Evolutionary links between reproductive morphology, ecology and mating behavior in opisthobranch gastropods

Sexual coevolution in morphological and behavioral traits has rarely been studied. Using phylogenetic analyses, we explore relationships between sexual characters based on a new molecular phylogeny of 33 opisthobranch taxa (Aglajidae and Gastropteridae). Our measurements of these simultaneous hermaphrodites include male and female reproductive anatomy, mating behavior, and spatial gregariousness. After phylogenetic correction, we found evidence for correlated evolution between male and female reproductive organs such as the size of the seminal fluid producing prostate gland and that of the sperm digesting bursa copulatrix. Our findings suggest that reproductive trait variation is mediated by sexual coevolution, where putatively manipulative male organs evolved in association with female organs involved in sperm selection. Furthermore, low gregariousness was associated with long, reciprocal copulations. We interpret this result as an adaptation to infrequent mate encounters, where it pays to mate longer with and presumably transfer more sperm to a rare partner. Several complex reproductive traits were repeatedly gained or lost across our phylogeny. This pattern is consistent with a scenario in which sexual selection generates dynamic coevolutionary cycles similar to those expected under sexual antagonism. We finally outline approaches for experimentally assessing the proposed functional links that underlie the evolutionary correlations revealed by our study.     

Developmental profiles of gangliosides in mouse and rat cerebral cortex

Summary Developmental profiles of 11 gangliosides, concentration of lipid- and glycoprotein-bound sialic acid, and activity of AChE of the rat and mouse cerebral cortex were followed from the 7^th day of gestation to the 21^st postnatal day.There are three main changes in ganglioside concentration, which are similar in both species. The first occurs from gestation day 10 until birth: parallel to decreased proliferation, cell migration, and neuroblast differentiation, G_M3 and G_D3 in mouse cortex and G_D3 in the rat's decreases in favor of G_Q1b, G_T1b, and G_D1a.The second occurs from birth until the first postnatal week: Parallel to increased growth and arborization of dendrites and axons as well as synaptogenesis in rats and mice, there is a two-fold rise of G_D1a, whereas G_Q1b and G_T1b remain on a nearly constant level. Concomitantly, G_M3 and G_D3 decreases. The third period of ganglioside changes starts in the second postnatal week, parallel to onset of myelination, and is characterized by an increase of G_M1 in parallel with a decrease of the polysialogangliosides G_T1b and G_Q1b.     

Effects of development and altered gravity conditions on cytochrome oxidase activity in a vestibular nucleus of the larval teleost brain: A quantitative electronmicroscopical study

The mitochondrial enzyme, cytochrome oxidase, was localized cytochemically in the nucleus magnocellularis, a primary relay nucleus of vestibular information within the area octavolateralis in the fish brain. Larvae of the cichlid fish Oreochromis mossambicus were analyzed at different developmental stages (4, 10, and 35 days posthatching) and after long-term exposure (8 days) to increased gravity (2–4 g). Quantification of highly reactive, moderately reactive, and nonreactive mitochondria reveals differences in the cytochrome oxidase activity of various cellular structures, for example, perikarya of neurons, presynaptic terminals, and myelinated and nonmyelinated cell profiles. Cytochrome oxidase activity in the mitochondria of neuronal perikarya increases during development which parallels the differentiation of the area octavolateralis. This possibly reflects the increasing energy demand during maturation and innervation of the magnocellular nucleus. Hyper-g-exposure of the larvae for 8 days (centrifuge) caused a further augmentation of cytochrome oxidase activity in the perikarya within the nucleus magnocellularis. This may reflect an increased oxidative metabolism resulting from the need for compensation of altered inputs from gravity-sensitive epithelia in the inner ear. Another possibility is that acceleration within a centrifuge causes physiological stress for the animals and, therefore, influences the cytochrome oxidase activity in neurons. © 1993 John Wiley & Sons, Inc.     

Modulatory effects of different temperatures and Ca2+ concentrations on gangliosides and phospholipids in monolayers at air/water interfaces and their possible functional role

Gangliosides are neuraminic acid-containing glycolipids preferently localized in nervous membranes and showing physicochemical peculiarities, e.g., drastically changing amphiphilic properties by Ca2+ binding. On account of this they are favorite compounds to act as modulators of membraneous organization and functions during synaptic transmission. Lipid monolayers are suitable experimental systems for the study of the surface behavior of amphipatic molecules and therefore are useful to interpret membraneous organization. The surface pressure/area isotherms of monolayers of different individual gangliosides (GM1, GD1a, GD1b, GT1b) of an artificial reconstituted and a natural ganglioside mixture from bovine brain and of ganglioside mixtures from different brain parts of summer- and winter-adapted dsungarian hamsters were compared at three temperatures (11, 20, and 37 degrees C) with egg phosphatidylcholine (PC) and phosphatidylserine (PS) monolayers. The monolayers were formed in a Teflon trough on a triethanolamine/HCl-buffered (pH 7.4) subphase, in some cases containing different amounts of CaCl2. The surface pressure/area isotherms of ganglioside monolayers, in contrast to phospholipids, generally showed slowly rising slopes, with transitions from the liquid-expanded to the liquid-condensed state at a surface pressure of 20-30 mN/m. Ganglioside monolayers, in particular from GD1a or GT1b versus GD1b or from mixtures from summer- versus winter-adapted hamster brain, were differently affected by temperature and/or by Ca2+. PS monolayers were slightly condensed only by Ca2+. PC monolayers, however, were influenced neither by temperature nor by Ca2+. In mixed monolayers of the unpolar natural lipid cholesterol (Ch) and the disialoganglioside GD1a, intermolecular interactions were indicated. Ganglioside monolayers, in contrast to phospholipids, were shown to be easily modulated by temperature and/or Ca2+ ions, thus enabling gangliosides to act as possible membrane modulators, e.g., during synaptic transmission. In particular, the differences concerning the influences of temperature and/or Ca2+ on the surface behavior of ganglioside mixtures from the brain of summer- compared with winter-adapted hamsters are correlated with other physiologically relevant data.     

