Diverse Vertebrate Species Research Articles

Distribution of Pax6 protein during eye development suggests discrete roles in proliferative and differentiated visual cells.

Although Pax6 is required during eye development in rodents and humans, little is known about the precise role of the protein in this process. To aid in the interpretation of functional studies, we have determined the precise spatial and temporal distributions of the Pax6 protein in the eye. We find that Pax6 is initially distributed contiguously throughout a large domain of the anterior neural plate of zebrafish, including the presumptive eye fields and the dorsal diencephalon. After evagination of the optic vesicle, Pax6 becomes restricted to all proliferating cells of the pigment epithelial and neural layers of the retina. Pax6 is downregulated in most cells concomitant with differentiation. However, it remains present in several mature cell types of the eye including amacrine cells and the lens and corneal epithelia. This expression is conserved across diverse vertebrate species and suggests that Pax6 has additional conserved functions in the mature eye.

Circadian oscillators in vertebrate retinal photoreceptor cells.

Recent progress in research on retinal circadian rhythmicity is reviewed. Important advances include the discovery that circadian oscillators are present in the retinas of diverse vertebrate species, and evidence that circadian rhythmicity is generated by the photoreceptor cells. Research on the cellular and molecular mechanisms of photoreceptor circadian rhythms has revealed that expression of a subset of genes associated with photoreception, melatonin synthesis and transcriptional control are regulated by a circadian oscillator. Finally, it has been found that cAMP mimics darkness in resetting the phase of the retinal photoreceptor circadian oscillator, suggesting that it may be a component of a transduction pathway for entrainment of the oscillator.

Comparative Effects of Diverse Vertebrate Gonadotropins on Estradiol-17β Formationin Vitroin an Immature Rat Sertoli Cell Bioassay

The biopotencies of pituitary gonadotropins (GTHs) from various vertebrate classes were examined in anin vitrorat Sertoli cell bioassay which was previously established for mammalian follicle-stimulating hormones (FSHs). Potencies of the gonadotropins were determined by incubation of Sertoli cells obtained from 10-day-old rats, with increasing doses of GTHs, which resulted in dose-related and parallel estradiol-17β formation converted from added 19-hydroxy-androstenedione. In general, mammalian (human and ovine) FSHs were most potent, avian (chicken, turkey, and ostrich) FSHs were intermediate, and reptilian (snapping turtle) and amphibian (bullfrog) FSHs were the least potent. By contrast, mammalian and bullfrog luteinizing hormones (LHs) were inactive or negligibly active in this assay; avian LHs possessed one-fifth to one-half of the potency of the FSH preparations of the same species. The data suggest that the assay is specific for FSHs from mammalian and amphibian species and is relatively specific for FSHs from avian species. Both snapping turtle FSH and LH exhibited low and similar potencies in this bioassay. Black silver carp GTH was also active in this assay, although its potency was much lower. The present study has demonstrated that the immature rat Sertoli cell aromatase assayin vitrois useful for measurement of FSH contents in mammalian species and of FSH activity in diverse nonmammalian species. It also provides an approach for the investigation of structure–function relations of gonadotropin in diverse vertebrate species in relation to phylogenic patterns and specificity of hormone–receptor interaction. The findings from the present study imply that the binding sites of vertebrate FSHs share a certain degree of homology and that the binding sites of FSH receptors on Sertoli cells from immature rat have a relatively low degree of animal class specificity.

Conservation Prioritization Using GAP Data

Data collected by the Gap Analysis Program in the state of Idaho (U.S.A.) are used to prioritize the selection of locations for conservation action and research. Set coverage and integer programming algorithms provide a sequence of localities that maximize the number of species or vegetation classes represented at each step. Richness maps of vegetation cover class diversity, terrestrial vertebrate species diversity (“hot spot analysis”), endangered, threatened, and candidate species diversity, and unprotected vertebrate species diversity (“gap analysis”), when prioritized, show a rapid accumulation of species as more localities are chosen for terrestrial vertebrates and unprotected vertebrates. Gap analysis identifies four target areas (“gaps”) that include 79 of the 83 vertebrate species not currently protected. Accumulation of vegetation cover classes and endangered, threatened, and candidate species is much slower. Sweep analysis is used to determine how well prioritizing on one component of diversity accumulates other components. Endangered, threatened, and candidate species do not sweep total vertebrates as well as unprotected vertebrates do, but are better than vegetation classes. Total vertebrates sweep endangered, threatened, and candidate species better than unprotected vertebrates do, which in turn are better than vegetation classes. We emphasize that prioritization must be part of conservation efforts at multiple scales and that prioritization points out important localities where more detailed work mast be undertaken.

