C. elegans food choice exhibits effort discounting-like behavior
- Institute of Neuroscience, University of Oregon, United States
Figures
Figure 1 with 1 supplement
Establishment of an effort-discounting paradigm in C. elegans.
(A) Pharyngeal pumping frequency in suspensions of normal (CON) and elongated (CEPH) bacteria. Symbols (box and whisker plot): filled circles, single-worm data points; diamonds, means; numbers, sample size. (B1) Quantification of Oil-Red-O staining of lipid in worms cultured on normal (CON) or elongated (CEPH) bacteria. Median worms from each condition are shown. (B2) Mean pixel intensity of Oil-Red-O staining of lipid in worms cultured on normal (CON) or elongated (CEPH) bacteria. Diamonds, means; numbers, sample size; *, p = 3.20E-04. (C, D) Protein and carbohydrate in worms cultured on normal (CON) and elongated bacteria (CEPH). Columns of data points of the same color are biological replicates run in parallel. Symbols: filled circles, technical replicates (n = 6); diamonds, means of technical replicates. (E) Lipid concentration in worms cultured on normal (CON) and elongated bacteria (CEPH). Symbols: filled circles, biological replicates (n = 3); diamonds, means of biological replicates. (F1) T-maze assay for relative attractiveness of normal and elongated bacteria. Food patches contained sodium azide as a paralytic agent. (F2) Mean preference index in the T-maze assay. Error bars, ± 95% CI.
Figure 1—figure supplement 1
Cephalexin-treated bacteria.
Representative images of control (CON) and cephalexin-treated bacteria (CEPH) labeled with the fluorescent dye BacLight Green. The contrast in CON and CEPH images was optimized separately for each image. After treatment with cephalexin, Comamonas formed long filaments.
Figure 2 with 1 supplement
Food preference in T-maze assays.
(A) T-maze assay for preference for normal (Control) versus elongated bacteria (cephalexin). (B) Effect on preference of raising the optical density of elongated bacteria (CEPH). Mean preference index is shown for assays in which three different optical densities (OD) of elongated bacteria (CEPH) were paired with normal bacteria (CON) at optical density (OD) 1.0. Worms are indifferent when elongated bacteria are at OD 1.5. Numbers, sample size; *, p = 1.52E-08. Error bars ± 95% CI. (C) Tests of predicted indifference points. Mean preference index is shown for three different pairs of optical densities of normal (CON) and elongated (CEPH) bacteria. The gray bar is the indifference point found in panel B. The black bars are novel indifference points found by scaling the optical density of elongated bacteria by the discount factor of 2/3 obtained from the gray bar. Numbers, sample size. Error bars ± 95% CI.
Figure 2—figure supplement 1
Standard models of effort discounting.
There are three main models of effort discounting, each with a unique equation relating effort and reward. is the value of the reward if it were given effort-free. is the level of effort required to obtain the effortful reward. is the discounted value of under conditions of indifference, given level of effort . The quantity is a positive constant representing the chooser’s sensitivity to effort. The quantity in the generalized hyperbolic model is the shape parameter. Discount factors are constant at fixed . In the graph, = 100, α = 0.05, and = 1.5.
Figure 3 with 1 supplement
Kinetic analysis of food-patch-leaving assays.
(A) Food-patch-leaving assays for normal (control) and elongated (cephalexin-treated) bacteria. Open circles, arenas; colored circles, food. A representative track of a single worm is superimposed on each diagram. (B) Three-state kinetic model of behavior in the assay. Each state represents the indicated zone in the arena. (C) Probability of states F, B, and O for normal (CON) and elongated (CEPH) bacteria. Significance was assessed using compositional statistics as described in Figure 3—figure supplement 1. *, p = 4.62-E-05. (D) Rate constants for normal (CON) and elongated (CEPH) bacteria. *, p < 1.19E-03. (E) Locomotion speed for normal (CON) and elongated (CEPH) bacteria on or off food. *, p = 4.59E-04.
Figure 3—figure supplement 1
Statistical test of the effect of cephalexin on state probabilities in Figure 3C.
State probabilities are an instance of compositional data, meaning data that sum to a constant (1 in this case). Such data require special treatment because a decrease in one variable means an increase in at least one other variable. Accordingly, data were first subjected to an isometric log ratio transform (see Materials and methods). The transformation quantifies the change in balance between subsets of the data. Balances are indicated by the numbers in the figure. Here, the control balance between and the reciprocal probabilities and (1.47) is decreased by cephalexin treatment (0.85). A t-test on individual worm balances revealed that significantly decreased while the joint and data significantly increased. In contrast, a similar approach showed that the balance between and was not significantly affected. This indicates that and increased by similar amounts.
