Hormone Titers Research Articles

Recovery by the Norway lobster Nephrops norvegicus (L.) from the physiological stresses of trawling: Influence of season and live-storage position

Live Norway lobsters ( Nephrops norvegicus L.) were trawled at depths of 30 to 55 m off the coast of Jutland (Denmark) in late winter (March) and in summer (August) in 2006. Water temperatures at the bottom and surface of the sea were 7 °C and 2 °C during the winter, and 12 °C and 21 °C in the summer, respectively. The recovery of specific physiological and metabolic variables from the intense stresses associated with capture (trawling and air-exposure during sorting) was followed in seawater at 5 °C in winter or 18 °C in summer. Recovery was compared in lobsters held individually in two different live-storage positions, either resting vertically on the tail or sitting horizontally. In winter, many animals were alive when brought on board and approximately 86% were still alive at the end of experimentation (96 h). In summer very few animals were alive when brought on board and, of these, approximately 95% were dead at 24 h. When compared with values measured in laboratory controls, the stresses of capture elicited very high haemolymph lactate contents in both seasons, although levels recovered within 24 h. Trawling also caused very high haemolymph glucose concentrations, which differed with season. In winter, haemolymph glucose was elevated for 24 h to levels significantly higher than in summer. In summer, glucose had returned to control levels by 4 h. At 4 h after trawling, haemolymph O 2 status was not markedly influenced in either season, but there were significant disturbances of acid-base status. In winter, a potential metabolic lactic acidosis was compensated by a marked respiratory alkalosis, with significantly increased haemolymph pH and decreased CO 2 total content and partial pressure. These effects disappeared gradually over 96 h. Summer lobsters showed combined metabolic and respiratory acidosis at 4 h, although this had recovered to control values in the small number of survivors sampled at 24 h. The capture stresses elicited very high haemolymph crustacean hyperglycaemic hormone (CHH) titres, significantly higher in summer than in winter. In winter, CHH titre had declined significantly at 24 h, whereas it exhibited a further significant increase at 24 h in summer. Live-storage position had no significant effect on survival or recovery from capture stresses in either season. The results demonstrate that Nephrops were much more stressed by trawling at high summer temperatures and had difficulty recovering from this, with pronounced negative effects on their survival, irrespective of their live-storage position.

Endocrine signatures underlying plasticity in postembryonic development of a lower termite, Cryptotermes secundus (Kalotermitidae)

Wood-dwelling termites are characterized by an extremely high and unique developmental flexibility that allows workers, which are immatures, to explore all caste options. The endocrine signatures underlying this flexibility are only vaguely understood. We determined juvenile hormone (JH) and ecdysteroid hemolymph titers during postembryonic development and in terminal instars of the drywood termite Cryptotermes secundus using field and laboratory colonies. Postembryonic development is characterized by a drop in JH titers at the transition from larval (individuals without wing buds) to nymphal (individuals with wing buds) instars. JH titers were low in winged sexuals and reproducing primary reproductives (<200 pg/microl) but were by an order of magnitude higher in neotenic replacement reproductives. The unique regressive molts of termites seem to be characterized by elevated JH titers, compared with progressive or stationary molts. Ecdysteroid titers were generally low in nymphal instars and in primary reproductives (<50 pg/microl). It was only during the third and fourth nymphal instars and in winged sexuals where some individuals showed elevated ecdysteroid titers. These results are the most comprehensive endocrinological data set available for any lower termite, with the potential to serve as baseline for understanding the extreme developmental flexibility underlying the evolution of social life in termites.

Induction of supernumerary larval moulting in the tobacco hornworm Manduca sexta: interaction of bisacylhydrazine ecdysteroid agonists with endogenous Juvenile Hormone

