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Changes in tracheal system structure and function within an instar in the caterpillar, Manduca sexta (879.23)
Author(s) -
Greenlee Kendra,
Pedersen Paul,
Back Barbarah
Publication year - 2014
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.28.1_supplement.879.23
Subject(s) - instar , anatomy , moulting , biology , manduca sexta , caterpillar , ecdysis , insect , ecology , larva
Juvenile grasshoppers and caterpillars are less tolerant of hypoxia as they grow between molts. One possible explanation is that substantial soft tissue growth occurs between molts, compressing the tracheal system when the exoskeleton can expand no further. In grasshoppers, femoral air sacs become compressed, as they age between molts. Juvenile insects periodically molt their exoskeletons to enable the expansion of larger cuticular structures within. Respiratory structures are part of the exoskeleton and must also molt to grow larger. However, the mechanism for the decrease in hypoxia tolerance in caterpillars is unknown. To test the hypothesis that the caterpillar tracheal system becomes compressed during the intermolt period (instar), we used synchrotron x‐ray imaging to record tracheal system structure and function. Caterpillars at the beginning and end of each instar were placed in 21% and 1% oxygen. Maximum and minimum diameters of two major tracheae, one in the head and one in the hind segment were measured, along with body size and mass. Body mass and length increased logarithmically from hatchling to fifth instar, while head width increased only when insects molted. Maximum tracheal diameter also increased after molting, most significantly from the fourth to the fifth instar. In support of our hypothesis, both minimum and maximum tracheal diameters varied with stage differently depending on the instar. Minimum tracheal diameter decreased depending on the instar, because only older caterpillars exhibit tracheal compression in hypoxia. In older instars, head tracheae were larger than hind tracheae. In addition, in contrast to our previous work, tracheae in both the head and hind segments scaled with mass to the 0.3 power. Together, these data demonstrate that the decreased hypoxia tolerance within an instar is due to the fixed size of major tracheae and provide a comprehensive view of how the caterpillar respiratory system changes in structure and function within an instar. Grant Funding Source : Supported by NSF IOS 0953297