Snakes exhibit extreme cranial kinesis that facilitates ingestion of prey with large cross-sectional area, but this ability is widely predicted to reduce bite performance due to decreased structural rigidity. Consequently, most large-bodied snakes rely on envenomation or constriction to subdue prey prior to ingestion. Species within the genus Drymarchon represent a notable exception: these large, non-venomous, non-constricting snakes routinely consume a wide range of prey, including large and potentially dangerous vertebrates, using only simple seizing and pinioning behaviors. Here, we quantify bite performance in three species of Drymarchon (D. corais, D. couperi, and D. melanurus), examine morphological predictors of biting performance, compare biting pressure to constriction pressure in similarly sized snakes, and synthesize dietary records across the genus. Our results showed that bite force scaled isometrically with head dimensions but showed negative allometry relative to body length, reflecting ontogenetic body elongation rather than diminished cranial performance. When expressed as pressure, biting by Drymarchon generated tissue-level stresses exceeding those produced by constriction in comparably sized snakes. Dietary synthesis revealed extreme trophic breadth dominated by non-avian reptiles, particularly snakes, with no relationship between predator size and prey size. Together, these results resolve a biomechanical paradox by demonstrating that high bite pressure, prolonged jaw engagement, and behavioral persistence can support lethal prey subjugation in the absence of venom or constriction. These findings highlight simple seizing as an effective and underappreciated prey-handling strategy, and underscore the importance of integrating biomechanics, behavior, and natural history to understand the evolution of snake feeding systems.
Toads produce potent poison in their parotoid macroglands, a rich source of toxic molecules against predators, parasites and pathogens. Production of such complex and toxic secretions is energetically costly and competes for energy resources with other physiological processes. We hypothesized that poison secretion from toad parotoids by electrical stimulation induces a short, transient stress response manifested by an increase in the neutrophil to lymphocyte (N:L) ratio, a marker of acute stress. We studied the effects of poison excretion on N:L ratio using 27 male common toads (Bufo bufo Linnaeus, 1758), which were randomly divided into three groups: control (no treatment), milked by electrical stimulation (poison release) and sham-stimulated (no poison release). Blood was sampled from clipped toes of toads. Bleeding and smears were done at four time points (0, 12, 24, and 48 h after treatment). At 12 h after treatment we found elevated N:L ratio in milked toads, but this effect disappeared before 24 h. Our results indicate that poison secretion may cause transient disruption of homeostasis, leading to temporary stress. However, the short duration of stress response suggests that the technique of electrical stimulation is less harmful than previously assumed and can be applied to obtain poison samples.
Sloths exhibit specialized morphological and behavioral adaptations for crypsis, including slow movement and camouflaged pelage that reduces detection by predators. However, adult males of three three-fingered sloth species (Bradypus spp.) possess a distinctive dorsal patch called a speculum, characterized by bright pigmentation and oily secretions, presenting an apparent evolutionary paradox. The function of the speculum is unknown, especially due to the logistical constraints of conducting research on wild sloths. Here, we present the first quantitative analysis of speculum morphology in Brown-Throated Sloths (Bradypus variegatus) to evaluate potential functional hypotheses. Morphometric measurements revealed a positive correlation between speculum area with body size, while color analysis revealed weak correlations between body length and pigmentation patterns. These findings are consistent with sexual selection hypotheses and support the speculum as a sexually selected trait, yet its persistence is puzzling given the species' rod monochromacy and vulnerability to visually acute predators. The speculum's sexually dimorphic expression and secretory properties suggest potential multimodal signaling functions, possibly integrating visual and olfactory components. This study provides the first test of the relationship of the speculum's relationship to body size in sloths, which informs hypotheses about its functional and evolutionary significance.
