Influence of cortisol on the attachment and metamorphosis of larval Utterbackia imbecillis on bluegill sunfish (Lepomis macrochirus)

The larvae of unionid freshwater mussels (i.e., glochidia) undergo a parasitic stage requiring their attachment to the external epithelia of fish hosts, where they metamorphose into free-living juveniles. We describe the physiological effects in bluegill sunfish (Lepomis macrochirus) of infection with glochidia from the paper pondshell (Utterbackia imbecillis). Glochidia accumulation on bluegill increased dramatically at concentrations of 2000 glochidia liter(-1) and above, reaching a maximum attachment density of about 30 glochidia g(-1) fish at 4000 glochidia liter(-1). Plasma cortisol was the most sensitive indicator of biological effect to glochidial exposure, increasing significantly in hosts exposed to 2000 glochidia liter(-1) or greater. Glochidia were 31% more likely to undergo successful juvenile metamorphosis when attached to bluegill with elevated plasma cortisol, largely due to the enhanced survivorship of these larvae during the first 48 h after infection. We tested the hypothesis that glochidial attachment and juvenile metamorphosis were stimulated directly by plasma cortisol in fish hosts. Bluegill were given an intraperitoneal injection of cortisol, then infected with 1000 glochidia liter(-1) at 48 h after hormone supplementation. Cortisol-injected fish had a 42% increase in the number of attached glochidia g(-1) fish and a 28% increase in larval metamorphosis compared to sham-injected and control fish. We provide evidence that cortisol enhances glochidial metamorphosis on hosts by improving the retention of attached glochidia. This study gives insights into the influence of host physiology on glochidial attachment and juvenile mussel transformation.     

Mitochondrial genome sequence of the bluegill sunfish (Lepomis macrochirus)

The bluegill sunfish (Lepomis macrochirus) belongs to Lepomis genera of the family Centrarchidae, which is an economically important freshwater species in China. This study presents the complete mitochondrial genome of L. macrochirus, which is the first complete sequence from sunfish species. L. macrochirus mitochondrial DNA is 16,489 bp long, with the genome organization and gene order being identical to that of the typical vertebrate.     

Ultrastructure of the mushroom body: digestion during metamorphosis of Utterbackia imbecillis (Bivalvia: Unionidae)

Abstract. Larvae of the freshwater mussel Utterbackia imbecillis metamorphose to juveniles either during their attachment to a host fish, or in vitro in a culture medium. This transformation includes degeneration of larval structures and development of the juvenile morphology. Early in metamorphosis the cells comprising the larval mantle enlarge and project into the mantle cavity, forming a structure referred to as the mushroom body. Its cells, which are ultrastructurally very similar to digestive cells of adult bivalves, are involved in pinocytosis or phagocytosis of the larval adductor muscle and of tissue from the host fish that is enclosed between the larval shells. Ingested material is passed from pinosomes to heterophagosomes which in turn fuse with heterolysosomes, where final degradation of ingested material occurs. Acid phosphatase activity was detected in heterophagosomes and heterolysosomes of all animals examined. In larvae that metamorphosed in vitro , the apical cytoplasm of the cells of the mushroom body, and the extracellular spaces among them, also exhibited acid phosphatase activity. Larvae reared on a host fish accumulated substantial deposits of lipids and glycogen within larval mantle cells during metamorphosis, whereas larvae reared in vitro did not. The larval mantle cells which constitute the mushroom body appear to be the primary sites of intracellular digestion of the larval adductor muscle and host tissue during metamorphosis.     

