Invertebrate Biology 

About: Invertebrate Biology is an academic journal published by Wiley. The journal publishes majorly in the area(s): Population & Biology. It has an ISSN identifier of 1077-8306. Over the lifetime, 968 publications have been published receiving 17475 citations.

On bivalve phylogeny: a high‐level analysis of the Bivalvia (Mollusca) based on combined morphology and DNA sequence data

Abstract: . Bivalve classification has suffered in the past from the crossed-purpose discussions among paleontologists and neontologists, and many have based their proposals on single character systems. More recently, molecular biologists have investigated bivalve relationships by using only gene sequence data, ignoring paleontological and neontological data. In the present study we have compiled morphological and anatomical data with mostly new molecular evidence to provide a more stable and robust phylogenetic estimate for bivalve molluscs. The data here compiled consist of a morphological data set of 183 characters, and a molecular data set from 3 loci: 2 nuclear ribosomal genes (18S rRNA and 28S rRNA), and 1 mitochondrial coding gene (cytochrome c oxidase subunit I), totaling ∼3 Kb of sequence data for 76 molluscs (62 bivalves and 14 outgroup taxa). The data have been analyzed separately and in combination by using the direct optimization method of Wheeler (1996), and they have been evaluated under 12 analytical schemes. The combined analysis supports the monophyly of bivalves, paraphyly of protobranchiate bivalves, and monophyly of Autolamellibranchiata, Pteriomorphia, Heteroconchia, Palaeoheterodonta, and Heterodonta s.l., which includes the monophyletic taxon Anomalodesmata. These analyses strongly support the conclusion that Anomalodesmata should not receive a class status, and that the heterodont orders Myoida and Veneroida are not monophyletic. Among the most stable results of the analysis are the monophyly of Palaeoheterodonta, grouping the extant trigoniids with the freshwater unionids, and the sister-group relationship of the heterodont families Astartidae and Carditidae, which together constitute the sister taxon to the remaining heterodont bivalves. Internal relationships of the main bivalve groups are discussed on the basis of node support and clade stability.

Cladistic analysis of Medusozoa and cnidarian evolution

Abstract: . A cladistic analysis of 87 morphological and life history characters of medusozoan cnidarians, rooted with Anthozoa, results in the phylogenetic hypothesis (Anthozoa (Hydrozoa (Scyphozoa (Staurozoa, Cubozoa)))). Staurozoa is a new class of Cnidaria consisting of Stauromedusae and the fossil group Conulatae. Scyphozoa is redefined as including those medusozoans characterized by strobilation and ephyrae (Coronatae, Semaeostomeae, and Rhizostomeae). Within Hydrozoa, Limnomedusae is identified as either the earliest diverging hydrozoan lineage or as the basal group of either Trachylina (Actinulida (Trachymedusae (Narcomedusae, Laingiomedusae))) or Hydroidolina (Leptothecata (Siphonophorae, Anthoathecata)). Cladistic results are highly congruent with recently published phylogenetic analyses based on 18S molecular characters. We propose a phylogenetic classification of Medusozoa that is consistent with phylogenetic hypotheses based on our cladistic results, as well as those derived from 18S analyses. Optimization of the characters presented in this analysis are used to discuss evolutionary scenarios. The ancestral cnidarian probably had a sessile biradial polyp as an adult form. The medusa is inferred to be a synapomorphy of Medusozoa. However, the ancestral process (metamorphosis of the apical region of the polyp or lateral budding involving an entocodon) could not be inferred unequivocally. Similarly, character states for sense organs and nervous systems could not be inferred for the ancestral medusoid of Medusozoa.

Dormancy in invertebrates

Abstract: The ability to survive in a dormant state is a widespread, yet unevenly distributed feature among invertebrates. Organisms belonging to classes and phyla that include fresh-water or terrestrial representatives are more likely to possess a dormant stage than those in groups that are exclusively marine. Moreover, within taxa where dormancy has evolved, it is more common among fresh-water and terrestrial species than in marine species. This correlation between dormancy and habitat across 29 free-living invertebrate phyla raises the question of cause and effect. Are dormant stages more commnon in fresh-water and terrestrial habitats because there is greater selection for dormancy in those environments, or is dormancy a prerequisite for the successful invasion of non-marine systems? The mechanism of dormancy varies among species and ranges from a specialized diapausing embryo to a quiescent adult. Dormancy has most likely arisen multiple times in invertebrate life histories, both within and between phyla. Although dormancy may facilitate the invasion of fresh-water and terrestrial habitats, it is not always a requirement: many non-marine species do not exhibit dormancy. Additional key words: diapause, quiescence, life history, fresh-water, marine All natural environments vary, and organisms may occasionally experience conditions that are limiting for growth, survival, or reproduction. The form and nature of this variability differ among habitats, however, and this has led to the evolution of a wide array of life histories (reviewed by Roff 1992; Stearns 1992). For example, some species are iteroparous and offset the negative effects of temporal variation with long-lived adults that reproduce multiple times (Murphy 1968; Goodman 1984). Alternatively, other organisms avoid deleterious environmental conditions with reliable migration (Dingle 1978; Levin et al. 1984; Wiener & Tuljapurkar 1994). However, many species without either of these traits persist in variable environments. Often, these taxa inhabit relatively isolated, transient systems that can support life only for a fraction of the year (e.g., arctic tundra, deserts, temporary ponds). When organisms cannot migrate away from declining environmental conditions, and active adults cannot survive, the only viable option is persistence through dormancy. Dormancy has evolved in numerous bacterial, fungal, protist, plant, and animal species, but is completely unknown in many groups. Although all forms result a Present address: Illinois Natural History Survey, Champaign, IL 61820, USA. Voice: 217-244-2139. Fax: 217333-6294. E-mail: caceres@mail.inhs.uiuc.edu in some type of metabolic and/or developmental depression, the term "dormancy" actually encompasses a wide range of physiological states (see Hand 1991). Therefore, the form and duration of the dormant state vary widely among taxa. Whereas some species remain dormant only as long as conditions are unfavorable, others remain dormant for time periods much longer than the unfavorable environmental conditions, in :some cases for a century or more (Harper & White 1974; Henis 1987; Hairston et al. 1995; Caiceres 1997). ]Dormancy that extends beyond the duration of the environmental hardship introduces potential costs and benefits. When dormancy is not terminated upon the return of favorable conditions, there is the potential cost of lost reproduction. However, when the dormant prcpagules from a single cohort continue to introduce recruits into the active population for several years, populations of short-lived adults can sample different environments much in the same way as a long-lived iteroparous species (Seger & Brockmann 1987). Thus, overlapping generations are established in populations that might otherwise consist of discrete cohorts (Templeton & Levin 1979). ]In theory, the evolution of prolonged dormancy should be an alternative to either iteroparity or dispersal (Venable & Lawlor 1980; Levin et al. 1984; Rees 1994). In fact, these alternative life histories have been found in some natural systems. Rees (1993), in This content downloaded from 157.55.39.127 on Wed, 29 Jun 2016 04:32:53 UTC All use subject to http://about.jstor.org/terms

