Copyright (c) 2013 University of Nebraska - Lincoln All rights reserved. http://digitalcommons.unl.edu/bioscizera Recent documents in Anthony Zera Publications en-us Thu, 24 Jan 2013 12:20:32 PST 3600 http://digitalcommons.unl.edu/bioscizera/40 http://digitalcommons.unl.edu/bioscizera/40 Mon, 16 Nov 2009 14:51:52 PST A productive synthesis of endocrinology and evolutionary genetics has occurred during the past two decades, resulting in the first direct documentation of genetic variation and correlation for endocrine regulators in nondomesticated animals. In a number of insect genetic polymorphisms (dispersal polymorphism in crickets, butterfly wing-pattern polymorphism), blood levels of ecdysteroids and juvenile hormone covary with morphology, development, and life history. Genetic variation in insulin signaling may underlie life history trade-offs in Drosophila. Vertebrate studies identified variation in brain neurohormones, bone-regulating hormones, and hormone receptor gene sequences that underlie ecologically important genetic polymorphisms. Most work to date has focused on genetically variable titers (concentrations) of circulating hormones and the activities of titer regulators. Continued progress will require greater integration among (a) traditional comparative endocrine approaches (e.g., titer measures); (b) molecular studies of hormone receptors and intracellular signaling pathways; and (c) fitness studies of genetically variable endocrine traits in ecologically appropriate conditions.

]]> Anthony J. Zera et al. http://digitalcommons.unl.edu/bioscizera/39 http://digitalcommons.unl.edu/bioscizera/39 Fri, 16 Oct 2009 09:03:15 PDT Previous studies demonstrated a high-amplitude, diel cycle for the hemolymph JH titer in the wing-polymorphic cricket, Gryllus firmus. The JH titer rose and fell in the flight-capable morph (long-winged, LW(f)) above and below the relatively temporally invariant JH titer in the flightless (short-winged, SW) morph. The morph-specific JH titer cycle appeared to be primarily driven by a morph-specific diel cycle in the rate of JH biosynthesis. In the present study, cycles of the JH titer and rate of JH biosynthesis in the LW(f) morph persisted in the laboratory under constant darkness with an approximate 24 h periodicity. The JH titer cycle also shifted in concert with a shift in the onset of the scotophase, was temperature compensated in constant darkness, and became arrhythmic under constant light. These results provide strong support for the circadian basis of the morph-specific diel rhythm of the JH titer and JH biosynthetic rate. Persistence of the JH titer cycle under constant darkness in multiple LW-selected and SW-selected stocks also provides support for the genetic basis of the morph-associated circadian rhythm. The morph-specific JH titer cycle was observed in these stocks raised in the field, in both males and females, in each of 3 years studied. The onset of the cycle in the LW(f) morph, a few hours before sunset, correlated well with the onset of the cycle, a few hours before lights-off, in the laboratory. The morph-specific JH titer cycle is a general feature of G. firmus, under a variety of environmental conditions, and is not an artifact of specific laboratory conditions or specific genetic stocks. It is a powerful experimental model to investigate the mechanisms underlying endocrine circadian rhythms, their evolution, and their impact on life history evolution.

]]> Anthony J. Zera et al. http://digitalcommons.unl.edu/bioscizera/38 http://digitalcommons.unl.edu/bioscizera/38 Thu, 02 Jul 2009 14:46:31 PDT 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.

]]> Simon Mole et al. http://digitalcommons.unl.edu/bioscizera/37 http://digitalcommons.unl.edu/bioscizera/37 Fri, 19 Jun 2009 09:24:19 PDT 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.

]]> Gretchen Cisper et al. http://digitalcommons.unl.edu/bioscizera/36 http://digitalcommons.unl.edu/bioscizera/36 Fri, 29 May 2009 11:50:22 PDT 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 pro¬portion 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.

