Enzymological and radiotracer studies of lipid metabolism in the flight-capable and flightless morphs of the wing-polymorphic cricket,Gryllus firmus

The flight-capable morph of the wing-polymorphic cricket, Gryllus firmus, exhibited significantly higher activities of each of five lipogenic enzymes compared with the obligately flightless morph on a standard and a high-carbohydrate diet during early adulthood. Similarly, the rate of incorporation of [14C]-acetate into total lipid was higher in the flight-capable morph during this time. By contrast, activities of lipogenic enzymes and rates of lipid biosynthesis, in general, did not differ between morphs on a low nutrient diet during early adulthood. Differences in lipid biosynthesis account for previously documented differences in lipid reserves between morphs on some, but not all, diets. Results of the present and previous studies indicate that increased lipid biosynthesis in the flight capable morph on standard and high-carbohydrate diets constitutes an important adaptation for flight (production of lipid flight fuel). Lipid biosynthesis is negatively correlated with ovarian growth, and may be an important biochemical component of the trade-off between flight capability and ovarian growth in G. firmus. Morphs also differed in activities of three enzymes of lipid catabolism. However, the extent to which variation in activities of these enzymes between morphs results in variation in lipid catabolism is unclear. Finally, the flight-capable morph had a substantially higher activity of alanine aminotransferase in the fat body. Amino acids may be utilized for lipid biosynthesis or energy production to a greater degree in the dispersing morph compared with the oligately flightless morph. This study is the first to document differences in intermediary metabolism that underlie adaptations of morphs of a dispersal-polymorphic species for flight vs. egg production.     

Morph-dependent fatty acid oxidation in a wing-polymorphic cricket: implications for the trade-off between dispersal and reproduction

Although a considerable amount of information is available on the ecology and physiology of wing polymorphism, much less is known about the biochemical-genetic basis of morph specialization for dispersal versus reproduction. Previous studies have shown that the dispersing morph of the wing-polymorphic cricket, Gryllus firmus, prioritizes the accumulation of triglyceride flight fuel over ovarian growth, while the opposite occurs in the flightless morph during the first week of adulthood. In this study, we compared the in vivo rate of lipid oxidation between genetic stocks of flight-capable versus flightless morphs to determine the role of lipid catabolism in morph specialization for flight versus reproduction. During the first five days of adulthood, in the absence of flight, fatty acid oxidation was substantially lower in the dispersing morph relative to the flightless morph, when either radiolabeled acetate or palmitate was used as a substrate. Differences between the morphs in fatty acid oxidation were genetically based, occurred co-incident with morph-specific differences in triglyceride accumulation and ovarian growth, and were observed on a variety of diets. A genetically based trade-off in the relative conversion of palmitate into CO(2) versus triglyceride was observed in morphs of G. firmus. Decreased oxidation of fatty acid and increased biosynthesis of triglyceride, both appear to play an important role in flight fuel accumulation, and hence morph specialization for flight. Conversely, increased oxidation of fatty acid likely fuels the enhanced ovarian growth in the flightless morph. The results of the present study on fatty acid catabolism, and previous studies on triglyceride and phospholipid biosynthesis, provide the first direct evidence that genetically based differences in in vivo flux through pathways of intermediary metabolism underlie a trade-off between flight capability and reproduction--a trade-off of central importance in insects.     

Intermediary metabolism and life-history trade-offs: differential metabolism of amino acids underlies the dispersal-reproduction trade-off in a wing-polymorphic cricket

Although the differential flow of metabolites through alternate pathways of intermediary metabolism is thought to be an important functional cause of life-history trade-offs, this phenomenon remains understudied. Using a radiolabeled amino acid, we quantified genetic differences in in vivo amino acid metabolism between morphs of the wing-polymorphic cricket Gryllus firmus that trade off early-age reproduction and dispersal capability. Lines selected for the flight-capable morph, which delays reproduction, oxidized a greater proportion of radiolabeled glycine and converted a greater amount into somatic lipid, mainly triglyceride (flight fuel). By contrast, lines selected for the flightless, reproductive morph converted a substantially greater proportion of glycine into ovarian protein. Compensatory interactions between amino acid and lipid metabolism make up a key aspect of specialization for dispersal versus reproduction in G. firmus: increased oxidation of amino acids by the flight-capable morph spares fatty acid for enhanced conversion into triglyceride flight fuel. By contrast, increased oxidation of fatty acid by the flightless morph spares amino acids for enhanced biosynthesis of ovarian protein. Studies of amino acid and lipid metabolism in G. firmus currently represent the most detailed analyses of genetic modifications of intermediary metabolism that underlie a functionally important life-history trade-off found in natural populations.     

