Effects of suppressed oviposition activity and flight muscle histolysis on food consumption and ovarian development in a wing-dimorphic cricket: an explanation for sporadic conclusions related to physiological trade-offs

The effects of deprivation of oviposition substrate on food consumption and egg production were compared between the long-winged (LW) and the short-winged (SW) morph of a cricket, Modicogryllus confirmatus, to determine how suppressed oviposition activity would influence these traits in each wing morph. Food consumption was greatly suppressed in females deprived of oviposition substrate (-OS) compared to those given access to it (+OS) during the 2-week feeding trial in the SW morph but not in the LW morph. Some LW females shed their hindwings and histolyzed the flight muscles. Such de-alated LW (DLW) morphs tended to consume more food than intact LW (ILW) morphs. In all morphs, ovarian weight was heavier under -OS conditions than under +OS conditions during the second week of adulthood, although the differences were greater in SW morphs than in ILW morphs. In DLW morphs in which flight muscle histolysis was induced by artificial de-alation at adult emergence, the temporal changes in ovarian weight were similar to those of SW morphs.In SW morphs, food consumption was also significantly reduced when ovipositing females were deprived of oviposition substrate for 2 days compared to those allowed to oviposit continuously, but food consumption was not reduced in ILW or DLW morphs. SW females from which one ovary was extirpated at adult emergence, SW (-o), also showed a significant difference in food consumption when treated as above, indicating that food consumption was not determined simply by the number of ovarian eggs. The crop content was positively correlated to food consumption and smaller under -OS conditions than under +OS conditions. The 2-day deprivation of oviposition substrate caused no significant difference in the total number of deposited and ovarian eggs in any group, but the ovarian mass of developing oocytes tended to be smaller under -OS than under +OS conditions, particularly in SW morphs.These results indicate the possibility that some inconsistent results and conclusions discussed in recent studies, concerning the physiological trade-offs between flight capability and reproduction, were caused by the suppressed oviposition activity and failure to recognize the occurrence of flight muscle growth and histolysis in the test crickets.     

Physiological trade‐offs between flight muscle and reproductive development in the wing‐dimorphic cricket Velarifictorus ornatus

Morphology, flight muscles, and reproductive development were compared between long‐winged (LW) and short‐winged (SW) morphs of the cricket Velarifictorus ornatus (Shiraki) (Orthoptera: Gryllidae). There was no difference in body weight and pre‐oviposition between the two morphs, but LW individuals had better‐developed flight muscles than SW individuals during and after emergence of the adult. The flight muscles at adult emergence represented 11.9% of the total body weight in the LW female and 4.9% in the SW female. In addition, the weight of the flight muscle of LW females increased by 50% during the first 5 days, whereas the flight muscle of the SW variant increased only slightly after adult emergence. The process of oviposition in LW, SW, and de‐alated females varied: SW females produced more eggs at the early stage than LW females, but de‐alation could shorten the time until the peak of egg laying and caused histolysis of flight muscles of LW females. There was no significant difference in total egg production between the above three groups. In the male, unlike the female, the accessory glands of the two wing morphs enlarged continuously at the same rate. There was no difference between the two wing morphs in the mass of the testes during the first 7 days after adult emergence.     