Abstract When given in a critical dietary dose range, the insecticidal bisacylhydrazine ecdysteroid agonists RH‐5849 or tebufenozide (RH‐5992) cause fifth stage Manduca sexta (L.) larvae to moult to a supernumerary sixth‐stage giant larva. The effect is dependent on exposure to the chemicals immediately after the previous ecdysis. Previous removal of the corpora allata does not interfere with the induction of premature moulting by RH‐5849 but completely prevents the formation of supernumerary larvae. The juvenilizing effect is therefore due to the interaction of the moult‐promoting effect of the ecdysteroid agonists with the high titre of endogenous Juvenile Hormone that is present just after ecdysis to the fifth stage in this insect. The ecdysteroid agonists themselves appear to have no intrinsic Juvenile Hormone‐agonist properties. Sixth‐stage larvae resulting from exposure to critical dietary concentrations of RH‐5849 are morphologically completely larval in character. When transferred to diet without the ecdysteroid agonist, they feed normally and gain weight, growing much larger than control fifth stage insects. At the end of the supernumerary stage, they cease to feed, wander in the usual way, and form a normal pupal cuticle but then die as pharate pupae without shedding the sixth‐stage larval cuticle.

Changes in sex steroid levels in women with epilepsy on treatment: Relationship with antiepileptic therapies and seizure frequency

Reproductive dysfunction in epilepsy is attributed to the seizures themselves and also to antiepileptic drugs (AEDs), which affect steroid production, binding, and metabolism. In turn, neuroactive steroids may influence neuronal excitability. A previous study in this cohort of consecutive women with epilepsy showed that patients with more frequent seizures had higher cortisol and lower dehydroepiandrosterone sulfate levels than those with rare or absent seizures. The present study was aimed at evaluating, in these same women, the possible relationship between some clinical parameters, seizure frequency, AED therapies, and sex hormone levels. Estradiol (E2), progesterone (Pg), sex hormone-binding globulin (SHBG), and free estrogen index (FEI) were measured during the luteal phase in 113 consecutive females, 16-47 years old, with different epilepsy syndromes on enzyme-inducing AED (EIAED) and/or non-enzyme-inducing AED (NEIAED) treatments, and in 30 age-matched healthy women. Hormonal data were correlated with clinical parameters (age, epilepsy syndrome, disease onset, and duration), seizure frequency assessed on the basis of a seizure frequency score (SFS), and AED therapies. E2, Pg, and FEI were lower, whereas SHBG levels were higher in the epilepsy patients than in the controls. However, sex steroid and SHBG levels were not different between groups of patients categorized according to SFS. Therapies with EIAEDs accounted for changes in E2 levels and FEI. Despite globally decreased sex steroid levels in serum, actual hormone titers were not significantly correlated with SFS in consecutive epilepsy women; rather, these hormonal changes were explained by AED treatments, mainly when EIAED polytherapies were given.

Influence of dietary concentrations of protein, lipid and carbohydrate on growth, protein and energy utilization, body composition, and plasma titres of growth hormone and insulin-like growth factor-1 in non-transgenic and growth hormone transgenic coho salmon, Oncorhynchus kisutch (Walbaum)

