Phyletic Trends Research Articles

Pseudoteloceras, a new stephanoceratid genus (Ammonitida) of the lower Humphriesianum Zone (lower Bajocian, Middle Jurassic) from western Tethys

The new dimorphic genus Pseudoteloceras (type-species: P. crosillense gen. et sp. nov.) is defined within the subfamily Stephanoceratinae. It constitutes the terminal step of an early Bajocian phyletic trend that produces Teloceras-like morphologies throughout the lower Humphriesianum Zone of the western Mediterranean-Caucasian Subrealm, at an older chronological interval and with morpho-structural features that stand apart from those of the best known genus Teloceras of the uppermost Humphriesianum and lower Niortense zones at the early/late Bajocian transition. Three new species are described: P. croisillense, P. maerteni and P. boursicoti. Their biochronostratigraphical ranges are confirmed by the distribution in expanded sections of the Subalpine Basin in Submediterranean Province (Digne area) and the taphonomic analysis of fossil assemblages from the condensed sections of the “Oolithe ferrugineuse de Bayeux” Formation in Calvados, North West European Province. The biochronostratigraphical range of Pseudoteloceras gen. nov. is limited to the Romani Subzone, lower Humphriesianum Zone. P. crosillense gen. et sp. nov. marks a well-defined biohorizon of the upper Romani Subzone in the Digne stratigraphical successions. The extreme degree of the cadiconic morphology in the inner whorls of P. boursicoti gen. et sp. nov., and the biostratigraphical gap separating the first appearance of the genus Teloceras in the upper Humphriesianum Zone, support its erection as a new taxon Pseudoteloceras gen. nov. A fourth species, Pseudoteloceras geometricum (Maubeuge), is interpreted as the earliest species of this phyletic lineage, derived from Stemmatoceras and widely distributed through western Tethys in the lower Humphriesianum Zone.

Phylogeny and evolution of body mass in didelphid marsupials (Marsupialia: Didelphimorphia: Didelphidae)

Most extant New World marsupials belong in the Didelphidae, which comprises ca. 110 currently recognized species of opossums. Didelphids are small mammals with their mean body mass, at species level, ranging from ca. 7 g to 2.2 kg. The largest species belong in a single clade, while substantial variation remains scattered across the remaining groups. We seek out to explore the details of this mass variation in an evolutionary framework. To this end, we first reconstructed the phylogeny of didelphids based on an extensive, although fragmentary sample of sequences from ten genes. We recovered a fully resolved, highly robust phylogeny that tested and confirmed most previously reported groupings, providing a simultaneous depiction of phylogenetic relationships for 81 % of currently recognized species and all relevant supra-specific clades. As much as 69 % of total body mass variation in didelphids was explained by this phylogenetic hypothesis. Mapped on it, mass variation evolved as much as 6.8 kg of total changes, starting from a reconstructed ancestral body mass range of 22–33 g. No single, family-wide pattern was evident; in fact, the dominant pattern for mass variation was that of increases in body mass along a few successive branches, or phyletic giantism, followed by apomorphic nanism, i.e., decreases localized in single terminal branches. Phyletic trends indicated the persistence of gradual, directional changes along considerable spans of geological time and show that substantial variation of interest resides in this and perhaps most groups of small mammals.

Decompression syndrome in plesiosaurs (Sauropterygia: Reptilia)

ABSTRACT Recognition of avascular necrosis through propodial head subsidence in fossils indicates that plesiosaurs were susceptible to decompression syndrome and implies deep, prolonged or repetitive diving behavior for these animals. Contrary to the situation in mosasaurs, plesiosaur vertebrae were not targets of avascular necrosis. This suggests that the anastomosing internal vascularization of plesiosaur vertebral centra was functionally adaptive. No phyletic trend is evident in the susceptibility of plesiosaurs to the pathology, although stem group sauropterygians were almost never affected (not surprising for near-shore, shallow water animals). Cryptoclididae were the only plesiosaur family not regularly afflicted with decompression syndrome. The difference between this and other groups is most likely to have been behavioral and/or ecological.

Specialization and phyletic trends of sweetness reception in animals

Abstract During the last decades, the comparison in various animal species of their gustatory responses to compounds eliciting a sweet taste in humans has extended our knowledge of the great biodiversity of the taste responses and evidenced some specialization and/or phyletic trends within species. Our interest was focused on responses to natural sugars, polyols, and naturally occurring sweeteners, but also on various artificial sweetening compounds, including the very powerful guanidine sweeteners. New results obtained with kangarooswhich originated about 130 MYAhave shown that their sweetness receptor is not designed to taste any of the artificial sweeteners tested. Therefore, the ability to taste complicated artificial sweeteners must have evolved later in higher developed mammals, about 100 million years ago.