Promoter Structure of the Mouse TATA-Binding Protein (TBP) Gene

5′-RACE and genomic cloning were used to determine that the mouse TBP (mTBP) gene consists of one 5′-terminal non-coding exon followed by seven protein-coding exons. The region upstream of the first exon lacks a TATA-box. Hence, as with the case of other genes carrying TATA-less promoter, transcription starts from a cluster of sites which are located at the restricted region of mTBP gene. Interestingly, sequences of this region are well conserved between human and mouse TBP genes, suggesting that both mouse and human TBP genes drive mRNA synthesis in a similar way, and the sequence homology between two genes was used to assign a putative start point for the human TBP gene. Mouse, human, andTrimersurus gramineus(green habu snake) TBP genes share two GC-rich regions in their promoter regions. Thus, it is probable that diverse species of vertebrates commonly use TATA-less promoter bearing GC-rich regions to direct ubiquitous TBP expression.

A reverse transcription-polymerase chain reaction (RT-PCR) approach for cloning Ah receptors from diverse vertebrate species: Partial sequence of an Ah receptor from the teleost Fundulus heteroclitus

The aromatic hydrocarbon receptor (AhR) is a ligand-activated transcription factor that mediates many of the biological effects of 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) and related halogenated aromatic hydrocarbons. AhR proteins are expressed in most vertebrate animals, including teleost and elasmobranch fish, but the relationship between piscine and mammalian Ah receptors is uncertain. In the present studies, cloning of an Ah receptor cDNA from the teleost Fundulus heteroclitus was pursued using a reverse transcription-polymerase chain reaction (RT-PCR) approach. Degenerate oligodeoxynucleotides were designed based on conserved regions of mammalian Ah receptors and the related PAS proteins Per, ARNT and Sim. The oligonucleotides were used as primers in the RT-PCR to amplify a portion of an AhR expressed in Fundulus liver. A fragment of approximately 700 bp was amplified and directly sequenced. The deduced amino acid sequence of this fragment (212 residues) shares significant sequence identity with the PAS domains of the mouse (64%), rat (64%) and human (62%) Ah receptors. These data reveal conservation of Ah receptor structure between mammals and fish, vertebrate groups separated by over 400 million years of evolution. The successful use of RT-PCR to amplify a Fundulus AhR establishes the utility of this approach in the phylogenetic analysis of Ah receptor structure and function.

Target-independent diversification and target-specific projection of chemically defined retinal ganglion cell subsets.

In diverse vertebrate species, defined subsets of retinal ganglion cells (RGCs, the neurons that project from retina to brain) are distinguishable on the basis of their dendritic morphology, physiological properties, neurotransmitter content and synaptic targets. Little is known about when this diversity arises, whether diversification requires target-derived signals, and how subtype-specific projection patterns are established. Here, we have used markers for two chemically defined RGC subsets in chick retina to address these issues. Antibodies to substance P (SP) and the nicotine acetylcholine receptor (AChR) beta 2 subunit label two small ( < 10%), mutually exclusive groups of RGCs in mature retina. SP and AChRs accumulate in distinct RGCs before retinotectal synapses have formed. Moreover, both populations of RGCs form in retinae that develop following tectal ablation or transplantation to the coelomic cavity. Thus, RGC subsets acquire distinct neurotransmitter phenotypes in the absence of extraretinal cues. In the mature optic tectum, SP- and AChR-positive RGC axonal arbors are confined to distinct retinorecipient (synaptic) laminae. In the developing tectum, SP- and AChR-positive axons are initially intermingled in a superficial fiber layer, but then enter and arborize in appropriate laminae soon after those laminae form. Importantly, SP-positive axons, which synapse in a superficial lamina, never extend into the deeper, AChR-positive lamina. Tectal interneurons rich in SP receptors are concentrated in the lamina to which SP-positive RGC axons project, and a set of cholinergic (choline acetyltransferase-positive) tectal projection neurons elaborate dendrites in the lamina to which AChR-positive RGC axons project. These populations of tectal neurons, which are likely targets of the RGC subsets, form in tecta that develop following enucleation. Thus, RGCs and their targets can diversify in each others absence. Accordingly, we propose that the lamina-selective connectivity we observe reflects the presence of complementary cues on RGC subsets and their laminar targets.