This study compared the ability of juvenile non-transgenic (NT) and transgenic growth hormone (T; gene construct OnMTGH1) coho salmon ( Oncorhynchus kisutch) to metabolically utilize energy from lipid and carbohydrate for growth at two dietary protein concentrations. Triplicate groups of size-matched (initial weight, 28.2–29.1 g) NT and T salmon held in 10.5–10.8 °C well water on a natural phototocycle (12.25 h → 8.25 h) were each fed one of four isoenergetic (~ 17.5 MJ of digestible energy (DE)/kg) dry diets twice daily to satiation for 83 days. These diets contained 340 g (LP) or 430 g (HP) of estimated digestible protein (DP)/kg and either 123 g (LL) or 164 g (HL) of estimated digestible lipid (DL)/kg at each DP level (dry weight basis). Estimated digestible carbohydrate (DCHO) concentrations ranged from 45 to 269 g/kg to equalize dietary DE. Under the preceding conditions 46–66% of NT and 18.7–27.5% of T coho, depending upon diet treatment, exhibited no growth or lost weight during the study. NT coho are known to grow slowly or lose weight between the fall equinox and winter solstice but this was unexpected for T coho. Considering all fish T coho, regardless of diet treatment, exhibited significantly higher specific growth rates (SGR) than NT fish due to enhanced feed intake, feed and protein (gross and available deposited) utilization and generally improved available energy utilization. Diet treatment did not affect the growth performance of T fish. Within NT fish, the HP diets supported best gross and available protein and energy utilization. SGR values for growing fish (F G) only followed identical trends to those for all fish in relation to diet treatment. Regardless of fish genotype, terminal hepatosomatic indices for F G were directly related to dietary DCHO content and maximum values were noted in NT fish fed LP–LL (significantly higher than observed in NT or T fish fed HP–HL). Final whole body protein concentrations adjusted for dissimilar fish size were higher in T fish fed HP–HL than in T fish fed LP diets and NT fish fed LP–LL. This was also true for T fish fed HP–LL versus T fish fed the LP diets. Within HP groups, whole body lipid and energy contents were generally higher in NT versus T fish whereas within the LP groups energy content was significantly higher in T versus NT fish and was highest in T fish fed LP–LL. Terminal plasma titres for GH and IGF–1 (all fish) were significantly higher in T than in NT fish and were generally uninfluenced by diet treatment. Non-growing NT and T fish had elevated GH relative to NT and T fish that grew. Also, GH was higher in growing T fish relative to growing NT fish whereas the opposite was true in non-growing fish. Plasma IGF-1 levels were higher in growing NT and T fish than in their respective non-growing counterparts. Within F G only, IGF-1 levels were higher in T versus NT fish. It is concluded that T coho have enhanced ability to effectively utilize DE from DCHO relative to NT fish especially when DP is near the bottom of the optimal range and DL is concurrently suboptimal for NT fish. This is likely due to the elevated titres of GH, IGF-1 and 3,5,3′-triiodo- l-thyronine (measured in another study) in T fish. Also, the enhanced ability of T fish to store energy under these dietary conditions suggests enzymatic improvements in their anaerobic and aerobic metabolism of glucose.

Characterization of a novel Cotesia vestalis polydnavirus (CvBV) gene containing a ser-rich motif expressed in Plutella xylostella larvae

Cotesia vestalis is an endoparasitoid of Plutella xylostella larvae and injects a polydnavirus (CvBV) into its host during oviposition. In this report we characterize the gene, CvBV3307, and its products. CvBV3307 is located on segment S33 of the CvBV genome, is 517 bp, and encodes a putative protein of 122 amino acids, including a serine-rich region. The expression pattern of CvBV3307 in parasitized larvae and the subcellular localization of CvBV3307 only in granulocytes indicated that it might be involved in early protection of parasitoid eggs from host cellular encapsulation and in manipulating the hormone titer and developmental rhythm of host larvae. Western blot analysis showed that the size of the immunoreactive protein (about 55 kDa) in parasitized hosts at 48 hours post parasitization (h p.p.) is much larger than the predicted molecular weight of 13.6 kDa, which suggests that CvBV3307 undergoes extensive post-translational modification in hosts.

Characterization of a protein tyrosine phosphatase gene CvBV202 from Cotesia vestalis polydnavirus (CvBV)

Cotesia vestalis (Haliday) (Hymenoptera: Braconidae) is an endoparasitoid of the larval stage of the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae) and injects a polydnavirus (CvBV) into its host during oviposition. In this paper we characterize CvBV202 and its product. CvBV202 is located on segment S2 of CvBV genome; it has a size of 984 bp and encodes a putative protein of 328 amino acids, including protein phosphatase domain and tyrosine-specific protein phosphatase domain. Gene transcripts were detected in extracts of the host as early as 2 h post-parasitization (p.p.) and continued to be detected for 6 days. Tissue-specific patterns of this gene expression showed that CvBV202 had a close relationship with the host's physiological alternations including immunosuppression, modulation of hormone titer, and nutrition metabolism. The protein was detected in the parasitized hosts at 12 h p.p. using western blot assay. The product of CvBV202 was found to be around 59 kDa, much larger than the predicted molecular weight of 37.8 kDa, suggesting that post-translational modification of CvBV202 occurs in host cells, corresponding with the existence of many post-translational modification sites. Immunofluorescence staining and confocal laser scanning microscopy revealed that CvBV202 and the fused protein eGFP-CvBV202 were observed both in the nuclear region and cytoplasm of the hemocytes of the naturally parasitized host larvae and rBac-eGFP-CvBV202-infected Tn-5B1-4 cells, respectively.

