Amphibious adaptations in a newly recognized amphibious fish: Terrestrial locomotion and the influences of body size and temperature

Amphibious animals are adapted for both aquatic and terrestrial habitats. The conflicting requirements for dual habitats are perhaps most pronounced in the air‐breathing fishes, which represent an intermediate stage between the totally aquatic habitat and terrestrial colonization. A key requirement for amphibious fishes is terrestrial locomotion. The different densities and compositions of air and water impose constraints for efficient terrestrial locomotion that differ from those required for aquatic locomotion. I investigated terrestrial locomotion in a small South African fish, Galaxias ‘nebula’, by exposing 60 individual fish to air in specially designed raceways and quantifying movement type and occurrence as a function of availability of water, fish size and environmental temperature. Nebula showed a sustained undulating form of terrestrial locomotion characteristic of amphibious fishes and also a transient ballistic locomotion (jumps) typical of fully aquatic species. Terrestrial movement was influenced by fish size, with medium‐sized fish undertaking more jumps towards water, and fewer jumps away from water, than their smaller or larger conspecifics. In contrast, axial undulation was mainly influenced by temperature. However, there was no consistent pattern in temperature effects presumably because temperature is just one of a suit of environmental factors that may affect terrestrial locomotion. Nebula's amphibious adaptations allow it to cope with the unpredictability inherent in its natural environment.     

Morphological and anatomical changes of Melaleuca cajuputi under submergence

Melaleuca cajuputi is a woody plant of the Myrtaceae which is a dominant species in tropical peat swamps in southern Thailand, where the groundwater level fluctuates greatly. Although the current year seedlings are likely submerged, their adaptive responses have never been studied. The objective of the present study was to examine their responses to submergence, and especially their morphological and anatomical changes. Not only did the seedlings of M. cajuputi survive submergence for 56 days, but they could also increase their dry weight, shoot length, and leaf number during submergence. These growth responses to submergence indicate that the seedlings of M. cajuputi could make photosynthetic production under water. The leaves that developed under water were heterophyllous “aquatic leaves” that appear to represent adaptations to improve the uptake of gases from the water. Intercellular spaces in the stems and leaves were more strongly developed in the submerged seedlings than in non-submerged seedlings with the shoot and leaves in the air. The intercellular spaces appear to be schizogenous aerenchyma that facilitates gas exchange. The growth responses and anatomical responses in stems and leaves to submergence, which were found in M. cajuputi, are commonly known in herbaceous plants with amphibious characteristics, but had not been reported in woody plants. And our results suggest that M. cajuputi adapts to submergence similarly to other amphibious plants, thereby ensuring continuing biomass production.     

Crocodiles don't focus underwater

Summary Crocodilians are amphibious reptiles which hunt prey both on land and in water. Previous refractive and anatomical studies have suggested that their eyes can focus objects in air and that their ability to refocus the eye underwater may be limited. Examination of the plane of focus of six species of crocodilians both in air and underwater has revealed that they are generally well focused in air for distant targets and severely defocused underwater. These results suggest that sensory systems other than vision must play an important role in prey capture underwater.Abbreviation D diopter     

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.     

Amphibious fish: why do they leave water?

Summary Amphibious behaviour in fish has evolved separately many times since the first amphibious fishes, the rhipidistian crossopterygians, ventured onto land about 350 million years ago. This behaviour has resulted in the colonization and eventual domination by vertebrates of the terrestrial habitat. It is generally proposed that aquatic hypoxia, owing to metabolic oxygen consumption and organic decay, was the most important selective force in the evolution of air-breathing vertebrates (e.g. Randall et al., 1981). Modern amphibious fish species give an insight into the reasons for leaving and eventually abandoning the aquatic habitat. Amphibious fishes today leave the water for a variety of reasons associated with degradation of their aquatic habitat, or biotic factors within it.The possible causal factors which may elicit an emergence response are summarized in Fig. 1(a) and (b). Amphibious fish inhabiting closed systems, as typified by freshwater or intertidal pools, may leave water for any of the reasons detailed in Fig. 1(a). The relative importance of any one stimulus is likely to vary between different species. However, it is possible that in closed systems, adverse fluctuations in physico-chemical parameters will have a more important effect in eliciting amphibious behaviour than will biotic factors. In open systems, such as coastal waters or large freshwater bodies, effectively two routes of escape from adverse aquatic conditions are available to amphibious fish. They may move onto land, or alternatively they may move underwater to find better conditions. In such a system, where physico-chemical parameters remain relatively constant, abiotic factors are unlikely to have a significant influence on amphibious behaviour. The dominant stimulus in open systems is possibly the three-way interaction between predation, competition, and short-or long-term food availability (Fig. 1(b)).It is unlikely that any one of the factors discussed in this review will act alone in causing amphibious behaviour, and in this respect the available literature on fish leaving water is lacking. Much of it is fragmentary and partly anecdotal, and the limited amount of experimental work tends to concentrate on individual causal factors. There is evidently scope for detailed examination of emersion in a number of amphibious fishes, testing a matrix of environmental and biotic stimuli, in an attempt to determine in more detail the reasons for such behaviour.     

