Ambush Foragers Research Articles

Spatial-Temporal Activity Patterns of the Mexican Plateau Horned Lizard in a Natural Protected Area

Lizard activity patterns are restricted by both intrinsic and extrinsic variables. The Mexican Plateau Horned Lizard (Phrynosoma orbiculare) is endemic to México and an ambush forager and viviparous species that becomes dormant during the cooler months. The objective of this study was to determine the spatiotemporal activity patterns of P. orbiculare and the environmental conditions related to its occurrence in the natural protected area Statal Park Sierra Morelos, State of Mexico, México. We conducted samplings during 2018 and 2019. We assessed temporal activity patterns with Watson's U2 test to determine differences in activity hours between age classes, sexes, and seasons, and we evaluated spatial activity patterns through a hotspot analysis. We conducted a logistic regression model by using landsat 8 bands and indices as independent variables. Differences in temporal activity patterns (activity timing) were detected between age classes and seasons (in the juvenile group) but not between sexes. Within the natural protected area, P. orbiculare aggregated in solar glades. There is an important contribution of ultrablue and blue landsat bands to P. orbiculare occurrence. Differences in activity between age classes could be related to the heat acquisition rate of smaller individuals; meanwhile, no differences between sexes suggests that the thermal optima of females are similar to male optima. Hotspot analysis and the distribution model reveal that P. orbiculare appears on the windward slope where sunrise occurs. Solar glades are important for the species occurrence and should be protected in the studied area. These data allow future monitoring studies to help prevent population declines and illegal extraction.

Rattlesnake colouration affects detection by predators

AbstractCrypsis, or the ability of an animal to avoid detection by other animals, is strongly impacted by an animal’s colouration and pattern. Crypsis may be especially important for ambush foragers, which spend much of their time above ground and therefore benefit from being inconspicuous to predators and prey. The purpose of this study was to investigate the effect of rattlesnake skin colouration on the likelihood of it being detected and attacked by a predator, on the latency (time) to attack, and on the attack frequency on each physical body section of the models. Clay models representing four commonly observed rattlesnake colour morphs (light, dark and two intermediate colour patterns) were deployed in two different habitat types (wooded area and open field), and the marks made on the models by predators were quantified over time. We found that light snake models, which have little contrast with substrate, were less likely to be attacked and were attacked later than darker model types, which have higher contrast with substrate. Predators attacked the various body segments of the models at similar frequencies. Our data suggest dark‐coloured rattlesnakes, which have the most contrast with the golden‐coloured grasses and therefore have the lowest crypsis, are most at risk from predation.

Foraging mode, relative prey size and diet breadth: A phylogenetically explicit analysis of snake feeding ecology.

Foraging modes (ambush vs. active foraging) are often correlated with a suite of morphological, physiological, behavioural and ecological traits known as the "adaptive syndrome" or "syndrome hypothesis." In snakes, an ecological correlate often reported in the literature is that ambush-hunting snakes have a higher relative meal size compared to actively foraging snakes which feed on smaller prey items. This "large meal versus small meal" feeding hypothesis between ambush and active foragers has become a widely accepted paradigm of snake feeding ecology, despite the fact that no rigorous meta-analysis has been conducted to support this generalization. We conducted a phylogenetically explicit meta-analysis, which included ca. 100 species, to test this paradigm of snake feeding ecology. We gathered data on prey size by inducing regurgitation by palpation in free-ranging snakes and by examining the stomach contents of preserved museum specimens. When we found prey, we recorded both snake and prey mass to estimate relative prey mass (prey mass/snake mass). We also reviewed published studies of snake feeding ecology to gather similar information for other species. Ambush and active foragers did not differ in minimum or average meal size but the maximum meal sizes consumed by ambush-foraging snakes were larger than the maximum meal sizes eaten by active foragers. This results in ambush-foraging snakes consuming a significantly wider range of meal sizes, rather than being large meal specialists compared to active foragers. We argue that ambush foragers evolved to be more opportunistic predators because they encounter prey less frequently compared to active foragers. This hypothesis is further supported by the fact that ambush foragers also exhibited marginally wider diet breadths, consuming a broader range of prey types in comparison with active foragers. Our study challenges aspects of the foraging syndrome as it is currently conceived, and our results have important implications for our understanding of how foraging mode has shaped the behaviour and physiology of ambush-foraging snakes.

