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

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

Density‐Dependent Foraging and Interference Competition by Common Gartersnakes are Temperature Dependent

The ideal free distribution (IFD) predicts that optimal foragers will select foraging patches to maximize food rewards and that groups of foragers should thus be distributed between food patches in proportion to the availability of food in those patches. Because many of the underlying mechanisms of foraging are temperature dependent in ectotherms, the distribution of ectothermic foragers between food patches may similarly depend on temperature because the difference in fitness rewards between these patches may change with temperature. We tested the hypothesis that the distribution of Common Gartersnakes (Thamnophis sirtalis) between food patches can be explained by an IFD, but that conformance to an IFD weakens as temperature departs from the optimal temperature because fitness rewards, interference competition and the number of individuals foraging are highest at the optimal temperature. First, we determined the optimal temperature for foraging. Second, we examined group foraging at three temperatures and three density treatments. Search time was optimized at 27°C, handling time at 29°C and digestion time at 32°C. Gartersnakes did not match an IFD at any temperature, but their distribution did change with temperature: snakes at 20°C and at 30°C selected both food patches equally, while snakes at 25°C selected the low food patch more at low density and the high food patch more at high density. Food consumption and competition increased with temperature, and handling time decreased with temperature. Temperature therefore had a strong impact on foraging, but did not affect the IFD. Future work should examine temperature‐dependent foraging in ectotherms that are known to match an IFD.     

The influence of housefly Musca domestica embryo age on viability in water and at low temperatures

The sensitivity of housefly Musca domestica L. (Diptera: Muscidae) embryos to storage at low temperatures (5 and 10 °C on moist sponges in Petri dishes) and in water at 26 °C was investigated to develop suitable protocols for the storage and transport of housefly eggs. The youngest embryos (aged 0–3 h) were the most sensitive to storage at 5 °C, with 45% survival after storage for 24 h. Storage of embryos aged 3–12 h at 5 °C for 24 h had no negative effect; longer storage resulted in significantly decreased larval survival (30–34% after 48–72 h, compared with 61% in the control group) and reduced hatching rates (83% after 72 h storage). No negative effects were observed when embryos aged 0–9 h were stored at 10 °C for 24 h, but this temperature did not completely inhibit development and eggs began to hatch if stored for longer than 24 h. All age groups of embryos showed high mortality after storage in water at 26 °C for 24 h, with the youngest embryos being least resistant to submersion.     

Effect of meteorological variates on persistence of primary conidia and capilliconidia of Erynia radicans (Zygomycotin: ntomophthorales) under natural conditions

Persistence of conidia of an isolate of Erynia radicans (Syn. Zoophthora radicans) was investigated in relation to the meteorological conditions which occurred during autumn-winter of 1990–91 in the coastal plain in Israel. Capilljconidia shielded from the sun, placed on the abaxial surface of leaves of Plumeria acuminata, persisted for 24 h to at least 120 h. Exposed capilliconidia, placed on the adaxial surface of the same leaves, died within 24 h. Almost all the primary conidia shielded from the sun (placed on the abaxial surface of the same leaves) died within a single day. Conidial viability was expressed in subsequent germination on an agar medium. Capilliconidial persistence was closely related to the daily air temperatures, expressed as cumulative day-degrees. Differences in relative humidity had no substantial effect on capilliconidial mortality. At daytime temperatures of ≤ 20°C, mortality after 24 h incubation was lowest (≤ 34%) and the persistence duration, longest (at least 120 h). Increases in daytime temperature up to 24°C for a few hours increased mortality (37–57% after 24 h incubation) and shortened the persistence duration (72–120 h). Exposure to 24–29°C during daytime greatly increased mortality (65–58% after 24 h) and further shortened the persistence duration (24–48 h). Daytime temperatures of > 29°C were lethal to all capilliconidia within 24 h. Temperature had a profound effect on capilliconidial persistence also under controlled environmental conditions. The significance of capiliiconidial persistence is discussed in relation to activity of the fungus in its natural environment.     

Thermal Dependence of Tongue-flicking and Comments on Use of Tongue-flicking as an Index of Squamate Behavior

Tongue-flicking rate has often been used as a dependent variable or a component of a dependent variable taken as a measure of responsiveness to chemical stimuli by lizards and snakes. Because temperature has been controlled in most studies, effects of temperature have been largely overlooked. In this study, a constant stimulus, the adult cloacal odor of a conspecific female, was presented to adult scincid lizards (Eumeces laticeps) and temperature was from 15 ° to 35 °C. Tongue-flicking rates by adult Eumeces laticeps in response to cloacal odors of conspecific females were strongly thermally dependent in 20 s and 60 s trial periods. The tongue-flick-temperature curve appears to be roughly quadratic over the entire 15 °-35 °C range studied, with very low rates at 15 ° and 20 °C followed by a rapid rise to maximum tongue-flicking rate at 30 ° and rapid decline to 35 °C. Presumably, similar relationships apply to other lizards and snakes with modifications related to ecological characteristics such as diel activity cycle and foraging mode, to relative position on a scale of eurythermy-stenothermy, and to taxon. Thermal response curves for other stimuli, especially prey odors, are likely to have the same basic form, but have not been determined.     