Nutrient availability and nutrient use efficiency in plants growing in the transition zone between land and water

The transition zone between terrestrial and freshwater habitats is highly dynamic, with large variability in environmental characteristics. Here, we investigate how these characteristics influence the nutritional status and performance of plant life forms inhabiting this zone. Specifically, we hypothesised that: (i) tissue nutrient content differs among submerged, amphibious and terrestrial species, with higher content in submerged species; and (ii) PNUE gradually increases from submerged over amphibious to terrestrial species, reflecting differences in the availability of N and P relative to inorganic C across the land–water ecotone. We found that tissue nutrient content was generally higher in submerged species and C:N and C:P ratios indicated that content was limiting for growth for ca. 20% of plant individuals, particularly those belonging to amphibious and terrestrial species groups. As predicted, the PNUE increased from submerged over amphibious to terrestrial species. We suggest that this pattern reflects that amphibious and terrestrial species allocate proportionally more nutrients into processes of importance for photosynthesis at saturating CO₂ availability, i.e. enzymes involved in substrate regeneration, compared to submerged species that are acclimated to lower availability of CO₂ in the aquatic environment. Our results indicate that enhanced nutrient loading may affect relative abundance of the three species groups in the land–water ecotone of stream ecosystems. Thus, species of amphibious and terrestrial species groups are likely to benefit more from enhanced nutrient availability in terms of faster growth compared to aquatic species, and that this can be detrimental to aquatic species growing in the land–water ecotone, e.g. Ranunculus and Callitriche.     

Repeated evolution of amphibious behavior in fish and its implications for the colonization of novel environments

We know little about on how frequently transitions into new habitats occur, especially the colonization of novel environments that are the most likely to instigate adaptive evolution. One of the most extreme ecological transitions has been the shift in habitat associated with the move from water to land by amphibious fish. We provide the first phylogenetic investigation of these transitions for living fish. Thirty‐three families have species reported to be amphibious and these are likely independent evolutionary origins of fish emerging onto land. Phylogenetic reconstructions of closely related taxa within one of these families, the Blenniidae, inferred as many as seven convergences on a highly amphibious lifestyle. Taken together, there appear to be few constraints on fish emerging onto land given amphibious behavior has evolved repeatedly many times across ecologically diverse families. The colonization of novel habitats by other taxa resulting in less dramatic changes in environment should be equally, if not, more frequent in nature, providing an important prerequisite for subsequent adaptive differentiation.     

Where do fish go when stranded on land? Terrestrial orientation of the mangrove rivulus Kryptolebias marmoratus

The goal of the present study was to determine which sensory cues the mangrove rivulus Kryptolebias marmoratus, a quasi-amphibious, hermaphroditic fish, uses to orient in an unfamiliar terrestrial environment. In a laboratory setting, K. marmoratus were placed on a terrestrial test arena and were provided the opportunity to move toward reflective surfaces, water, dark colours v. light colours, and orange colouration. Compared with hermaphrodites, males moved more often toward an orange section of the test arena, suggesting that the response may be associated with camouflage or male–male competition, since only males display orange colouration. Younger individuals also moved more often toward the orange quadrant than older individuals, suggesting age-dependent orientation performance or behaviour. Sloped terrain also had a significant effect on orientation, with more movement downhill, suggesting the importance of the otolith-vestibular system in terrestrial orientation of K. marmoratus. By understanding the orientation of extant amphibious fishes, we may be able to infer how sensory biology and behaviour might have evolved to facilitate invasion of land by amphibious vertebrates millions of years ago.     

