Predatory Lifestyle Research Articles

Caspase-9 regulates apoptosis/proliferation balance during metamorphic brain remodeling in Xenopus

During anuran metamorphosis, the tadpole brain is transformed producing the sensorial and motor systems required for the frog's predatory lifestyle. Nervous system remodeling simultaneously implicates apoptosis, cell division, and differentiation. The molecular mechanisms underlying this remodeling have yet to be characterized. Starting from the observation that active caspase-9 and the Bcl-X(L) homologue, XR11 are highly expressed in tadpole brain during metamorphosis, we determined their implication in regulating the balance of apoptosis and proliferation in the developing tadpole brain. In situ hybridization showed caspase-9 mRNA to be expressed mainly in the ventricular area, a site of neuroblast proliferation. To test the functional role of caspase-9 in equilibrating neuroblast production and elimination, we overexpressed a dominant-negative caspase-9 protein, DN9, in the tadpole brain using somatic gene transfer and germinal transgenesis. In both cases, abrogating caspase-9 activity significantly decreased brain apoptosis and increased numbers of actively proliferating cells in the ventricular zone. Moreover, overexpression of XR11 with or without DN9 was also effective in decreasing apoptosis and increasing cell division in the tadpole brain. We conclude that XR11 and caspase-9, two key members of the mitochondrial death pathway, are implicated in controlling the proliferative status of neuroblasts in the metamorphosing Xenopus brain. Modification of their expression during the critical period of metamorphosis alters the outcome of metamorphic neurogenesis, resulting in a modified brain phenotype in juvenile Xenopus.

Predatory Mechanisms of Bdellovibrio and Like Organisms

Bdellovibrio and like organisms (BALOs) are predatory, Gram-negative delta-proteobacteria with a complex developmental lifecycle. In the free-living attack phase they are highly motile and seek out prey bacteria that they invade. The ensuing intracellular growth and replication is characterized by the development of a long filament that septates into individual cells that differentiate further into the flagellated attack-phase bacterium. The prey bacterium is lysed and motile predators are released. BALOs have recently been considered to have potential as living antibiotics. The idea of using predatory bacteria as therapeutic agents to combat pathogenic Gram-negative bacteria is intriguing, as they can prey upon human pathogenic bacteria including Salmonella, Pseudomonas and Escherichia coli. However, our current knowledge of the amazing biology of these prokaryotes that cause the systematic destruction of Gram-negative bacteria is still rather limited. More has to be learned about their predatory lifestyle before their application as therapeutic agents will become feasible.

ASPECTS OF THE HINDLIMB MORPHOLOGY OF SOME AUSTRALIAN BIRDS OF PREY: A COMPARATIVE AND QUANTITATIVE STUDY

We quantified the extent of adaptive radiation in the evolution of the hindlimb in the bird-of-prey community on Tasmania. Assessments of the ecological capabilities of raptor species are often based on a visual inspection of their hindlimb structure, with little recourse to direct biomechanical or functional evidence. We examined the links between hindlimb structure and patterns of diet, foraging, and habitat use in raptors by analytically investigating tarsus, toe, and talon measurements. We identified groupings on the basis of dietary preference, hunting-killing technique, and phylogeny. We found that the bird-catching specialists, which possessed relatively long digits with short talons, were consistently separable. The large-mammal and fish specialists were equipped with relatively short and robust tarsi, and short digits with long and robust talons. The hindlimbs of medium-mammal specialists were characterized by long digits and a large digit 1 talon. However, the generalist group did not possess any specializations, because their structural elements were comparable to those of other dietary groups. An association was found between the ratio of toe to talon length and the selective pressures of prey capture and ease of killing. Morphological variation in this feature was consistent with phylogeny, because the Accipitridae were characterized by a larger ratio of toe to talon length on digits 1 and 2 than the Falconidae, and the diurnal raptors possessed an interdigital pattern of larger variation in ratio of toe to talon length than the nocturnal raptors. No link was found between dietary habit and tarsus length or robustness, because these features were apparently attributed to variations in hunting style. Our analysis highlights the interrelationship between the morphology of hindlimb structure and the functional pressures associated with predatory lifestyles. Aspects de la morphologie des membres postérieurs de quelques oiseaux de proie australiens : Une étude comparative et quantitative

Water Balance Components in Adults of Terrestrial Red Mite <I>Balaustium</I> sp. (Acarina: Erythraeidae)

Balaustium spp. mites are noted for their quickness, red color, population bursts, and ubiquity. Water balance characteristics of adults were assessed to determine their primary source of water to gain insight into the biology and physiology of these poorly studied mites. Characteristics of this mite show that it is xeric adapted, featuring a 71% body water content, 39% dehydration tolerance limit, and a modest water loss rate of 2% h−1. This species is unable to absorb water vapor from atmospheric air which is unusual for mites. This is illustrated by net water losses at water vapor activities close to saturation, failure to maintain the uptake after first day passive gains, and no detectable salt accumulation around the base of the mouthparts in scanning electron micrographs. Thus, enhanced water conservation enables this mite to withstand desiccation, and their aggressive predatory life style has apparently not necessitated evolution of an active uptake mechanism for absorption of water vapor for this mite that obtains most of its water from feeding.

