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38 results for “Tigriopus californicus”
Food deprivation exposes sex-specific trade-offs between stress tolerance and lifespan in the copepod Tigriopus californicus
<p>Long life is standardly assumed to be associated with high stress tolerance. Previous work shows that the copepod <em>Tigriopus californicus</em> breaks this rule, with longer lifespan under benign conditions found in males, the sex with lower stress tolerance. Here we extended this previous work, raising animals from the same families in food-replete conditions until adulthood and then transferring them to food-limited conditions until all animals perished. As in previous work, survivorship under food-replete conditions favored males. However, under food deprivation lifespan strongly favored females in all crosses. Compared to benign conditions, average lifespan under nutritional stress was reduced by 47% in males but only 32% in females. Further, the sex-specific mitonuclear effects previously found under benign conditions were erased under food limited conditions. Results thus demonstrate that sex-specific lifespan, including mitonuclear interactions, are highly dependent on nutritional environment.</p>
Latitudinal cline for hypoxia but not low pH in Tigriopus californicus
<p>Intertidal organisms must tolerate daily fluctuations in environmental parameters, and repeated exposure to co-occurring conditions may result in tolerance to multiple stressors correlating. The intertidal copepod <em>Tigriopus californicus</em> experiences diurnal variation in dissolved oxygen levels and pH as the opposing processes of photosynthesis and cellular respiration lead to coordinated highs during the day and lows at night. While environmental parameters with overlapping spatial gradients frequently result in correlated traits, less attention has been given to exploring temporally correlated stressors. We investigated whether hypoxia tolerance correlates with low pH tolerance by separately testing the hypoxia and low pH stress tolerance separately of 6 genetically differentiated populations of <em>T. californicus</em>. We independently checked for similarities in tolerance for each of the two stressors by latitude, sex, size, and time since collection as predictors. We found that although hypoxia tolerance correlated with latitude, low pH tolerance did not, and no predictor was significant for both stressors. We concluded that temporally coordinated exposure to low pH and low oxygen did not result in populations developing equivalent tolerance for both. Although climate change alters several environmental variables simultaneously, organisms' abilities to tolerate these changes may not be similarly coupled. </p>
Variance components of sex determination in the copepod Tigriopus californicus estimated from a pedigree analysis
<p>Extensive theory exists regarding population sex ratio evolution that predicts equal sex ratio (when parental investment is equal). In most animals, sex chromosomes determine the sex of offspring, and this fixed genotype for sex has made theory difficult to test since genotypic variance for the trait (sex) is lacking. It has long been argued that the genotype has become fixed in most animals due to the strong selection for equal sex ratios. The marine copepod <em>Tigriopus californicus</em> has no sex chromosomes, multiple genes affecting female brood sex ratio and a brood sex ratio that responds to selection. The species thus provides an opportune system in which to test established sex ratio theory. In this paper, we further our exploration of polygenic sex determination in <em>T. californicus</em> using an incomplete diallel crossing design for analysis of the variance components of sex determination in the species. Our data confirm the presence of extra-binomial variance for sex, further confirming that sex is not determined through simple Mendelian trait inheritance. In addition, our crosses and backcrosses of isofemale lines selected for biased brood sex ratios show intermediate phenotypic means, as expected if sex is a threshold trait determined by an underlying "liability" trait controlled by many genes of small effects. Furthermore, crosses between families from the same selection line had similar increases in phenotypic variance as crosses between families from different selection lines, suggesting families from artificial selection lines responded to selection pressure through different underlying genetic bases. Finally, we estimate heritability of an individual to be male or female on the observed binary scale as 0.09 (95% CI: 0.034-0.14). This work furthers our accumulating evidence for polygenic sex determination in <em>T. californicus</em> laying the foundation for this as a model species in future studies of sex ratio evolution theory.</p>
Statistical methods and data for: Absence of heterosis for hypoxia tolerance in F1 hybrids of Tigriopus californicus
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Latitudinal cline for hypoxia but not low pH in Tigriopus californicus
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Food deprivation exposes sex-specific trade-offs between stress tolerance and lifespan in the copepod Tigriopus californicus
