Christian S. Wirkner

Finding Our Way through Phenotypes

Imagine if we could compute across phenotype data as easily as genomic data; this article calls for efforts to realize this vision and discusses the potential benefits.

Evolutionary morphology of the circulatory system in Peracarida (Malacostraca; Crustacea)

We demonstrate that by formulating guidelines for evolutionary morphology the transparency, reproducibility, and intersubject testability of evolutionary hypotheses based on morphological data can be enhanced. The five main steps in our concept of evolutionary morphology are (i) taxon sampling, (ii) structural analysis, (iii) character conceptualization, (iv) phylogenetic analysis, and (v) evolutionary interpretation. We illustrate this concept on the example of the morphology of the circulatory organs in peracarid Malacostraca. The analysis is based on recently published accounts in which detailed structural analyses were carried out, and on the older literature. Detailed conceptualizations of 22 characters of the circulatory system are given for 28 terminals. In a further step these characters are included in a recently revised matrix, resulting in 110 characters. The resulting parsimony analysis yielded a single most parsimonious tree with a length of 309 steps. The most significant results are that Peracarida is monophyletic, Amphipoda is the sister taxon to the Mancoida sensu stricto, the relict cave‐dwelling taxa Thermosbaenacea, Spelaeogriphacea, and Mictocarididae form a monophylum and Tanaidacea is the sister group to a monophylum comprising Cumacea and Isopoda. The evolutionary analysis shows that the ground pattern features of the circulatory organs in Peracarida are a tubular heart extending through the whole thorax, a posterior aorta with lateral arteries, and a ventral vessel system. Important features within the Peracarida are the backward shift of the anterior border of the heart, the reduction of the ventral vessel system, and two patterns of cardiac arteries, one common to the amphipod and tanaidacean terminals, and one to the cumacean and isopod terminals.

Evolutionary morphology of the hemolymph vascular system in hermit and king crabs (Crustacea: Decapoda: Anomala).

The morphological transformation of hermit crabs into crab‐like king crabs in the evolution of decapod crustaceans represents a remarkable case of carcinization or evolutionary shaping into a crab‐like form. In this study, we focus on internal organs such as the hemolymph vascular system and adjacent anatomical structures of several Recent hermit crab (Paguridae) and king crab (Lithodidae) species. There are various correspondences in the morphology of the arterial systems in the dorsal cephalothorax of the two taxa, especially with regard to the anterior aorta, anterior lateral arteries, and hepatic arteries. In the pleon, the posterior aorta in both taxa displays a proximal bifurcation and follows an asymmetrical course. The ventral vessel system, on the other hand, which mainly supplies the limbs, differs significantly between the taxa, with pagurids displaying the plesiomorphic condition. The pattern of the ventral vessel system in Lithodidae is influenced by morphological transformations of integumental structures during carcinization. One of these transformations was the broadening of the sternites, which resulted in a widening of the space between the endosternites. In addition, changes in the morphology of the endophragmal skeleton in Lithodidae led to an increase in the potential for intraspecific variability and interspecific variation in the arterial branching pattern. J. Morphol., 2013.

Evolutionary morphology of the organ systems in squat lobsters and porcelain crabs (crustacea: Decapoda: Anomala): an insight into carcinization.

Porcelain crabs (Porcellanidae) are one of three taxa within anomuran crustaceans (Anomala) which possess a crab‐like body form. Curiously, these three lineages evolved this shape independently from true crabs (Brachyura) in the course of the evolutionary process termed carcinization. The entire pleon in porcelain crabs is flexed under the cephalothorax and the carapace is approximately as broad as long. Despite their crab‐like habitus, porcelain crabs are phylogenetically nested within squat lobsters (Munidopsidae, Munididae, Galatheidae). With a pleon which is only partly flexed under the cephalothorax and a cephalothorax which is longer than it is broad, squat lobsters represent morphologically intermediate forms between lobster‐like and crab‐like body shapes. Carcinization has so far mostly been studied with respect to outer morphology; however, it is evident that internal anatomical features are influenced through this change of body shape too. In this paper, the situation in Galatheoidea is elucidated by adding more taxa to existing descriptions of the hemolymph vascular systems and associated structures and organs. Micro‐computer tomography and 3D reconstruction provide new insights. Autapomorphic states of various internal anatomical characters are present in nearly all the studied species, also reflecting some degree of anatomical disparity found within Galatheoidea. The ventral vessel system of porcelain crabs differs distinctly from that of squat lobsters. The differences in question are coherent (i.e. structural dependent) with morphological transformations in the integument, such as the shortening of the sternal plastron, which evolved in the course of carcinization. Shifts in the gonads and the pleonal neuromeres are coherent with the loss of the caridoid escape reaction, which in turn is a consequence of carcinization. The arterial transformations, however, are minor compared to other instances of carcinization in anomuran crustaceans since the last common ancestor of squat lobsters and porcelain crabs was already “half carcinized”. J. Morphol. 276:1–21, 2015.