Evolution and ecology of developmental processes and of the resulting morphology: directional asymmetry in hindlimbs of Agamidae and Lacertidae (Reptilia: Lacertilia)

In this paper, the evolution and ecology of directional asymmetry (DA) during the developmental trajectory (DT) is compared with that of its product, morphological DA (MDA). DT and MDA are calculated for two bilateral morphological scale characters of lizards, the number of subdigital lamellae beneath the fourth toe in 10 agamid and 28 lacertid taxa, and the number of rows of ventral scales in 12 lacertid taxa. MDA, the subtraction between left and right sides (classical measure of DA), is functional in adult animals. Results confirm the hypothesis that, in DT, the regression parameters a (constant) and b (regression slope) of counts on the right side with those on the left describe a developmental process. No phylogenetic or environmental effects were observed on a and b, but analyses considering both a andb together show non-random phyletic patterns. Independent analyses deduced the same ancestral DT in Agamidae and Lacertidae. In Lacertidae, distance between pairs of taxa in a+b (standardized values) correlates positively with the phylogenetic distance between taxa. Phyletic trends in MDA are indirect, and due to the link of MDA witha +b. The MDA of species is more dissimilar in sympatry than in allopatry. The phyletic trends suggest evolution of DT, while the association of MDA with sympatry suggests that ecological pressures shape MDA in adult animals. Evolution of DT is independent from that of its product, MDA—adaptive determinism defines the result of, but not the mechanistic process of, development. Deterministic environmental processes define MDA, and deterministic evolutionary processes define the interactive result of a and b, but not each separately. According to circumstances, different DTs produce similar or different MDA, and a particular DT can produce different MDAs.

Evolution and ecology of developmental processes and of the resulting morphology: directional asymmetry in hindlimbs of Agamidae and Lacertidae (Reptilia: Lacertilia)

In this paper, the evolution and ecology of directional asymmetry (DA) during the developmental trajectory (DT) is compared with that of its product, morphological DA (MDA). DT and MDA are calculated for two bilateral morphological scale characters of lizards, the number of subdigital lamellae beneath the fourth toe in 10 agamid and 28 lacertid taxa, and the number of rows of ventral scales in 12 lacertid taxa. MDA, the subtraction between left and right sides (classical measure of DA), is functional in adult animals. Results confirm the hypothesis that, in DT, the regression parameters a (constant) and b (regression slope) of counts on the right side with those on the left describe a developmental process. No phylogenetic or environmental effects were observed on a and b, but analyses considering both a andb together show non-random phyletic patterns. Independent analyses deduced the same ancestral DT in Agamidae and Lacertidae. In Lacertidae, distance between pairs of taxa in a+b (standardized values) correlates positively with the phylogenetic distance between taxa. Phyletic trends in MDA are indirect, and due to the link of MDA witha +b. The MDA of species is more dissimilar in sympatry than in allopatry. The phyletic trends suggest evolution of DT, while the association of MDA with sympatry suggests that ecological pressures shape MDA in adult animals. Evolution of DT is independent from that of its product, MDA—adaptive determinism defines the result of, but not the mechanistic process of, development. Deterministic environmental processes define MDA, and deterministic evolutionary processes define the interactive result of a and b, but not each separately. According to circumstances, different DTs produce similar or different MDA, and a particular DT can produce different MDAs.

Comparative biology of sperm storage in female salamanders

Females in seven of the ten families of salamanders possess cloacal glands called spermathecae that store sperm. The annual cycle of sperm storage has been studied by light and electron microscopy in eight species representing five families. In these taxa, we recognized 14 characters associated with the spermathecae and traced their evolution on a phylogeny of salamanders based upon other characters. The plasticity and phyletic significance of the spermathecal characters varied greatly. Plethodontids have complex spermathecae while other families possess simple spermathecae; thus, this character has phyletic value as well as being highly conserved within the Salamandroidea. Other characters, such as carbohydrate histochemistry, are highly plastic and show no obvious phyletic trends. The significance of some of these variable characters, such as duration of sperm storage, is apparent only after including in the analysis other aspects of the reproductive cycle, such as length of the mating season. Additional comparative studies, employing the protocol used in this paper, will help further clarify the relationships between phyletic and functional variability in sperm storage mechanisms in salamanders.

