Animal distributions are shaped by the environment and antecedents. Here I show how the temperature dependence of aerobic scope (the difference between maximum and minimum rates of oxygen uptake) is a useful tool to examine the fundamental temperature niches of salmonids and perhaps other fishes. Although the concept of aerobic scope has been recognized for over half a century, only recently has sufficient evidence accumulated to provide a mechanistic explanation for the optimal temperature of salmonids. Evidence suggests that heart rate is the primary driver in supplying more oxygen to tissues as demand increases exponentially with temperature. By contrast, capacity functions (i.e. cardiac stroke volume, tissue oxygen extraction and haemoglobin concentration) are exploited only secondarily if at all, with increasing temperature, and then perhaps only at a temperature nearing that which is lethal to resting fish. Ultimately, however, heart rate apparently becomes a weak partner for the cardiorespiratory oxygen cascade when temperature increases above the optimum for aerobic scope. Thus, the upper limit for heart rate may emerge as a valuable, but simple predictor of optimal temperature in active animals, opening the possibility of using biotelemetry of heart rate in field situations to explore properly the full interplay of environmental factors on aerobic scope. An example of an ecological application of these physiological discoveries is provided using the upriver migration of adult sockeye salmon, which have a remarkable fidelity to their spawning areas and appear to have an optimum temperature for aerobic scope that corresponds to the river temperatures experienced by their antecedents. Unfortunately, there is evidence that this potential adaptation is incompatible with the rapid increase in river temperature presently experienced by salmon as a result of climate change. By limiting aerobic scope, river temperatures in excess of the optimum for aerobic scope directly impact upriver spawning migration and hence lifetime fecundity. Thus, use of aerobic scope holds promise for scientists who wish to make predictions on how climate change may influence animal distributions.

Larvae of the sunburst diving beetle, Thermonectus marmoratus, have a cluster of six stemmata (E1-6) and one eye patch on each side of the head. Each eye has two retinas: a distal retina that is closer to the lens, and a proximal retina that lies directly underneath. The distal retinas of E1 and E2 are made of a dorsal and a ventral stack of at least twelve photoreceptor layers. Could this arrangement be used to compensate for lens chromatic aberration, with shorter wavelengths detected by the distal layers and longer wavelengths by the proximal layers? To answer this question we molecularly identified opsins and their expression patterns in these eyes. We found three opsin-encoding genes. The distal retinas of all six eyes express long-wavelength opsin (TmLW) mRNA, whereas the proximal retinas express ultraviolet opsin (TmUV I) mRNA. In the proximal retinas of E1 and E2, the TmUV I mRNA is expressed only in the dorsal stack. A second ultraviolet opsin mRNA (TmUV II), is expressed in the proximal retinas of E1 and E2 (both stacks). The finding that longer-wavelength opsins are expressed distally to shorter-wavelength opsins makes it unlikely that this retinal arrangement is used to compensate for lens chromatic aberration. In addition, we also described opsin expression patterns in the medial retina of E1 and in the non-tiered retina of the lensless eye patch. To our knowledge, this is also the first report of multiple UV opsins being expressed in the same stemma.

Honeybee (Apis mellifera) society is characterized by a helper caste of essentially sterile female bees called workers. Workers show striking changes in lifespan that correlate with changes in colony demography. When rearing sibling sisters (brood), workers survive for 3-6 weeks. When brood rearing declines, worker lifespan is 20 weeks or longer. Insects can survive unfavorable periods on endogenous stores of protein and lipid. The glyco-lipoprotein vitellogenin extends worker bee lifespan by functioning in free radical defense, immunity and behavioral control. Workers use vitellogenin in brood food synthesis, and the metabolic cost of brood rearing (nurse load) may consume vitellogenin stores and reduce worker longevity. Yet, in addition to consuming resources, brood secretes a primer pheromone that affects worker physiology and behavior. Odors and odor perception can influence invertebrate longevity but it is unknown whether brood pheromone modulates vitellogenin stores and survival. We address this question with a 2-factorial experiment where 12 colonies are exposed to combinations of absence vs presence of brood and brood pheromone. Over an age-course of 24 days, we monitor the amount of vitellogenin stored in workers' fat body (adipose tissue). Thereafter, we track colony survival for 200 days. We demonstrate that brood rearing reduces worker vitellogenin stores and colony long-term survival. Yet also, we establish that the effects can result solely from exposure to brood pheromone. These findings indicate that molecular systems of extreme lifespan regulation are integrated with the sensory system of honeybees to respond to variation in a primer pheromone secreted from larvae.

