Role of the skeleton in determination of the branching points in hydroid colonies

Colonial hydroids of the suborder Thecaphora have rigid outer skeleton that possesses species-specific shape of the colony elements. Organisation of the elements within a colony shows strict spatial patterning. The points of branching (emergence of the new growing tip) within shoots are strictly determined and show positive correlation with the place of the most pronounced curvature of the elements skeleton. As it was shown earlier, the shoot growing tip, after emergence, performs its program of functioning independently from the colony condition. Several modifications of experiments with grafting of the growing tip together with rotation around its longitudinal axis were fulfilled. As the result of such grafting the normal orientation of the formed skeleton was altered. In overwhelming cases of further tip growth and shoot development the new growing tip emerged in correspondence with new orientation of the formed skeleton. The orientation of the hydranth of the maternal shoot element had no effect upon the orientation of the new tip emergence after grafting. It is supposed that the place of the new tip emergence is regulated hierarchically. At first level, the interaction of the soft tissues with the skeleton has priority. Anisotropy of mechanical tensions within cell layers due to interaction with the skeleton at the point of its most curvature serves as a primary stimulus in the chain of events leading to the initiation of the new growing tip. If this does not work the intrinsic tissue property (polarity) determines the place of the tip emergence. Such two-level mechanism of determination of the place of the new tip emergence in sympodial shoots stabilises spatial organisation of the entire shoot and decreases the probability of epigenetic mistakes.     

Directionality of a one way movement detector in the crayfishCherax destructor

Summary Directionality curves for vertical one way movement detector neurons in the crayfish were obtained during whole animal oscillation around continuously varying horizontal axes. Results are presented in detail for one easily monitored unit, M.D.I. In a fresh animal, maximum sensitivity was shown to rotation in the rolling plane. In an adapted animal, the maximum sensitivity, was shifted by 45° and the directionality curve became markedly asymmetrical. Right and left adapted M.D.I cells have axes for maximum response 90° apart. The results can be explained simply by a reduction in excitability of input cells coding the set of orthogonal components of a rotation at 45° to the pitch and roll set of orthogonal components.     

Totipotent migratory stem cells in a hydroid

Hydroids, members of the most ancient eumetazoan phylum, the Cnidaria, harbor multipotent, migratory stem cells lodged in interstitial spaces of epithelial cells and are therefore referred to as interstitial cells or i-cells. According to traditional understanding, based on studies in Hydra, these i-cells give rise to several cell types such as stinging cells, nerve cells, and germ cells, but not to ectodermal and endodermal epithelial cells; these are considered to constitute separate cell lineages. We show here that, in Hydractinia, the developmental potential of these migratory stem cells is wider than previously anticipated. We eliminated the i-cells from subcloned wild-type animals and subsequently introduced i-cells from mutant clones and vice versa. The mutant donors and the wild-type recipients differed in their sex, growth pattern, and morphology. With time, the recipient underwent a complete conversion into the phenotype and genotype of the donor. Thus, under these experimental conditions the interstitial stem cells of Hydractinia exhibit totipotency.     

Changes in the patterning of a hydroid colony

It is a widely held view that colonial hydroids (Cnidaria, Hydroidomedusae) are formed on the basis of a repetition of uniform elements. The dominant opinion is that the equal spatial organisation of the colony exists during all stages of its development except the primary polyp, which develops from the settled larva. However, the complex structure and large dimensions of shoots in certain thecate species (subcl. Leptomedusae) suggest that the organisation of the primary shoot differs strongly from that of established colonies. The present study based on a thorough collection and examination of the collected material allowed to describe the entire sequence of the colony ontogeny in Hydrallmania falcata (Sertulariidae). The established shoots of this species are characterised by relatively large size, spiral arrangement of pinnate branches over the shoot stem, and hydranths arranged in one row along the upper side of branches. We showed that the primary shoot developing from the larva has much smaller dimensions and an alternate arrangement of hydranths. During further colony development the shoot organisation undergoes a gradual transformation ending with the emergence of large shoots with 'characteristic' species-specific features. The discovered sequence of changes in shoot patterning shows certain correlations with alterations of the growing tip dimensions. The dimensions of the growing tip seem to determine the patterning in accordance with the particular spatial location of the tip. This finding implies the necessity of a detailed reinvestigation of the entire colony development in thecate hydroids, which would make a significant contribution to the understanding of the morphogenetic evolution and patterning mechanisms within this group of colonial organisms.     