Initial Development of a Novel Amphibious Robot with Transformable Fin-Leg Composite Propulsion Mechanisms

Amphibious robots are very attractive for their broad applications in resource exploration, disaster rescue, and recon- naissance. However, it is very challenging to develop the robots for their complex, amphibious working environments. In the complex amphibious environment, amphibious robots should possess multi-capabilities to walk on rough ground, maneuver underwater, and pass through transitional zones such as sandy and muddy terrain. These capabilities require a high-performance propulsion mechanism for the robots. To tackle a complex task, a novel amphibious robot （AmphiHex-I） with,transformable fin-leg composite propulsion mechanisms is developed. With the fin-leg composite propulsions, AmphiHex-I can walk on rough and soft substrates and swim in water with many maneuvers. This paper presents the structural design of the transformable fin-leg propulsion mechanism and its driving module. A hybrid model is used to explore the dynamics between the trans- formable legs and transitional environment such as granular medium. The locomotion performances of legs with various ellip- tical shapes are analyzed, which is verified by the coincidence between the model predictions and the simulation results. Further, an orthogonal experiment is conducted to study the locomotion performance of a two-legged platform walking with an asyn- chronous gait in the sandy and muddy terrain. Finally, initial experiments of AmphiHex-I walking on various lands and swimming in water are implemented. These results verify that the transformable fin-leg mechanisms enable the amphibious robot to pass through a complex, amphibious working environment.     

Gill remodelling during terrestrial acclimation in the amphibious fish Polypterus senegalus

Fishes are effectively weightless in water due to the buoyant support of the environment, but amphibious fishes must cope with increased effective weight when on land. Delicate structures such as gills are especially vulnerable to collapse and loss of surface area out of water. We tested the ‘structural support’ hypothesis that amphibious Polypterus senegalus solve this problem using phenotypically plastic changes that provide mechanical support and increase stiffness at the level of the gill lamellae, the filaments, and the whole arches. After 7 d in terrestrial conditions, enlargement of an inter-lamellar cell mass filled the water channels between gill lamellae, possibly to provide structural support and/or reduce evaporative water loss. Similar gill remodelling has been described in several other actinopterygian fishes, suggesting this may be an ancestral trait. There was no change in the mechanical properties or collagen composition of filaments or arches after 7 days out of water, but 8 months of terrestrial acclimation caused a reduction in gill arch length and mineralized bone volume. Thus, rather than increasing the size and stiffness of the gill skeleton, P. senegalus may instead reduce investment in supportive gill tissue while on land. These results are strikingly similar to the evolutionary trend of gill loss that occurred during the tetrapod invasion of land, raising the possibility that genetic assimilation of gill plasticity was an underlying mechanism.     

The structural mechanics and evolution of aquaflying birds

Mass‐specific bone strength was examined in the forelimb and hindlimb of 64 species of birds to determine if aquaflying birds (which utilize the wings for propulsion underwater) differ in their skeletal strength compared with other avian taxa. Long bone strengths were estimated from cross‐sectional measurements. Compared with the expectation from geometric similarity, humeral section modulus in volant birds scales nearly isometrically, while femoral strength scales with significant positive allometry. Penguin mass‐specific humeral strength is greatly elevated, but the average humeral strength in species that are propelled by the wings in both air and water do not differ from the values calculated in non‐diving taxa. However, amphibious flyers have gracile femora. Comparative analyses using independent contrasts were utilized to examine the impact of phylogenetic signal. The residual measured for the penguin–procellariiform humeral strength contrast was larger in magnitude (residual of 2.14) than at any other node in the phylogeny. The data strongly indicate that the transition from an amphibious flight condition to a fully aquatic condition involves greater changes in mechanical factors than the transition from purely aerial locomotion to amphibious wing use. There remains the possibility that a historical effect, such as ancestral body size, has impacted the mechanical scaling of penguins. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 687–698.     