Identification and characterization of T-cell antigen receptor-related genes in phylogenetically diverse vertebrate species.

Characterization of the structure, multiplicity, organization, and cell lineage-specific expression of T-cell receptor (TCR) genes of nonmammalian vertebrate species is central to the understanding of the evolutionary origins of rearranging genes of the vertebrate immune system. We recently described a polymerase chain reaction (PCR) strategy that relies on short sequence similarities shared by nearly all vertebrate TCR and immunoglobulin (Ig) variable (V) regions and have used this approach to isolate a TCR beta (TCRB) homolog from a cartilaginous fish. Using these short PCR products as probes in spleen cDNA and genomic libraries, we were able to isolate a variety of unique TCR and TCR-like genes. Here we report the identification and characterization of a chicken TCR gamma (TCRG) homolog, apparent Xenopus and pufferfish TCR alpha (TCRA) homologs, and two horned shark TCR delta (TCRD)-like genes. In addition, we have identified what could be a novel representative of the Ig gene superfamily in the pufferfish. This method of using short, minimally degenerate PCR primers should speed progress in the phylogenetic investigations of the TCR and related genes and lend important insights into both the origins and functions of these unique gene systems.

Paleoenvironment of a Diverse Marine Vertebrate Fauna from the Yazoo Clay (Late Eocene) at Copenhagen, Caldwell Parish, Louisiana: ABSTRACT

ABSTRACT The vertebrate fauna from the exposures of the Tullos Member, Yazoo Clay (Jackson Group, Late Eocene) at Copenhagen represents the most diverse assemblage documented from Louisiana and is one of the richest faunas known from the Tertiary of the Gulf coastal plain. Studies of the diverse assemblage of marine vertebrates revealed 70 vertebrate species, including 14 sharks, 5 rays, 46 teleosts (34 based on otoliths), 3 reptiles, and 2 mammals. Over 8,000 specimens have been collected making paleoenvironmental interpretations possible. The Copenhagen fauna has the greatest abundance and diversity of vertebrate species in comparison to previously described Jackson faunas in Louisiana, Texas, Arkansas, Mississippi, Alabama, Georgia, and Florida. Open marine conditions are suggested by the occurrence and variety of open-water and pelagic species such as the sharks Isurus, Abdounia, and Alopias, teleosts such as Bregmaceros, Cylindracanthus, Myripristis, Sphyraena, and Xiphiorhynchus, and cetaceans. Paleoecologic comparisons to extant species support an interpretation of an inner shelf deepening to middle shelf upsection as pelagics increase. The Yazoo Clay's invertebrate macrofauna which consisted mainly of oysters, corals, crabs, gooseneck barnacles, comatulid crinoids, and other rare bivalves and gastropods is not especially helpful for paleoecologic comparisons to the vertebrate fauna. However, diverse and abundant foraminiferal and ostracode microfaunas in the Yazoo Clay support an interpretation of deposition in middle shelf waters as suggested by the vertebrate distribution.

Cytochrome P4501A induction and inhibition by 3,3′,4,4′-tetrachlorobiphenyl in an Ah receptor-containing fish hepatoma cell line (PLHC-1)

The induction of cytochrome P4501A1 (CYP1A1) in rat hepatoma cells has been used by some investigators to determine ‘dioxin equivalents’ in environmental samples, including extracts of fish tissues. However, the relative potency of inducing compounds may vary between species, suggesting the need for taxon-specific model systems. In this paper we present an initial characterization of CYP1A induction in one such system, a teleost liver cell line (PLHC-1) derived from a hepatocellular carcinoma of Poeciliopsis lucida (Hightower, L.E. and Renfro, J.L., 1988. J. Exp. Zool. 248, 290). Specific binding of the photoaffinity ligand 2-azido-3-[ 125I]iodo-7,8-dibromodibenzo- p-dioxin([ 125I]N 3Br 2DD) to proteins in PLHC-1 cytosol indicated the presence of the Ah receptor, which is known to control CYP1A induction in mammals. 3,3′,4,4′-Tetrachlorobiphenyl (TCB) induced a microsomal protein in PLHC-1 cells that was recognized by monoclonal antibody (MAb) 1-12-3 to scup CYP1A1 (P450E) on immunoblots. Immunohistochemical staining of whole cells with MAb 1-12-3 showed specific recognition of CYP1A induced by TCB. No staining was seen in untreated or vehicle-treated cells. There was an excellent quantitative correlation between amounts of CYP1A protein detected immunohistochemically and in immunoblots of cell homogenates. In a dose response experiment, maximal induction of ethoxyresorufin O-deethylase (EROD) activity occurred at 0.1 μM TCB; at higher concentrations (1 and 10 μM), EROD activity was reduced as compared to the activity at 0.1 μM TCB. In contrast, immunoreactive CYP1A protein increased with increasing TCB concentration up to 10 μM. The loss of EROD activity at high concentrations of TCB did not result from changes in cell number or viability. The apparent inhibition or inactivation of CYP1A catalytic activity by the higher concentrations of halogenated biphenyls has been seen, but not generally recognized, both in vivo and in cultured cells from diverse vertebrate species. PLHC-1 cells may be a good model system for studying Ah receptor-mediated regulation of gene expression, for determining the fish-specific toxic or inducing potency of halogenated aromatic hydrocarbon congeners, and for investigating the mechanism of CYP1A inhibition or inactivation by environmental contaminants such as TCB.