The biogenic amine tyramine (TA) is a potent diuretic factor when applied to the Malpighian tubule (MT) of Drosophila melanogaster, stimulating both urine production and transepithelial chloride conductance. Isolated MTs can respond not only to TA but also to its precursor, tyrosine; this observation led to the proposal that MTs are able to synthesize TA from applied tyrosine through the action of the enzyme tyrosine decarboxylase (TDC). In the current study it is shown that the non-neuronal isoform of TDC, Tdc1, is expressed in the principal cells of the MT. A mutant allele of Tdc1, Tdc1^f03311, was identified that reduced expression of the mature Tdc1 transcript by greater than 100-fold. MTs isolated from Tdc1^f03311 homozygous flies showed no significant depolarization of their transepithelial potential (TEP) or diuresis in response to tyrosine while retaining normal sensitivity to TA. By contrast, a previously identified null mutant allele of the neuronal TDC isoform Tdc2 had no effect on either tyrosine or TA sensitivity. To determine in which cell type of the MT Tdc1 expression is required, flies were generated carrying a UAS-Tdc1 transgene and cell-type-specific Gal4 drivers on a Tdc1^f03311 homozygous background. Rescue of Tdc1 expression in principal cells fully restored sensitivity to tyrosine whereas expression of Tdc1 in stellate cells had no rescuing effect. It is concluded that synthesis of TA by Tdc1 in the principal cells of the MT is required for physiological responses to tyrosine. TA synthesis in the MT is the first reported physiological role for Drosophila Tdc1.

Learning plays an important role in food acquisition for a wide range of insects and has been demonstrated to be essential during flower foraging in taxa such as bees, parasitoid wasps, butterflies and moths. However, little attention has been focused on differences in floral cue learning abilities among species and sexes. We examined the associative learning of flower colour with nectar in four butterfly species: Idea leuconoe, Argyreus hyperbius, Pieris rapae and Lycaena phlaeas. All butterflies that were trained learned the flower colours associated with food. The flower colour learning rates were significantly higher in I. leuconoe and A. hyperbius than in P. rapae and L. phlaeas. Among the four species examined, the larger and longer-lived species exhibited higher learning rates. Furthermore, female butterflies showed a significantly higher learning rate than males. This study provides the first evidence that learning abilities related to floral cues differ among butterfly species. The adaptive significance of superior learning abilities in the larger and longer-lived butterfly species and in females is discussed.

Songbirds exhibit seasonal plasticity in a broad variety of behavioral and morphological traits associated with reproduction. Changes in song production are well described while changes in song reception are not. In the present study, we test for seasonal variation in auditory processing of the house sparrow (Passer domesticus L.) using auditory brainstem responses (ABRs) to tone bursts. We measured amplitude and latency of the first ABR peak in spring, summer and autumn at stimulus frequencies from 0.8 to 6.4 kHz and intensity levels from 24 to 80 dB SPL. ABR thresholds were determined at each frequency using cross-correlation. Amplitude was greater in spring than in autumn at frequencies from 3.2 to 6.4 kHz whereas latency and thresholds exhibited no seasonal variation. The results indicate an increase in the number or temporal synchrony of responses from peripheral auditory neurons during the early breeding season. Changes in peripheral auditory processing may enhance temporal coding of the fine structure and envelope of song; thereby, improving assessment of encoded information in both sexes (e.g. individual identity and dominance status) and auditory feedback during song production in males. Peripheral auditory changes may be mediated by reproductive hormones, and could involve changes in hair cell density on the basilar papilla. Our results suggest that peripheral auditory processing of songbirds changes seasonally in parallel with other behavioral and morphological traits, such as song production.

