Volume 87, Issue 2,
, Pages 197-202
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Female preference for male fin elaborations in Poeciliid fishes may be driven by a sensory bias for increased lateral projection area (LPA) that has existed since the lineages diverged from a common ancestor. Previous research supports this hypothesis demonstrating female Poecilia latipinna, Poecilia mexicana, and Poecilia reticulata prefer males of larger body and dorsal fin size, but exhibit no such preferences when controlling for total LPA. In the current study, we further tested this hypothesis by presenting female platys, Xiphophorus variatus, with pairs of dummy males differing in: (1) body size (holding dorsal fin size constant); (2) dorsal fin size (holding body size constant); and (3) dorsal fin: body size ratio (holding total LPA constant). Females spent more time near dummies of greater body and dorsal fin size; however, in the third experiment, neither fin size, body size, nor any particular dorsal fin+body size combination was preferred. These results provide additional support for the LPA and sensory bias hypotheses, demonstrating that female X. variatus not only prefer males with “swords”, but sailfin-like dorsal fins as well when body size is held constant. Shared preference for increased LPA is consistent with common ancestry of the sensory/neural systems in females of all four species.
► Female preference for male fin enhancements in Poeciliid fishes may be driven by a sensory bias for larger male apparent size or lateral projection area. ► Female Xiphophorus variatus in this study preferred males of larger body size. ► Female X. variatus also preferred males with artificially enhanced sailfin-like dorsal fins. ► Females showed no such preferences when male total lateral projection area was held constant. ► These results provide support for the lateral projection area and sensory bias hypotheses.
Females may develop perceptual biases in mate preferences due to a sensory bias in their nervous systems formed by natural selection, sexual selection, or pleiotropic effects (Kirkpatrick and Ryan, 1991, Endler, 1992). Such biases may reflect ecological constraints (Proctor, 1991, Endler, 1992) or basic properties of nervous systems (Ryan and Keddy-Hector, 1992, Rosenthal and Evans, 1998, MacLaren, 2006). Regardless of the bias origin, females are preferentially attracted to males that stimulate their sensory systems more than other males. If a male sends a novel signal which taps into a latent bias, these males are preferred as mates. Thus, a preexisting bias may affect the nature and direction of sexual selection when a new trait arises (Basolo, 1995a).
Support for the preexisting bias hypothesis requires evidence that the female preference evolved within the species’ lineage prior to the evolution of the male trait that exploits the preference (Basolo, 1990a). The role of preexisting biases on female preference for male traits has been well studied in certain species of live-bearing fishes (Poecilidae). For example, males of some species of the genus Xiphophorus possess an elongation of certain ventral caudal fin rays (the sword) that even females of related but unsworded species find attractive (e.g. X. maculatus; Basolo, 1990b, Xiphophorus variatus; Basolo, 1995b, Priapella olmecae; Basolo, 1995a). Phylogenetic information and mate choice tests suggest that female preference for swords arose before the Xiphophorus-Priapella clade diverged, pre-dating the evolution of the sword within Xiphophorus (Basolo, 1996).
Species within the subgenus Poecilia (mollies) provide additional evidence of female bias for male fin elaborations. Male sailfin mollies (Poecilia latipinna) have an enlarged dorsal fin (sailfin) that is presented to females in courtship (Ptacek and Travis, 1996). Female P. latipinna as well as Poecilia mexicana (a species whose males do not naturally possess the sailfin phenotype) prefer to associate and mate with males of larger dorsal fin (MacLaren et al., 2004, MacLaren and Rowland, 2006, Jordan et al., 2006) and body size (Ptacek and Travis, 1997, MacLaren et al., 2004, MacLaren and Rowland, 2006). As with the sword ornament of Xiphophorus, phylogenetic information (Ptacek and Breden, 1998, Breden et al., 1999) suggests that female preference for enlarged dorsal fins arose before the monophyletic sailfin clade diverged from a shortfin ancestor, pre-dating the evolution of the sailfin trait within the subgenus Poecilia.
Additionally, males of numerous guppy populations (Poecilia reticulata) show polymorphism in dorsal and caudal fin length including homoplastic “swords”, elongated tails and enlarged dorsal fins (Houde, 1997, Brooks and Endler, 2001, Karino and Matsunaga, 2002, MacLaren et al., submitted for publication) that along with body size (Endler and Houde, 1995, Karino and Matsunaga, 2002; MacLaren et al., unpublished data) offer a selective advantage in female mate choice in at least some populations (Bischoff et al., 1985, Endler and Houde, 1995, MacLaren et al., submitted for publication).
