Astatotilapia Burtoni Research Articles

Social status regulates growth rate: consequences for life-history strategies.

The life-history strategies of organisms are sculpted over evolutionary time by the relative prospects of present and future reproductive success. As a consequence, animals of many species show flexible behavioral responses to environmental and social change. Here we show that disruption of the habitat of a colony of African cichlid fish, Haplochromis burtoni (Günther) caused males to switch social status more frequently than animals kept in a stable environment. H. burtoni males can be either reproductively active, guarding a territory, or reproductively inactive (nonterritorial). Although on average 25-50% of the males are territorial in both the stable and unstable environments, during the 20-week study, nearly two-thirds of the animals became territorial for at least 1 week. Moreover, many fish changed social status several times. Surprisingly, the induced changes in social status caused changes in somatic growth. Nonterritorial males and animals ascending in social rank showed an increased growth rate whereas territorial males and animals descending in social rank slowed their growth rate or even shrank. Similar behavioral and physiological changes are caused by social change in animals kept in stable environmental conditions, although at a lower rate. This suggests that differential growth, in interaction with environmental conditions, is a central mechanism underlying the changes in social status. Such reversible phenotypic plasticity in a crucial life-history trait may have evolved to enable animals to shift resources from reproduction to growth or vice versa, depending on present and future reproductive prospects.

Nasotemporal asymmetry during teleost retinal growth: preserving an area of specialization.

Teleost fish retinas grow throughout adult life through both cell addition and stretching. Cell division occurs at the periphery of the retina, resulting in annular addition of all cell types except rod photoreceptors, which are added in the central retina. Since many teleosts have a region of high cellular density at the temporal pole of the eye, we analyzed whether and how this specialized region of high visual acuity maintained its relative topographical position through asymmetric circumferential growth. To do this, we measured the pattern of long-term retinal growth in the African cichlid Haplochromis burtoni. We found that the retina expands asymmetrically along the nasotemporal axis, with the nasal retina growing at a higher rate than the temporal, dorsal, or ventral retinae, whose growth rates are equal. This nasotemporal asymmetry is produced via significantly greater expansion of retinal tissue at the nasal pole rather than through differential cell proliferation. The mechanisms responsible for this differential retinal enlargement are unknown; however, such asymmetric expansion very likely minimizes disruption in vision during rapid growth.

Ontogeny of Gonadotropin-Releasing Hormone (GnRH) Gene Expression Reveals a Distinct Origin for GnRH-Containing Neurons in the Midbrain

In the teleost fish,Haplochromis burtoni, three gonadotropin-releasing hormone (GnRH) peptides and their corresponding cDNA sequences and full-length genes have previously been reported. Here we describe the ontogeny of mRNA expression for these three GnRH forms inH. burtoni. Each of the three forms has been shown to have a distinct spatial expression pattern in the adult brain. {Ser8}GnRH (the releasing form) is expressed exclusively in the hypothalamus, {His5Trp7Tyr8}GnRH is expressed in the midbrain mesencephalon, and {Trp7Leu8}GnRH is expressed in the terminal nerve area of the telencephalon. Previous work in other animals has shown that GnRH-containing neurons in the preoptic area arise from the olfactory placode and that these cells migrate into their final positions in the brain during early development. By using molecular probes to identify the cell types expressing distinct GnRH forms, our data are consistent with the migration of both {Ser8}GnRH and {Trp7Leu8}GnRH neurons from the placode to their appropriate adult locations in the brain. In contrast, we show that {His5Trp7Tyr8}GnRH neurons arise from the germinal zone of the third ventricle. By usingin situhybridization with digoxigenin-labeled cRNA probes, {His5Trp7Tyr8}GnRH mRNA was first evident at day 4, {Trp7Leu8}GnRH mRNA at day 8, and {Ser8}GnRH mRNA at day 14. However, by using the reverse-transcriptase polymerase chain reaction (RT-PCR), all three GnRH mRNAs were found in whole embryos at day 4 of the 14 days of embryogenesis. This striking difference may be due to the greater sensitivity of RT-PCR compared within situhybridization. Alternatively, it is possible that {Ser8}GnRH and {Trp7Leu8}GnRH are expressed outside the brain during early development and only later inside the brain.

