Locally adapted populations of a copepod can evolve different gene expression patterns under the same environmental pressures

As populations diverge in allopatry, but under similar thermal conditions, do similar thermal performance phenotypes evolve by maintaining similar gene expression patterns, or does genetic divergence lead to divergent patterns of gene expression between these populations? We used genetically divergent populations of the copepod Tigriopus californicus , whose performance at different thermal conditions is well characterized, to investigate transcriptome-wide expression responses under two different thermal regimes: (1) a nonvariable temperature regime and (2) a regime with variable temperature. Our results show the expression profiles of the response to these regimes differed substantially among populations, even for populations that are geographically close. This pattern was accentuated when populations were raised in the variable temperature environment. Less heat-tolerant populations mounted strong but divergent responses to the different thermal regimes, with a large heat-shock response observed in one population, and an apparent reduction in the expression of genes involved in basic cellular processes in the other. Our results suggest that as populations diverge in allopatry, they may evolve starkly different responses to changes in temperature, at the gene expression level, while maintaining similar thermal performance phenotypes

Investigations of fine-scale phylogeography in Tigriopus californicus reveal historical patterns of population divergence

<p>Abstract</p> <p>Background</p> <p>The intertidal copepod <it>Tigriopus californicus </it>is a model for studying the process of genetic divergence in allopatry and for probing the nature of genetic changes that lead to reproductive isolation. Although previous studies have revealed a pattern of remarkably high levels of genetic divergence between the populations of this species at several spatial scales, it is not clear what types of historical processes are responsible. Particularly lacking are data that can yield insights into population history from the finest scales of geographic resolution.</p> <p>Results</p> <p>Sequence variation in both cytochrome b (<it>CYTB</it>, mtDNA) and the rieske iron-sulfur protein (<it>RISP</it>, nuclear) are examined at a fine scale within four different regions for populations of <it>T. californicus</it>. High levels of genetic divergence are seen for both genes at the broader scale, and genetic subdivision is apparent at nearly all scales in these populations for these two genes. Patterns of polymorphism and divergence in both <it>CYTB </it>and <it>RISP </it>suggest that selection may be leading to non-neutral evolution of these genes in several cases but a pervasive pattern of neither selection nor coadaptation is seen for these markers.</p> <p>Conclusion</p> <p>The use of sequence data at a fine-scale of resolution in this species has provided novel insights into the processes that have resulted in the accumulation of genetic divergence among populations. This divergence is likely to result from an interplay between a limited dispersal ability for this copepod and the temporal instability of copepod habitat. Both shorter-term processes such as the extinction/recolonization dynamics of copepod pools and longer-term processes such as geological uplift of coastline and sea level changes appear to have impacted the patterns of differentiation. Some patterns of sequence variation are consistent with selection acting upon the loci used in this study; however, it appears that most phylogeographic patterns are the result of history and not selection on these genes in this species.</p

The Evolution of the Thermal Niche Across Locally Adapted Populations of the Copepod Tigriopus californicus

Local adaptation to different thermal environments is often expected to result in trade-offs in other measures of performance, thermal or otherwise. Populations of the copepod Tigriopus californicus found along the Pacific coast of North America have previously been shown to display patterns consistent with local adaptation and thermal trade-offs. Much of the work on this species has focused on performance at high and moderate temperatures with the lower thermal performance explored to a lesser degree. In this study, measures of both high and low thermal performance are examined for a set of eight T. californicus populations spanning a range from Central Baja California, Mexico to the State of Washington, USA. High temperature survival decreases with increasing latitude while chill coma recovery improves with increasing latitude. Comparisons of these measures among populations along with previous results suggest that there is a shift in the thermal niche in this species rather than other forms of trade-offs such as specialist/generalist trade-offs

Complex Deleterious Interactions Associated with Malic Enzyme May Contribute to Reproductive Isolation in the Copepod Tigriopus californicus

Dobzhansky-Muller incompatibilities can result from the interactions of more than a single pair of interacting genes and there are several different models of how such complex interactions can be structured. Previous empirical work has identified complex conspecific epistasis as a form of complex interaction that has contributed to postzygotic reproductive isolation between taxa, but other forms of complexity are also possible. Here, I probe the genetic basis of reproductive isolation in crosses of the intertidal copepod Tigriopus californicus by looking at the impact of markers in genes encoding metabolic enzymes in F2 hybrids. The region of the genome associated with the locus ME2 is shown to have strong, repeatable impacts on the fitness of hybrids in crosses and epistatic interactions with another chromosomal region marked by the GOT2 locus in one set of crosses. In a cross between one of these populations and a third population, these two regions do not appear to interact despite the continuation of a large effect of the ME2 region itself in both crosses. The combined results suggest that the ME2 chromosomal region is involved in incompatibilities with several unique partners. If these deleterious interactions all stem from the same factor in this region, that would suggest a different form of complexity from complex conspecific epistasis, namely, multiple independent deleterious interactions stemming from the same factor. Confirmation of this idea will require more fine-scale mapping of the interactions of the ME2 region of the genome

Functional plasticity of antibacterial EndoU toxins.