Importance of interspecific competition in the abundance of Aphanizomenon flos-aquae (Cyanophyceae)

The population dynamics of Aphanizomenon flos-aquae var. klebahnii Elenk. (Cyanophyceae) was studied in an artificial pond for 32 months from May 2002 to December 2004. Our previous in vitro study showed that the lower limits of water temperature and pH for its growth are within the ranges of 11°–14°C and 7.1–7.4, respectively, and it appeared that these findings are applicable to the emergence and disappearance of Ap. flos-aquae in the pond. Based on the change in the water temperature, the emergence of Ap. flos-aquae in 2004 was expected to be in late April, whereas emergence occurred after a 1-month lag period. During this period, Ankistrodesmus falcatus (Corda) Ralfs (Chlorophyceae) dominated the phytoplankton assemblage, which raised the possibility that the growth of Ap. flos-aquae was restricted by the existence of An. falcatus. We conducted mixed cultures of Ap. flos-aquae and An. falcatus at four temperatures (14°, 19°, 24°, and 29°C). After 18 days of incubation, An. falcatus dominated at 14° and 29°C whereas Ap. flos-aquae dominated at 19°C. This result indicates that a slightly higher water temperature than the growth threshold value is needed for Ap. flosaquae to outcompete An. falcatus, which agrees with the field observation. Contrary to the results of the mixed culture, the summer phytoplankton assemblage was dominated by Ap. flos-aquae, and the population of An. falcatus was less or almost absent. This variation seemed to be partly caused by the difference in nutrient conditions; concentrations of dissolved inorganic nitrogen and phosphorus in the pond were far lower than those in the culture medium. The lack of nitrogen fixation of An. falcatus seemed to be a growth disadvantage during the summer when the concentration of dissolved inorganic nitrogen was low.     

Influences of Temperature and Desiccation on Breaking Diapause in the Gemmules of Eunapius fraqilis (Leidy)

Summary

Most specimens of Eunapius fraqilis in Gallup Pond (Connecticut) apparently formed gemmules in September and then died. The gemmules were initially in a protracted diapause which was gradually broken during the winter. They germinated in the pond between late March and late April. Gemmules collected during the fall did not germinate during four months when they were kept at 20°C. Other gemmules from the same collections, which were kept at 5°C for several months before they were placed at 20°C, exhibited good germination. Finally, gemmules that did not germinate following a cold treatment could be activated by drying them at 20°C for seven days and then maintaining them in pond water at 20°C. These results suggest that low temperature and desiccation are effective in breaking gemmule diapause of Eunapius fraqilis.     

Spatial variation in the annual reproductive cycle of Turbo (Batillus) cornutus (Gastropoda: Trochidae) at Jeju Island,Korea

The annual reproductive cycle of the top shell Turbo cornutus from Jeju Island was investigated in two populations using histology. In the northern population, gametogenesis commenced in January as the surface water temperature reached 14?°C, while in the southern population gametogenesis began a month earlier, as the water temperature remained at 17?°C. Ripe top shells first appeared in June and spawning continued from June to October when water temperatures were between 20 and 24?°C. Histology indicated that the spawning period of the southern population was a month earlier and lasted longer (June–October) than in the northern population (July–September). The percentage gonad area of animals in the southern population in March and April was significantly higher than in the northern population (p?相似文献   

Temperature linked degenerative tissue rots in Capsicum annuum (L.) varieties diseased with Phytophthora capsici

Five-week-old seedlings of Capsicum annuum variety SAMPEP 4, Californian Wonder and Ex Dandamasa drenched with 15,000 infectious units per ml of Phytophthora capsici were incubated at 5°C, 20°C, 30°C and 35°C in alternating light–dark cool cycle Gallenkamp incubators and monitored for root rot development. Each host–pathogen system was replicated five times. Successful disease development was contingent on been incubated at ambient temperature for not less than 3.5 ± 0.5 h. Depending on variety, degenerate tissue rots were aggravated ≤2–3 days after a preconditioning temperature treatment for 24 h possibly linked to cell wall constitution, composition and permeability. Lesion development on stem heightened (27.8%) when incubated at temperatures above 20°C. Ten days after treatment, plant mortality and disease severity were not affected significantly by post-inoculation temperature.     