Figure 4
Effect of dopamine signaling mutations on preference for normal versus elongated bacteria.
Data are mean preferences measured in T-maze assays. Dopamine signaling was reduced by a nonsense mutation in cat-2 or by deletions of three dopamine receptor genes (dop). Dopamine signaling was increased by a deletion in dat-1. Numbers, sample size; *, p = 1.92E-02. Error bars ± 95% CI.
Figure 5
Preference for normal versus elongated bacteria in N2 and five wild-isolate strains.
Data are mean preferences measured in T-maze assays. N2 and DL238 are significantly different from zero. Numbers, sample size; *, p = 1.12E-02. Error bars ± 95% CI.
Tables
Table 1
Statistical information.
Bold p-values denote significant effects. Note that the Tukey and Dunnett tests are multiple comparison tests and their p-values do not need to be adjusted for multiple comparisons. Replicates were biological unless otherwise indicated.
| Row | Figure | Test | Effect or comparison tested | Units of replication or sampling | Number of replicates | Statistic | Statistic value | DF 1 or combined DF | p | Effect size metric | Effect size |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 1A | Mann–Whitney | Cephalexin | Worms | 99, 98 | U | 4178 | – | 9.23E−02 | Rank-biserial correlation (r) | 0.13 (small) |
| 2 | 1B2 | Mann–Whitney | Cephalexin | Worms | 44, 49 | U | 618 | – | 3.20E−04 | Rank-biserial correlation (r) | 0.43 (moderate) |
| 3 | 1C | t-Test | Cephalexin | Biol. Replicate | 3, 3 | t | 0.1 | 2 | 9.28E−01 | Cohen's d | 0.08 (small) |
| 4 | 1D | t-Test | Cephalexin | Biol. Replicate | 3, 3 | t | 0.1 | 2 | 9.31E−01 | Cohen's d | 0.08 (small) |
| 5 | 1E | t-Test | Cephalexin | Tech. Replicate | 3, 3 | t | 0.12 | 2 | 9.91E−01 | Cohen's d | 0.01 (small) |
| 6 | 1F2 | t-Test | Mean not = 0 | Assay plates | 108 | t | 1.65 | 104 | 3.56E−01 | Cohen's d | 0.16 (small) |
| 7 | 2B | One-way ANOVA | OD ratios | Assay plates | 137, 106, 73 | F | 19.07 | 2 | 1.52E−08 | Eta squared | 0.11 (moderate) |
| 8 | 2B | t-Test | Mean not = 0 | Assay plates | 137 | t | 3.2 | 136 | 1.69E−03 | Cohen's d | 0.27 (small) |
| 9 | 2B | t-Test | Mean not = 0 | Assay plates | 73 | t | 1.99 | 72 | 2.06E−07 | Cohen's d | 0.67 (large) |
| 10 | 2B | t-Test | Mean not = 0 | Assay plates | 106 | t | 1.08 | 105 | 2.82E−01 | Cohen's d | 0.10 (small) |
| 11 | 2C | One-way ANOVA | OD ratios | Assay plates | 120, 106, 132 | F | 0.83 | 2 | 4.37E−01 | Eta squared | 0.00 (negligible) |
| 12 | 2C | t-Test | Mean not = 0 | Assay plates | 120 | t | 0.71 | 119 | 4.80E−01 | Cohen's d | 0.06 (small) |
| 13 | 2C | t-Test | Mean not = 0 | Assay plates | 106 | t | 1.08 | 105 | 2.82E−01 | Cohen's d | 0.10 (small) |
| 14 | 2C | t-Test | Mean not = 0 | Assay plates | 132 | t | 0.64 | 131 | 5.22E−01 | Cohen's d | 0.06 (small) |
| 15 | 3C | t-Test | PF vs (PO, PB) | Single worm | 66, 60 | t | 4.22 | 123.57 | 4.62E−05 | Cohen's d | 0.75 (medium) |
| 16 | 3C | t-Test | PO vs PB | Single worm | 66, 60 | t | 0.57 | 116.99 | 5.73E−01 | Cohen's d | 0.10 (small) |
| 17 | 3D | One-way ANOVA | Transition type | Single worm | 66, 60 | F | 24.71 | 3 | 4.22E−14 | Eta squared | 0.22 (large) |