Sea turtles are known to detect chemical cues, but in contrast to most marine animals, turtles surface to breathe and thus potentially have access to olfactory cues both in air and in water. To determine whether sea turtles can detect airborne chemical cues, captive loggerhead turtles (Caretta caretta) were placed into a circular, water-filled arena in which odorants could be introduced to the air above the water surface. Air that had passed across the surface of a cup containing food elicited increased activity, diving and other behavior normally associated with feeding. By contrast, air that had passed across the surface of an identical cup containing distilled water elicited no response. Increases in activity during food odor trials occurred only after turtles surfaced to breathe and peaked in the first post-breath minute, implying that the chemical cues eliciting the responses were unlikely to have been detected while the turtles were under water. These results provide the first direct evidence that sea turtles can detect airborne odors. Under natural conditions, this sensory ability might function in foraging, navigation or both.

This study aimed to examine whether the stenohaline freshwater stingray, Potamotrygon motoro, which lacks a functional ornithine—urea cycle, would up-regulate glutamine synthetase (GS) activity and protein abundance, and accumulate glutamine during a progressive transfer from freshwater to brackish (15) water with daily feeding. Our results revealed that, similar to other freshwater teleosts, P. motoro performed hyperosmotic regulation, with very low urea concentrations in plasma and tissues, in freshwater. In 15 water, it was non-ureotelic and non-ureoosmotic, acting mainly as an osmoconformer with its plasma osmolality, [Na⁺] and [Cl^–] comparable to those of the external medium. There were significant increases in the content of several free amino acids (FAAs), including glutamate, glutamine and glycine, in muscle and liver, but not in plasma, indicating that FAAs could contribute in part to cell volume regulation. Furthermore, exposure of P. motoro to 15 water led to up-regulation of GS activity and protein abundance in both liver and muscle. Thus, our results indicate for the first time that, despite the inability to synthesize urea and the lack of functional carbamoyl phosphate synthetase III (CPS III) which uses glutamine as a substrate, P. motoro retained the capacity to up-regulate the activity and protein expression of GS in response to salinity stress. Potamotrygon motoro was not nitrogen (N) limited when exposed to 15 water with feeding, and there were no significant changes in the amination and deamination activities of hepatic glutamate dehydrogenase. In contrast, P. motoro became N limited when exposed to 10 water with fasting and could not survive well in 15 water without food.

Carbonic anhydrase (CA) is critical for CO₂ excretion in adult fish, but little is known of the expression or function of CA during early development. The present study examined the hypothesis that, as rates of CO₂ production increased during early development in zebrafish (Danio rerio), CA would become necessary for effective CO₂ excretion, and that the pattern of CA expression during early development would reflect this transition. Real-time RT-PCR was used to examine the mRNA expression of the two main intracellular CA isoforms over a time course of early development ranging from 0 to 120 h post fertilization (h.p.f.). The mRNA expression of zCAb was generally higher than that of zCAc, particularly during the earliest stages of development. Rates of CO₂ excretion increased approximately 15-fold from 24 to 48 h.p.f. whereas rates of O₂ uptake increased only 6.7-fold over the same period, indicating a relative stimulation of CO₂ excretion over O₂ uptake. Treatment of 48 h.p.f. larvae with the CA inhibitor acetazolamide resulted in CO₂ excretion rates that were 52% of the value in control larvae, a significant difference that occurred in the absence of any effect on O₂ uptake. Antisense morpholino oligonucleotides were used to selectively knock down one or both of the main intracellular CA isoforms. Subsequent measurement of gas transfer rates at 48 h.p.f. indicated that CA knockdown caused a significant relative inhibition of CO₂ excretion over O₂ uptake, regardless of which cytosolic CA isoform was targeted for knockdown. These results suggest that between 24 h.p.f. and 48 h.p.f., developing zebrafish begin to rely on CA to meet requirements for increased CO₂ excretion.