Who does bask longer? A comparison between elapid and viperid snakes in the field and in experimental conditions

Temperature profoundly influences the biology of ectotherm organisms, for example reptiles, which mostly regulate their body temperature behaviorally by shuttling between heat sources and sinks. The thermal quality of the environment directly affects the amount of time that a reptile takes to keep the body temperature within the optimal range. The foraging strategy of reptiles is often correlated to the thermoregulatory strategies. Depending on their foraging strategy, carnivorous reptiles can be high-energy consumers (active foragers) or low-energy consumers (ambush foragers). Our study allowed to get insights into basking versus non-basking behaviors of (i) snakes belonging to two different families (eight viperids and four elapids) with contrasted life-styles by either field or captive observations, (ii) free-ranging snakes (n = 3245) inhabiting contrasted habitats (forest versus savannah), and (iii) captive snakes (n = 4) outside the feeding activity and during digestion phase. We observed a tendency to spend more time in thermoregulation in the viperids than in the elapids and this pattern were consistent between field and experimental observations. We suggest that the higher basking activity of viperids is correlated to their predominantly nocturnal and ambush habits compared to the diurnal and active-foraging habits of the elapids. We also observed an effect of the thermal environmental quality with the savannah species tending to bask less than forest species. As for postprandial termophily, viperids showed a longer postprandial basking time than elapids even if all the snakes in the captivity sample were fed identically in terms of prey type and relative prey mass. Conservation insights related to the observed pattern are also provided.

Climate and foraging mode explain interspecific variation in snake metabolic rates.

The energy cost of self-maintenance is a critical facet of life-history strategies. Clarifying the determinant of interspecific variation in metabolic rate (MR) at rest is important to understand and predict ecological patterns such as species distributions or responses to climatic changes. We examined variation of MR in snakes, a group characterized by a remarkable diversity of activity rates and a wide distribution. We collated previously published MR data (n = 491 observations) measured in 90 snake species at different trial temperatures. We tested for the effects of metabolic state (standard MR (SMR) versus resting MR (RMR)), foraging mode (active versus ambush foragers) and climate (temperature and precipitation) while accounting for non-independence owing to phylogeny, body mass and thermal dependence. We found that RMR was 40% higher than SMR, and that active foragers have higher MR than species that ambush their prey. We found that MR was higher in cold environments, supporting the metabolic cold adaptation hypothesis. We also found an additive and positive effect of precipitation on MR suggesting that lower MR in arid environments may decrease dehydration and energetic costs. Altogether, our findings underline the complex influences of climate and foraging mode on MR and emphasize the relevance of these facets to understand the physiological impact of climate change.

How phylogeny and foraging ecology drive the level of chemosensory exploration in lizards and snakes.

The chemical senses are crucial for squamates (lizards and snakes). The extent to which squamates utilize their chemosensory system, however, varies greatly among taxa and species' foraging strategies, and played an influential role in squamate evolution. In lizards, 'Scleroglossa' evolved a state where species use chemical cues to search for food (active foragers), whereas 'Iguania' retained the use of vision to hunt prey (ambush foragers). However, such strict dichotomy is flawed as shifts in foraging modes have occurred in all clades. Here, we attempted to disentangle effects of foraging ecology from phylogenetic trait conservatism as leading cause of the disparity in chemosensory investment among squamates. To do so, we used species' tongue-flick rate (TFR) in the absence of ecological relevant chemical stimuli as a proxy for its fundamental level of chemosensory investigation, that is baseline TFR. Based on literature data of nearly 100 species and using phylogenetic comparative methods, we tested whether and how foraging mode and diet affect baseline TFR. Our results show that baseline TFR is higher in active than ambush foragers. Although baseline TFRs appear phylogenetically stable in some lizard taxa, that is a consequence of concordant stability of foraging mode: when foraging mode shifts within taxa, so does baseline TFR. Also, baseline TFR is a good predictor of prey chemical discriminatory ability, as we established a strong positive relationship between baseline TFR and TFR in response to prey. Baseline TFR is unrelated to diet. Essentially, foraging mode, not phylogenetic relatedness, drives convergent evolution of similar levels of squamate chemosensory investigation.