Migration is the primary strategy employed by temperate birds to avoid experiencing harsh winter conditions. Consequently, the bones and wings of migratory birds have evolved distinctive morphological, structural, and microstructural characteristics that enable various environmental adaptations. These characteristics vary substantially among species, depending on environmental factors and, most importantly, flight capability. In the present study, Laser-Induced Breakdown Spectroscopy, Double Staining Techniques (Alcian Blue and Alizarin Red), and Hematoxylin and Eosin (H&E) staining were employed to investigate the morphology and morphometry of the wings and legs, as well as the trabecular structure and mineral content of the humerus, in migratory birds (Anas crecca crecca) and non-migratory birds (Cairina moschata domesticus) at two and six months of age. The findings revealed that the migratory species exhibited significantly shorter bone lengths and lower mineral content compared to the non-migratory species. Moreover, histological examination of the humerus showed marked differences between the two groups. In migratory species, the metaphysis exhibited a dense cortical bone, numerous fused and compact bony trabeculae with regularly arranged lamellae, many empty lacunae, medullary bone, and evident osteoclastic activity. Conversely, the metaphysis of non-migratory species showed a thin periosteum, a less dense cortical bone, numerous well-developed trabeculae with osteoblastic rimming, fewer and faintly stained lamellae, many lacunae with large osteocytes, medullary bone, and extensive areas of calcified cartilage. In conclusion, both migratory (Anas crecca) and non-migratory (Cairina moschata) have evolved species-specific skeletal adaptations to accommodate their respective environmental conditions, resulting in enhanced physical endurance and performance.
Blindsnakes (Scolecophidia) are among the most morphologically conservative reptiles, yet the extent and nature of their phenotypic variation is poorly documented. We provide an integrative assessment of allometry and trophic ecology in two sympatric species of Amerotyphlops from the Atlantic Forest of northeastern Brazil, A. brongersmianus and A. paucisquamus. Based on 100 individuals, we combined morphometric, reproductive, dietary, and phenological data to discuss how fossoriality influences body shape and ecological strategies. A. brongersmianus exhibited greater overall robustness, with females displaying significant allometric shifts in snout and trunk width, whereas A. paucisquamus showed somatic isometry (including body mass), contrasting with strong positive allometry in reproductive organs. Regarding sexual dimorphism, neither species exhibited statistically significant differences in body proportions after correction for multiple comparisons, although A. brongersmianus presented higher SSD indices. Reproductive allometry revealed divergent strategies, contrasting the negative scaling of testis width in A. brongersmianus with the marked positive scaling of testicular dimensions in A. paucisquamus. Furthermore, while A. brongersmianus lacked significant bilateral asymmetry, A. paucisquamus exhibited directional asymmetry in testis width. The species displayed distinct phenologies associated with rainfall, yet shared an exceptionally narrow myrmecophagous niche, feeding almost exclusively on ant brood. Morphological differences in cranial width and trunk robustness align with distinct prey assemblages and soil use, although these differences fall within a narrowly conserved morphofunctional space, implying fine-scale ecological partitioning. Our results show that morphological stasis in Amerotyphlops may coexist with modest, non-pervasive adaptive adjustments along constrained functional axes, highlighting how subtle developmental and ecological modulations sustain evolutionary persistence in fossorial lineages.
Developmental instability reflects an organism's ability to buffer genetic and environmental perturbations during growth and is commonly assessed through fluctuating asymmetry and canalization. Evidence from diverse animal groups suggests that developmental instability can be sex specific, often showing sex-biased sensitivities to developmental perturbations. Additionally, reproductive mode can shape developmental environments, potentially influencing how morphological variation is buffered during ontogeny. Yet, the relative importance of sex and reproductive mode in shaping developmental instability remains poorly studied. We tested whether developmental instability is sex specific in two spiny lizards with contrasting reproductive modes: the viviparous Sceloporus grammicus and the oviparous Sceloporus aeneus. We analyzed a curated subset of 69 adults (40 S. grammicus, 29 S. aeneus) from high-elevation sites in Estado de México, photographed the dorsal head, digitized 22 landmarks, and conducted Procrustes superimposition to extract shape variables. Fluctuating asymmetry was quantified using Procrustes distances, while canalization was assessed through comparisons of within-group variance-covariance matrices and principal component analysis. Fluctuating asymmetry did not differ between sexes in either species, and asymmetry variance was similar between males and females within species but differed between species. Canalization analyses revealed stronger buffering in S. grammicus males compared to both sexes of S. aeneus, while no sexual dimorphism in head shape was detected in either species. Together, these results suggest that developmental stability is more strongly associated with reproductive mode than with sex, and that size-related sexual differences do not translate into shape divergence. Our findings highlight how developmental environments linked to reproductive strategies, but not sex, can modulate morphological buffering.
