3.1. Multi-generational effects on fitness
Reproductive influences represent the first aspect in fitness evaluation. The effects of DEHTP on the reproduction are shown in Figure 1(A). Collectively, DEHTP caused oscillatory effects over generations. For example, at 0.8 mg/L, DEHTP showed stimulation in F1, inhibition in F2 and stimulation again in F3, and the stimulation was much less in F4. Generally, the stimulations were commonly greater in F3 than in F1, and the inhibitions were usually less severe in F4 than in F2. Moreover, the results of reproduction even showed a regular oscillation pattern, with stimulation in F1 and F3 and inhibition in F2 and F4.
(Figure 1 around here)
The influences on the lifespan represent the second aspect in fitness evaluation. The effects on lifespan (Figure 1(B)) also showed alterations between inhibition and stimulation, but there were no particular concentration- or generation-dependent patterns. Notably, the stimulation of DEHTP on reproduction (Figure 1(A)) was accompanied with inhibition of lifespan in F1 and F3 at most concentrations (Figure 1(B)). Meanwhile, the inhibition on reproduction in F2 and F4 was accompanied with the stimulation on lifespan in the corresponding generations. The opposite relationship between effects on reproduction and those on lifespan showed potential trade-off relationships. Further parallel analysis was performed with the data of reproduction and lifespan in each individual. Results showed that the individual with the greatest stimulation on reproduction showed the greatest inhibition on lifespan, and that with the greatest inhibition on reproduction showed stimulation on lifespan (Figure 1(C)). Moreover, such relationship covered 65% of the total cases, and confirmed the trade-off relationships.
The impacts on the behavior represent the third aspect in fitness evaluation. Nematodes have more quiescence duration at satiety with reverse and Omega turns or no locomotion. In F1, DEHTP inhibited the satiety quiescence duration at 0.8 and 8.0 mg/L (Figure 2(A) and Figure S1). The shorter satiety quiescence duration should spare more time for foraging via body bending and head swing. Out of expectation, the effects of DEHTP in F1 showed inhibitions on body bending at 8.0 mg/L (Figure 2(A) and Figure S2), with stimulations on reverse and Omega turns. In other generations, the effects showed similarities, i.e., inhibition on the satiety quiescence duration and body bending, and stimulation on reverse and Omega turns (Figure 2(B-D)). Such similarities were supported by Spearman’s correlation analysis where the satiety quiescence duration was positively correlated with body bending and head swing but negatively correlated with reverse locomotion (Figure 2(E)). Collectively, the results showed that DEHTP dispatched less time in foraging but more time in backward movement. Moreover, DEHTP also inhibited the pharyngeal pumping (Figure S2), which further aggravated the lack of food supply.
(Figure 2 around here)