Developmental cost of leg-regenerated Coccinella septempunctata (Coleoptera: Coccinellidae)

Abstract

As larval cannibalism is common under intensive rearing conditions, leg regeneration can help ladybugs adapt to the competitive environment, but whether the leg regeneration leads to side effects on development remains unclear. To analyze the potentially developmental cost of leg regeneration, the developmental period and weight of leg-regenerated Coccinella septempunctata were studied in the laboratory. The results showed that, when the time intervals between the emergency of 4th-instar larva and leg amputation increased, the developmental period of leg-regenerated 4th-instar larvae was gradually prolonged. Significantly developmental delay were also examined at prepupal and pupal stages, and various timings of leg amputation affected the periods of leg-regenerated prepupae/pupae similarly. After the leg was amputated at different larval instars, the developmental delay only occurred at the larval instar when the leg was amputated, whereas other larval instars failed to be extended, and the developmental periods of leg-regenerated prepupae/pupae were affected similarly by the instars of leg amputation. Developmental delays possibly resulted in more consumption by leg-regenerated larvae, and then weight gains at prepupal/pupal stages, but different larval instars of leg amputation affected the weight gain similarly. Both the developmental delay (at 4th-instar larval, prepupal and pupal stages) and weight gain (at pupal and adult stages) in complete/bilateral amputation were longer or greater than those in half/unilateral amputation. However, the thoracic locations of leg amputation impacted the developmental delay and weight gain similarly. Our study indicates that although leg regeneration triggers the developmental cost decreasing the competitive superiority or agility, C. septempunctata larvae still choose to completely regenerate the leg to adapt to complex environments. Thus, in order to remain competitive at adult stages, leg-impaired larvae may make an investment tradeoff between leg regeneration and developmental cost.

Fig 1. Complete amputation: The larval leg of C. septempunctata was amputated at the base of the coxa.

Half amputation: the larval leg was amputated at the base of the tibia. Unilateral amputation: one larval leg was amputated. Bilateral amputation: a pair of legs was amputation. Scale bars equal 1000 μm.

Fig 2. Mean (± SE) developmental periods (d) of leg-regenerated ladybugs at various stages after the leg was amputated at different timings of 4th-instar.

A. Fourth instar larva; B. Prepupa; C. Pupa. Different letters indicate significant differences among the treatments (Tukey’s HSD, P < 0.05).

Fig 3. Mean (± SE) developmental periods (d) of leg-regenerated ladybugs at 4th-instar larval, prepupal and pupal stages.

A. Results in amputation at various larval stages, i.e., the 2nd-, 3rd- or 4th instar, together with CK (normal developmental duration); B. Results in half and complete amputations; C. Results in amputations at various thoracic locations (fore-, mid- or hind leg); D. Results in unilateral and bilateral amputations. Different letters indicate significant differences among the treatments (Tukey’s HSD, P < 0.05). Asterisks indicate significant differences between two treatments (independent t-test, *P < 0.05; **P < 0.01).

Fig 4. Mean (± SE) weights (mg) of leg-regenerated ladybugs at pupal and adult stages.

A. Results in amputations at the 2nd-, 3rd- or 4th instar larval stage, together with CK (normal weight); B. Results in half and complete amputations; C. Results in amputations at various thoracic locations (fore-, mid- or hind leg); D. Results in unilateral and bilateral amputations. Different letters indicate significant differences among the treatments (Tukey’s HSD, P < 0.05). Asterisks indicate significant differences between two treatments (independent t-test, *P < 0.05; **P < 0.01).

Fig 5. Regeneration of fore-, mid- or hind legs of C. Septempunctata adults after the legs bilaterally amputated at 4th-instar larval stages.

Phenotypes after half amputation (A) and complete amputation (C) are shown. In the two columns on the right, B and D are color-level inversion images of the leg segments highlighted, both partial regeneration (red mark) and complete regeneration (aqua mark) are shown. Each scale bar equals 500 μm.