Praying mantises (Mantodea) are well known for their predatory behavior and striking appearance, yet surprisingly little is known about their tarsal attachment systems. Comparative studies on other polyneopteran insect clades based on large taxon samplings suggest distinct ecomorphological adaptations in the attachment systems. Detailed investigations into the micromorphology of mantis attachment pads remain scarce, although ecomorphs in Mantodea predict similar attachment pad specialisations. We studied the tarsal morphology of a selection of 33 species of Mantodea across the phylogeny including the early-diverging lineages Chaeteessa, Mantoida and Metallyticus, as well as representatives for the range of mantodean habitats. Scanning electron microscopy investigations revealed that both functional principles of animal attachment pads (smooth and hairy) are found within Mantodea: Chaeteessa, which is considered the sister group to all other mantises, features split tenent setae with spatula-shaped tips on their tarsal pads (euplantulae), while the remaining mantodean species possess smooth attachment pads. Some ecomorphological adaptations are observed among the studied species, such as pad asymmetry, ridge-like microstructures on the pad surfaces, and variations in the shape of the euplantulae However, these adaptations are much less pronounced and variable than the microstructural adaptations found in other Polyneoptera. The predatory behavior of mantises potentially results in less strict substrate-specific constraints on their attachment organs compared to herbivorous insect groups that evolved to specialize on certain plant surfaces. Furthermore, functional aspects of the morphological adaptations of the attachment systems of Mantodea are discussed.
During mating, male cephalopods generally use a modified arm (the hectocotylus) to transfer spermatophores to the female. To shed some light on the functional morphology of such an important organ in cephalopod reproduction, we have thoroughly investigated the male and female arms of the loliginid squid Doryteuthis pleii (Blainville, 1823) by applying light and electron microscopy. In D. pleii, the distal region of the left ventral arm of mature males is modified, with the suckers of the dorsal row being greatly reduced in size and supported by narrow pedicels. Moreover, the epithelia between the dorsal and ventral sucker rows and between the ventral row and its protective membrane have two types of exclusive secretory cells. These cells secrete neutral sugars and basic proteins and can be distinguished mainly by the size of their granules as well as their affinity for hematoxylin. Additionally, they display a particular distribution: type I cells are predominant in the area between dorsal and ventral rows, while type II cells are prevalent in the region between the ventral row and ventral protective membrane. Several hypotheses may explain the function of this sexually dimorphic glandular system, e.g.: control over spermatophore eversion by coating them with a viscous substance; manipulation of the female physiology/behavior through chemical signaling; and production of an adhesive secretion that would enable the hectocotylus to firmly hold spermatophores without damaging them. The external morphology of the hectocotylus of other species suggests a similar glandular system is likely widespread across decapodiform cephalopods.
Lizard tail regeneration and limb amputation provide contrasting amniote models for regenerative failure. A limb wound healing model was established in 48 Scincella tsinlingensis through standardized surgical amputation protocols, followed by comprehensive anatomical observation, histological evaluation, and immunohistochemical characterization of regenerative processes. Four fibrotic stages-hemostasis, inflammation, proliferation, and remodeling-were delineated through histopathological analysis and further categorized into five histologically distinct stages. Stages I-II (0-9 days post-amputation, dpa) showed PCNA dominance over Caspase-3, reflecting proliferative priority. Collagen degradation correlated with expression of MMP-9 by fibroblasts and epithelial cells, whereas collagen deposition correlated with α-SMA+ myofibroblasts in stages IV-V. VEGF/TSP-1 immunostaining peaked during stages II-III (3-18 dpa) in accordance with angiogenesis and transitioned to restricted expression suggestive of vascular pruning by stage V. Epidermal maturation was associated with Cytokeratin 6 expression during re-epithelialization in stages II-IV (3-40 dpa). Persistent macrophage activity and inflammatory signaling correlated with sustained fibrosis. Key regulators (PCNA, Caspase-3, Cytokeratin 6, MMP-9, α-SMA, VEGF, TSP-1) displayed spatiotemporally restricted roles in scar formation. Despite robust proliferation and remodeling, limb regeneration failed, with myofibroblast-driven ECM accumulation and chronic inflammation overriding regenerative programs, yielding nonfunctional scar tissue devoid of muscle regeneration. These results represent the lizard exhibits no limb regeneration post-amputation, advancing investigation into mechanisms of regenerative failure.
