Phylogenetic Origin of the Chloroplast*†

SYNOPSIS. The 16S ribosomal RNA of the chloroplast of Euglena gracilis strain Z has been characterized in terms of its 2-dimensional electrophoretic “fingerprint” (T1 ribonuclease). Over 100 spots were resolved on the “fingerprint” and each spot was characterized as to which RNA oligonucleotide fragment(s) it contained. When compared to similar analyses of prokaryotic 16S rRNAs and eukaryotic cytoplasmic 18S rRNAs, the chloroplast 16S rRNA was a typically prokaryotic RNA, but bore little if any relationship to eukaryotic 18S rRNAs. Therefore, the cistrons for chloroplast 16S rRNA are related to the equivalent prokaryotic cistrons, but, apparently, are not related to the equivalent eukaryotic cistrons. Among the organisms available for comparison, the Euglena chloroplast 16S rRNA appears most closely related to the 16S rRNA of the eukaryote, Porphyridium cruentum (a red alga), and at least distantly related to the 16S rRNAs of the blue-green algae and perhaps also to the bacilli.     

The Origin of Cladocera (Crustacea,Branchiopoda): A New Understanding of an Old Hypothesis

Comparative analysis of the ontogeny of representatives of two sister taxa (Cladocera and Cyclestherida) showed that the paedomorphic morphology of cladocerans (the small number of thoracic segments and segments of branches of antennae II, and the reduction of the carapace) was caused by the cessation of development of the somatic structures at early larval stages of ontogeny. It is demonstrated that this stop is not associated with the accelerated development of the reproductive system (progenesis), since it takes place long prior to the beginning of reproduction. In accordance with this fact, the past hypotheses that cladocerans evolved from the reproducing larvae of the ancestral form or that they are early maturing metanauplii should be recognized as erroneous. Cyclestheria. The origin of Cladocera from a Cyclestheria-like ancestor should be regarded as neotenic, taking into consideration the extended interpretation of this term.     

Origin and diversification of the clawed lobster genus Metanephrops (Crustacea: Decapoda: Nephropidae)

A phylogenetic analysis of all 17 extant species of the clawed lobster genus Metanephrops based on mitochondrial 12S rRNA, 16S rRNA and cytochrome c oxidase I, and nuclear histone H3 gene sequences supports the morphological groupings of two of the traditional groups of the genus (the binghami and japonicus groups) but refutes monophyly of the other two groups (the arafurensis and thomsoni groups). The results in general support a recent morphology-based cladistic analysis of this genus except that this study suggests M. neptunus to be a basal rather than a derived species as indicated in the morphological analysis. This species is genetically diverse over its geographical range. Moreover, the two color forms of M. thomsoni are genetically distinct, most likely representing different species. The molecular phylogeny and current distribution pattern of the extant species, together with the fossil record, suggest that the genus originated in the Antarctica in the Cretaceous, followed by diversification and dispersal along the continental shelf of different continents as a result of the vicariant events associated with the breakup of the Southern Temperate Gondwana since Late Cretaceous.     

Regional variation in the spatial scale of selection at MPI* and GPI* in the acorn barnacle Semibalanus balanoides (Crustacea)

Elucidating the ecological processes by which adaptive genetic polymorphism is maintained in heterogeneous environments requires knowledge on the spatial scale at which alternate habitats affect genotype-specific fitness. The general objective of this study was to document patterns of temporal and spatial variation of genetic polymorphism in the acorn barnacle (Semibalanus balanoides) at MPI* and GPI* allozyme loci. A total of 7261 barnacles were sampled in the intertidal at various locations north and south of the Miramichi estuary, New Brunswick, Canada. The results of this study supported the hypothesis that both MPI* and GPI* are under the effect of strong directional selection south of the Miramichi, whereas neutrality cannot be ruled out at sampling sites located north of the estuary. Comparisons between this study and previous ones also question the generality of current hypotheses regarding ecological processes that are responsible for maintaining polymorphism at MPI* and GPI* in the acorn barnacle.     

Studies on the Origin of the Methyl Groups of Choline in Ochromonas malhamensis*

SYNOPSIS. Five- to 6-day-old resting cells of Ochromonas malhamensis were incubated at pH 6.5 with glucose and appropriate C¹⁴ precursors of the methyl groups of phospholipid-choline. Under the experimental conditions L-methionine-C¹⁴H₃ was the most efficient source of choline-methyl groups, followed by formate-C¹⁴, formaldehyde-C¹⁴ and DL-serine-3-C¹⁴, respectively. Glycine-2-C¹⁴ was not incorporated into choline. Both L-methionine-C¹⁴H₃ and formate-C¹⁴ served as precursors for the methyl groups of monomethylethanolamine, dimethylethanolamine and choline. Addition of non-radio-active L-methionine depressed the incorporation of formate-C¹⁴ into choline-methyl groups by 50%. The results support the hypothesis that methionine can be the source of all 3 methyl groups of choline, and that formate is probably converted to the methyl group of methionine before transmethylation to choline. However, an alternate pathway from single-carbon sources cannot be excluded.     

An Annotated List of Protozoan Parasites,Hyperparasites, and Commensals of Decapod Crustacea*

SYNOPSIS. An approximately complete list of the known protozoan associates (exclusive of a few aberrant forms like Amallocystis) of decapods is presented. A few taxonomic changes are suggested. Host, site of infection and geographic location are mentioned. Some comments on pathogenicity are made.     