THE GENETIC BASIS OF THE TRADE-OFF BETWEEN CALLING AND WING MORPH IN MALES OF THE CRICKET GRYLLUS FIRMUS

Wing dimorphisms exist in a wide range of insects. In wing-dimorphic species one morph is winged has functional flight muscles (LW), and is flight-capable, whereas the other has reduced wings (SW) and cannot fly The evolution and maintenance of wing dimorphisms is believed to be due to trade-offs between flight capability and fitness-related traits. Although there are well-established phenotypic trade-offs associated with wing dimorphism in female insects, there only exist two studies that have established a genetic basis to these trade-offs. The present study provides the first evidence for a genetically based trade-off in male insects, specifically in the sand cricket Gryllus firmus. Because they have to expend energy to maintain the flight apparatus (especially flight muscles), LW males are predicted to call less and therefore to attract fewer females. To be of evolutionary significance, call duration wing morph, and wing muscle condition (size and functionality) should all have measurable heritabilities and all be genetically correlated. Differences between morphs in male G. firmus in the likelihood of attracting a female were tested in the laboratory using a T-maze where females chose between a LW male and a SW male. Call duration for each male was recorded on the sixth day of adult life. A significant difference in call duration was found between SW and LW males (SW = 0.86 ± 0.01, LW = 0.64 ± 0.01 h). SW males attracted significantly more females than did LW males (63% vs. to 37%). All the traits involved in the trade-off had significant heritabilities (call = 0 75 ± 0 33; wing morph = 0.22 ± 007; muscle weight = 0.38 ± 0.09) and genetic correlations (call and wing morph = -0.46 ± 0.20 for SW, -0.68 ± 0.16 for LW; LW call and muscle weight = -0.80 ± 0.14). These results provide the first documented evidence that trade-offs between a dimorphic trait and a fitness-related character in males has a genetic basis and hence can be of evolutionary significance.     

Food digestion capability and digestive enzyme activity in female adults of the wing‐dimorphic cricket Velarifictorus ornatus

Velarifictorus ornatus (Shiraki) (Orthoptera: Gryllidae) display distinct wing variation, and a physiological trade‐off between reproduction and flight muscles has been observed in long‐winged (LW) and short‐winged (SW) females. To understand the physiological basis of this trade‐off, we investigated the difference in the food digestion capability and digestive enzyme activity between LW and SW females. We found that the efficiency of conversion of digested food into body matter of SW females was significantly higher than that of the LW females, although there was no difference in the approximate digestibility between LW and SW females during the first 12 days after the adult emergence. Similarly, growth and relative growth were significantly higher in SW females. The food consumption of SW females was significantly higher than that of the LW females only in the first 6 days after the adult emergence, suggesting enhanced ovary development in SW females is probably because of the elevated efficiency of conversion of digested food into body matter coupled with greater consumption in the early stage after the adult emergence. Trypsin‐like activity was higher in SW females than in LW females, whereas no differences in the fresh weight of the midguts (including content) were observed between LW and SW females at 1, 3, or 5 h after refeeding after starvation for 18 h. In contrast, amylase activity varied significantly depending on time lapse after refeeding, being significantly higher in LW females than in SW females at 1 h after refeeding, but significantly lower in LW females than in SW females at 3 and 5 h after refeeding. The lipase activity displayed a similar trend in both LW and SW females after refeeding, with an initial decline followed by a slight increase; and no difference was observed between LW and SW females at any stage after refeeding.     

长颚斗蟋长翅和短翅型雌成虫飞行肌发育、生殖力及寿命的比较

为探讨长颚斗蟋Velarifictorus asperses (Walker)翅型分化的生态学意义, 对室内饲养获得的长翅和短翅型雌成虫飞行肌和卵巢的发育, 以及长、 短翅型雌成虫的生殖力和寿命进行了比较研究。结果表明： 羽化当日, 长翅型雌成虫飞行肌重38.68±9.15 mg, 显著高于短翅型的17.53±4.44 mg （P<0.05）; 而二者卵巢重量无显著差异（P>0.05）, 分别为4.69±1.04 mg和4.88±0.97 mg。羽化后8 d内, 长翅型雌成虫飞行肌重量增加了48.9%, 短翅型雌成虫飞行肌重量无明显增加; 而短翅型雌成虫卵巢的重量增加至93.5±11.7 mg, 约为长翅型雌成虫的4.5倍。短翅型雌成虫的产卵前期显著短于长翅型, 其早期产卵量及总产卵量亦显著高于长翅型; 而两翅型雌成虫中后期产卵量及寿命无显著差异（P>0.05）。此外, 长翅型雌成虫在羽化后12 d开始发生飞行肌的降解, 飞行肌降解个体的卵巢重量显著高于未降解个体, 与短翅型相似。结果提示, 飞行肌与生殖系统的发育之间存在资源分配的权衡关系（trade-off), 且这种资源分配的差异可能会导致长翅型与短翅型个体在生活史策略上出现分化, 即长翅型个体具有飞行能力, 而短翅型个体则在生殖方面获得更高的收益, 且飞行肌的降解可能是长翅型个体由飞行转向生殖发育的生理信号。     