The peripheral olfactory system of teleosts reveals great morphological diversity, which directly affects the delivery of water-borne odorants in an aquatic environment. In pelagic teleosts, hydrodynamic conditions also play an important role in olfaction, as they continuously experience a flow of water across their tapered head. In this study, the structure of the olfactory chamber, olfactory rosette, and nostrils of two species of pelagic teleosts, the southern bluefin tuna Thunnus maccoyii, and the black marlin Istiompax indica, are examined in order to understand the morphology of their peripheral olfactory system. The inter-nostril distance and the volume of the ventilatory sac are also assessed using light microscopy and diffusible iodine-based contrast-enhanced computed tomography to quantitatively assess the theoretical hydrodynamics of olfaction. The results show that both species have their olfactory chambers distant from the tip of the snout, possess a thick boundary layer above the nostrils, a circular olfactory rosette, and a radiating arrangement of olfactory lamellae. A comparison between the two species reveals that T. maccoyii has a long inter-nostril distance (20.05 mm), small nostril openings (incurrent: 0.13 mm2, excurrent: 4.88 mm2), a horizontally long olfactory chamber, and a relatively small ventilatory sac (209.81 mm3), while I. indica has a short inter-nostril distance (3.60 mm), large nostril openings (incurrent: 4.50 mm2, excurrent: 8.15 mm2), a vertically long olfactory chamber, and a large ventilatory sac (308.14 mm3). The morphological similarities between the two species suggest olfactory adaptations for a pelagic lifestyle, while the differences highlight the adaptations suitable for the unique hydrodynamic conditions associated with different swimming speeds.
Blood biochemistry offers reliable tools for assessing the physiological condition of wildlife populations, thus aiding their management and conservation. This study provides reference blood biochemistry values for free-living Eleonora’s falcon nestlings based on 135 samples collected from 2018 to 2022 in an eastern Crete colony. Significant inter-annual differences in analytes highlight strong environmental effects. Albumin and glucose levels increased with age, whereas phosphorus decreased. Nestlings in better body condition showed higher globulin, calcium, and phosphorus concentrations but lower glucose levels compared to those in poorer condition. Falcons from low-quality nest sites had elevated sodium and uric acid concentrations. No significant differences were detected based on hatching order or sex, except for higher albumin levels in females. Although haemoglobin levels decreased with increasing hatching order and brood size, this trend was not significant, suggesting mild physiological stress in younger fledglings due to intra-brood competition. Relationships between haemoglobin and total protein, calcium, glucose, and uric acid suggest potential biomarkers for monitoring the health of colonies of this species and other raptor populations.
Egg size is a key determinant of reproductive success in birds, influencing nestling growth, survival, and overall fitness. For Lesser Kestrels Falco naumanni, a small raptor often supported by nest-box programs, we hypothesized that female condition would significantly predict egg size, with higher-quality females producing larger eggs. Thus, over four breeding seasons, we investigated the influence of female condition, expressed as the Scaled Mass Index (SMI), and clutch size on egg dimensions (length, breadth, and volume) in a nest-box population in central Greece. We found that female condition significantly and positively affected both egg breadth and volume but did not influence egg length, and clutch size had no discernible effect on any egg dimension. Among the traits measured, breadth exhibited the highest repeatability, suggesting a stronger genetic component, whereas length and volume were more sensitive to environmental factors. Our findings suggest that conservation efforts should prioritize maintaining or improving female body condition - through, for example, ensuring high habitat quality, adequate food availability, and minimizing stress - to support optimal reproductive investment by female Lesser Kestrels in nest-box populations.
Egg size is a key determinant of reproductive success in birds, influencing nestling growth, survival, and overall fitness. For Lesser Kestrels Falco naumanni, a small raptor often supported by nest-box programs, we hypothesized that female condition would significantly predict egg size, with higher-quality females producing larger eggs. Thus, over four breeding seasons, we investigated the influence of female condition, expressed as the Scaled Mass Index (SMI), and clutch size on egg dimensions (length, breadth, and volume) in a nest-box population in central Greece. We found that female condition significantly and positively affected both egg breadth and volume but did not influence egg length, and clutch size had no discernible effect on any egg dimension. Among the traits measured, breadth exhibited the highest repeatability, suggesting a stronger genetic component, whereas length and volume were more sensitive to environmental factors. Our findings suggest that conservation efforts should prioritize maintaining or improving female body condition – through, for example, ensuring high habitat quality, adequate food availability, and minimizing stress – to support optimal reproductive investment by female Lesser Kestrels in nest-box populations.
