Development of the swimbladder in the European eel (Anguilla anguilla)

The swimbladder of the adult eel, Anguilla anguilla, with its bipolar countercurrent system, the rete mirabile, is a widely used model for swimbladder function, but very little is known about the development of this swimbladder. Our histological studies on the developing swimbladder revealed that during metamorphosis the swimbladder becomes present as a dorsal outgrowth of the esophagus. It is filled with surfactant, and gas was not detected in the swimbladder. In the young glass-eel, the epithelial (gas gland) cells of the swimbladder are columnar, but do not yet have the typical basolateral labyrinth established in adult animals. Few blood vessels are found in the swimbladder tissue, and the submucosa is present as a thick layer of connective tissue, giving a large diffusion distance between blood vessel and swimbladder lumen. Within the next 2 or 3 months of development, gas gland cells develop their typical basolateral labyrinth, and the thickness of the submucosa is significantly reduced, resulting in a short diffusion distance between blood vessels and the swimbladder lumen. The first filling of the swimbladder with gas is observed while the gas gland cells are still in a poorly differentiated status and it appears unlikely that these cells can accomplish their typical role in gas deposition. The presence of small gas bubbles in the swimbladder as well as in the ductus pneumaticus at the time of initial swimbladder inflation suggests that the swimbladder is filled by air gulping or possibly by taking up gas bubbles from the water.     

Local adaptation of fish consumers alters primary production through changes in algal community composition and diversity

Ecological research has focused on understanding how changes in consumer abundance affects community structure and ecosystem processes. However, there is increasing evidence that evolutionary changes in consumers can also alter community structure and ecosystem processes. Typically, the effects of consumer phenotype on communities and ecosystem processes are measured as net effects that integrate numerous ecological pathways. Here, we analyze new data from experimental manipulations of Trinidadian guppy Poecilia reticulata presence, density and phenotype to examine how effects on the algal community cause changes in gross‐primary production (GPP). We combine analytical tools borrowed from path analysis with experimental exclosures in mesocosms to separate the ecological and evolutionary effects of guppies into direct and indirect components. We show that the evolutionary effects of guppy phenotype act through different ecological pathways than the effects of guppy presence and density on GPP. As reported in previous studies that used a different measure of algal biomass, adding guppies and doubling their densities decreased algal biovolume through direct effects. In contrast to these previously reported results, exchanging guppy phenotypes that live without predators for phenotypes that live with predators did not affect algal biovolume. Instead, guppies from populations that live with predators increased the diversity of algal species and increased GPP compared to guppies that live without predators. These changes in the algal community were driven primarily by guppy phenotypes that live with predators—algal communities in mesocosms without fish were similar to those with guppies from predator‐free locations, but both were different from mesocosms with guppies from populations that live with predators. Changes in the algal community were driven directly by differences in foraging behavior between the two consumer phenotypes. We reconcile these results with our previous findings, thereby enhancing our understanding of the relationship between ecological and evolutionary processes.     

Histological demonstration of glucose transporters,fructose-1,6-bisphosphatase,and glycogen in gas gland cells of the swimbladder: Is a metabolic futile cycle operating?

Luminal surface of the swimbladder is covered by gas gland epithelial cells and is responsible for inflating the swimbladder by generating O(2) from Root-effect hemoglobin that releases O(2) under acidic conditions. Acidification of blood is achieved by lactic acid secreted from gas gland cells, which are poor in mitochondria but rich in the glycolytic activity. The acidic conditions are locally maintained by a countercurrent capillary system called rete mirabile. To understand the regulation of anaerobic metabolism of glucose in the gas gland cells, we analyzed the glucose transporter expressed there and the fate of ATP generated by glycolysis. The latter is important because the ATP should be immediately consumed otherwise it strongly inhibits the glycolysis rendering the cells unable to produce lactic acid anymore. Expression analyses of glucose transporter (glut) genes in the swimbladder of fugu (Takifugu rubripes) by RT-PCR and in situ hybridization demonstrated that glut1a and glut6 are expressed in gas gland cells. Immunohistochemical analyses of metabolic enzymes demonstrated that a gluconeogenesis enzyme fructose-1,6-bisphosphatase (Fbp1) and a glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (Gapdh) are highly expressed in gas gland cells. The simultaneous catalyses of glycolysis and gluconeogenesis reactions suggest the presence of a futile cycle in gas gland cells to maintain the levels of ATP low and to generate heat that helps reduce the solubility of O(2).     