Nutrient absorption and utilization by wing and flight muscle morphs of the cricket Gryllus firmus: implications for the trade-off between flight capability and early reproduction

Absorption efficiency (AD, approximate digestibility, assimilation efficiency) of various macronutrients and conversion of absorbed nutrients to biomass (ECD) were compared among the two types of flightless morph and the flight-capable morph of the cricket, Gryllus firmus. No biologically significant phenotypic or genetic difference in AD for carbohydrate, protein or lipid was observed among morphs fed either a high-nutrient (100%) or a low-nutrient (25%) diet. Thus, previously-documented differences among adult morphs in carbohydrate and lipid content must be caused by processes other than variation in nutrient absorption by morphs during adulthood. Relative absorption efficiency of total dry mass of food by morphs of G. firmus appears to be a valid indicator of relative AD of total calories. Morphs did not differ phenotypically or genetically in the excretion of end products of nitrogen metabolism (uric acid, hypoxanthine plus xanthine) on either the high nutrient or the low nutrient diet. Nutritional indices corrected for excreted nitrogenous metabolites were very similar to uncorrected indices, and the pattern of variation among the morphs was the same for corrected or uncorrected values. Each of the two types of flightless morph converted a greater proportion of absorbed nutrients into body mass, mainly ovaries, and allocated a smaller proportion of assimilated nutrients to respiration than did the flight-capable morph. Moreover, the trade-off between respiration and early reproduction was substantially magnified on the low nutrient diet. These results extend previous findings of a trade-off between flight capability and early reproduction in wing-polymorphic Gryllus species (1) to diets of very different nutrient quantity, and (2) to flightlessness arising from different causes: blockage of flight muscle development in juveniles vs histolysis of fully-developed flight muscles in adults.     

Life-history evolution and the microevolution of intermediary metabolism: activities of lipid-metabolizing enzymes in life-history morphs of a wing-dimorphic cricket

Although a considerable amount of information is available on the ecology, genetics, and physiology of life-history traits, much more limited data are available on the biochemical and genetic correlates of life-history variation within species. Specific activities of five enzymes of lipid biosynthesis and two enzymes of amino acid catabolism were compared among lines selected for flight-capable (LW[f]) versus flightless (SW) morphs of the cricket Gryllus firmus. These morphs, which exist in natural populations, differ genetically in ovarian growth (100-400% higher in SW) and aspects of flight capability including the size of wings and flight muscles, and the concentration of triglyceride flight fuel (40% greater in LW[f]). Consistently higher activity of each enzyme in LW(f) versus SW-selected lines, and strong co-segregation between morph and enzyme activity, demonstrated genetically based co-variance between wing morph and enzyme activity. Developmental profiles of enzyme activities strongly paralleled profiles of triglyceride accumulation during adulthood and previous measures of in vivo lipid biosynthesis. These data strongly imply that genetically based elevation in activities of lipogenic enzymes, and enzymes controlling the conversion of amino acids into lipids, is an important cause underlying the elevated accumulation of triglyceride in the LW(f) morph, a key biochemical component of the trade-off between elevated early fecundity and flight capability. Global changes in lipid and amino-acid metabolism appear to have resulted from microevolutionary alteration of regulators of metabolism. Finally, strong genotype x environment (diet) interactions were observed for most enzyme activities. Future progress in understanding the functional causes of life-history evolution requires a more detailed synthesis of the fields of life-history evolution and metabolic biochemistry. Wing polymorphism is a powerful experimental model in such integrative studies.     

