Terrestrial Substrate Research Articles

Operational Mapping of Submarine Groundwater Discharge into Coral Reefs: Application to West Hawai‘i Island

Submarine groundwater discharge (SGD) is a recognized contributor to the hydrological and biogeochemical functioning of coral reef ecosystems located along coastlines. However, the distribution, size, and thermal properties of SGD remain poorly understood at most land–reef margins. We developed, deployed, and demonstrated an operational method for airborne detection and mapping of SGD using the 200 km coastline of western Hawai‘i Island as a testing and analysis environment. Airborne high spatial resolution (1 m) thermal imaging produced relative sea surface temperature (SST) maps that aligned geospatially with boat-based transects of SGD presence–absence. Boat-based SST anomaly measurements were highly correlated with airborne SST anomaly measurements (R2 = 0.85; RMSE = 0.04 °C). Resulting maps of the relative difference in SST inside and outside of SGD plumes, called delta-SST, revealed 749 SGD plumes in 200 km of coastline, with nearly half of the SGD plumes smaller than 0.1 ha in size. Only 9% of SGD plumes were ≥1 ha in size, and just 1% were larger than 10 ha. Our findings indicate that small SGD is omnipresent in the nearshore environment. Furthermore, we found that the infrequent, large SGD plumes (>10 ha) displayed the weakest delta-SST values, suggesting that large discharge plumes are not likely to provide cooling refugia to warming coral reefs. Our operational approach can be applied frequently over time to generate SGD information relative to terrestrial substrate, topography, and pollutants. This operational approach will yield new insights into the role that land-to-reef interactions have on the composition and condition of coral reefs along coastlines.

Phytostabilization Potential of Salix alba as Biomonitors of Heavy Metals in Soil Pollution near the Erzeni Riverbank

The great sources of water pollution in Albania in the last decade are urban discharges which indicate in other sistems. The aim of this study was to evaluate the concentration of heavy metals in the soil and plant of Salix alba. Samples was collected from the Erzen riverbed. The objectives are based on assessment of the concentrations of physico-chemical characteristics heavy metals obtained from the sediment and willow (Salix alba) in Erzeni river. The presence of organic matter in soil - the willow plant - was also analyzed. The use of plants in the recuperation of contaminated soil is low cost, sustainable, and environmentally sound. Heavy metals concentration in soil range as follows: Ni (42.2–98.4 mg/kg); Cr (18.9- 34.5 mg/kg), and Pb (53.2-98.4 mg/kg). Some statistically significant differences were observed in the data on the amounts of metals accumulated in the soil, significantly more than in the data on the metal concentrations achieved in the tissues of the Salix alba plant. Heavy metal concentration in plants reach values Ni (0.9–3.54 mg/kg); Cr (0.57 - 0.89 mg/kg), and Pb (0.06 -0.19 mg/kg). Average concentrations in heavy metal plant samples were listed in the order Ni> Cr> Pb. The results of nickel, chromium, and lead clearly show higher concentrations in samples 0-25 cm across the range of extractors. The use of diversified plant materials is essential and optimal for the phytoremediation process. These species offer different opportunities through their metallic tolerance and accumulation of underground biomass metals for the permanent removal of these metals from the terrestrial substrate.

Permafrost Landscape History Shapes Fluvial Chemistry, Ecosystem Carbon Balance, and Potential Trajectories of Future Change

