Meanings of the Market: The Free Market in Western Culture

Meanings of the Market: The Free Market in Western Culture. James G. Carrier. ed. New York: New York University Press, 1997.276 pp.     

Metamorphosis of the amphibian eye

For many metamorphosing amphibians, the visual system must remain functional as the animal changes from an aquatic to a terrestrial habitat. Thyroid hormone, the trigger for metamorphosis, brings about changes at all levels of the animal, and profoundly alters the visual system, from cellular changes within the eye to new central connections subserving the binocular vision that develops during metamorphosis in some species. I will survey the alterations in the visual system in the metamorphosis of several Amphibian groups, and consider the role of thyroid hormone in bringing about these transformations through action at the molecular level.     

Hormonal Interaction in Amphibian Metamorphosis

SYNOPSIS. The climactic stages of amphibian metamorphosis constitutea period characterized by radical morphological changes thatare driven primarily by the thyroidal hormones. Radioimmunoassaysshow that levels of thyroid hormones (TH) rise to a peak duringmetamorphic climax. Accompanying peaks are reported for ACTH,adrenal corticoids (AC), insulin (I) and prolacdn (PRL). ACenhance the metamorphic action of TH by increasing their bindingto nuclei of target cells. TH, in turn, act to raise levelsof AC by stimulating the differentiation of the median eminencethus facilitating the flow of a CRF from the hypothalamus tothe adenohypophysis, by synergizing with ACTH and bystimulationof the interrenals through some other route. During the metamorphicperiod, at least as far as climax, PRL antagonizes TH, perhapsat the thyroidal level and certainly at the level of targetcells. PRL may antagonize by inhibiting induction of hydrolyticenzymes by TH, by alteration of hydromineral responses or byaltering levels of binding of TH to receptors. The antagonisticaction of PRL is mimicked by cAMP. A surge of PRL that is releasedinto the plasma during metamorphic climax seemingly producesno antagonistic effect on thyroidal actions.     

Metamorphosis in a Silurian barnacle

Exceptionally preserved fossils from the Wenlock Series (Silurian) of Herefordshire, UK, provide unique evidence of metamorphosis from free-swimming cyprid larva to attached juvenile in a Palaeozoic barnacle. The larva had large brush-like anterior limbs. The juvenile shows the head transformed into a stalk and the development of the primordial condition of five mineralized plates within the carapace. The discovery of a cyprid larva indicates that crown group cirripedes had evolved by the Silurian.     

Metamorphosis of a protein

All insects appear to have a transport lipoprotein in the hemolymph (blood) that is responsible for moving hydrophobic materials through aqueous compartments. This has been called lipophorin because it is believed to be a reversible transport shuttle. Since most insects undergo some degree of metamorphosis from larval stages to the adult, the need to transport hydrophobic materials or the nature of these materials may change in the course of the life span. This is especially marked in the case of the holometabolous insects – those which undergo drastic change of form, e.g. caterpillar-pupa-adult moth. We have found that lipophorin undergoes a molecular metamorphosis paralleling that of the insect.     

Larval Development and Metamorphosis in Sipuncula

In a brief review of development of the phylum Sipuncula, fourpatterns of development are recognized: (1) direct with no pelagicstage; (2) one larval stage, a lecithotrophic trochophore; (3)two larval stages, a lecithotrophic trochophore and a lecithotrophicpelagosphera; (4) two larval stages, a lecithotrophic trochophoreand a planktotrophic pelagosphera. Larval types and their metamorphosesare described, with special attention to the development andmorphology of the larval cuticle. In the majority of speciesstudied, the egg envelope is transformed into the larval cuticleat metamorphosis of the trochophore. The cuticle of many planktotrophicpelagosphera larvae is characterized by surface papillae ofdiverse form and pattern. The underlying cuticle in some speciesis composed of layers of fibers at right angles to one another.     

Urban Market Gardening and Rodent-Borne Pathogenic Leptospira in Arid Zones: A Case Study in Niamey,Niger

Leptospirosis essentially affects human following contact with rodent urine-contaminated water. As such, it was mainly found associated with rice culture, recreational activities and flooding. This is also the reason why it has mainly been investigated in temperate as well as warm and humid regions, while arid zones have been only very occasionally monitored for this disease. In particular, data for West African countries are extremely scarce. Here, we took advantage of an extensive survey of urban rodents in Niamey, Niger, in order to look for rodent-borne pathogenic Leptospira species presence and distribution across the city. To do so, we used high throughput bacterial 16S-based metabarcoding, lipL32 gene-targeting RT-PCR, rrs gene sequencing and VNTR typing as well as GIS-based multivariate spatial analysis. Our results show that leptospires seem absent from the core city where usual Leptospira reservoir rodent species (namely R. rattus and M. natalensis) are yet abundant. On the contrary, L. kirschneri was detected in Arvicanthis niloticus and Cricetomys gambianus, two rodent species that are restricted to irrigated cultures within the city. Moreover, the VNTR profiles showed that rodent-borne leptospires in Niamey belong to previously undescribed serovars. Altogether, our study points towards the importance of market gardening in maintain and circulation of leptospirosis within Sahelian cities. In Africa, irrigated urban agriculture constitutes a pivotal source of food supply, especially in the context of the ongoing extensive urbanization of the continent. With this in mind, we speculate that leptospirosis may represent a zoonotic disease of concern also in arid regions that would deserve to be more rigorously surveyed, especially in urban agricultural settings.     

