Functional morphology and evolutionary ecology

Functional morphology studies physico-chemical properties and biological roles of organs. If applied to fossils this approach is connected with specific methodological problems. The fields of application of functional morphology in paleontology are illustrated with examples. In a working concept it is shown how the results of functional morphology can be integrated into an account of the evolutionary ecology of fossil taxa.     

Functional morphology and evolutionary origin of the three-part pharynx in nematodes

The distinct morphological regions of the typical tripartite pharynx found in the nematode taxon Secernentea have distinctive functions. Besides the basic functions of sucking and pumping food against the pressure in the body cavity, the pharynx of Secernentea such as rhabditids serves two additional functions restricted to two pharyngeal subunits. The corpus traps bacteria behind the stoma and at its posterior end. The newly discovered pharyngeal pocket valve helps to trap particles behind the corpus in the rhabditid Poikilolaimus oxycercus and the cephalobid Acrobeles ciliatus (both Secernentea). The grinder of the terminal bulb serves for chewing trapped bacteria. The separated sites of trapping and chewing are connected by the isthmus that transports bacteria towards the grinder. It is likely that this complex feeding structure originated step by step from a two-part pharynx comprising a propharynx and the terminal bulb as in "Plectidae" (that probably include the closest relatives of the Secernentea within the "Adenophorea"). Analysis of video sequences of feeding rhabditids and plectids provided new data to reconstruct this transformation. Within the "Plectidae" two types of grinders occur. The first type or "parietinus type" has triangular chewing plates that can bulge medially and crush food particles. When they retract, new ingested particles are drawn into the grinder. The second type with more solid chewing plates called "butterfly valves" occurs in Ceratoplectus, Plectus parvus, and Wilsonema and can be homologized with the grinder in Secernentea ("Plectidae" is a paraphyletic taxon). Because butterfly valves cannot be retracted, the evolution of such valves required the evolution of an alternative mechanism to fill the grinder with bacteria. The differentiated closing pattern of the dilated pharynx lumen in Ceratoplectus, Plectus parvus, and Wilsonema can be interpreted as the first step in the development of a functional separation of trapping bacteria and of transporting them towards the grinder, which led to the morphologically discernible units of corpus and isthmus found in the Secernentea.     

Phylogeny and evolutionary biology

The phylogenetic system of Hennig, which was designed for classification of synchronous organisms, has only been adapted secondarily to total reconstruction of phylogeny. All fields of fundamental biology are related to the development of evolutionary theory. A better understanding of the origin of life requires new concepts of the historical geology of prebiological environment and new concepts of molecular genetics and biochemistry concerning ribonucleic acids as the initial units for the origin of life.     

The basic body plan of arthropods: insights from evolutionary morphology and developmental biology

Phylogenetic, morphological, and developmental data concerning the Arthropoda are reviewed and discussed with the aim of reconstructing the ancestral body plan of the mandibulate arthropods (Myriapoda, Hexapoda, Crustacea). Comparative morphology as well as embryology of malacostracans and hexapods (cell-lineages, patterns of mitotic domains, patterns of en-stripe formation, expression zones of pair-rule, homeotic, and gap-like genes) suggest that (a) the basic boundary subdividing the mandibulate body into the primary embryonic regions, anterior protocephalon and posterior protocorm, runs anteriorly to parasegment PS1 (=within the mandibular segment); (b) protocephalon (pregnathal region) probably is not a unitary body region; (c) maxillary segments are closely related to the postgnathal trunk segments; (d) the “typical” mandibulate head (pregnathal-mandibular-maxillary) is not developed in all Mandibulata and has evolved several times in parallel; and (e) postcephalic tagmosis is much less conserved, and probably more recent, than tagmosis of more anterior areas. The arachnomorphan anterior tagma, the prosoma, is compared with the hypothesized ancestral mandibulate head.     

Functional evolutionary developmental biology (evo-devo) of morphological novelties in plants

The origin of morphological and ecological novelties is a long-standing problem in evolutionary biology.Understanding these processes requires investigation from both the development and evolution standpoints,which promotes a new research field called evolutionary developmental biology (evo-devo).The fundamental mechanism for the origin of a novel structure may involve heterotopy,heterochrony,ectopic expression,or loss of an existing regulatory factor.Accordingly,the morphological and ecological traits cont...     

Comparative genomics and evolutionary biology

Data of large-scale DNA sequencing are relevant to some of the most fundamental issues in evolutionary biology: suboptimality, homology, hierarchy, ancestry, novelties, the role of natural selection, and the relative importance of directional versus stabilizing selection. Already, these data provided the best available evidence for some evolutionary phenomena, and in several cases led to refinement of old concepts. Still, the Darwinian evolutionary paradigm will successfully accommodate comparative genomics.     