Variation in the upland heathlands of Great Britain: Conservation importance

The two main communities of British upland heaths are heather Calluna vulgaris moor and heather-dominated blanket bog, which occur towards dry and wet ends, respectively, of a climatic gradient. The four developmental phases of heather—pioneer, building, mature and degenerate—also contribute to the variability, particularly for animal species. Spatial variation in the invertebrates often reflects these primary determinants of ecological variation, although soil or geological differences can be important. Temporal variation relates to the succession after heather burning or cutting. Examples of spatial and temporal variation are drawn from studies on the North York Moors, an upland area with 15% of British ground beetles Carabidae, 20% of British spiders Araneae, but only 2·2% of the British vascular plants. There are many fewer species of vertebrates on upland heaths, but for the breeding birds (15% of British species), three questions are discussed in detail—what is desired, what management options are available and can heathlands be managed for assemblages as well as for individual species? The review concludes that (i) burning on blanket bog be minimised; (ii) variable burning cycles to improve habitat complexity be used; (iii) wet flushes be conserved; (iv) upland heathland margins be burnt less intensively; and (v) scattered mosaics of scrub and woodland be established. The mosaic structure of upland heathlands is critical for wildlife conservation. The invertebrate assemblages rely for their diversity on this mosaic structure. Several scales of mosaic on any one moor are likely to lead to the greatest diversity of vertebrate species.

The Vertebrate Fauna of Broombush Melaleuca-Uncinata Vegetation in Northwestern Victoria, With Reference to Effects of Broombush Harvesting

The vertebrate fauna of broombush Melaleuca uncinata vegetation in north-western Victoria was assessed by censusing in marked quadrats, trapping and wide-ranging observations. Most species of vertebrates known to occur in mallee shrublands in Victoria we recorded in broombush (those recorded included four amphibian, 42 reptile, 126 bird and 18 mammal species). This high diversity resulted from a substantial variation in vertebrate (particularly reptile and bird) species composition between broombush of differing ages (0-80 years). Some floristic variation between broombush stands and the local presence within these stands of particular plant species (notably Triodia irritans and Banksia ornata) also added to vertebrate species diversity. Locally, broombush patches were characteristically simple in structure and of low floristic diversity. Bird species diversity and density were low (&lt;3 individuals per ha). Broombush is being harvested at an accelerating rate in Victoria. The effects of this industry on vertebrates generally are minor. No vertebrate species is restricted to broombush, and most vertebrate species recorded in this survey were found in harvested areas. Nonetheless, broombush is an important habitat for several species (e.g. Ctenophorus pictus, Ctenotus uber, C. brooksi, Leipoa ocellata, Pachycephala rufogularis, Psophodes nigrogularis, Drymodes brunneopygia, Cercartetus lepidus and Notomys mitchelli). Information on the ecology of most species of vertebrates living in the mallee is very limited, and some species may be affected by broombush cutting through a decrease in area of habitat of suitable age.