On the evolutionary pathway of parental care in mouth–brooding cichlid fishes

Evolutionary theory predicts that differences in parental care patterns among species arose from interspecific differences in the costs and benefits of care for each sex. In Galilee St Peter9s fish, Sarotherodon galilaeus (Cichlidae), male care, female care and biparental care all occur in the same population. We exploit this unusual variability to isolate conditions favouring biparental versus uniparental mouth–brooding by males or females. We first review a game–theoretic model of parental care evolution, predictions of which we test experimentally in this paper. Manipulations of the operational sex ratio show that males and females desert their offspring more frequently when the costs of care are high (in terms of lost mating opportunities). Breeding trials with males of different sizes show that small fathers desert more frequently than large fathers. We attribute this to the associated difference in the fitness benefit of biparental care relative to female–only care. Our experimental results confirm that in St Peter9s fish the probability of caring is determined facultatively according to current conditions at each spawn. The experiments and model together suggest that interspecific variation in remating opportunities and clutch size may be responsible for differences in care patterns within the sub–family Tilapiini. Our results support the hypothesis that biparental mouth–brooding was the ancestral state of both male and female uniparental mouth–brooding in cichlid fishes.

The olfactory system of a cichlid fish responds to steroidal compounds

Electro‐olfactogram (EOG) responses to a diverse range of steroid hormones were recorded in he African cichlid Haplochromis burtoni. Olfactory receptor responsiveness was sensitive to the attachment sites of sulphate and glucuronide groups.

The embryogenesis of rod photoreceptors in the teleost fish retina, Haplochromis burtoni

Development of the retina, like that of other tissues, occurs via an orderly sequence of cell division and differentiation, producing the functional retina. In teleost fish, however, cell division and differentiation in the retina continue throughout the life of the animal in two distinct ways. Stem cells in a circumferential germinal zone at the periphery of the retina give rise to all retinal cell types and progenitor cells located throughout the retina in the outer nuclear layer (ONL) produce new rod photoreceptors. These processes in adult retina recapitulate in space the embryonic events responsible for forming the retina. Analysis of these events in an African cichlid fish, Haplochromis burtoni, confirmed that cone photoreceptors differentiate first, followed by rod photoreceptors. Correspondingly, at the margin of the eye, cone photoreceptors differentiate nearer to the margin than do rods. Control of photoreceptor production is not understood. Here we present the time of appearance and distribution pattern of GABA and vimentin which are candidates for the control of retinal cell division and differentiation. Antibody staining reveals that both GABA and vimentin exhibit unique patterns of expression during embryonic retinal development. Vimentin immunoreactivity is evident throughout the retina in a spoke-like pattern between developmental Days 4 and 7, as both cone and rod photoreceptors are being formed. GABA is expressed in horizontal cells between Days 5 and 7, corresponding to the onset of rod differentiation in time and in position within the retina. Moreover, the wave of GABAergic staining in the horizontal cells parallels the wave of rod differentiation across the embryonic retina of H. burtoni. Thus, GABA may play a role in the development of rod photoreceptors.

Cell movement and cell cycle dynamics in the retina of the adult teleostHaplochromis burtoni

The authors analyzed the pattern of neurogenesis, the time frame of cell movement, and the cell cycle kinetics of a population of stem cells located in the outer nuclear layer in the retina of the adult teleost Haplochromis burtoni. These stem cells continue to give rise to new rod photoreceptors throughout life. The new rods move vitread after the last cell division. The authors investigated events during cell division and cell differentiation by using one marker that labels dividing cells transiently (proliferating cell nuclear antigen) along with another marker that labels dividing cells permanently (bromodeoxyuridine). The bulk of cell movement does not occur within 24 hours after S-phase labeling but is clearly underway 12 hours later, shortly after mitosis. The cell cycle length was estimated to be approximately 25 hours. The distribution of labeled cells at various times after S-phase suggests that new rods are generated by asymmetric cell division, that is, one of the daughter cells moves after mitosis and becomes postmitotic, while the other daughter cell remains in place and reenters the cell cycle. The proliferation patterns across the retina suggest that the location of areas of mitotic activity changes over time. The authors hypothesize that local extracellular factors control the rate of cell division in a given area, thereby keeping the overall rod density constant.

