Genetic and acclimatory variation in biophysical properties of insect cuticle lipids (original) (raw)
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Intra-individual variation in cuticular lipids studied using Fourier transform infrared spectroscopy
Journal of Insect Physiology, 1991
We report here a method for studying phase transitions in cuticular lipids of insects. This technique, Fourier transform infrared spectroscopy (FTIR), is more sensitive than previous biophysical methods and is applicable to either lipid extracts or lipids in situ (in cast skins or intact wings). We used FTIR to compare biophysical properties of cuticular lipids in different regions of individual insects. Lipid melting points varied by approx. 10°C in different body regions of the tropical cockroach, Blaberus craniijk, and by almost 30°C in the grasshopper, Melanoplus sunguinipes. Using cast skins, we followed the time course of lipid acclimation to temperature in single individuals of M. sanguinipes. We conclude that FTIR is useful for studies of spatial and temporal differences in cuticular lipids of arthropods.
Journal of Chemical Ecology, 2000
We analyze patterns of variation in cuticular lipids across and within 5 populations of the meadow grasshopper Chorthippus parallelus. This reveals considerable differences between the sexes and between populations, and differences in the pattern of sexual dimorphism between populations. The presence of sexual dimorphism and the extent of differences between populations suggests that divergence has been driven by sexual selection acting through the cuticle's role as a contact pheromone. However, those lipids which differ most between the sexes are not the same as those which vary the most between populations, suggesting that sexual selection alone is not responsible for driving divergence in cuticular composition. We also examine differences in cuticular composition with adult age, revealing that the proportion of all but one of the 14 lipid classes we identify changes significantly with age in at least one population. Overall the pattern of variation with age is fairly consistent across populations, with the proportion of shorter chain compounds increasing with age.
The Journal of experimental biology, 1998
The desert fruit fly Drosophila mojavensis experiences environmental conditions of high temperature and low humidity. To understand the physiological mechanisms allowing these small insects to survive in such stressful conditions, we studied the effects of thermal acclimation on cuticular lipids and rates of water loss of adult D. mojavensis. Mean hydrocarbon chain length increased at higher temperatures, but cuticular lipid melting temperature (Tm) did not. Lipid quantity doubled in the first 14 days of adult life, but was unaffected by acclimation temperature. Despite these changes in cuticular properties, organismal rates of water loss were unaffected by either acclimation temperature or age. Owing to the smaller body size of warm-acclimated flies, D. mojavensis reared for 14 days at 33 degrees C lost water more rapidly on a mass-specific basis than flies acclimated to 25 degrees C or 17 degrees C. Thus, apparently adaptive changes in cuticular lipids do not necessarily result in...
Biochemical Systematics and Ecology, 1995
Cuticular lipids of adult Schistocerca shoshone from six different localities in the southwestern United States were analyzed. All the insects had the same hydrocarbons, but their relative abundance varied between populations and, within a locality, remained more or less constant over time. There were some statistically significant differences in the abundance of some compounds in relation to sex and maturity, but the differences were generally small and of doubtful biological significance. Food type had only minor effects on the relative frequencies of compounds, and insects from different populations retained their identities even when reared together in the laboratory. The cuticular lipids of insects from a population living in an area with high summer temperatures included higher proportions of n-alkanes than those of insects from a less extreme environment. If cuticular hydrocarbons are to be used in taxonomic studies of grasshoppers, it is important to examine specimens from a variety of populations and habitats.
Scientific Reports, 2016
Cuticular hydrocarbons (CHCs) play a major role in the evolution of reproductive isolation between insect species. The CHC profiles of two closely related sympatric grasshopper species, Chorthippus biguttulus and C. mollis, differ mainly in the position of the first methyl group in major methyl-branched CHCs. The position of methyl branches is determined either by a fatty acid synthase (FAS) or by elongases. Both protein families showed an expansion in insects. Interestingly, the FAS family showed several lineage-specific expansions, especially in insect orders with highly diverse methyl-branched CHC profiles. We found five putative FASs and 12 putative elongases in the reference transcriptomes for both species. A dN/dS test showed no evidence for positive selection acting on FASs and elongases in these grasshoppers. However, one candidate FAS showed species-specific transcriptional differences and may contribute to the shift of the methyl-branch position between the species. In addition, transcript levels of four elongases were expressed differentially between the sexes. Our study indicates that complex methyl-branched CHC profiles are linked to an expansion of FASs genes, but that species differences can also mediated at the transcriptional level. Cuticular hydrocarbons (CHCs) are omnipresent on the surface of insects and play a dual role in waterproofing and in chemical communication 1. In many insect species, CHCs are regarded as a central component of mate recognition systems and thus contribute to behavioral isolation between species 2-5. Insects have evolved a vast number of CHCs (> 1000) differing in chain lengths, number and position of double bonds and methyl groups, respectively 6,7. Comparative studies have demonstrated that CHC profiles tend to be species-specific mixtures ranging in complexity from a couple to more than a hundred compounds 8,9. The fundamentals of the CHC biosynthesis in insects are well established 10. The majority of CHCs are synthesized de novo in oenocytes by a sophisticated network of fatty acid synthases (FASs), elongases, desaturases, reductases, and a decarbonylase 10-12. Methyl-branched CHCs result from the incorporating of methylmalonyl-CoA instead of malonyl-CoA early during chain elongation by a microsomal FAS 10,12. Animal FASs are single multifunctional enzymes consisting of two identical monomers 13,14. The FAS monomer contains seven distinct functional domains in the following order (from the N-terminus): β-ketoacyl synthase (KS), malonyl-/acetyl transferase (MAT), β-hydroxyacyl dehydratase (DH), enoyl reductase (ER), β-ketoacyl reductase (KR), acyl carrier protein (ACP), and thioesterase (TE). In most biological systems, the major product released by FASs is palmitic acid (C16:0) 10,13,14. Subsequently, palmitic acid is further elongated to very long-chain fatty acids by members of the elongase family, characterized by the ELO domain (PF01151; GNS1/SUR4 family), with a conserved LHXXHH histidine box motif 15. Despite our basic knowledge about the biosynthesis and composition of many CHC profiles (phenotypes) in a broad range of insect taxa we lack understanding of how new phenotypes may evolve.