Speciation patterns and trends in the fossil record

Phyletic trends in the fossil record can be explained by alternative models involving anagenesis andcladogenesis, the latter being favoured by the propounders of punctuated equilibrium theory. To render fossil material suitable for evolutionary analysis of morphospecies it is necessary to make allowance for a full range of populational variation. A number of studies suggest that fossil morphospecies are sufficiently representative of biological species to allow valid generalisation about speciation patterns. Punctuated equilibrium, with long periods of stasis interrupted by relatively brief episodes of change, appears to be the dominant mode, but the evidence for producing trends by species selection or sorting is weak. Instead, most of the trends described can be readily attributable either to a combination of anagenesis and heterochrony, or to phyletic size increase. Examples are given from Jurassic ammonites and bivalves, and an attempt made to relate key changes to an ecological model involving changing adaptive strategies related to environmental fluctuations.

Multiple developmental origin of the upper incisor in mouse: histological and computer assisted 3-D-reconstruction studies.

Heads of 11-15-day-old mouse embryos were cut in frontal serial sections. Early development of the maxillary incisor was analyzed using series of thick (5 and 7 microns) and semi-thin (1 micron) frontal sections and computer assisted 3-D-reconstructions of the epithelial component. The enamel organ of the mouse maxillary incisor was found to be a complex structure of multiple origin, involving several epithelial anlagen--primary dental laminae--, which could hypothetically correspond to the 5 upper incisors of early mammals. The transitory existence of at once distinct and then fusing dental primordia could reflect heterochronic changes in ontogeny which might be related to phyletic trends.

Affinities of European Upper Palaeolithic Homo sapiens and later human evolution

We investigate the evolutionary affinities of European Upper Palaeolithic populations, using cranial measurements and multivariate techniques. Results indicate that cranial morphology of these populations accords with long-term phyletic trends within Pleistocene hominids. The data indicate an interpretation of differential velocities of change, and results do not support the view that Neanderthals contributed to recent populations.

Morphometric studies of radiolarian evolution

Radiolarians are the most diverse of the 4 major fossil forming plankton groups, with several hundred living species, and an equally diverse range of biologic specializations for planktonic existence. Studies of radiolarian evolution are mostly from the Cenozoic, where the opaline silica skeletons of radiolarians are well preserved in most areas of the world's oceans. Cenozoic radiolarian skeletons are mostly too small (50-150 μm) and delicate to easily manipulate individually. Washed sieved skeletons are strewn at random orientations onto glass microslides and viewed in transmitted light. At the required magnifications, most skeletons cannot be viewed in their entirety within a single focus-plane. Many (perhaps the majority) of taxonomic characters in radiolarians are not visible in the skeleton outline, but are internal. These characteristics make normal image analysis techniques more difficult to employ. Computer assisted manual digitizers (one version working in 3 dimensions) have sometimes been used to measure skeletons. Distance, angle, area, and shape outline measurements have all been used to quantify radiolarian morphology.Radiolarian skeletal growth is determinate, and relatively little ontogenetic or within-population allometric variation is seen. Geographic variation in radiolarian species morphology is common, but little studied. Perhaps due to the effort involved, most ordinary taxonomic work does not employ morphometric data: its use has largely been in species-level evolutionary studies. Phyletic trends in size, shape, and in other characters have long been used to delineate stratigraphically useful chronospecies, and some of these anagenetic series have been morphometrically measured. Cladogenesis has also been morphometrically quantified in a few cases. Most studies of both cladogenesis and anagenetic evolution have documented gradual rates of morphologic change.Integrated studies of paleogeographic variation and temporal change are still needed, as is better information on modern radiolarian biology. Much more efficient measurement tools are also needed, to handle the very large number of specimens required by integrated studies.

Heterochronic evolution in theHeliolites interstinctus‐decipienslineage of the Chaleur Bay region, eastern Canada

A study of the Heliolites interstinctus-decipiens lineage from the Silurian of the Chalcur Bay region, eastern Canada, indicates that most morphological characters of this lineage, including tabularium diameter, coenenchymal tubule diameter and corallite spacing, remain relatively invariate through a Llandovery to Pridoli interval of about 20 million years. In contrast, septal development and corallite wall erenulation show pronounced evolutionary changes due to heterochrony, as shown by comparison of astogenies throughout the lineage. The reduction of septa and the replacement of crenulate corallites by smooth ones in the ‘decipiens’ type descendent appear to have been by paedomorphosis from the ‘interstinctus’ type ancestor. The problems of speciation in this lineage are discussed including the alternative hypotheses of a speciation event in the early Ludlow or a phyletic trend within a single species whose longevity is due in part to the stabilization processes of niche separation.