Pressure Effects on Cholesterol and Lipid Synthesis by the Swimbladder of an Abyssal Coryphaenoides Species

SYNOPSIS. The swimbladder gas gland is recognized as a cholesterolsynthesis site in abyssal rattail fishes, Coryphaenoides sp.(from 2000 m depth), and Galápagos Islands surface fish,Orthopristis forbesi, Seriola mazatlana, and Sphoeroides annulatus.This relates to high levels of cholesterol in the gas gland(up to 21% of lipid) and high cholesterol levels in the fattyswimbladder interior (up to 49% of lipid). The gas gland hasmore protein (45.4%) than the internal fatty mass (18%). Lipidssynthesized include phospholipids and triglycerides in 2:1 ratioin the gas gland and 1:2 ratio in the liver. Deep fish havefatty livers (66%) compared to shallow fish (28%). Shallow fishincorporated five times as much acetate-l-¹⁴C into lipids asdid deep fish, and seven to eight times as much acetate-l-¹⁴Cinto cholesterol. Pressure facilitation of cholesterol synthesiswas observed in gas gland and liver of O. forbesi and Coryphaenoides,whereas total lipid synthesis was inhibited by higher pressures.Optimal acetate-l-¹⁴C incorporation into lipids occurred at5000 psi and 2°C in Coryphaenoides; it occurred at 14.7psi and 15° in O. forbesi. These conditions closely approximatethe environment of the fish.     

Influence of prey foraging posture on flight behavior and predation risk: predators take advantage of unwary prey

Foraging in animals is often associated with characteristicbody postures, such as the head-down posture. When foragingconflicts with the ability to detect predators or to flee, individualsmay incur a greater risk of mortality to predation than otherwise.Here we investigate the influence of different foraging postures(horizontal versus nose-down body posture) on the ability ofindividuals to respond to approaching predators and on the riskof mortality to predation in the guppy (Poecilia reticulata).Individuals engaged in nose-down foraging were assumed to beable to visually scan a smaller area for predators and to escapeless effectively due to their body posture, and thus are morevulnerable to stalking predators than horizontally foragingones. In a first experiment, we separately exposed nonforaging,horizontally foraging, and nose-down foraging guppies to anapproaching cichlid fish predator model. Nonforaging guppiesreacted sooner to and initiated flight further away from theapproaching model than did foraging fish collectively, and horizontallyforaging individuals responded sooner to the model than nose-downforaging ones. Comparing all test guppies, nose-down foragingindividuals were the most likely not to exhibit any responseto the predator model. When presented with a simultaneous choiceof two guppies behind a one-way mirror, individual blue acaracichlid (Aequidens pulcher), a natural predator of the guppy,preferred to attack foraging guppies over nonforaging ones andnose-down foraging guppies over horizontally foraging individuals.In a final experiment with free-swimming cichlids and guppies,we demonstrated that individual risk of predation for guppiesforaging nose down was greater than for guppies foraging horizontally,and both were at greater risk than nonforaging guppies. Thislatter result is consistent with the above differences in theguppy's responsiveness to approaching predators depending ontheir foraging behavior, and with the finding that cichlid predatorspreferred fish that were less likely to show any response tothem. Our results therefore indicate that the ability to respondto approaching predators and the risk of mortality to predationin the guppy is strongly influenced by their foraging activity,and in particular their foraging posture, and that cichlid predatorspreferentially select less wary and more vulnerable guppies.[BehavEcol 7: 264–271 (1996)]     

Life-history evolution in guppies. VII. The comparative ecology of high- and low-predation environments