Food supplementation affects the foraging ecology of a low-energy, ambush-foraging snake

The effect of food availability on the spatial ecology of animals varies within and across study systems because a multitude of factors can affect the spatial activity of organisms. Low-energy specialists, such as ambush-foraging snakes, feed infrequently and can endure long periods without food. Because they have low-energy requirements, one possible tactic for feeding may be to simply ambush for longer periods when prey availability is low, thereby decreasing the potential costs associated with locating new ambush sites. We used radiotelemetry, supplemental feeding, and remote video cameras on free-ranging male puff adders (Bitis arietans) in South Africa to test the hypothesis that food intake affects the foraging ecology of extreme low-energy, ambush foragers and to quantify their natural feeding rates. Supplementally fed puff adders improved their body condition, spent less time foraging, and decreased distance traveled compared to control snakes. However, movement frequency and home range size did not differ between the two groups. These findings indicate that control snakes traveled farther within similar-sized home ranges compared to fed snakes and did so at no survival cost. Further, naturally foraging puff adders successfully caught a prey of small size once every 10 days on average. Hence, despite their “sit-and-wait” foraging strategy and their low-energy intake/requirements, underfed puff adders travel widely to presumably find appropriate ambush sites that maximize prey capture. Our research provides the first strong evidence that the spatial activity of a terrestrial vertebrate species with extremely low energetic demands is significantly affected by food intake. Because animals travel their home range partly to forage, their space use can be affected by the amount of food available in nature. We show that, despite a low-energy lifestyle, the movement level of an ambush-foraging snake that feed infrequently is linked to the amount of food they eat. Underfed snakes traveled greater distances in search of prey, within similar-sized home ranges, compared to well-fed snakes, and they did so at no survival cost. Hence, our research adds to our understanding of the effect of food on the spatial ecology of animals, by providing conclusive evidence that the spatial response of an organism with extremely low-energy demands can be affected by food.

An ambusher's arsenal: chemical crypsis in the puff adder (Bitis arietans).

Ambush foragers use a hunting strategy that places them at risk of predation by both visual and olfaction-oriented predators. Resulting selective pressures have driven the evolution of impressive visual crypsis in many ambushing species, and may have led to the development of chemical crypsis. However, unlike for visual crypsis, few studies have attempted to demonstrate chemical crypsis. Field observations of puff adders (Bitis arietans) going undetected by several scent-orientated predator and prey species led us to investigate chemical crypsis in this ambushing species. We trained dogs (Canis familiaris) and meerkats (Suricata suricatta) to test whether a canid and a herpestid predator could detect B. arietans using olfaction. We also tested for chemical crypsis in five species of active foraging snakes, predicted to be easily detectable. Dogs and meerkats unambiguously indicated active foraging species, but failed to correctly indicate puff adder, confirming that B. arietans employs chemical crypsis. This is the first demonstration of chemical crypsis anti-predatory behaviour, though the phenomenon may be widespread among ambushers, especially those that experience high mortality rates owing to predation. Our study provides additional evidence for the existence of an ongoing chemically mediated arms race between predator and prey species.

