process, whether PGCs exhibit active cell migration and/or passive movement driven by the surrounding tissue that is growing is an open question. As a first step towards elucidating these mechanisms, we aim to characterize the cellular dynamics of PGCs moving through the surrounding embryonic tissue. We also aim to determine the molecular identity of the directional cues that eventually guide PGCs to the correct abdominal segments. Here we present progress on (1) a quantitative description of PGC migration, and (2) a candidate gene approach to determine the molecular basis of this process.

Null Hypotheses for Developmental Evolution

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How much evolutionary change in development do we expect? In this Spotlight, we argue that, as developmental biologists, we are in a prime position to contribute to the definition of a null hypothesis for developmental evolution: in other words, a hypothesis for how much developmental evolution we expect to observe over time. Today, we have access to an unprecedented array of developmental data from across the tree of life. Using these data, we can now consider development in the light of evolution, and vice versa, more deeply than ever before. As we do this, we may need to re-examine previous assumptions that appeared to serve us well when data points were fewer. Specifically, we think it is important to challenge assumptions that change is very rare for all developmental traits, especially if this assumption is used to sustain an erroneous view that evolution always optimizes adaptive traits toward increasing complexity.

Shared Cell Biological Functions May Underlie Pleiotropy of Molecular Interactions in the Germ Lines and Nervous Systems of Animals

Abstract:

Evolutionary developmental biology focuses on understanding the origin and evolution of extant biological variation, and the genetic basis for this variation. The genetic toolkit appears largely finite across animals, such that a combination of regulatory evolution, gene recruitment (co-option) and genetic modularity often allow morphological and developmental diversity to arise. Here we summarize a number of observations from across animals, which together suggest that many genes and gene product interaction “modules” originally characterized for their role in the germ line also have neural roles. We explore potential explanations for this observation, noting that in the context of the germ line, these genes appear to have molecular and biochemical properties that make them well-suited to breaking symmetry within cells. The resulting asymmetry is often caused by gene products co-localizing asymmetrically to sub-cellular, non-membrane bound, electron dense compartments known as ribonucleoprotein (RNP) granules. RNP granules contain high concentrations of translationally quiescent messenger RNAs and proteins and are thought to act as hubs of localized translational control. We propose that the use of strict translational control, which may be achieved via molecular processes important for RNP granule formation and/or small RNA-related processes, is an important property of and a commonality between the germ line and nervous tissues, and helps explain, at least in part, the close relationship between these two tissue types.