Prior research has demonstrated a strong association between the species of predators that co-occur with guppies and the evolution of guppy life histories. The evolution of these differences in life histories has been attributed to the higher mortality rates experienced by guppies in high-predation environments. Here, we evaluate whether there might be indirect effects of predation on the evolution of life-history patterns and whether there are environmental differences that are correlated with predation. To do so, we quantified features of the physical and chemical environment and the population biology of guppies from seven high- and low-predation localities. We found that high-predation environments tend to be larger streams with higher light levels and higher primary productivity, which should enhance food availability for guppies. We also found that guppy populations from high-predation environments have many more small individuals and fewer large individuals than those from low-predation environments, which is caused by their higher birth rates and death rates. Because of these differences in size distribution, guppies from high-predation environments have only one-fourth of the biomass per unit area, which should also enhance food availability for guppies in these localities. Guppies from high-predation sites allocate more resources to reproduction, grow faster, and attain larger asymptotic sizes, all of which are consistent with higher levels of resource availability. We conclude that guppies from high-predation environments experience higher levels of resource availability in part because of correlated differences in the environment (light levels, primary productivity) and in part as an indirect consequence of predation (death rates and biomass density). These differences in resource availability can, in turn, augment the effect of predator-induced mortality as factors that shape the evolution of guppy life-history patterns. We found no differences in the invertebrate communities from high- and low-predation localities, so we conclude that there do not appear to be multitrophic, indirect effects associated with these differences in predation.     

Uptake of3H-adrenaline and14C-noradrenaline into neuronal and extraneuronal tissue compartments in the perfused gas gland of the swimbladder of the Atlantic cod,Gadus morhua

Summary The neuronal and extraneuronal accumulation of radiolabelledl-adrenaline andl-noradrenaline was studied in the gas gland of the swimbladder of the Atlantic cod,Gadus morhua. Both amines are taken up into the tissue compartments, and a preference for noradrenaline for both uptake processes was demonstrated. A relatively high neuronal accumulation compared to earlier results (cod spleen; Ungell and Nilsson 1984) was seen and this is probably due to the more dense innervation of the swimbladder gas gland. A higher extraneuronal accumulation may be due to the presence of arterial smooth muscle.It is concluded that the adrenergic nerves of the swimbladder gas gland of the cod preferentially accumulate noradrenaline, a situation similar to that in mammals.Abbreviations A/NA adrenaline/noradrenaline ratio - PBA phenoxybenzamine - PNMT phenylethanolamine-N-methyl tranferase     

Metabolic stoichiometry and the ecology of fear in Trinidadian guppies: consequences for life histories and stream ecosystems

Consumer-driven nutrient recycling, the release of chemicals as byproducts and excesses of consumer physiology, can alter ecosystems by changing the availability of limiting nutrients at the base of the food web. The mere presence of predators can alter consumer physiology by restricting food intake and inducing stress. Predation risk, then, can influence ecosystem function by modifying the role of prey as nutrient recyclers, yet there are few empirical tests of how predation risk alters nutrient recycling by prey. Here, we present the results of a test for the effects of predation risk on the C and N budgets of Trinidadian guppies (Poecilia reticulata). We reared female guppies for 7 weeks on diets of varying quality, and we compared control individuals to those exposed continuously to chemical cues emitted by a guppy predator, Crenicichla alta. We measured food consumption, growth rate, tissue elemental stoichiometry and N excretion by guppies on all treatments. Guppies strongly reduced food intake in the presence of predator cues; however, cue-exposed guppies assimilated nutrients more efficiently than controls. Specifically, cue-exposed guppies strongly increased N retention efficiency while only moderately increasing C efficiency. Consequently, guppies reared with predator cues excreted 39 % less N than control guppies. We suggest that reduced foraging, enhanced nutrient efficiency, and decreased N excretion are adaptive responses to the extrinsic mortality threat posed by guppy predators. The resulting substantial reduction in N excretion by guppies may influence ecosystem function in natural streams by reducing the supply of a limiting nutrient.     