RNA interference with the allatoregulating neuropeptide genes from the fall armyworm Spodoptera frugiperda and its effects on the JH titer in the hemolymph

The juvenile hormone (JH) titer was measured by liquid chromatography–mass spectrometry (LC–MS) with electrospray ionization (ESI). Three JH homologs, the JH I–III were detected in various amounts in larvae, prepupae and virgin adult females of Spodoptera frugiperda. In penultimate larvae, the JH II and III titers were relatively high, but decreased continuously during the 3 days of that stage, whereas JH I was detectable at low amounts only on the first 2 days. At the beginning of the last larval stage almost no JH could be detected but thereafter, a consistent low amount of JH III was present until the prepupal stage. In adult virgins, the JH titer peaked on the 2nd and 6th day after the imaginal molt. The measured hormone titers well agree with general lepidopteran physiology, because in larvae the JH titer should be high to prevent premature metamorphosis, but decrease in last instar larvae before pupation, whereas in adults JH returns to control various aspects of reproduction. JH biosynthesis is thought to be the main factor influencing the JH titer in the hemolymph and there is evidence that neuropeptides either act stimulatory (allatotropins) or inhibitory (allatostatins) on this process. After silencing of either the allatostatin AS-C-type (Spofr/Manse-AS) or the allatotropin AT 2 (Spofr-AT 2) gene the transcript level was reduced in brain and gut of last instar larvae as well as of adult S. frugiperda. This suppression led to an increased JH titer in larvae, suggesting an allatostatic activity of both the peptides in this stage. As a result of the elevated hormone titer, the last larval stage was prolonged. In prepupae, the JH titer was decreased, but the animals pupated and molted normally. In adult female virgin moths the effect on the JH titer was inversely dependent on the age of the moths and varied among the JH homologs, indicating that the peptides act either allatostatic or allatotropic. For both peptides, gene silencing clearly reduced the oviposition rates of adult females.

Starvation influences allatotropin gene expression and juvenile hormone titer in the female adult oriental armyworm, Mythimna separata

The first day of adult life is the sensitive stage for shifting migrants into the resident morphs of the oriental armyworm (OAW), Mythimna separata (Walker). The juvenile hormone (JH) titer, expression of the allatotropin (AT) gene, and their relationship were investigated in adult female migrants starved in the sensitive stage, to understand the underlying mechanism of changing migrants into resident OAWs. Haemolymph JH titers of the starved female adults were mostly elevated earlier than in controls, although not all differences were statistically significant. JH I titers in the starved moths were significantly higher than those in the controls on 1, 2, and 5 days after treatment (DAT), respectively. JH II titers in the starved moths were significantly higher than the controls through the period tested except on 5 DAT. JH II is the most likely regulator in changing migrants into resident morphs. The relative quantities of AT expression in the starved moths were higher through the period tested except on 5 DAT. AT expression and JH titers appear to be positively correlated, especially for those in earlier days of the adult life. We infer that AT is the important regulator of JH levels. A model for the shifting of migrants into resident morphs in the OAW is proposed.

Molecular cloning and expression profiles of the acyl‐CoA‐binding protein gene from the cotton bollworm Helicoverpa armigera

Acyl-CoA-binding protein (ACBP), also known as the diazepam-binding inhibitor (DBI), has been identified in diverse species and is evolutionarily conserved in plants and animals. In a recent study, an ACBP cDNA (HaACBP) encoding 85 amino acids was isolated from the cotton bollworm Helicoverpa armigera. The isolated protein is highly homologous to the ACBP present in the Bombyx mori midgut, where it is highly expressed. Northern and Western blot analyses revealed that HaACBP is expressed predominantly in the midgut. Moreover, Northern blotting revealed that HaACBP was probably stimulated by a high juvenile hormone titer at ecdysis and increased along with feeding at 12 h post-ecdysis. Immunohistochemistry of the midgut revealed that HaACBP is localized in columnar cells. Data from the Northern blotting and immunohistochemistry suggested that HaACBP was expressed during the larval period and is probably responsible for nutrition absorption. However, Western blot analysis of the midgut at different developmental stages indicated that HaACBP was upregulated during larval molting and metamorphosis, which suggested that HaACBP expression was posttranscriptionally regulated.