The immune system plays a crucial role in protecting animals from the attack of pathogens and hence determines their survival. However, animals’ immunity is influenced by many environmental factors. Cage feeding density is one of the most important factors influencing immune function in animals. To test whether high cage feeding density would suppress animals’ immunity, female striped hamsters (Cricetulus barabensis) were divided into the One/Cage, Two/Cage, and Three/Cage groups. Phytohaemagglutinin (PHA) responses were higher in the One/Cage group than the other two groups, implying that cellular immunity was suppressed by high cage feeding density. The numbers of white blood cell (WBC) and lymphocytes (LYMF), the coagulation ability indicated by blood platelet count (PLT), mean platelet volume (MPV) and platelet distribution width (PDW) were the highest in the Three/Cage group among the three groups, implying the occurrence of the fight and injury in the high cage feeding density. Other immunological parameters including the masses of thymus and spleen, intermediate granulocytes (MID), neutrophil granulocytes (GRAN) were all not impacted by cage feeding density. Total body fat mass, the levels of blood glucose, leptin and corticosterone did not differ among the three groups, and these parameters were not correlated with PHA responses, WBC, LYMF, MID and GRAN except that LYMF was positively correlated with blood glucose levels, indicating that the changes in immunity might not be caused by the energy status and stress hormone in hamsters. Suppression of cellular immunity and the increase of WBCs, LYMF under high feeding density might help us to understand the adverse effect of high population density on animals’ survival in the wild. Our findings may also provide some useful information on animal welfare, laboratory animals preparation and wildlife management.
Understanding how feeding strategies influence oral morphology is fundamental to fish functional anatomy and trophic ecology. However, comparative data on tongue structure across dietary groups remain scarce in teleosts. This study examined tongue morphology in Boops boops (bogue), an omnivorous teleost with opportunistic feeding habits, and Pagrus pagrus (red porgy), a carnivorous benthic feeder with specialized prey preferences. By selecting species with distinct trophic niches, we aimed to elucidate how tongue architecture reflects dietary adaptations within teleosts. Morphometric analysis supported by light and scanning electron microscopy revealed that the bogue exhibited a higher tongue length-to-body weight ratio (34.1%) than the red porgy (14.3%). In contrast, the red porgy showed a greater tongue length-to-body length ratio (7.1% vs. 5.4%) and consistently broader tongue dimensions. The bogue tongue was sword-shaped with a pointed apex, while the red porgy’s tongue featured a rounded apex. Papillary patterns differed markedly: the bogue displayed gustatory structures including fungiform papillae at the apex, mixed filiform and fungiform papillae in the body, and volcano-like filiform papillae at the root. In contrast, the red porgy exhibited predominantly mechanical structures, such as filiform papillae at the apex, dome-like filiform papillae in the body, and dome-to scale-like papillae at the root. Histologically, both species shared a common organization of mucosa, submucosa (with connective and adipose tissues), ento-glossal hyaline cartilage, and striated muscle fibers. However, the bogue’s tongue showed stratified squamous epithelium with gustatory papillae, apical taste buds, and nerve endings. At the same time, the red porgy had abundant mucous cells and mechanical papillae concentrated at the root. Additionally, vascular channels with nucleated erythrocytes were observed in both species. These findings highlight distinct structural specializations of the tongue associated with omnivorous versus carnivorous feeding modes, offering new insights into the functional morphology and evolutionary adaptation of oral structures in teleost fishes.
Understanding what determines species distribution is a central goal in biogeography and macroecology, particularly in the context of ongoing environmental change. In this study we explored how intrinsic (biological) and extrinsic (environmental) factors influence the distribution of Liolaemus lizards occurring east of the Andes, and evaluated the extent to which their distribution patterns support Rapoport's rule. We analyzed 38 species, spanning Argentina from 52°S to 23°S, covering about 50 % of the genus distribution from sea level to 4300 masl. We used two main approaches, polygons and ecological niche models (ENMs), to evaluate the role of intrinsic factors such as critical thermal minimum (CTmin), thermal tolerance range, body size, and diet; and extrinsic factors including temperature, precipitation, elevation, and vegetation index. Our results show that CTmin is a strong predictor of range size under the ENMs approach, suggesting that greater cold tolerance is associated with broader distributions. Under the polygon approach, broader ranges correlated with colder, drier climates with pronounced seasonality. Although diet showed a weak tendency for narrower ranges in herbivorous species, it was a poor predictor overall. Thermal tolerance range, expected to increase with latitude under the climatic variability hypothesis, did not show a significant association with range size, and thus Rapoport's rule was not supported. Furthermore, taxonomic uncertainties may obscure biogeographic patterns, particularly in widely distributed species that might represent species complexes not yet formally described. These findings highlight the combined role of biological and environmental factors, challenge the general applicability of Rapoport's rule in Liolaemus, and underscore cold tolerance as a key distribution driver.