Photosynthetic use of inorganic carbon among primary and secondary water plants in streams

1. We analysed photosynthetic rates and inorganic carbon use of thirty-five vascular macrophyte species collected submerged in eight nutrient- and CO₂-rich Danish lowland streams. The species were classified in four groups as mainly terrestrial, homophyllous and heterophyllous amphibious and truly submerged. These groups represent plant species differently adapted to life in water. 2. Photosynthetic rates measured in water increased in the gradual transition from mainly terrestrial, through amphibious to truly submerged species. Species normally in contact with air adapted to submergence by increasing the photosynthetic rate at limiting CO₂. Photosynthetic rates of submerged parts of heterophyllous amphibious species were close to those of submerged species. Submerged species with thin or finely dissected leaves had the highest photosynthetic rates, probably because of low diffusional resistance to uptake of nutrients and gases. 3. In contrast to submerged species, terrestrial and amphibious species were unable to use HCO₃^?. Extensive oversaturation with CO₂ in the streams allows, however, many amphibious species to photosynthesize well under water, based on CO₂-use alone. Amphibious CO₂-users, with very few structural adaptations to life under water, can therefore be as dominant in the submerged vegetation of lowland streams as HCO₃^?-using water plants. Moreover, the streams provide open space for colonization from the dense vegetation ashore. 4. Among the 1265 Danish herbaceous species no less than seventy-five terrestrial species occasionally grow submerged, forty-five species are amphibious, and fifty-one are true water plants. These numbers suggest that adaptation to permanent or temporary submergence is an ongoing process involving many species and that the land-water interface does not represent as difficult a barrier as often believed.     

Evolution of alternative foraging tactics driven by water temperature and physiological constraints in an amphibious snake

Amphibious predatory ectotherms live and forage in two environments (aquatic and terrestrial) that can drastically differ in temperature means and variance across space and time. The locomotor performance of ectotherms is known to be strongly affected by temperature. However, how differences in water temperature may drive the evolution of alternative foraging tactics in amphibious animals remains poorly understood. Fish‐eating Viperine snakes Natrix maura occur from high altitude cold water streams to warm shallow lakes, and employ two main feeding strategies: sentinel foraging (underwater sit‐and‐wait behaviour) and active foraging (fish chasing). Using 272 juvenile snakes we measured: the performance kinetics of diving and swimming in a wide range of water temperatures; basal metabolic levels in relation to body temperature; and the type of foraging mode expressed in water‐temperature‐acclimated snakes. Individual swimming performances increased with testing temperature (10, 15, 20, 25 or 30 °C). Apnoea time followed an opposite trend however, plausibly reflecting the fact that oxygen demands are related to the metabolic rate of ectotherms. That is, snake heart rates increased with body temperature. Snakes acclimated to 10 °C water mostly displayed sentinel foraging. By contrast, 20 °C and 30 °C water‐acclimated snakes were extremely active fish chasers. Individual apnoea times at the various testing temperatures were all correlated; as were individual swimming speeds. There was however no clear relationship between an individual's ability to hold its breath and its ability to swim, suggesting that both performance traits may be the target of different selective pressures. Fast swimming speed and long breath holding abilities are likely key determinants of both foraging success and predatory evasion, although in a context dependent manner. Active swimming foraging is likely to be advantageous in warm water (> 20 °C), while sentinel foraging appears better suited to cold water (< 14 °C). The physiological aspects of foraging tactics of amphibious snakes combined with field and laboratory observations support the idea that physiological and environmental constraints may generate shifts in habitat use and associated foraging tactics in amphibious ectotherms. Avenues for further research are discussed. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 115 , 411–422.     

Clonal integration facilitates spread of Paspalum paspaloides from terrestrial to cadmium‐contaminated aquatic habitats

• Cadmium (Cd) is a hazardous environmental pollutant with high toxicity to plants, which has been detected in many wetlands. Clonal integration (resource translocation) between connected ramets of clonal plants can increase their tolerance to stress. We hypothesised that clonal integration facilitates spread of amphibious clonal plants from terrestrial to Cd‐contaminated aquatic habitats.
• The spread of an amphibious grass Paspalum paspaloides was simulated by growing basal older ramets in uncontaminated soil connected (allowing integration) or not connected (preventing integration) to apical younger ramets of the same fragments in Cd‐contaminated water.
• Cd contamination of apical ramets of P. paspaloides markedly decreased growth and photosynthetic capacity of the apical ramets without connection to the basal ramets, but did not decrease these properties with connection. Cd contamination did not affect growth of the basal ramets without connection to the apical ramets, but Cd contamination of 4 and 12 mg·l^?1 significantly increased growth with connection. Consequently, clonal integration increased growth of the apical ramets, basal ramets and whole clones when the apical ramets were grown in Cd‐contaminated water of 4 and 12 mg·l^?1. Cd was detected in the basal ramets with connection to the apical ramets, suggesting Cd could be translocated due to clonal integration. Clonal integration, most likely through translocation of photosynthates, can support P. paspaloides to spread from terrestrial to Cd‐contaminated aquatic habitats.
• Amphibious clonal plants with a high ability for clonal integration are particularly useful for re‐vegetation of degraded aquatic habitats caused by Cd contamination.