Bacteria use several different secretion systems to deliver toxic EndoU ribonucleases into neighboring cells. Here, we present the first structure of a prokaryotic EndoU toxin in complex with its cognate immunity protein. The contact-dependent growth inhibition toxin CdiA-CTSTECO31 from Escherichia coli STEC_O31 adopts the eukaryotic EndoU fold and shares greatest structural homology with the nuclease domain of coronavirus Nsp15. The toxin contains a canonical His-His-Lys catalytic triad in the same arrangement as eukaryotic EndoU domains, but lacks the uridylate-specific ribonuclease activity that characterizes the superfamily. Comparative sequence analysis indicates that bacterial EndoU domains segregate into at least three major clades based on structural variations in the N-terminal subdomain. Representative EndoU nucleases from clades I and II degrade tRNA molecules with little specificity. In contrast, CdiA-CTSTECO31 and other clade III toxins are specific anticodon nucleases that cleave tRNAGlu between nucleotides C37 and m2 A38. These findings suggest that the EndoU fold is a versatile scaffold for the evolution of novel substrate specificities. Such functional plasticity may account for the widespread use of EndoU effectors by diverse inter-bacterial toxin delivery systems

Can we predict ectotherm responses to climate change using thermal performance curves and body temperatures?

Thermal performance curves (TPCs), which quantify how an ectotherm\u27s body temperature (Tb ) affects its performance or fitness, are often used in an attempt to predict organismal responses to climate change. Here, we examine the key - but often biologically unreasonable - assumptions underlying this approach; for example, that physiology and thermal regimes are invariant over ontogeny, space and time, and also that TPCs are independent of previously experienced Tb. We show how a critical consideration of these assumptions can lead to biologically useful hypotheses and experimental designs. For example, rather than assuming that TPCs are fixed during ontogeny, one can measure TPCs for each major life stage and incorporate these into stage-specific ecological models to reveal the life stage most likely to be vulnerable to climate change. Our overall goal is to explicitly examine the assumptions underlying the integration of TPCs with Tb , to develop a framework within which empiricists can place their work within these limitations, and to facilitate the application of thermal physiology to understanding the biological implications of climate change

The role of leadership in implementing lean manufacturing

It is widely accepted that for the successful implementation of lean manufacturing, the senior management commitment is of great importance. However, the lean journey is usually a long one, and eventually management commitment creeps. Furthermore, the involvement of employees in daily improvements is also critical for the success of implementation. Lean leadership can be considered as a way of sustaining and improving the employee performance in lean production systems. In the present study, a thorough literature review is presented focusing in reviewing the principles of lean leadership and the practices that can lead in improving the employee performance. Furthermore, the characteristics and qualities of lean leader are discussed Paper originally presented at Manufacturing Systems 4.0 – Proceedings of the 50th CIRP Conference on Manufacturing Systems, held 3 – 5 May, 2017, Taichung City, Taiwan

Genomic signatures of mitonuclear coevolution across populations of Tigriopus californicus

The copepod Tigriopus californicus shows extensive population divergence and is becoming a model for understanding allopatric differentiation and the early stages of speciation. Here, we report a high-quality reference genome for one population (similar to 190 megabases across 12 scaffolds, and similar to 15,500 protein-coding genes). Comparison with other arthropods reveals 2,526 genes presumed to be specific to T. californicus, with an apparent proliferation of genes involved in ion transport and receptor activity. Beyond the reference population, we report re-sequenced genomes of seven additional populations, spanning the continuum of reproductive isolation. Populations show extreme mitochondrial DNA divergence, with higher levels of amino acid differentiation than observed in other taxa. Across the nuclear genome, we find elevated protein evolutionary rates and positive selection in genes predicted to interact with mitochondrial DNA and the proteins and RNA it encodes in multiple pathways. Together, these results support the hypothesis that rapid mitochondrial evolution drives compensatory nuclear evolution within isolated populations, thereby providing a potentially important mechanism for causing intrinsic reproductive isolation