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Cerebrovascular organization and dynamics in cephalopods

N. Joan Abbott and J. A. Miyan

in Cephalopod Neurobiology: Neuroscience Studies in Squid, Octopus and Cuttlefish

This chapter reviews the anatomy and physiology of the cerebral circulation in cephalopods, and its behaviour in experimental preparations. Cephalopods have a closed vasculature, and the arrangement ... More

This chapter reviews the anatomy and physiology of the cerebral circulation in cephalopods, and its behaviour in experimental preparations. Cephalopods have a closed vasculature, and the arrangement of cerebral arteries, arterioles, capillaries, and veins follows a similar pattern to that of vertebrates, with some differences at the electron microscopic level. ‘Gliovascular’ channels may act as routes for flow of interstitial fluid while ‘lymphoid’ channels return the fluid to the venous system. Cephalopod molluscs are the only invertebrate animal group to possess a fully closed vascular system in which a substantial hydrostatic pressure is generated by the heart. However, the relative inefficiency of cephalopod haemocyanin compared with vertebrate haemoglobin as blood oxygen transport protein means that the cephalopod vascular system is forced to work close to its physiological limits. The cardiovascular specializations that are necessary to maintain tissue oxygen supply in cephalopods give instructive insights into basic principles of cardiovascular physiology. Cephalopod neural tissue, in common with neural tissues in most animal groups, maintains a high metabolic rate and a predominantly aerobic metabolism, requiring efficient supply of oxygen and aerobic substrates from the blood. Comparison of the vascularity of brain and non-brain tissues and study of regional differences within the brain can highlight important aspects of neural metabolism.Less

The statocysts of cephalopods

Roddy Williamson

in Cephalopod Neurobiology: Neuroscience Studies in Squid, Octopus and Cuttlefish

This chapter details statocysts of cephalopods. The statocysts of most cephalopods are sense organs of great sophistication with macula/statolith systems that respond to gravity and crista/cupula ... More

This chapter details statocysts of cephalopods. The statocysts of most cephalopods are sense organs of great sophistication with macula/statolith systems that respond to gravity and crista/cupula systems operating as angular velocity transducers. Cephalopod statocysts, unlike those of most other invertebrates, have both primary and secondary sensory hair cells that have a unidirectional morphological and physiological polarization. Within the central nervous system, the sensory input from the statocysts is integrated into a variety of behaviors, including locomotion, posture, control of eye movements, and control of body-colour pattern. The sensory solutions to the problems of balance and orientation that cephalopods and vertebrates have evolved show close parallels. It is anticipated that a comparison of these two systems will give a greater understanding of the basic mechanisms which are important for the operation of all such sensory systems. Recent research has not only confirmed the statocysts as detectors of linear and angular accelerations, but has shown that their level of performance and sophistication rivals other such systems in the animal kingdom, including the human vertebrate vestibular system. Within the living cephalopod groups there are three main types of statocysts, discussed in detail in the chapter.Less

Retina and Optic Centers of Cephalopods

Javier DeFelipe

in Cajal's Neuronal Forest: Science and Art

This section contains a gallery of original Cajal drawings pertaining to the retina and optic centers in cephalopods.

Towards a Model for Speciation in Ammonoids

Margaret M. Yacobucci

in Species and Speciation in the Fossil Record

Ammonoid cephalopods show a remarkably high rate of speciation when compared to other metazoans although the drivers of this evolutionary volatility are not clear. Ammonoid evolution is characterized ... More

Ammonoid cephalopods show a remarkably high rate of speciation when compared to other metazoans although the drivers of this evolutionary volatility are not clear. Ammonoid evolution is characterized by high degrees of homeomorphy, heterochrony, and other patterns that reveal a flexible developmental growth program. Ammonoid biodiversity through time appears to be linked to major environmental changes, particularly sea level change. The model of speciation presented synthesizes these observations with contemporary views on ecological speciation, emphasizing the role of developmental flexibility in permitting the rapid production of new anatomical variants that then sort into ecological niches and diverge. In this model, a newly formed habitat space plays host to the rapid endemic radiation of ammonoids from one or a few ancestral species. Anatomical variants are produced via changes in developmental timing and then sort into different niches based on microhabitats within the environment. Assortative mating and disruptive selection lead to reproductive isolation and speciation among these morphs. The same processes will occur each time sea level rises; given developmental constraints on shell form, homeomorphic species will result. More data on the phylogeny, biogeography, ecology, and developmental flexibility of ammonoids, will allow us to test this speciation model in other ammonoid clades.Less

