THE EVOLUTION OF ALTERNATE MORPHOLOGIES: FITNESS AND WING MORPHOLOGY IN MALE SAND CRICKETS

Many organisms show distinct morphological types. We argue that the evolution of these alternate morphologies depends upon both fitness differences between morphs within each sex and the genetic correlation between sexes. In this paper, we examine the evolution of alternate morphologies using wing dimorphism in insects as a model system. Many insect species are wing dimorphic, one morph having wings and being capable of flight, the other lacking functional wings. While there is a well established trade-off in females between macroptery and reproduction, there are few data on the possible costs in males. We examine trade-offs between macroptery and life-history traits in male sand crickets, Gryllus firmus, and estimate the genetic correlation of wing dimorphism between the sexes. Macropterous males develop faster than micropterous males and are either larger or the same size depending upon rearing conditions. There is no difference in absolute or relative testis size at eclosion or 7 d thereafter. Finally, there is no difference between macropterous and micropterous males in relative success at siring offspring. Thus, with respect to the above traits, there are no costs associated with being winged in male G. firmus. It is possible that there may be a trade-off between calling rate and macroptery. A comparison of the relative frequency of macroptery between males and female across different orders of insects supports this hypothesis. The genetic correlation of wing dimorphism between the sexes is high (r₈ = 0.86), and hence the frequency of macroptery in males may be strongly influenced by selection acting on females.     

A fractal model for the characterization of mycelial morphology

A new technique based on a fractal model has been developed for the quantification of the macroscopic morophology of mycelia. The morphological structuring is treated as a fractal object, and the fractal dimension, determined by an ultrasonic scattering procedure developed for the purpose, serves as a quantitative morphological index. Experimental observations reported earlier and simulations of mycelial growth, carried out using a probabilistic-geometric growth model developed for the purpose, both validate the applicability of the fractal model. In experiments with three different species, the fractal dimensions of pelletous structures were found to be in the range 1.45-2.0 and those of filamentous structures were in the range 1.9-2.7, with values around 2.0 representing mixed morphologies. Fractal dimensions calculated from simulated mycelia are in rough agreement with these ranges. The fractal dimension is also found to be relatively insensitive to the biomass concentration, as seen by dilution of the original broths. The relation between morphology and filtration properties of the broths has also been studied. The fractal dimension shows a strong correlation with the index of cake compressibility and with the Kozeny constant, two filtration parameters that are known to be morphology dependent. This technique could thus be used to develop correlations between the morphology, represented by the fractal dimension, and important morphology-dependent process variables. (c) 1993 John Wiley & Sons, Inc.     

Shaping intraspecific variation: Development,ecology and the evolution of morphology and life history variation in tiger salamanders

The tiger salamander,Ambystoma tigrinum, is a geographically widespread, morphologically variable, polytipic species. It is among the most variable species of salamanders in morphology and life history with two larval morphs (typical and cannibal) and three adult morphs (metamorphosed, typical branchiate, cannibal branchiate) that vary in frequency between subspecies and between populations within subspecies. We report morphometric evidence suggesting that branchiate cannibals arose through intraspecific change in the onset or timing of development resulting in the wider head and hypertrophied tooth-bearing skull bones characteristic of this phenotype. We also quantified bilateral symmetry of gill raker counts and abnormalities, then evaluated fluctuating asymmetry as a measure of the developmental stability of each morph. There was a significant interaction between fluctuating asymmetry of developmental abnormalities in cannibals and typicals and the locality where they were collected, suggesting that relative stability of each phenotype could vary among populations. While altered timing of developmental events appears to have a role in the evolution and maintenance of morphs, novel phenotypes persist only under favorable ecological conditions. Predictability of the aquatic habitat, genetic variation, kinship, body size, intraspecific competition and predation all affect expression and survival of the morphs inA. tigrinum. This taxon provides an excellent model for understanding the diversity and complexity of developmental and ecological variables controlling the evolution and maintenance of novel phenotypes.     

Principal directions of the evolution of Monimotrochida

Phylogenetic relations among the main groups of Monimotrochida are considered. The principal directions of monimotrochid evolution were defined by comparative investigations of mastax morphology (SEM), basic body structures, and general biology. On the basis of these results we propose a revision of previous rotifer taxonomy. We suggest to place the Monimotrochida in the order Protoramida divided into two suborders Flosculariina and Conochilina.     