Seasonal growth and profile structure development of Elodea nuttallii (Planch.) St. John in pond Ojaga-Ike,Japan

Phenological and quantitative observations on Elodea nuttallii (Planch.) St. John, an exotic aquatic plant in Japan, were made in a shallow pond throughout 1979. Shoot elongation began in spring (late March) when the bottom water temperature became higher than about 10°C. Elongation ceased when the shoot apices reached the pond surface and vigorous branching then occurred. The community formed a dense canopy, with 40–65% of the shoot biomass in the topmost 30-cm water layer during the growing season. Maximum plant biomass (712 g dry wt. m^?2) was attained in late July, while the peak root biomass occurred around June, coincident with peak flowering. The anchoring roots and stems eventually died, and after September, the population existed as a floating mat of non-anchored leafy short shoots and decaying old branch stems. This mat sank suddenly to the bottom in December, when water temperatures dropped below approximately 10°C, and overwintered there. The ecological significance of the perennial growth habit and the formation of a floating mat is discussed in terms of the adventive spread of this plant, and an estimation of annual net production and P/B quotient is also made.     

Husbandry of the little file snake,Acrochordus granulatus

Aquatic snakes of the family Acrochordidae are unusual in terms of appearance, biology, and natural history. In spite of many attractive and fascinating features, there are few zoological exhibits of acrochordid snakes, and as a result many aspects of their husbandry are poorly understood. The present paper summarizes aspects of acrochordid biology related to health and welfare of captive snakes, with emphasis on the little file snake, Acrochordus granulatus. Several key points emerge having crucial relevance to successful husbandry. (1) File snakes are sensitive to low temperatures and to rapid thermal change. Captive snakes do well when maintained at water temperatures of 27–30°C and will not thrive if water temperatures are below 25°C. (2) File snakes can be kept in either fresh water or seawater. Snakes in sea or brackish water dehydrate, however, and must be allowed to drink fresh water periodically. If snakes from marine populations are maintained in saline water, 60–70% seawater is recommended. In all cases, water should be filtered or changed periodically to maintain quality. (3) File snakes feed almost exclusively on fishes which are usually captured in body coils. Snakes are more inclined to feed well if live prey are offered in shallow water where they are more easily captured. (4) File snakes are nocturnal and prefer quiescent seclusion within darkened refugia during daylight hours. Providing snakes with refugia such as sections of PVC pipe (which simulate burrows) helps reduce stress and improves the chances of snakes feeding regularly. (5) Snakes tend to burrow, and they locomote by crawling as well as by swimming. Use of sharp or rough materials in aquaria should be avoided because of possible skin abrasion which increases permeability and provides sites for bacterial infection. © 1996 Wiley-Liss, Inc.     

Rainbow trout responses to water temperature and dissolved oxygen stress in two southern California stream pools

Habitat use by rainbow trout Oncorhynchus mykiss is described for a southern California stream where the summer water temperatures typically exceed the lethal limits for trout (>25°C). During August 1994, water temperature, dissolved oxygen (DO), and trout distribution were monitored in two adjacent pools in Sespe Creek, Ventura County, where summer water temperature reached 28.9° C. Water temperature was an important factor in trout distribution in the two pools. During 1–11 August 1994, water temperatures in pool 1 ranged from 21.5°C at the bottom (4.1 m) to 28.9° C at the surface. After 5 August, trout were no longer found in this pool, suggesting that trout had moved out of the high temperature water or died. In the adjacent, shallower (1.5m) pool 2, surface water temperatures were as high as 27.9° C, but temperatures on the bottom remained cooler (17.5–21° C) than pool 1, presumably due to groundwater seeps. Consistent aggregations of trout were observed in pool 2 throughout the study period. During the day when water temperature was highest, most trout were found in a region of the pool with the lowest water temperature (mean=18.3° C). Conversely, regions with the highest water temperatures had the fewest trout during the day. The seeps may have introduced water with low dissolved oxygen into pool 2, as the DO in many locations on the bottom ranged from <1 mg 1^?1 to 5 mg 1^?1 over 24 h, while the surface DO ranged from 4.1 to 10.0mg 1^?1. Lowest DO occurred from 2400 to 0600 hours. During August, water temperature and DO were positively related. Thus, rainbow trout faced a trade-off between the relatively cool water temperature with low, possibly lethal levels of DO (e.g. 1.7 to 3.4 mg 1^?1 in region 3), and lethally high water temperature but high DO. Seeps may serve as important thermal refugia for trout, and an increased understanding of their role as potential critical refugia in Southern California is necessary.     