Effects of Ocean Acidification on Nektonic Organisms

Hans-O. Pörtner and Magda Gutowska

in Ocean Acidification

The average surface-ocean pH is reported to have declined by more than 0.1 units from the pre-industrial level ( Orr et al. 2005 ), and is projected to decrease by another 0.14 to 0.35 units by the ... More

The average surface-ocean pH is reported to have declined by more than 0.1 units from the pre-industrial level ( Orr et al. 2005 ), and is projected to decrease by another 0.14 to 0.35 units by the end of this century, due to anthropogenic CO2 emissions (Caldeira and Wickett 2005 ; see also Chapters 3 and 14). These global-scale predictions deal with average surface-ocean values, but coastal regions are not well represented because of a lack of data, complexities of nearshore circulation processes, and spatially coarse model resolution (Fabry et al. 2008 ; Chapter 3 ). The carbonate chemistry of coastal waters and of deeper water layers can be substantially different from that in surface water of offshore regions. For instance, Frankignoulle et al. ( 1998 ) reported pCO2 (note 1) levels ranging from 500 to 9400 μatm in estuarine embayments (inner estuaries) and up to 1330 μatm in river plumes at sea (outer estuaries) in Europe. Zhai et al. (2005) reported pCO2 values of > 4000 μatm in the Pearl River Estuary, which drains into the South China Sea. Similarly, oxygen minimum layers show elevated pCO2 levels, associated with the degree of hypoxia (Millero 1996). These findings suggest that some coastal and mid-water animals, both pelagic and benthic, are regularly experiencing hypercapnic hypercapnic conditions (i.e. elevated pCO2 levels), that reach beyond those projected in the offshore surface ocean. These organisms might, therefore, be preadapted to relatively high ambient pCO2 levels. The anthropogenic signal will nonetheless be superimposed on the pre-existing natural variability. These phenomena lead to the question of whether future changes in the ocean’s carbonate chemistry pose a serious problem for marine organisms. Those with calcareous skeletons or shells, such as corals and some plankton, have been at the centre of scientific interest. However, elevated CO2 levels may also have detrimental effects on the survival, growth, and physiology of marine animals more generally (Pörtner and Reipschläger 1996; Seibel and Fabry 2003; Fabry et al. 2008; Pörtner 2008; Melzner et al. 2009a). Less

Effects of Ocean Acidification on Marine Biodiversity and Ecosystem Function

James P. Barry and Stephen Widdicombe

in Ocean Acidification

The biodiversity of the oceans, including the striking variation in life forms from microbes to whales and ranging from surface waters to hadal trenches, forms a dynamic biological framework ... More

The biodiversity of the oceans, including the striking variation in life forms from microbes to whales and ranging from surface waters to hadal trenches, forms a dynamic biological framework enabling the flow of energy that shapes and sustains marine ecosystems. Society relies upon the biodiversity and function of marine systems for a wide range of services as basic as producing the seafood we consume or as essential as generating much of the oxygen we breathe. Perhaps most obvious is the global seafood harvest totalling over 100 Mt yr–1 (82 and 20 Mt in 2008 for capture and aquaculture, respectively; FAO 2009) from fishing effort that expands more broadly and deeper each year as fishery stocks are depleted (Pauly et al. 2003). Less apparent ecosystem services linked closely to biodiversity and ecosystem function are waste processing and improved water quality, elemental cycling, shoreline protection, recreational opportunities, and aesthetic or educational experiences (Cooley et al. 2009). There is growing concern that ocean acidification caused by fossil fuel emissions, in concert with the effects of other human activities, will cause significant changes in the biodiversity and function of marine ecosystems, with important consequences for resources and services that are important to society. Will the effects of ocean acidification on ecosystems be similar to those arising from other environmental perturbations observed during human or earth history? Although changes in biodiversity and ecosystem function due to ocean acidification have not yet been widely observed, their onset may be difficult to detect amidst the variability associated with other human and non-human factors, and the greatest impacts are expected to occur as acidification intensifies through this century. In theory, large and rapid environmental changes are expected to decrease the stability and productivity of ecosystems due to a reduction in biodiversity caused by the loss of sensitive species that play important roles in energy flow (i.e. food web function) or other processes (e.g. ecosystem engineers; Cardinale et al. 2006). In practice, however, most research concerning the biological effects of ocean acidification has focused on aspects of the performance and survival of individual species during short-term studies, assuming that a change in individual performance will influence ecosystem function. Less