Cell movement and cell cycle dynamics in the retina of the adult teleost Haplochromis burtoni

Cell movement and cell cycle dynamics in the retina of the adult teleost Haplochromis burtoni

Effect of social rank on brain monoaminergic activity in a cichlid fish.

In Haplochromis burtoni, an African cichlid fish, male sexual maturation is regulated via social interactions, and these effects are mediated by gonadotropin-releasing-hormone (GnRH)-containing neurons in the preoptic area of the brain. Since brain monoaminergic systems are known to be involved in the regulation of GnRH release, and the activity of these systems is influenced by agonistic interactions, we analyzed the effect of social status on brain monoaminergic activity in H. burtoni. Animals were either (1) in normal social groups consisting of two males and four females or (2) in groups of one male and five females. Quantitative behavioral observations were made on each group of animals and, following sacrifice several physiological measurements were made. Concentrations of serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA, the main 5-HT metabolite) and tryptophan (TRP, the amino acid precursor of 5-HT), dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC, the main DA metabolite) were measured. The 5-HIAA/5-HT and DOPAC/DA ratios were calculated and used as indexes of 5-HT and DA activity, respectively. In addition, the gonadosomatic index was calculated from body and gonadal weights and used as an index of reproductive status. Concentrations of 5-HIAA as well as 5-HIAA/5-HT ratios were significantly higher in the brainstem of non-territorial males than in that of territorial males, and similar trends were seen in the telencephalon and hypothalamus. Moreover, TRP concentrations in the telencephalon and brainstem were significantly lower in non-territorial males. In this species, sexual maturation in females is not socially regulated, and there was no significant correlation between measured antagonistic behavior and biochemical indices. These results suggest a fundamental difference in the neurochemical responses between male and female H. burtoni.

Androgen Regulation of Hypothalamic Neurons Containing Gonadotropin-Releasing Hormone in a Cichlid Fish: Integration with Social Cues

Reproduction in vertebrates is regulated by internal signals such as hormone levels and by external signals such as social interactions. In an African cichlid fish,Haplochromis burtoni,the effect of social interactions is evident in the hypothalamo-pituitary-gonadal (HPG) axis of males. Territorial males, characterized by aggressive and reproductive activity, have significantly larger hypothalamic gonadotropin-releasing hormone (GnRH)-containing neurons and larger testes than nonterritorial males. Furthermore, a switch in the social status of an adult male causes a corresponding change in GnRH neuron size and testis size. Here we show that the GnRH-containing neurons in the hypothalamus of adult territorial males are also influenced by gonadal hormones. Castration of territorial males caused GnRH neurons to increase in size. This neuronal hypertrophy in castrated animals was prevented either by testosterone (T) or 11-ketotestosterone (KT) treatment. Estradiol (E2) treatment did not reduce GnRH cell size in castrated animals. These results suggest that androgens reduce the size of GnRH cells through negative feedback. Since E2 had no effect, androgen influence on GnRH cell size appears to be independent of aromatization. These data are consistent with the hypothesis that the setpoint for hypothalamic GnRH cell size is determined by social cues and that this setpoint is maintained by negative feedback from gonadal androgens.