| 18 | 3D | Tukey | kFB, kBF | Single worm | 66, 60 | q | 3.68 | 122 | <1.00E−07 | Cohen's d | 2.199391 (large) |
| 19 | 3D | Tukey | kBO, kOB | Single worm | 66, 60 | q | 3.68 | 122 | 4.30E−06 | Cohen's d | 0.68 (medium) |
| 20 | 3D | Tukey | kBO, kBF | Single worm | 66, 60 | q | 3.68 | 122 | 6.00E−07 | Cohen's d | 1.60 (large) |
| 21 | 3D | Tukey | kOB, kBF | Single worm | 66, 60 | q | 3.68 | 122 | 9.77E−01 | Cohen's d | 0.051 (negligible) |
| 22 | 3D | Tukey | kFB, kBO | Single worm | 66, 60 | q | 3.68 | 122 | 4.86E−01 | Cohen's d | 0.91 (large) |
| 23 | 3D | Tukey | kOB, kFB | Single worm | 66, 60 | q | 3.68 | 122 | 0 | Cohen's d | 0.88 (large) |
| 24 | 3D | MANOVA | Cephalexin | Single worm | 66, 60 | F | 16.44 | 4121 | 8.77E−11 | Eta squared (partial) | 0.35 (large) |
| 25 | 3D1 | t-Test | Cephalexin | Single worm | 66, 60 | t | 7.38 | 79.39 | 1.36E−10 | Cohen's d | 1.36 (large) |
| 26 | 3D2 | t-Test | Cephalexin | Single worm | 66, 60 | t | 3.32 | 118.69 | 1.18E−03 | Cohen's d | 0.60 (medium) |
| 27 | 3D3 | t-Test | Cephalexin | Single worm | 66, 60 | t | 0.28 | 123.25 | 7.83E−01 | Cohen's d | 0.05 (negligible) |
| 28 | 3D4 | t-Test | Cephalexin | Single worm | 66, 60 | t | 1.38 | 95.7 | 1.70E−01 | Cohen's d | 0.24 (small) |
| 29 | 3E | Two-way ANOVA | Cephalexin | Single worm | 66, 60 | F | 5.24 | 1 | 2.29E−02 | Eta squared | 0.02 (small) |
| 30 | 3E | Two-way ANOVA | Food | Single worm | 66, 60 | F | 0.7 | 1 | 4.00E−01 | Eta squared | 0.00 (negligible) |
| 31 | 3E | Two-way ANOVA | Cephalexin × Food | Single worm | 66, 60 | F | 6.66 | 1 | 1.10E−02 | Eta squared | 0.03 (small) |
| 32 | 3E | t-Test | Cephalexin | Single worm | 66, 60 | t | 3.68 | 115.91 | 4.59E−04 | Cohen's d | 0.66 (medium) |
| 33 | 3E | t-Test | Cephalexin | Single worm | 66, 60 | t | 0.19 | 123.94 | 8.47E−01 | Cohen's d | 0.034 (negligible) |
| 34 | 4 | One-way ANOVA | Strain | Assay plates | 137, 179, 165, 160, 175, 180 | F | 7.69 | 3 | 4.71E−05 | Eta squared | 0.03 (small) |
| 35 | 4 | Dunnett test | q | 2.5 | 649 | ||||||
| 36 | N2 vs cat-2 | Assay plates | 137, 179 | q | 0.97 | 7.72E−01 | |||||
| 37 | N2 vs dat-1 | Assay plates | 137, 164 | q | 1.3 | 5.37E−01 | |||||
| 38 | N2 vs dop-1 | Assay plates | 137, 180 | q | –1.61 | 3.33E−01 | |||||
| 39 | N2 vs dop-2 | Assay plates | 137, 176 | q | 1.25 | 5.71E−01 | |||||
| 40 | N2 vs dop-3 | Assay plates | 137, 160 | q | 2.78 | 1.92E−02 | Cohen's d | 0.50 (medium) | |||
| 41 | 4 | t-Test | Mean not = 0 | Assay plates | 180 | t | 0.65 | 159 | 5.14E−01 | Cohen's d | 0.05 (small) |
| 42 | 5 | One-way ANOVA | Strain | Assay plates | 137, 137, 129, 184, 178, 146 | F | 3.3 | 5 | 5.83E−03 | Eta squared | 0.018 (small) |
| 43 | 5 | Dunnett test | q | 2.51 | 905 | ||||||
| 44 | N2 vs DL238 | Assay plates | 137, 137 | q | 0.31 | 9.98E−01 | |||||
| 45 | N2 vs CB4856 | Assay plates | 137, 129 | q | 0.51 | 9.81E−01 | |||||
| 46 | N2 vs JU258 | Assay plates | 137,184 | q | 2.26 | 9.42E−02 | |||||
| 47 | N2 vs MY23 | Assay plates | 137, 178 | q | 2.46 | 5.81E−02 | |||||
| 48 | N2 vs JU775 | Assay plates | 137, 146 | q | 3.03 | 1.12E−02 | Cohen's d | 0.68 (medium) | |||
