Evolutionary determinants of normal arterial plasma pH in ectothermic vertebrates.
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Mean values of normal arterial pH in different species of fish, amphibians and reptiles at 15 and 25 degrees C, taken from the literature, are negatively correlated with arterial P(CO(2)) and plasma [Na(+)]. At either temperature, the data accord with the hypothesis that extracellular acid-base homeostasis evolved to maintain an optimal pH at particular cell-surface sites that are similar in all species. These hypothetical sites bear fixed negative charges that attract H(+), but which are partially screened by Na(+); for the surface pH to be constant, the bulk interstitial pH should then vary inversely with [Na(+)], as is the case. At the same time, the bulk interstitial fluid must be more acid than arterial plasma by an amount that increases with decreasing arterial P(CO(2)). With allowance made for additional screening by Ca(2+) and Mg(2+), the relevant cell-surface pH is probably approximately 6.2. (+info)
Evolutionary transitions in parental care and live bearing in vertebrates.
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We provide the first review of phylogenetic transitions in parental care and live bearing for a wide variety of vertebrates. This includes new analyses of both numbers of transitions and transition probabilities. These reveal numerous transitions by shorebirds and anurans toward uniparental care by either sex. Whereas most or all of the shorebird transitions were from biparental care, nearly all of the anuran transitions have been from no care, reflecting the prevalence of each form of care in basal lineages in each group. Teleost (bony) fishes are similar to anurans in displaying numerous transitions toward uniparental contributions by each sex. Whereas cichlid fishes have often evolved from biparental care to female care, other teleosts have usually switched from no care to male care. Taxa that have evolved exclusive male care without courtship-role reversal are characterized by male territoriality and low costs of care per brood. Males may therefore benefit from care through female preference of parental ability in these species. Primates show a high frequency of transitions from female care to biparental care, reflecting the prevalence of female care in basal lineages. In the numerous taxa that display live bearing by females, including teleosts, elasmobranchs, squamate reptiles and invertebrates, we find that live bearing has always evolved from a lack of care. Although the transition counts and probabilities will undoubtedly be refined as phylogenetic information and methodologies improve, the overall biases in these taxa should help to place adaptive hypotheses for the evolution of care into a stronger setting for understanding directions of change. (+info)
Roles of diversifying selection and coordinated evolution in the evolution of amphibian antimicrobial peptides.
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Antimicrobial peptides are expressed in the skin of amphibians and are used to prevent infection by microorganisms. Frog species store distinct collections of antimicrobial peptides that show variation in size, charge, conformation, and bactericidal activity, and so the evolution of antimicrobial peptide gene families may reflect the adaptive diversification of these loci. We examined the molecular evolution of antimicrobial peptide transcripts from hylid and ranid frog species. Our results show that after the gene family arose in the common ancestor of the Hylidae and Ranidae, before the divergence of these families in the Mesozoic, it subsequently diversified within these groups with numerous duplication events and divergence of loci. Moreover, we provide evidence that suggests that members of the antimicrobial peptide gene family have been subject to diversifying selection within both propiece and mature domains of hylids and solely within the mature domain of ranids. Finally, our results suggest that coordinated and compensatory amino acid replacements have occurred within the acidic propiece and cationic mature domain of hylid antimicrobial peptide precursors, as has been observed for mammalian defensin genes, but not among those of ranid precursors. (+info)
Production of polyclonal antibodies to Batrachochytrium dendrobatidis and their use in an immunoperoxidase test for chytridiomycosis in amphibians.
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Polyclonal antibodies were produced for diagnosing chytridiomycosis in amphibians. Two sheep and 4 rabbits were inoculated with homogenized whole culture of Batrachochytrium dendrobatidis in Freund's complete adjuvant or triple adjuvant. Antisera from all animals reacted strongly with all stages of B. dendrobatidis and stained the walls, cytoplasm, rhizoids and zoospores in an indirect immunoperoxidase test. Significant cross-reactivity occurred only with some fungi in the Chytridiomycota, and there are no members of this phylum besides B. dendrobatidis that infect frogs. The immunoperoxidase stain is a useful screening test when combined with recognition of the morphology and infection site of B. dendrobatidis. (+info)
Clues from wildlife to create an assay for thyroid system disruption.