Hierarchical Sensory Guidance of Mauthner-Mediated Escape Responses in Goldfish (<i>Carassius auratus</i>) and Cichlids (<i>Haplochromis burtoni</i>) (Part 2 of 2)

Acoustically-evoked escape behaviors were compared between goldfish <i>(Carassius auratus), </i>a hearing specialist, and the cichlid <i>Haplochromis burtoni, </i>a hearing nonspecialist. Fish were startled with compressive and rarefying, stimuli presented alone or together, and with compressive pulses preceded by a visual cue or after exposure to cobalt, an inhibitor of lateral line-innervated neuromast hair cells. These acoustic startle stimuli can evoke Mauthner neuron firing and are similar to but weaker than those produced by a largemouth bass <i>(Micropterus salmoides) </i>feeding on guppies. When sound stimuli were presented alone, both species avoided the direction of either the compressive or rarefying stimulus. If a light preceded and was contralateral to the compressive sound pulse, goldish continued to avoid the sound source; cichlids avoided the visual cue and turned toward the sound. Goldfish performance improved significantly when the visual cue was in the same direction as the sound source. Goldfish performance also improved significantly after exposure to 0.1 mmol I^-1 cobalt solution for 24 hours before testing, but cichlids would not startle after cobalt acclimation. A compressive pulse presented to one side of a fish simultaneously with a rarefying pulse on the other side causes the entire fish to accelerate with the water current. This strongly and directly accelerates the ear but tends to reduce both the pressure changes transduced by the swimbladder and activation of the mechanosensory lateral line. In this test, goldfish reliably avoided the compressive pulse. Cichlids, however, randomly avoided either speaker polarity but significantly avoided the speaker which had a faster onset. With more closely matched speakers, cichlids also preferentially avoided the compressive stimulus. Thus, the primitive sensory condition for auditory activation and guidance of Mauthner-neuron-initiated escape responses may have evolved to detect the initially compressive sounds associated with ram-type predators.

Primary structure of solitary form of gonadotropin-releasing hormone (GnRH) in cichlid pituitary; three forms of GnRH in brain of cichlid and pumpkinseed fish

GnRH is a decapeptide family with at least nine distinct structures. Vertebrates, except for most placental mammals, have more than one of these GnRH forms within the brain. We report chromatographical and immunological evidence that three forms of GnRH are in the brains of both cichlid ( Haplochromis burtoni) and pumpkinseed ( Lepomis gibbosus) fishes. We argue that the three forms correspond to those previously described as sea bream GnRH (sbGnRH), chicken GnRH-II and salmon GnRH. In contrast, only one GnRH form was present in the pituitary of the cichlid and is identified as sbGnRH by amino acid sequence. This is the first report in which the primary structure of GnRH is determined from pituitary tissue. The N-terminus was identified by monitoring the digestion of the peptide by pyroglutamate aminopeptidase with matrix assisted laser desorption/ionization (MALDI) mass spectrometry (MS). The amidation of the C-terminus was established using an esterification procedure for monitoring with MALDI-MS. This report supports the idea that three forms of GnRH within one species is widespread in the order Perciformes. The present study establishes sbGnRH as the third GnRH form in H. burtoni and predicts that sbGnRH is synthesized in preoptic neurons, then transported to the pituitary in the preoptic-hypophyseal axons for the release of one or both gonadotropins.

Localization and expression of insulin-like growth factor in the teleost retina.

Teleost fish retinas continue to add neurons throughout life, and evidence from in vitro experiments have implicated insulin-like growth factors (IGFs) in this process. To discover whether these factors are expressed in vivo, we have examined their expression in the cichlid fish, Haplochromis burtoni. Three lines of evidence show that IGFs are present in the fish retina. An IGF-I specific antibody, sm 1.2, binds preferentially to the retinal outer plexiform layer, in areas of cone photoreceptor synaptic endings. Northern blots of mRNA hybridized with riboprobes from trout IGF-I and IGF-II genes revealed transcripts of approximately 6.5 and 4.9 kb, respectively. The IGF-I probe detected an additional transcript of 1.2 kb in liver but not in retinal mRNA. In situ hybridization with digoxigenin-labeled riboprobes revealed that the IGF gene product is localized in the cone photoreceptors. These results show that cone photoreceptors are the source of IGFs in the fish retina, consistent with the hypothesis that IGFs play a role in regulating production of new neurons in the teleost retina.