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Variance components of sex determination in the copepod Tigriopus californicus estimated from a pedigree analysis
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Sublethal reproductive costs associated with experimental heat waves in the copepod, Tigriopus californicus
<p>Physiological stress may induce sublethal effects on fitness by limiting energy availability and shifting energy allocation, which can incur reproductive costs. Sublethal reproductive costs may affect vital rates, linking stress events such as heat waves to population demography. Here, we test the hypothesis that heat wave intensity and consecutive days of exposure to heat wave temperatures impact survival and individual reproductive success. We subjected groups of the marine harpacticoid copepod, <i>Tigriopus californicus,</i> to six heat wave regimes that differed in maximum exposure temperature, 26°C or 32°C, and number of consecutive exposure days (1, 2, or 7), and predicted that survival and reproductive costs would increase with heat wave intensity and duration. We measured individual survival and offspring production during the heat waves and for two weeks following the last day of each experimental heat wave. Despite similar survivorship between the two maximum temperature treatments, sublethal effects of heat wave intensity were observed. Consistent with our predictions, individuals that experienced the higher maximum temperature 32°C heat waves produced fewer offspring overall than those that experienced the 26°C heat wave. Furthermore, the number of naupliar larvae (nauplii) per clutch was lower in the 32°C group for egg clutches produced immediately after the final day of exposure. Our results are consistent with the hypothesis that increasing thermal stress can lead to sublethal costs, even with no discernible effects on mortality. Heat waves may not always have lethal effects on individuals, especially for individuals that are adapted to routine exposures to high temperatures, such as those occupying the high intertidal. Costs, however, associated with stress and/or reduced performance due to non-linearities, can affect short-term demographic rates. The effect of these short-term sublethal perturbations is needed to fully understand the potential for population rescue and evolution in the face of rapid climate change.</p>
Data from: Differential gene expression and mitonuclear incompatibilities in fast- and slow-developing inter-population Tigriopus californicus hybrids
<p>Mitochondrial functions are intimately reliant on proteins and RNAs encoded in both the nuclear and mitochondrial genomes, leading to inter-genomic coevolution within taxa. Hybridization can break apart coevolved mitonuclear genotypes, resulting in decreased mitochondrial performance and reduced fitness. This hybrid breakdown is an important component of outbreeding depression and early-stage reproductive isolation. However, the mechanisms contributing to mitonuclear interactions remain poorly resolved. Here we scored variation in developmental rate (a proxy for fitness) among reciprocal F2 inter-population hybrids of the intertidal copepod <em>Tigriopus californicus</em>, and used RNA sequencing to assess differences in gene expression between fast- and slow-developing hybrids. In total, differences in expression associated with developmental rate were detected for 2,925 genes, whereas only 135 genes were differentially expressed as a result of differences in mitochondrial genotype. Up-regulated expression in fast developers was enriched for genes involved in chitin-based cuticle development, oxidation-reduction processes, hydrogen peroxide catabolic processes, and mitochondrial respiratory chain complex I. In contrast, up-regulation in slow developers was enriched for DNA replication, cell division, DNA damage, and DNA repair. Eighty-four nuclear-encoded mitochondrial genes were differentially expressed between fast- and slow-developing copepods, including twelve subunits of the electron transport system (ETS) which all had higher expression in fast developers than in slow developers. Nine of these genes were subunits of ETS complex I. Our results emphasize the major roles that mitonuclear interactions within the ETS, particularly in complex I, play in hybrid breakdown, and resolve strong candidate genes for involvement in mitonuclear interactions.</p>
Data from: Developmental rate displays effects of inheritance but not of sex in interpopulation hybrids of Tigriopus californicus