Metamorphosis of the central nervous system of Drosophila

The study of the metamorphosis of the central nervous system of Drosophila focused on the ventral CNS. Many larval neurons are conserved through metamorphosis but they show pronounced remodeling of both central and peripheral processes. In general, transmitter expression appears to be conserved through metamorphosis but there are some examples of possible changes. Large numbers of new, adult-specific neurons are added to this basic complement of persisting larval cells. These cells are produced during larval life by embryonic neuroblasts that had persisted into the larval stage. These new neurons arrest their development soon after their birth but then mature into functional neurons during metamorphosis. Programmed cell death is also important for sculpting the adult CNS. One round of cell death occurs shortly after pupariation and a second one after the emergence of the adult fly.     

Genie Control of Axolotl Metamorphosis

SYNOPSIS. Neoteny in the Mexican axolotl, Ambystoma mexicanum,is caused by homozygosity for a single recessive gene. The dominantallele causing physical metamorphosis is found in the closelyrelated species, Ambystoma tigrinum, with which it can hybridize.Despite the failure of axolotls to undergo physical metamorphosis,they do undergo a cryptic metamorphosis. A larval-to-adult hemoglobinform change, serum protein changes and other physiological eventsusually associated with amphibian metamorphosis occur duringearly larval life at ages comparable to the age at which Ambystomatigrinum undergoes both the cryptic and external metamorphicevents. Axolotl cryptic metamorphosis can be induced precociouslyby immersion of the larvae in low concentrations of thyroxine;physical metamorphosis can be induced with higher thyroxineconcentrations. The site of action of the gene responsible foraxolotl neoteny has not been identified. A change in the sensitivityof external metamorphic processes to thyroxine, or reduced hormonalstimulation by the pituitary or hypothalamus may be responsible.A comparison of these functions in Ambystoma tigrinum and theaxolotl may identify the lesion.     

Metamorphosis from the Phoront to the Trophont in Hyalophysa*

SYNOPSIS. The nature and sequence of changes involved in the metamorphosis of the phoront of Hyalophysa have been examined in the light microscope using both living and silver-impregnated ciliates. The phoront's infraciliature, which resembles that of the migratory tomite, differentiates to the trophont (feeding stage) infraciliature without an intervening dedifferentiation. The primary visible event of metamorphosis is the growth of the metastomial area that distorts the meridional somatic kineties so that they curve or spiral around it. The distinct borders and intense argentophilia of the metastomial area suggest that it is a discrete organelle which is probably involved in the management and concentration of a large volume of dilute food. The anterior ventral field of kinetosomes, whose presence distinguishes Hyalophysa from Gymnodinioides, forms from a disorganized anterior segment of falciform field 9. The rapid and pronounced elongation of the somatic kineties supports our view that the kinetodesmos elongates by the sliding of its component subfibrils upon one another, and that the accessory kinetosomes seen in the electron microscope become functional at metamorphosis. The movement of the kineties and contractile vacuole pore during metamorphosis suggests that differentiation in this instance is not directed by pellicular “fields” but by morphogenetic movements of the underlying cytoplasm.     

Changes in the Gut Microbiome of the Sea Lamprey during Metamorphosis

Vertebrate metamorphosis is often marked by dramatic morphological and physiological changes of the alimentary tract, along with major shifts in diet following development from larva to adult. Little is known about how these developmental changes impact the gut microbiome of the host organism. The metamorphosis of the sea lamprey (Petromyzon marinus) from a sedentary filter-feeding larva to a free-swimming sanguivorous parasite is characterized by major physiological and morphological changes to all organ systems. The transformation of the alimentary canal includes closure of the larval esophagus and the physical isolation of the pharynx from the remainder of the gut, which results in a nonfeeding period that can last up to 8 months. To determine how the gut microbiome is affected by metamorphosis, the microbial communities of feeding and nonfeeding larval and parasitic sea lamprey were surveyed using both culture-dependent and -independent methods. Our results show that the gut of the filter-feeding larva contains a greater diversity of bacteria than that of the blood-feeding parasite, with the parasite gut being dominated by Aeromonas and, to a lesser extent, Citrobacter and Shewanella. Phylogenetic analysis of the culturable Aeromonas from both the larval and parasitic gut revealed that at least five distinct species were represented. Phenotypic characterization of these isolates revealed that over half were capable of sheep red blood cell hemolysis, but all were capable of trout red blood cell hemolysis. This suggests that the enrichment of Aeromonas that accompanies metamorphosis is likely related to the sanguivorous lifestyle of the parasitic sea lamprey.