Differential allocation of resources underlies the dispersal-reproduction trade-off in the wing-dimorphic cricket,Gryllus rubens

The cricket, Gryllus rubens (Orthoptera, Gryllidae), exists in natural populations as either a fully-winged (LW), flight-capable morph or as a short-winged (SW) morph that cannot fly. The SW morph is substantially more fecund than the LW morph. In this study we report on the physiological basis of this trade-off between flight capability and fecundity. Results from gravimetric feeding trials indicate that LW and SW morphs are equivalent in their consumption and digestion of food. However, during the adult stage, the LW morph is less efficient in converting assimilated nutrients into biomass. This may be a consequence of the respired loss of assimilated nutrients due to the maintenance of functional flight muscles in the LW morph. In both morphs the gross biomass devoted to flight muscles does not change significantly during the first 14 days of adult growth while there is a significant biomass gain in ovarian tissue mass during the same period. SW morphs have vestigial flight muscles and gain substantially more ovarian mass relative to the LW morphs. These data are consistent with a trade-off between flight muscle maintenance in the LW morph and ovarian growth in the SW form. This is the first evidence for a life-history trade-off that has a physiological basis which is limited to the allocation of acquired and assimilated nutrients within the organism.     

长颚斗蟋长翅和短翅型雄成虫营养物质的积累与分配差异

[目的]翅多型雄虫在繁殖方面的能量投入与雌虫相异,这种差异可能会导致雄虫飞行与繁殖权衡的生理机制发生改变.因此,本研究旨在探究翅二型长颚斗蟋Velarifictorus aspersus雄成虫在营养物质积累与分配方面是否存在飞行与繁殖的权衡关系.[方法]选取长颚斗蟋V.aspersus头幅相近的长翅和短翅型雄成虫,对羽...     

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.     

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.     

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.     

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.     

Potential Reproductive Advantage of Short-over Long-Winged Adult Males of the Cricket <Emphasis Type="Italic">Velarifictorus ornatus</Emphasis>

A trade-off between flight capability and reproduction is well known in adult females of the wing-dimorphic cricket Velarifictorus ornatus, but it is not clear whether such a trade-off exists in adult males of the species. In the present study, we investigated sexual maturation time, mating frequency, and the fertilization success of spermatophores after sequential mating in long-winged (LW) and short-winged (SW) adult males of V. ornatus to evaluate the potential reproductive advantage of the SW over the LW male morph. We found that the SW males of V. ornatus attained sexual maturity earlier and produced heavier spermatophores during the early stage after adult emergence than their LW counterparts. Additionally, within a 24-h mating period, the SW males showed a higher mating frequency, greater spermatophore weight, and shorter intermating time interval compared with their LW counterparts. Although females copulated with the two male morphs produced eggs of similar size, fertilization success by SW males was significantly higher than by the LW males. These results provide support for a trade-off between dispersal capability and reproduction success in wing-dimorphic males of V. ornatus.     

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.     