<p>Coevolved genetic interactions within populations can be disrupted by hybridization resulting in loss of fitness in hybrid individuals (i.e., hybrid breakdown). However, the extent to which variation in fitness-related traits among hybrids is inherited across generations remains unclear, and variation in these traits may be sex-specific in hybrids due to differential effects of genetic incompatibilities in females and males. Here we present two experiments investigating variation in developmental rate among reciprocal inter-population hybrids of the intertidal copepod <em>Tigriopus</em> <em>californicus</em>. Developmental rate is a fitness-related trait in this species that is affected by interactions between mitochondrial-encoded and nuclear-encoded genes in hybrids that result in variation in mitochondrial ATP synthesis capacities. First, we show that F<sub>2</sub>-hybrid developmental rate is equivalent in two reciprocal crosses and is unaffected by sex, suggesting that breakdown of developmental rate is likely experienced equally by females and males. Second, we demonstrate that variation in developmental rate among F<sub>3</sub> hybrids is heritable; times to copepodid metamorphosis of F<sub>4</sub> offspring of fast-developing F<sub>3</sub> parents (12.25 ± 0.05 d, μ ± SEM) were significantly faster than those of F<sub>4</sub> offspring of slow-developing parents (14.58 ± 0.05 d). Third, we find that ATP synthesis rates in these F<sub>4</sub> hybrids are unaffected by the developmental rates of their parents, but that mitochondria from females synthesize ATP at faster rates than mitochondria from males. Taken together, these results suggest that sex-specific effects vary among fitness-related traits in these hybrids and that effects likely associated with hybrid breakdown display substantial inheritance across hybrid generations.</p>
Data from: Developmental rate displays effects of inheritance but not of sex in interpopulation hybrids of Tigriopus californicus
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Sublethal reproductive costs associated with experimental heat waves in the copepod, Tigriopus californicus
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Data from: Variation in developmental temperature alters adulthood plasticity of thermal tolerance in Tigriopus californicus
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Data from: Differential gene expression and mitonuclear incompatibilities in fast- and slow-developing inter-population Tigriopus californicus hybrids
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Data from: Genetic incompatibilities in reciprocal hybrids between populations of Tigriopus californicus with low to moderate mitochondrial sequence divergence
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Data from: Sex without sex chromosomes: genetic architecture of multiple loci independently segregating to determine sex ratios in the copepod Tigriopus californicus
Sex determining systems are remarkably diverse and may evolve rapidly. Polygenic sex determination systems are predicted to be transient and evolutionarily unstable yet examples have been reported across a range of taxa. Here we provide the first direct evidence of polygenic sex determination in Tigriopus californicus, a harpacticoid copepod with no heteromorphic sex chromosomes. Using genetically distinct inbred lines selected for male- and female-biased clutches, we generated a genetic map with 39 SNPs across 12 chromosomes. Quantitative trait locus mapping of sex ratio phenotype (the proportion of male offspring produced by an F2 female) in four F2 families revealed six independently segregating quantitative trait loci on five separate chromosomes, explaining 19% of the variation in sex ratios. The sex ratio phenotype varied among loci across chromosomes in both direction and magnitude, with the strongest phenotypic effects on chromosome 10 moderated to some degree by loci on four other chromosomes. For a given locus, sex ratio phenotype varied in magnitude for individuals derived from different dam lines. These data, together with the environmental factors known to contribute to sex determination, characterize the underlying complexity and potential lability of sex determination, and confirm the polygenic architecture of sex determination in T. californicus.
Data from: Potential fitness tradeoffs for thermal tolerance in the intertidal copepod Tigriopus californicus
Thermal adaptation to spatially varying environmental conditions occurs in a wide range of species, but what is less clear is the nature of fitness trade-offs associated with this temperature adaptation. Here, populations of the intertidal copepod Tigriopus californicus are examined at both local and latitudinal scales to determine whether these populations have evolved differences in their survival under high temperature stress. A clear pattern of increasing high temperature stress tolerance is seen with decreasing latitude, consistent with temperature adaptation. Additionally, there is also evidence for significant variation in thermal tolerance on a smaller scale. The competitive fitness of pairs of northern and southern copepod populations were also examined under a series of lower, more moderate temperatures. These fitness assays show that the southern populations that have the best survival under extreme high temperatures have lowered competitive fitness at the lower temperatures tested, whereas the fitness of the southern populations exceeded that of the northern populations at the highest temperatures tested. Combined, these results suggest that there may be evolutionary trade-offs between performance at high and stressful temperatures and fitness at moderate temperatures in this species.