Effects of temperature on germination and hyphal growth from ascospores of A-group and B-group Leptosphaeria maculans (phoma stem canker of oilseed rape)

Ascospores of both A‐group and B‐group Leptosphaeria maculans germinated at temperatures from 5–20°C on distilled water agar or detached oilseed rape leaves. After 2 h of incubation on water agar, some A‐group ascospores had germinated at 10–20°C and some B‐group ascospores had germinated at 5–20°C. The percentages of both A‐group and B‐group ascospores that had germinated after 24 h of incubation increased with increasing temperature from 5–20°C. The observed time (Vo₅₀) which elapsed from inoculation until 50% of the spores had germinated was shorter for B‐group than for A‐group ascospores. Germ tube length increased with increasing temperature from 5–20°C for both ascospore groups. Germ tubes from B‐group ascospores were longer than germ tubes from A‐group ascospores at all temperatures tested, but the mean diameter of germ tubes from A‐group ascospores (1.8 μm) was greater than that of those from B‐group ascospores (1.2μm) at 15°C and 20°C. The average number of germ tubes produced from A‐group ascospores (3.8) was greater than that from B‐group ascospores (3.1) after 24 h of incubation at 20°C, on both water agar and leaf surfaces. Germ tubes originated predominantly from interstitial cells or terminal cells of A‐group or B‐group ascospores, respectively, on both water agar and leaf surfaces. Hyphae from A‐group ascospores grew tortuously with extensive branching, whilst those from B‐group ascospores were predominantly long and straight with little branching, whether the ascospores were produced from oilseed rape debris or from crosses between single ascospore isolates, and whether ascospores were germinating on water agar or leaf surfaces.     

The effect of temperature and body size on digestive efficiency in Fundulus heteroclitus (L.)

The digestive efficiency of temperature acclimated mummichogs, Fundulus heteroclitus (L.), was determined using the amphipod Orchestia grillus Bosc as prey. Experiments were conducted on three size groups of mummichogs (<1 g, 1–3 g, > 3 g) at 5, 13, 21, and 29 °C. No difference was found in digestive efficiency by different sizes of mummichogs. There was, however, a statistically significant difference in efficiency over the range of acclimation temperatures, with the efficiencies being temperature independent from 13 to 29 °C and dropping slightly at 5 °C. From 13 to 29 °C, digestive efficiencies were the maximum possible. Temperatures in this range are normal late spring, summer, and early fall habitat temperatures in Maine estuaries. The ability to maintain a maximum efficiency of digestion over this 16°C temperature range allows mummichogs to get the maximum amount of energy from their prey during the time of year when they are utilizing substantial energy for growth (somatic and gonadal, and for activity (foraging and mating). The digestive efficiency at 5 °C was only about 13.5% less than at 21 and 29 °C. This drop is probably of little ecological or energetic significance, so that mummichogs are actually able to absorb food energy across their alimentary tract relatively independent of acclimation temperature over a 24 °C range.     

Feeding by Priapulus caudatus (Cephalorhyncha: Priapulidae): observations of the effects of seasonal temperature change and molting

The ecdysozoan Priapulus caudatus belongs to a phylum of exclusively marine worms that reigned among the most abundant benthic metazoans during the Cambrian. Usually found at great depths, this species can occasionally be found among intertidal habitats fed by exceptionally cold sea water and predominated by soft mud, as in the Lower Bay of Fundy. Live priapulids were collected there and the effects of molting and seasonally changing ambient sea water temperature on feeding were observed in the laboratory beginning in February. Feeding increased as ambient sea water temperatures increased from March through April, a relationship significantly correlated (p < 0.001). This association rapidly deteriorated once 11 °C was reached in May with no animals feeding above 13 °C. Priapulids fed until the first molt day when feeding significantly decreased (p = 0.016). This response was short-lived, and feeding slowly resumed among animals within a week post-molt. Exuvia were not consumed. The onset of molting followed color changes in cuticle appearance and was significantly correlated with increasing temperature (p < 0.001). Molting was rapid, with the exuviae clearly separated from the new cuticle within 24 h at places where the process began. Without substrate to burrow into, animals emerged from shed exuviae between 3 and 29 days, with larger animals taking longer. While the cold deep-sea is the primary habitat of P. caudatus, this species shares some of the effects of temperature and molting on feeding shown by other ecdysozoans. The observations made during this study place a limit on where P. caudatus might be found intertidally.     

