Sensory ecology: giant eyes for giant predators?

Mathematical models suggest the enormous eyes of giant and colossal squid evolved to see the bioluminescence induced by the approach of predatory whales.     

Molecular phylogeny of Megaloceros giganteus--the giant deer or just a giant red deer?

Two fragments of mitochondrial DNA (mtDNA) of the cytochrome b gene (137 bp and 167 bp) were successfully isolated and sequenced from antlers and bones of five specimens of the Giant Deer (Megaloceros giganteus) to examine the phylogenetic position of Megaloceros giganteus within the family Cervidae. This is the first report on ancient DNA (aDNA) sequences from Megaloceros giganteus. A phylogenetic analysis based on parameter-rich models describes the evolutionary relationships between five individuals of fossil Megaloceros giganteus and 37 individuals of 11 extant species of the family Cervidae. The results support a "Cervus-Megaloceros" clade. The phylogenetic positions of sympatric Megaloceros and Cervus elaphus specimens in particular indicate either that the Megaloceros mtDNA gene pool did not evolve for a substantial time period as an entity distinct from Cervus elaphus until its extinction, or that Megaloceros contributed mtDNA to Cervus elaphus or vice versa. The results of this study allow the conclusion that the European Megaloceros giganteus is more related to its modern regional counterparts of the species of Cervus elaphus than recent claims have suggested.     

A giant step towards artificial life?

Step by step, the components of an artificial form of cellular life are being assembled by researchers. Lipid vesicles the size of small bacteria can be prepared and under certain conditions are able to grow and divide, then grow again. Polymerase enzymes encapsulated in the vesicles can synthesize RNA from externally added substrates. Most recently, the entire translation apparatus, including ribosomes, has been captured in vesicles. Substantial amounts of proteins were produced, including green fluorescent protein used as a marker for protein synthesis. Can we now assemble a living cell? Not quite yet because no one has produced a polymerase that can be reproduced along with growth of the other molecular components required by life. But we are closer than ever before.     

What does the giant squid Architeuthis dux eat?

Architeuthis dux diet has been analysed according to information available from literature and from the analysis of gut contents of five females and two males from Mediterranean and Atlantic Iberian waters (20 specimens in total). This is the first time that A. dux diet from Atlantic and Mediterranean waters is described. Body weight of specimens ranged from 22.5 to 200 kg. In order to infer common patterns in giant squid diet according to its geographic distribution range, size and sex, available data on their diet composition structure were joined and examined with multivariate techniques. No significant differences in the trophic level on which A. dux prey on were found, considering size, sex and location. Thus, A. dux seems to play the same role in the trophic webs throughout the distribution range examined in this paper, which takes up a very wide geographic area. The trophic level estimated from the diet composition is 4.7. Obtained results show that this species preys mainly on pelagic fast swimmers and shoaling fishes and cephalopods as an opportunistic ambushing hunter.     

Phylogeography and history of giant Galápagos tortoises

Abstract.— We examined the phylogeography and history of giant Galàpagos tortoise populations based on mito-chondrial DNA sequence data from 161 individuals from 21 sampling sites representing the 11 currently recognized extant taxa. Molecular clock and geological considerations indicate a founding of the monophyletic Galàpagos lineage around 2–3 million years ago, which would allow for all the diversification to have occurred on extant islands. Founding events generally occurred from geologically older to younger islands with some islands colonized more than once. Six of the 11 named taxa can be associated with monophyletic maternal lineages. One, Geochelone porteri on Santa Cruz Island, consists of two distinct populations connected by the deepest node in the archipelago-wide phylogeny, whereas tortoises in northwest Santa Cruz are closely related to those on adjacent Pinzón Island. Volcan Wolf, the northernmost volcano of Isabela Island, consists of both a unique set of maternal lineages and recent migrants from other islands, indicating multiple colonizations possibly due to human transport or multiple colonization and partial elimination through competition. These genetic findings are consistent with the mixed morphology of tortoises on this volcano. No clear genetic differentiation between two taxa on the two southernmost volcanoes of Isabela was evident. Extinction of crucial populations by human activities confounds whether domed versus saddleback carapaces of different populations are mono- or polyphyletic. Our findings revealed a complex phylogeography and history for this tortoise radiation within an insular environment and have implications for efforts to conserve these endangered biological treasures.     