Data from: Reverse genetics in the tidepool: knockdown of target gene expression via RNA interference in the copepod Tigriopus californicus
Reverse genetic tools are essential for characterizing phenotypes of novel genes and testing functional hypotheses generated from next-generation sequencing studies. RNA interference (RNAi) has been a widely used technique for describing or quantifying physiological, developmental or behavioural roles of target genes by suppressing their expression. The marine intertidal copepod Tigriopus californicus has become an emerging model for evolutionary and physiological studies, but this species is not amenable to most genetic manipulation approaches. As crustaceans are susceptible to RNAi-mediated gene knock-down, we developed a simple method for delivery of gene-specific double-stranded RNA that results in significant suppression of target gene transcription levels. The protocol was examined on five genes of interest, and for each, at least 50% knock-down in expression was achieved. While knock-down levels did not reach 100% in any trial, a well-controlled experiment with one heat-shock gene showed unambiguously that such partial gene suppression may cause dramatic changes in phenotype. Copepods with suppressed expression of heat-shock protein beta 1 (hspb1) exhibited dramatically decreased tolerance to high temperatures, validating the importance of this gene during thermal stress, as proposed by a previous study. The application of this RNAi protocol in T. californicus will be invaluable for examining the role of genes putatively involved in reproductive isolation, mitochondrial function and local adaptation.
Data from: Fitness and morphological outcomes of many generations of hybridization in the copepod Tigriopus californicus
Hybridization between genetically divergent populations is an important evolutionary process, with an outcome that is difficult to predict. We used controlled crosses and freely mating hybrid swarms, followed for up to 30 generations, to examine the morphological and fitness consequences of interpopulation hybridization in the copepod Tigriopus californicus. Patterns of fitness in two generations of controlled crosses were partly predictive of long-term trajectories in hybrid swarms. For one pair of populations, controlled crosses revealed neutral or beneficial effects of hybridization, and hybrid swarm fitness always equalled or exceeded that of the midparent. For a second pair, controlled crosses showed F2 hybrid breakdown, but elevated fitness in backcrosses, and hybrid swarm fitness deviated both above and below that of the parentals. Nevertheless, individual swarm replicates exhibited divergent fitness trajectories over time that were not related in a simple manner to their hybrid genetic composition, and fixation of fitter hybrid phenotypes was not observed. Hybridization did not generally increase overall morphological variation, and underlying genetic changes may have been masked by phenotypic plasticity. Nevertheless, one type of hybrid swarm exhibited a repeatable pattern of transgressively large eggsacs, suggesting a positive effect of hybridization on individual fecundity. Additionally both parental and hybrid swarms exhibited common phenotypic trends over time, indicating common selective pressures in the laboratory environment. Our results suggest that, in a system where much work has focused on F2 hybrid breakdown, the long-term fitness consequences of interpopulation hybridization are surprisingly benign.
Data from: Gene conversion yields novel gene combinations in paralogs of GOT1 in the copepod Tigriopus californicus
Background: Gene conversion of duplicated genes can slow the divergence of paralogous copies over time but can also result in other interesting evolutionary patterns. Islands of genetic divergence that persist in the face of gene conversion can point to gene regions undergoing selection for new functions. Novel combinations of genetic variation that differ greatly from the original sequence can result from the transfer of genetic variation between paralogous genes by rare gene conversion events. Genetically divergent populations of the copepod Tigriopus californicus provide an excellent model to look at the patterns of divergence among paralogs across multiple independent evolutionary lineages. Results: In this study the evolution of a set of paralogous genes encoding putative aspartate transaminase proteins (called GOT1 here) are examined in populations of the copepod T. californicus. One pair of duplicated genes, GOT1p1 and GOT1p2, has regions of high divergence between the copies in the face of apparent on-going gene conversion. The GOT1p2 gene also has unique haplotypes in two populations that appear to have resulted from a transfer of genetic variation via inter-paralog gene conversion. A second pair of duplicated genes GOT1Sr and GOT1Sd also shows evidence of gene conversion, but this gene conversion does not appear to have maintained each as a functional copy in all populations. Conclusions: The patterns of conservation and sequence divergence across this set of paralogous genes among populations of T. californicus suggest that some interesting evolutionary patterns are occurring at these loci. The results for the GOT1p1/GOT1p2 paralogs illustrate how gene conversion can factor in the creation of a mosaic pattern of regions of high divergence and low divergence. When coupled with rare gene conversion events of divergent regions, this pattern can result in the formation of novel proteins differing substantially from either original protein. The evolutionary patterns across these paralogs show how gene conversion can both constrain and facilitate diversification of genetic sequences.
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