Perception of the steroid hormone 20-hydroxyecdysone modulates agonistic interactions in Homarus americanus

The American lobster, Homarus americanus , becomes more aggressive just before moulting. This increased aggression is accompanied by an increase in the blood and urine titres of the moulting hormone, 20-hydroxyecdysone (20-HE). During combats with conspecifics, lobsters urinate upon each other to signal their aggressive and/or sexual status. We videotaped staged combats between large intermoult nongravid female lobsters exposed to 20-HE, α-ecdysone or artificial sea water (ASW) and small nongravid female lobsters that could not smell. The nephropores of both combatants were plugged to prevent urine-release. Aggressive, defensive and avoidance behaviours were ranked according to aggressiveness in a rank of aggression hierarchy, which included opponent-directed and (nonopponent) redirected behaviours. Exposure to 20-HE increased the state of arousal of large lobsters: they performed more highly aggressive behaviours, more defensive and more avoidance behaviours than either α-ecdysone-exposed or ASW-exposed lobsters. The small opponents of large 20-HE-exposed lobsters performed more aggressive behaviours. The summed aggressive intensity of all behaviours of both lobsters in a fight was greater in 20-HE fights than in ASW or α-ecdysone fights. The difference in aggressive intensity of all behaviours between the 20-HE-exposed lobsters and their opponents was significantly smaller in 20-HE fights than in α-ecdysone or ASW fights. Our results indicate that 20-HE exposure alters the agonistic behaviour of a lobster, which then evokes an increase in the aggressive behaviour of an opponent lobster. The findings suggest that 20-HE acts as a pheromone modulating aggressive interactions in lobsters.

Type B pigmentary demarcation lines in a Chinese amenorrheic woman

A 51‐year‐old Chinese woman (phototype III) presented to our dermatology clinic with a 3‐month history of asymptomatic pigmented maculae on the lower limbs that developed in the 11th month of amenorrhea. She had noticed no other areas of pigmentary change and denied any inflammatory episode or topical medication before their development. No personal or family history of hormonal imbalance or pigmentary demarcation lines (PDLs) was found. Physical examination revealed broad, band‐like pigmentation symmetrically distributed all over the flexor aspects of the lower limbs (Fig. 1). The medial borders of the pigmented areas were sharply demarcated, but the lateral borders merged imperceptibly into the normal skin. The patient was otherwise healthy. Laboratory examination, including full blood count, liver tests, triiodothyronine (T3), thyroxine (T4), and thyrotropic‐stimulating hormone (TSH), were normal. Hormonal investigations (Table 1) were within normal limits, except that estradiol (E2) was sharply decreased and follicle‐stimulating hormone (FSH) was highly elevated. Ultrasonic B‐mode examination showed a normal uterus and ovaries. No treatment was applied to the lesions. At a follow‐up visit, 16 months after onset, the pigmentary lines had resolved spontaneously. Moreover, the titers of hormones in serum had moved closer to normal values (Table 1).Pigmentary demarcation lines on the buttocks and flexor aspect of the legs. The outer part is darkerimage Hormone investigations on the serum of our patient with pigmentary demarcation lines (PDLs) 3 months after onset 16 months after onset Normal results Abnormal results Normal results Abnormal results 1. Prolactin 1. Estradiol, 12.9 pmol/L Normal, 40.0–100 pmol/L 1. Prolactin 1. Estradiol, 36.46 pmol/L Normal, 40.0–100 pmol/L 2. Luteotropic hormone 2. Follicle‐stimulating hormone, 94.3 U/L Normal, 1.5–33.4 U/L 2. Luteotropic hormone 2. Follicle‐stimulating hormone, 53.2 U/L Normal, 1.5–33.4 U/L 3. Progestone 3. Progestone 4. Total testosterone 4. Total testosterone 5. Free triiodothyronine 5. Free triiodothyronine 6. Free thyroxine 6. Free thyroxine 7. Thyroid‐stimulating hormone 7. Thyroid‐stimulating hormone

Juvenile Hormone Regulates Butterfly Larval Pattern Switches

Insect color patterns can be very diverse. This variation is also seen among many larval instar stages, which can take on vastly different phenotypes. Young caterpillars of the swallowtail butterfly, Papilio xuthus, are mimics of bird droppings, whereas the fifth larval instar is camouflaged among the leaves of host plants (cryptic pattern). We find that juvenile hormone (JH) titers decrease during the fourth larval instar. Furthermore, treatment with JH analog at the beginning of the fourth instar stage resulted in reproducing the mimetic pattern instead of the usual cryptic one and likewise altered gene expression patterns to that associated with the mimetic pattern. These findings suggest that JH regulates the progressive larval pattern switch of this insect.