Pharmacological characteristics of four giant neurons identified in the cerebral ganglia of an African giant snail (Achatina fulica Férussac)

Two giant neurons, d-RCDN (dorsal-right cerebral distinct neuron) and d-LCDN (dorsal left cerebral distinct neuron), with a diameter of about 100 microns, were found symmetrically on the dorsal surface of the cerebral ganglia of an African giant snail (Achatina fulica Férussac). They showed spontaneous spike discharges at a stable frequency. Two giant neurons, v-RCDN (ventral-right cerebral distinct neuron) and v-LCDN (ventral-left cerebral distinct neuron), (diameter, approx. 150 microns) were identified on the ventral surface of the same ganglia. No spontaneous spike discharges were evident. Both d-RCDN and d-LCDN were equally inhibited by dopamine, octopamine, 5-hydroxytryptamine and histamine. Acetylcholine sometimes showed inhibitory effects, but they were not so stable. No substance having excitatory effects on the neurons was found. Both v-RCDN and v-LCDN were equally excited by octopamine, 5-hydroxytryptamine, GABA and acetylcholine and inhibited by dopamine and beta-hydroxy-L-glutamic acid.     

Further study of effects of synthetic peptides on identifiable giant neurones of an african giant snail (Achatina fulica Férussac)

• 1.1. Effects of the following peptides at 10⁻⁴ M on identifiable giant neurones of Achatina fulica Férussac were examined: physalaemin, eledoisin, bradykinin, neurokinin A, neurokinin B, neuromedin B, gastrin releasing peptide decapeptide (neuromedin C), gastrin releasing peptide (14–27), cholecystokinin tetrapeptide, cholecystokinin octapeptide, thyrotropin releasing hormone, Arg-vasotocin, γ-melanocyte stimulating hormone.
• 2.2. The six neurones tested were as follows: PON (periodically oscillating neurone), TAN (tonically autoactive neurone), RAPN (right anterior pallial neurone), d-RPLN (dorsal-right parietal large neurone), VIN (visceral intermittently firing neurone) and d-VLN (dorsal-visceral large neurone).
• 3.3. Of the peptides examined, only Arg-vasotocin at 10⁻⁴ M produced the excitatory effects on PON, VIN and d-VLN. Physalaemin showed slight inhibitory effects on TAN; this substance was sometimes almost ineffective on the neurone.
• 4.4. The other peptides examined were completely ineffective on all of the neurones tested.

     

Further study of effects of synthetic peptides on identifiable giant neurones of an African giant snail (Achatina fulica Férussac)

1. Effects of the following peptides at 10(-4) M on identifiable giant neurones of Achatina fulica Férussac were examined: physalaemin, eledoisin, bradykinin, neurokinin A, neurokinin B, neuromedin B, gastrin releasing peptide decapeptide (neuromedin C), gastrin releasing peptide (14-27), cholecystokinin tetrapeptide, cholecystokinin octapeptide, thyrotropin releasing hormone, Arg-vasotocin, gamma-melanocyte stimulating hormone. 2. The six neurones tested were as follows: PON (periodically oscillating neurone), TAN (tonically autoactive neurone), RAPN (right anterior pallial neurone), d-RPLN (dorsal-right parietal large neurone), VIN (visceral intermittently firing neurone) and d-VLN (dorsal-visceral large neurone). 3. Of the peptides examined, only Arg-vasotocin at 10(-4) M produced the excitatory effects on PON, VIN and d-VLN. Physalaemin showed slight inhibitory effects on TAN; this substance was sometimes almost ineffective on the neurone. 4. The other peptides examined were completely ineffective on all of the neurones tested.     

