TY - JOUR
T1 - Morpho-functional analysis of the explosive defensive system of basal bombardier beetles (Carabidae
T2 - Paussinae: Metriini)
AU - Muzzi, Maurizio
AU - Moore, Wendy
AU - Di Giulio, Andrea
N1 - Funding Information:
We are grateful to Richard C. Brusca for the helpful comments and suggestions; we thank Roberto Romani for his kind help in preparing some of the samples for electron microscopy and Kipling Will for collecting some of the specimens. We appreciated the comments of three reviewers that improved the manuscript. The research was possible thanks to research grants to A. Di Giulio ( CAL, University Roma Tre, Rome, IT ) and the co-funding of the Department of Science of Roma Tre University for the use of LIME electron microscopy facilities.
Publisher Copyright:
© 2019 Elsevier Ltd
PY - 2019/4
Y1 - 2019/4
N2 - Bombardier beetles, belonging to the carabid subfamilies Paussinae and Brachininae, are famous for their unique ability to explosively discharge a hot spray of quinones from their pygidial glands when threatened. The paussine tribe Metriini is broadly acknowledged as the most basal group of bombardiers. In order to complement the available information on the chemical substances and the primitive discharging mechanism of Metriini, we provide a detailed morpho-functional analysis of the explosive defensive system of Metrius contractus Eschscholtz, 1829 and Sinometrius turnai Wrase and J. Schmidt, 2006, representatives of the two genera in this tribe. We use dissections, histology, scanning electron microscopy (SEM), and focused ion beam microscopy (FIB/SEM) to describe and illustrate various levels of anatomical complexity. FIB/SEM microscopy is used to analyse ultrastructural features of the cellular regions, replacing the classical transmission electron microscopy (TEM). Compared to other Paussinae tribes, Metriini lacks the typical flange of Coanda, the elytral fold used to direct the defensive secretions forward, but has a similar arrangement of internal components. We find that the internal components of the explosive defensive system, including the secretory lobes, collecting duct, reservoir chamber, valve, reaction chamber, accessory chamber and accessory glands, are only slightly different between Metrius Eschscholtz, 1829 and Sinometrius Wrase and J. Schmidt, 2006. The accessory chamber to the reaction chamber is a unique, derived character state common to all Paussinae examined and therefore represents a clear apomorphy of the Paussinae. We use the same microscopy techniques as used in a recent publication on the Brachininae, to compare the defensive systems of Metriini and Brachininae. We find a lack of morphological similarity at the ultrastructural level, suggesting that the bombarding mechanism may have evolved independently in the Paussinae and the Brachininae, perhaps in response to different ecological pressures.
AB - Bombardier beetles, belonging to the carabid subfamilies Paussinae and Brachininae, are famous for their unique ability to explosively discharge a hot spray of quinones from their pygidial glands when threatened. The paussine tribe Metriini is broadly acknowledged as the most basal group of bombardiers. In order to complement the available information on the chemical substances and the primitive discharging mechanism of Metriini, we provide a detailed morpho-functional analysis of the explosive defensive system of Metrius contractus Eschscholtz, 1829 and Sinometrius turnai Wrase and J. Schmidt, 2006, representatives of the two genera in this tribe. We use dissections, histology, scanning electron microscopy (SEM), and focused ion beam microscopy (FIB/SEM) to describe and illustrate various levels of anatomical complexity. FIB/SEM microscopy is used to analyse ultrastructural features of the cellular regions, replacing the classical transmission electron microscopy (TEM). Compared to other Paussinae tribes, Metriini lacks the typical flange of Coanda, the elytral fold used to direct the defensive secretions forward, but has a similar arrangement of internal components. We find that the internal components of the explosive defensive system, including the secretory lobes, collecting duct, reservoir chamber, valve, reaction chamber, accessory chamber and accessory glands, are only slightly different between Metrius Eschscholtz, 1829 and Sinometrius Wrase and J. Schmidt, 2006. The accessory chamber to the reaction chamber is a unique, derived character state common to all Paussinae examined and therefore represents a clear apomorphy of the Paussinae. We use the same microscopy techniques as used in a recent publication on the Brachininae, to compare the defensive systems of Metriini and Brachininae. We find a lack of morphological similarity at the ultrastructural level, suggesting that the bombarding mechanism may have evolved independently in the Paussinae and the Brachininae, perhaps in response to different ecological pressures.
KW - Brachininae
KW - Carabidae
KW - FIB/SEM
KW - Paussinae
KW - Pygidial glands
KW - Ultrastructure
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U2 - 10.1016/j.micron.2019.01.003
DO - 10.1016/j.micron.2019.01.003
M3 - Article
C2 - 30660089
AN - SCOPUS:85059952954
SN - 0968-4328
VL - 119
SP - 24
EP - 38
JO - Micron
JF - Micron
ER -