Neuropeptide Y-like immunoreactivity is absent from most perivascular noradrenergic axons in a marsupial, the brush-tailed possum

Noradrenergic perivascular axons were demonstrated in all systemic arteries and veins of a marsupial, the brush-tailed possum ( Trichosurus vulpecula), by a catecholamine fluorescence procedure and with antisera directed against the catecholamine-synthesizing enzymes tyrosine hydroxylase (TH) and dopamine-β-hydroxylase (DβH). Perivascular axons with neuropeptide Y-like immunoreactivity (NPY-LI) were not found in most systemic arteries and veins using antisera which recognize NPY and other members of the pancreatic polypeptide family in diverse vertebrate species. The exceptions were the renal, coeliac, main mesenteric and iliac arteries, where up to 50% of axons with TH-LI or DβH-LI also showed NPY-LI with two of the 4 antisera used. No noradrenergic nerve cell bodies in thoracic sympathetic ganglia had NPY-LI, whilst 3% of noradrenergic nerve cell bodies in lumbar sympathetic chain ganglia had weak NPY-LI. This marsupial is the first vertebrate species found to date in which the majority of perivascular noradrenergic axons do not contain NPY-LI. If these axons contain an as yet unidentified neuropeptide, it is unlikely to be closely related to NPY.

Broad phylogenetic expression of heavy-chain determinants detected by rabbit antisera to V Ha allotypes

Immunoglobulin molecules from diverse vertebrate species were examined, using an enzyme-linked immunosorbent assay (ELISA), for the expression of determinants detectable by rabbit antisera to V Ha allotypes. The data indicate that immunoglobulins of elasmobranchs, teleosts, amphibians and birds express determinants cross-reactive with those specified by the a1, a2 and a3 alleles in the domestic rabbit. We localize V Ha cross-reactive specificity to the denatured heavy chain of a primitive vertebrate, the Galapagos shark ( Carcharhinus galapagensis). Furthermore, the N-terminal amino acid sequence of the shark heavy chain shows significant homology with rabbit heavy chains of known V Ha type at positions where allotype-correlated differences have been implicated. V Ha-related determinants are shared by immunoglobulins of a wide range of vertebrates from sharks to man and thus seem to be epitopes which have been conserved during vertebrate evolution. The determinants detected on immunoglobulins of lower vertebrates by rabbit anti-V Ha allotype sera most probably are V H-subgroup rather than allotypic markers. Their distribution demonstrates a strong phylogenetic conservation of V H-regions.

Identification and localization of synaptophysin, an integral membrane glycoprotein of Mr 38,000 characteristic of presynaptic vesicles

A polypeptide of Mr 38,000 has been identified as a specific component of the membrane of presynaptic vesicles, using the monoclonal antibody SY38. This protein, which is acidic (isoelectric at approximately pH 4.8) and glycosylated, appears to be an integral membrane protein, as suggested by its solubilization with the nonionic detergent Triton X-100 and the finding that the epitope recognized by antibody SY38 is located on the cytoplasmic surface of those vesicles. It is found in presynaptic vesicles of neurons of the brain, spinal cord, and retina as well as at neuromuscular junctions. It is also found in the adrenal medulla. Its occurrence in diverse vertebrate species indicates its stability during evolution. This protein, for which we propose the name synaptophysin*, provides a molecular marker for the presynaptic vesicle membrane and may be involved in synaptic vesicle formation and exocytosis.

LDH k in the retina of diverse vertebrate species: a possible link to the Warburg effect

LDHk is a cancer-associated lactate dehydrogenase which is also found at high levels in normal mammalian retina. Such retinas share with most cancer tissues a dependence on aerobic glycolysis, leading to high production of lactate. However, retinas of lower vertebrate species are significantly less dependent on aerobic glycolysis. We find that retinas of species less dependent on aerobic glycolysis express significantly lower levels of an LDHk-like activity, less than or equal to the low levels seen in brains. The enzymes from lower species differ from the mammalian retinal enzyme in their pH optima and responsiveness to oxygen; but share a similar degree of inhibition by 5'-5'-dinucleoside tetraphosphates. Therefore, the expression pattern of LDHk in brain and retina of diverse vertebrate species suggests a link with the Warburg effect.

Molecular cloning of integrated Gardner-Rasheed feline sarcoma virus: genetic structure of its cell-derived sequence differs from that of other tyrosine kinase-coding onc genes.