Laboratory constraints on feeding behaviours in polymorphic bluegill sunfish (Lepomis macrochirus)

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Predator-induced delayed maturity in bluegill sunfish (Lepomis macrochirus): variation among populations

Previous studies suggested that differences in age at maturity among populations of bluegill sunfish (Lepomis macrochirus) were not genetically based, but rather were a phenotypic response to the presence of predators. I conducted two experiments to determine if the presence of largemouth bass affected age at maturity in bluegill sunfish. Bluegills from three populations were tested to see if the response to the threat of predation varied among source populations. Juvenile bluegills were maintained in the presence of predators or in controls with no contact with predators. Refuge use and growth were monitored during the experiments and reproductive activity was evaluated when bluegills reached age 1. Bluegills from one population exhibited delayed maturity in the presence of predators. Individuals from the other two populations showed no significant differences between predator and control treatments. The population that responded to the presence of predators had a history of high predation levels over the past 30–40 years. The other populations had a history of low levels of predation. This study suggests that presence of predators can induce phenotypic shifts in age at maturity of bluegills, but that the magnitude of response varies among populations in a manner consistent with historical patterns of coexistence. Received: 7 August 1996 / Accepted: 8 August 1997     

Genetic paternity analysis and breeding success in bluegill sunfish (Lepomis macrochirus)

Fish have some of the most complex mating systems known in the animal kingdom. With the advent of powerful genetic markers and an emerging mathematical framework to calculate parentage, it is now possible to analyze genetic relatedness and gene flow in these systems. An important example is the bluegill sunfish (Lepomis macrochirus) which consists of parental males that provide sole care for the young, cuckolder males that parasitize the parentals, and females that actively choose among males within dense breeding colonies. In this article genetic markers for bluegill are characterized and their utility in parentage studies is demonstrated by calculating the genetic relatedness of parental males to their broods for an entire natural breeding colony. A novel Monte Carlo simulation is developed to calculate the confidence in the relatedness estimates and these data are used to provide an estimate of the mean breeding success of parental and cuckolder males. Finally, the applications of genetic analyses to understanding mating systems, parental care, and life-history evolution in bluegill are discussed.     

Sperm investment and alternative mating tactics in bluegill sunfish (Lepomis macrochirus)

Although alternative mating tactics are found in males of manyspecies, little is known about tactic-specific adaptations tosperm competition and the mechanism by which fertilization successis obtained. We now report on the sperm investment patternsof males that use alternative mating tactics in bluegill sunfish(Lepomis macrochirus). Bluegill males are characterized by threealternative mating tactics: parentals, sneakers, and satellites.Parentals delay maturation and adopt a courting and guardingtactic, whereas sneakers and satellites mature precociouslyand, respectively, use sneaking and female mimicry to stealfertilizations from parentals. We found differences among thetactics in testes weight, sperm longevity, and ejaculate spermdensity and competitiveness. Parentals had the largest testes,but the smallest relative to their body weight. Satellites hadintermediate-sized testes, and sneakers had the smallest testes,but the largest relative to their body weight. Within each tactic,there was a positive relationship between testes weight andbody weight, but the exact relationship differed among the tacticsand could not be attributed solely to allometry. Parentals hadlonger-lived sperm compared with that of both sneakers and satellites.Ejaculate sperm density was greatest in sneakers, satelliteswere intermediate, and parentals had the lowest. Competitionexperiments involving equal volumes of ejaculate showed thatfertilization success increased linearly with sperm number,consistent with a rafflelike process. However, independent ofsperm number, parental sperm were superior at fertilizing eggs.We interpret these sperm investment patterns in relation todifferences in sperm competition risk, number of mating opportunities,and alternative investment options.     

Choice in the bluegill (Lepomis macrochirus)

To study matching in a species distantly related to mammals and birds, seven bluegill were trained to break a photobeam using a nose-poke response for access to pelleted food in their home aquaria during one-h sessions. Reinforcer ratios available from the two response alternatives varied among the following: 16:1, 8:1, 4:1, 1:1, 1:4, 1:8, and 1:16. The overall reinforcement rate was held at 0.8/min. All experiments were conducted in a closed economy, i.e., the fish's daily food ration was available only during experimental sessions. Matching functions are reported for each fish using all combinations of scheduled and obtained reinforcer ratios as the independent variables and response and time ratios as the dependent variables. All matching functions had slopes less than 1.0 and r² values above 0.70. Overall response rates were unrelated to the reinforcer ratios but, as with other species studied, changeover rates were highest for the 1:1 condition and lowest for the 16:1 conditions. These results are consistent with data obtained from more traditionally studied taxa (e.g., birds, mammals, and primates), and similar previous studies with fish, suggesting that matching has been conserved since fish, birds, and mammals evolved from a common ancestor over 400 million years ago.     

