Factors affecting terrestrial movement in the amphibious mangrove rivulus (Kryptolebias marmoratus)

We hypothesised that the exploration tendency of the amphibious mangrove rivulus Kryptolebias marmoratus would be inhibited in the terrestrial environment because of constraints on terrestrial locomotion or orientation. Using a novel object test, we showed that the fish explored objects in the aquatic but not the terrestrial environment, supporting the existence of constraints on terrestrial exploration. In further tests of the effects of extrinsic factors on terrestrial movement between aquatic refuges, shallow water depth simulating desiccation risk and the presence of a conspecific simulating intraspecific competition increased emersion outside of refuges, while high water salinity had no effect. These extrinsic factors had little effect on terrestrial movement between different aquatic refuges, except possibly for the lowest water depth tested. A significant association observed between emersion activity and movement between aquatic refuges suggested that terrestrial movement in K. marmoratus might depend on the tendency of individuals to emerse.     

Voluntary emergence and water detection in a newly recognized amphibious fish

Galaxias ‘nebula’, a small fish which has adaptations for air‐breathing but is not known to be amphibious, voluntarily emerged from water and, in an unfamiliar environment, moved preferentially towards an alternative water source. Nebula may thus be considered one of the few truly amphibious fishes, and their ability to detect water provides a selective advantage which aids their survival in unpredictable natural environments.     

Fish out of water: terrestrial jumping by fully aquatic fishes

Many teleosts that live at the water's edge will voluntarily strand themselves to evade predators or escape poor conditions-this behavior has been repeatedly observed in the field for killifishes (Cyprinodontiformes). Although most killifishes are considered fully aquatic and possess no obvious morphological specializations to facilitate terrestrial locomotion, individuals from several different species have been observed moving across land via a "tail flip" behavior that generates a terrestrial jump. Like aquatic fast starts, terrestrial jumps are produced by high-curvature lateral flexion of the body (stage one), followed by contralateral flexion of the posterior body (stage two). Here, terrestrial jumps and aquatic fast starts are quantified for two littoral teleosts: Gambusia affinis (a killifish, Cyprinodontiformes) and Danio rerio (a small carp, Cypriniformes) to determine if the tail flip is produced by other (non-killifish) teleosts and to test the null hypothesis that the tail flip is a fast start behavior, performed on land. Both Danio and Gambusia produce tail flip-driven terrestrial jumps, which are kinematically distinct from aquatic escapes and characterized by (1) a prolonged stage one, during which the fish bends, lifting and rolling the center of mass over the caudal peduncle, and (2) a relatively brief stage two, wherein the caudal peduncle pushes against the substrate to launch the fish into the aerial phase. The ability of these fully aquatic fishes to employ the same structure to produce distinct kinematic patterns in disparate environments suggests that a new behavior has evolved to facilitate movement on land and that anatomical novelty is not a prerequisite for effective terrestrial locomotion.     

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.     

Tolerance of forced air emergence by a fish with a broad vertical distribution, the rockpool blenny, Hypsoblennius gilberti (Blenniidae)

Many intertidal fishes, particularly among the Blenniidae and Cottidae, possess amphibious adaptations, including the ability to breathe in air and to avoid desiccation in terrestrial conditions. These traits are absent in subtidal species of blennies and cottids. Hypsoblennius gilberti, the rockpool blenny, is found in shallow rockpools in the mid to high intertidal areas of Southern California, and deeper to 18 m in the subtidal zone. This broad vertical distribution could indicate that this blenny is adapted for tidal air emergence, although H. gilberti has not been observed out of water in its natural habitat. H. gilberti does not emerge voluntarily from hypoxic sea water in the laboratory, but it easily withstands 3 h out of water. The aerial respiratory exchange ratio (CO2 released compared to O2 consumed) is 0.70, similar to that of amphibious intertidal fishes in air, indicating sufficient release of metabolically produced CO2 while emerged. There is no increase in aquatic respiration following emergence. However, unlike other amphibious fishes that maintain aerial oxygen consumption at a level similar to aquatic oxygen consumption, H. gilberti has an aerial oxygen consumption rate one-third that in water. H. gilberti can recover rapidly from terrestrial water loss, and shows no change in evaporative water loss rates at 93% and 77% relative humidities. The amphibious capabilities in H. gilberti, even if rarely used, permit survival in air during tidal emergence. These findings suggest that H. gilberti may demonstrate an intermediate condition between the amphibious species of intertidal fishes that regularly emerge from water, and the subtidal fishes that do not survive air emergence and are completely restricted to an aquatic habitat.     