Intraspecific behavioural variation in the lacertid lizard Meroles cuneirostris (Strauch, 1867) (Sauria:Lacertidae)

We characterised behavioural variation between adult male, adult female and juvenile Meroles cuneirostris, a diurnal lacertid lizard endemic to the Namib Desert. Variation in microhabitat preference was significant between age classes, as adults spent more time underneath vegetative cover than juveniles. Movement patterns varied between demographic classes as juveniles exhibited movements of higher average durations than adults overall, and spent a greater percentage of time moving than adult females. Juveniles turned their heads more often than adults; all individuals scan their surroundings more frequently in the open sand and near vegetation. An analysis of foraging behaviour indicates that M. cuneirostris exhibits relatively few movements per minute (MPM) and a wide range of percentage of time spent moving (PTM), making it difficult to categorise this species as either an ambush or active forager. Furthermore, intraspecific variation in foraging behaviour within this species exists, as adult males and juveniles exhibited higher PTM values than adult females.

Genetic selection of the ambush foraging entomopathogenic nematode, Steinernema carpocapsae for enhanced dispersal and its associated trade-offs

Dispersal of organisms is influenced by environmental and innate population variability. It results in redistribution of populations with potential consequences for gene flow, population resilience and stability, and evolutionary diversification of traits in response to specific selection pressures. However, dispersal behavior in soil-dwelling organisms is understudied. Species of entomopathogenic nematodes, a group of soil-inhabiting lethal insect parasites used in biological pest control show a dichotomy in foraging behavior. Some species have been classified as ambushers while others as cruisers. We previously discovered that the ambush foraging Steinernema carpocapsae possesses a small group of sprinters that disperse faster than the fastest moving cruisers. In this study, we genetically selected S. carpocapsae for enhanced dispersal in the absence of hosts by capturing the fastest and farthest reaching infective juveniles (IJs) emanating from a nematode-infected Galleria mellonella cadaver, in soil. S. carpocapsae showed positive response to selection for dispersal with 13–23 and 21–37 fold increase in the percent IJs dispersing to the farthest distance from the source cadaver, after five and ten rounds of selection, respectively. There was also a significant increase in the average displacement of the selected lines (6.85–7.54 cm/day) than the foundation population (5.54 cm/day) maintained by passing through G. mellonella larvae in Petri dishes. The overall mean realized heritability for dispersal was 0.60. The farthest reaching IJs of the selected lines comprised more males (72 %) than the foundation population (44 %) at most time points. Trade-offs associated with enhanced dispersal included reduced reproduction capacity and nictation ability, a trait associated with ambush foraging. In conclusion, this study revealed the costs and benefits associated with selection for enhanced dispersal in a soil-dwelling insect parasite, enhancing our understanding of the evolution of new behavioral patterns, which could have important implications in biological control.

Morphology, Reproduction and Diet in Australian and Papuan Death Adders (Acanthophis, Elapidae)

Death adders (genus Acanthophis) differ from most other elapid snakes, and resemble many viperid snakes, in their thickset morphology and ambush foraging mode. Although these snakes are widely distributed through Australia and Papua New Guinea, their basic biology remains poorly known. We report morphological and ecological data based upon dissection of >750 museum specimens drawn from most of the range of the genus. Female death adders grow larger than conspecific males, to about the same extent in all taxa (20% in mean adult snout-vent length, = SVL). Most museum specimens were adult rather than juvenile animals, and adult males outnumbered females in all taxa except A. pyrrhus. Females have shorter tails (relative to SVL) than males, and longer narrower heads (relative to head length) in some but not all species. The southern A. antarcticus is wider-bodied (relative to SVL) than the other Australian species. Fecundity of these viviparous snakes was similar among taxa (mean litter sizes 8 to 14). Death adders encompass a broad range of ecological attributes, taking a wide variety of vertebrate prey, mostly lizards (55%), frogs and mammals (each 21%; based on 217 records). Dietary composition differed among species (e.g. frogs were more common in tropical than temperate-zone species), and shifted with snake body size (endotherms were taken by larger snakes) and sex (male death adders took more lizards than did females). Overall, death adders take a broader array of prey types, including active fast-moving taxa such as endotherms and large diurnal skinks, than do most other Australian elapids of similar body sizes. Ambush foraging is the key to capturing such elusive prey.