The Effects of Acute Temperature Change on Prey Capture Kinematics in Largemouth Bass, Micropterus Salmoides

The effects of temperature on prey capture kinematics were investigated in the Largemouth Bass, Micropterus salmoides. Five individuals were first acclimated to 22 C and then acutely exposed to temperatures of 15, 20, 25, and 30 C. At each temperature, feeding events were recorded using high-speed video at 500 frames s−1. An analysis of variance on the five fastest feeding events from each individual at each temperature resulted in a significant trend for the fastest feeding events to occur at 25 C. This effect confirmed the expectation of thermal dependence of mouth opening movements, which was based on an inverse relationship between water viscosity and temperature and the assumption that temperatures outside optimum decrease muscular power and contraction rates. However, the Q10 value between 15–25 C was only 1.28, well below the minimum expected value of 2.0. Thus, we suggest the possibility that Largemouth Bass partially compensate for the effects of acute temperature changes by recruiting additional motor units at lower temperatures. The capacity of Largemouth Bass to mitigate the impact of acute temperature change on muscle physiology and the physical properties of water may represent a physiological adaptation to a predatory lifestyle in a thermally variable environment.

Transcriptional Activity of the Host-Interaction Locus and a Putative Pilin Gene of Bdellovibrio bacteriovorus in the Predatory Life Cycle

Bdellovibrio bacteriovorus is a predatory bacterium that grows and replicates within the periplasm of a large variety of Gram-negative bacteria. So far, the host-interaction locus (hit locus) is the only genetic locus that is implicated in the obligate predatory lifestyle. Sequence analysis revealed that upstream of the hit locus, the genomic regions of the two obligate predatory B. bacteriovorus-type strains HD100 and HD114 encode genes for pilus formation. As pili might be involved in the invasion process, the transcriptional activity of the hit locus and of a putative pilin gene (flp1) of the pilus cluster were studied in synchronized cultures of B. bacteriovorus with Escherichia coli K-12 as prey bacteria. Stages of the life cycle were monitored with scanning electronic microscopy and transcriptional analyses were performed by quantitative reverse transcription polymerase chain reaction. Our study revealed an increased expression level of the putative hit and flp1 genes in the attack phase of B. bacteriovorus, whereas the transcriptional activity significantly decreased during the intracellular replication phase.

Molecular evidence from Ciona intestinalis for the evolutionary origin of vertebrate sensory placodes

Cranial sensory placodes are focused areas of the head ectoderm of vertebrates that contribute to the development of the cranial sense organs and their associated ganglia. Placodes have long been considered a key character of vertebrates, and their evolution is proposed to have been essential for the evolution of an active predatory lifestyle by early vertebrates. Despite their importance for understanding vertebrate origins, the evolutionary origin of placodes has remained obscure. Here, we use a panel of molecular markers from the Six, Eya, Pax, Dach, FoxI, COE and POUIV gene families to examine the tunicate Ciona intestinalis for evidence of structures homologous to vertebrate placodes. Our results identify two domains of Ciona ectoderm that are marked by the genetic cascade that regulates vertebrate placode formation. The first is just anterior to the brain, and we suggest this territory is equivalent to the olfactory/adenohypophyseal placodes of vertebrates. The second is a bilateral domain adjacent to the posterior brain and includes cells fated to form the atrium and atrial siphon of adult Ciona. We show this bares most similarity to placodes fated to form the vertebrate acoustico-lateralis system. We interpret these data as support for the hypothesis that sensory placodes did not arise de novo in vertebrates, but evolved from pre-existing specialised areas of ectoderm that contributed to sensory organs in the common ancestor of vertebrates and tunicates.