Genetic and diurnal variation in the juvenile hormone titer in a wing-polymorphic cricket: implications for the evolution of life histories and dispersal

The wing-polymorphic cricket, Gryllus firmus, contains (1) a flight-capable morph (LW(f)) with long wings and functional flight muscles, (2) a flightless morph with reduced wings and underdeveloped flight muscles (SW), and (3) a flightless morph with histolyzed flight muscles but with fully developed wings (LW(h)). The LW(f) morph differed genetically from the SW morph and phenotypically from the LW(h) morph in the size of flight muscles, ovarian growth during the first week of adulthood, and the hemolymph titer of juvenile hormone (JH). This is the first study to document that phenotypes that differ genetically in morphological aspects of dispersal capability and in ovarian growth also differ genetically in the titer of a hormone that potentially regulates those traits. The JH titer rose 9-100-fold during the photophase in the flight-capable LW(f) morph but did not change significantly during this time in either flightless morph. Prolonged elevation of the in vivo JH titer in flight-capable females, by topical application of a hormone analogue, caused a substantial increase in ovarian growth and histolysis of flight muscles. The short-term, diurnal rise in the JH titer in the dispersing morph may be a mechanism that allows JH to positively regulate nocturnal flight behavior, while not causing maladaptive histolysis of flight muscles and ovarian growth. This is the first demonstration of naturally occurring, genetically based variation for diurnal change in a hormone titer in any organism.     

The physiology of life-history trade-offs: experimental analysis of a hormonally induced life-history trade-off in Gryllus assimilis

Abstract Adult Gryllus assimilis given an analog of juvenile hormone exhibited reduced flight muscles and enlarged ovaries similar to those found in naturally occurring flightless individuals of species that are polymorphic for dispersal capability. Control and hormone-treated (flightless) G. assimilis did not differ in the amount of food consumed or assimilated on any of three diets that differed in nutrient quantity. Thus, enhanced ovarian growth of flightless individuals resulted from increased allocation of internal nutrients to reproduction (i.e., a trade-off) rather than from increased acquisition of nutrients. Compared with flight-capable controls, flightless G. assimilis also had reduced whole-organism respiration, reduced respiration of flight muscles, and reduced lipid and triglyceride (flight fuel) reserves. These differences are remarkably similar to those between naturally occurring flightless and flight-capable morphs of other Gryllus species. Results collectively suggest that the increased allocation of nutrients to ovarian growth in flightless G. assimilis and other Gryllus species results from reduced energetic costs of flight muscle maintenance and/or the biosynthesis or acquisition of lipids. Reduction in these energetic costs appears to be an important driving force in the evolution of flightlessness in insects. Respiratory metabolism associated with flight capability utilizes an increasing proportion of the energy budget of crickets as the quantity of nutrients in the diet is decreased. This leads to a magnification of greater ovarian growth of flightless versus flight-capable individuals on nutrient-poor diets.     

The endocrine-genetic basis of life-history variation: the relationship between the ecdysteroid titer and morph-specific reproduction in the wing-polymorphic cricket Gryllus firmus

The hormonal basis of variation in life-history traits is a poorly studied topic in life-history evolution. An important step in identifying the endocrine-genetic causes of life-history variation is documenting statistical and functional associations between hormone titers and genotypes/phenotypes that vary in life-history traits. To this end, we compared the blood ecdysteroid titer and the mass of the ovaries during the first week of adulthood among a flight-capable morph and two flightless morphs of the wing-polymorphic cricket Gryllus firmus. Ecdysteroids are a group of structurally related hormones that regulate many important aspects of reproduction in insects. Both the ecdysteroid titer and ovarian mass were significantly higher in each of two flightless morphs compared with the flight-capable morph throughout the first week of adulthood. Genetically based differences in the ecdysteroid titer and ovarian mass between morphs from different selected lines were similar to phenotypically based differences among morphs from the same control (unselected) lines. By day 7 of adulthood, ovaries were typically 200-400% larger and the ecdysteroid titer was 60-300% higher in flightless versus the flight-capable morph. In addition, highly significant, positive, phenotypic correlations were observed between the ecdysteroid titer and ovarian mass in pooled samples of the two flightless and flight-capable crickets from control lines or from selected lines. The ecdysteroid titer was sufficiently elevated in the flightless morphs to account for their elevated ovarian growth. This is the first direct documentation that naturally occurring phenotypes/genotypes that differ in early fecundity, a key life-history trait, also differ phenotypically and genetically in the titer of a key reproductive hormone that potentially regulates that trait.     