Daily rhythm of cell proliferation in the teleost retina

To determine whether the number of cell divisions in the teleost retina exhibited a regular daily variation, we labeled dividing cells with an antibody to proliferating cell nuclear antigen. The number of dividing rod precursor cells in the outer nuclear layer of the retina were counted in retinas from the telost fish Haplochromis burtoni, sacrificed at 4-h intervals during a standard light-dark cycle and in constant darkness. These rod precursor cells exhibited a striking rhythm of cell division. The highest number of cell divisions (acrophase) was found to occur at night when it was ≈3 times higher than during the day. The observed rhythm persisted in animals held in constant darkness. We suggest that this endogenous 24-h rhythm of rod precursor cell division may be controlled by a circadian clock. Although there are several examples of continuously proliferating cell populations which exhibit circadian or diurnal rhythms, this appears to be the first documentation of a rhythm of division in cells destined to become neurons.

The Population of GnRH-Containing Neurons Showing Socially Mediated Size Changes Project to the Pituitary in a Teleost, &lt;i&gt;Hapiochromis burtoni&lt;/i&gt;

Reproductive function in all vertebrates is controlled by the brain-pituitary-gonadal axis. In teleost fish, endocrine cells within the adenohypophysis are grouped together and each collection of cells is innervated by specific neuropeptide fibers. An important regulatory step in reproductive control is gonadotropin-releasing hormone (GnRH), whose delivery to the pituitary is responsible for its release of gonadotropins. The hormone GnRH has been shown to play a critical role in the social control of reproduction in a teleost fish, Haplochromis burtoni. However, there has been no direct evidence that the preoptic area GnRH neurons project to the pituitary. In this study, we used a retrograde tracer and immunohistochemistry to identify those GnRH containing neurons that project to the adenohypophysis. We compared reproductively active territorial males with quiescent non-territorial males to discover whether the connectivity of the preoptic area GnRH neurons depends on the reproductive status of the male. We found that, irrespective of reproductive status, most GnRH neurons in the preoptic area project to the pituitary and that all of these GnRH neurons show the soma size change that has been associated with reproductive status in Haplochromis burtoni. Based on these data, we propose that there is a single population of GnRH containing cells in the preoptic area that change size as a function of reproductive state and that this entire population projects to the pituitary. This is the first direct demonstration that this essential circuit, linking GnRH neurons in the preoptic area to the pituitary, exists.

Molecular Cloning of a cDNA Encoding the Prepro-Salmon Gonadotropin-Releasing Hormone of the Red Seabream

Complementary DNA fragments encoding the prepro-salmon gonadotropin-releasing hormone ([Trp7, Leu8]GnR, sGnRH) of the red seabream Pagrus major were amplified from mRNA of the olfactory bulbs using a reverse transcriptase-polymerase chain reaction (RT-PCR), and the full-length cDNA was cloned from a cDNA library using the PCR-amplified cDNA as a probe. The cDNA consisted of 442 bp, including an open reading frame of 270 bp which encoded the prepro-sGnRH (90 amino acid residues). The prepro-sGnRH had the same architecture as that reported in other species. It was composed of a signal peptide, sGnRH and a GnRH-associated peptide (GAP), which was connected to sGnRH by a Gly-Lys-Arg sequence. The prepro-sGnRH of the red seabream had 90% amino acid identity to the prepro-sGnHR from an African cichlid Haplochromis burtoni which belongs to the same suborder as the red seabream; however, identity was lower to the prepro-sGnRH from Atlantic salmon Salmo salar (74%), and masu salmon Oncorhynchus mason (70%). The GnRH peptide itself and the Gly-Lys-Arg sequence in the prepro-GnRH are highly conserved among vertebrates. The red seabream GAP also shows significant amino acid identity to the GAPs of the African cichlid (89%), Atlantic salmon (74%), and masu salmon (67%), but exhibits no significant identity to chicken or mammalian GAP.