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.     

The feeding ecology of freshwater fishes in two rivers of the Australian wet tropics

Synopsis The fish fauna of the Mulgrave and South Johnstone rivers is diverse relative to other Australian rivers and this study examines the diets of many of the resident fish species. Most species were small (< 200 g), and although considerable overlap in the size of the mouth was observed, closely related species tended to have non-overlapping ranges in mouth size. Five trophic guilds were recognised and substantial discrimination between guilds on the basis of body size was noted. Small fishes (< 5 gm body weight) consumed a variety of insect larvae and small terrestrial insects. The diet of large fish was characterised by the presence of large aquatic invertebrates and fish. A third group of intermediate sized fishes (10–20 gm), which included the 0+ age class of three species of large fish, also consumed aquatic invertebrates but only a small proportion of terrestrial invertebrates. Vegetable material was present in the diet of all three guilds but the source of that material varied. In groups 1 to 3 above, the source of that material was desmids and diatoms, aquatic macrophytes or filamentous alga respectively. A fourth guild fed predominately on detritus and some bivalve molluscs, and a fifth group, containing only two species, fed feavily on gastropod molluscs. The extent of dietary overlap varied both within- and between-rivers. In habitats dominated by low water velocities and sandy substrates, resource partitioning was pronounced and the number of fishes with empty or near empty guts was high, suggesting that food was more limited in this type of habitats. Little resource partitioning was observed in habitats characterised by a coarse substrate, high water velocity and dense riparian canopy.     

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.

     

Gross and fine anatomy of the respiratory vasculature of the mudskipper,Periophthalmodon schlosseri (Gobiidae: Oxudercinae)

To illustrate vascular modification accompanying transition from aquatic to amphibious life in gobies, we investigated the respiratory vasculatures of the gills and the bucco‐opercular cavities in one of the most terrestrially‐adapted mudskippers, Periophthalmodon schlosseri, using the corrosion casting technique. The vascular system of Pn. schlosseri retains the typical fish configuration with a serial connection of the gills and the systemic circuits, suggesting a lack of separation of O₂‐poor systemic venous blood and O₂‐rich effluent blood from the air‐breathing surfaces. The gills appear to play a limited role in gas exchange, as evidenced from the sparsely‐spaced short filaments and the modification of secondary lamellar vasculature into five to eight parallel channels that are larger than red blood cell size, unlike the extensive sinusoidal system seen in purely water‐breathing fishes. In contrast, the epithelia of the bucco‐opercular chamber, branchial arches, and leading edge of the filaments are extensively laden with capillaries having a short (<10 μm) diffusion distance, which strongly demonstrate the principal respiratory function of these surfaces. These capillaries form spiral coils of three to five turns as they approach the epithelial surface. The respiratory capillaries of the bucco‐opercular chamber are supplied by efferent blood from the gills and drained by the systemic venous pathway. We also compared the degree of capillarization in the bucco‐opercular epithelia of Pn. schlosseri with that of the three related intertidal‐burrowing gobies (aquatic, non‐air‐breathing Acanthogobius hasta; aquatic, facultative air‐breathing Odontamblyopus lacepedii; amphibious air‐breathing Periophthalmus modestus) through histological analysis. The comparison revealed a clear trend of wider distribution of denser capillary networks in these epithelia with increasing reliance on air breathing, consistent with the highest aerial respiratory capacity of Pn. schlosseri among the four species. J. Morphol. 2011. © 2011 Wiley‐Liss, Inc.     