Effects of synthetic peptides on giant neurons identified in the ganglia of an African giant snail (Achatina fulica Férussac)--II

Thirteen synthetic biologically-active peptides, which were classified into the peptides proposed as neurotransmitters in mammals and invertebrates and neural venom peptides, were investigated for their effects on the following six identifiable giant neurons of an African giant snail (Achatina fulica Férussac): RAPN (right anterior pallial neuron), INN (intestinal nerve neuron), RPeNLN (right pedal nerve large neuron), LPeNLN (left pedal nerve large neuron), d-LPeLN (dorsal-left pedal large neuron) and d-LPeCN (dorsal-left pedal constantly firing neuron). Oxytocin and proctolin at 10(-4)M excited the RAPN membrane potential, whereas FMRFamide at the same concentration inhibited the same neuron. FMRFamide at 10(-4)M markedly inhibited the d-LPeLN membrane potential, sometimes produced inhibition of RPeNLN and LPeNLN, showed varied effects (excitatory or inhibitory) on INN, and had no effect on d-LPeCN. The other peptides examined had almost no effect on any of the neurons tested.     

Identification and pharmacological characteristics of giant neurones situated in the buccal ganglia of an African giant snail (Achatina fulica Férussac)

1. The following four giant neurones were identified on the dorsal surface of the left buccal ganglion of an African giant snail (Achatina fulica Ferussac): d-LBAN (dorsal-left buccal anterior neurone), d-LBMN (dorsal-left buccal medial neurone), d-LBCN (dorsal-left buccal central neurone) and d-LBPN (dorsal-left buccal posterior neurone). The axonal pathways of the neurones were studied by the intracellular injection of Lucifer Yellow; their pharmacological characteristics with respect to common putative neurotransmitters were also investigated.2. The axonal pathways of d-LBAN and d-LBCN were simple, innervating some left lateral buccal nerves or the left accessory connective buccal nerve. On the other hand, those of d-LBMN and d-LBPN were much more widespread, projecting not only to the left buccal nerves, but also to the right buccal nerves through the buccal commissure.3. No direct axonal pathway from any of the four buccal neurones tested to the other ganglioncomplexes through the cerebral buccal connectives was demonstrated.4. The pharmacological characteristics of the four neurones tested were not identical. Only 5-hydroxytryptamine excited all of the neurones, whereas dopamine, l-epinephrine and acetylcholine inhibited all of them. However, the other effective substances, such as dl-octopamine, GABA, l-homocysteic acid, erythro-β-hydroxy-l-glutamic acid and histamine, were either excitatory or inhibitory according to the neurone.     

Squid giant axons. A model for the neuron soma?

Insertion of electrically floating wires along the axis of a squid giant axon produces an apparent increase in diameter in the region where the wire surface has been treated to give it a low resistance. The shape of action potentials propagating into this region depend upon the surface resistance (and the length) of the wire. As this segment's internal resistance is lowered by reducing the wire's surface resistance, the following characteristic sequence of changes in the action potential is seen at the transition region: (a) the duration increases; (b) two peaks develop, the first one generated in the normal axon region and the second one generated later in the axial wire region, and; (c) blockage occurs (for a very low resistance wire). Action potentials recorded at the membrane region near the tip of the axial wire in (b) resemble those recorded at the initial segment of neurons upon antidromic invasions. Squid axon action potentials propagated from a normal region into that containing the low resistance wire also resemble antidromic invasions recorded in neuron somas. Hyperpolarizing current pulses applied through the wire act as if the wire surface resistance was momentarily reduced. For example, the two components of the action potential recorded at the axial wire membrane region noted in (b) can be sequentially blocked by the application of increasing hyperpolarizing current through the wire. Similar effects are seen when hyperpolarizing currents are injected into motoneuron somas. It is concluded that the geometrical properties of the junction of a neuron axon with its soma may be in themselves sufficient to determine the shape of the action potentials usually recorded by microelectrodes.     