]]> Anthony J. Zera et al. http://digitalcommons.unl.edu/bioscizera/35 http://digitalcommons.unl.edu/bioscizera/35 Fri, 03 Apr 2009 12:26:46 PDT The flight-capable morph of the wing-polymorphic cricket, Gryllus firmus, accumulated a substantially greater quantity of total lipid and triglyceride, compared with the obligately flightless morph, during the first five days of adulthood. Increased lipid accumulation in the flight-capable morph was genetically based, and was produced when ovarian growth is substantially reduced in that morph. Temporal changes in lipid levels suggest that the higher triglyceride reserves in the flight-capable morph fed a high-nutrient diet were produced by elevated lipid biosynthesis. By contrast, on a low-nutrient or high carbohydrate diet, increased lipid levels in the flight-capable morph appeared to result primarily from decreased lipid utilization. Increased biosynthesis or retention of triglyceride (the major flight fuel in Gryllus) by the flight-capable morph may significantly divert nutrients from egg production and hence may be an important physiological cause of its reduced ovarian growth. The obligately flightless morph allocated a greater proportion of total lipid to phospholipid than did the flight-capable morph. No functionally-significant differences in total lipid or triglyceride were produced between morphs during the last nymphal stadium. A second flightless morph, derived from the flight-capable morph by histolysis of flight muscles during adulthood, also had reduced amounts of total lipid and triglyceride but increased ovarian growth compared with the flight capable morph on the standard (high-nutrient) diet. Important qualitative and quantitative aspects of lipid metabolism differ genetically between the flight-capable and flightless morphs of G. firmus and likely contribute importantly to their respective adaptations for flight capability vs. reproduction. This is the first study to document genetically-based differences in energy reserves between morphs of a complex (phase, caste, flight) polymorphism in which morphs also differ genetically in key life history traits.

]]> Anthony J. Zera et al. http://digitalcommons.unl.edu/bioscizera/34 http://digitalcommons.unl.edu/bioscizera/34 Wed, 04 Feb 2009 11:18:37 PST 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.

]]> Z. Zhao et al. http://digitalcommons.unl.edu/bioscizera/33 http://digitalcommons.unl.edu/bioscizera/33 Mon, 08 Dec 2008 12:06:09 PST The Gerridae (Hemiptera: Insecta) is a worldwide family whose constituent species exhibit dramatic inter- and intra-specific variation in the degree of winglessness (Brinkhurst, 1960; Vepsäläinen, 1978; Calabrese, 1979). At one extreme, the family contains species which are fully winged in all populations and during all seasons, while several species consist almost exclusively of wingless morphs over large geographical ranges and during all seasons. Many species exhibit the intermediate case of wingpolymorphism: the occurrence of various combinations of fully winged, partially winged and/ or wingless morphs in the same population at the same time. Various wing-polymorphic species show differing patterns of spatial and/or temporal changes in morph ratios and patterns may vary both inter- and intraspecifically.

The dramatic differences in frequency of winged morphs pose intriguing questions regarding the evolutionary forces responsible for degree of winglessness and the relationship between degree of winglessness and genetic structure of water-strider species. One might expect genetic structure to be strongly influenced by degree of winglessness via reduction of flight dispersal ability and consequent reduced gene flow. Thus, species composed almost exclusively of wingless individuals should exhibit patterns of marked genetic differentiation and reduced levels of within-population variability typically found in organisms with reduced dispersal (Avise and Selander, 1972; Laing et al., 1976; Selander, 1976). However, additional factors may counteract the effects of reduced dispersal by flight. Gene flow among populations may occur via alternate modes of dispersal, including passive stream drift and overland dispersal (Riley, 1920). Furthermore, marked genetic differentiation among populations is not a necessary consequence of severely reduced dispersal if locality-independent balancing selection is operating (McKechnie et al., 1975).

In this study I compare patterns of spatial variation of polymorphic enzyme-loci and levels of variability in two species of waterstriders (Gerridae: Hemiptera) with differing degrees of winglessness: the nearly wingless Gerris remigis and the wing-polymorphic Limnoporus canaliculatus.

]]> Anthony J. Zera http://digitalcommons.unl.edu/bioscizera/32 http://digitalcommons.unl.edu/bioscizera/32 Mon, 08 Dec 2008 12:06:08 PST 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 CO₂ 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.

]]> Anthony J. Zera et al. http://digitalcommons.unl.edu/bioscizera/31 http://digitalcommons.unl.edu/bioscizera/31 Mon, 08 Dec 2008 12:06:06 PST 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.