Refractive index distribution and spherical aberration in the crystalline lens of the African cichlid fish haplochromis burtoni

Refractive index distribution in the teleost crystalline lens was measured with a nondestructive method in freshly excised lenses of the African teleost fish Haplochromis burtoni. Independently, spherical aberration was measured in a parallel set of lenses. The measured refractive index profiles show a continual decrease of refractive index from the center to the surface of the lens. The H. burtoni lens is of high optical quality and slightly overcorrected for spherical aberration. Details of the small residual spherical aberration were accurately predicted by ray-tracing model calculations based on the measured refractive index profile. The refractive index profile and the spherical aberration both show more complex characteristics than suggested by earlier measurements and lens models.

Regulation of eye growth in the African cichlid fish Haplochromis burtoni

Fish were reared in 6 conditions: broad spectrum white light, total darkness, scotopic illumination, and 3 monochromatic colors matched to the absorption spectra of the three cone types to study the influence of the light regime on the regulation of eye growth in the African cichlid fish Haplochromis burtoni. Fish reared in total darkness showed high variability in naso-temporal diameter and axial length of the eye. Animals reared in darkness and in scotopic illumination had significantly larger eyes relative to lens size in comparison to fish reared in white light. Eye size and shape was nearly identical in fish reared in monochromatic and in white light. Because of overlap in the absorption spectra of the three cone types of H. burtoni it could not be resolved whether the regulatory mechanism receives input from all three cone types or only from the green (523 nm) sensitive cones. It is clear from our results, however, that neither the blue (455 nm) nor the yellow sensitive (562 nm) cones alone are responsible for eye size regulation. It seems equally unlikely that all three cone types have to act in concert for normal growth of the eye.

Ontogeny of gonadotropin releasing hormone-containing neurons in the teleost brain

We investigated changes in two gonadotropin releasing hormone (GnRH)-containing neuronal populations during juvenile development in the African teleost, Haplochromis burtoni. Juveniles were sampled at weekly intervals and GnRHir neurons were identified through immunocytochemistry (ICC), then counted and measured on computer-captured video images. Soma size of GnRH neurons in the preoptic area (POA), which regulate gonadotropin release from the pituitary, is socially modulated in adults. Here we show that in juveniles the soma size of these neurons increases as a linear function of body weight. Terminal nerve (TN) GnRHir neurons, in contrast, are not involved in pituitary regulation and their soma size is not socially modulated in adults. In juveniles, soma size of these neurons is a quadratic function of body size and the covariance of soma size and body size is much less than in the POA GnRHir neurons. In both populations, GnRHir neuronal number covaries with body size or age only in the earliest juvenile stages. Analysis of the development of these two distinct GnRHir neuronal populations provides insight into their functional differentiation in adults.

Metabolic rate, hypoxia tolerance and aquatic surface respiration of some lacustrine and riverine African cichlid fishes (Pisces: Cichlidae)

The oxygen uptake rate (VO 2 as μg O 2/g/hr), the critical partial oxygen pressure (Pc 2 ) and the presence/absence of aquatic surface behavior (ASR) under hypoxia was studied for 10 cichlid species from different habitats ( Oreochromis niloticus, Steatocranus tinanti, Astatotilapia burtoni, Dimidiochromis compressiceps, Nimbochromis venustus, Melanochromis auratus. Tropheus moorii, Neolamprologus brichardi, Julidochromis marlieri and Eretmodus cyanostictus). After correcting for differences in bodyweight, the differences in VO 2 were shown to be not statistically significant between cichlids from lacustrine and fluvial habitats. The capacity to regulate VO 2 as μg O 2/g/hr under gradually increasing hypoxia (P o 2 < Pc o 2 ) differs markedly among the studied species. Under the given experimental conditions two species ( Julidochromis marlieri, Neolamprologus brichardi) were conformers at 0 < P o 2 < 150 torr. Six species that naturally occur in well aerated water were not able to perform ASR when subjected to severe hypoxia (0.8–1.5 ppm O 2) ( Julidochromis marlieri, Neolamprologus brichardi, Eretmodus cyanostictus. Tropheus moorii, Melanochromis auratus, Steatocranus tinanti).