Aggressive habituation and rim circling in the social organization of bluegill sunfish (Lepomis macrochirus)

Synopsis The rim circling (RC), and aggressive habituation of nesting bluegills were studied in natural colonies during the six days of the reproductive period following spawning. To examine the stimulus specificity of aggressive habituation, selected test individuals and four neighbors were observed on four occasions during one day. After the first observation period established baseline data on aggressive interactions, the appearances of three of the neighbors were manipulated and further observations were made. Two more observation periods followed, separated by a sham manipulation to allow for possible disturbance effects. Fish lengths, inter-nest distances, and positions in the colony were also recorded.An analysis of the data demonstrated that aggressive interaction increased for the three manipulated neighbors. There were no significant differences among the data for the fourth (control) neighbors. The enhanced aggressive interactions between the test and manipulated males were initiated by the males at least partially in response to the changed appearance of the neighbor. Further, the level of aggressive interaction returned to normal after about 2 hours, indicating that the test male had habituated to the new appearances of his neighbors. Thus visual appearance plays an important role in the habituation of aggression between neighboring bluegills. It was not possible to determine if the behavior of the neighbor was also an important cue used in aggressive habituation, but this seems likely. Advantages of aggressive habituation are discussed. It is noteworthy that aggression decreased as internest distance increased.Levels of RC varied significantly over the six days, in a time course dissimilar from aggression. The RC rate is dependent on size of male, nest locality, and circling activity of neighbors. Observations on the synchrony of rim circling indicated social facilitation. It is argued that RC probably fulfills an advertisement function important in defending the brood. The motivation for RC is likely complex, and its performance reflects a mixed aggressive and reproductive strategy in the nesting population. Aggressive habituation functions in the social organization of bluegills to facilitate the occurrence of group displays such as RC.     

Aspects of color vision in bluegill sunfish (Lepomis macrochirus): ecological and evolutionary relevance

Summary Spectral sensitivity curves were measured for bluegills using a heart-rate conditioning technique. A mean spectral sensitivity curve (n=3) determined using a white background exhibited two main peaks, indicating the possible presence of two cone photoreceptors mechanisms. Chromatic adaptation was used to separate the contribution of the cone mechanisms to sensitivity. Peak sensitivities were located at 540 and 640 nm against red and blue-green backgrounds, respectively.Light adaptation curves were measured for each cone mechanism indicating that these cone mechanisms have their greatest contrast sensitivity at higher background intensities. Spatial summation properties were also measured for each cone mechanism revealing a critical diameter (summation area) of 5° for both mechanisms.Microspectrophotometric (MSP) measurements were made on individuals from the same group of bluegills used in the above experiments. The results showed the presence of two cone types: single green-sensitive cones with an average _max of 536 nm (SD±1.8nm,n=11) and twin redsensitive cones with an average _max of 620 nm (SD ±1.9 nm,n=11).The correlation between the visual pigment absorption spectra and action spectra of the two cone mechanisms indicate a sound physiological basis for sensitivity. The functional properties of the two cone mechanisms, will be discussed in relation to the ecological and behavioral aspects of bluegills.Abbreviation TVI threshold vs intensity     

Effects of different acids on the bluegill sunfish, Lepomis macrochirus Rafinesque

The concentration of hydrogen ions which caused 50% mortality of bluegill in 96 h (96 h LC50) was between pH 3.5 and 3.0 for four acids; sulphuric, nitric, phosphoric and hydrochloric. Therefore, it appears that any contribution by the anions of these acids to fish toxicity is similar. This suggests that the quantity rather than the quality of acids is the primary factor in fish toxicity brought about by acid precipitation.
At sublethal concentrations of acids, bluegill became hypoactive with respect to their swimming behaviour.     

