Julian Lombardi

1 The Maternal-Embryonic Relationship in Viviparous Fishes

Publisher Summary This chapter discusses the maternal–embryonic relationship in viviparous fishes. Viviparity is a highly successful mode of reproduction that has evolved independently many times and with many variations in widely separated taxonomic groups. It occurs in all classes of vertebrates, except birds, and among many different groups of invertebrates. Initial steps in the evolution of viviparity involved a shift from external to internal fertilization and the retention of fertilized eggs in the female reproductive system. The osmoregulation of early embryos can be accomplished more efficiently and with less expenditure of embryonic energy in a maternally controlled uterine environment, but as development progresses to term, the embryos presumably acquire an increasing degree of osmoregulatory independence. Available evidence suggests that maternal regulation of the osmotic and chemical environment of the embryo also confers a selective advantage on viviparous teleosts. The uterine wall of most viviparous elasmobranchs and the coelocanth both delimits and defines the embryonic environment. The most spectacular maternal specializations for uterine gestation involve the uterine wall and involve (1) the amplification of the surface area in the form of folds, villi, or trophonemata; (2) the production of histotrophe or uterine milk’ (3) the compartmentalization of embryos; and (4) the development of placental attachment sites.

Ultrastructure of coelomic lining in echinoderm podia: significance for concepts in the evolution of muscle and peritoneal cells

SummaryUltrastructural data are presented on the histological organization of coelomic lining in the podia of ten species of the five major groups of extant echinoderms. Further evidence of the incorporation of podial retractor muscle cells (myocytes) into a monociliated myoepithelial coelomic lining is provided. In the podia of the crinoid Nemaster rubinginosa and the ophiuroid Ophiophragmus wurdemani as well as in the feeding tentacles of the holothurian Leptosynapta tenuis, coelomic linings are organized as simple myoepithelia consisting of non-contractile peritoneal cells (peritoneocytes) and myocytes. Coelomic linings in the holothurian Thyonella gemmata, the echinoids Eucidaris cf. tribuloides and Lytechinus variegatus, and the asteroids Asterias forbesi and Astropecten sp. are pseudostratified or bipartite pseudostratified myoepithelia consisting of subapical myocytes and apically situated peritoneocytes. The ophiuroid podia of Ophioderma brevispinum and Ophiothrix angulata exhibit transitions from simple myoepithelia to partially pseudostratified epithelia. Intermediate forms between the extremes in myoepithelial organization also occur in the podial lining of single species (e.g. Eucidaris cf. tribuloides). These data supplement recent ultrastructural studies on the podial lining of echinoderms and, in conjunction with published ultrastructural data on the myoepithelial organization of other coelomic linings in echinoderms and in other coelomates, suggest myoepithelial organization of the coelomic lining is a plesiomorph feature in Bilateria.

Embryonic growth and trophotaenial development in goodeid fishes (Teleostei: Atheriniformes)

Embryonic growth and trophotaenial development are examined in two species of goodeid fish, Ameca splendens and Goodea atripinnis. During gestation of A. splendens, embryonic dry mass may increase from 0.21 mg at the onset of development to 31.70 mg at term. In G. atripinnis, embryonic dry mass ranges from 0.25 mg at the onset of development to 3.15 mg at term. Increase in mass is primarily due to the uptake of maternally derived nutrients by trophotaeniae, externalized embryonic gut derivatives. Trophotaenial development in both species is divisible into five phases. During the first phase, the anus is formed. The second phase involves dilation of the anus, enlargement of the perianal lips, differentiation of the hindgut absorptive epithelium, and formation of the trophotaenial peduncle. The third phase is characterized by a further marked hypertrophy and lateral expansion of the perianal lips that results in the formation of short trophotaenial processes. During the fourth phase, there is continued outward expansion of the inner mucosal surface of the trophotaenial peduncle that results in its eversion and lobulation. Placental function is established by this phase. Axial elongation and dichotomous branching of trophotaenial processes occurs during the fifth phase. Development of rosette and ribbon trophotaeniae differ in the degree of axial elongation during the fifth and final phase.

Chemical composition of uterine fluid in four species of viviparous sharks (Squalus acanthias, carcharhinus plumbeus, mustelus canis and rhizoprionodon terraenovae)

Abstract 1. 1. Uterine fluid and blood plasma samples from pregnant specimens of the viviparous sharks Squalus acanthias, Carcharhinus plumbeus, Mustelus canis and Rhizoprionodon lerraenovae were analysed for total protein, total lipid, total glucose and osmolarity. 2. 2. Intracapsular uterine fluids of the matrotroph, Rhizoprionodon terraenovae , whose embryos bear appendiculae, exhibit higher concentrations of protein, lipid and glucose than those of placenta! matrotrophs lacking appendiculae. 3. 3. In near-term specimens R. terraenovae , intracapsular protein and lipid levels in excess of those within the maternal blood plasma suggest active concentration of these molecules within intracapsular fluids. 4. 4. There exists a significant osmotic differential between maternal blood plasma and intracapsular uterine fluid in both R. terraenovae and M. canis . 5. 5. These results are discussed in relation to the evolution of maternal-embryonic transfer mechanisms in viviparous sharks.