Biochemical basis of specialization for dispersal vs. reproduction in a wing-polymorphic cricket: morph-specific metabolism of amino acids

The biochemical basis of specializations for dispersal vs. reproduction is an understudied aspect of dispersal polymorphism in insects. Using a radiolabelled amino acid, we quantified differences in in vivo amino acid metabolism between morphs of the wing-polymorphic cricket, Gryllus firmus, that trade-off early age reproduction and dispersal capability. Studies were conducted in crickets fed a variety of diets expected to influence amino acid and lipid metabolism. On the day of molt to adulthood, prior to the morph-specific trade-off between ovarian growth and biochemical preparation for flight (e.g. biosynthesis of triglyceride flight fuel), morphs did not differ in any aspect of amino acid metabolism. However, on day 5 of adulthood, when the morph-specific trade-off between ovarian growth and flight fuel production was manifest, the morphs differed substantially in each of the three aspects of amino acid metabolism studied: conversion to protein, oxidation, and conversion to lipid. Morphs also differed in degree of allocation of products of amino acid metabolism to ovaries vs. the soma. Most importantly, morphs differed in the relative metabolism of radiolabelled glycine through these pathways (i.e. biochemical trade-offs), and in the relative allocation of end products of amino acid metabolism to the soma vs. ovaries (allocation trade-offs). A functionally important interaction between amino acid and lipid metabolism was noted: greater oxidation of amino acids in the flight-capable morph spared fatty acids for enhanced conversion into triglyceride flight fuel. By contrast, greater oxidation of fatty acids by the flightless morph spared amino acids for enhanced conversion into ovarian protein. Diet significantly affected amino acid metabolism. However, MORPHxDIET interactions were rare and morphs differed in amino acid metabolism to a similar degree under the range of diets tested.     

Effect of a juvenile hormone analogue on lipid metabolism in a wing-polymorphic cricket: implications for the endocrine-biochemical bases of life-history trade-offs

The wing-polymorphic cricket, Gryllus firmus, has a flight-capable morph (LW[f]: long winged with functional flight muscles) and a flightless morph (SW: short winged with reduced nonfunctional flight muscles) that differ genetically in many aspects of lipid metabolism. To determine whether these differences result from genetically based alterations in endocrine regulation, the juvenile hormone mimic, methoprene, was applied to the LW(f) morph. This hormone manipulation converted the LW(f) morph into a SW phenocopy with respect to all aspects of lipid metabolism studied; that is, methoprene application decreased in vivo biosynthesis of total lipid and triglyceride, increased absolute and relative biosynthesis of phospholipid, increased oxidation of fatty acids, and decreased in vitro specific activities of each of six lipogenic enzymes and a transaminase. Furthermore, methoprene increased ovarian growth and decreased fat body mass and flight muscle mass in the LW(f) morph. Differences in each of these biochemical, morphological, or reproductive traits between hormone-treated and control LW(f) females were similar in magnitude to differences between unmanipulated LW(f) and SW females. Variation in endocrine regulation contributes significantly to genetically based differences in lipid metabolism between LW(f) and SW females. This is the first evidence for endocrine regulation of a genetically based life-history trade-off operating via hormonal effects on specific metabolic pathways and enzymes of intermediary metabolism.     