The Origin of the Chordates

The study of development and comparisons of the adult structures of the several groups of protochordate animals reveals something of their interrelationships and origin. The hemichordates are perhaps closer to the echinoderms than to the chordates, but these groups appear to have been derived from a bilaterally symmetrical dipleurula ancestor, not from a sessile pterobranch-like form. The origin of the chordates is speculative but the idea of a prototunicate stage is rejected. The tunicate is viewed as a highly modified end product, with fewer similarities to the ancestral form than amphioxus. Amphioxus is quite suggestive of the vertebrate, yet it is more like the tunicate in the details of its embryology and along with that rather extreme peripheral group is best thought of as constituting a subphylum, the Acraniata. The idea of the early vertebrate as a filter feeder must be rejected since it is assumed here that perfection of that function led to a sessile or inactive way of life (as in the acraniates or lamprey larva) and failed to lead to the active creature with highly developed sensory, neural, and locomotor systems identified here as the protovertebrate. Further, the muscular plastic pharynx and moveable mouth of the protovertebrate suggest feeding on larger organisms, predation, and the abandonment of ciliary water-current feeding.     

Five new species of leaf litter harpacticoids (Crustacea,Copepoda) from Nepal*

From leaf litter samples collected at altitudes varying between 1900 m and 3800 m a.s.l. five new species of harpacticoid copepods are described. One, Parbatocamptus jochenmartensi represents a new genus in the formerly monotypic family Phyllognathopodidae. Four, Attheyella (Chappuisella) ilami, Moraria ilami, Elaphoidella jochenmartensi and Elaphoidella pseudocornuta, are new Canthocamptidae, related to leaf axil faunas of the tropical lowland forest of Indonesia.     

The optic neuropiles and chiasmata of Crustacea

Summary On the basis of ontogeny and adult morphology, an interpretation of the arrangement of optic neuropiles and fibre connexions of the Crustacean compound eye is presented. In the embryo of phyllopods and decapods, the ommatidia, the lamina ganglionaris, and the medulla externa are developed synchronously from a common medial proliferation zone. As this zone persists in all investigated adult Crustacea that possess compound eyes, such a derivation of the mentioned structures is taken to be universal within the group. The direction of growth of the lamina ganglionaris is parallel with the row of ommatidia, the growth direction of the medulla externa is perpendicular to it and parallel with the long axis of the eyestalk. This arrangement is more or less retained in most adult non-Malacostracan Crustacea, and the axons of fully developed neurons pierce the optic neuropiles and leave and enter on the neuropile side. As a result, there is no chiasma in the non-Malacostracan groups.The Malacostraca have an extra neuropile, the medulla interna, derived from the medulla terminalis. Chiasmata occur between the lamina ganglionaris and the medulla externa, and between the medulla externa and the medulla interna. This difference from the non-Malacostracans depends on the course of the fibres. Those coming from the lamina ganglionaris leave the lamina on the neuropile side and enter medulla externa between the cell bodies in the perikaryon layer of the medulla externa neurons and the neuropile of the medulla. The fibres from the medulla externa to the lamina come from T-shaped neurons and emanate from the perikaryon layer side, entering the lamina on its neuropile side. The fibre relations between the medulla externa and the medulla interna are similar. Thus in both cases, chiasmata are present from the beginning, but they become obvious when the medulla externa rotates through part of a circle.The directed growth of the optic neuropiles and the course of the fibre connexions are consequently crucial to the understanding of the topographic relations between the neuropiles. A pattern with short neurons connecting neighbouring optic neuropiles and long neurons connecting the medulla externa with the central nervous system is common to all crustaceans.In memoriam Bertil Hanström.This work has been supported by a grant from the Swedish Natural Science Research Council 2760-3, 99-35.     

The Origin of the Vertebrate Eye

In his considerations of “organs of extreme perfection,” Charles Darwin described the evidence that would be necessary to support the evolutionary origin of the eye, namely, demonstration of the existence of “numerous gradations” from the most primitive eye to the most perfect one, where each such tiny change had provided a survival advantage (however slight) to the organism possessing the subtly altered form. In this paper, we discuss evidence indicating that the vertebrate eye did indeed evolve through numerous subtle changes. The great majority of the gradual transitions that did occur have not been preserved to the present time, either in the fossil record or in extant species; yet clear evidence of their occurrence remains. We discuss the remarkable “eye” of the hagfish, which has features intermediate between a simple light detector and an image-forming camera-like eye and which may represent a step in the evolution of our eye that can now be studied by modern methods. We also describe the important clues to the evolutionary origin of the vertebrate eye that can be found by studying the embryological development of our own eye, by examining the molecular genetic record preserved in our own genes and in the genes of other vertebrates, and through consideration of the imperfections (or evolutionary “scars”) in the construction of our eye. Taking these findings together, it is possible to discuss in some detail how the vertebrate eye evolved.     

Origin and occurrence of sexual and mating systems in Crustacea: A progression towards communal living and eusociality

Crustaceans are known for their unrivalled diversity of sexual systems, as well as peculiar mating associations to achieve maximum mating success and fertilization accomplishment. Although sexes are separate in most species, various types of hermaphroditism characterize these predominantly aquatic arthropods. A low operational sex ratio between female and male, together with temporally limited receptivity of females towards males, imposes restrictions on the structuring of mating systems in crustaceans. The basic mating systems consist of monogamy, polygamy, mate guarding and pure searching. Understandably, ecological influences may also play a determinative role in the evolution of such sexual and mating systems in crustaceans. An important outcome of the crustacean sexual biology is the development of complex social structures in many aquatic species, in much the same way insects have established them in terrestrial conditions. In addition, groups like isopods and certain families of brachyuran crabs have shown terrestrial adaptation, exhibiting peculiar reproductive modes, sometimes reminiscent of their terrestrial counterparts, insects. Many caridean shrimps, living in symbiotic relationship with other marine invertebrates in the coral reef habitats, have reached pinnacle of complexity in sexuality and peculiar mating behaviours, resulting in communal living and establishing advanced social systems, such as eusociality.