These elongated caudal and dorsal fins, among other poeciliid fin elaborations may have originated from a shared female preference for larger apparent size in males, a preference that is common in many species (Andersson, 1994) and widespread among the Poecilidae (Ryan, 1998). Because a larger male projects a larger image onto the female's retina at a given viewing distance (O’Brien et al., 1976, O’Brien et al., 1985, Rowland, 1989a, Rowland, 1989b), this could elicit a stronger sexual response (MacLaren, 2006). Fin elaborations may therefore have evolved as a way for males to increase their apparent size or lateral projection area (LPA) and consequent attractiveness to females (Haines and Gould, 1994, Rosenthal and Evans, 1998, Karino and Matsunaga, 2002, MacLaren et al., 2004).
If females respond primarily to greater LPA rather than increased body or fin size per se, then female preference should be proportional to the male's total LPA (body+fin area) regardless of his fin: body size ratio (MacLaren et al., 2004). The LPA hypothesis predicts that females: (1) prefer males of larger body and fin size; (2) show no preference between two males whose total LPAs (fin+body surface areas) are equal (i.e. increases in fin surface area compensate for decreases in body surface area and vice versa); and (3) show no preference for males with the fin elaboration over a finless male of equivalent LPA. Preference experiments with P. latipinna (MacLaren et al., 2004), P. mexicana (MacLaren and Rowland, 2006), and P. reticulata (MacLaren et al., submitted for publication) support all three of the predictions above.
In this study we further test the LPA hypotheses by examining female preferences for male body size, dorsal fin size, and dorsal fin: body size ratio in X. variatus—a series of experiments similar to those previously conducted with P. latipinna, P. mexicana, and P. reticulata. Moreover, we want to know whether this preference stems from a preexisting bias. Female preference for increased male LPA not only in the subgenera Poecilia (“mollies”) and Lebistes (“guppies”) but the more distantly related genus Xiphophorus would support the preexisting bias hypothesis, demonstrating that female X. variatus (a species sexually monomorphic with respect to fin morphology) not only prefer males with artificial “sword” ornaments (Basolo, 1995b) but supernormal size dorsal fins and perhaps other forms of size manipulation that increase male LPA (Haines and Gould, 1994). A shared preference for sailfin-like dorsal fins and/or increased LPA would be consistent with common ancestry of the sensory/neural systems in females of P. latipinna, P. mexicana, P. reticulata, and X. variatus.
Test subjects were X. variatus, Zarco collected from the Arroyo Zarco locality west of Encino, Tamaulipas, Mexico (locale described by Borowsky (1984); stock source: Dr. Steve Kazianis, New York University, 6th of September 1996). The fish were shipped to the laboratory at Merrimack College from the Xiphophorus Genetic Stock Center, Texas State University, San Marcos, TX in the fall of 2008, placed in 378-l and 70-l mixed-sex stock tanks (water temperature 23–25°C; 16h light:8h dark cycle) and
The female behaviors observed during both experiments included unison swimming, circling, and backing toward the male, all of which are activities attributed to mating behavior in the literature for poeciliids (Farr, 1989, Houde, 1997, Basolo, 2002a). There were no significant effects of dummy presentation order on female strength of preference in any of the three experiments (expt I: one-way repeated measures ANOVA, df=2, F=0.327, P=0.723; expt II: one-way repeated measures ANOVA, df=2, F=
As demonstrated in similar studies with P. latipinna, P. mexicana, and P. reticulata, the preferences of female X. variatus satisfy all three predictions of the LPA hypothesis, suggesting that increased dorsal fin size can compensate for decreased body size and vice versa, and that preference is for male LPA rather than for dorsal fin and body size per se. Haines and Gould (1994) explored the basis of female preference for a male fin elaboration – the sword – in X. variatus and came to a
This study was supported in part by a Merrimack College Faculty Development Grant. E. ElAchi, and P. Imbriano offered valuable assistance in data collection and analysis. C. MacLaren and two anonymous reviewers provided helpful comments on the manuscript. We thank D. Tombarelli for her assistance in lab maintenance. We also thank the Xiphophorus Genetic Stock Center, Texas State University, San Marcos, TX. for supplying the fish used in this study. The research methods presented herein were
- A.L. Basolo
Female preference for male sword length in the green swordtail Xiphophorus helleri (Pisces: Poeciliidae)
- A.L. Basolo
A further examination of a preexisting bias favoring a sword in the genus Xiphophorus
- A.L. Basolo
Female discrimination against sworded males in a poeciliid fish
- F. Breden et al.
