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80 results for “Tigriopus”
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.
Data from: Ecological novelty by hybridization: experimental evidence for increased thermal tolerance by transgressive segregation in Tigriopus californicus
Early generations of hybrids can express both genetic incompatibilities and phenotypic novelty. Insights into whether these conflicting interactions between intrinsic and extrinsic selection persist after a few generations of recombination require experimental studies. To address this question, we use interpopulation crosses and recombinant inbred lines (RILs) of the copepod Tigriopus californicus, and focus on two traits that are relevant for the diversification of this species: survivorship during development and tolerance to thermal stress. Experimental crosses between two population pairs show that most RILs between two heat-tolerant populations show enhanced tolerance to temperatures that are lethal to the respective parentals, whereas RILs between a heat-tolerant and a heat-sensitive population are intermediate. Although interpopulation crosses are affected by intrinsic selection at early generational hybrids, most of the sampled F9 RILs have recovered fitness to the level of their parentals. Together, these results suggest that a few generations of recombination allows for an independent segregation of the genes underlying thermal tolerance and cytonuclear incompatibilities, permitting certain recombinant lineages to survive in niches previously unused by parental taxa (i.e., warmer thermal environments) without incurring intrinsic selection.
FIGURE 4 in Phylogenetic relationships among species of Tigriopus (Multicrustacea: Copepoda Harpacticoida) with comments on its biogeography
FIGURE 4. Approximate known distribution range of Tigriopus species in rock-pools of the world (the coordinates of species distributions are shown).
FIGURE. 1 in Phylogenetic relationships among species of Tigriopus (Multicrustacea: Copepoda Harpacticoida) with comments on its biogeography
FIGURE. 1. Phylogenetic strict consensus tree of the genus Tigriopus constructed from morphological data using Bayesian inference. The tree is rooted with Perissocope adiastaltus, P. biarticulatus, P. bayeri, Harpacticella jejuensis, Harpacticus purpureus, Zaus wonchoelleei, Z. hiranoi and Z. aurelia. Numbers on branches correspond to Bayesian posterior probabilities (BPP ≥ 0.95).
FIGURE 3 in Phylogenetic relationships among species of Tigriopus (Multicrustacea: Copepoda Harpacticoida) with comments on its biogeography
FIGURE 3. Ancestral area reconstruction for the genus Tigriopus. Letters refer to the geographical origin of the material analyzed and considered in this study (A=outgroup geographic area, B=Northern Pacific, C= Southern Pacific, D=Indian Ocean, E=Indo-Pacific, F= Northern Atlantic, G=Southern Atlantic, H=Mediterranean Sea, and I= Southern Sea). Nodes are numbered, and ancestral area probability (%) for each node is provided.
FIGURE 2 in Phylogenetic relationships among species of Tigriopus (Multicrustacea: Copepoda Harpacticoida) with comments on its biogeography
FIGURE 2. Distribution of phylogeographic lineages of the genus Tigriopus based of morphologic data.
Data from: Hybrid breakdown weakens under thermal stress in population crosses of the copepod Tigriopus californicus.
The outcome of hybridization can be impacted by environment conditions, which themselves can contribute to reproductive isolation between taxa. In crosses of genetically divergent populations, hybridization can have both negative and positive impacts on fitness, the balance between which might be tipped by changes in the environment. Genetically divergent populations of the intertidal copepod Tigriopus californicus have been shown to differ in thermal tolerance at high temperatures along a latitudinal gradient. In this study a series of crosses were made between pairs of genetically divergent populations of T. californicus and the thermal tolerance of these hybrids was tested. In most cases the first generation hybrids had relatively high thermal tolerance and second generation hybrids were not generally reduced below the less-tolerant parental population for high temperature tolerance. This pattern contrasts with previous studies from crosses of genetically divergent populations of this copepod which often show hybrid breakdown in these second generation hybrids for other measures of fitness. These results suggest that high temperature stress could either increase the positive impacts of hybridization or decrease the negative impacts of hybridization resulting in lowered hybrid breakdown in these population crosses.
Figure 10 in A new species of Tigriopus (Copepoda: Harpacticoida: Harpacticidae) from Thailand with a key to the species of the genus
Figure 10. Tigriopus sirindhornae sp. nov., male. (A) Right antennule, anterior view; (B) A1 distal part; (C) right antenna, anterior view.
Figure 8 in A new species of Tigriopus (Copepoda: Harpacticoida: Harpacticidae) from Thailand with a key to the species of the genus
Figure 8. Tigriopus sirindhornae sp. nov., male. (A) Habitus, dorsal view; (B) habitus, lateral view; (C) caudal seta V.
Figure 5 in A new species of Tigriopus (Copepoda: Harpacticoida: Harpacticidae) from Thailand with a key to the species of the genus
Figure 5. Tigriopus sirindhornae sp. nov., female. (A) Maxilla, posterior view; (B) praecoxal endite; (C, D) coxal endites; (E) basis; (F) maxilliped, anterior view.
Figure 9 in A new species of Tigriopus (Copepoda: Harpacticoida: Harpacticidae) from Thailand with a key to the species of the genus
Figure 9. Tigriopus sirindhornae sp. nov., male. (A) Urosome, dorsal view; (B) urosome, ventral view.
Figure 3 in A new species of Tigriopus (Copepoda: Harpacticoida: Harpacticidae) from Thailand with a key to the species of the genus
Figure 3. Tigriopus sirindhornae sp. nov., female. (A) rostrum, dorsal view; (B) right antennule, anterior view; (C) left antenna, anterior view.
Figure 2 in A new species of Tigriopus (Copepoda: Harpacticoida: Harpacticidae) from Thailand with a key to the species of the genus
Figure 2. Tigriopus sirindhornae sp. nov., female. (A) P5; (B) urosome, ventral view; (C) urosome, dorsal view.
Figure 1 in A new species of Tigriopus (Copepoda: Harpacticoida: Harpacticidae) from Thailand with a key to the species of the genus
Figure 1. Tigriopus sirindhornae sp. nov., female. (A) Habitus, dorsal view; (B) habitus, lateral view; (C) caudal seta V.
FIGURE 9 in Two new species of Tigriopus Norman, 1869 from Chonburi Province, Thailand (Crustacea: Copepoda: Harpacticidae)
FIGURE 9. Tigriopus namsaiensis sp. nov. (♂): (A) urosome, with P6 on both lateral sides; (B) P2, anterior.
FIGURE 13 in Two new species of Tigriopus Norman, 1869 from Chonburi Province, Thailand (Crustacea: Copepoda: Harpacticidae)
FIGURE 13. Tigriopus wannapaensis sp. nov. (♀): (A) mandible, anterior; (B) maxillule, anterior; (C) maxilla, anterior; (D) maxilliped, anterior.
FIGURE 18 in Two new species of Tigriopus Norman, 1869 from Chonburi Province, Thailand (Crustacea: Copepoda: Harpacticidae)
FIGURE 18. Tigriopus wannapaensis sp. nov. (♂): (A) urosome, with P6 on both lateral sides; (B) P2, anterior.
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