]]> Zhangwu Zhao et al. http://digitalcommons.unl.edu/bioscizera/30 http://digitalcommons.unl.edu/bioscizera/30 Mon, 08 Dec 2008 12:06:05 PST A previous study documented a high amplitude, morph-specific daily cycle in the hemolymph JH titer in the wing-polymorphic cricket, Gryllus firmus. The JH titer rose and fell 10–20 fold in the flight-capable [LW(f), long-winged] morph during the late-photophase- early scotophase, while it was relatively constant during that time in the flightless (SW, short-winged) morph. In the present study we documented a dramatic morph-specific daily cycle in the in vitro rate of juvenile hormone (JH) biosynthesis that was tightly correlated with the hemolymph JH titer on days 5–7 of adulthood. Biosynthetic rates rose and fell 1–2 fold between the late photophase-early scotophase on each of days 5–6 and 6–7 of adulthood in the LW(f) morph, while biosynthetic rates were relatively constant during this period in the flightless, short-winged morph (SW), except for a slight dip in the rate of biosynthesis late in the photophase on these days. Similar morph-specific patterns of JH biosynthesis were observed whether rates were measured on corpora allata attached to corpora cardiaca in males or females, or on corpora allata alone. Hemolymph juvenile hormone esterase activity was significantly higher in the LW(f) vs. the SW morph during the beginning of scotophase, when the JH titer is decreasing rapidly in the LW(f) morph. Results indicate that the morph-specific daily cycle in the JH titer in G. firmus is primarily regulated by a morph-specific daily cycle in the rate of JH biosynthesis and to a lesser degree by hemolymph JH esterase activity. This is the first documentation of a diurnal cycle in the rate of JH biosynthesis in any insect, or a daily cycle in the rate of JH biosynthesis that is correlated with a specific morph in a polymorphic species. Results have important implications for the endocrine regulation of dispersal polymorphism, circadian rhythms of insect hormone titers and their regulators, and general studies of the JH titer and its regulation in insects.

]]> Zhangwu Zhao et al. http://digitalcommons.unl.edu/bioscizera/29 http://digitalcommons.unl.edu/bioscizera/29 Mon, 08 Dec 2008 12:06:04 PST Fat body and midgut juvenile hormone esterase (JHE) and juvenile hormone epoxide hydrolase (JHEH) specific activities, and plasma JHE activity, were measured throughout the last stadium in two pairs (blocks) of lines of the cricket Gryllus assimilis, each pair of which had been artificially selected for high- or low-plasma JHE activity. Highly significant differences were observed between high- and low-activity lines of each block on most days for fat body JHE, and on one day for midgut JHE activity. In each block, line differences in developmental profiles for fat body JHE activity paralleled line differences in plasma JHE activity during the early-mid stadium, but not during the latter part of the stadium. The developmental profile of midgut JHE activity differed from that of plasma and fat body JHE activity, exhibiting peaks during the early and latter parts of the stadium. Midgut and fat body JHEH activities exhibited a mid-stadium peak in all lines, but activities were very similar in all lines. Fat body JHE appears to be a more significant contributor to plasma JHE than is midgut JHE. During the middle of the last stadium (day 4), Jhe transcript abundance was significantly higher in fat body or midgut of highvs. low-JHE-activity lines. Jhe transcript abundance was positively correlated with JHE enzyme activity in either fat body or midgut, and with plasma JHE activity. Natural populations of G. assimilis harbor genetic variation for Jhe gene expression which appears to contribute to genetic variation in JHE specific activity in fat body and midgut. These genes appear to have been the targets of artificial selection that resulted in lines that differ dramatically in high- or low-plasma JHE activity. These genes appear to have little, if any, pleiotropic effects on JHEH specific activity.

]]> Anurag Anand et al. http://digitalcommons.unl.edu/bioscizera/28 http://digitalcommons.unl.edu/bioscizera/28 Wed, 05 Mar 2008 09:53:12 PST 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 ally 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 call 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.

]]> Anthony J. Zera et al. http://digitalcommons.unl.edu/bioscizera/27 http://digitalcommons.unl.edu/bioscizera/27 Wed, 12 Dec 2007 12:24:38 PST The 458 amino acid sequence of a mature JHE protein from the cricket Gryllus assimilis was identified after isolating the partial cDNA sequence encoding this protein from a fat body and midgut cDNA library. This hemimetabolan JHE sequence shows over 40% amino acid similarity to the known JHE sequences of several holometabolous insects. It also includes previously determined peptide sequences for G. assimilis JHE as well as two other motifs associated with JHE enzymes in holometabolous insects. The predicted molecular weight of the protein agrees with that of the JHE previously purified from G. assimilis. Partial genomic sequence encoding the Jhe contains two large (1330 and 2918 bp) introns. No coding DNA sequence variation was observed over a 1293 bp region between selected lines differing six to eight-fold in hemolymph JHE activity. However, a 19 bp indel was found in one of the introns; the insertion was strongly associated with elevated hemolymph activity, both in the selected lines and in the F2 progeny of crosses between them. Phylogenetic analyses localised the G. assimilis JHE to a clade containing dipteran and coleopteran JHEs, with lepidopteran JHEs occurring in a separate clade.