Molecular Phylogeny of the live-bearing fish genus Poecilia (Cyprinodontiformes: Poeciliidae)
Mol. Phylogent. Evol.
- H.C. Proctor
Courtship in the water mite Neumania papillator: males capitalize on female adaptations for predation
- M.B. Ptacek et al.
Inter-population variation in male mating behaviours in the sailfin molly, Poecilia latipinna
- G.G. Rosenthal et al.
Secondary reduction of preference for sword ornament in the pygmy swordtail Xiphophorus nigrensis (Pisces: Poeciliidae)
- W.J. Rowland
The ethological basis of mate choice in male threespine sticklebacks, Gasterosteus aculeatus
- M. Andersson
- A.L. Basolo
Female preference predates the evolution of the sword in swordtail fish
Phylogenetic evidence for the role of a pre-existing bias in sexual. selection
Proc. Roy. Soc. Lond. B: Biol.
Phylogenetic distribution of a female preference
Congruence between the sexes in preexisting receiver responses
Sexual behaviour of immature. male eastern mosquitofish: a way to measure intensity of intra-sexual selection
J. Fish Biol.
Tail size and female choice in the guppy (Poecilia reticulata)
Behav. Ecol. Sociobiol.
The evolutionary genetics of Xiphophorus
Direct and indirect sexual selection and quantitative. genetics of male traits in guppies (Poecilia reticulata)
Female size influences mate preferences of male guppies
Signals, signal conditions and the direction of evolution
Geographic variation in female preferences for male traits. in Poecilia reticulata
Sexual selection and secondary sexual differentiation in poeciliids: determinants of male mating success and the evolution of female choice
The Genetical Theory of Natural Selection
Male swordtails court with an audience in mind
Association patterns of sailfin mollies (Poecilia latipinna): alternative hypotheses
Behav. Ecol. Sociobiol.
Female platys prefer long tails
Sexual selection and species recognition in the pygmy swordtail Xiphophorus pygmaeus: conflicting preferences
Behav. Ecol. Sociobiol.
Synthetic progestin etonogestrel negatively affects mating behavior and reproduction in Endler's guppies (Poecilia wingei)
2019, Science of the Total Environment
Citation Excerpt :
In the present study, a longer dorsal fin was observed in males exposed to the highest level of etonogestrel (320 ng L−1). Worthy of note is that Poecilia latipinna and Poecilia mexicana display a sexual dimorphism of dorsal fin, where females prefer males with longer dorsal fins (MacLaren et al., 2011). In addition, exposure to etonogestrel at both concentrations caused changes in the shape of the gonopodium, namely it reduced the ratio of the 4th to 6th ray.
High rates of progestins consumption in the form of active ingredients in women's oral contraceptives and other hormonal preparations may lead to their increased concentrations in aquatic environments and subsequent harmful effect on fish reproduction. The objective of the present study was to assess the effect of etonogestrel, a third-generation synthetic progestin, on the reproductive behavior, fertility, gonads histology, and secondary sexual characteristics of male and female Endler's guppies (Poecilia wingei). Fish were subjected for 34 days to two concentrations of etonogestrel, including one possibly environmentally relevant (3.2 ng L−1) and one sublethal (320 ng L−1) concentration. A mating behavior study was subsequently conducted and revealed that the treatment with etonogestrel significantly reduced mating frequency in the exposed fish compared to controls. All the exposed females were unable to reproduce. In addition, female fish exposed to the highest level of etonogestrel were masculinized, as their anal fins and body coloration showed patterns similar to those of male fish. Etonogestrel-exposed females also had fewer developed oocytes. In conclusion, the low etonogestrel concentration (3.2 ng L−1) led to a reduction of mating activity in males without effect on their reproductive success, but it completely inhibited reproduction in females. Exposure to etonogestrel clearly has more severe consequences for females than males.
Does fin coloration signal social status in a dominance hierarchy of the livebearing fish Xiphophorus variatus?