AbstractIntensifying permafrost thaw alters carbon cycling by mobilizing large amounts of terrestrial substrate into aquatic ecosystems. Yet, few studies have measured aquatic carbon fluxes and constrained drivers of ecosystem carbon balance across heterogeneous Arctic landscapes. Here, we characterized hydrochemical and landscape controls on fluvial carbon cycling, quantified fluvial carbon fluxes, and estimated fluvial contributions to ecosystem carbon balance across 33 watersheds in four ecoregions in the continuous permafrost zone of the western Canadian Arctic: unglaciated uplands, ice‐rich moraine, and organic‐rich lowlands and till plains. Major ions, stable isotopes, and carbon speciation and fluxes revealed patterns in carbon cycling across ecoregions defined by terrain relief and accumulation of organics. In previously unglaciated mountainous watersheds, bicarbonate dominated carbon export (70% of total) due to chemical weathering of bedrock. In lowland watersheds, where soil organic carbon stores were largest, lateral transport of dissolved organic carbon (50%) and efflux of biotic CO2 (25%) dominated. In watersheds affected by thaw‐induced mass wasting, erosion of ice‐rich tills enhanced chemical weathering and increased particulate carbon fluxes by two orders of magnitude. From an ecosystem carbon balance perspective, fluvial carbon export in watersheds not affected by thaw‐induced wasting was, on average, equivalent to 6%–16% of estimated net ecosystem exchange (NEE). In watersheds affected by thaw‐induced wasting, fluvial carbon export approached 60% of NEE. Because future intensification of thermokarst activity will amplify fluvial carbon export, determining the fate of carbon across diverse northern landscapes is a priority for constraining trajectories of permafrost region ecosystem carbon balance.

Biogenic elements in terrestrial substrates, freshwater pools and subice seamples of the Argentine islands – Kyiv peninsula region, the Maritime Antarctic

Aim. The aim was to estimate inflow of nitrogen and phosphorus to the terrestrial substrate, freshwater pools, as well as in the ice core and subglacial waters, from the sea-bird colonies, and locations of non-colonial flying birds, or individual colonial birds activity. Methods. The samples of substrates, fresh waters, ice cores and samples from the subglacial waters collected during the 25th (2019/20) and 26th (2020/21) Ukrainian Antarctic expeditions in the area of the Argentine Islands – Kyiv Peninsula were analyzed by selected indicators of ornithogenic impact – concentration of bioaviable forms of nitrogen and phosphorus. Results. The concentration for nitrogen and phosphorus are shown to be ornitogenic in samples from all explored locations. High concentrations of ornithogenic compounds were detected not only inflowing from birds colonies, in particular penguins, but also in samples without their influence. Conclusions. The obtained data confirm the high level of influence of both colonial and non-colonial birds on terrestrial and freshwater ecosystems of the Argentine Islands-Kyiv Peninsula. It is shown that the edifying effect and inflow of significant amounts of nitrogen and phosphorus occurs not only in large penguin colonies, but also in single nesting or feeding and resting areas of non-colonial flying birds, or in the presence of individual colonial birds in the study area. However, in the locations of large penguin colonies, easily disolved bioavailable forms of nitrogen and phosphorus are found in much higher, hypertrophic concentrations. Relatively low concentrations of nutrients are currently found only in areas that have recently been released from the glacier and remain uninhabited, unattractive or inaccessible to birds. Such locations are currently marked only on the coast of the Kyiv Peninsula and are associated with the recent retreat of local glaciers. In case of the presence of penguins or the activity of non-colonial or individual colonial birds, all studied freshwater pools were eutrophied to varying extend. The dynamics of organic matter inflow to some of the studied freshwater pools of the region probably indicates the permanent eutrophication. Studies of the ice core of the Galindez Island Glacier and subglacial freshwaters have shown that ornithogenic effects have been observed here for a long time.Key words: eutrophication, seabirds, the Antarctic, substrates, freshwater pools.

High‐speed terrestrial substrate transitions: How a fleeing cursorial day gecko copes with compliance changes that are experienced in nature