]]> E. J. Crone et al. http://digitalcommons.unl.edu/bioscizera/26 http://digitalcommons.unl.edu/bioscizera/26 Wed, 12 Dec 2007 12:18:01 PST Hemolymph juvenile hormone esterase (JHE) activity on the third day of the last stadium in the cricket, Gryllus assimilis, exhibited a significant response to selection in each of six replicate lines. Mean realized heritability was 0.26 ± 0.04. The response was due to changes in whole-organism enzyme activity as well as to changes in the proportion of enzyme allocated to the hemolymph compartment. In vivo juvenile hormone metabolism differed between some lines selected for high vs. low enzyme activity. Only minimal differences were observed between lines with respect to hemolymph protein concentration or whole-cricket activity of juvenile hormone epoxide hydrolase, the other major JH-degrading enzyme. Dramatic correlated responses to selection, equal in magnitude to the direct response, were observed for JHE activity on each of three other days of the last juvenile stadium. In contrast, no correlated responses in JHE activity were observed in adults. This indicates that JHE activities throughout the last stadium will evolve as a highly correlated unit independent of adult activities and the evolution of endocrine mechanisms regulating juvenile development can be decoupled from those controlling adult reproduction. This study represents the first quantitative-genetic analysis of naturally occurring endocrine variation in an insect species.

]]> Anthony J. Zera et al. http://digitalcommons.unl.edu/bioscizera/25 http://digitalcommons.unl.edu/bioscizera/25 Mon, 19 Nov 2007 13:46:41 PST Studies of dispersal polymorphism in insects have played a pivotal role in advancing our understanding of population dynamics, life history evolution, and the physiological basis of adaptation. Comparative data on wing-dimorphic insects provide the most definitive evidence to date that habitat persistence selects for reduced dispersal capability. The increased fecundity of flightless females documents that a fitness tradeoff exists between flight capability and reproduction. However, only recently have studies of nutrient consumption and allocation provided unequivocal evidence that this fitness trade-off results from a trade-off of internal resources. Recent studies involving wing-dimorphic insects document that flight capability imposes reproductive penalties in males as well as females. Direct information on hormone titers and their regulation implicates juvenile hormone and ecdysone in the control of wing-morph determination. However, detailed information is available for only one species, and the physiological regulation of wing-morph production remains poorly understood. Establishing a link between the ecological factors that influence dispersal and the proximate physiological mechanisms regulating dispersal ability in the same taxon remains as a key challenge for future research.

]]> Anthony J. Zera et al. http://digitalcommons.unl.edu/bioscizera/24 http://digitalcommons.unl.edu/bioscizera/24 Mon, 19 Nov 2007 13:43:56 PST Genetically marked individuals were used to study differential mating success between male wing morphs of the cricket, Gryllus rubens. Previous studies of Gryllus rubens and other wing-dimorphic insects have documented that flightless short-winged or wingless females typically attain reproductive maturity earlier and oviposit more eggs relative to their long-winged counterparts. This study was done to determine if flightless males also exhibit enhanced reproductive characteristics. Segregation analyses documented the genetic basis of allozymes used to infer paternity in subsequent experiments. Control experiments documented the absence of effects on mating success independent of wing morph due to (1) the genetic stock from which males were taken; (2) male size; or (3) female wing morph. Mating trials involving a long-winged male, a short-winged male and a female of either wing morph documented no significant differences in the number of progeny sired by male wing morphs. This pattern was true for both the first group of offspring and for the entire set of offspring produced during a 20-day period. Thus, in contrast to females, we observed no increase in reproductive output in males resulting from the loss of the flight apparatus. However, substantial variance in mating success was observed between males independent of wing morph. This result was likely due to the existence of a dominance hierarchy and the increased mating success of the dominant male.

