The ontogenetic complexity of developmental constraints

Developmental constraint is a theoretically important construct bridging ontogenetic and evolutionary studies. We propose a new operationalization of this notion that exploits the unusually rich measurement structure of landmark data. We represent landmark configurations by their partial warps, a basis for morphospace that represents a set of localized features of form. A finding of developmental constraint arises from the interplay between age-varying means and age-specific variances in these subspaces of morphospace. Examination of variances and means in 16 ventral skull landmarks in the cotton rat S. fulviventer at ages 1, 10, 20, and 30 days yielded three types of developmental constraint: canalization (constraint to relatively constant form age by age); chreods (reduction of variance orthogonal to the mean trajectory over ages); and opposition (reduction of age-specific variance along the mean trajectory over ages). While canalization and chreodic constraints have been noted previously, the oppositional type of constraint appears novel. Only one of our characters, relative length and orientation of the incisive foramen, appears to be canalized. Although skull growth becomes increasingly integrated through ontogeny, our characters display a remarkable spatiotemporal complexity in patterns of variance reduction. The specific assortment of constraints observed may be related to the precociality of Sigmodon. We suggest that Waddington's diagrammatic presentation of the “epigenetic landscape” may be misleading in quantitative studies of developmental regulation.     

The ontogenetic development of the follicular dendritic cell

Summary After intravenous injection of horseradish peroxidase (HRP)-anti-HRP complexes in 21-day-old rats, complex trapping occurs on reticulum cells, forming the stroma of primary follicles of spleens. After intravenous injection of the same complexes in young adult rats (48 days old), trapping occurs on characteristic follicular dendritic cells (FDCs) located in well-developed germinal centers. These results strongly suggest that the follicular dendritic cell originates from a reticulum cell.Abbreviations FDC follicular dendritic cell - FRC fibroblastic reticulum cells - HRP horseradish peroxidase - RC reticulum cell     

Intersexual ontogenetic conflict

Evolutionary conflict has been investigated at many levels of organization, from interactions between loci within a genome to the coevolution of species. Here we review evidence for intersexual ontogenetic conflict, a type of conflict that has received relatively little attention both theoretically and empirically. It is manifest during development when expression of the same allele, on average, moves one sex towards, and the other sex away from, its phenotypic optimum. We first introduce this type of conflict with an illustrative example and assess conditions for maintaining polymorphism for alleles underlying the conflict. We then summarize evidence from our own experiments with Drosophila melanogaster that show substantial genome‐wide sexually antagonistic fitness variation. Finally we discuss evidence from other organisms and some of the ramifications of widespread polymorphism for sexually antagonistic fitness variation.     

The evolution of ontogenetic allometric trajectories in mammalian domestication

Morphological divergence of domesticated as compared to wild forms must result from changes in the ontogenetic process. Species‐specific tests for heterochrony have rejected a single explanation of domestic forms representing juveniles of their wild relatives. Ontogenetic allometric trajectories for 12 pairs of wild and domestic mammals were examined using skull growth data for 1070 specimens, including representatives from all lineages in which domestication has occurred. A suite of tests were performed to quantify allometric disparity in wild and domestic forms and assess the extent and patterning of modification to allometric trajectories. Domestication has modified postnatal ontogenetic allometric trajectories in mammals, and has generated disparity, achieved through lengthening of trajectory slopes and alteration to slope angles. Allometric disparity was similar for domestic forms compared to their wild relatives, whereas the magnitude of dispersion along allometric vectors differed between precocial mammals and altricial mammals, underscoring the importance of life history and shared evolutionary history in patterns of ontogenetic variation. The results verify the importance of scaling in the morphological changes associated with domestication. The response to domestication for all measured trajectory parameters was variable across species, suggesting multiple pathways of change.     

