Visual accommodation and active pursuit of prey underwater in a plunge-diving bird: the Australasian gannet

Australasian gannets (Morus serrator), like many other seabird species, locate pelagic prey from the air and perform rapid plunge dives for their capture. Prey are captured underwater either in the momentum (M) phase of the dive while descending through the water column, or the wing flapping (WF) phase while moving, using the wings for propulsion. Detection of prey from the air is clearly visually guided, but it remains unknown whether plunge diving birds also use vision in the underwater phase of the dive. Here we address the question of whether gannets are capable of visually accommodating in the transition from aerial to aquatic vision, and analyse underwater video footage for evidence that gannets use vision in the aquatic phases of hunting. Photokeratometry and infrared video photorefraction revealed that, immediately upon submergence of the head, gannet eyes accommodate and overcome the loss of greater than 45 D (dioptres) of corneal refractive power which occurs in the transition between air and water. Analyses of underwater video showed the highest prey capture rates during WF phase when gannets actively pursue individual fish, a behaviour that very likely involves visual guidance, following the transition after the plunge dive's M phase. This is to our knowledge the first demonstration of the capacity for visual accommodation underwater in a plunge diving bird while capturing submerged prey detected from the air.     

Performance of Fast Routing Algorithms in Large Optical Switches Built on the Vertical Stacking of Banyan Structures

Vertical stacking of multiple optical banyan networks is a novel scheme for building banyan-based nonblocking optical switches. The resulting network, namely vertically stacked optical banyan (VSOB) network, preserves the properties of small depth and absolutely loss uniformity but loses the nice self-routing capability of banyan networks. To guarantee a high switching speed, routing in VSOB network needs special attentions so that paths can be established as fast as possible. The best known global routing algorithm for an N×N nonblocking VSOB network has the time complexity of O(NlogN), which will introduce an unacceptable long delay in path establishment for a large size optical switch. In this paper, we propose two fast routing algorithms for the VSOB network based on the idea of inputs grouping. The two algorithms, namely plane fixed routing (PFR) algorithm and partially random routing (PRR) algorithm, have the time complexities of O(logN) and O( ) respectively, and FR algorithm can actually turn a VSOB network into a self-routing one. Extensive simulation based on a network simulator indicates that for large VSOB networks our new algorithms can achieve a reasonably low blocking probability while guarantee a very high switching speed.     

Environmental regulation of photosynthetic metabolism in the amphibious sedge Eleocharis baldwinii and comparisons with related species

The amphibious leafless sedge, Eleocharis baldwinii, expresses C₄ characteristics in the terrestrial form and intermediate characteristics between C₃ and C₄ photosynthesis in the submerged form. This study examined the immunocytochemical localization of C₃ and C₄ enzymes in culms of the two forms to elucidate the regulatory mechanism of photosynthetic metabolism and compared the activities and amounts of C₃ and C₄ enzymes with those in other Eleocharis species, E. vivipara and E. retroflexa, which show C₄ characteristics on land but C₃ and C₄ characteristics under water. The terrestrial form of E. baldwinii exhibited a C₄‐like pattern of enzyme localization. The submerged form exhibited a modified anatomy with well‐developed mesophyll cells and small Kranz cells. The C₄ enzyme levels declined conspicuously in outer mesophyll cells adjacent to the epidermis, whereas Rubisco levels increased throughout the mesophyll in the submerged form. These results suggest that intermediate photosynthesis between C₃ and C₄ photosynthesis in the submerged form results from the predominant operation of the C₃ pathway in the outer mesophyll cells and the C₄ pathway in both the inner mesophyll and Kranz cells. Differences in the degree of C₄ expression in terrestrial forms of Eleocharis species may cause the differences in the expression of photosynthetic modes under water.     

Characterization of fungal antagonistic bacilli isolated from aerial roots of banyan (Ficus benghalensis) using intact‐cell MALDI‐TOF mass spectrometry (ICMS)

Aims

To characterize fungal antagonistic bacilli isolated from aerial roots of banyan tree and identify the metabolites responsible for their antifungal activity.