]]> Cami L. Holtmeier et al. http://digitalcommons.unl.edu/bioscizera/23 http://digitalcommons.unl.edu/bioscizera/23 Mon, 19 Nov 2007 13:39:17 PST Juvenile hormone esterase (JHE) from the serum of the cricket, Gryllus assimilis, was purified to homogeneity in a four-step procedure involving polyethylene glycol precipitation, hydrophobic interaction FPLC, and ion exchange FPLC. This procedure could be completed in 4 days and resulted in a greater than 900-fold purification with greater than 30% recovery. The purified enzyme exhibited a single band on a silver-stained SDS PAGE gel and had an apparent subunit molecular mass of 52 kDa. The native subunit molecular mass, determined by gel permeation FPLC, was 98 kDa, indicating that JHE from Gryllus assimilis is a dimer of two identical or similar subunits. The turnover number of the purified enzyme (1.41 s^-1), K_M(JH-III) (84 ± 12 nM) of nearly-purified enzyme, and k_cat /K_M (1.67 × 10⁷ s^-1 M^-1) were similar to values reported for other well-established lepidopteran and dipteran JHEs. JHE from Gryllus assimilis was strongly inhibited by the JHE transition-state analogue OTFP (octylthio-1,1,1-trifluoro-2-propanone; I₅₀ = 10^-7 M) and by DFP (diisopropyl fluorophosphate; I₅₀ = 10^–7 M). The shapes of the inhibition profiles suggest the existence of multiple binding sites for these inhibitors or multiple JHEs that differ in inhibition. Isoelectric focusing separated the purified protein into 4 isoforms with pIs ranging from 4.7–4.9. N-terminal amino acid sequences (11–20 amino acids) of the isoforms differed from each other in 1–4 positions, suggesting that the isoforms are products of the same or similar genes. Homogeneously purified JHE hydrolyzed α-napthyl esters, did not exhibit any detectable acetylcholinesterase, acid phosphatase, or aminopeptidase activity, and exhibited only very weak alkaline phosphatase activity. JHE exhibited a low (11 μM) KM for long-chain α-naphthyl esters, indicating that JHE may have physiological roles other than the hydrolysis of JH-III. Purification of JHE represents a key step in our attempts to identify the molecular causes of genetically-based variation in JHE activity in G. assimilis. This represents the first homogeneous purification of JHE from a hemimetabolous insect.

]]> Anthony J. Zera et al. http://digitalcommons.unl.edu/bioscizera/22 http://digitalcommons.unl.edu/bioscizera/22 Mon, 19 Nov 2007 13:30:37 PST Genetic lines of the cricket Gryllus assimilis selected for elevated vs. decreased activity of hemolymph juvenile hormone esterase (JHE) exhibited a 6.8-fold difference in enzyme activity by the seventh generation of selection. This documents that hemolymph JHE activity has the capability for rapid evolutionary change. This is the only insect endocrine trait for which such data are currently available. The difference in hemolymph JHE activity between the lines was due, to an equivalent degree, to variation in whole-cricket enzyme activity and allocation of JHE activity to the hemolymph compartment. No differences in kinetic or thermostability characteristics were observed between JHEs from the high- vs. low-selected lines. This suggests that the variation in JHE activity between the lines resulted from selection of variable regulatory genetic factors affecting the synthesis, degradation, or activation of enzyme activity. JHE and JH-binding activity in the hemolymph are genetically correlated, possibly due to co-regulation by the same genetic factors. Finally, in vivo JH degradation was significantly elevated in lines selected for elevated JHE activity. This documents that evolutionary changes in JHE activity alter in vivo JH metabolism.

]]> Anthony J. Zera et al. http://digitalcommons.unl.edu/bioscizera/21 http://digitalcommons.unl.edu/bioscizera/21 Fri, 28 Sep 2007 09:35:25 PDT Wing polymorphism commonly occurs in many insects, especially species of Orthoptera, Coleoptera, Homoptera, and Hemiptera (Harrison, 1980). The polymorphism consists of discrete differences in wing length with morphs exhibiting fully developed, reduced, or totally absent wings. In addition to differences in wing length, morphs often differ in a number of other characteristics such as degree of flight muscle development, duration of nymphal development, time to first reproduction, fertility and diapause (Anderson, 1973; Vepsäläinen, 1978; Harrison, 1980).

Wing polymorphism is an attractive system for investigating the evolution of dispersal in natural populations (Vepsäläinen, 1978; Denno and Grissell, 1979; Harrison, 1980). A key step in such studies is the identification of the environmental and genetic components of morph determination. Numerous studies of insects from several different orders have clearly demonstrated that environmental variables such as photoperiod, temperature and density may strongly influence the development of an individual into a particular morph (see references in Harrison, 1980). However, the genetic component of morph determination is poorly understood.

In this study we focused on the genetic influences of morph determination in the wingpolymorphic waterstrider, Limnoporus canaliculatus. We wished to determine if the inheritance of morph type could be explained by the single locus (or supergene) model proposed by most workers for other gerrid species, or whether a more complex genetic explanation was required. We used “split brood” experiments to determine if the mode of inheritance was different under different photoperiods as well as to assess the influence of photoperiod on morph determination.

]]> Anthony J. Zera et al.