2014, Behavioural Processes
In each population of the livebearing fish Xiphophorus variatus, only a small portion of the adult males develop bright yellow-red (YR) coloration on the dorsal and caudal fins. Here we characterized the dominance hierarchy in X. variatus and tested whether YR coloration is related to a male's position in the hierarchy and can therefore serve as a reliable cue to rival males. Populations varied considerably in the frequency of YR males. Across all populations, males with YR coloration were significantly larger than the rest of the males in the population. Observations of aggressive interactions among males in small groups in the laboratory revealed a sized-based dominance hierarchy with YR males at the top. Aggression was more common among males of a similar size and fighting increased as male body size differences decreased. However, despite the reliability of YR coloration as a signal of dominance status, males at lower social ranks did not avoid aggression with YR males and YR males did not experience fewer aggressive attacks compared to non-YR males. Our findings demonstrate that fin coloration is a reliable cue of a male's social status but rival males appear to not use this information to avoid potentially costly interactions with dominant males, suggesting that YR fin coloration has not evolved as a cue in agonistic interactions.
Incongruence between the sexes in preferences for body and dorsal fin size in Xiphophorus variatus
2013, Behavioural Processes
Citation Excerpt :
For the Constant LPA Series (expt III), number designations were based specifically on body LPA, from smallest (1), to largest (5) (Fig. 1). The testing environment consisted of three 17.5-l aquaria (50 cm × 26 cm × 13.5 cm each) lined up end to end using an apparatus and protocol identical to that used in previous female preference experiments with X. helleri (MacLaren and Daniska, 2008), P. reticulata (MacLaren and Fontaine, 2012) and X. variatus (MacLaren et al., 2011). Male subjects were placed in an aquarium that was divided into three zones by two black vertical lines drawn on the front wall: a 30 cm × 26 × 13.5 cm ‘neutral zone’ flanked on each side by a 10 cm × 26 cm × 13.5 cm ‘preference zone’.
Female preference for male fin enhancements in poeciliid fishes may be driven by a preexisting perceptual bias for increased male lateral projection area (LPA). This hypothesis suggests that a male with enlarged body and/or fin size projects a larger image onto the female's retina at a given viewing distance, eliciting a greater sensory and thus behavioral response out of the female than a smaller male. Given the shared sensory/neural systems of opposite sex conspecifics, we might expect the LPA bias to also be present in males of at least some poeciliid species. However, we need not expect congruence between the sexes in the state of the bias over evolutionary time. To examine whether the sexes share a bias for sailfin-like dorsal fins, a trait not present in their evolutionary history, the bias favoring increased dorsal fin size and LPA observed in female Xiphophorus variatus, among other poeciliids, was investigated by testing male preference for dummy females varying in dorsal fin size, body size, and dorsal fin:body size ratio. In three sets of simultaneous choice experiments, males preferred females of larger body size when fin size was held constant and when total LPA was held constant, but showed no preference for larger fins when body size was held constant. The LPA bias is therefore less permissive in males than females with selection favoring a male's ability to discriminate between female body size – an indicator of fertility/fecundity – and fin size, which offers no known fitness benefits.
Taking the sensory approach: How individual differences in sensory perception can influence mate choice
2012, Animal Behaviour
Citation Excerpt :
Endler (1995) originally suggested that the sensory drive hypothesis does not assume that sensory biases are fixed. Nevertheless, most empirical studies only evaluate its predictions at the population level (Egger et al. 2011; MacLaren et al. 2011). We suggest that the degree to which a sensory bias can act as a selective mechanism in female choice could be diminished when the salient components of a sensory trait are condition dependent.
Many male signallers convey information to female receivers in multimodal courtship displays. While much is known about how males vary in terms of signalling, variation in female detection of these multimodal signals is relatively unexplored. We suggest that there is a critical, albeit underdeveloped, link between multimodal sensory reception and individual variation in mate choice. This review addresses the potential effects of developmental and conditional factors (e.g. nutrient availability, hormone profiles and age) on female multimodal processing, and illustrates that differences in the (1) source of individual variation and (2) the number of sensory processing modes affected by this variation can influence the receiver's mate choice patterns. Based on these two factors, we outline novel predictions of preference functions and choosiness in a redundant multimodal signalling context. Moreover, we explore the theoretical implications of individual variation in multimodal signal perception in relation to sensory drive, honest signalling, assortative mating and intrasexual selection. We propose that understanding the role of variation in sensory processing and its relation to mate choice can help us better identify the factors that influence sender and receiver fitness, and subsequently the rate and direction of signal evolution.