Archives of Insect Biochemistry and Physiology, 1995
We examined the biophysical properties of cuticular lipids isolated from the housefly, Musca domestica. Melting ternperaturcs (T,) of surface lipids isolated from female houseflies decreased from 39.3"C to 35.3"C as the females attained sexual maturity and produced sex pheromone, whereas those prepared from males did not change with age. Lipids melted over a 10-25°C temperature range, and their physical properties were a complex function of the properties of the component lipids. The T,,, of total cuticular lipids was slightly below that of cuticular hydrocarbons (HC), the predominant lipid fraction. Hydrocarbons were further fractionated into saturated, unsaturated, and methylbranched components. The order of decreasing Tm was total alkanes > total HCs > methyl-branched alkanes z alkenes. For 1-day-old flies, measured T, s of hydrocarbons were 1.3-5.5"C lower than T, s calculated from a weighted average of T, s for saturated and unsaturated components. For 4-day-old flies, calculated Tms underestimated T, by 11-14°C. o 1995 WiIey-Liss, Inc.
2000
Hydrocarbons (HC) are the most important waterproofing barrier on the cuticle of most terrestrial insects. Yet, the relationships among the type, amount, biophysical properties, and water retardation capacity of constituent HC are poorly understood. Melting temperatures and gas chromatographic profiles of HC of German cockroach tissues of various ages and stages were compared. The melting temperature (T m ) of oothecal HC was highest, T m of epicuticular HC was substantially lower, and that of hemolymph HC was lowest. The epicuticular HC of older nymphs and adults had higher T m than HC of the same sex and stage soon after the molt. The HC of females had higher T m than did male HC. Principal components analysis suggested that normal and 3-and 5-methylalkanes, which were more prevalent on the epicuticle, were associated with higher T m , implicating these components of the HC blend in waterproofing roles. The cockroach ootheca is particularly well protected by an abundance of n-alkanes and its external HC exhibit the highest T m of any HC blend. The methyl ketone sex pheromone components, which are derived from HC, appear to only slightly reduce the T m of the epicuticular HC, probably because the methyl ketones represent only 1.12% of the mass of epicuticular HC. We suggest that the evolution of polar epicuticular chemical signals may be constrained by their tendency to increase water transpiration.
Variation in the surface lipids of the grasshopper, Schistocerca americana (Drury)
Biochemical Systematics and Ecology, 1994
Cuticular lipids of adult Schistocerca americana from a number of different localities were analysed. The most abundant n-alkanes had chain lengths of C25, C27, C29 and C31. The principal methylbranched alkanes had 33, 35 and 37 carbon atoms in the backbone. There was greater variation in the overall patterns of components between populations than within populations. Insects reared in the laboratory on three different species of plant exhibited the same ranges of components, but the pattern differed according to the food plant. No differences were observed in the cuticular hydrocarbons of the two sexes. The variation in the hydrocarbon patterns of laboratory-reared insects was generally within the range of that observed in the field-collected insects, but the effects of food plant show that for taxonomic studies the use of laboratory-reared insects must be viewed with caution.
Lipid melting and cuticular permeability: new insights into an old problem
Journal of Insect Physiology, 2002
The idea that the physical properties of cuticular lipids affect cuticular permeability goes back over 65 years. This proposal has achieved textbook status, despite controversy and the general lack of direct supporting evidence. Recent work supports the standard model, in which lipid melting results in increased cuticular permeability. Surprisingly, although all species studied to date can synthesize lipids that remain in a solid state at environmental temperatures, partial melting often occurs due to the deposition of lipids with low melting points. This will tend to increase water loss; the benefits may include better dispersal of lipids or other compounds across the cuticle or improved communication via cuticular pheromones. In addition, insects with high melting-point lipids are not necessarily less permeable at low temperatures. One likely reason is variation in lipid properties within the cuticle. Surface lipids differ from one region to another, and biophysical studies of model mixtures suggest the occurrence of phase separation between melted and solid lipid fractions. Lipid phase separation may have important implications for insect water balance and chemical communication.
Journal of Chromatography A, 2013
The organic compounds occurring naturally on the cuticles (surfaces) of insects are important for insect communication, help to act as protective water barriers and are useful in chemical taxonomy. Typically the cuticular lipids are only studied by gas chromatography-mass spectrometry (GC-MS) of hexane or pentane extracts, so the normal limitations of GC-MS makes it perhaps unsurprising that compounds with more than about 35 carbon atoms have only rarely been reported. Here we show by high temperature (HT) GC and HTGC-MS of extracts of eleven species of insects from nine genera, that longer chain compounds are actually common. Wax esters and triacylglycerides are virtually ubiquitous in such extracts, but long chain (>C 35) hydrocarbons also sometimes occur. Whilst the latter have occasionally been reported previously from mass spectrometry studies, the use of the HTGC combination with MS allowed even some isobaric isomers to be separated and thus more complete lipid distributions to be monitored. Since the physical properties of cuticular compounds depend on this composition of the mixtures, such differences may influence the water loss rates of the insects, amongst other effects. In addition, the high molecular weight compound profiles may allow species to be more easily differentiated, one from another. It would be interesting to apply these methods to examination of the cuticular lipids of insects on a more routine basis, ideally in combination with MALDI-TOF-MS and imaging methods.