Juvenile hormone titer and morph-specific reproduction in the wing-polymorphic cricket,Gryllus firmus

Juvenile hormone titers and reproductive characteristics were measured in adult wing and flight-muscle morphs of the wing-polymorphic cricket, Gryllus firmus, during the first week of adulthood. This species has three morphs: one flight capable morph with fully-developed wings and fully-developed flight muscles [LW(F)], one flightless morph with fully-developed wings and histolyzed (non-functional) flight muscles [LW(H)], and another flightless morph with underdeveloped (short) wings and underdeveloped flight muscles (SW). Both flightless morphs [LW(H) and SW] had larger ovaries which contained a greater number of postvitellogenic eggs compared with the flight capable [LW(F)] morph. The juvenile hormone titer was significantly higher in SW compared with LW(F) females on days 3-7 of adulthood. On these days, the JH titer also was significantly higher in the other flightless morph, LW(H), compared with flight-capable [LW(F)] females as determined by one statistical test, but did not differ significantly by another test. The JH titer was positively correlated with ovarian mass or terminal oocyte length, but not with the number of post-vitellogenic eggs. This study is the first direct comparison of juvenile hormone titers in adult wing morphs of a wing-polymorphic insect. Results indicate that an elevated juvenile hormone titer may be at least partly responsible for one of the most distinctive features of wing-polymorphic species, the increased early fecundity of flightless females.     

The hemolymph JH titer exhibits a large-amplitude, morph-dependent, diurnal cycle in the wing-polymorphic cricket, Gryllus firmus

The hemolymph juvenile hormone (JH) titer was measured in over 500 flight-capable and flightless, adult female Gryllus firmus at 3-6 h intervals during each of days 2-8 of adulthood. The flight-capable morph exhibited a large-amplitude daily cycle in the hemolymph JH titer, while the flightless morph exhibited a barely perceptible cycle. The JH titer cycle was observed on all days in the flight-capable morph, but the large amplitude cycle (>15-20 fold increase in mean titer; >100-fold increase in some individuals), began on day 5. For both the large and small amplitude cycles, the JH titer peaked near the end of the photophase-beginning of the scotophase. The hemolymph ecdysteroid titer did not exhibit a corresponding large amplitude daily cycle, although a low amplitude cycle (1-3-fold change) was seen in both morphs. The large magnitude rise in the JH titer in the flight-capable morph during the photophase was not due to decreased hemolymph volume or JH degradation. Daily cycles in the JH titer may be common, but may have gone unnoticed in other insect species due to restricted temporal sampling. Failure to identify these cycles can result in substantial errors in inferring biological roles for JH. Because JH regulates flight behaviors, morph-specific daily cycles in the JH titer may be especially common in dispersal-polymorphic insects, in which flight is restricted to one morph during a limited period of the day or night. However, because JH regulates numerous biological traits, analogous cycles may be common in insects exhibiting other types of complex (e.g. caste or phase) polymorphism, in which morphs differ in a biological characteristic that is restricted to a specific period of the photophase or scotophase.     

Biochemical aspects of flight and flightlessness in Gryllus: flight fuels,enzyme activities and electrophoretic profiles of flight muscles from flight-capable and flightless morphs

Female Gryllus assimilis subjected to 4.5-7.7h continuous tethered flight had significantly lower amounts of total lipid, triglyceride and total soluble carbohydrate compared with unflown controls. A much greater amount of total lipid (6.3mg) was used during flight compared with carbohydrate (0.14mg). Flown individuals also had substantially reduced amounts of injected, radiolabeled [(14)C]-oleic acid. Activities of lipid, carbohydrate and amino acid catabolizing enzymes in flight muscles of G. assimilis and its wing-polymorphic congener, G. firmus, were very similar to activities in insects which primarily utilize lipid to power flight. By contrast, enzyme activities were very different from those in insects which primarily or exclusively use carbohydrate or proline as a flight fuel. These results strongly implicate lipid as the major flight fuel in Gryllus. Previous studies have shown that lipid levels are higher in flight-capable (long-winged) G. firmus that have small ovaries compared with flightless (short-winged) females that have large ovaries. Results of the present and previous studies collectively indicate that elevated lipid in long-winged G. firmus represents an energetic cost of flight capability which reduces (trade-offs with) reproduction in Gryllus. In G. firmus, mass-specific activities of nearly all enzymes were considerably reduced in underdeveloped, and to a lesser degree in histolyzed muscle, compared with fully-developed flight muscle. An important exception was alanine aminotransferase, whose activity was the highest in histolyzed muscle, and which may be involved in the catabolism of amino acids derived from muscle degradation. Despite the dramatic differences in enzyme activity, electrophoretic profiles of soluble flight-muscle proteins differed only subtly between fully-developed and underdeveloped or histolyzed flight muscles.     