Maintenance of female mimicry as a reproductive strategy in bluegill sunfish (Lepomis macrochirus)

Synopsis In species where male reproductive success is dependent on male competition and aggression, alternative reproductive patterns, thought to represent a reduction in male reproductive effort, sometimes occur. Female mimicry in bluegill sunfish (Lepomis macrochirus) is an example of an obligate alternative male strategy. Female mimics are small, sexually mature males which mimic the details of female behavior, and gain access to functional females attracted to the nests of large, aggressive territorial males. The costs of female mimicry relative to nesting male behavior are discussed and two hypotheses, deception and mutual gain, are presented to explain the tolerance and courtship of female mimics by nesting males.     

Musculoskeletal morphology and regionalization within the dorsal and anal fins of bluegill sunfish (Lepomis macrochirus)

Ray‐finned fishes actively control the shape and orientation of their fins to either generate or resist hydrodynamic forces. Because of the emergent mechanical properties of their segmented, bilaminar fin rays (lepidotrichia), and actuation by multiple muscles, fish can control the rigidity and curvature of individual rays independently, thereby varying the resultant forces across the fin surfaces. Expecting that differences in fin‐ray morphology should reflect variation in their mechanical properties, we measured several musculoskeletal features of individual spines and rays of the dorsal and anal fins of bluegill sunfish, Lepomis macrochirus, and assessed their mobility and flexibility. We separated the fin‐rays into four groups based on the fin (dorsal or anal) or fin‐ray type (spine or ray) and measured the length of the spines/rays and the mass of the three median fin‐ray muscles: the inclinators, erectors and depressors. Within the two ray groups, we measured the portion of the rays that were segmented vs. unsegmented and branched vs. unbranched. For the majority of variables tested, we found that variations between fin‐rays within each group were significantly related to position within the fin and these patterns were conserved between the dorsal and anal rays. Based on positional variations in fin‐ray and muscle parameters, we suggest that anterior and posterior regions of each fin perform different functions when interacting with the surrounding fluid. Specifically, we suggest that the stiffer anterior rays of the soft dorsal and anal fins maintain stability and keep the flow across the fins steady. The posterior rays, which are more flexible with a greater range of motion, fine‐tune their stiffness and orientation, directing the resultant flow to generate lateral and some thrust forces, thus acting as an accessory caudal fin. J. Morphol., 2012. © 2011 Wiley Periodicals, Inc.     

The effects of noise on the auditory sensitivity of the bluegill sunfish,Lepomis macrochirus

As concerns about the effects of underwater anthropogenic noises on the auditory function of organisms increases, it is imperative to assess if all organisms are equally affected by the same noise source. Consequently, auditory capabilities of an organism need to be evaluated and compared interspecifically. Teleost fishes provide excellent models to examine these issues due to their diversity of hearing capabilities. Broadly, fishes can be categorized as hearing specialists (broad hearing frequency range with low auditory thresholds) or hearing generalists (narrower frequency range with higher auditory thresholds). The goal of this study was to examine the immediate effects of white noise exposure (0.3-2.0 kHz, 142 dB re: 1 microPa) and recovery after exposure (1-6 days) on a hearing generalist fish, bluegill sunfish (Lepomis macrochirus). Noise exposure resulted in only a slight, but not statistically significant, elevation in auditory threshold compared to fish not exposed to noise. In combination with results from our previous studies examining effects of noise on a hearing specialist fish, the fathead minnow (Pimephales promelas), this study provides evidence supporting the hypothesis that fish's auditory thresholds can be differentially affected by noise exposure.     

Methods of DNA extraction and PCR amplification for individual freshwater mussel (Bivalvia: Unionidae) glochidia,with the first report of multiple paternity in these organisms

Freshwater mussels (Unionidae) are among North America's most imperilled organisms. Mussels produce small larvae (glochidia) that parasitize aquatic vertebrates. We modified the Epicentre QuickExtract protocol to extract DNA from a single glochidium, collected directly from the marsupium of a female mussel, to use as template in polymerase chain reactions (PCRs). Yield per glochidium in a 40 µL extraction volume provided enough DNA for ≥ 15 PCRs per individual. We were successful in using this DNA for microsatellite analysis of up to three loci per individual. Offspring from one female showed evidence for multiple paternity within her brood. Our results are the first documentation of this phenomenon in freshwater mussels.     