A useful immunohistochemical approach to evaluate intraductal proliferative lesions of the breast and to predict their prognosis

An examination was performed on 16 intraductal proliferative breast lesions diagnosed as intraductal papillomas (IP) or usual ductal hyperplasia (UDH), which were followed up for more than 3 years. An immunohistochemical marker panel combining myoepithelial markers, high-molecular-weight keratin (HMWK) and neuroendocrine markers was used. Two of 11 IP cases were re-evaluated as atypical ductal hyperplasia (ADH) and ductal carcinoma in situ (DCIS). These cases developed breast cancer after the first operation. One IP case showed repeated recurrences. None of the other IP and UDH cases had breast cancer or recurrence. The ADH, DCIS and the recurrent IP showing a solid growth lacked myoepithelia, but the recurrent IP expressed HMWK, immunohistochemically. Interestingly, these three lesions were weakly positive for neuroendocrine markers. All other IPs and UDHs, including lesions having solid components, were negative for neuroendocrine markers, and most of them were positive for myoepithelial markers and/or HMWK. A combination of the above immunohistochemical markers seems useful to evaluate intraductal proliferative lesions and to predict their prognosis. In particular, intraductal proliferative lesions with solid components exhibiting positivity for neuroendocrine markers should be followed up carefully to monitor breast cancer risk or recurrence.     

Implications of guppy (Poecilia reticulata) life‐history phenotype for mosquito control

Guppies (Poecilia reticulata) are frequently introduced to both natural and artificial water bodies as a mosquito control. Laboratory studies have demonstrated that guppies can consume large numbers of larval mosquitoes. Our study investigates how intraspecific variability in guppy phenotype affects their importance as a mosquito biocontrol and how habitat conditions (natural ponds vs. water storage containers) may influence insect biomass and guppy feeding. Using a blocked experimental design, we established stream‐side mesocosm ponds with half receiving gravel substrate to simulate pond‐bottom habitat. To provide realistic diet choices and insect abundances, we allowed the mesocosms to colonize naturally with aquatic insect larvae for 1 month before introducing guppies. We tested two distinct guppy phenotypes (from high‐ and low‐predation streams) alongside fish‐free controls. After 1 month, we measured insect biomass in the mesocosms and examined guppy gut contents to document direct predation. While overall insect biomass was not significantly different across the three fish treatments, we observed a significant reduction in mosquito biomass in fish treatments compared to fish‐free controls, as well as intraspecific differences in feeding. Overall insect biomass was significantly higher in mesocosms without gravel, while habitat condition had no effect on mosquito biomass. As guppy phenotype responds to changes in their environments, it is an important consideration for biocontrol policy to anticipate potential ecosystem effects. We close by relating our findings to other studies and by discussing the implications and potential risks of using guppies to control mosquitoes.     

O2-filled swimbladder employs monocarboxylate transporters for the generation of O2 by lactate-induced root effect hemoglobin

The swimbladder volume is regulated by O(2) transfer between the luminal space and the blood In the swimbladder, lactic acid generation by anaerobic glycolysis in the gas gland epithelial cells and its recycling through the rete mirabile bundles of countercurrent capillaries are essential for local blood acidification and oxygen liberation from hemoglobin by the "Root effect." While O(2) generation is critical for fish flotation, the molecular mechanism of the secretion and recycling of lactic acid in this critical process is not clear. To clarify molecules that are involved in the blood acidification and visualize the route of lactic acid movement, we analyzed the expression of 17 members of the H(+)/monocarboxylate transporter (MCT) family in the fugu genome and found that only MCT1b and MCT4b are highly expressed in the fugu swimbladder. Electrophysiological analyses demonstrated that MCT1b is a high-affinity lactate transporter whereas MCT4b is a low-affinity/high-conductance lactate transporter. Immunohistochemistry demonstrated that (i) MCT4b expresses in gas gland cells together with the glycolytic enzyme GAPDH at high level and mediate lactic acid secretion by gas gland cells, and (ii) MCT1b expresses in arterial, but not venous, capillary endothelial cells in rete mirabile and mediates recycling of lactic acid in the rete mirabile by solute-specific transcellular transport. These results clarified the mechanism of the blood acidification in the swimbladder by spatially organized two lactic acid transporters MCT4b and MCT1b.     