Hormones in the field: evolutionary endocrinology of juvenile hormone and ecdysteroids in field populations of the wing-dimorphic cricket Gryllus firmus

Virtually no published information exists on insect endocrine traits in natural populations, which limits our understanding of endocrine microevolution. We characterized the hemolymph titers of juvenile hormone (JH) and ecdysteroids (ECDs), two key insect hormones, in field-collected short-winged, flightless (SW) and long-winged, flight-capable (LW(f)) morphs of the cricket Gryllus firmus. The JH titer exhibited a dramatic circadian rhythm in the LW(f) morph but was temporally constant in the flightless SW morph. This pattern was consistent in each of three years; in young, middle-aged, and older G. firmus; and in three other cricket species. The ECD titer was considerably higher in SW than in LW(f) females but did not exhibit temporal variation in any morph and did not differ between male morphs. JH and ECD may control different aspects of the morph-specific trade-off between nocturnal dispersal and reproduction. Results confirm and extend laboratory studies on young female G. firmus; most, but not all, important aspects of morph-specific differences in JH and ECD titers can be extrapolated from field to laboratory environments and vice versa. Hormone titers in Gryllus are more complex than those proposed in evolutionary endocrine models. Directly measuring hormone titer variation remains a fundamentally important task of insect evolutionary endocrinology.     

Male sand crickets trade-off flight capability for reproductive potential

In this paper, we test the hypothesis that male sand crickets, Gryllus firmus, experience a trade-off between flight capability and reproductive potential expressed as reduced testis weight in flight-capable morphs. We used a half-sib design with 130 sires, three dams per sire and an average of 5.66 males per dam family, for a total of 2206 F1 offspring. Traits measured were head width, somatic dry weight, testis weight, wing morph (micropterous/macropterous), weight of the dorso-longitudinal flight muscles (DLM) and the functional status of these muscles. Heritabilities of all traits were significant and ranged from 0.14 to 0.43. All traits were positively correlated with body size, but removal of this covariance revealed a highly significant trade-off, both phenotypically and genetically, between testes size and flight capability as measured by wing morph, DLM size or DLM status. The possible implications of this for morph-specific reproductive tactics are discussed.     

Intermediary Metabolism and Life History Trade-offs: Lipid Metabolism in Lines of the Wing-polymorphic Cricket, Gryllus firmus, Selected for Flight Capability vs. Early Age Reproduction

The extent to which modifications in intermediary metabolismcontribute to life history variation and trade-offs is an importantbut poorly understood aspect of life history evolution. Artificialselection was used to produce replicate genetic stocks of thewing-polymorphic cricket, Gryllus firmus, that were nearly pure-breedingfor either the flight-capable (LW[f]) morph, which delays ovariangrowth, or the flightless (SW) morph, which exhibits enhancedearly-age fecundity. LW(f) lines accumulated substantially moretriglyceride, the main flight fuel in Gryllus, compared withSW-selected lines, and enhanced accumulation of triglyceridewas strongly associated with reduced ovarian growth. Increasedtriglyceride accumulation in LW(f) lines resulted from elevatedde novo biosynthesis of fatty acid and two morph-specific trade-offs:(1) greater proportional utilization of fatty acid for glyceridebiosynthesis vs. oxidation, and (2) a greater diversion of fattyacids into triglyceride vs. phospholipid biosynthesis. Eventhough SW lines produced less total lipid and triglyceride,they produced more phospholipid (important in egg development)than did LW(f) lines. Differences between LW(f) and SW morphsin lipid biosynthesis resulted from substantial alterationsin the activities of all studied lipogenic enzymes, a resultthat is consistent with expectations of Metabolic Control Theory.Finally, application of a juvenile hormone analogue to LW(f)females produced a striking SW phenocopy with respect to allaspects of lipid metabolism studied. Global alterations of lipidmetabolism, most likely produced by alterations in endocrineregulation, underlie morph specializations for flight vs. early-agefecundity in G. firmus. Modification of the endocrine controlof intermediary metabolism is likely to be an important mechanismby which intermediary metabolism evolves and contributes tolife history evolution.     