Gametes and their Production

Gametogenesis is the sequence of events that occur as germ cells, or gonocytes, of the sex cell line form gametes. This complex process occurs within the gonadal tissues. The general process of gametogenesis is divisible into two main phases; a gonial phase and a gametogenic phase. These phases can be distinguished by the mode of cell division that gamete precursors undergo. During the gonial phase, cells of the germ cell line within the gonad undergo successive mitotic divisions and establish a population of gonial cells. In males, this phase is referred to as the spermatogonial phase during which spermatogonial cells are produced. In females of most vertebrates, the gonial phase occurs very early in the life cycle and establishes a population of oogonia within the ovary. During the subsequent gametogenic phase of both males and females, descendents of these gonial cells undergo meiotic divisions and are transformed into mature gametes.

The use of 13C-magnetic resonance spectroscopy in metabolic research

Abstract Magnetic resonance spectroscopy (MRS) is a powerful investigative tool that has rapidly become accepted as a valuable means of assessing metabolic phenomena. 13C MRS provides a rapid and nondestructive means of studying metabolism in intact tissues, organs, and whole organisms. A major feature of the technique is the ability to follow metabolism noninvasively and nondestructively. Benefits of a wide spectral window for 13C (>200 ppm), makes 13C MRS ideal for obtaining semiquantitative information about enriched substrates and their intermediates within living tissues in real time. The increased commercial availability of a wide range of 13C-enriched biomolecules combined with the development of more sensitive instrumentation has made it possible to begin exploiting the full potential of 13C magnetic resonance spectroscopy in metabolic research. This review is intended to introduce readers to the application of 13C magnetic resonance spectroscopy to selected problems in metabolic research.

Free amino acids in the uterine fluids of four species of viviparous sharks (Squalus acanthias, Carcharhinus plumbeus, Mustelus Canis and Rhizoprionodon terraenovae)

Abstract 1. 1. Uterine fluid and blood plasma samples from pregnant specimens of the viviparous sharks Squalus acanthias, Carcharhinus plumbeus, Mustelus canis and Rhizoprionodon terraenovae were subjected to analysis of free amino acids by high-pressure liquid chromatography. 2. 2. Intracapsular uterine fluid of the matrotroph, Rhizoprionodon terraenovae , whose embryos bear appendiculae, is rich in taurine, glutamate, valine, nor-leucine and phenylalanine and exhibits higher concentrations of all amino acids than the uterine fluids of placental matrotrophs lacking appendiculae. 3. 3. Results are discussed in relation to the evolution of maternal-embryonic transfer mechanisms in viviparous sharks.

NMR studies of glucose and alanine utilization and maternal-embryonic nutrient transfer in the smooth dogfish, Mustelus canis

Abstract Captive dogfish, Mustelus canis , were injected with saline containing 13 C-enriched alanine or glucose and permitted to metabolize labeled substrates. Blood plasma and other body fluids were analyzed using high field 13 C nuclear magnetic resonance (NMR) spectroscopy. Both injected glucose and alanine are converted to lactate with alanine conversion more rapid than that of glucose. 13 C-enriched alanine and lactate appear in intracapsular fluids after injection of 13 C-enriched alanine into the maternal blood vascular system. Studies involving the injection of 13 C-enriched nutrients into the maternal circulation can yield information on metabolite utilization and embryonic nutrition in viviparous matrotrophs.

Introduction to Vertebrate Reproductive Biology

This chapter reviews some of the basic concepts involved in the comparative study of vertebrate reproduction.

Sex and Sexual Differentiation

The sexual phenotype, or gender, of vertebrates is determined through either one of two main mechanisms. In most forms, it is determined by genetic factors such as the presence of certain genes that reside on particular combinations of specialized chromosomes. In others, maleness or femaleness is not as clearly rooted in genotype and is acquired independently of chromosomal composition. The sexual phenotype of such forms is under epigenetic control and is the result of environmental influences that act on the genes and regulatory mechanisms involved in sexual differentiation. Many species have evolved ways of taking advantage of this epigenetic nature of sexual differentiation. In a few species, individuals are even capable of switching from one gender to another according to the environmental conditions that they encounter.