Evolutionary implications of large-scale patterns in the ecology of Trinidadian guppies, Poecilia reticulata

Previous investigations of the guppy, Poecilia reticulata , in Trinidad have demonstrated rapid population differentiation at small geographic scales. However, most studies to date have focused on localities in Trinidad's Northern Range where barrier water falls mark sharp discontinuities in the selection regime and limit scope for gene flow. There is little information on the ecology of the guppy in the rest of the island even though its distribution amongst fish communities and habitats has important evolutionary implications. To determine how large-scale distribution patterns might affect the evolutionary potential of the guppy we surveyed 80 sites representative of a broad range of freshwater environments. We found guppies, which occurred in 80% of our samples, to be the most widely distributed freshwater fish in Trinidad. Guppies are common in predator-rich and turbid habitats, precisely those localities where female preferences are likely to be undermined. Moreover, the widespread distribution of this adaptable species, combined with its promiscuous mating system, may promote gene flow across geographical scales that transcend local selection regimes. These factors are likely to impede the evolution of reproductive isolation.     

Shoaling in juvenile guppies: the effects of body size and shoal size

While factors affecting shoal mate choice have been examined extensively in adult guppies (Poecilia reticulata), few studies have focused on the shoaling behavior of juveniles. In this study, juvenile guppies were tested for their ability to shoal as well as their response to shoal mates of different body size and to shoals with different numbers of individuals. In dichotomous choice tests, 10-day-old guppies (mean body length=8.83 mm), 30-day-old guppies (13.17 mm) and 50-day-old guppies (18.6mm) were given the opportunity to swim near shoals of five fish or an empty chamber. In most cases, the juvenile fish demonstrated shoaling behavior, swimming near a group of fish rather than an empty chamber, regardless of the age of the stimulus shoal. When presented with two shoals, one of similar age and body size and one of dissimilar age and body size, only the 50-day-old guppies showed a significant preference for the age-matched shoal. Similarly, when choosing between a large shoal and a small shoal, only the 50-day-old guppies spent significantly more time near the larger shoal. Thus, while juveniles at each age shoaled, only 50-day-old fish demonstrated the shoal mate discrimination seen in adult fish.     

Effect of <Emphasis Type="Italic">Tetrahymena</Emphasis> on the occurrence of achlyosis in the guppy

Tetrahymena infection has become the most problematic parasitic disease of the guppy Poecilia reticulata in Southeast Asia. Tetrahymena corlissi was isolated from guppies with a fungal infection in Thailand, and the fungus was identified as Achlya bisexualis. Male and female guppies were artificially infected with both organisms. The results showed that guppies could easily be artificially infected with a culture of Tetrahymena corlissi and that female guppies were more sensitive than male guppies. Achlya bisexualis infection was shown to be a secondary infection after the Tetrahymena infection. Received: April 29, 2001 / Accepted: September 6, 2001     

Swimbladder and skeletal deformations in hatchery bred Spams aurata

Among hatchery bred Sparus aurata , 5.4% of the offspring of a single parent pair showed severe skeletal deformations coupled with marked growth retardation and pathological changes in the swimbladder. This resulted from extreme proliferation, then hypertrophy, of the cuboidal epithelial cells of the gas gland and proliferation of the rete mirabile. This caused almost complete congestion of the swimbladder air space. The nature of the pathological changes in the swimbladder and the possibility of hereditary origin for both the skeletal and swimbladder deformations are discussed.     

Multiple cystic sweat gland tumors in transgenic mice

Here we describe gross and microscopic sweat gland tumors found in a transgenic mouse model of breast cancer, which had transforming growth factor α under the control of mouse mammary tumor virus promoter (MMTV-TGFα). Initially, 20% of the mice in the colony were affected. Cystic lesions formed on the phalanges, palmar surfaces of the metacarpals, and plantar surfaces of the metatarsals. The lesions were multifocal and nonulcerated with straw-colored fluid, ranging in size from 1 to 30 mm at the largest dimension. The colony was monitored for 6 mo; during that time, the prevalence of lesions increased to 52% of the mice. Histologically, in most cases the cyst walls were lined by 1 or 2 layers of normal-appearing epithelial cells that resembled basal cells, indicating adenoma. However, 2 cysts from 2 different mice had papillary proliferative projections and extensive disorganized glandular structures that protruded into the cyst cavities, indicating adenocarcinoma. In these 2 cases, the neoplastic cells revealed architectural and cytologic atypia with rare mitoses. Similar findings have previously been observed in sweat gland tumors; however, multiple sweat-gland tumors have not been reported in mice.     