How long would it take to become a giant squid?

Laboratory and field studies suggest that cephalopod growth occurs rapidly and is linked to temperature throughout a short life span. For giant squid such as Architeuthis, a paucity of size-at-age data means that growth is only inferred from isolated field specimens, based on either statoliths or isotopic analyses of tissue. In this study we apply simple growth models to obtain projections of the life span required to achieve the Architeuthis average body mass in scenarios which include an energy balance between rates of food intake and expenditure on growth and metabolism. Although the analysis shows that a wide range for the estimated life span is possible, energy conservation suggests that achievement of a larger size would be assisted by slower exponential growth early on. The results are compared with a sparse set of size-at-age data obtained from male and female Architeuthis wild specimens and possibly hint at some behavioural differences between males and females.     

The Mrp system: a giant among monovalent cation/proton antiporters?

Mrp systems are a novel and broadly distributed type of monovalent cation/proton antiporter of bacteria and archaea. Monovalent cation/proton antiporters are membrane transport proteins that catalyze efflux of cytoplasmic sodium, potassium or lithium ions in exchange for external hydrogen ions (protons). Other known monovalent cation antiporters are single gene products, whereas Mrp systems have been proposed to function as hetero-oligomers. A mrp operon typically has six or seven genes encoding hydrophobic proteins all of which are required for optimal Mrp-dependent sodium-resistance. There is little sequence similarity of Mrp proteins to other antiporters but three of these proteins have significant sequence similarity to membrane embedded subunits of ion-translocating electron transport complexes. Mrp antiporters have essential roles in the physiology of alkaliphilic and neutralophilic Bacillus species, nitrogen-fixing Sinorhizobium meliloti and in the pathogen Staphylococcus aureus, although these bacteria contain multiple monovalent cation/proton antiporters. The wide distribution of Mrp systems leads to the anticipation of important roles in an even wider variety of pathogens, extremophiles and environmentally important organisms. Here, the distribution, established physiological roles and catalytic activities of Mrp systems are reviewed, hypotheses regarding their complexity are discussed and major open questions about their function are highlighted.     

Axonal pathways of giant neurons identified in the right parietal and visceral ganglia in the suboesophageal ganglia of an African giant snail (Achatina fulica Férussac)