     

Plant distribution and abundance in relation to physical conditions and location within Danish stream systems

The distribution of obligate submerged plants, amphibious plants and terrestrial plants in streams was examined in relation to water depth, substrate and distance to the banks using univariate and mulitivariate analyses. The analyses were based on recordings in more than 40000 quadrats (25×25 cm) in 208 unshaded sites in the predominantly small and shallow (<1.6 m) Danish streams. Also, the distribution of plant abundance and richness from the source to the outlet of the stream system was determined.The submerged plants in Danish streams include 87 terrestrial, 22 amphibious and 30 obligate submerged taxa. The distribution of plant types was mainly related to water depth and distance to the bank among the physical conditions, while the type of bottom substrate had no significant influence. Terrestrial plants and amphibious plants (excluding Sparganium emersum) dominated in shallow water near the bank, but declined rapidly with increasing depth and distance to the bank, reflecting the importance of dispersal by ingrowth from populations on the banks to the water among these plants. Accordingly, these two plant groups constituted a higher proportion of total plant abundance in small streams than large streams. S. emersum dominated on great depth and distance to the banks, probably reflecting the lengthwise dispersal of this species from upstream to downstream parts of the stream system, the tolerance of the species to weed cutting and the adaptation to grow at low light intensities. Obligate submerged plants dominated at intermediate depths and at all distances from the bank except from 0 to 50 cm. This distribution reflects the ability of these species to disperse lengthwise in streams and live permanently submerged.The species number of all species and obligate submerged plants was lower in the smallest stream sites compared to larger downstream sites, while there was no difference for terrestrial and amphibious plants. The downstream increase of submerged species can be explained by the increase of habitat area and the dispersal of plants with the current, implying that the species pool accumulates with distance from the source. This result is at variance with a maximum richness of submerged plant species predicted for intermediate-sized streams according to the River Continuum Concept developed for large North American streams having forested shallow upstream sections and unshaded, deep downstream sections both unsuitable to submerged plant growth. The results for Danish streams imply that both the longitudinal connection through the flowing water and the transversal connection to the local species on the banks are important for plant distribution in the streams.     

Moving in two worlds: aquatic and terrestrial locomotion in sea snakes (Laticauda colubrina,Laticaudidae)

Yellow‐lipped sea kraits (Laticauda colubrina) are amphibious in their habits. We measured their locomotor speeds in water and on land to investigate two topics: (1) to what degree have adaptations to increase swimming speed (paddle‐like tail etc.) reduced terrestrial locomotor ability in sea kraits?; and (2) do a sea krait’s sex and body size influence its locomotor ability in these two habitats, as might be expected from the fact that different age and sex classes of sea kraits use the marine and terrestrial environments in different ways? To estimate ancestral states for locomotor performance, we measured speeds of three species of Australian terrestrial elapids that spend part of their time foraging in water. The evolutionary modifications of Laticauda for marine life have enhanced their swimming speeds by about 60%, but decreased their terrestrial locomotor speed by about 80%. Larger snakes moved faster than smaller individuals in absolute terms but were slower in terms of body lengths travelled per second, especially on land. Male sea kraits were faster than females (independent of the body‐size effect), especially on land. Prey items in the gut reduced locomotor speeds both on land and in water. Proteroglyphous snakes may offer exceptional opportunities to study phylogenetic shifts in locomotor ability, because (1) they display multiple independent evolutionary shifts from terrestrial to aquatic habits, and (2) one proteroglyph lineage (the laticaudids) displays considerable intraspecific and interspecific diversity in terms of the degree to which they use terrestrial vs. aquatic habitats.     