Ventricular haemodynamics inPython molurus: separation of pulmonary and systemic pressures

Vascular pressure separation by virtue of a two-chambered ventricle evolved independently in mammals and birds from a reptilian ancestor with a single ventricle, and allowed for high systemic perfusion pressure while protecting the lungs from oedema. Within non-crocodilian reptiles, ventricular pressure separation has only been observed in varanid lizards and has been regarded as a unique adaptation to an active predatory life style and high metabolic rate. The systemic and pulmonary sides of the ventricle in Python molurus are well separated by the muscular ridge, and a previous study using in situ perfusion of the heart revealed a remarkable flow separation and showed that the systemic side can sustain higher output pressures than the pulmonary side. Here we extend these observations by showing that systemic blood pressure P(sys) exceeded pulmonary pressure P(pul) almost seven times (75.7+/-4.2 versus 11.6+/-1.1 cm H(2)O). The large pressure difference between the systemic and pulmonary circulation persisted when P(sys) was altered by infusion of sodium nitroprusside or phenylephrine. Intraventricular pressures, measured in anaesthetised snakes, showed an overlap in the pressure profile between the pulmonary side of the ventricle (cavum pulmonale) and the pulmonary artery, while the higher pressure in the systemic side of the ventricle (cavum arteriosum) overlapped with the pressure in the right aortic arch. This verifies that the pressure differences originate within the ventricle, indicating that the large muscular ridge separates the ventricle during cardiac contraction.

Borings in Cloudina Shells: Complex Predator-Prey Dynamics in the Terminal Neoproterozoic

Abstract Predation as an important driver of evolutionary change long has been assumed, despite difficulties to substantiate it with specific examples of predatory interaction, especially for the early Paleozoic diversification of animal life. This study corroborates the existence of shell-drilling predation in the uppermost Neoproterozoic of China. Nearly one-fifth of almost one hundred tubular shells of one of the earliest mineralized animals, Cloudina, are perforated by undoubted predatory borings 15–85 µm wide. By contrast, no specimens of co-occurring shells belonging to Sinotubulites were affected. The identity of the predator remains elusive, but variation in size of the borings suggests a predatory lifestyle throughout its growth, after it reached a minimum size. The relatively uniform distance of the borings from the shell apertures points to either control by the life orientation of the shells, such as the position of the sediment surface, or, more likely, an avoidance response by the predator t...

Survival Mode between the Yearly Reproduction Periods, and Reproductive Biology of Scambus pomorum (Hymenoptera: Ichneumonidae: Pimplinae), a Parasitoid of the Apple Blossom Weevil Anthonomus pomorum (Coleoptera: Curculionidae)

First evidence is given for the hitherto unknown survival mode of females [♀♀] of the parasitoid Scambus pomorum (Ratzeburg 1848), which propagates once every spring, on larvae of the apple blossom weevil, Anthonomus pomorum Linnaeus 1758. After mating, the ♂♂ die, and the ♀♀ continue as predators of leafminer larvae, and perhaps other concealed insects, while they remain in a state of reproductive diapause. In captivity, the female parasitoids attack the mines of moths of different families, of agromyzid flies and sawflies, living on various tree species. A similar explicitly predatory life style of a parasitoid wasp has not been reported before. Leafminers as prey are not responsible for the absence of oogenesis before winter, for eggs develop in overwintered ♀♀ on the same food. Single ♀♀ kill, and feed upon, up to two Phyllonorycter blancardella (Fabricius 1781) (Lepidoptera: Gracillariidae) larvae per day at 20°C, both in early summer and autumn. Predation is linearly related to temperature. In captivity, predation by well-fed ♀♀ showed a dip in August. ♀♀ fed this way, overwintered successfully in coniferous trees, like they are known to do in nature. They became active again in late March. ♀♀ are ready to oviposit when the first suitable host stages appear, on the earliest flowering apple varieties, or on pear. One ♀ lays up to 14 eggs per day at 16.5°C, and total egg production may exceed 100 eggs, but about 50 eggs is more usual, and many ♀♀ are even less fecund. Some ♀♀ are still alive, and probably reproducing, when suitable host stages are becoming scarce. Parasitism levels should be determined when approximately 75% of the host weevils have become pupae; dissections of capped blossoms and parasitoid rearings gave similar results. Her extended lifespan makes the female wasp vulnerable to calamities like pesticide applications. Perhaps, more elevated leafminer densities in nearby hedgerows could seduce ♀♀ to leave the apple planting in time.

Evolutionary biology: lamprey Hox genes and the origin of jaws.