Abstract Animal movement is often largely determined by abiotic conditions of the environment, including substrate properties. While a large body of work has improved our understanding of how different substrate properties can impact locomotor performance and behaviour, few of these studies have investigated this relationship during transitions within a single locomotor event. In nature, terrestrial animals frequently encounter substrate transitions, or changes in substrate level, incline, texture and/or compliance during a single bout of movement, which can be sudden for high‐speed animals. These animals often adjust their posture and kinematics during transitions, and in some cases lose forward velocity. We examined the occurrence and effect of non‐elastic compliance transitions in Rhoptropus afer, a cursorial day gecko known for its ability to sprint rapidly for several metres at a time. We recorded substrate use during provoked escapes in the field and conducted locomotor trials on a trackway that mimicked natural structural habitat conditions with transitions from a rigid surface into sand and from sand back to a rigid surface. During escapes, R. afer used substrates of different compliance (i.e. rock, gravel and sand) and transitioned to and from the more compliant surfaces with even frequency, which matched substrate and compliance availability estimates. In laboratory experiments, sprint speed was not significantly affected by acute changes in compliance, which was likely facilitated by an increased body angle and duty factor upon entering the sand, and potentially a high yield strength of the sand relative to applied forces. We speculate that this species' ability to maintain speed during compliance transitions underlies their apparent indiscriminate substrate use during escapes, and that this behaviour may offer a selective advantage for evading larger terrestrial predators. Using field data to inform and contextualize laboratory experiments thus yields important insights as to how animals accommodate acute changes in substrate conditions encountered during critical locomotor events. A free Plain Language Summary can be found within the Supporting Information of this article.

Positional behavior and substrate use in wild adult bearded capuchin monkeys (Sapajus libidinosus).

Natural selection for positional behavior (posture and locomotion) has at least partially driven the evolution of anatomical form and function in the order Primates. Examination of bipedal behaviors associated with daily activity patterns, foraging, and terrestrial habitat use in nonhuman primates, particularly those that adopt bipedal postures and use bipedal locomotion, allows us to refine hypotheses concerning the evolution of bipedalism in humans. This study describes the positional behavior of wild bearded capuchins (Sapajus libidinosus), a species that is known for its use of terrestrial substrates and its habitual use of stones as tools. Here, we test the association of terrestrial substrate use with bipedal posture and locomotion, and the influence of sex (which co-varies with body mass in adults of this species) on positional behavior and substrate use. Behavior and location of 16 wild adult bearded capuchins from two groups were sampled systematically at 15 s intervals for 2 min periods for 1 year (10,244 samples). Despite their different body masses, adult males (average 3.5 kg) and females (average 2.1 kg) in this study did not differ substantially in their positional behaviors, postures, or use of substrates for particular activities. The monkeys used terrestrial substrates in 27% of samples. Bipedal postures and behaviors, while not a prominent feature of their behavior, occurred in different forms on the two substrates. The monkeys crouched bipedally in trees, but did not use other bipedal postures in trees. While on terrestrial substrates, they also crouched bipedally but occasionally stood upright and moved bipedally with orthograde posture. Bearded capuchin monkeys' behavior supports the suggestion from anatomical analysis that S. libidinosus is morphologically better adapted than its congeners to adopt orthograde postures.

Inventory of ferns and lycophytes within forest fragments of Araucaria in southern Brazil

Abstract: The Araucaria Forest is a unique plant formation, practically restricted to the Atlantic Forest biome, in the South and Southeast of Brazil. It is immensely fragmented and its area is reduced to a minimum fraction, from 13 to 2% of the original area, due to intense anthropic exploitation. Our study evaluated the richness and floristic composition of ferns and lycophytes within three Araucaria forest fragments, in Rio Grande do Sul, Brazil. For the floristic inventory, a parcel of 1 ha (100x100m) was demarcated inside three fragments, which were classified by size: large (246 ha - H1LF), medium (57 ha - H2MF) and small (5.2 ha - H3SF). Occurring species life forms and preferential substrates up to 4 meters above ground were recorded. In total, 55 species were catalogued, only two of which were lycophytes, distributed in 32 genera and 17 families. Considering the area of fragments, the recorded species richness has decreased, presenting greater numbers in H1LF (48), followed by H2MF (33), and H3SF (29). In the three sites, terrestrial substrate and the hemicryptophyte species life form predominated. We observed that one hectare of a larger forest fragment presented 65% more species than that of a smaller one, considering that the smaller fragment total area represents only 2% of the larger forest's area. On the other hand, one hectare of the smaller fragment contributed 17% to fern and lycophyte species conservation occurring in Brazilian Araucaria Forests, and 8% to the state of Rio Grande do Sul's total richness. The diverse heterogeneity and species composition grants floristic identity to each of the studied forest interiors. Our results highlight the need to include the botanical parameters here analyzed in management, conservation degree evaluation, and maintenance of Araucaria Forests plant biodiversity.

