3.1 Gut microbes enhance the survival of A. erythraea on
the DA diet
To investigate the DA resistance of A. erythraea , we fed the
copepods toxic P. cuspidata , which had a DA concentration of 4.9
± 0.7 fg cell⁻¹, as well as non-toxic P. brasiliana . Our results
indicate that the respiration rate of A. erythraea was
significantly higher when fed the toxic diet compared to the non-toxic
diet, starting from the second day (p < 0.05, t-test)
(Fig. 2A). Ingestion rates peaked at 2000 cells mL⁻¹ (Fig. S1), which
was used for subsequent daily measurements of A. erythraea’s ingestion rate on different PSN diets. In daily grazing
experiments, A. erythraea maintained a consistent ingestion rate
when fed the non-toxic PSN , averaging 2390 ± 359 cells copepod⁻¹
hour⁻¹. In contrast, the ingestion rate on the toxic diet showed a
slight but significant decline starting from the second day (p < 0.05, t-test) (Fig. 2B). However, survival rates of A.
erythraea over five days revealed no significant differences among the
different diets (log-rank test, p > 0.05; Fig. 2A;
Table S1). These results suggest that although the DA dietsuppressed A. erythraea growth by reducing grazing and
increasing respiration, it did not affect the survival of this
copepod.
To further investigate the role of the gut microbiota of A.
erythraea when copepods have a DA diet, we treated copepods on
different diets with antibiotics and examined their survival. Before
antibiotic treatment, each field-collected copepod harbored an
average of 163,174 gut microbiota. After 24 hours of antibiotic
treatment, the gut microbiota count per copepod decreased to 16,428,
indicating an approximate 90% reduction (Figure S2). When A.
erythraea was treated with antibiotics, resulting in a substantial
reduction in gut microbiota, survival on the toxic diet was
significantly lower than on the non-toxic diet (log-rank test, p < 0.001; Fig. 2A; Table S1). These findings suggest that the
gut microbiota of A. erythraea plays a crucial role in
detoxifying DA and enhancing survival on a DA diet.