Overexpression of Drosophila juvenile hormone esterase binding protein results in anti-JH effects and reduced pheromone abundance

The titer of juvenile hormone (JH), which has wide ranging physiological effects in insects, is regulated in part by JH esterase (JHE). We show that overexpression in Drosophila melanogaster of the JHE binding protein, DmP29 results in a series of apparent anti-JH effects. We hypothesize that DmP29 functions in transport of JHE such that over- or under-expression of DmP29 results in increased or decreased JH degradation at specific sites respectively. Overexpression of DmP29 during the first or second instar was lethal, while overexpression during the third instar resulted in eclosion of small adults. Overexpression of DmP29 in newly eclosed flies reduced ovarian development and fecundity in addition to reducing the abundance of aggregation pheromone ( cis-vaccenyl acetate) in males and courtship pheromone ( cis, cis-7,11-heptacosadiene) in females. Both sexes also had lower levels of 23 and 25 carbon monoenes. Females exhibited reduced receptivity to mating, and males exhibited male–male courtship behavior, with both sexes being hyperactive: Male flies covered 2.7 times the distance of control flies at 2.9 times the maximum velocity. Application of the JH analog methoprene reversed impaired ovarian development, supporting a role for reduced JH in production of this phenotype. Rather than increasing lifespan as expected from a JH deficiency, overexpression of DmP29 reduced the life span of adult flies which may result from the hyperactivity of these flies. Underexpression of DmP29 resulted in reduced longevity, increased fecundity and reduced titers of pupal JHE. An alternative hypothesis, that mitochondrial dysfunction rather than JHE results in the JH-mediated phenotypes, is discussed.

Social and nonsocial stimuli and juvenile hormone titer in a male burying beetle, Nicrophorus orbicollis

We investigated the interaction of social and nonsocial stimuli on juvenile hormone (JH) titer in male burying beetles ( Nicrophorus orbicollis). The initial JH response to discovery of a carcass was substantial (10–15-fold increase over controls) and rapid (<1 h), and occurred whether or not a female was present. By 3 h after discovery, JH titers were declining, the decline being more pronounced when a female was not present. We also tested the effect of larval stimulation on JH titer in care-giving males by removing a male's brood and replacing it with a brood of first or third instar larvae. Males initially providing care for begging first instar larvae continued to maintain high titers of JH when the replacement broods were first but not third instars. Males caring for third instar larvae (normally low JH titers) maintained low levels of JH regardless of the developmental stage of the replacement brood. This suggests that once males begin to care for nutritionally independent third instar larvae, JH titers remain low regardless of subsequent larval stimulation. Burying beetles are socially and hormonally complex organisms in which stimuli from a breeding resource, mating partners, rivals and young interact to alter the JH profile of breeding adults.

Effect on mandibular length of juvenile hormones and regulation of soldier differentiation in the termite Reticulitermes speratus (Isoptera: Rhinotermitidae)

To understand the relationship between juvenile hormone (JH) titers and morphogenetic changes associated with soldier differentiation of the termite Reticulitermes speratus, mandibular length (length between apex and first teeth) of presoldiers induced by various concentrations of JH III (0–320 μg per dish) was measured. Presoldiers were observed when treated with more than 20 μg JH III. Both left and right mandibular lengths were significantly different among differentiated presoldiers treated with different concentrations of JH III. Concentration-dependent effects on mandibular lengths were observed: higher JH III concentrations (160 and 320 μg) caused differentiation in presoldiers with longer mandibles, and lower concentrations (40 and 80 μg) caused differentiation in presoldiers with shorter mandibles. These results suggest that morphogenetic changes specific to soldiers are influenced by JH titers (endogenous JH+applied JH III) in workers. Live soldiers could inhibit presoldier differentiation in R. speratus workers. Interestingly, mandibular lengths of presoldiers induced by JH III were influenced by soldier presence, which could influence morphological changes, probably by regulation of JH titers in workers, as recently shown in the termite Coptotermes formosanus.