Methods and Results

Seven gram positive, endospore‐forming, rod‐shaped endophytic bacterial strains exhibiting a broad‐spectrum antifungal activity were isolated from the surface‐sterilized aerial roots of banyan tree. The isolates designated as K1, A2, A4 and A12 were identified as Bacillus subtilis, whereas isolates A11 and A13 were identified as Bacillus amyloliquefaciens using Biolog Microbial Identification System. The antifungal lipopeptides, surfactins, iturins and fengycins with masses varying in the range from m/z 900 to m/z 1550 could be detected using intact‐cell MALDI‐TOF mass spectrometry (ICMS). On the basis of mass spectral and carbon source utilization profile, all seven endophytes could be distinguished from each other. Furthermore, ICMS analysis revealed higher extent of heterogeneity among iturins and fengycins produced by B. subtilis K1, correlating well with its higher antifungal activity in comparison with other isolates.

Conclusion

Seven fungal antagonistic bacilli were isolated from aerial roots of banyan tree, exhibiting broad spectrum of antifungal activity, among which B. subtilis K1 isolate was found to be most potent. The ICMS analysis revealed that all these isolates produced cyclic lipopeptides belonging to surfactin, iturin and fengycin families and exhibited varying degree of heterogeneity.

Significance and Impact of the study

The endophytes are considered as a potential source of novel bioactive metabolites, and this study describes the potent fungal antagonistic bacilli from aerial roots of banyan tree. The isolates described in this study have a prospective application as biocontrol agents. Also ICMS analysis described in this study for characterization of antifungal metabolites produced by banyan endophytic bacilli may be used as a high throughput tool for screening of microbes producing novel cyclic lipopeptides.     

Electron transport system activity and oxygen consumption of two amphibious isopods,epigean Ligia italica Fabricius and hypogean Titanethes albus (Koch), in air and water

Electron transport system (ETS) activity and oxygen consumption (i.e. respiration, R) were measured in two amphibious isopods, epigean Ligia italica and hypogean Titanethes albus. The measurements were made in air and in water to estimate the exploitation of metabolic potential for actual metabolism in the two media. Oxygen consumption was measured in animals in air before their transfer to water, in water and again after their transfer back to air. Both species showed greater oxygen consumption during submergence in water than in air. Although epigean L. italica had higher oxygen consumption and ETS activity than hypogean T. albus, both species exhibited high and variable ETS/R ratios. A high and variable ETS/R ratio is one of the characteristics of amphibious isopods that enables them to cope with specific environmental conditions in their habitats.     

Rowing locomotion by a stonefly that possesses the ancestral pterygote condition of co-occurring wings and abdominal gills

A leading hypothesis for the origin of insect wings is that they evolved from thoracic gills that were serial homologues of the abdominal gills present in fossil pterygotes and in the nymphs of some modern mayflies, damselflies and stoneflies. Co-occurrence of thoracic wings and abdominal gills is the primitive condition for fossil pterygote insects, whereas the winged stage of modern insects almost exclusively lacks abdominal gills. Here we examine the locomotor behaviour and gill morphology of a stonefly, Diamphipnopsis samali (Plecoptera), which retains abdominal gills in the winged adult stage. This species can fly, but also uses its forewings as oars to accomplish rowing locomotion along the surface of water. The abdominal gills are in contact with both air and water during rowing, and their elaborately folded surface suggests an ability to contribute to gas-exchange. D. samali nymphs also have behaviours that place them in locations where their gills are exposed to air; they forage at night at the stream margin and within bubble curtains in rapids. These traits may exemplify an early pterygote condition in which gill and protowing function overlapped in an amphibious setting during a transition from aquatic to aerial locomotion and gas exchange. Rowing locomotion provides a novel and mechanically intermediate stage for the wings-from-gills and surface-skimming hypotheses for the origin of insect wings and flight.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 79, 341–349.     