While adult zebrafish, Danio rerio, possess ammonia and urea transporters (Rh and UT proteins, respectively) in a number of tissues, they are most heavily concentrated within the gills. UT has a diffuse expression pattern within Na⁺-K⁺-ATPase (NKA)-type mitochondrion-rich cells and Rh proteins form a network similar to the arrangement seen in pufferfish gills (Nakada et al., 2007b). Rhag expression appeared to be limited to the pillar cells lining the blood spaces of the lamellae while Rhbg was localized to the outer layer of both the lamellae and the filament, upon the pavement cells. Exposure to high external ammonia (HEA) or phloretin increased tissue levels of ammonia and urea, respectively, in adult and juvenile zebrafish; however, the responses to these stressors were age dependent. HEA increased mRNA levels for a number of Rh proteins in embryos and larvae but did not elicit similar effects in adult gills, which appear to compensate for the unfavourable ammonia excretory gradient by increasing expression of V-type H⁺-ATPase. Phloretin exposure increased UT mRNA levels in embryos and larvae but was without effect in adult gill tissue. Surprisingly, in both adults and juveniles, HEA increased the mRNA expression of UT and phloretin increased the mRNA expression of Rh proteins. These results imply that, in zebrafish, there may be a tighter link between ammonia and urea excretion than is thought to occur in most teleosts.

Photoperiod is an important cue regulating biological rhythms in mammals, including ‘blind’ subterranean and sighted fossorial rodent species. These species may respond differentially to changes in light quality according to their retinal complexity. The effects of increasing light intensity on daily rhythms of urine excretion and urinary output of 6-sulfatoxymelatonin levels were compared in ‘blind’ mole rats Spalax ehrenbergi and sighted social voles, Microtus socialis. Our results show that the threshold irradiance required to entrain rhythms of voles is three magnitudes greater than that for mole rats. The results suggest that mole rats have an operational photoreceptive pathway with a lower threshold irradiance than voles. Such a low threshold reflects the remarkable capability of this ‘blind’ species to utilize light signals even under challenging light conditions.

The fatty acid composition of muscle membrane phospholipids and fat stores may affect migration performance in birds. The purpose of this study was to investigate seasonal changes in the fatty acid composition of (1) pectoralis muscle phospholipids, (2) intramuscular triglyceride stores and (3) adipose tissue triglycerides in free-living white-throated sparrows (Zonotrichia albicollis). During migratory seasons there was an increase in the n-6:n-3 ratio of muscle membrane phospholipid fatty acids without a change in the proportion of unsaturated fatty acids. This change was driven mainly by an increase in the proportion of 18:2n-6 and a decrease in the proportion of 22:6n-3. An increase in the proportion of 18:2n-6 was also observed in the intramuscular and adipose tissue triglyceride stores during the migratory seasons. These increases in 18:2n-6 were offset by a decrease in 16:0; resulting in an elevated proportion of unsaturated fatty acids and elevated double bond index in both fat stores of migrants. The elevated levels of 18:2n-6 in migrant fat stores indicates a high dietary component of this fatty acid, as white-throated sparrows feed mainly on tree seeds and some insects during migration and may not have access to a diet high in n-3 fatty acids. We suspect that elevated dietary levels of 18:2n-6 also caused the observed increases in the proportion of this fatty acid in muscle phospholipids. Overall, we conclude that seasonal changes in adipose and muscle fatty acid composition are likely attributable to diet more than other factors such as migratory exercise or mitochondrial density.