Burrowing behavior in mudskippers represents a key adaptation to intertidal environments, providing shelter from predators, buffering against temperature and salinity fluctuations, and serving as breeding sites. Despite its ecological significance, little is known about the burrow morphology of Scartelaos histophorus, a large mudskipper species widely distributed throughout Southeast Asia. This study investigated the burrow morphology of the mudskipper S. histophorus in the intertidal mudflats of Hiep Thanh, Ca Mau, Vietnam. The study was designed under the hypothesis that the burrow morphology of S. histophorus varies according to environmental parameters such as salinity, pH, and temperature, reflecting adaptive responses to intertidal conditions. A total of 64 burrows were cast and analyzed, revealing four structural types: L-shaped (57.81 %), U-shaped (23.44 %), J-shaped (6.25 %), and complex forms (12.50 %). The number of burrow openings ranged from 1 to 4, while chambers varied from 0 to 5, indicating structural variability. Burrow dimensions showed considerable variability, with total length ranging from 6 to 142 cm and burrow weight from 12.70 to 429.66 g, while depth and mouth diameter were relatively stable. Statistical analyses revealed significant differences in burrow size among structural types, with U-shaped and complex burrows generally larger than L- and J-shaped forms. Environmental variables, including pH, temperature, and salinity, were also significantly associated with burrow characteristics. Direct behavioral observations, including sediment excavation, entrance maintenance, air-bubble injection, and courtship displays, confirmed the ecological functions of different burrow types. These findings demonstrate that S. histophorus exhibits flexible burrowing strategies shaped by both environmental conditions and reproductive requirements, underscoring their adaptive role in sustaining intertidal biodiversity and contributing to a broader understanding of coastal ecosystem resilience at a global scale.
Bite force is a biomechanical trait that serves as a valuable proxy for assessing ecological interactions, feeding specialisations, and evolutionary pressures. Chelonians are a unique model system in studies of masticatory performances due to their akinetic skull and lack of teeth. It is known that body size, head morphology and sex-related differences influence bite performance of some chelonian species. In this study, we investigated the variation in bite force within and among five populations of the European pond turtle (Emys orbicularis) in Serbia. We examined relationship of bite force with phenotypic traits such as body size, head dimensions, body condition and muscle strength, as well as body temperature and seasonality. Bite force was measured in the field (N = 209) with an adapted digital force sensor. Our results showed significant differences in bite force across populations, suggesting that local ecological conditions may play a crucial role in shaping bite performance. In particular, turtles from more diverse and structurally complex environments, and turtles sharing their habitat with non-native pond sliders (Trachemys scripta ssp.) exhibited higher bite forces. We also detected a positive association between bite force and maximal pulling force, volumetric body condition index, body size and head height. Surprisingly, sex, cloacal temperature and seasonality were not significant predictors of bite force. Despite the challenges of measuring maximal performance under field conditions, our findings illustrate how variation in functional traits can reflect both intrinsic factors and ecological context, with implications for the study of biomechanical adaptations across animal taxa.
Aquatic and amphibious fishes produce a variety of behaviors when stranded on land, including a ballistic movement called a tail-flip jump. Although recent studies have examined jump performance (distance) in several cyprinodontiform species, less is known about the diversity of behaviors produced by teleosts when stranded on land. Here, seven species from four major teleost lineages (individual n = 4-12) were manually stranded in a terrestrial arena for two-minute trials. From videos of the trials, the number of jumps, flops (movements <1 body length), displacement (total and mean), latency (time to onset of movement), and percent time moving were quantified for each individual. A principal components analysis of these variables was used to define four "behavioral spaces:" species that produced effective displacement and spent the majority of the trial period moving (Danio); species that produced less effective displacement and spent the majority of the trial period moving (Pseudomugil); species that produced less effective displacement and spent little time moving (Umbra); and species that produced effective displacement, but spent little time moving (Kryptolebias). Based on the literature and metabolic data collected for this study, it appears that the ability to extract oxygen from air (vs. water) predicts the amount of time spent moving when stranded on land. Air-breathing fishes appear to adopt a "wait and see strategy," while species that lack the ability to breathe air move immediately and frequently, likely an attempt to return to the water as quickly as possible.