San Marco and evolutionary biology

Gould and Lewontin use San Marco, Venice, to criticise the adaptationist program in biology. Following their lead, the architectural term “spandrel” is now widely used in biology to denote a feature that is a necessary byproduct of other aspects of the organism. I review the debate over San Marco and argue that the spandrels are not necessary in the sense originally used by Gould and Lewontin. I conclude that almost all the claims that Gould makes about San Marco are wrong and that it is reasonable to view the architectural spandrel as an adaptation. The spandrels example has not provided a good illustration of why adaptive explanations should be avoided. In fact, it can be used as an example of how adaptive explanations can be dismissed even when there is evidence in their favour. I also discuss the use of the concept of a spandrel in biology.     

Functional and evolutionary morphology of lingual feeding in squamate reptiles: phylogenetics and kinematics

Use of the tongue as a prehensile organ during the ingestion stage of feeding in lizards was studied cinegraphically in seven species. Within Squamata, lingual prehension is limited to a single clade, the Iguania (Iguanidae, Agamidae and Chamaeleontidae), which includes all 'fleshy-tongued' lizards. All remaining squamates (Scleroglossa) use the jaws alone for prey prehension. Lingual prehension and a 'fleshy' tongue are primitive squamate characteristics. Kinematically, lingual ingestion cycles are similar to previously described transport cycles in having slow open, fast open, fast close and slow close-power stroke phases. Tongue movements are sequentially correlated with jaw movements as they are in transport. However, during ingestion, anterior movement of the tongue includes an extra-oral, as well as intra-oral component. Tongue protrusion results in a pronounced slow open-II phase at a large gape distance. A high degree of variability in quantitative aspects of ingestion and transport cycles suggests that modulation through sensory feedback is an important aspect of lizard feeding. Preliminary evidence indicates an important role for hyoid movement in tongue protrusion. Our results are consistent with the Bramble & Wake (1985) model generalized feeding cycle and support their contention that specialized feeding mechanisms often represent modifications of a basic pattern, particularly modification of the slow open phase.     

On the origin of Cetartiodactyla: Comparison of data on evolutionary morphology and Molecular biology

The data on phylogeny and early evolution of Cetartiodactyla are analyzed and a model for the initial stage of their history is proposed. It is shown that the roots of Cetartiodactyla go back to generalized Cretaceous terrestrial Eutheria, and a hypothetical basal group of Cetartiodactyla was probably ancestral to the orders Artiodactyla and Cetacea. The Artiodactyla-Cetacea divergence and adaptive radiation of Artiodactyla, which gave rise to the suborders Ruminantia, Tylopoda, and Suiformes, apparently occurred in the pre-Eocene time, earlier than 55 Ma. Molecular similarity between Hippopotamidae and Cetacea is evidence of common origin of Artiodactyla and Cetacea and adaptation to aquatic environment.     

Iconometrographics in evolutionary biology

The essential dialogue between Apollinian and Dionysiac poles required for the advance of music and art was likened to the scientific debate between «justifiers» and «innovators». The use of ratios and simple algorithms was indicted as being retrogressive in terms of modern microcomputer technology and iconometrographic models. Three examples were used to illustrate the approach in the resolution of complex data sets comparing samples: (1) 45,XO with a 46,XY controls, (2) sexual dimorphism in young adults and (3) Black and White Olympic athletes. The iconometrographic approach was proposed as a primary orientation in human biology, particularly in secular trend studies concerned with the recognition and assessment of complex evolutionary trends.     

Flower morphology and biology of Myrsine laetevirens, structural and evolutionary implications of anemophily in Myrsinaceae

This study deals with the phenology, pollination biology and floral morphology of Myrsine laetevirens , a neotropical dioecious tree. In Punta Lara (Argentina), its flowering period occurs during January-February. Both pistillate and staminate flowers are small, with a yellowish-green perianth and produce neither nectar nor odour. Staminate flowers have five stamens and a vestigial gynoecium while pistillate flowers, have non-functional anthers and a conspicuous stigma. The floral characteristics of staminate and pistillate plants are related to the syndrome of anemophily. Fruit set in inflorescences covered with mesh bags and observations prove that animals are not involved in the pollination process. A provisional cladistic analysis of Myrsinaceae shows that dioecy evolved as one of the most recent apomorphies of Myrsine and is part of the anemophilous syndrome.     

Antennal circulatory organs in Onychophora,Myriapoda and Hexapoda: Functional morphology and evolutionary implications