Aerial and aquatic visual acuity of the grey bichir Polypterus senegalus,as estimated by optokinetic response

The present study assessed the aerial and aquatic visual abilities of juvenile grey bichir Polypterus senegalus, fish capable of terrestrial locomotion, by measuring the optokinetic response to stimuli of varying speed and spatial frequency. In water, fish tracked slow-moving (2° s⁻¹) stimuli moderately well and fast-moving stimuli very poorly. Spatial acuity was very low compared with many other species, with maximum response observed at 0.05–0.075 stimulus cycles per degree of visual arc; however, it should be noted that adult fish, with their larger eyes, are likely to have somewhat improved spatial acuity. Low spatial acuity and limited stimulus tracking ability might be expected in a nocturnal ambush predator such as P. senegalus, where gaze stabilization may be less crucial and other sensory inputs may have greater importance in perception of the environment. In air, spatial and temporal acuity were both poorer by every measure, but some visual ability persisted. As the eye shows no anatomical specialization for aerial vision, poor vision was expected; however, the large decrease in saccade velocity observed in air trials was unexpected. Stimulus parameters typically have little effect on the characteristics of the saccade, so this finding may suggest that the function of the reflex system itself could be compromised in the aerial vision of some fishes capable of terrestrial locomotion.     

Influence of fishes on macroinvertebrate communities and insect emergence production in intermittent stream refuges

1. Drying intermittent stream networks often have permanent water refuges that are important for recolonisation. These habitats may be hotspots for interactions between fishes and invertebrates as they become isolated, but densities and diversity of fishes in these refuges can be highly variable across time and space.
2. Insect emergence from streams provides energy and nutrient subsidies to riparian habitats. The magnitude of such subsidies may be influenced by in-stream predators such as fishes.
3. We examined whether benthic macroinvertebrate communities, emerging adult insects, and algal biomass in permanent grassland stream pools differed among sites with naturally varying densities of fishes. We also manipulated fish densities in a mesocosm experiment to address how fishes might affect colonisation during recovery from hydrologic disturbance.
4. Fish biomass had a negative impact on invertebrate abundance, but not biomass or taxa richness, in natural pools. Total fish biomass was not correlated with total insect emergence in natural pools, but orangethroat darter (Etheostoma spectabile) biomass was inversely correlated with emerging Chironomidae biomass and individual midge body size. The interaction in our models between predatory fish biomass and date suggested that fishes may also delay insect emergence from natural pools, altering the timing of aquatic–terrestrial subsidies.
5. There was an increase over time in algal biomass (chlorophyll-a) in mesocosms, but this did not differ among fish density treatments. Regardless, fish presence in mesocosms reduced the abundance of colonising insects and total invertebrate biomass. Mesocosm invertebrate communities in treatments without fishes were characterised by more Chironomidae, Culicidae, and Corduliidae.
6. Results suggest that fishes influence invertebrates in habitats that represent important refuges during hydrologic disturbance, hot spots for subsidy exports to riparian food webs, and source areas for colonists during recovery from hydrologic disturbance. Fish effects in these systems include decreasing invertebrate abundance, shifting community structure, and altering patterns of invertebrate emergence and colonisation.