Physical Characteristics Influencing Nearshore Habitat Use by Juvenile Chinook Salmon in the Sacramento River, California

AbstractUrban and agricultural development has resulted in drastically modified riverine corridors that are often considered to be detrimental to the recovery of anadromous salmonid populations. Although mitigation features (e.g., large wood and shallow‐water areas) are frequently incorporated in flood control infrastructure to offset the impacts of streambank stabilization, little is known regarding their effectiveness and the habitat characteristics associated with enhanced nearshore rearing conditions in large rivers. We evaluated two measures of habitat use by emigrating juvenile Chinook Salmon Oncorhynchus tshawytscha relative to different shoreline types (rock revetment [riprap], mitigated, and natural) and analyzed associations between environmental characteristics and habitat occupancy using a large number of presence/absence samples in the lower Sacramento River, California. We found both measures of habitat use to be significantly higher at natural shorelines and those including mitigation features than at shorelines consisting predominantly of rock revetment. A predictive logistic regression model suggested that the density of woody material and inundated terrestrial vegetation, depth, and substrate type significantly affected habitat occupancy. Despite a moderate predictive capability (62% of correctly classified records in a leave‐one‐out simulation), the model was useful in identifying habitat characteristics associated with significantly increased habitat use in this large, low‐gradient river, most notably the presence of instream cover (wood or vegetation), gently sloping streambanks, fine substrate, and variable nearshore current velocity. Conversely, habitat occupancy by juvenile Chinook Salmon diminished with large, rocky substrate and increased depth, characteristics favored by introduced predatory Smallmouth Bass Micropterus dolomieu. This study illustrates the value of incorporating mitigation features and identifies characteristics that enhance habitat use by emigrating juvenile Chinook Salmon.

Forelimb morphology and substrate use in extant Cercopithecidae and the fossil primate community of the Hadar sequence, Ethiopia

It is suggested that joint architecture of the extant cercopithecid forelimb differentiates terrestrial from arboreal quadrupedal species. Linear dimensions of forelimb joint morphology have also been used to assign fossil species to locomotor categories. However, many primates use a mix of terrestrial and arboreal behaviors, which can be problematic when developing models of behavior reconstruction using morphological variation. The current study uses multivariate analyses to identify morphology related to substrate use in primates, including determination of semiterrestriality. Measurements collected from distal humeri and proximal ulnae of 49 extant cercopithecid primate species were selected based on studies indicating that they could individually predict substrate use. Analyses including one-way analysis of variance, principal components, and discriminant functions were conducted to assess their ability to differentiate between arboreal and terrestrial substrate use. The functions created in these analyses are then applied to data from fossil specimens from the Hadar sequence, Ethiopia, sampling both the Hadar and overlying Busidima Formations, to retrodict possible substrate behavior of fossil monkeys at Hadar through time. As this study is designed to identify function and behavior rather than phylogeny, the taxonomic assignment of the fossil specimens is sometimes uncertain, but substrate behavior can still be inferred. Results suggest that substrate use, including semiterrestrial behavior, in extant and extinct primates can be inferred successfully from multivariate analyses based on joint morphology of the monkey elbow. This study reveals that the ecological distribution of primarily terrestrial fossil primate species of the Hadar sequence is comparable to modern-day communities in habitats similar to those reconstructed for the Hadar members.

Gait characteristics and spatio-temporal variables of climbing in bonobos (Pan paniscus).