• 1.1. The axonal pathways of thirteen giant neurons identified in the right parietal and the visceral ganglia, found in the suboesophageal ganglia of an African giant snail (Achatina fulica Férussac), were investigated by intracellular injections of Lucifer Yellow, with regard to their axonal projections into the following six peripheral nerves: lap n (left anterior palliai nerve), lpp n (left posterior palliai nerve), int n (intestinal nerve), anal n (anal nerve), rpp n (right posterior palliai nerve) and rap n (right anterior palliai nerve).
• 2.2. These projections were confirmed by the recording of the axonal responses from the nerves.
• 3.3. On the dorsal surface of the right parietal ganglion, the following four giant neurons were identified: PON (periodically oscillating neuron), TAN (tonically autoactive neuron), RAPN (right anterior palliai neuron), and d-RPLN (dorsal-right parietal large neuron).
• 4.4. The PON axonal pathways projected into int n; those of TAN into all of the nerves examined; those of RAPN into lap n, lpp n, int n, anal n and rap n.; and those of d-RPLN into pd nn (pedal nerves) through the pedal ganglia, lpp n, anal n, rap n and sometimes lap n.
• 5.5. On the dorsal surface of the visceral ganglion, the following four giant neurons were also identified: VIN (visceral intermittently firing neuron), FAN (frequently autoactive neuron), INN (intestinal nerve neuron) and d-VLN (dorsal-visceral large neuron).
• 6.6. The VIN axonal pathways, which had no branch into the six nerves examined, went to both the right and the left pedal ganglia, sending a branch into the cerebro-pleural connective; those of FAN projected into lap n, anal n and rap n, and sometimes into lpp n and rpp n; those of INN into int n; and those of d-VLN into pd nn, lap n, lpp n, anal n and rap n.
• 7.7. On the ventral surface of the right parietal ganglion, v-RPLN (ventral-right parietal large neuron) was identified. The axonal pathways went to pd nn, lap n, lpp n, anal n and rap n.
• 8.8. On the ventral surface of the visceral ganglion, the four giant neurons, v-VNAN (ventral-visceral noisy autoactive neuron), v-VLN (ventral-visceral large neuron), r-VMN (right-visceral multiple spike neuron) and 1-VMN (left-visceral multiple spike neuron) were identified.
• 9.9. The axonal pathway of v-VNAN projected into rpp n and rap n; those of v-VLN into pd nn, lap n, anal n, rap n and sometimes to lpp n; those of r-VMN into int n and rpp n; and those of 1-VMN also into int n and rpp n.
• 10.10. The present morphologial investigations of the giant neurons confirmed well the identifications of the neurons previously studied. The axon of the neurons examined here, except for VIN, projected into some of the peripheral nerves, while the VIN axon extended into the cerebro-pleural connective.
• 11.11. The five neurons, PON, TAN, v-VNAN, r-VMN and 1-VMN, formed fine axonal arborizations terminating at the neuropile, while the arborizations of the other neurons were not clearly observed.
• 12.12. Although the anatomical structures of the portion examined of the suboesophageal ganglia are asymmetrical, three pairs of symmetrically-situated neurons, d-RPLN and d-VLN, v-RPLN and v-VLN, and r-VMN and 1-VMN, were found, indicating the existence of symmetrical components in the ganglia.

     

Microsatellite analysis of genetic divergence among populations of giant Galápagos tortoises

Giant Galápagos tortoises represent an interesting model for the study of patterns of genetic divergence and adaptive differentiation related to island colonization events. Recent mitochondrial DNA work elucidated the evolutionary history of the species and helped to clarify aspects of nomenclature. We used 10 microsatellite loci to assess levels of genetic divergence among and within island populations. In particular, we described the genetic structure of tortoises on the island of Isabela, where discrimination of different taxa is still subject of debate. Individual island populations were all genetically distinct. The island of Santa Cruz harboured two distinct populations. On Isabela, populations of Volcan Wolf, Darwin and Alcedo were significantly different from each other. On the other hand, Volcan Wolf showed allelic similarity with the island of Santiago. On Southern Isabela, lower genetic divergence was found between Northeast Sierra Negra and Volcan Alcedo, while patterns of gene flow were recorded among tortoises of Cerro Azul and Southeast Sierra Negra. These tortoises have endured heavy exploitation during the last three centuries and recently attracted much concern due to the current number of stochastic and deterministic threats to extant populations. Our study complements previous investigation based on mtDNA diversity and provides further information that may help devising tortoise management plans.     

Genetic analysis of a successful repatriation programme: giant Galápagos tortoises

As natural populations of endangered species dwindle to precarious levels, remaining members are sometimes brought into captivity, allowed to breed and their offspring returned to the natural habitat. One goal of such repatriation programmes is to retain as much of the genetic variation of the species as possible. A taxon of giant Galápagos tortoises on the island of Espa?ola has been the subject of a captive breeding-repatriation programme for 33 years. Core breeders, consisting of 12 females and three males, have produced more than 1200 offspring that have been released on Espa?ola where in situ reproduction has recently been observed. Using microsatellite DNA markers, we have determined the maternity and paternity of 132 repatriated offspring. Contributions of the breeders are highly skewed. This has led to a further loss of genetic variation that is detrimental to the long-term survival of the population. Modifications to the breeding programme could alleviate this problem.