Ambush Foraging Entomopathogenic Nematodes Employ ‘Sprinters' for Long-Distance Dispersal in the Absence of Hosts

Ambush foragers must employ a long-distance dispersal strategy to maximize reproductive success in the absence of hosts. This hypothesis was tested by comparing lateral dispersal of the ambusher, Steinernema carpocapsae , and the cruiser, Heterorhabditis bacteriophora , nematodes from infected host cadavers in autoclaved, silt-loam soil in large microcosms (0.05-1.5 m(2)) with or without vegetation in the absence of hosts. Dispersal was estimated by taking soil cores (5 × 2 cm in diameter) from the microcosms at different intervals (6-240 hr) and distances (3.8-61 cm) from the infected host cadavers and baiting with Galleria mellonella larvae. The numbers of baited larvae killed and the numbers of infective juveniles (IJs) penetrated in dead baits were counted to compute the percentage of IJs dispersed from the source cadavers, based on the emergence potential and penetration efficiency of the 2 species, and analyzed. Vegetation enhanced dispersal of both species but more so for H. bacteriophora . Although the pattern of dispersal differed spatio-temporally for the 2 species, average population displacement was similar (∼6 cm/day). A majority of the S. carpocapsae population ambushed close to the source cadaver (<3.8 cm), whereas a majority of H. bacteriophora population dispersed between 7-12 cm away from the source cadaver. About 4% of the S. carpocapsae population dispersed faster than the fastest H. bacteriophora , reaching 30-61 cm, compared to only 2% of the H. bacteriophora population dispersing this far. This use of 'sprinters' for long-distance dispersal may represent an adaptive dispersal strategy by the otherwise ambush forager S. carpocapsae in the absence of hosts.

Does foraging mode affect metabolic responses to feeding? A study of pygopodid lizards

Abstract Foraging mode (ambush vs. active) profoundly affects many aspects of organismal biology, including metabolic rates and their relationship with food intake. Previous studies on snakes suggest that ambushers tend to have lower standard metabolic rates (SMR) and higher energetic costs of digestion and assimilation of prey (specific dynamic action, or SDA) than do active foragers. However, phylogenetic considerations may be at least partly responsible for such patterns, as foraging mode is strongly conserved evolutionarily and most SDA studies have focused on species from only two lineages of ambush foragers (pythonid and viperid snakes) and one lineage of active foragers (colubrid snakes). We sought to deconfound the effects of phylogeny and foraging mode, investigating SMR and SDA in two closely related pygopodid lizards, the common scaly-foot Pygopus lepidopodus (active forager) and Burton’s legless lizard Lialis burtonis (ambush forager). Consistent with the pattern seen in snakes, L. burtonis exhibits a significantly lower SMR and a higher SDA than does P. lepidopodus. The magnitude of SDA in L. burtonis is comparable to that of some pythons and vipers, providing yet more evidence for the remarkable convergence between this species and ambush-foraging snakes.

Ecology and Behaviour of Burton&amp;rsquo;s Legless Lizard (Lialis burtonis, Pygopodidae) in Tropical Australia

The elongate, functionally limbless flap-footed lizards (family Pygopodidae) are found throughout Australia, ranging into southern New Guinea. Despite their diversity and abundance in most Australian ecosystems, pygopodids have attracted little scientific study. An intensive ecological study of one pygopodid, Burton's legless lizard (Lialis burtonis Gray 1835), was conducted in Australia's tropical Northern Territory. L. burtonis eats nothing but other lizards, primarily skinks, and appears to feed relatively infrequently (only 20.8% of stomachs contained prey). Ovulation and mating occur chiefly in the late dry-season (beginning around September), and most egg-laying takes place in the early to middle wet-season (November-January). Females can lay multiple clutches per year, some of which may be fertilised with stored sperm. Free-ranging L. burtonis are sedentary ambush foragers, with radio-tracked lizards moving on average < 5 m/day. Most foraging is done diurnally, but lizards may be active at any time of day or night. Radiotracked lizards were usually found in leaf-litter microhabitats, a preference that was also evident in habitat-choice experiments using field enclosures. Lizards typically buried themselves in 6-8 cm of litter; at this depth, they detect potential prey items while staying hidden from predators and prey and avoiding lethally high temperatures.