Intestinal HCO₃^– secretion is essential to marine teleost fish osmoregulation and comprises a considerable source of base efflux attributable to both serosal HCO₃^– and endogenous CO₂ hydration. The role of intestinal HCO₃^– secretion in dynamic acid—base balance regulation appears negligible in studies of unfed fish, but evidence of high intestinal fluid [HCO₃^–] in fed marine teleosts led us to investigate the source of this HCO₃^– and its potential role in offsetting the postprandial ‘alkaline tide’ commonly associated with digestion. Specifically, we hypothesized that elevated metabolic rate and thus endogenous CO₂ production by intestinal tissue as well as increased transepithelial intestinal HCO₃^– secretion occur post-feeding and offset a postprandial alkaline tide. To test these hypotheses changes in HCO₃^– secretion and O₂ consumption by gulf toadfish (Opsanus beta) isolated intestine were quantified 0, 3, 6, 12, 24 and 48 h post-feeding. Intestinal tissue of unfed fish in general showed high rates of HCO₃^– secretion (15.5 µmol g^–1 h^–1) and O₂ consumption (8.9 µmol g^–1 h^–1). Furthermore, postprandial increases in both intestinal HCO₃^– secretion and O₂ consumption (1.6- and 1.9-fold peak increases, respectively) were observed. Elevated intestinal HCO₃^– secretion rates preceded and outlasted those of O₂ consumption, and occurred at a magnitude and duration sufficient to account for the lack of alkaline tide. The dependence of these high rates of postprandial intestinal base secretion on serosal HCO₃^– indicates transepithelial HCO₃^– transport increases disproportionately more than endogenous CO₂ production. The magnitude of postprandial intestinal HCO₃^– secretion indicates the intestine certainly is capable of postprandial acid#x02014;base balance regulation.

We have studied the passive maintenance of high angle of attack and its lift generation during the crane fly's flapping translation using a dynamically scaled model. Since the wing and the surrounding fluid interact with each other, the dynamic similarity between the model flight and actual insect flight was measured using not only the non-dimensional numbers for the fluid (the Reynolds and Strouhal numbers) but also those for the fluid—structure interaction (the mass and Cauchy numbers). A difference was observed between the mass number of the model and that of the actual insect because of the limitation of available solid materials. However, the dynamic similarity during the flapping translation was not much affected by the mass number since the inertial force during the flapping translation is not dominant because of the small acceleration. In our model flight, a high angle of attack of the wing was maintained passively during the flapping translation and the wing generated sufficient lift force to support the insect weight. The mechanism of the maintenance is the equilibrium between the elastic reaction force resulting from the wing torsion and the fluid dynamic pressure. Our model wing rotated quickly at the stroke reversal in spite of the reduced inertial effect of the wing mass compared with that of the actual insect. This result could be explained by the added mass from the surrounding fluid. Our results suggest that the pitching motion can be passive in the crane fly's flapping flight.

This study reveals the peculiar in vivo cell kinetics and cell turnover of the marine sponge Halisarca caerulea under steady-state conditions. The tropical coral reef sponge shows an extremely high proliferation activity, a short cell cycle duration and massive cell shedding. Cell turnover is predominantly confined to a single cell population, i.e. the choanocytes, and in this process apoptosis only plays a minor role. To our knowledge, such fast cell kinetics under steady-state conditions, with high turnover by shedding in the absence of apoptosis, has not been observed previously in any other multicellular organism. The duration of the cell cycle in vivo resembles that of unicellular organisms in culture. Morphological and histochemical studies demonstrate compartmentalization of choanocytes in the sponge tissue, which corresponds well with its remarkable cellular kinetics. Coral reef cavity sponges, like H. caerulea, inhabit low nutrient tropical waters, forcing these organisms to filter large volumes of water and to capture the few nutrients efficiently. Under these oligotrophic conditions, a high cell turnover may be considered as a very useful strategy, preventing permanent damage to the sponge by environmental stress. Halisarca caerulea maintains its body mass and keeps its food uptake system up to date by constantly renewing its filter system. We conclude that studies on cell kinetics and functional morphology provide new and essential information on the growth characteristics and the regulation of sponge growth in vivo as well as in vitro and the role of choanocytes in tissue homeostasis.

The melanocortin 5 receptor (MC5R) plays a key role in the regulation of exocrine secretion in mammalian species. This receptor has also been characterized in some fish species but its function is unknown. We report the molecular and pharmacological characterization, as well as the tissue expression pattern, of sea bass MC5R. Cloning of five active alleles showing different levels of sensitivity to endogenous melanocortin and one non-functional allele demonstrate the allelic complexity of the MC5R locus. The sea bass receptor was activated by all the melanocortins tested, with ACTH and desacetyl-MSH and β-MSH showing the lowest efficiency. The acetylation of the MSH isoforms seems to be critical for the effectiveness of the agonist. Agouti-related protein had no effect on basal or agonist-stimulated activation of the receptor. SbMC5R was mainly expressed in the brain but lower expression levels were found in several peripheral tissues, including liver. Progressive fasting did not induce up- or downregulation of hypothalamic MC5R expression, suggesting that central MC5R is not involved in the regulation of food intake in the sea bass. MTII, a sbMC5R agonist, stimulated hepatic lipolysis in vitro, measured as free fatty acid release into the culture medium after melanocortin agonist exposure of liver fragments, suggesting that MC5R is involved in the regulation of hepatic lipid metabolism. Taken together, the data suggest that different allelic combinations may confer differential sensitivity to endogenous melanocortin in tissues where MC5R is expressed and, by extension, in hepatic lipid metabolism.