Evolutionary morphology of the hemolymph vascular system in scorpions: A character analysis

Phylogenetically informative characters from the internal anatomy of scorpions were first reported more than 150 years ago, but the subject received little attention after the mid-1920s. Recent investigations, using traditional dissection, illustration and histological sectioning, microscopy, and innovative new methods for investigating complex soft tissue anatomy identified a new wealth of variation. Additionally, these investigations confirmed the phylogenetic significance of previously identified structures. Building on earlier work we present a more detailed description of the hemolymph vascular system (HVS) in scorpions, based on comparison of the vascular structures of the heart and the branching pattern of the prosomal arteries among 45 exemplar species representing most of the major scorpion lineages. Using corrosion-casting, MicroCT in combination with computer-aided 3D-reconstruction, and scanning electron microscopy, we conceptualize a series of phylogenetically informative characters for the anterior aorta system and characters of the heart and associated structures (e.g. arrangement of the ostia) of scorpions. Furthermore, we optimize the possible evolution of these new characters on a previous hypothesis of scorpion phylogeny, and discuss alternative character state transformations, their evolutionary consequences, and possible underlying evolutionary mechanisms acting on the HVS.

Symmetry variation in the heart-descending artery system of the parthenogenetic marbled crayfish.

The internal anatomy of freshwater crayfish is strictly bilaterally symmetric, with the conspicuous exception of the vertically oriented descending artery (sternal artery), which originates from the heart and terminates in the subneural artery. Serial sectioning of 133 juveniles of the parthenogenetic marbled crayfish revealed that the descending artery was bilaterally symmetric in 4.5% of the specimens, right asymmetric in 45.1%, and left asymmetric in 50.4%. In the bilaterally symmetric variant two branches arise from the left and right chambers of the bulbus of the heart, run laterally around the hindgut, and fuse underneath it. The asymmetric variants have only one dorsal branch, which loops around the hindgut on either the left or the right side. Other structures of the heart, such as the paired antennary and hepatopancreatic arteries and the ostia or the unpaired anterior and posterior aortae, showed no symmetry variation. Because of the genetic identity of the experimental animals and their culture under identical environmental conditions, the variation in symmetry of the descending artery observed is interpreted as the result of developmental variation. We recommend that the marbled crayfish be considered for investigation of the epigenetic mechanisms responsible for the maintenance and breaking of bilateral symmetry in metazoans. J. Morphol., 2009.

Comparative morphology of the hemolymph vascular system in krill (Euphausiacea; Crustacea).

The phylogenetic position of Euphausiacea within Malacostraca is still under debate. Either they are seen as sister group to a taxon comprising Pancarida and Peracarida or closer related to Decapoda. Both hypotheses can be supported by characters of the circulatory system. Therefore, a comparative re-evaluation of the circulatory system seems to be feasible. Here we present the first three-dimensional data of the circulatory system of three euphausiacean species based on semi-thin sections and micro computer tomography in combination with corrosion casting. We were also able to study for the first time representatives of Bentheuphausia amblyops, the suggested sister taxon to all other euphausiaceans. The main pumping structure in the open circulatory system of Euphausiacea is the globular heart in the rear thoracic segments. From the anterior and posterior end of the heart two unpaired and four pairs of arteries emanate. The unpaired anterior aorta runs below the carapace from the anterior part of the heart into the anterior cephalothorax, where it supplies the first antennae, the brain and the eyes. The paired posterior aortae run into the pleon supplying the pleopods, uropods and the telson. The four pairs of cardiac arteries supply appendages in the cephalic region and viscera in the trunk. The unpaired descending artery connects to the subneural vessel supplying the thoracopods. A myoarterial formation of the anterior aorta is described in Bentheuphausia amblyops. The observed pattern of a globular heart situated in the posterior cephalothorax and comprising a meshwork of muscular strands (also running through its lumen) is highly likely to be homologous in Euphausiacea and Decapoda. The data are compared with the scarce literature present to date.