Effects of recent movement, starting distance and other risk factors on escape behaviour by two phrynosomatid lizards

Cost–benefit models of escape behaviour predict that flight initiation distance (FID, predator-prey distance when the prey starts to flee from an approaching predator) increases as the cost of not fleeing (risk) increases. This prediction has been verified for many risk factors and prey species. The same predictions may apply to other aspects of escape, but testing has been much less extensive. For the lizards Callisaurus draconoides and Sceloporus magister, we tested several such predictions and examined the effect of a previously unstudied risk factor, recent movement by prey. Starting distance (predator-prey distance when approach begins) was unrelated to FID in C. draconoides, as in previously studied ambush foragers. Because movement increases probability of being detected, we predicted that FID would be greater for prey that had moved immediately before being approached than those that had been immobile. FID and distance fled (DF) were longer for lizards that had moved recently. In C. draconoides DF and probability of entering refuge were greater for the second of two approaches, as predicted from greater threat posed by a persistent predator. Callisaurus draconoides had shorter FID and shorter DF, and fewer entered refuge where lizards were habituated than unhabituated to human presence. In S. magister FID increased as distance to refuge increased, FID and DF were longer for fast than slow approaches; probability of fleeing and FID were larger for direct than indirect approach. Effects of these risk factors on FID are consistent across studies, but approach speed has affected DF in only half of studies, perhaps due to constraints by refuge entry and variable distance to refuge. Similarities in effects of risk factors across escape variables, types of predator-prey encounters, and latency to emerge from refuge suggest that similar risk assessment mechanism are used for all variables and settings.

Foraging Strategies of Coexisting Lacertid Lizards in the Arid Tankwa Karoo Basin of South Africa

Four lacertid lizards, Pedioplanis laticeps, P. lineo-ocellata, Meroles knoxii and Nucras tessellata, occur sympatrically on the arid plains of the Tankwa Karoo Basin in South Africa. The aim of this study was to evaluate the significance of foraging strategy in resource partitioning among the four species, allowing them to co-occur in a structurally simple system with a limited number of potential niches. Previous workers already identified P. lineo-ocellata and M. knoxii as sit-and-wait foragers and N. tessellata as an active forager. We recorded data on three foraging variables: movements per minute, proportion of time spent moving, and proportion of attacks on prey whilst moving, for juveniles and adults of P. laticeps. By comparing the foraging data obtained for P. laticeps to those for other lacertid species, we were able to demonstrate that adult P. laticeps are ambush foragers. We also noted a significant ontogenetic shift in foraging behaviour in P. laticeps, and, due to a significantly higher frequency of short brief movements, we classified juveniles as mixed foragers. The sharing of an ambush foraging strategy by at least three of the four lacertid species co-occurring on the Tankwa plains, suggests considerable overlap along the trophic dimension of ecological space. This overlap presumably promotes occupation of separate microhabitats by the three ambush foragers in the Tankwa Karoo Basin.

Foraging strategies of coexisting lacertid lizards in the arid Tankwa Karoo Basin of South Africa

Four lacertid lizards, Pedioplanis laticeps, P. lineo-ocellata, Meroles knoxii and Nucras tessellata, occur sympatrically on the arid plains of the Tankwa Karoo Basin in South Africa. The aim of this study was to evaluate the significance of foraging strategy in resource partitioning among the four species, allowing them to co-occur in a structurally simple system with a limited number of potential niches. Previous workers already identified P. lineo-ocellata and M. knoxii as sit-and-wait foragers and N. tessellata as an active forager. We recorded data on three foraging variables: movements per minute, proportion of time spent moving, and proportion of attacks on prey whilst moving, for juveniles and adults of P. laticeps. By comparing the foraging data obtained for P. laticeps to those for other lacertid species, we were able to demonstrate that adult P. laticeps are ambush foragers. We also noted a significant ontogenetic shift in foraging behaviour in P. laticeps, and, due to a significantly higher frequency of short brief movements, we classified juveniles as mixed foragers. The sharing of an ambush foraging strategy by at least three of the four lacertid species co-occurring on the Tankwa plains, suggests considerable overlap along the trophic dimension of ecological space. This overlap presumably promotes occupation of separate microhabitats by the three ambush foragers in the Tankwa Karoo Basin.

