Lipid Incorporation During Experimental Decay of Arthropods - Biopolymers: A Molecular Paleontology Approach - page 110

Fig. 6.1 Scanning electron microscopy of cross section of undecayed and decayed shrimp cuticle
( a , b ) and 44 week decayed scorpion cuticle ( c ). ( d ) and ( e ) show surface of shrimp cuticle, unde-
cayed and after 44 weeks decay respectively. ( c ) and ( f ) reveal SEM of the cross section and sur-
face of scorpion cuticle. Note loss of exocuticle in shrimp cuticle after 44 week decay and reduction
in thickness. In contrast, SEM of undecayed and decayed scorpion cuticles showed no obvious
change in thickness and surface features after 44 weeks decay. The scales are in microns
Changes in Macromolecular Chemistry During Decay
Analysis of undecayed shrimp, scorpion and cockroach cuticle using py-GC-MS
revealed the presence of diagnostic chitin markers: 3-acetamidofuran, 3-methyl-5-
acetamidofuran, oxazoline structures, acetylpyridone and 3-acetamido-4-pyrone
together with protein-amino acid derived markers such as phenols, indoles, ben-
zenes and diketopiperazine structures (Figs. 6.2a , 6.3a , 6.4a ). Following 4 weeks
decay (Fig. 6.2b ) the shrimp carcass showed chitin-protein moieties, but in addition
it revealed the presence of n -alkane/alkene homologues extending up to C 24 derived
from a macromolecular n -alkyl (aliphatic) component. Such an n -alkyl component
was also observed in the pyrolyzate after thermodesorption at 310 °C without any
prior chemical treatment, indicating that the n -alkyl component is not an artifact of
analysis. This aliphatic component was detected in all the samples that were allowed
to decay for more than 4 weeks; the fi nal sample (Fig. 6.2c ), at 44 weeks, also
revealed a general reduction in the relative abundance of protein derived moieties
compared to chitin. In contrast, the scorpion and cockroach showed little chemical
change (Fig. 6.3b ); the chitin-protein moieties were retained in relative abundances
similar to those in the fresh sample (Fig. 6.3a ) and there was no evidence of the
presence of n -alkane/alkene peaks (i.e., a macromolecular aliphatic component) in
any of the decayed samples, including the one that decayed for 44 weeks (Fig. 6.4b ).
Figure 6.4a shows an expanded view of the 13 C NMR spectra of model compound
chitin, providing a basis for identifying chitin peaks in the undecayed scorpion and
shrimp sample (Fig. 6.4b ) and those in shrimp and scorpion cuticle decayed for