The telotrophic-meroistic ovary of megaloptera. I. The ontogenetic development

Sialis flavilatera L. (Sialidae, Megaloptera) has telotrophic-meroistic ovarioles. The germ cells of the tropharium are organized into two distinct tissues, the central syncytium and the germ cell tapetum. The central syncytium consists of nurse cell nuclei embedded in a common cytoplasm which is rich in ribosomes and mitochondria. Cell membranes are totally absent. The germ cell tapetum surrounds the syncytium and consists of a monolayer of cells, each of which is connected with the central syncytium by an intercellular bridge. The oocytes differentiate from basal tapetum cells by previtellogenic growth. Their nutritive cords remain connected to the central syncytium by the intercellular bridge. Ovariole development starts soon after hatching with the immigration of germ cells into the ovariole-anlagen and is finished during pupal stages 23 months later. In apical regions of each tropharium, mitoses occur throughout larval life. The descendants enter the prophase of meiosis which lasts until pre-vitellogenesis; thus, a differential gradient of position and time is established. About 12 months after hatching, the central syncytium arises at the base of the tropharium from a membrane labyrinth in which intercellular bridges are entangled. Evidence is presented that endopolyploidization does not occur during germ cell differentiation. Finally, the results are compared with those found in Hemiptera and polyphage Coleoptera. The great diversities are interpreted as an indication for a polyphyletic origin of the telotrophic ovary.     

Parametric models of ontogenetic diversities

Modeling of morphogenesis demonstrates that they form rather wide regions of structural stability and narrow zones of instability in parametric space. Within instability zones, small parameter shifts lead to drastic changes in the morphology of buds. These particular zones are the sources of ontogenetic diversities and represent the reserve for evolutionary variation. A topical problem is to construct models based on universal schemes of negative feedbacks between dynamic components of ontogenesis; moreover, the specificity of ontogenesis should be determined by the values of genetic and epigenetic parameters.     

Classification of types of ontogenetic reproduction

The object of this paper is to present an original classification of ontogenetic reproduction. The main general criterion used is the degree and type of phylogenetic differentiation. In relation to this criterion, criteria are given for the classification of the fundamental types of ontogenetic reproduction and for the classification of the types of ontogenetic generation cycles. Between the fundamental types of ontogenetic reproduction and the types of ontogenetic generation cycles there is a hierarchical relationship which shows that the former are components of the latter. Between the well-defined types of ontogenetic reproduction there exist many intermediate types.     

The adaptive significance of ontogenetic colour change in a tropical python

Ontogenetic colour change is typically associated with changes in size, vulnerability or habitat, but assessment of its functional significance requires quantification of the colour signals from the receivers' perspective. The tropical python, Morelia viridis, is an ideal species to establish the functional significance of ontogenetic colour change. Neonates hatch either yellow or red and both the morphs change to green with age. Here, we show that colour change from red or yellow to green provides camouflage from visually oriented avian predators in the different habitats used by juveniles and adults. This reflects changes in foraging behaviour and vulnerability as individuals mature and provides a rare demonstration of the adaptive value of ontogenetic colour change.     

Quantification of ontogenetic allometry in ammonoids

Ammonoids are well‐known objects used for studies on ontogeny and phylogeny, but a quantification of ontogenetic change has not yet been carried out. Their planispirally coiled conchs allow for a study of “longitudinal” ontogenetic data, that is data of ontogenetic trajectories that can be obtained from a single specimen. Therefore, they provide a good model for ontogenetic studies of geometry in other shelled organisms. Using modifications of three cardinal conch dimensions, computer simulations can model artificial conchs. The trajectories of ontogenetic allometry of these simulations can be analyzed in great detail in a theoretical morphospace. A method for the classification of conch ontogeny and quantification of the degree of allometry is proposed. Using high‐precision cross‐sections, the allometric conch growth of real ammonoids can be documented and compared. The members of the Ammonoidea show a wide variety of allometric growth, ranging from near isometry to monophasic, biphasic, or polyphasic allometry. Selected examples of Palaeozoic and Mesozoic ammonoids are shown with respect to their degree of change during ontogeny of the conch.     

The effect of ontogenetic development on the anticonvulsant activity of midazolam.