Latency to flee from an immobile predator: effects of predation risk and cost of immobility for the prey

When a predator is immobile near an immobile prey, the probability that the predator will detect and attack increases over time. The prey’s cost of moving, thereby abandoning crypsis due to immobility, therefore decreases. Cost of not moving increases over time if movement is required for prey to conduct fitness-enhancing activities. We tested a cost-benefit model that predicts effects of factors that affect predation risk and cost of not moving on a prey’s latency to flee. Acting as simulated predators, we conducted experiments on the lizards Iberolacerta cyreni and Podarcis lilfordi. All predictions for 5 risk factors and a cost of moving factor were verified. Lizards fled sooner when the predator stood closer, approached rapidly rather than slowly before stopping, approached directly rather than indirectly, and gazed at the lizard rather than away from it, and after the second of 2 successive approaches. Latency to move was shorter in the presence than absence of a mealworm, suggesting the importance of opportunity cost of immobility. The effect of standing distance has 2 components, greater rate of detection by the predator and greater risk of being captured if detected at shorter distances. Escape theory has been highly successful in predicting how close a prey allows a predator to approach before fleeing. Our model extends an economic approach to study of escape decisions in response to an immobile predator that may be an ambush forager or an active forager that has stopped moving nearby. Key words: ambush, escape, latency to flee, opportunity cost, predation risk, standing distance. [Behav Ecol]

The postpulmonary septum of Varanus salvator and its implication for Mosasaurian ventilation and physiology

AbstractThe postpulmonary septum (PPS) is a relatively thick sheet of connective tissue covering the inferior surface of the lungs in varanid lizards. The primary connection of the PPS is to the medial surface of the ribs; additional connections occur to the inferior midline of the dorsal vertebrae, the pericardium, and a direct (through loose connective tissue) link to the surface of the lung. The PPS effectively partitions the coelomic cavity into peritoneal and pleural cavities. Investigation demonstrates that the PPS is not capable of preventing displacement of the more caudal (peritoneal) viscera, which is displaced cranially during terrestrial locomotion; this cranial displacement could impinge on the tidal volume of the lungs. Kinematic analyses of terrestrial and aquatic locomotion in Varanus salvator document the different propulsive mechanics used during movement through these two media, and, most importantly, the marked reduction in lateral displacement of the trunk during swimming. These findings, when combined with previous studies of the cardiovascular and respiratory system of varanids performing terrestrial locomotion, suggest that mosasaurs had a versatile, effective respiratory system and were likely capable of both sustained swimming and prolonged submersion, such as during ambush foraging.

Entomopathogenic nematode foraging strategies – is Steinernema carpocapsae really an ambush forager?

For many years, entomopathogenic nematodes have been classified as either ‘ambush’, ‘cruise’ or ‘intermediate’ foragers. Here, we critically examine the evidence that Steinernema carpocapsae, the most studied ‘ambush’ forager, does actually use an ambush foraging strategy in nature. We propose an alternative hypothesis for the characteristic behaviours of S. carpocapsae (and other supposed ‘ambush’ foragers) based on adaptation to habitats other than mineral soils in which S. carpocapsae can ‘cruise’. Several papers are reviewed in which S. carpocapsae was used successfully to control sedentary or cryptic pests in organic habitats, thus supporting our hypothesis. If this hypothesis is correct, it does not preclude S. carpocapsae (or any entomopathogenic nematode species) using an ambushing strategy under certain circumstances, but we believe on current evidence that the classification of S. carpocapsae as an ambush forager cannot be sustained.