Environmentally Realistic Waterborne Atrazine Exposure Affects Behavior in Poecilia latipinna
2023, Water (Switzerland)
Sex differences in behavioural and anatomical estimates of visual acuity in the green swordtail, Xiphophorus helleri
2021, Journal of Experimental Biology
Intratumoral macrophage phenotype and CD8+ T lymphocytes as potential tools to predict local tumor outgrowth at the intervention site in malignant pleural mesothelioma
Lung Cancer, Volume 88, Issue 3, 2015, pp. 332-337
In patients with malignant pleural mesothelioma (MPM), local tumor outgrowth (LTO) after invasive procedures is a well-known complication. Currently, no biomarker is available to predict the occurrence of LTO. This study aims to investigate whether the tumor macrophage infiltration and phenotype of and/or the infiltration of CD8+ T-cells predicts LTO.
Ten mesothelioma patients who developed LTO were clinically and pathologically matched with 10 non-LTO mesothelioma patients. Immunohistochemistry was performed on diagnostic biopsies to determine the total TAM (CD68), the M2 TAM (CD163) and CD8+ T-cell count (CD8).
The mean M2/total TAM ratio differed between the two groups: 0.90±0.09 in the LTO group versus 0.63±0.09 in patients without LTO (p<0.001). In addition, the mean CD8+ T-cell count was significantly different between the two groups: 30 per 0.025cm2 (range 2–60) in the LTO group and 140 per 0.025cm2 (range 23–314) in the patients without LTO (p<0.01).
This study shows that patients who develop LTO after a local intervention have a higher M2/total TAM ratio and lower CD8+ cell count at diagnosis compared to patients who did not develop this outgrowth. We propose that the M2/total TAM ratio and the CD8+ T-cell amount are potential tools to predict which MPM patients are prone to develop LTO.
Generation and characterization of the sea bass Dicentrarchus labrax brain and liver transcriptomes
Gene, Volume 544, Issue 1, 2014, pp. 56-66
The sea bass Dicentrarchus labrax is the center of interest of an increasing number of basic or applied research investigations, even though few genomic or transcriptomic data is available. Current public data only represent a very partial view of its transcriptome. To fill this need, we characterized brain and liver transcriptomes in a generalist manner that would benefit the entire scientific community. We also tackled some bioinformatics questions, related to the effect of RNA fragment size on the assembly quality.
Using Illumina RNA-seq, we sequenced organ pools from both wild and farmed Atlantic and Mediterranean fishes. We built two distinct cDNA libraries per organ that only differed by the length of the selected mRNA fragments. Efficiency of assemblies performed on either or both fragments size differed depending on the organ, but remained very close reflecting the quality of the technical replication. We generated more than 19,538Mbp of data. Over 193million reads were assembled into 35,073 contigs (average length=2374bp; N50=3257). 59% contigs were annotated with SwissProt, which corresponded to 12,517 unique genes. We compared the Gene Ontology (GO) contig distribution between the sea bass and the tilapia. We also looked for brain and liver GO specific signatures as well as KEGG pathway coverage. 23,050 putative micro-satellites and 134,890 putative SNPs were identified.
Our sampling strategy and assembly pipeline provided a reliable and broad reference transcriptome for the sea bass. It constitutes an indisputable quantitative and qualitative improvement of the public data, as it provides 5 times more base pairs with fewer and longer contigs. Both organs present unique signatures consistent with their specific physiological functions. The discrepancy in fragment size effect on assembly quality between organs lies in their difference in complexity and thus does not allow prescribing any general strategy. This information on two key organs will facilitate further functional approaches.
Females of the annual killifish Austrolebias reicherti (Cyprinodontiformes: Rivulidae) recognize conspecific mates based upon chemical cues
Behavioural Processes, Volume 155, 2018, pp. 33-37
Olfactory abilities to discriminate conspecifics can be determinant to prevent hybridization between closely-related species in many taxa. Annual killifish Austrolebias reicherti and A. charrua are sister species inhabiting temporary ponds within Eastern Wetlands of Uruguay with an overlapping area in their distributions. Herein, we assess species recognition sensory abilities in females of A. reicherti in classic dual-choice tests. We exposed two different groups of females, one to olfactory but not visual cues, and the other to visual but not olfactory cues, from conspecific and heterospecific A. charrua males. Austrolebias reicherti females preferred conspecific males when based solely on olfactory cues, and showed no discrimination when exposed to visual traits only. Austrolebias inhabit shallow, muddy and highly turbid ponds that may promote the use of non-visual cues. Although preliminary, the results of this study suggest the importance of chemical communication in species mate recognition in A. reicherti and points annual fishes as a promising model to study the role of mate choice in reproductive isolation and speciation.