The development of jaws was a critical event in vertebrate evolution because it ushered in a transition to a predatory lifestyle, but how this innovation came about has been a mystery. In the embryos of jawed vertebrates (gnathostomes), the jaw cartilage develops from the mandibular arch, where none of the Hox genes is expressed; if these are expressed ectopically, however, jaw development is inhibited. Here I show that in the lamprey, a primitively jawless (agnathan) fish that is a sister group to the gnathostomes, a Hox gene is expressed in the mandibular arch of developing embryos. This finding, together with outgroup comparisons, suggests that loss of Hox expression from the mandibular arch of gnathostomes may have facilitated the evolution of jaws.

The photoreceptor system in the retinae of two dogfishes, Scyliorhinus canicula and Galeus melastomus: possible relationship with depth distribution and predatory lifestyle

The small spotted dogfish Scyliorhinus canicula and the blackmouth dogfish Galeus melastomus, whose depth distributions overlap in the upper part of the slope (c. 500 m depth), where they have access to the same prey community, have well-developed eyes and a pure-rod retina with a single layer of photoreceptors. Interspecific differences in rod outer segment length (LROS) within retinal regions were found. In the periphery and the retinal centre G. melastomus showed a LROS 24 and 30% longer, respectively, than S. canicula and, therefore, a potential for increased sensitivity. In both species longer LROS were always found in correspondence with the retinal centre where the ganglion cell topography formed a horizontal meridian that allowed for better discrimination of the horizon in the visual field. In this area LROS reached 53·4±4·1μm in S. canicula and 77·1±10·5μm in G. melastomus against 46·3±4·2μm and 61·1±10·1μm in the retinal periphery. No significant differences were recorded in LROS and rod density during growth. In both species, a rapid increase of theoretical visual acuity was found to be related to an increase in fish LT and lens size. Visual acuity ranged between 1·7 and 3 cycles degree-1 in S. canicula and 2·4 and 4·2 in G. melastomus. The G. melastomus rod visual pigment showed the characteristic spectral adaptation to vision in deep-water (λmax of 481 nm), but was also well placed to detect the bioluminescence of some of its main prey species. In S. canicula the visual pigment absorption (λmax of 496 nm) was more typical of shallow water living fishes. The opsin sequences of the two visual pigments are discussed and key amino acid sites were identified where sequence changes could be responsible for the spectral absorption differences between the two species. The possible relationship between LROS, visual acuity, visual pigment absorption, depth distribution and feeding behaviour are discussed.

The photoreceptor system in the retinae of two dogfishes, Scyliorhinus canicula and Galeus melastomus: possible relationship with depth distribution and predatory lifestyle

The small spotted dogfish Scyliorhinus canicula and the blackmouth dogfish Galeus melastomus, whose depth distributions overlap in the upper part of the slope (c. 500 m depth), where they have access to the same prey community, have well‐developed eyes and a pure‐rod retina with a single layer of photoreceptors. Interspecific differences in rod outer segment length (LROS) within retinal regions were found. In the periphery and the retinal centre G. melastomus showed a LROS 24 and 30% longer, respectively, than S. canicula and, therefore, a potential for increased sensitivity. In both species longer LROS were always found in correspondence with the retinal centre where the ganglion cell topography formed a horizontal meridian that allowed for better discrimination of the horizon in the visual field. In this area LROS reached 53·4±4·1μm in S. canicula and 77·1±10·5μm in G. melastomus against 46·3±4·2μm and 61·1±10·1μm in the retinal periphery. No significant differences were recorded in LROS and rod density during growth. In both species, a rapid increase of theoretical visual acuity was found to be related to an increase in fish LT and lens size. Visual acuity ranged between 1·7 and 3 cycles degree‐1 in S. canicula and 2·4 and 4·2 in G. melastomus. The G. melastomus rod visual pigment showed the characteristic spectral adaptation to vision in deep‐water (λmax of 481 nm), but was also well placed to detect the bioluminescence of some of its main prey species. In S. canicula the visual pigment absorption (λmax of 496 nm) was more typical of shallow water living fishes. The opsin sequences of the two visual pigments are discussed and key amino acid sites were identified where sequence changes could be responsible for the spectral absorption differences between the two species. The possible relationship between LROS, visual acuity, visual pigment absorption, depth distribution and feeding behaviour are discussed.

Environmental factors which may have led to the appearance of colour vision.

It is hypothesized that colour vision and opponent processing of colour signals in the visual system evolved as a means of overcoming the extremely unfavourable lighting conditions in the natural environment of early vertebrates. The significant flicker of illumination inherent in the shallow-water environment complicated the visual process in the achromatic case, in particular preventing early detection of enemies. The presence of two spectral classes of photoreceptors and opponent interaction of their signals at a subsequent retinal level allowed elimination of the flicker from the retinal image. This new visual function provided certain advantages concerning reaction times and favoured survival. This assumption explains why the building blocks for colour vision arose so early, i.e. just after the active predatory lifestyle was mastered. The principal functions of colour vision inherent in extant animals required a more complex neural machinery for colour processing and evolved later as the result of a change in visual function favouring colour vision.