Morph-specific diurnal variation in allatostatin immunostaining in the corpora allata of Gryllus firmus: Implications for the regulation of a morph-specific circadian rhythm for JH biosynthetic rate

Previous studies have documented a circadian cycle in juvenile hormone (JH) biosynthesis in the long-winged, flight-capable morph, but not in the short-winged flightless morph of the cricket Gryllus firmus. One rapid and reversible inhibitor of in vitro JH biosynthesis by the corpora allata (CA) in crickets is the neuropeptide Phe-Gly-Leu/Ile-amide type of allatostatins (ASTs). To investigate the possible role of allatostatin regulation of the morph-specific circadian cycle of JH production, the quantity of this type of AST in the nerves within the CA was determined by the density of anti-AST-immunostaining in confocal images using the Image J program. The density of immunostaining was inversely related to the rate of JH biosynthesis: Immunostaining in the CA was high and did not differ between morphs early in the photophase when the in vitro rate of JH biosynthesis is low and equivalent in the morphs. However, during the end of the photophase, when the rate of JH biosynthesis rises dramatically in the flight-capable morph, but not in the flightless morph, immunostaining was significantly lower in the flight-capable compared to the flightless morph. These results indicate that morph-specific differences in delivery of AST to the CA and its probable release likely regulate the morph-specific circadian pattern of JH biosynthesis. Also, the negative correlation between AST density and JH production provides evidence for predicting the periods of altered release of these rapid-acting paracine regulators of JH biosynthesis.     

Lipid, carbohydrate and nitrogen content of long- and short-winged Gryllus firmus: Implications for the physiological cost of flight capability

Concentrations of total lipid, triglyceride, soluble carbohydrate, total nitrogen and water were measured in the long-winged (LW) and short-winged (SW) morphs of the cricket, Gryllus firmus. In addition, the weights and composition of wings and oviposited eggs were compared between morphs. This was done to obtain information on the energetic cost of flight capability in the LW morph. Whole-cricket content (% dry mass) of triglyceride was significantly higher in LW vs SW individuals of both sexes. Since triglyceride is a likely flight fuel in G. firmus, the biosynthesis of elevated levels of this high energy substance in the LW morph may represent an important energetic cost of flight capability. The existence of such a cost is consistent with the elevated respiratory metabolism previously observed in LW vs SW G. firmus. A highly significant negative correlation was observed between triglycerides and non-triglycerides in LW but not SW crickets. This suggests that lipid biosynthesis may be operating under some constraint in the LW morph. Increased triglyceride biosynthesis may require a concomitant decreased biosynthesis of non-triglycerides. In contrast to the elevated triglyceride level in the LW morph, carbohydrate concentration was higher in the SW morph during early adulthood. Carbohydrate content also decreased with age in the SW but not in the LW adults. No differences were observed between morphs in (1) the total nitrogen or water contents of whole crickets, (2) the nitrogen content of wings or (3) the wet weight, dry weight, lipid content, or total nitrogen content of oviposited eggs.     

The physiological costs of flight capability in wing-dimorphic crickets

Nutritional indices, triglyceride levels and flight muscle developmental profiles were compared between long-winged (LW) and short-winged (SW; flightless) morphs of the cricketsGryllus rubens Scudder andG. firmus Scudder. This was done to identify potential physiological costs of flight capability in adults. The LW morph of each species converted a lower proportion of assimilated nutrients into biomass (reduced ECD) than did the SW morph. This documents increased respiratory metabolism in the LW morph. Triglyceride concentration was higher in LW vs. SW adults. This suggests that the elevated respiration in the LW morph may be at least partially due to the increased biosynthesis of this high energy substance. Preliminary data indicate higher respiration rates of LW functional vs. SW vestigial flight muscles. Collectively, these data suggest that the energetic cost of flight capability in adults results from biosynthesis of triglyceride flight fuel and flight muscle maintenance but not flight muscle growth. No flight muscle growth was observed in adults.