Individual variation in endocrine systems: moving beyond the ‘tyranny of the Golden Mean’

Twenty years ago, Albert Bennett published a paper in the influential book New directions in ecological physiology arguing that individual variation was an 'underutilized resource'. In this paper, I review our state of knowledge of the magnitude, mechanisms and functional significance of phenotypic variation, plasticity and flexibility in endocrine systems, and argue for a renewed focus on inter-individual variability. This will provide challenges to conventional wisdom in endocrinology itself, e.g. re-evaluation of relatively simple, but unresolved questions such as structure-function relationships among hormones, binding globulins and receptors, and the functional significance of absolute versus relative hormone titres. However, there are also abundant opportunities for endocrinologists to contribute solid mechanistic understanding to key questions in evolutionary biology, e.g. how endocrine regulation is involved in evolution of complex suites of traits, or how hormone pleiotropy regulates trade-offs among life-history traits. This will require endocrinologists to embrace the raw material of adaptation (heritable, individual variation and phenotypic plasticity) and to take advantage of conceptual approaches widely used in evolutionary biology (selection studies, reaction norms, concepts of evolutionary design) as well as a more explicit focus on the endocrine basis of life-history traits that are of primary interest to evolutionary biologists (cf. behavioural endocrinology).

Repeatability of baseline corticosterone concentrations

One major assumption for endocrine studies is that hormone titers are consistent within an individual so that if hormone titers are low relative to the cohort on one day, they are relatively low compared to the cohort on other days. This is an especially important assumption for most field studies where researchers may have access to an individual animal only once. We used a laboratory study with captive house sparrows ( Passer domesticus) to test this assumption using glucocorticoid titers. Baseline corticosterone titers were measured five different times for each bird under six different experimental conditions: during both day and night while birds were held on a short day photoperiod (11L, 13D), a long day photoperiod (19L, 5D), and while birds were undergoing a prebasic molt. Although the variation within an individual was often larger than the variation between individuals, the relative ranks of birds compared to their cohort were consistent during the night in all three conditions. In contrast, during the day the relative ranks of birds compared to their cohorts were only consistent on short days; on long days and during molt there was no significantly consistent ranking among individuals. Furthermore, the overall rank of an individual in its cohort was often different during the day and night. These data indicate that it is not always a good assumption that birds can be categorized as individuals with higher and lower titers, which will complicate analyses of the causes of interindividual variation.

A mathematical model for the regulation of juvenile hormone titers

The titer of juvenile hormone (JH) is determined by three factors: its rate of synthesis, its rate of degradation, and the degree to which JH is protected from degradation by binding to a diversity of JH-binding proteins. All three of these factors vary throughout the life history of an insect and contribute to variation in the JH titer. The relative importance of each of these factors in determining variation in the JH titer is not known and can, presumably, differ in different life stages and different species. Here we develop a mathematical model for JH synthesis, degradation, and sequestration that allows us to describe quantitatively how each of these contribute to the titer of total JH and free JH in the hemolymph. Our model allows for a diversity of JH-binding proteins with different dissociation constants, and also for a number of different modes of degradation and inactivation. The model can be used to analyze whether data on synthesis and degradation are compatible with the observed titer data. We use the model to analyze two data sets, from Manduca and Gryllus, and show that in both cases, the known data on synthesis and degradation cannot account for the observed JH titers because the role of JH sequestration by binding proteins is greatly underestimated, and/or the in vivo rate of JH degradation is greatly overestimated. These analyses suggest that there is a critical need to develop a better understanding of the in vivo role of synthesis, sequestration and degradation in JH titer regulation.

Hormones in the Field: Evolutionary Endocrinology of Juvenile Hormone and Ecdysteroids in Field Populations of the Wing‐Dimorphic CricketGryllus 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.