Although much is known about the terrestrial locomotion of great apes, their arboreal locomotion has been studied less extensively. This study investigates arboreal locomotion in bonobos (Pan paniscus), focusing on the gait characteristics and spatio-temporal variables associated with locomotion on a pole. These features are compared across different substrate inclinations (0°, 30°, 45°, 60°, and 90°), and horizontal quadrupedal walking is compared between an arboreal and a terrestrial substrate. Our results show greater variation in footfall patterns with increasing incline, resulting in more lateral gait sequences. During climbing on arboreal inclines, smaller steps and strides but higher stride frequencies and duty factors are found compared to horizontal arboreal walking. This may facilitate better balance control and dynamic stability on the arboreal substrate. We found no gradual change in spatio-temporal variables with increasing incline; instead, the results for all inclines were clustered together. Bonobos take larger strides at lower stride frequencies and lower duty factors on a horizontal arboreal substrate than on a flat terrestrial substrate. We suggest that these changes are the result of the better grip of the grasping feet on an arboreal substrate. Speed modulation of the spatio-temporal variables is similar across substrate inclinations and between substrate types, suggesting a comparable underlying motor control. Finally, we contrast these variables of arboreal inclined climbing with those of terrestrial bipedal locomotion, and briefly discuss the results with respect to the origin of habitual bipedalism. Am. J. Primatol. 78:1165-1177, 2016. © 2016 Wiley Periodicals, Inc.

Locomotion in degus on terrestrial substrates varying in orientation – implications for biomechanical constraints and gait selection

To gain new insights into running gaits on sloped terrestrial substrates, metric and selected kinematic parameters of the common degu (Octodon degus) were examined. Individuals were filmed at their maximum voluntary running speed using a high-speed camera placed laterally to the terrestrial substrate varying in orientations from −30° to +30°, at 10° increments. Degus used trotting, lateral-sequence (LS) and diagonal-sequence (DS) running gaits at all substrate orientations. Trotting was observed across the whole speed range whereas DS running gaits occurred at significantly higher speeds than LS running gaits. Metric and kinematic changes on sloped substrates in degus paralleled those noted for most other mammals. However, the timing of metric and kinematic locomotor adjustments differed significantly between individual degus. In addition, most of these adjustments took place at 10° rather than 30° inclines and declines, indicating significant biomechanical demands even on slightly sloped terrestrial substrates. The results of this study suggest that DS and LS running gaits may represent an advantage in small to medium-sized mammals for counteracting some level of locomotor instability. Finally, changes in locomotor parameters of the forelimbs rather than the hindlimbs seem to play an important role in gait selection in small to medium-sized mammals.

Verreaux’s sifaka (<i>Propithecus verreauxi</i>) and ring-tailed lemur (<i>Lemur catta</i>) endoparasitism at the Bezà Mahafaly Special Reserve

As hosts, primate behavior is responsible for parasite avoidance and elimination as well as parasite acquisition and transmission among conspecifics. Thus, host behavior is largely responsible for the distribution of parasites in free - ranging populations. We examined the importance of host behavior in acquiring and avoiding parasites that use oral routes by comparing the behavior of sympatric Verreaux’s sifaka (Propithecus verreauxi) and ring - tailed lemurs (Lemur catta) inhabiting the Beza Mahafaly Special Reserve (BMSR) in Madagascar. For each species, two groups lived in a protected parcel and two groups lived in anthropogenically - disturbed forests. Analysis of 585 fecal samples revealed that the BMSR ring - tailed lemurs harbored six species of nematode worms and three species of protistan parasites. The sifaka harbored only two nematodes. Differences in richness and prevalence appear to be linked to host behavior and the ecological distribution of their parasites. To understand the interplay between behavioral mechanisms to avoid or transmit parasites, we analyzed 683 hours of behavioral observations. BMSR ring - tailed lemurs were observed on the ground significantly more than sifaka and this terrestrial substrate use provides greater opportunities for soil - transmitted parasites to acquire a host. Ring - tailed lemurs using the anthropogenically - disturbed forests harbored parasites not found in the groups inhabiting the protected parcel which they may be acquiring via coprophagy or contact with feces. The arboreality of sifaka allows them to evade most soil-transmitted endoparasites and the patterns of parasitism exhibited by sifaka living in the anthropogenically - disturbed forests did not deviate from the patterns observed among the sifaka living in the protected parcel.