Distribution system formation in hydroid polyp development

The formation of the pulsatory distribution system, which is the basis of the colonial organization in hydroids, was studied in Gonothyrea loveni (Allm., 1859). The patterns of the distribution system functioning were established at different developmental stages.     

Distribution system formation in hydroid polyp development

The formation of the pulsatory distribution system, which is the basis of the colonial organization in hydroids, was studied in Gonothyrea loveni (Allm., 1859). The patterns of the distribution system functioning were established at different developmental stages.     

Morphogenetic evolution of hydroid colony pattern

A scheme of evolution of hydrozoan colony pattern is proposed based upon the consideration of macro-morphogenesis. Four main processes play decisive roles(1) hard skeleton formation by soft tissues, (2) changes in duration of the growth phase relative to the transition to differentiation in interdependent zones of growth, (3) ratio in growth rates between adjacent zones of growth within the rudiment, the shoot, or the whole colony, and (4) spatial relationships among growth zones. The main tendency in morphological evolution of the hydroids is an increasing integration of the colony as revealed by increasing complexity of its structure. That is from a temporary colony towards the permanent one with highly organised shoots, as hydranths and branches are localised in a strictly arranged manner. An analysis of diverse data allows one to state that the main morphogenetic mechanism of increasing complexity in the hydroid colony is convergence, then fusion, of adjacent growth zones, a variant of heterochrony.     

Age‐specific survival and movement among major African Penguin Spheniscus demersus colonies

Reliable estimates of survival and dispersal are crucial to understanding population dynamics, but for seabirds, in which some individuals spend years away from land, mortality and emigration are often confounded. Multistate mark–recapture methods reduce bias by incorporating movement into the process of estimating survival. We used a multistate model to provide unbiased age‐specific survival and movement probabilities for the Endangered African Penguin Spheniscus demersus based on 5281 nestlings and 31 049 adults flipper‐banded and resighted in the Western Cape, South Africa, between 1994 and 2012. Adult survival was initially high (≥ 0.74) but declined after 2003–2004 coincident with a reduction in the availability of Sardine Sardinops sagax and Anchovy Engraulis encrasicolus on the west coast of South Africa. Juvenile survival was poorly estimated, but was lower and more variable than adult survival. Fidelity to the locality of origin varied over time, but was high in adults at Robben and Dassen islands (≥ 0.88) and above 0.55 for juvenile and immature Penguins at all localities. Movement occurred predominantly during 1994–2003 and was indicative of immigration to Robben and Dassen islands. Our results confirm that a prolonged period of adult mortality contributed to the observed decline in the African Penguin population and suggest a need for approaches operating over large spatial scales to ensure food security for marine top predators.     

Sclerotization of the perisarc of the calyptoblastic hydroid, Laomedea Flexuosa 1. The identification and localization of dopamine in the hydroid

With histochemical methods, the perisarc and a certain cell type in Laomedea flexuosa have been shown to contain a catecholamine. The only catecholamine detected in methanolic extracts of the hydroid is dopamine. It is thought to be transferred from spherical inclusions in these cells to the perisarc and to be involved in sclerotization. The dopamine-containing cells appear to differentiate in specific regions of the colony and migrate out to all other regions by active amoeboid movement between ectodermal epithelial cells. The rivets (or desmocytes) contain an unidentified phenolic substance and may also be sclerotized structures.     