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In 1996 the U.S. Congress charged the U.S. Environmental Protection Agency to develop a screening program to test chemicals for their possible estrogenic and other endocrine effects. Shortly thereafter, the Chemical Guidelines Program of the Organisation for Economic Co-operation and Development's (OECD) Environmental Directorate organized a Task Force on Endocrine Disruption Testing and Assessment to coordinate development of internationally harmonized screening and testing protocols. Most of the research devoted to this effort has focused on detecting impaired estrogenicity, androgenicity, and/or steroidogenesis, with little progress toward developing assays to detect chemicals that might interfere with thyroid function. Despite the fact that wildlife biologists have been reporting abnormal thyroid gland development and unusual thyroid hormone (TH) and retinoid ratios in fish and birds since the early 1960s, few studies have demonstrated an association between an environmental contaminant and a particular health end point other than reduced reproductive success at the population level. This article is a review of the literature that specifically examines THs and their role in normal behavior and development in wildlife. It presents several studies that associated changes in the thyroid gland, TH concentrations, and behavior with contaminant exposure. The goal of this article is to provide fodder for the creation of simple screens to detect possible thyroid system agonists and antagonists. (+info)
Synergism between trematode infection and pesticide exposure: a link to amphibian limb deformities in nature?
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The apparently rapid increase in the prevalence of amphibian limb deformities has led to substantial interest from ecologists and public health professionals. Hypotheses proposed to explain the deformities fall into two broad categories: chemical contaminants and trematode infection. Although there are convincing experimental demonstrations that certain factors can lead to some deformities, the causes for recent increases in amphibian malformation remain controversial. Moreover, no experimental studies on amphibian deformities have been conducted in the field, and no studies have attempted to examine the synergistic effects of trematode infection and exposure to chemical contaminants. Here, I present the results of field and laboratory experiments that link increased trematode infection, and increased limb deformities, to pesticide exposure. Field experiments conclusively demonstrated that exposure to trematode infection was required for the development of limb deformities in wood frogs, Rana sylvatica. However, deformities were more common at sites adjacent to agricultural runoff. Laboratory experiments corroborated the association between pesticide exposure and increased infection with pesticide-mediated immunocompetency as the apparent mechanism. Given the conservative contaminant exposure levels used [Environmental Protection Agency (EPA) drinking water standards] and the widespread use of many pesticides, these negative impacts may help to explain pathogen-mediated amphibian declines in many regions. (+info)
Studies on the gastrulation of amphibian embryos: light and electron microscopic observation of a urodele Cynops pyrrhogaster.
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The course of gastrulation in embryos of a urodele, Cynops pyrrhogaster, was studied with 1 mum Epon sections and transmission and scanning electron microscopy. During the initial period of gastrulation, the bottle cells and a groove are formed in the dorsal part. The outer ends of the bottle cells have many microvilli, an electron-dense layer and many small vesicles. Microtubules are present parallel to the long axis of the bottle cells, and a yolk-platelet-free region is observed at the inner end. Thereafter, the archenteric roof makes contact with the inner surface of the blastocoelic wall. Cells of the archenteric roof form lobopodia, filopodia and lamellipodia. These cells make many focal contact, having gaps of less tha 20 nm, with the blastocoelic wall. Invaginating mesodermal cells of the lateral and ventral parts also form pseudopodia, and are in contact with the blastocoelic wall. Some of these cells appear to flatten against the wall. These observations suggest that, after the bottle cells and the blastoporal groove are formed, the invaginating cells actively migrate along the inner surface of the blastocoelic wall, and that these locomotive forces have an important role in the morphogenetic movements during gastrulation. (+info)
A molecular phylogeny of ichthyophiid caecilians (Amphibia: Gymnophiona: Ichthyophiidae): out of India or out of South East Asia?
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Recent molecular phylogenetic studies indicate that the rafting Indian plate harboured several isolated vertebrate lineages between ca. 130 and 56 Myr ago that dispersed and diversified 'out of India' following accretion with Eurasia. A single family of the amphibian order Gymnophiona, the Ichthyophiidae, presently occurs on the Indian plate and across much of South East Asia. Ichthyophiid phylogeny is investigated in order to test competing out of India and out of South East Asia hypotheses for their distribution. Partial sequences of mitochondrial 12S and 16S rRNA and cytochrome b genes for 20 ichthyophiids and proximate outgroups were assembled. Parsimony, maximum-likelihood and distance analyses all recover optimum trees in which uraeotyphlids plus Ichthyophis cf. malabarensis are the sister taxa to all other Ichthyophis, among which the South East Asian taxa are monophyletic. Tree topology and branch lengths indicate that the Indian lineages are more basal and older, and thus are more consistent with the hypothesis that ichthyophiids dispersed from the Indian subcontinent into South East Asia. The estimated relationships also support monophyly of Sri Lankan Ichthyophis, and non-monophyly of striped and unstriped Ichthyophis species groups. Mitochondrial DNA sequences provide evidence that should assist current problematic areas of caecilian taxonomy. (+info)