Riqueza de samambaias e licófitas de uma mata de galeria na região central de Mato Grosso do Sul, Brasil

Neste trabalho é apresentado o levantamento florístico das samambaias e licófitas ocorrentes em uma mata de galeria, na região central de Mato Grosso do Sul, Brasil. Foram registradas na área de estudo 29 espécies e duas variedades. Dryopteridaceae e Pteridaceae foram as famílias mais ricas (oito e cinco espécies, respectivamente) e Elaphoglossum e Blechnum foram os gêneros mais ricos (três espécies cada). Preferencialmente, as espécies listadas ocorrem no interior da mata (68%), ocupam o substrato terrícola (77,4%), são hemicriptófitas (77,4%) e rosuladas (64,5%). Observamos quatro espécies ainda não citadas para Mato Grosso do Sul, sendo essas Blechnum lanceola L., Elaphoglossum pachydermum (Fée) T. Moore, Lindsaea lancea (L.) Bedd var lancea e ainda Mickelia nicotianifolia (Sw.) R. C. Moran et al., que possui seu limite sul de distribuição no Brasil, na área de estudo.

Diving times and feeding rate by pecking in the Eurasian coot (Fulica atra)

We acquired data on diving times and feeding rates by pecking on three different substrates in a small wetland of central Italy, in order to improve the scant knowledge on foraging behaviour of the Eurasian coot (Fulica atra) in the Mediterranean area. Diving times showed a mean value of 2.59 sec (± 1.81 SD; n = 186). A large proportion of diving times (about 72%) were between 1 and 3 sec, a range corresponding to intrinsic physio-ecological times allowing a coot to search for food items below the water surface. The feeding rate by pecking was significantly higher in muddy soils when compared with either shallow water or rush beds. The data may be explainable in terms of the easier detectability and availability of different food items in muddy soils, which may increase the feeding rate by pecking on this substrate. The lower feeding rate in rush beds, when compared to muddy soils, could also be explained in terms of the spatial arrangement of this terrestrial substrate and, consequently, the higher level of predatory risk.

Spatial distribution of cyanobacteria and algae from the tombstone in a historic cemetery in Bratislava, Slovakia.

This study focuses on species composition and spatial distribution of cyanobacterial and algal communities colonizing the surface of the tombstone. Ecological and taxonomical data were used for evaluation of changes in their vertical distribution. A total of 25 taxa were identified, 13 of them belonging to chlorophytes, 12 to other groups of algae and cyanobacteria; in addition four mosses and one liverwort occurred at 17 sampling sites. Three species, Klebsormidium crenulatum, Desmococcus olivaceus and Stichococcus bacillaris, were found as the most abundant taxa. The aeroplanctonic species Desmococcus olivaceus, Stichococcus bacillaris and Klebsormidium crenulatum were detected from the air-fall. Investigated microhabitats offer relatively stabile microclimatic conditions and, likely, they are responsible for the observed vertical distribution of cyanobacteria and algae. Humidity was the main microclimatic factor influencing diversity, distribution and abundance of algae on investigated terrestrial substrate.

Foraging guild structure within a primaeval mixed forest bird assemblage: a comparison of two concepts

