Lipid Incorporation During Experimental Decay of Arthropods - Biopolymers: A Molecular Paleontology Approach - page 107

fundamental to understanding the formation of hydrogen-rich kerogens (e.g. type
II kerogen; Briggs 1999 ). Analysis of successively older fossil examples revealed
that the transformation to a recalcitrant aliphatic composition is gradual and time
dependent but it has been assumed to require many millions of years. The source
of the aliphatic components is not external (Gupta et al. 2007c ); they are generated
by polymerization of molecules present within the original organism. Analysis of
cuticles showed that these molecules are incorporated lipids (Versteegh et al. 2004 ;
Gupta et al. 2006c , 2007a , c ) often fatty acyl moieties with a dominance of chain
lengths C 16 and C 18 . However, the constituent chitin and protein biopolymers and
lipid molecules are prone to degradation during decay and presumably undergo
transformation prior to and during diagenesis. Thus, we set up a series of experi-
ments to determine the fate of the lipid components and other constituent biopoly-
mers in a decaying arthropod.
Some earlier experimental investigations of the molecular taphonomy of
arthropods focused on the cuticle components of crustaceans (Baas et al. 1995 ;
Stankiewicz et al. 1998a ) and were run for 8 weeks. They revealed the loss of
protein within the fi rst 2 weeks, while chitin remained largely intact for the dura-
tion of the experiments, attesting to its greater preservation potential (Stankiewicz
et al. 1998a ). For the present investigation we used laboratory incubation tech-
niques to determine the fate of the constituent biopolymers over a much longer
period (44 weeks), and compared the chemical changes in shrimps, cockroaches
and scorpions.
Materials and Methods
Specimens of the penaeid shrimp Litopenaeus setiferus (Linnaeus) (~10 cm long),
the scorpion Heterometrus spinifer (~11 cm long), and the cockroach Eublaberus
posticus (~6 cm long) were killed by asphyxiation in air (shrimp) or drowning in
deionised water (scorpion and cockroach - the latter was wrapped in aluminium foil
to make it sink). Six specimens of each arthropod were placed in individual 400 ml
beakers (i.e., 18 in all) with 200 ml of natural sea water obtained from Long Island
Sound at West Haven. An inoculum was prepared in advance by decaying a small
piece of scorpion cuticle and associated tissue for a week in a quantity of the same
sea water with anoxic sediment for a week. This resulted in the development of a
biofi lm. A sample of fresh scorpion cuticle and tissue was reinoculated two more
times successively with a sample of seawater and biofi lm obtained from immedi-
ately adjacent to the tissue in the previous sample in an attempt to concentrate those
microbes colonizing the carcass. Five milliliters of this inoculum was added to the
sea water in each beaker which was then covered with aluminum foil and placed in
an environmental chamber maintained at 30 °C and 80 % relative humidity. A speci-
men of each arthropod was removed from the incubator and processed after 1, 2, 4,
8, 12, and 24 weeks. Material remaining from the second week sample was returned
to the incubator to monitor chemical changes after 44 weeks decay.