Quaternary and recent Lamprothamnium groves (Charophyta) from Argentina

Only recently have extant Lamprothamnium species been reported from the American continent. L. succinctum (A. Br. in Asch.) R. D. W. was found in Lago Titicaca, Bolivia and L. haesseliae Dont. en Laguna Luro and Laguna La Salada, Argentina.Fossil gyrogonites of L. succinctum and L. haesseliae, however, are here reported to be widely distributed in Quaternary sediments of Argentina, associated with other charophytes, ostracods and foraminiferans. Localities include Laguna del Siasgo, Laguna Salada Grande, Laguna Mar Chiquita, Laguna La Amarga and Salina del Bebedero. Lamprothamnium is a genus that prefers shallow, alkaline, hyposaline to mesosaline environments. Analysis of the characteristics of Laguna La Salada contributes information on the factors that influence the distribution of the genus.The morphology characteristics of the gyrogonites and oospores of L. haesseliae and the gyrogonites of L. succinctum are described. The use of Lamprothamnium as a biomarker and its application in the reconstruction of Quaternary saline environments are also discussed.     

Seasonal succession of phytoplankton in a lake of the Paraná river floodplain,Argentina

Phytoplankton biomass, morphological and taxonomic composition, species diversity and productivity were analyzed in a shallow lake of the Middle Paraná River floodplain (El Tigre, 31 ° 41 S and 60° 42 W), between November 1986 and July 1988. Lake inundation (filling and through-flow phases) constituted an intense long-term perturbation in the physical and chemical environment. As the lake filled with river water, K-selected species (netplanktonic filamentous bluegreens, > 37 µm, with low surface area/volume (SA/V) ratios) that had existed prior to filling (late spring 1986) were replaced in summer-fall by r-selected species (nannoplanktonic chlorophytes and cryptophytes, < 37 µm, mainly stout forms with high SA/V ratios). During the through-flow phase, lentic phytoplankton was replaced by lotic flagellate populations due to the direct flushing by river water. During the period of falling water (drainage and isolation phases), nanoplanktonic algae with similar characteristics to those of the filling phase dominated in late winter-spring. Later in the isolation phase, these were succeeded by K-selected species (netplanktonic algae, mainly motile spherical dinoflagellates and filamentous bluegreens with low SA/V ratios). Simultaneously, primary production per unit biomass decreased and total biomass and specific diversity increased. Seasonal changes of phytoplankton in floodplain lakes can be interpreted as the interaction between true successional development (as observed in the drainage and isolation phases) and intermediate disturbance. Using Reynolds' terminology, short-term disturbance (slight inflow of nutrient-rich river water) caused reversion to an earlier stage in the former succession, and long-term disturbance (lake inundation) truncated the successional progression and a new (or shifted) succession was initiated.     

Flow patterns and endothelial cell morphology in a simplified model of an artificial ventricle

The aim of this study was to delineate the flow patterns in a non-unidirectional flow field inside a ventricle-shaped cell culture chamber, and examine the resulting morphology and integrity of the endothelium in select regions of the monolayer. The chamber was perfused by pulsatile flow, and the coherent motion of the fluid was studied using flow visualization aided by image analysis. Four distinct flow patterns were discerned and examined: central jet, flow impingement, flow separation, and recirculating eddies. The influence of these patterns on endothelial cell morphology was assessed after 20 h of exposure to flow. There were no signs of damage to the endothelium in the jet region nor was there evidence of cell alignment with the flow. Yet, there were changes in cell morphology and cytoskeletal architecture as compared to control. By contrast, within the eddies where the flow was highly disturbed, there was apparent damage to the endothelium. Thus, exposure of cells to random velocity fluctuations in regions of quasi-static flow compromises the integrity of the monolayer. Identification of such sites and acquisition of the knowledge necessary to protect the cells from denudation will be valuable for the endothelialization efforts of cardiac prostheses.     

Normania,an endemic Macaronesian genus distinct fromSolanum (Solanaceae)

Morphological data and results from scanning electron microscopy of seeds and pollen show thatNormania Lowe [syn.Solanum L. subg.Potatoe (G. Don)D'Arcy sect.Normania (Lowe)Bitter] (Solanaceae: Solaneae) should be considered as a distinct genus fromSolanum L. It has two species, one restricted to the island of Madeira [Normania triphylla (Lowe)Lowe] and the other to Tenerife and Gran Canaria [Normania nava (Webb & Berthel.)Franc.-Ort. & R. N. Lester]. These species are extremely rare and had not been found for about 100 years, untilN. nava was rediscovered in two different localities in Tenerife in 1973 and 1982.Normania triphylla was reported in two different places from northern Madeira in 1991. Both species have the highest conservation priority in the Macaronesian region.     

Morphological phylogenetics of theAsteraceae-Asteroideae,with notes on character evolution

The relationships within theAsteraceae-Asteroideae are scrutinized by means of cladistic analyses of morphological and chemical data. New data are presented, and novel interpretations of features previously used in cladistic analyses are made. Examples are insertion of anther filaments in the corolla, and morphology of disc floret styles, respectively. The results include a polyphyletic or paraphyleticInuleae s. l., and a paraphyleticHeliantheae s.l. in which theEupatorieae constantly form a subclade. Comparisons are made with previous cladistic analyses of morphological data, and those acquired from molecular data. Speculations about the evolution of certain organs are presented.