Two basic concepts of guild definition were developed in community ecology that enable simplification of complex communities or ecosystems into structural building blocks of species with similar niches. Root defined guild as a group of species utilising the same environmental resources by a similar foraging method. MacMahon et al. simplified the original definition even more by excluding a foraging method. This concept is focused on utilisation patterns of resources by species regardless the purpose of use. Our objectives were: (1) to test guild structure within a model ecosystem from matrices reflecting the differences between the two concepts, (2) to compare guild patterns detected by the two concepts, (3) to test whether the mixed forest ecosystem consists of significantly different groups of species representing deciduous and coniferous faunal elements. The study was conducted in a primeval beech-fir forest in NW Slovakia during 1997–2000. In total, 26 bird species were used for further numerical analyses. Two data matrices were constructed reflecting the differences between the two guild concepts. To statistically determine guild structure without arbitrary fusion criteria, a bootstrapped cluster analysis (UPGMA) of chord distances was employed to analyse the data matrices. Symmetric correspondence analysis (CA) was applied for extraction of eigenvectors responsible for the segregation of species into guilds. The classification proposed by Root produced two guild models at the levels of 6 or 9 group partitions at α = 0.10, while the classification following MacMahon et al. detected 7 guild types. The guild structures based on the two concepts were significantly different when tested by two-tailed Wilcoxon paired sample tests and the Monte Carlo among-cluster error sum of squares (SSQ) distance simulation test. Six out of the eight interpretable factors (75%) indicated analogous environmental gradients when comparing two CA ordinations. The most important environmental gradients were: (1) vertical foraging substrate — habitat structure, (2) water — terrestrial foraging substrate gradient, (3) spatial tree morphology, (4) terrestrial foraging substrate gradient, (5) arboreal — airspace gradient, and (6) mountain stream environmental gradient. We did not detect significantly different guilds for generalists and for coniferous and deciduous forest specialists.

The biodynamics of arboreal locomotion: the effects of substrate diameter on locomotor kinetics in the gray short-tailed opossum (Monodelphis domestica)

Effects of substrate diameter on locomotor biodynamics were studied in the gray short-tailed opossum (Monodelphis domestica). Two horizontal substrates were used: a flat 'terrestrial' trackway with a force platform integrated into the surface and a cylindrical 'arboreal' trackway (20.3 mm diameter) with a force-transducer instrumented region. On both terrestrial and arboreal substrates, fore limbs exhibited higher vertical impulse and peak vertical force than hind limbs. Although vertical limb impulses were lower on the terrestrial substrate than on the arboreal support, this was probably due to speed effects because the opossums refused to move as quickly on the arboreal trackway. Vertical impulse decreased significantly faster with speed on the arboreal substrate because most of these trials were relatively slow, and stance duration decreased with speed more rapidly at these lower speeds. While braking and propulsive roles were more segregated between limbs on the terrestrial trackway, fore limbs were dominant both in braking and in propulsion on the arboreal trackway. Both fore and hind limbs exerted equivalently strong, medially directed limb forces on the arboreal trackway and laterally directed limb forces on the terrestrial trackway. We propose that the modifications in substrate reaction force on the arboreal trackway are due to the differential placement of the limbs about the dorsolateral aspect of the branch. Specifically, the pes typically made contact with the branch lower and more laterally than the manus, which may explain the significantly lower required coefficient of friction in the fore limbs relative to the hind limbs.

Stimulation of terrestrial-substrate preferences and locomotor activity in newly transformed tiger salamanders ( Ambystoma tigrinum) by exogenous or endogenous thyroxine

Recently transformed adult tiger salamanders ( Ambystoma tigrinum) that had never resided on land were treated with increasing, alternate-day injections of thyroxine (experiment 1) or single injections of particular dosages of this hormone (experiment 2). In all cases control salamanders received equivalent volumes of saline on a similar schedule. In both experiments, subjects treated with thyroxine displayed significant levels of terrestrial-substrate preference in a moisture-gradient apparatus. Salinetreated controls never emerged from the water. In experiment 2, animals that received single thyroxine treatments also displayed heightened levels of land-directed locomotor activity. In experiment 3, blood plasma was collected from salamanders displaying spontaneous land preference and others displaying water preference. Radioimmunoassay for thyroxine indicated that salamanders that had moved to, and resided upon, a terrestrial substrate some time subsequent to metamorphosis had significantly higher plasma levels of this hormone than did animals preferring to remain submerged. These results indicate (1) that thyroxine stimulates, and possibly maintains, emergence from water and terrestrial preference in newly transformed tiger salamanders and (2) that this hormone stimulates a locomotor activity component associated with the movement of formerly aquatic adults to the terrestrial habitat.