Nervous system ganglioside composition of normothermic and hibernating dormice (Glis glis)

The ganglioside pattern of seven different regions, olfactory bulb, forebrain cortex, midbrain (corpora quadrigemina), cerebellum, brain stem, pons and spinal cord, of nervous system of normothermic and hibernating dormice (Glis glis) were investigated by two dimensional thin layer chromatography and densitometric quantification. Up to thirty different ganglioside spots were resolved, fifteen of which belonging to alkali labile species. Alkali labile gangliosides were present in all the regions obtained from normothermic animals, and their content, expressed as percentage of total ganglioside-bound sialic acid, ranged from a minimum of 10.2% in olfactory bulb, to a maximum of 30.1% in spinal cord. The most abundant alkali labile gangliosides were O-Ac-GT1b, O-Ac-GQ1b and an unidentified one, we coded I3. Alkali labile gangliosides were practically undetectable in hibernating dormice. They could be recognized only in brain stem, 3.3% and olfactory bulb, 0.6%.     

The possible functional role of neuronal gangliosides in temperature adaptation of vertebrates

Comparative studies on brain gangliosides of more than 60 vertebrate species show correlations between concentration and the level of evolutionary organization: poikilothermic lower vertebrates (fish, amphibs, reptiles) contain about 110 to 700 μg ganglioside bound NeuAc/g. fresh wt., homeothermic birds and mammals, on the other side, 500 to 1000 μg. The composition of brain gangliosides in poikilotherms is much more complex and variable (more multisialogangliosides) as compared with homeotherms (domination of less polar fractions). There are distinct correlations between brain ganglioside composition and state of thermal adaptation: Fishes being adapted to habitates with extreme temperatures (antarctic icefish — tropic fish) are characterized by quite opposite ganglioside patterns (domination of high versus less polar fractions). During seasonal acclimatization and experimental acclimation of fish to cold or during hibernation and early postnatal development of mammals poly-sialylations of brain gangliosides occur. With regard to this the individual brain structures react differently.

The results are taken for evidence that variations in the composion of synaptic membrane-bound gangliosides may induce long-term alterations in viscosity and permeability of the neuronal membrane by which the neuronal transmission might be kept on a constant level during the process of temperature adaptation.     

Gangliosides and regeneration of the goldfish optic nerve in vivo and in vitro.

One to forty days after optic nerve transection, goldfish received an i.p. injection of [3H]proline (proteins), 3HNAcGluc (gangliosides) or [3H]thymidine (DNA). After 1 or 2 days of incorporation, both optic systems were analyzed by biochemical and autoradiographical procedures. In the regenerating retina an enhanced retinal mitotic activity, protein synthesis (up to 2-fold) and ganglioside synthesis (up to 1.5-fold) was found. Simultaneously, a transiently enhanced accumulation (up to 4.5-fold) of axonally transported protein- and ganglioside-bound radioactivity in the regenerating optic nerve stump occurred. These regeneration-related proliferative and metabolic changes were found to be maximal at 6-8 days post lesion, but still measurable after 40 days. Concerning the endogenous ganglioside metabolism, in the regenerating retina no obvious change in ganglioside synthesis and composition could be observed, while in the regenerating optic nerve there was an enhanced accumulation of the ganglioside GP1c. Daily i.p. application of a ganglioside mixture from bovine brain (GMix) or of the monosialoganglioside GM1, did not alter significantly the degree and time course of the above regeneration induced metabolic changes or the regain of visual acuity. Sprouting activity of goldfish retinal explants was found to strongly depend upon a conditioning lesion of the optic nerve, reaching a maximum 8 days after nerve transection. This result strictly coincided with the profile of metabolic changes observed in vivo. Again, daily i.p. or i.o. injection of exogenous gangliosides did not influence the lesion induced increase of retinal sprouting activity. However, in normal, not regenerating animals, a local i.o. injection of GMix or GM1 led to a significant enhancement of the "basal" sprouting activity, normally occurring after lesion of the retina after injection of 0.9% NaCl. This ganglioside related stimulation was maximal at low concentrations (3 micrograms/eye) and did not occur at high concentrations (> 30 micrograms/eye). Injection of the phospholipid phosphatidylcholine or phosphatidylserine had no or a slightly inhibitory effect, when compared to NaCl controls. These data suggest an involvement of gangliosides in the complex process of induction of axonal sprouting.