丽斗蟋翅二型雄虫食物消化能力及消化酶活性比较

【目的】丽斗蟋Velarifictorus ornatus具明显的翅二型现象,为探讨翅型分化对丽斗蟋翅二型雄虫消化能力及中肠内消化酶活性产生的影响,对长翅型与短翅型雄虫食物消化能力及中肠内消化酶活性进行了检测比较。【方法】我们采取重量营养指数测定了羽化后12 d内丽斗蟋两型雄成虫增长量、相对增长率、取食量、食物利用率、近似消化率和食物转化率。为进一步明确丽斗蟋翅二型成虫食物消化能力与中肠内消化酶活性的关系,我们采用4种专用底物测定了中肠内用于分解蛋白质、脂肪和碳水化合物的总蛋白酶、胰蛋白酶、脂肪酶和淀粉酶的活性。【结果】结果表明,丽斗蟋两型雄虫取食量、食物转化率、食物利用率与增长量均无统计差异,但中肠内消化酶活性变化规律不同。成虫羽化后4 d时,长翅型雄虫中肠内总蛋白酶与胰蛋白酶活性显著高于短翅型雄虫,相反,羽化后0 d时,短翅型雄虫中肠内总蛋白酶与胰蛋白酶活性则显著高于长翅型雄虫,而羽化后12 d时,虽然短翅型雄虫总蛋白酶活性高于长翅型雄虫,但胰蛋白酶活性在两型雄虫间并无差异。成虫羽化后0 d时,两型雄虫脂肪酶活性无差异,但无论是羽化后4 或 12 d,长翅型雄虫中肠内脂肪酶活性皆显著大于短翅型雄虫。成虫羽化后4 d时,短翅型雄虫中肠内淀粉酶活性显著高于长翅型雄虫,而羽化后0与12 d时,两型雄虫间无显著差异。【结论】丽斗蟋翅二型雄虫食物消化能力无显著差异,但羽化后不同时间,中肠内消化酶活性存在差异,该差异可能与成虫羽化后不同时期,翅二型雄虫在飞行与繁殖投资中对不同能源物质的需求有关。     

Morph‐specific differences in biochemical composition related to flight capability in the wing‐polyphenic Sitobion avenae

Flight performance at various times after emergence in the alate morph and age‐dependent changes in biochemical composition of winged and wingless morphs were evaluated in the wing‐polyphenic aphid Sitobion avenae (Fabricius) (Hemiptera: Aphididae). Alates exhibited the highest flight activity at 18–36 h after adult emergence. Throughout the nymphal and adult development, the whole‐body content of total lipid was significantly higher in the winged vs. wingless morph, whereas the content of water, soluble sugar, glycogen, phospholipid, and soluble protein showed significantly higher levels in the wingless vs. winged morph. There were no significant differences in the content of triglyceride and free fatty acid during nymphal and adult stages in both morphs. However, triglyceride content was significantly higher in the winged vs. wingless morph during adulthood. Differences in biochemical composition between morphs indicate that there is an energetic cost of flight capability. Our results from S. avenae adults showed that total lipid and triglyceride for the winged morph accumulated significantly to a maximum, and water content decreased significantly to a minimum, on days 1 and 2 after the final molt, exactly when the highest flight activity was reached. This study suggests that flight activity is associated with triglyceride and water content.     

Juvenile Hormone and the endocrine regulation of wing polymorphism in insects: new insights from circadian and functional‐genomic studies in Gryllus crickets

For decades, Juvenile Hormone (JH) has been a major focus of studies investigating the endocrine regulation of wing‐polymorphism. The most general model postulates a single threshold, above which JH causes the expression of traits that define the short‐winged morph (SW), and below which JH causes the expression of traits that define the long‐winged morph (LW). Early studies in aphids and crickets reported ambiguous results as a result of the small size of aphids or the very low JH titre in nymphal crickets. Detailed studies in wing morphs of adult Gryllus firmus Scudder uncovered an unexpected and novel morph‐specific JH titre circadian cycle (cycling in LW but not in SW) in both the laboratory and field. This finding clearly contradicts the classic model. Morph‐specific daily rhythms in global gene expression are strongly associated with (and are possibly caused by) the morph‐specific JH titre rhythm. Daily rhythms for hormonal traits and gene expression, which are largely ignored in studies of life‐history evolution, may be common and play an important role in adaptation. Juvenile Hormone has likely evolved a specialized within‐morph function in G. firmus, regulating aspects of daily flight in the LW morph, which exhibits circadian flight. Other hormones, such as insulin‐like peptides and ecdysteroids, possibly regulate the expression of chronic (long‐term, noncircadian) differences between LW and SW morphs. Future studies should aim to investigate JH titres in more detail, as well as other hormones, most notably peptides and biogenic amines, which are largely ignored in endocrine studies of wing polymorphism.     

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.     