Evolutionary change: facultative virulence by brood parasites and tolerance and plastic resistance by hosts
Animal Behaviour, Volume 125, 2017, pp. 101-107
Coevolutionary theory predicts that parasitism selects for defensive traits in the hosts that counteract the negative effects of parasites. Such antagonistic interactions may continuously coevolve within cycles without end, or result in host specialization and speciation of parasites. Here, we argue that particularities of brood parasite–host systems explain whether the coevolutionary relationships result in parasite specialization and speciation. Highlighted particularities of the system are (1) virulence of the parasites, (2) the ability of parasites to alter host behaviour, (3) the relative importance of defensive tolerance and defensive resistance of hosts, and (4) phenotypic plasticity of parasite virulence and host resistance. Fixed virulence of parasites selects for fixed resistance of hosts and both enhance the process of specialization and speciation of parasites. In contrast, phenotypic plasticity in virulence of the parasites would select for tolerance and facultative resistance in their hosts. These host characteristics imply limited escalation in resistance defences and therefore would facilitate continuous coevolutionary cycles preventing parasite specialization. Thus, when studying the diversification of brood parasites within the avian phylogeny, considering these three factors would help us understand what drives their evolution. To illustrate the importance of virulence, phenotypic plasticity and defensive tolerance for the evolution of parasites, we compare evolutionary radiation experienced by the genus Clamator and the Tribe Cuculinii, which includes the genus Cuculus, and speculate whether particularities of brood parasitism by the great spotted cuckoo, Clamator glandarius, and the common cuckoo, Cuculus canorus, explain differences in evolutionary radiation experienced by these two groups of brood parasites.
MHC in a monogamous lizard – Characterization of class I MHC genes in the Australian skink Tiliqua rugosa
Developmental & Comparative Immunology, Volume 53, Issue 2, 2015, pp. 320-327
The major histocompatibility complex (MHC) is a highly variable region of vertebrate genomes that encodes cellular proteins involved in the immune response. In addition to the benefits of MHC research in understanding the genetic basis of host resistance to disease, the MHC is an ideal candidate for studying genetic diversity under strong natural selection. However, the MHC of many non-model vertebrate taxa are poorly characterized, hindering an understanding of disease resistance and its application to conservation genetics in these groups. Squamates (lizards and snakes) remain particularly underrepresented despite their being the most diverse order of non-avian sauropsids. We characterized MHC class I sequence diversity from an Australian skink, the sleepy lizard (Tiliqua rugosa), using both cDNA and genomic sequence data and also present genomic class I sequences from the related skinks Tiliqua adelaidensis and Egernia stokesii. Phylogenetic analysis of Tiliqua and other published sqamate MHC class I sequences suggest that MHC diverged very early in Tiliqua compared with the other studied squamates. We identified at least 4 classical MHC class I loci in T.rugosa and also shared polymorphism among T.rugosa, T. adelaidensis and E.stokesii in the sequences encoding peptide-binding α1 and α2 domains.
Flatfish metamorphosis: A hypothalamic independent process?
Molecular and Cellular Endocrinology, Volume 404, 2015, pp. 16-25
Anuran and flatfish metamorphosis are tightly regulated by thyroid hormones that are the necessary and sufficient factors that drive this developmental event. In the present study whole mount in situ hybridization (WISH) and quantitative PCR in sole are used to explore the central regulation of flatfish metamorphosis. Central regulation of the thyroid in vertebrates is mediated by the hypothalamus–pituitary–thyroid (HPT) axis. Teleosts diverge from other vertebrates as hypothalamic regulation in the HPT axis is proposed to be through hypothalamic inhibition although the regulatory factor remains enigmatic. The dynamics of the HPT axis during sole metamorphosis revealed integration between the activity of the thyrotrophes in the pituitary and the thyroid follicles. No evidence was found supporting a role for thyroid releasing hormone (trh) or corticotrophin releasing hormone (crh) in hypothalamic control of TH production during sole metamorphosis. Intriguingly the results of the present study suggest that neither hypothalamic trh nor crh expression changes during sole metamorphosis and raises questions about the role of these factors and the hypothalamus in regulation of thyrotrophs.
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