The brain in three crustaceans from cavernous darkness

BackgroundWhile a number of neuroanatomical studies in other malacostracan taxa have recently contributed to the reconstruction of the malacostracan ground pattern, little is known about the nervous system in the three enigmatic blind groups of peracarids from relict habitats, Thermosbaenacea, Spelaeogriphacea, and Mictocarididae. This first detailed description of the brain in a representative of each taxon is largely based on a combination of serial semi-thin sectioning and computer-aided 3D-reconstructions. In addition, the mictocaridid Mictocaris halope was studied with a combination of immunolabeling (tubulin, nuclear counter-stains) and confocal laser scanning microscopy, addressing also the ventral nerve cord.ResultsAdjacent to the terminal medulla, all three representatives exhibit a distal protocerebral neuropil, which is reminiscent of the lobula in other Malacostraca, but also allows for an alternative interpretation in M. halope and the thermosbaenacean Tethysbaena argentarii. A central complex occurs in all three taxa, most distinctively in the spelaeogriphacean Spelaeogriphus lepidops. The deutocerebral olfactory lobe in M. halope and S. lepidops is large. The comparably smaller olfactory lobe in T. argentarii appears to be associated with a unique additional deutocerebral neuropil. A small hemiellipsoid body exists only in the protocerebrum of T. argentarii. Distinctive mechanosensory neuropils corresponding to other malacostracans are missing.ConclusionsThe considerable reduction of the optic lobe in the studied taxa is higher than in any other blind malacostracan. The large size of deutocerebral olfactory centers implies an important role of the olfactory sense. The presence of a distinctive central complex in the blind S. lepidops adds further support to a central-coordinating over a visual function of this structure. The lack of a hemiellipsoid body in M. halope and S. lepidops suggests that their terminal medulla takes over the function of a second order olfactory center completely, as in some other peracarids. The reduction of the optic lobe and hemiellipsoid body is suggested to have occurred several times independently within Peracarida. The missing optic sense in the studied taxa is not correlated with an emphasized mechanosense.

An “ancient” complexity? Evolutionary morphology of the circulatory system in Xiphosura

Horseshoe crabs (Xiphosura) have been an object of zoological research for almost 200 years. Although some morphological work on the circulatory system has been done, the three-dimensional structure of this complex organ system has never been shown satisfactorily and some crucial questions remain unanswered. Here, the circulatory systems of juveniles of the horseshoe crab taxa Limulus polyphemus and Carcinoscorpius rotundicauda were investigated using a combination of an injection method and micro-computed tomography. Data were processed and 3D-visualized using reconstruction software. Furthermore, the heart was examined using scanning electron microscopy. Additionally, the histology of some structures was investigated via light microscopy and transmission electron microscopy. The results show the high degree of complexity of the arterial and lacunar systems of Xiphosura and provide insights into their three-dimensional structure and relationship to other organ systems such as the central nervous system. We show that the major lacunae, previously described as vessel-like - though indeed highly ramified - can clearly be distinguished from arteries in histological sections because they have no distinct walls. Similarities and differences between the xiphosuran species and arachnids are highlighted and possible phylogenetic implications and evolutionary scenarios discussed.

The Circulatory System of Spiders

The spider circulatory system is a structurally complex and elaborately regulated system with a broad range of functionalities. Apart from its well-known role in metabolism and, plesiomorphically at least, in oxygen distribution, its main functions are hydraulic. This article reviews the state of knowledge on both the evolutionary and functional morphological levels.