     

Metabolism,gas exchange,and acid‐base balance of giant salamanders

The giant salamanders are aquatic and paedomorphic urodeles including the genera Andrias and Cryptobranchus (Cryptobranchidae), Amphiuma (Amphiumidae), Siren (Sirenidae), and Necturus (Proteidae, of which only N. maculosus is considered ‘a giant'). Species in the genera Cryptobranchus and Necturus are considered aquatic salamanders well adapted for breathing water, poorly adapted for breathing air, and with limited abilities to compensate acid‐base disturbances. As such, they are water‐breathing animals with a somewhat fish‐like respiratory and acid‐base physiology, whose habitat selection is limited to waters that do not typically become hypoxic or hypercarbic (although this assertion has been questioned for N. maculosus). Siren and Amphiuma species, by contrast, are dependent upon air‐breathing, have excellent lungs, inefficient (Siren) or no (Amphiuma) gills, and are obligate air‐breathers with an acid‐base status more similar to that of terrestrial tetrapods. As such, they can be considered to be air‐breathing animals that live in water. Their response to the aquatic hypercarbia that they often encounter is to maintain intracellular pH (pH_i) and abandon extracellular pH regulation, a process that has been referred to as preferential pH_i regulation. The acid‐base status of some present‐day tropical air‐breathing fishes, and of Siren and Amphiuma, suggests that the acid‐base transition from a low PCO₂‐low [] system typical of water‐breathing fishes to the high PCO₂‐high [] systems of terrestrial tetrapods may have been completed before emergence onto land, and likely occurred in habitats that were typically both hypoxic and hypercarbic.     

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.     

Terrestrial feeding in the Mudskipper Periophthalmus (Pisces: Teleostei): A cineradiographic analysis

Mudskipping gobies (Periophthalminae) are among the most terrestrial of amphibious fishes. Specializations associated with terrestrial prey capture and deglutition have been studied in Periophthalmus koelreuteri by light and X-ray cinematography which permits direct visualization of pharyngeal jaw movement during deglutition. Anatomical specializations of the pharyngeal jaws are described and include depressible teeth, a large ventral process on ceratobranchial five, and muscular modifications.
Multiple terrestrial feedings occur by Periophthalmus without a return to the water, and cineradiography reveals that the buccal cavity is often filled with air during terrestrial excursions in contrast to some previous hypotheses. Transport of the prey into the oesophagus occurs primarily by anteroposterior movement of the upper pharyngeal jaw. The lower pharyngeal jaw plays a limited role in food transport and may serve primarily to hold and position prey. The bite between upper and lower pharyngeal jaws occurs between the anterior teeth, and both jaws are protracted together during raking of food into the oesophagus. Functional specializations correlated with terrestrial feeding include obligatory use of pharyngeal jaws for swallowing even small prey items and positioning of the prey in the pharynx by pharyngeal jaw and hyoid movements alone.
This analysis of terrestrial feeding allows hypotheses of design constraints imposed by the aquatic medium on fishes to be raised and tested.     

Kinematics of terrestrial locomotion in harbor seals and gray seals: Importance of spinal flexion by amphibious phocids

Pinnipeds are amphibious mammals with flippers, which function for both aquatic and terrestrial locomotion. Evolution of the flippers has placed constraints on the terrestrial locomotion of phocid seals. The detailed kinematics of terrestrial locomotion of gray (Halichoerus grypus) and harbor (Phoca vitulina) seals was studied in captivity and in the wild using video analysis. The seals exhibited dorsoventral undulations with the chest and pelvis serving as the main contact points. An anteriorly directed wave produced by spinal flexion aided in lifting the chest off the ground as the fore flippers were retracted to pull the body forward. The highest length‐specific speeds recorded were 1.02 BL/s for a gray seal in captivity and 1.38 BL/s for a harbor seal in the wild. The frequency and amplitude of spinal movement increased directly with speed, but the duty factor remained constant. Substrate did not influence the kinematics except for differences due to moving up or down slopes. The highly aquatic nature of phocids seals has restricted them to locomote on land primarily using spinal flexion, which can limit performance in speed and duration.     