What brought the adaptive immune system to vertebrates?--The jaw hypothesis and the seahorse.

A hypothesis is discussed that the adaptive immune system of vertebrates evolved in the gastrointestinal regions of primitive jawed fish (placoderms) due to increased localized injuries and infections which were inadvertently brought about by the novel jaw structures and the predatory life style. The question whether the modern jawless fish, cyclostomes, have adaptive immunity or not is briefly but critically reviewed. The discovery that the gut-associated immune tissues in mammals constitute the primary immune tissues for the local T cells and that some epithelial gamma delta T cells have a unique propensity is summarized and discussed in relation to the jaw hypothesis. Initial study of the seahorse (Hippocampus) indicates that the gut-associated immune tissues may be absent in this teleost species, suggesting an evolutionary link between the adaptive immune system and the jaw structure or eating habit.

Locomotion in ancient seas: Constraint and opportunity in Cephalopod adaptive design

The locomotor system of shelled cephalopods (ectocochleates) is typically characterized by volumetrically large buoyancy devices, small mantle cavities, and little propulsive muscle. Equilibrium control is based on high hydrostatic stability. Drag is high and maximum swimming velocities are generally low. Ectocochleates having coiled shells were better designed in the locomotor sense, and out-performed apically ballasted non-coiled types. These in turn were propulsively superior to unballasted non-coiled forms. Locomotor design appears to be a key factor influencing the course of cephalopod evolutionary history. Shelled cephalopods dominated active predatory marine lifestyles only until the late Devonian diversification of jawed, paired-fin fishes of greatly superior locomotor design. After the appearance of such animals, ectocochleate evolution was canalized by locomotor disparities into paths that separated them ecologically from such advanced design swimmers. Ammonoids appear to have emphasized locomotion at very slow, but very efficient speeds, while nautiloids appear to have retained some slight capacity for higher velocities.

The anatomy of the pharynx of two predatory aquatic oligochaetes

The genera Haplotaxis (Haplotaxidae) and Phagodrilus (Lumbriculidae) have convergent modifications of the pharynx that are adaptations for ingesting prey, especially other oligochaetes. Neither these taxa nor the predatory lumbriculid Agriodrilus (which is not closely related to Phagodrilus within that family) need be considered to be directly related to the leeches or branchiobdellidans simply because of these modifications. The commensal and predatory life style has evolved quite independently in several oligochaetes. Haplotaxis does not have a furrow across the prostomium as previously described. The prostomium consists of a very short bulb on the end of a peristomium, which is elongate dorsally and divided by the first obvious external transverse groove. In the Oligochaeta the peristomium is considered by convention to be segment I, but in the Polychaeta segment numbers begin with the first setiger (regarded as II in Oligochaea). In leeches the prostomium is counted as I.

Attachment of diaminopimelic acid to bdelloplast peptidoglycan during intraperiplasmic growth of Bdellovibrio bacteriovorus 109J.

An early event in the predatory lifestyle of Bdellovibrio bacteriovorus 109J is the attachment of diaminopimelic acid (DAP) to the peptidoglycan of its prey. Attachment occurs over the first 60 min of the growth cycle and is mediated by an extracellular activity(s) produced by the bdellovibrio. Some 40,000 DAP residues are incorporated into the Escherichia coli bdelloplast wall, amounting to ca. 2 to 3% of the total initial DAP content of its prey cells. Incorporation of DAP occurs when E. coli, Pseudomonas putida, or Spirillum serpens are the prey organisms. The structurally similar compounds lysine, ornithine, citrulline, and 2,4-diaminobutyric acid are not attached. The attachment process is not affected by heat-killing the prey nor by the addition of inhibitors of either energy generation (cyanide, azide, or arsenate), protein or RNA synthesis (chloramphenicol and rifamycin), or de novo synthesis of cell wall (penicillin or vancomycin). Approximately one-third of the incorporated DAP is exchangeable with exogenously added unlabeled DAP, whereas the remaining incorporated DPA is solubilized only during the lysis of the bdelloplast wall. Examination of DAP incorporation at low prey cell densities suggests that bdellovibrios closely couple the incorporation to an independent, enzymatic solubilization of DAP by a peptidase. The data indicate that DAP incorporation is a novel process, representing the second example of the ability of the bdellovibrio to biosynthetically modify the wall of its prey.