Temnospondyli bite club: ecomorphological patterns of the most diverse group of early tetrapods

Temnospondyls were a successful group of early tetrapods that lived during the Palaeozoic and Mesozoic periods. Different ecomorphotypes were present (terrestrial, amphibious and fully aquatic) with a wide range of lifestyles. Herein, we analysed several clades of temnospondyls using geometric morphometrics, Finite Element Analysis, and comparative phylogenetic analysis. Some temnospondyli clades were 'crocodilomorph' feeding analogues. The skull analysis reveals a concordance between form and feeding function, in amphibious and fully aquatic feeders. The form of terrestrial feeders could be consequences of adaptative or phylogenetical constraints. Basal temnospondyls, as edopoids, were able to leave the water and feed on land. Eryopids continued as terrestrial feeders, although some members showed a shift to increased aquatic feeding. The aquatic environment was especially occupied by archegosaurs during the Permian. After the Permo-Triassic extinction, trematosaurs and capitosaurs returned to the aquatic environment and their members were amphibious and fully aquatic feeders until their disappearance.     

Evolution,ecology and physiology of amphibious killifishes (Cyprinodontiformes)

The order Cyprinodontiformes contains an exceptional diversity of amphibious taxa, including at least 34 species from six families. These cyprinodontiforms often inhabit intertidal or ephemeral habitats characterized by low dissolved oxygen or otherwise poor water quality, conditions that have been hypothesized to drive the evolution of terrestriality. Most of the amphibious species are found in the Rivulidae, Nothobranchiidae and Fundulidae. It is currently unclear whether the pattern of amphibiousness observed in the Cyprinodontiformes is the result of repeated, independent evolutions, or stems from an amphibious common ancestor. Amphibious cyprinodontiforms leave water for a variety of reasons: some species emerse only briefly, to escape predation or capture prey, while others occupy ephemeral habitats by living for months at a time out of water. Fishes able to tolerate months of emersion must maintain respiratory gas exchange, nitrogen excretion and water and salt balance, but to date knowledge of the mechanisms that facilitate homeostasis on land is largely restricted to model species. This review synthesizes the available literature describing amphibious lifestyles in cyprinodontiforms, compares the behavioural and physiological strategies used to exploit the terrestrial environment and suggests directions and ideas for future research.     

The quality of the aquatic environment and macrophytes of karstic watercourses

The quality of the aquatic environment and macrophytes were surveyed in the case of the remarkable karstic river Ljubljanica s. lat. (Slovenia). It consists of seven intermittent and permanent surface watercourses, connected by groundwater flows. We assessed 11 parameters describing the land use beyond the riparian zone, the structure of the riparian zone and stream channel morphology, as well as the distribution and abundance of macrophytes. The intermittent watercourses exhibited a relatively high level of naturalness, because the variable water regime prevents intensive human activity. Greater influence of the human activity on the permanent watercourses resulted in a modified riverine environment. The share of different ecological groups of macrophytes, i.e. submerged, emerged and amphibious species, reflected the water regimes of the different watercourses. A total of 62 taxa of macrophytes were identified in about 100 km of length examined. Of these, amphibious macrophytes dominated as a consequence of intermittent water regime. The relationship between environmental parameters and macrophytes, and the effects of the intermittent hydrology were investigated. All environmental parameters explained 28% of the variance in the distribution of macrophytes in watercourses, as determined by canonical correspondence analysis. Completeness of the riparian zone, bank undercutting and sediment accumulation were found to be the most influential.     

Comparison of Aerial and Submerged Leaves in Two Amphibious Species,Myosotis scorpioides and Ranunculus trichophyllus

Both amphibious species, Myosotis scorpioides and Ranunculus trichophyllus, thrive in a stressful environment (alternated flooding and drying), which is variable regarding water and radiation regimes. Plants from the field and plants grown under controlled water table maintained at 40 cm were analysed for content of chlorophyll (Chl) and UV-B screening compounds, and the efficiencies of PS2 and electron transport systems. We detected no significant differences in contents of Chl and UV-B screening compounds between submerged and aerial leaves. The measurements of respiratory potential and photochemical efficiency revealed the presence of permanent stress in M. sporpioides in the natural environment. Differences in physiological responses of submerged and aerial leaves indicated that the terrestrial environment was more favourable for M. scorpioides than for R. trichophyllus. Characteristics of both species suggested that R. trichophyllus might be a phylogenetically older aquatic plant than M. scorpioides.