| 49 | 5 | t-Test | Mean not = 0 | Assay plates | 146 | t | 0.36 | 145 | 1.03E−01 | Cohen’s d | 0.13 (small) |
| 50 | 5 | t-Test | Mean not = 0 | Assay plates | 137 | t | 2.02 | 136 | 4.56E−02 | Cohen's d | 0.17 (small) |
Key resources table
| Reagent type (species) or resource | Designation | Source or reference | Identifiers | Additional information |
|---|---|---|---|---|
| Strain, strain background (E. coli) | OP50 | CGC* | RRID:WB-STRAIN:WBStrain00041969 | Worm maintenance |
| Strain, strain background (Comamonas spp.) | DA1877 | CGC | RRID:WB-STRAIN:WBStrain00040995 | Behavioral testing |
| Strain, strain background (C. elegans) | N2 | CGC | RRID:WB-STRAIN:WBStrain00000001 | All WT assays |
| Strain, strain background (C. elegans) | cat-2(e1112) | CB | RRID:WB-STRAIN:WBStrain00004246 | Behavioral testing |
| Strain, strain background (C. elegans) | dat-1(ok157) | CGC | RRID:WB-STRAIN:WBStrain000333294 | Behavioral testing |
| Strain, strain background (C. elegans) | dop-1(vs101) | CGC | RRID:WB-STRAIN:WBStrain00026368 | Behavioral testing |
| Strain, strain background (C. elegans) | dop-2(vs105) | CGC | RRID:WB-STRAIN:WBStrain00026373 | Behavioral testing |
| Strain, strain background (C. elegans) | dop-3(vs106) | CGC | RRID:WB-STRAIN:WBStrain00026374 | Behavioral testing |
| Strain, strain background (C. elegans) | Wild isolate | CGC | RRID:WB-STRAIN:WBStrain00005835 | Behavioral testing |
| Strain, strain background (C. elegans) | Wild isolate | CGC | RRID:WB-STRAIN:WBStrain00004602 | Behavioral testing |
| Strain, strain background (C. elegans) | Wild isolate | CGC | RRID:WB-STRAIN:WBStrain00022850 | Behavioral testing |
| Strain, strain background (C. elegans) | Wild isolate | CGC | RRID:WB-STRAIN:WBStrain00027669 | Behavioral testing |
| Strain, strain background (C. elegans) | Wild isolate | CGC | RRID:WB-STRAIN:WBStrain00023072 | Behavioral testing |
| Chemical compound, drug | Cephalexin hydrate | Thermo Fisher | J6317206 | Bacteria elongation |
| Other | Oil-Red-O | Sigma-Aldrich | 00625 | Histological stain |
| Other | BacLight Green | Thermo Fisher | B-35000 | Histological stain |
| Software, algorithm | Igor Pro | Wavemetrics | Version 9.05 | Behavioral testing, image analysis |
| Software | R | R Core Team (2024) | Version 4.4.2 (2024-10-31) | Statistical analysis |
| Software, algorithm | WormLab | MBF Bioscience | Version 2024 | Video analysis |
-
*
Caenorhabditis Genetics Center.
Additional files
-
MDAR checklist
- https://cdn.elifesciences.org/articles/106792/elife-106792-mdarchecklist1-v1.docx
-
Source code 1
Electropharyngeogram analysis routines.
- https://cdn.elifesciences.org/articles/106792/elife-106792-code1-v1.zip
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Source data 1
Raw data for Figure 1A, B, F2, Figure 2B, C, Figure 3C, D, Figure 4 and Figure 5.
- https://cdn.elifesciences.org/articles/106792/elife-106792-data1-v1.xlsx
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C. elegans food choice exhibits effort discounting-like behavior
eLife 14:RP106792.
https://doi.org/10.7554/eLife.106792.3