We found strain differences in the ability of wild Alberta Lymnaea stagnalis to form long-term memory (LTM) following operant conditioning when L. stagnalis were collected from the wild and trained in the laboratory. Lymnaea stagnalis obtained from the Belly River watershed had an enhanced ability to form LTM compared with those from an isolated pond (referred to as Jackson snails). We therefore asked whether the differences in cognitive ability were an epiphenomenon as a result of training in the laboratory. To answer this question we trained each specific strain (Belly and Jackson) in both the laboratory and the field (i.e. in their home pond and in the pond where the other strain resided - referred to as the visitor pond). We found that within each strain there was no difference in the LTM phenotype whether they were trained in the lab or in either their home or visitor pond. That is, the strain differences in the ability to form LTM were still present. Interestingly, we found no strain differences in the ability to learn or the ability to form intermediate-term memory (ITM).

In mammals, pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) are involved in cardiovascular and respiratory regulation. Several studies have demonstrated the presence of PACAP, VIP and their receptors in various tissues of teleost fish, including the brain, but little is known about their respiratory and cardiovascular effects. The present study was undertaken to compare the central and peripheral actions of graded doses (25-100 pmol) of trout PACAP and trout VIP on ventilatory and cardiovascular variables in the unanaesthetized rainbow trout. Compared with vehicle, only intracerebroventricular injection of PACAP significantly (P<0.05) elevated the ventilation frequency and the ventilation amplitude, but both peptides significantly increased the total ventilation ( ). However, the maximum hyperventilatory effect of PACAP was approximately 2.5-fold higher than the effect of VIP at the 100 pmol dose (PACAP, =+5407±921 arbitrary units, a.u.; VIP, =+2056±874 a.u.; means ± s.e.m.). When injected centrally, only PACAP produced a significant increase in mean dorsal aortic blood pressure (P_DA) (100 pmol: +21%) but neither peptide affected heart rate (f_H). Intra-arterial injections of either PACAP or VIP were without effect on the ventilatory variables. PACAP was without significant action on P_DA and f_H while VIP significantly elevated P_DA (100 pmol: +36%) without changing f_H. In conclusion, the selective central hyperventilatory actions of exogenously administered trout PACAP, and to a lesser extent VIP, suggest that the endogenous peptides may be implicated in important neuroregulatory functions related to the central control of ventilation in trout.

Honeybee foragers are exposed to thermal stimuli when collecting food outside and receiving food rewards inside the nest. In both contexts, there is an opportunity for foragers to associate warmth with food rewards. However, honeybee thermal learning is poorly understood. Using an associative learning paradigm (the proboscis extension reflex), we show that honeybees can learn to associate a nectar reward with a heated stimulus applied to the antenna to mimic natural contact with a warm flower or nectar-offering forager. Conditioning with longer inter-trial intervals (ITI) significantly improved learning acquisition. We also trained bees to discriminate between temperatures above (warm) and below (cold) ambient air temperature. Learning acquisition improved by 38% per 10°C increase in absolute stimulus intensity (difference between the rewarded temperature and unrewarded ambient air temperature). However, bees learned positive temperature (warm) significantly better than negative temperature (cold) differences, approximately twice as well for 10°C as compared with a –10°C difference. Thus, thermosensation, a sensory modality that is relatively unexplored in honeybees, could play a role in the acquisition of information from nestmates (social learning) and in foraging decisions influenced by associations between floral temperature and nectar rewards.