Plants as amphibians

From the poles to the tropics flooding is a powerful discriminator in plant distribution. Although plants can be divided globally as to whether or not they are tolerant of high water tables, it does not follow that all flood-tolerant species achieve their ability to survive flooding by similar adaptations. Flooding implies a periodic but temporary rise of the water table, hence plants that live in such areas have an amphibious life style. Amphibious plants have to adjust, not only to inundation and the dangers of oxygen deprivation, but also to the eventual lowering of water tables and often sudden re-exposure to a fully aerated environment and the lack of the physical support that is provided by flooding. In this respect they are distinct from aquatic species that live constantly in water. It is often tacitly assumed that for amphibious species flooding is the stressed condition and non-flooding the norm. This pre-judgement is not appropriate, particularly as in many habitats the flooded condition predominates for a longer part of the year than the unflooded. For amphibians, re-adapting from the aquatic to the terrestrial habitat requires specialised adaptations, just as much as a change from unflooded to flooded. Many flood-tolerant species, including surface-rooting grasses and sedges, may not be tolerant of anoxia, and instead prevent the accumulation of an oxygen debt in submerged organs by aeration mechanisms, including oxygen diffusion through aerenchyma, thermally induced mass movement of air, and the elongation of submerged shoots. In other species, and particularly in perennial plants with buried perennating organs, flooding can impose prolonged periods of anaerobiosis (anoxia). Being able to survive such oxygen deprivation requires (1) energy reserves sufficient for cell maintenance, (2) the prevention of cytoplasmic acidosis under anoxia, and (3) the anaerobic mobilisation of starch reserves. Re-entry to the aerobic habitat is facilitated by (4) the dispersal and excretion of products that transfer hydrogen from anoxic or hypoxic tissues, either to the external environment, or to parts of the plant with access to oxygen, before the anaerobic tissues return to air, and (5) anti-oxidative activity to minimise post-anoxic injury.     

Observations of terrestrial locomotion in wild Polypterus senegalus from Lake Albert,Uganda

Polypterids, the most basal actinopterygians, are a group of fish long-considered living fossils and holding a key position for understanding fish and tetrapod evolution. Knowledge of the natural history of Polypterus is limited, their having been studied in little detail since the early 1900s. The locomotory habits of wild Polypterus senegalus from Lake Albert, Uganda, were investigated in 2014. High-speed videography demonstrated the capability of large Polypterus to move overland successfully. Contrary to previous evidence, field observations found that terrestrial locomotion in Polypterus is not inherently restricted by body size. Evidence that Polypterus exhibit this behaviour as part of their natural life history can be found in the existence of environmental challenges and the presence of adaptations for amphibious life.     

Effects of stolon severing on the expansion of Alternanthera philoxeroides from terrestrial to contaminated aquatic habitats

Few studies have examined the effects of clonal integration (translocation of resources between interconnected ramets) during the expansion of amphibious clonal plants from terrestrial to aquatic habitats. We conducted a greenhouse experiment to simulate the expansion of plants from terrestrial to contaminated aquatic habitats in the amphibious stoloniferous herb Alternanthera philoxeroides (alligator weed). The proximal ramets (i.e. relatively old) of clonal fragments grown in uncontaminated soils were connected to (allowing clonal integration) or disconnected from (preventing clonal integration) distal ramets (i.e. relatively young) grown either in uncontaminated water (control, no CuSO₄) or in four copper‐contaminated water treatments containing 31.25, 62.5, 125 and 250 mg/L CuSO₄, respectively. When a stolon connection was severed, all distal ramets grown in the contaminated water died. When the stolon connection was intact, however, the survival rate of the distal ramets was 85–100% when they were grown at the three lower levels of contamination and 43.75% at the highest level. Moreover, the survival rate and growth of the distal ramets grown in the three lower levels of contamination treatments did not differ from those in the control (uncontaminated water). These results suggest that clonal integration could greatly improve the survival and growth of alligator weed subjected to moderate levels of copper stress. Although clonal integration could also increase the survival rate of the connected distal ramets subjected to the highest level of copper stress (250 mg/L CuSO₄) compared with that of disconnected distal ramets, the survival rate and growth measures were still significantly lower than those in the control. This suggests that clonal integration plays a limited role in the survival and growth of alligator weed when it is subjected to severe stress by high levels of copper contamination.     

Seeing in the swamp: hydrogen sulfide inhibits eye metabolism and visual acuity in a sulfide-tolerant fish

In fish, vision may be impaired when eye tissue is in direct contact with environmental conditions that limit aerobic ATP production. We hypothesized that the visual acuity of fishes exposed to hydrogen sulfide (H₂S)-rich water would be altered owing to changes in cytochrome c oxidase (COX) activity. Using the H₂S-tolerant mangrove rivulus (Kryptolebias marmoratus), we showed that a 10 min exposure to greater than or equal to 200 µM of H₂S impaired visual acuity and COX activity in the eye. Visual acuity and COX activity were restored in fish allowed to recover in H₂S-free water for up to 1 h. Since K. marmoratus are found in mangrove pools with H₂S concentrations exceeding 1000 µM, visual impairment may impact predator avoidance, navigation and foraging behaviour in the wild.