Germination and Survival of Fusarium graminearum Macroconidia as Affected by Environmental Factors

The effects of temperature (4–20°C), relative humidity (RH, 0–100%), pH (3–7), availability of nutrients (0–5 g/l sucrose) and artificial light (0–494 μmol/m²/s) on macroconidial germination of Fusarium graminearum were studied. Germ tubes emerged between 2 and 6 h after inoculation at 100% RH and 20°C. Incubation in light (205 ± 14 μmol/m/s) retarded the germination for approximately 0.5 h in comparison with incubation in darkness. The times required for 50% of the macroconidia to germinate were 3.5 h at 20°C, 5.4 h at 14°C and 26.3 h at 4°C. No germination was observed after an incubation period of 18 h at 20°C in darkness at RH less than 80%. At RH greater than 80%, germination increased with humidity. Germination was observed when macroconidia were incubated in glucose (5 g/l) or sucrose (concentration range from 2.5 × 10^?4 to 5 g/l) whereas no germination was observed when macroconidia were incubated in sterile deionized water up to 22 h. Macroconidia germinated quantitatively within 18 h at pH 3–7. Repeated freezing (?15°C) and thawing (20°C) water agar plates with either germinated or non‐germinated macroconidia for up to five times did not prevent fungal growth after thawing. However, the fungal growth rate of mycelium was negatively related to the number of freezing events the non‐germinated macroconidia experienced. The fungal growth rate of mycelium was not significantly affected by the number of freezing events the germinated spores experienced. Incubation of macroconidia at low humidity (0–53% RH) suppressed germination and decreased the viability of the spores.     

Effect of Variation of Sporulation Time and Temperature on Thermostability of Bacillus cereus Spores

The optimum temperature for sporulation of a strain of Bacillus cereus was estimated at 30°–35°C, where the maximum yield of spores was obtained between 18 and 24 hours’ incubation. Sporulation was more rapid, but less extensive at 40°C and did not occur at all at 45°C. The heat resistance of the spores increased with the sporulation temperature from 20° to 40°C. The spores appear to be more susceptible to heat destruction in the early stage of spore production than after further incubation.     

Growth,trichome size and akinete production of Cylindrospermopsis raciborskii (cyanobacteria) under different temperatures: Comparison of two strains isolated from the same pond

Coiled morphotype Cylindrospermopsis raciborskii (Woloszynska) Seenayya et Subba Raju that forms a water bloom in a shallow pond in northern Taiwan exhibits a negative correlation between trichome size and temperature. To investigate how temperature influences the growth and trichome size of C. raciborskii, two C. raciborskii strains isolated from the pond in August and February were grown at three temperatures (18, 24 and 30°C). Both strains exhibited the lowest and highest specific growth rates at 18°C and 24°C, respectively, and the trichomes became the largest at 18°C. However, specific growth rates of the strain isolated in August exceeded those of the strain isolated in February, and the trichomes of the strain isolated in February were larger than those of the strain isolated in August regardless of temperature. Moreover, although both strains produced larger numbers of akinetes at higher temperatures, the strain isolated in August produced many more akinetes than did the other. These findings suggest that the two strains are not identical, leading to the conclusion that the C. raciborskii population in the pond consists of at least two ecotypes. Large trichome formation and akinete production are thought to be different types of countermeasure against cold of C. raciborskii, and the patterns of investment in developing these functions seemed to vary between the strains.     

Early ontogeny of Ancherythroculter nigrocauda and effects of delayed first feeding on larvae

Development of embryos and larvae in Ancherythroculter nigrocauda Yih et Woo (1964) and effects of delayed first feeding on larvae were observed after artificial fertilization. The fertilized eggs were incubated at an average temperature of 26.5°C (range: 25.7–27) and the larvae reared at temperatures ranging from 21.8 to 28°C. First cleavage was at 50 min, epiboly began at 7 h 5 min, heartbeat reached 72 per min at 24 h 40 min and hatching occurred at 43 h 15 min after insemination. Mean total length of newly hatched larvae was 4.04 ± 0.03 mm (n = 15). A one‐chambered gas bladder was observed at 70 h 50 min, two chambers occurred at 15 days, and scales appeared approximately 30 days after hatching. Larvae began to feed exogenously at day 4 post‐hatch at an average temperature of 24°C. Food deprivation resulted in a progressive atrophy of skeletal muscle fibres, deterioration of the larval digestive system and cessation of organ differentiation. Larval growth under food deprivation was significantly affected by the time of first exogenous feeding. Starved larvae began to shrink, with negative growth from day 6 post‐hatch. The point of no return (PNR) was reached at day 11 after hatching. Mortality of starved larvae increased sharply from day 12 after hatching.