Summary A comparative investigation of the antennal circulatory organs in representatives of the Onychophora, all subtaxa of the Myriapoda and numerous taxa of the Hexapoda (comprising a total of 54 species) revealed an unexpected diversity in structure and function.In the Onychophora, antennal vessels exist which are connected to the enlarged anterior end of the aorta dorsal to the brain.In the Chilopoda, Diplopoda and Symphyla, antennal vessels exist which originate from the dorsal vessel caudal to the brain. They extend under the optic lobes, lateral to the circumoesophageal connectives, into the antennae.In the Hexapoda, the investigations include representatives of all higher taxa, apart from the Paraneoptera and the Holometabola. Generally, antennal vessels exist. In the Diplura, they originate from the anterior end of the aorta in front of the brain. In all other insects the antennal vessels are separate from the dorsal vessel. Their proximal ends form ampullary enlargements which are attached to the frontal cuticle near the antenna bases. They communicate via valved ostia with the haemolymph sinus in front of the brain. In the Archaeognatha, Zygentoma, Odonata, certain Plecoptera and the Notoptera, no muscles are connected to these organs. In all other groups the ampullae are pulsatile as a result of associated muscles (antennal hearts). These muscles diverge widely in their attachments and act either as compressors (Dermaptera) or dilators of the ampullae (Embioptera, Blattopteroidea, Orthopteroidea, and some Plecoptera).In the Collembola and Ephemeroptera, special antennal circulatory organs are lacking. In some forms the anatomical arrangement of the inner organs, in conjunction with short diaphragms at the antenna bases, apparently leads to a channelling of haemolymph flow. This condition may be explained by the very short antennae of these insects and is considered as a convergent and apomorphic state in these taxa.The antennal vessels are supposed to be homologous within the Tracheata and to represent the lateral arteries of the antenna segment. An origin from the dorsal vessel is considered an ancestral state, which was lost in the stem lineage of the Ectognatha. Specific space constraints within the cephalic capsule are discussed as the possible reason for this loss. The evolution of pulsatile antennal circulatory organs in the Neoptera is the result of the association of muscles with the proximal ampullary ends of the antennal vessels. The attachments and innervation of these muscles indicate a derivation from precerebral pharyngeal dilators.Abbreviations Amp ampulla - Ant antenna - ant anterior - AN antennal nerve - Ao aorta - AV antennal vessel - Br brain - BrSi brain sinus - CC corpora cardiaca - CoeC circumoesophageal connectives - CM compressor muscle of ampulla - CT connective tissue - Dia diagphragm - do dorsal - DM dilator muscle of ampulla - DM1 ampullo-ampullary dilator muscle - DM2 ampullo-pharyngeal dilator muscle - DM3 ampullo-frontal dilator muscle - DM Acc accessory dilator muscle of ampulla - DV dorsal vessel - EB elastic band - FbDM fronto-buccal pharynx dilator muscle - FG frontal ganglion - FSa frontal sac - FSe frontal septum - FSi frontal sinus - Lb labium - LV lateral vessel of aorta - MA mouth-angle - Nr nervus recurrens - Oc ocellus - Oe oesophagus - OeSi oesophageal sinus - Ost ostium - Ph pharynx - Pl labial palpus - RM retractor muscle of mouth-angle - RMl lateral retractor of mouth-angle - RMm medial retractor of mouth-angle - SceSi supracerebral sinus - SD salivary duct - T tentorium     

Functional morphology and developmental biology of zebrafish: reciprocal illumination from an unlikely couple

Functional morphology has benefited greatly from the input oftechniques and thinking from other disciplines. This has beenespecially productive in situations where each discipline hasmade significant contributions to a particular research topic.A combination of methodologies from functional morphology anddevelopmental biology has allowed us to characterize feedingmechanics of first-feeding larval zebrafish (Danio rerio). Contraryto kinematic patterns commonly seen in adult teleosts, larvalzebrafish showed no lateral abduction during the expansive phaseof a suction-feeding event. Instead, dorsoventral expansionof the buccal chamber, more typical of patterns seen in primitivefishes, characterized the expansive phase. Moreover, a pronouncedpreparatory phase during which the buccal chamber is constrictedby the protractor hyoideus was consistently seen in first-feedinglarval kinematics. Key kinematic variables associated with firstfeeding correlated significantly with the hydrodynamic regimeas measured by the Reynolds number. Using the tools of bothfunctional morphology and developmental biology we have notonly determined which cranial muscles are important for successfulfeeding but also uncovered important physiological differencesin muscle structure. Muscles necessary for the rapid dorsoventralexpansion of the head are composed primarily of fast-twitchfibers while those involved in more tonic contractions suchas hyoid protraction have more slow-twitch muscle fibers. Whilemost evolutionary developmental studies have examined mechanismsresponsible for large evolutionary changes in morphology, wepropose that the type of data uncovered in functional studiescan lead to the generation of hypotheses concerning the developmentalmechanisms responsible for smaller intra- and/or interspecificchanges.     

Explanatory pluralism in evolutionary biology

The ontological dependence of one domain on another is compatible with the explanatory autonomy of the less basic domain. That autonomy results from the fact that the relationship between two domains can be very complex. In this paper I distinguish two different types of complexity, two ways the relationship between domains can fail to be transparent, both of which are relevant to evolutionary biology. Sometimes high level explanations preserve a certain type of causal or counterfactual information which would be lost at the lower level; I argue that this is central to the proper understanding of the adaptationist program. Sometimes high level kinds are multiply realised by lower level kinds: I argue that this is central to the understanding of macroevolution.