The anticonvulsant effects and duration of protective action of midazolam against Metrazol induced seizures were studied in 528 rats aged 7,12,18,25 and 90 days. The doses of 0.025, 0.05, 0.25, 0.5 and 1.0 mg/kg were administered immediately before Metrazol (100 mg/kg in all but 18-day-old animals where 90 mg/kg were given) for detection of antimetrazol activity at all age groups. The doses of 0.05, 0.25, and/or 0.5 mg/kg were used to study the time course of the protective action of midazolam. Each experimental group consisted of eight animals. Dose-dependent antimetrazol effects of midazolam till now described only in adult animals were demonstrated at all developmental stages studied. There were no qualitative differences in these effects among age groups studied. Midazolam action was better expressed against major Metrazol seizures than against minimal Metrazol seizures. Duration of the protective action depended on the dose tested at all developmental stages, as a rule, lasted longer in young animals than in adult rats. Only quantitative changes of action were found.     

The ontogenetic development of egg-spots in the haplochromine cichlid fish Astatotilapia burtoni

A series of Astatotilapia burtoni photographs were used to investigate the ontogenetic development of male egg-spots, a putative evolutionary key innovation of haplochromine cichlids. Four stages of egg-spot development were defined and all males had developed true egg-spots (stage 4) before reaching a standard length of 25 mm. Raising condition only slightly influenced the timing of the first appearance of true egg-spots.     

The relation between morphology and behaviour during ontogenetic and evolutionary changes

During development, form and function (behaviour) change while the match between them must be maintained. The quality of this match determines the importance of morphological parameters in constraining behaviour. If the match is close, the morphology of organisms will be more constraining to the behaviour than when there is a large reserve capacity that creates a certain flexibility. This leads to two questions: (1) How good is the match between form and function during development? The quality of the match necessarily changes during development because changes in structural capacity often cannot proceed at the same speed as changes in functional demand. The evidence for these changes is discussed. (2) What are the mechanisms that maintain the match between form and function during developmental and evolutionary changes? Two mechanisms for maintaining the match are discussed: (a) reserve capacity and (b) flexible muscle activity patterns. Special emphasis is given to fish examples throughout this review.     

The ontogenetic model of gravitation and weightlessness: theoretical and applied aspects

In the review we discuss the earlier postulated [1] natural motor strategies which are dependent on gravitation and temperature and which evolve during the human life span. The first of them, FM-strategy is the characteristic of the intrauterine immersion in the amniotic fluid and ofmicrogravitation in the spaceflight (G - 0). It is based on domination of fast muscle fibers and phasic movements and forms the fetal strategy to survive in heating, strongly hypoxic, albeit normal for fetus, immersion. In the adults, adaptive response separately to microgravitation, heat stress and hypoxia also shifts muscle fiber properties to faster values. In accordance with that paradigm the process of parturition can be considered as equivalent to cosmonaut's/astronaut's transition from microgravitation back to Earth gravitation (G = 1) during landing. This new GE-strategy) is opposite to the FM-strategy, because it decreases the motor unit firing and "slows" the activity of muscle fibers. The next, SJ-strategy is the characteristic of normal ageing that causes further dominance of slow motor units, thus simulating hypergravitation (>1G). Cooling evokes similar adaptive reactions. The synergy of sensory inputs which act across the motor system within the above said motor strategies suggests their mutual substitution. Thus, even moderate cooling may serve as partial "surrogate" for gravitation (approximately 0.2G), that could be utilized as a prophylactic countermeasure for unfavorable effects of the long term space flight.     

A new ontogenetic classification of stomatal types

A new ontogenetic classification of stomatal types is proposed which replaces the three ontogenetic types of Pant (1965) with seven new ones. The new classification clearly differentiates between the developmental involvement of the subsidiary cells and the purely structural relationship of the neighbouring cells. All known, and hypothetical, ontogenetic pathways of stomatal development can he incorporated into the new classification.
An, hitherto unknown, ontogenetic type which incorporates neighbouring, mesogene subsidiary, and perigene subsidiary cell elements into the stomatal complex is described from the fern, Polypodium vulgare L.