Variations in fuel use in the flight muscles of wing-dimorphic Gryllus firmus and implications for morph-specific dispersal

Although a considerable amount of information is available on tradeoffs in wing-polymorphic insects, only limited data are available on the relationship between flight and biochemical variation within species. In the current study, we compared the biochemical basis in the dorsolongitudinal flight muscle of the wing-dimorphic sand cricket, Gryllus firmus Scudder, with respect to tradeoffs in energy resources related to morph-specific flight, including glycogen, trehalose, and triglycerides. Our results show that levels of glycogen and trehalose in long-winged adults (LW[f]) were significantly higher before dispersal, on days 5 and 7. Considering that this is the period during which long-winged adults are flight-capable, these results suggest that both glycogen and trehalose are important to flight. However, levels of triglycerides in short-winged crickets (SW) were higher than in long-winged crickets, suggesting that triglycerides are not directly related to initial flight. In SW adults, triglyceride content on days 5 and 7 was significantly higher just before lights off than at the same time on day 1 or at any other time after lights on all other days. This suggests that triglycerides are probably related to reproductive behaviors, such as mating and oviposition, in the SW morph. In addition, flight muscle water content was significantly lower in the LW(f) morph than in the SW morph.     

Quantitative food utilization and reproductive allocation by adult milkweed bugs, Oncopeltus fasciatus

ABSTRACT. Age-specific and lifetime dry mass budgets were estimated for mated and virgin adult milkweed bugs, Oncopeltus fasciatus (Dallas) Hemiptera: Lygaeidae), fed air-dried milkweed seeds ( Asclepias syriacd ) in the laboratory at LD 14:10 and 23°C. Relative consumption rate (RCR) of all bugs was high during the first 8 days posteclosion (teneral period) as their fresh weight, dry weight, and fat content increased. Thereafter, the physiological syndrome associated with reproduction in mated females was indicated by their higher RCR, earlier and greater rate of egg production, greater lifetime relative metabolic rate and higher net and gross production efficiencies than virgin females and males. Males tended to live longer than virgin and mated females, which had similar lifespans. Mated females weighing less at eclosion remained lighter in weight on the day of mean peak weight, but food consumption, egg production and lifespan were independent of body-weight over a 25% range. Input of nymphal reserves or male reproductive secretions to egg production is probably minor in comparison with the adult female's food budget. The high proportion of the food budget allocated to egg production by mated females of O.fasciatus is consistent with its migratory, colonizing lifestyle.     

The evolution of trade-offs: effects of inbreeding on fecundity relationships in the cricket Gryllus firmus

The evolution of traits is modulated by their interrelationships with each other, particularly when those relationships result in a fitness trade-off. In this paper we explore the consequences of genetic architecture on functional relationships between traits. Specifically, we address the consequences of inbreeding on these relationships. We show that the linear regression between two traits will not be affected if there is no dominance genetic variance in either trait, whereas the intercept but not the slope of the regression will change if there is dominance genetic variance in one trait only. We test the latter hypothesis using fecundity relationships in the cricket Gryllus firmus. Data from pedigree analysis and an inbreeding experiment show that there is significant dominance genetic variance in fecundity, but not head width (an index of body size) or dorsal longitudinal muscle (DLM) mass. Fecundity increases with head width, but decreases with DLM mass. As predicted, the intercepts of the regressions of fecundity on these two morphological traits decrease with inbreeding, but there is little or no change in slope. Gryllus firmus is wing dimorphic, with the macropterous (LW) morph having a lower fecundity than the micropterous (SW) morph. We hypothesize that the difference in fecundity arises primarily because of a competition for resources in the LW females between DLM maintenance (i.e., mass) and egg production. As a consequence, we predict that the fecundity within each morph should decline linearly with the inbreeding coefficient at the same rate in both morphs. The result of this will be a change in the relative fitness of the two morphs, that of the SW morph increasing with inbreeding. This prediction is supported. These results indicate that trade-offs will evolve and such changes will affect evolutionary trajectories by altering the pattern of relationships among fitness components.