Gardner-Rasheed feline sarcoma virus (GR-FeSV) is an acute transforming retrovirus which encodes a gag-onc polyprotein possessing an associated tyrosine kinase activity. The integrated form of this virus, isolated in the Charon 21A strain of bacteriophage lambda, demonstrated an ability to transform NIH/3T3 cells at high efficiency upon transfection. Foci induced by GR-FeSV DNA contained rescuable sarcoma virus and expressed GR-P70, the major GR-FeSV translational product. The localization of long-terminal repeats within the DNA clone made it possible to establish the length of the GR-FeSV provirus as 4.6 kilobase pairs. The analysis of heteroduplexes formed between lambda feline leukemia virus (FeLV) and lambda GR-FeSV DNAs revealed the presence of a 1,700-base-pair FeLV unrelated segment, designated v-fgr, within the GR-FeSV genome. The size of this region was sufficient to encode a protein of approximately 68,000 daltons and was localized immediately downstream of the FeLV gag gene coding sequences present in GR-FeSV. Thus, it is likely that this 1.7-kilobase-pair stretch encodes the onc moiety of GR-P70. Utilizing probes representing v-fgr, we detected homologous sequences in the DNAs of diverse vertebrate species, implying that v-fgr originated from a well-conserved cellular gene. The number of cellular DNA fragments hybridized by v-fgr-derived probes indicated either that proto-fgr is distributed over a very large region of cellular DNA or represents a family of related genes. By molecular hybridization, v-fgr was not directly related to the onc genes of other known retroviruses having associated tyrosine kinase activity.

Molecular and cellular biology of Abelson virus transformation.

A tremendous increase in our knowledge of the variety of retroviral transforming genes and their complexity of structure and function has been attained within the last decade. Rapidly transforming, replication-defective retroviruses have gained a prominent position as systems to exploit in the study of the interactions of specific growth control genes and their host cells. A large number of independent isolates of such viruses from diverse vertebrate species (see Coffin et a1.1980) have been documented. The phenomenon of a specific host cell gene being recombined with part of the sequences of a replication-competent retrovirus and, hence, generating a new viral form and function has been demonstrated at the biological and molecular levels for a number of cases.

Desmoplakins of Epithelial and Myocardial Desmosomes are Immunologically and Biochemically Related

Guinea pig antibodies against desmoplakins from bovine muzzle epidermis showed specific reaction in several epithelial tissues with desmoplakin I (M r 250,000) and desmoplakin II (M r 215,000). By immunofluorescence microscopy, prominent punctate staining was observed in various lines of cultured epithelial cells, revealing desmosomal junctions at sites of established cell-to-cell contacts as well as hemidesmosomes and internalized desmosome-derived membrane domains. On frozen tissue sections punctate staining was observed along plasma membranes of epithelial cells, and electron microscopy using the immunoperoxidase technique revealed that the antibodies were specifically localized at the plaques associated with desmosomes and hemidesmosomes. Of a large number of non-epithelial cells examined positive staining was only observed on desmosome-like junctions of myocardial cells and Purkinje fiber cells. In both epithelial and myocardial tissues the antibodies showed a broad range of cross-reactivity between diverse vertebrate species such as man, cow, rodent, and chicken, indicating that desmoplakins contain determinants strongly conserved during evolution. When binding of these antibodies to cytoskeletal polypeptides separated by gel electrophoresis and blotted on nitrocellulose paper sheets was examined, specific reaction was noted with desmoplakin I and, to a variable degree, also desmoplakin II from various epithelial cells. Reaction was also observed with a myocardial polypeptide from bovine and human hearts which had a similar M r value (250,000) and isoelectric pH range as desmoplakin I. We conclude that desmoplakins are the major proteins present in the desmosomal plaques of both epithelial and myocardial cells and that the desmoplakin polypeptides present in these two different cell types are very similar, if not identical.

Hormone Specificity, Androgen Metabolism, and Social Behavior

SYNOPSIS. The ability of different sex hormones to activate social signals can provide important clues to the biochemical mechanisms underlying these signals. A pattern of hormone specificity in which testosterone (T) and estradiol (E), but not dihydrotestosterone (DHT), are effective suggests that conversion (aromatization) of T to E in the brain may be involved or required; a pattern in which T and DHT, but not E, are effective suggests that conversion of T to DHT may be involved. The hormone specificity of social signals in diverse species of vertebrates is reviewed. Aromatization seems to be of widespread behavioral significance in mammals andbirds. A role for conversion of T to DHT is suggested for some signals. Aromatization of T mayalso be important for the activation of adult female behavior in mammals and lizards, and for the early organization of behavior in mammals and birds. Patterns of hormone specificity differ both across species for a given social signal, and within a given species when different signals are compared. An attempt is made to integrate these findings by relating patterns of hormone specificity to hormone levels, steroid receptor and enzyme concentrations and distributions, signal function and dimorphism, and phylogenetic status.