Phylogeography of Walton’s Mudskipper,Periophthalmus waltoni Koumans, 1941 (Perciformes: Gobiidae), from the Persian Gulf and Gulf of Oman

Mudskippers are amphibious air breathing fish with terrestrial adaptations in contrast to entirely aquatic fish. They are adapted to living on mudflats and show morphological, physiological, and behavioural features that could affect their phylogeny and phylogeography. A comparative genetic analysis was carried out on 100 specimens of the mudskipper Periophthalmus waltoni Koumans, 1941 from eight different sites along the coast of the Persian Gulf and Gulf of Oman. Phylogeographic inference based on two mitochondrial markers (Cyt b and D-loop) suggests that P. waltoni populations are divided into two well-divergent clades western and eastern. This is likely related to the geohydrological history of the area during the last Pleistocene glaciations. The regional phylogeographies are apparently also influenced by ecological and geographical barriers such as salinity, water current, and the geographic position of the Strait of Hormuz.     

Inner architecture of vertebral centra in terrestrial and aquatic mammals: A two‐dimensional comparative study

Inner vertebral architecture is poorly known, except in human and laboratory animals. In order to document this topic at a broad comparative level, a 2D‐histomorphometric study of vertebral centra was conducted in a sample of 98 therian mammal species, spanning most of the size range and representing the main locomotor adaptations known in therian taxa. Eleven variables relative to the development and geometry of trabecular networks were extracted from CT scan mid‐sagittal sections. Phylogeny‐informed statistical tests were used to reveal the respective influences of phylogeny, size, and locomotion adaptations on mammalian vertebral structure. The use of random taxon reshuffling and squared change parsimony reveals that 9 of the 11 characteristics (the two exceptions are total sectional area and structural polarization) contain a phylogenetic signal. Linear discriminant analyses suggest that the sampled taxa can be arranged into three categories with respect to locomotion mode: a) terrestrial + flying + digging + amphibious forms, b) coastal oscillatory aquatic taxa, and c) pelagic oscillatory aquatic forms represented by oceanic cetaceans. Pairwise comparison tests and linear regressions show that, when specific size increases, the length of trabecular network (Tt.Tb.Le), as well as trabecular proliferation in total sections (Pr.Tb.Tt), increase with positive allometry. This process occurs in all locomotion categories but is particularly pronounced in pelagic oscillators. Conversely, mean trabecular width has a lesser increase with size in pelagic oscillators. Trabecular orientation is not influenced by size. All tests were corrected for multiple testing. By using six structural variables or indices, locomotion mode can be predicted with a 97.4% success rate for terrestrial forms, 66.7% for coastal oscillatory, and 81.3% for pelagic oscillatory. The possible functional meaning of these results and their potential use for paleobiological inference of locomotion in extinct taxa are discussed. J. Morphol., 2013. © 2013 Wiley Periodicals, Inc.     

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.     

Clonal integration supports the expansion from terrestrial to aquatic environments of the amphibious stoloniferous herb Alternanthera philoxeroides

Effects of clonal integration on land plants have been extensively studied, but little is known about the role in amphibious plants that expand from terrestrial to aquatic conditions. We simulated expansion from terrestrial to aquatic habitats in the amphibious stoloniferous alien invasive alligator weed ( Alternanthera philoxeroides ) by growing basal ramets of clonal fragments in soils connected (allowing integration) or disconnected (preventing integration) to the apical ramets of the same fragments submerged in water to a depth of 0, 5, 10 or 15 cm. Clonal integration significantly increased growth and clonal reproduction of the apical ramets, but decreased both of these characteristics in basal ramets. Consequently, integration did not affect the performance of whole clonal fragments. We propose that alligator weed possesses a double-edged mechanism during population expansion: apical ramets in aquatic habitats can increase growth through connected basal parts in terrestrial habitats; however, once stolon connections with apical ramets are lost by external disturbance, the basal ramets in terrestrial habitats increase stolon and ramet production for rapid spreading. This may contribute greatly to the invasiveness of alligator weed and also make it very adaptable to habitats with heavy disturbance and/or highly heterogeneous resource supply.