Choanoflagellates, choanocytes, and animal multicellularity

Abstract: . It is widely accepted that multicellular animals (metazoans) constitute a monophyletic unit, deriving from ancestral choanoflagellate-like protists that gave rise to simple choanocyte-bearing metazoans. However, a re-assessment of molecular and histological evidence on choanoflagellates, sponge choanocytes, and other metazoan cells reveals that the status of choanocytes as a fundamental cell type in metazoan evolution is unrealistic. Rather, choanocytes are specialized cells that develop from non-collared ciliated cells during sponge embryogenesis. Although choanocytes of adult sponges have no obvious homologue among metazoans, larval cells transdifferentiating into choanocytes at metamorphosis do have such homologues. The evidence reviewed here also indicates that sponge larvae are architecturally closer than adult sponges to the remaining metazoans. This may mean that the basic multicellular organismal architecture from which diploblasts evolved, that is, the putative planktonic archimetazoan, was more similar to a modern poriferan larva lacking choanocytes than to an adult sponge. Alternatively, it may mean that other metazoans evolved from a neotenous larva of ancient sponges. Indeed, the Porifera possess some features of intriguing evolutionary significance: (1) widespread occurrence of internal fertilization and a notable diversity of gastrulation modes, (2) dispersal through architecturally complex lecithotrophic larvae, in which an ephemeral archenteron (in dispherula larvae) and multiciliated and syncytial cells (in trichimella larvae) occur, (3) acquisition of direct development by some groups, and (4) replacement of choanocyte-based filter-feeding by carnivory in some sponges. Together, these features strongly suggest that the Porifera may have a longer and more complicated evolutionary history than traditionally assumed, and also that the simple anatomy of modern adult sponges may have resulted from a secondary simplification. This makes the idea of a neotenous evolution less likely than that of a larva-like choanocyte-lacking archimetazoan. From this perspective, the view that choanoflagellates may be simplified sponge-derived metazoans, rather than protists, emerges as a viable alternative hypothesis. This idea neither conflicts with the available evidence nor can be disproved by it, and must be specifically re-examined by further approaches combining morphological and molecular information. Interestingly, several microbial lin°Cages lacking choanocyte-like morphology, such as Corallochytrea, Cristidiscoidea, Ministeriida, and Mesomycetozoea, have recently been placed at the boundary between fungi and animals, becoming a promising source of information in addition to the choanoflagellates in the search for the unicellular origin of animal multicellularity.

Advertisement and concealment in the plankton: what makes a copepod hydrodynamically conspicuous?

Abstract: Euchaeta rimana, a pelagic marine copepod, roams a 3-dimensional environment and its antennular setal sensors are oriented to detect water-borne signals in 3 dimensions. When the copepod moves through water or moves water around itself, it creates a fluid dis- turbance distinct from the ambient fluid motion. As it swims and hovers, the copepod's laminar feeding current takes the unstable nature of small-scale turbulence, organizes it, and makes the local domain a familiar territory within which signals can be specified in time and space. The streamlines betray both the 3-dimensional spatial location (x, y, z) as well as the time (t) separating a signal caught in the feeding current and the copepod receptor-giving the copepod early warning of the approach of a prey, predator, or mate. The copepod reduces the complexity of its environment by fixing information from a turbulent field into a simpler, more defined laminar field. We quantitatively analysed small-scale fluid deformations created by copepods to document the strength of the signal. Physiological and behavioral tests confirm (a) that these disturbances are relevant signals transmitting information between zooplankters and (b) that hydrodynami- cally conspicuous structures, such as feeding currents, wakes, and vibrations, elicit specific responses from copepods. Since fluid mechanical signals do elicit responses, copepods shape their fluid motion to advertise or to conceal their hydrodynamic presence. When swimming, a copepod barely leaves a trace in the water; the animal generates its flow and advances into the area from which the water is taken, covering up its tracks with the velocity gradient it creates around itself. When escaping, it sheds conspicuous vortices. Prey caught in a flow field expose their location by hopping. These escape hops shed jet-like wakes detected by copepod mech- anoreceptors. Copepods recognize the wakes and respond adaptively.