Heterochrony as an alternative to species selectionin the generation of phyletic trends

Phyletic trends can be accounted for by anagenesis or cladogenesis in conjunction with species selection or effect maroevolution. Data from the fossil record support anagenesis, involving single ancestor-descendent relationships, rather than cladogenesis as the normal or dominant pattern. Examples are given from fossil invertebrates of paedomorphosis and peramorphosis, of which the former appears to predominate.

The ecological and evolutionary interdependence between web architecture and web silk spun by orb web weaving spiders

Spider orb webs are dynamic, energy absorbing nets whose ability to intercept prey is dependent on both the mechnical properties of web design and the material properties of web silks. Variation in web designs reflects variation in spider web spinning behaviours and variation in web silks reflects variation in spider metabolic processes. Therefore, natural selection may affect web function (or prey capture) through two independent and alternative pathways. In this paper, I examine the ways in which architectural and material properties, singly and in concert, influence the ability of webs to absorb insect impact energy. These findings are evaluated in the context of the evolution of diverse aerial webs. Orb webs range along a continuum from high to low energy absorbing. No single feature of web architecture characterizes the amount of energy webs can absorb, but suites of characters indicate web function. In general, webs that intercept heavy and fast flying prey (high energy absorbing webs) are large, built by large spiders, suspended under high tension and characterized by a ratio of radii to spiral turns per web greater than one. In contrast, webs that intercept light and slow flying prey (low energy absorbing webs) are suspended under low tension, are small and are characterized by radial to spiral turn ratios that are less than one. The data suggest that for spiders building high energy absorbing webs, the orb architecture contributes much to web energy absorption. In contrast, for spiders that build low energy absorbing webs, orb architecture contributes little to enhance web energy absorption. Small or slow flying insects can be intercepted by web silks regardless of web design. Although there exists variation in the material properties of silk collected from high and low energy absorbing webs, only the diameter of web fibres varies predictably with silk energy absorption. Web fibre diameter and hence the amount of energy absorbed by web silks is an isometric function of spider size. The significance of these results lies in the apparent absence of selective advantage of orb architecture to low energy absorbing webs and the evolutionary trend to small spiders that build them. Where high energy absorption is not an exacting feature of web design, web architecture should not be tightly constrained to the orb. Assuming the primitive araneoid web design is the orb web, I propose that the evolution of alternative web building behaviours is a consequence of the general, phyletic trend to small size among araneoids. Araneoids that build webs of other than orb designs are able to use new habitats and resources not available to their ancestors.

Resistance to and repair of shell breakage induced by durophages in Late Ordovician brachiopods

Repaired shell breakage in Late Ordovician brachiopods from the Cincinnatian Series in the tri-state area of Indiana-Kentucky-Ohio may be described in increasing order of severity as scalloped, divoted, cleft and embayed. Concavo-convex brachiopod taxa display disproportionately higher frequencies of shell repair assigned to each category, whereas inflated, biconvex, plicate, sulcate taxa display disproportionately lower frequencies of shell repair. Certain plicate biconvex taxa lack examples of cleft and embayed valves. Plano-convex and dorsi-biconvex, costate taxa showed intermediate frequencies of shell repair, but lack representatives of embayed valves. Selective pressure for evolution of morphologic characters resistant to shell breakage may have favored phyletic trends of increasing size, geniculation and progressive development of a commissural ridge around the lophophore platform of the interior of the concave brachial valve of Leptaena and Rafinesquina. Size-frequency distributions for repaired and undamaged valves provide equivocal evidence of a size refuge from predator-induced shell breakage in Rafinesquina. Among the contemporaneous, potentially durophagous predators, nautiloids probably inflicted the sublethal injuries sustained by the brachiopods. The incriminating evidence includes a fragment of a crushing element imbedded in a valve of Rafinesquina that bears a very striking resemblance to calcified rhyncholites of Mesozoic to Recent nautiloids.