Structure and signaling in polyps of a colonial hydroid

Abstract. After feeding, polyps of colonial hydroids contract regularly, dispersing food throughout the colony via the gastrovascular fluid. Such contractions may trigger signaling pathways that allow colonies to grow in an adaptive manner, i.e., to initiate development of more polyps in food‐rich areas and to suppress polyp development in food‐poor areas. In this context, we investigated the structure and potential signaling of the junction between polyps and stolons in colonies of the hydroid Podocoryna carnea. Using transmission electron microscopy, we found that the density of mitochondrion‐rich epitheliomuscular cells was low in polyp and stolon tissues except at or near the polyp‐stolon junction, where many of these mitochondrion‐rich cells occur in ectodermal tissue. In vivo fluorescence microscopy suggests that these mitochondria are a principal source of the metabolic signals of the colony. Both native fluorescence of NAD(P)H and fluorescence from peroxides (visualized with H₂DCFDA) co‐localize to this region of the polyp. Rhodamine 123 fluorescence suggests that both these metabolic signals emanate from mitochondria. To test whether such metabolic signals may be involved in colony pattern formation, inbred lines of P. carnea were used. Colonies of a runner‐like inbred line grow with widely spaced polyps and long stolonal connections, much like wild‐type colonies in a food‐poor environment. Colonies of a sheet‐like inbred line grow with closely spaced polyps and short stolonal connections, similar to wild‐type colonies in a food‐rich environment. Polyp‐stolon junctions in runner‐like and sheet‐like colonies were imaged for the fluorescence of H₂DCFDA. Densitometric analysis of this signal indicates that the mitochondria in epitheliomuscular cells of runner‐like polyps emit greater amounts of peroxides. Because peroxides and other reactive oxygen species are frequently intermediaries in metabolic signaling pathways, we suspect that such signaling may indeed occur at polyp‐stolon junctions, affecting colony pattern formation in these inbred lines and possibly in hydroid colonies in general.     

Nematocysts of the Mediterranean hydroid Halocordyle disticha

The morphology, distribution and function of nematocysts in the hydroid Halocordyle disticha were studied by light and scanning electron microscopy. Two types of stenoteles, two types of microbasic b-mastigophores (one with a capsular inclusion) and one type of desmoneme were identified. Prey-capturing experiments were performed with Artemia sp. nauplii. Stenoteles and microbasic mastigophores (those with inclusions) penetrated and paralyzed Artemia larvae, whereas desmonemes kept them in a firm grip by winding around setae.     

Seasonal spatial dynamics and causes of nest movement in colonies of the invasive Argentine ant (Linepithema humile)

Abstract.  1. Colony organisation and movement behaviour of the Argentine ant ( Linepithema humile ) was studied over 3 years in field populations in California and in captive colonies in the laboratory. This invasive species is highly polydomous and unicolonial; colonies consist of expansive and fluid networks of nests and trails. The spatial and temporal organisation of colonies may contribute to ecological dominance.
2. Argentine ant nests and inter-nest trails shift in size, abundance, and location, so that colony networks are spatially contracted in the winter and expanded spring to autumn. Colonies occupy permanent sites; ants migrated to and from the same winter nest locations year after year, and occupied 30% of the same nests repeatedly during seasonal migrations.
3. Nests were moved on average 2–3 m. Forty-two per cent were occupied less than 1 month, 4% the entire study, and the other 54% lasted 3.9 ± 2.3 months (mean ± SD).
4. Nests were located within 2–4 m of woody plants, in warm sites in the winter and cool sites in the summer. Both humidity and food availability influenced nest-site choice in laboratory colonies. However, when faced with a trade-off between factors, the ants chose humid nest boxes over nest boxes near food, and ants moved nests only in response to changes in humidity and not distance to food.
5. The results indicate that L. humile colonies are seasonally polydomous, and that nest movements are driven by changes in microclimate. Colony organisation maintains high local density and increases food supply, which may improve the competitive ability of L. humile colonies and reduce opportunities for species coexistence.     

Serotonin involvement in the metamorphosis of the hydroid Eudendrium racemosum

Hydroid planulae metamorphose in response to an inducing external stimulus, usually a bacterial cue. There is evidence that neurotransmitters participate in the signal transduction pathway of hydroid metamorphosis. Eudendrium racemosum is a colonial hydroid common in the Mediterranean Sea. It lacks the medusa stage and the planulae develop on female colonies during the fertile season. In this work, serotonin (5-HT) was localized in some planula ectodermal cells. Co-localization of serotonin and beta-tubulin suggested that 5-HT was present in sensory nervous cells and in different ectodermal cells. To investigate the role of neurotransmitters in metamorphosis, E. racemosum planulae were treated with serotonin and dopamine and with agonists and antagonists of the corresponding receptors. Serotonin and a serotonin receptor agonist induced metamorphosis, while a 5-HT receptor antagonist inhibited it. Dopamine and all dopaminergic drugs used did not show any significant effect on the onset of metamorphosis. Results from this work showed that 5-HT could stimulate metamorphosis in E. racemosum planulae in the presence of a natural inducer. A mechanism by which this neurotransmitter could act in this phase is proposed.