Locally adapted traits maintained in the face of high gene flow

Gene flow between phenotypically divergent populations can disrupt local adaptation or, alternatively, may stimulate adaptive evolution by increasing genetic variation. We capitalised on historical Trinidadian guppy transplant experiments to test the phenotypic effects of increased gene flow caused by replicated introductions of adaptively divergent guppies, which were translocated from high‐ to low‐predation environments. We sampled two native populations prior to the onset of gene flow, six historic introduction sites, introduction sources and multiple downstream points in each basin. Extensive gene flow from introductions occurred in all streams, yet adaptive phenotypic divergence across a gradient in predation level was maintained. Descendants of guppies from a high‐predation source site showed high phenotypic similarity with native low‐predation guppies in as few as ~12 generations after gene flow, likely through a combination of adaptive evolution and phenotypic plasticity. Our results demonstrate that locally adapted phenotypes can be maintained despite extensive gene flow from divergent populations.     

Exocrine pancreatic carcinogenesis in the guppy Poecilia reticulata

Exocrine pancreatic neoplasms developed in the guppy Poecilia reticulata following exposure to the direct-acting carcinogen methylazoxymethanol acetate (MAM-Ac). Fish 6 to 10 d old were exposed to nominal, non-toxic concentrations of 4 and 10 mg MAM-Ac l(-1) for 2 h and then transferred to carcinogen-free water for grow-out. Whole specimens were sampled monthly up to 9 mo post-exposure to follow the histologic progression of the lesions. No neoplasms occurred in 119 control specimens examined. Pancreatic acinar cell adenomas and carcinomas occurred in 42 of 243 (17%) of the specimens exposed to MAM-Ac. As in earlier studies, specimens exposed to the low MAM-Ac concentration exhibited a higher pancreatic neoplasm incidence (27.8%) than those exposed to the high concentration (7.8%). Acinar cell adenomas accounted for 27 of the 42 neoplasms. Adenomas exhibited a high degree of acinar cell differentiation and some contained foci of atypical acinar cells that were less differentiated and more basophilic than were surrounding adenoma cells. Carcinomas occurred in 15 specimens and exhibited a range of cellular patterns. Although no distant metastases were found, carcinomas tended to invade neighboring tissues and organs. The occurrence of carcinogen-induced pancreatic neoplasms in guppies strengthens the usefulness of small fish species in carcinogen testing and provides an additional model for studying pancreatic neoplasia.     

Whirling disease: host specificity and interaction between the actinosporean stage of Myxobolus cerebralis and rainbow trout Oncorhynchus mykiss

Scanning electron microscopic studies were conducted on rainbow trout Oncorhynchus mykiss in the first 60 min after their exposure to the triactinomyxon spores of Myxobolus cerebralis. The results demonstrated that as early as 1 min post exposure the whole process, from the attachment of the triactinomyxon spores to the complete penetration of their sporoplasm germs, had occurred. The triactinomyxon spores sought out the secretory openings of mucous cells of the epidermis, the respiratory epithelium and the buccal cavity of trout and used them as portals of entry. Exposure experiments of the triactinomyxon spores of M. cerebralis to non-salmonid fish, such as goldfish Carassius auratus, carp Cyprinus carpio, nose Chondrostoma nasus, medaka Oryzias latipes, guppy Poecilia reticulata and also the amphibian tadpole Rana pipiens as well as to rainbow trout fry indicated a specificity for salmonids. Attempts to activate the triactinomyxon spores by exposure to mucus prepared from cyprinid and salmonid fish showed no significant differences from those conducted in tap water. The results suggest that the simultaneous presence of both mechano- and chemotactic stimuli was required for finding the salmonid fish host.     

The effect of hydrocortisone on DNA synthesis by sebaceous gland epithelial cells]

The autoradiography method demonstrated a single injection of hydrocortisone (10 mg per 100 g of body weight) to result in suppression of the cell transition from the G1 phase of the mitotic cycle to the S phase and in prolongation of the S phase of the epithelium of the acinar portion (sebocytes) and stratified epithelium of the excretory ducts of the sebaceous gland of rats. Later, after a decrease of the proliferative processes by hydrocortisone there occurred their increase which was higher than control. Hydrocortisone induced a more pronounced effect on the proliferative activity of the stratified epithelium of the excretory ducts than on the sebocytes of the acini.