Evolutionary implications of predation on Recent comatulid crinoids from the Great Barrier Reef

Diving investigations of Recent comatulid crinoids at Lizard Island, Great Barrier Reef, indicate that, contrary to long-held notions, crinoids are subject to predation, principally by fishes of several families. Predation usually occurs as sublethal damage to the visceral mass and arms, from which the crinoids usually recover by regeneration. Aspects of the life habits, morphology, biochemistry, and physiology of comatulids are postulated to be adaptations that enable comatulid crinoids to resist predation. Comatulid versatility in coping with predation may account in large measure for their evolutionary success in the face of the late Mesozoic teleost radiation. Frequency of damage and repair in fossil crinoids can be used as a measure of predation pressure in order to assess the impact of predation during the Phanerozoic evolution of crinoids. Paleozoic stalked crinoids made a heavy investment in skeletal armor, while in contrast, comatulids reduced the calyx and became mobile. The relationship between these phyletic trends and predation pressure can now be critically examined.

Negentropy and the evolution of chemical recruitment in ants (Hymenoptera: Formicidae)

The applicability of the concept of negentropy to the study of evolution is tested by tracing the phylogeny of the information content of the communication systems used for recruitment in the Formicidae. Data from the literature is reviewed and ordered around theoretical evolutionary routes based on increasing negentropy of the chemical communication systems used. One pathway presupposes the development of chemical orientation prior to chemical attraction, i.e. signalling the presence of food; whereas the others begin with the chemical attraction of nestmates without orientation with chemical cues to the food. The results suggest that the Myrmicinae, Ponerinae, Dolichoderinae, Pseudomyrmycinae and possibly Dorylinae evolved chemical recruitment via chemical attraction, whereas the Formicinae evolved chemical recruitment via chemical orientation. These alternative patterns permit the establishment of phyletic trends based on glandular evolution for chemical recruitment. The results are compared with phylogenetic studies based on morphological and chemical characters, and it emerges that the recruitment behaviour proves to be a particularly conservative characteristic, in that it is evident in the same form in a wider range of species. The conclusion is reached that the negentropy content of living systems is a powerful tool in phylogenetic studies, even of small taxonomic groups.

The Orchids: Natural History and Classification

This lively examination of the structure, classification, evolution, and ecology of the Orchidaceae will appeal to anyone with an eye for beauty or a bent for natural history. It will provide professional biologists and amateur orchidists alike with a deeper understanding--and a thoroughly new classification--of this, the largest flowering family in the plant kingdom. book is richly illustrated, with 95 color photographs and 99 line drawings emphasizing orchid morphology. But in the context of serious orchidology, aesthetic richness is not a superficial vanity. It is the result of evolutionary processes that demand adaptation and reward diversity, and Dressler's exploration of these mechanisms demonstrates how well the orchids have met the challenge, with over 20,000 species, a geographical range from Sweden to Tierra del Fuego, and, at times, as many as 47 different species on a single tree. But both the orchids' success and their profligate beauty are grounded, in part, in their voluptuary nature, and one of Dressler's most engaging themes is the reproductive adaptations, worthy of a Renaissance courtesan, that orchids use to attract, deceive, and manipulate pollinating insects. orchid family is actively evolving, providing rich possibilities for comparative study. Yet no one, whether professional or amateur, could reasonably proceed without first addressing Robert Dressler's The Orchids, Its new classification alone, including pollination biology, phyletic trends, chromosome counts, and generic relationships, will stand as a watershed contribution to the field.

Ontogenesis and Morphological Diversification

SYNOPSIS. The role of development in constraining the directionality and patterns of morphological evolution is examined. The nature of morphological variation and appearance of morphological novelties is determined by the epigenetic properties of the organism. Consideration of these properties has profound implications for current theories of morphological evolution. Developmental constraints impose severe limitations on the gradualistic action of directional selection. Evolutionis viewed as the result of differential survival of morphological novelties. However, the production of morphological novelties by developmental programs is not random. This non-randomness in morphologically expressed genetic mutations—an epigenetic property—can result in phyletic trends, parallelisms and convergences.

Size and shape in ontogeny and phylogeny

We present a quantitative method for describing how heterochronic changes in ontogeny relate to phyletic trends. This is a step towards creating a unified view of developmental biology and evolutionary ecology in the study of morphological evolution. Using this representation, we obtain a greatly simplified and logical scheme of classification. We believe that this scheme will be particularly useful in studying the data of paleontology and comparative morphology and in the analysis of processes leading to adaptive radiation. We illustrate this scheme by examples drawn from the literature and our own work.