The effect of parthenogenic eggs in Daphnia magna on prey location by the bluegill sunfish (Lepomis macrochirus)

The distance at which the bluegill sunfish (Lepomis macrochirus) can locate Daphnia magna with parthenogenic eggs is shown to be significantly greater than the reactive distance for non-gravid Daphnia of the same size. This difference is due to greater visibility of the gravid prey and not to different locomotor behavior, since there was no correlation between the number of eggs carried by a Daphnia and the antennal beat frequency. Based on this experiment and other observations, an explanation is given for selective predation of polymorphic cladoceran populations.     

Evolution of active host-attraction strategies in the freshwater mussel tribe Lampsilini (Bivalvia: Unionidae)

Most freshwater mussels (Bivalvia: Unionoida) require a host, usually a fish, to complete their life cycle. Most species of mussels show adaptations that increase the chances of glochidia larvae contacting a host. We investigated the evolutionary relationships of the freshwater mussel tribe Lampsilini including 49 of the approximately 100 extant species including 21 of the 24 recognized genera. Mitochondrial DNA sequence data (COI, 16S, and ND1) were used to create a molecular phylogeny for these species. Parsimony and Bayesian likelihood topologies revealed that the use of an active lure arose early in the evolution of the Lampsiline mussels. The mantle flap lure appears to have been the first to evolve with other lure types being derived from this condition. Apparently, lures were lost independently in several clades. Hypotheses are discussed as to how some of these lure strategies may have evolved in response to host fish prey preferences.     

Evolution of bilaterally asymmetrical larvae in freshwater mussels (Bivalvia: Unionoida: Unionidae)

Bilaterally asymmetrical glochidia (i.e. bivalved parasitic larvae bearing a large marginal appendage on a single valve) have been reported from five Asian freshwater mussel genera belonging to two separate subfamilies, the Gonideinae (i.e. Pseudodon, Solenaia, and Physunio) and Rectidentinae (i.e. Contradens and Trapezoideus). This classification requires that the bilaterally asymmetrical glochidium‐bearing mussels are not monophyletic, and suggests that this atypical larval morphology evolved twice in the same geographic region. Although homoplastic glochidium characters are known (e.g. marginal appendages and size), we hypothesized that bilaterally asymmetrical glochidia represent a novel morphological synapomorphy. We tested the monophyly of the mussels bearing bilaterally asymmetrical glochidia using a molecular matrix consisting of representatives from all six freshwater mussel families and three molecular markers (28S, 16S, and COI). Bayesian inference, maximum likelihood, and ancestral state reconstruction were employed to estimate the phylogeny and larval trait transformations. The reconstructed phylogeny rejects the monophyly of the asymmetrical glochidium‐bearing mussels and resolves two putative origins of asymmetrical glochidia; however, ancestral state reconstruction supports asymmetrical glochidia as a synapomorphy of only one supraspecific taxon of the Rectidentinae. In the Gonideinae, asymmetrical glochidia were autapomorphic of Pseudodon cambodjensis (Petit, 1865). That is, no other taxa resolved among the Gonideinae had bilaterally asymmetrical glochidia, including other Pseudodon species. We describe how the alleged intrageneric glochidial variation in Pseudodon, and in the other genera of the Gonideinae reported to have asymmetrical glochidia (i.e. Solenaia and Physunio), challenge the resolved convergence of asymmetrical glochidia. Our results are discussed in the context of freshwater mussel larval evolution, patterns in life‐history traits, and the classification of freshwater mussels generally. © 2015 The Linnean Society of London     

Lead acetate: toxicity without effcts on the locomotor activity of the bluegill sunfish, Lepomis macrochirus Rafinesque

The concentration of lead acetate which caused 50% mortality of bluegill in 96 h (96 h LC50) is approximately 400 ppm. Sublethal concentrations of 0.1, 1, 10, 100, 200 and 300 ppm lead acetate did not produce any effects on the locpmotor activity of the bluegill. The observation that lead can reach concentrations which are lethal without sublethal effects on locomotor activity at lower concentrations is unusual and in sharp contrast to studies with other metals (Ellgaard et al. . 1978).