Transcript Gibbs
Temperature Relationships What do amphibians and reptiles have in common? Evolutionarily speaking, “herpetiles” are a somewhat unnatural grouping but ectothermy: is a reliance on solar radiation to raise body temperatures to a functional level provides an important link In contrast, endotherms (e.g. birds and mammals) regulate body temperature by metabolizing the food they eat Ectothermy vs. Endothermy Ectothermy: Greek ‘Ectos’ = outside, ‘Thermos’ = warm/heat Endothermy: Greek ‘Endo’ = within, ‘Thermos’ = warm/heat Why does body temperature matter? Biochemical reactions allow organisms to function Rates of depend strongly on temperature Temperature also affects the rate of travel of nerve impulses and rate of muscle contractions Regulation of body temperature is essential for organisms to function Why does body temperature matter? Effects of Temperature on Garter Snake Activity Map turtles… http://www.bioone.org/doi/pdf/10.1670/071881.1 Let’s not use “cold-blooded”! Ectothermy vs. Endothermy Ectotherms are FAR more energy efficient A lizard uses ~ 3% as much energy in a day as a similar sized mammal in the same habitat They are able to convert a greater percentage of the energy they consume into body tissue (50% compared to 2% for endotherms) Efficiency of Biomass Conversion Implications of Ectothermy When food is scarce, ectotherms can go into torpor Organism is out of sight and virtually inactive for sometimes months or years Allows for exploitation of episodic food resources Implications of Ectothermy Ectotherms are often extremely productive (prolific) Can produce lots of biomass with little energy input Thus, they can produce lots of offspring Ectothermy vs. Endothermy On the other hand….. It is difficult for ectotherms to maintain their body temperature in an ideal range in cold climates This limits their distribution in space and time Many species are only active in warm seasons At risk of predation during periods of inactivity Ectothermy vs. Endothermy Body Size Interactions…… Being a small endotherm is energetically very expensive Being a small ectotherm is relatively efficient Most amphibians and reptiles are small in comparison to birds and mammals It is simply not energetically feasible to be a small (< 10 g) bird or mammal! Size Matters…… Surface to SA = 24 SA = 6 volume ratio V=8 V=1 6:1 decreases with 3:1 increased size Surface Area = 6 x length2 Volume = length3 Heat gain and loss occurs more slowly in larger individuals Resting metabolic rate as a function of body size Ectothermy vs. Endothermy Body Size implications… Body Mass Mammals Salamanders Lizards Ectothermy and Body Size Allows ectotherms to exploit "small body size" niches that are unavailable to larger endotherms. “Small body size" niche dimensions include small habitat patches (e.g., cups formed by tropical bromeliads, cracks in bedrock) small food items small shelters (e.g., cracks in bark) Small size: Rapid control over body temperature by shuttling between different thermal regimes Large size: some advantage -- Inertial homeothermy. Ectothermy has important implications for how energy flows in ecosystems One example… Found about 10,000 redback salamanders/ha Each weigh about 1 g, so there’s about 10 kg salamanders/ha There are some 180 billion RBS in NYS! Energy conversion rate of 60% (Burton and Likens, 1975, Ecology 56:1068-1080) Redback salamanders •Regulate decomposition rates of the leaf litter by limiting invertebrate populations •Major food item for predators “above” them in the food chain •Essentially "repackage" energy from small prey items into forms that larger species (including endotherms) can exploit •Major conduit of energy and minerals •Without ectotherms, the abundance and diversity of endotherms would be much lower! •Play role in global carbon cycles. Gaining and losing heat Direct solar radiation Reflected solar radiation Convection Metabolic Heat Evaporation Infrared Loss Conduction Infrared Gain Terminology Thermal performance breadth (activity temperature range) - The temperature range over which an individual is active Critical thermal minima and maxima (CTmin, CTmax) - Lethal higher and lower temperatures Optimal temperature - The temperature over which performance of some biochemical or behavioral task is maximized. Different tasks may have different optima. Sevilleta box turtles project Lizards Radiating Heat Absorbing Solar Radiation Qabs = S ·A · vfs · a Rate of absorption of solar energy depends on: The intensity of the radiation (S) Surface area of the animal (A) Proportion of the animal’s surface that is exposed to the radiation (vfs) Absorptivity, proportion of the energy that is absorbed rather than reflected (a) Herps have substantial control over the amount of solar radiation they absorb Absorbing Solar Radiation Move between sun and shade Change the amount of surface area exposed to the sun Change orientation to the sun Change color (albedo) to change absorptivity Concentrate pigments in melanophores to expose reflective pigments and cast off light. Disperse melanin to absorb light Basking Common in reptiles and amphibians Involves relocation and postural adjustment to maximize surface area exposed to sun More on basking… Sun patches critical, especially in low light environments (forests, wetlands). Egg laying Varies by life stage Recent metamorphs of many nocturnal species are very diurnal Diurnal activity corresponds to higher growth rates and rates of fat storage Gestation in adult females Basking to purge diseases? Batrachochytrium dendrobatidis (Bd) is a fungus that can induce chytridiomycosis Bd cannot live above 30oC Gaining and losing heat Direct solar radiation Reflected solar radiation Convection Metabolic Heat Evaporation Infrared Loss Conduction Infrared Gain Absorbing Infrared Radiation Heat is constantly exchanged between an animal and its environment in the form of infrared radiation Heat is transferred from the warmer surface to the cooler surface The amount of heat an animal gains from infrared radiation depends partly on how easily a surface radiates and absorbs the infrared energy Gaining and losing heat Direct solar radiation Reflected solar radiation Convection Metabolic Heat Evaporation Infrared Loss Conduction Infrared Gain Producing Metabolic Heat Some chemical energy is lost as heat during metabolic processes A few reptiles, especially large species, use metabolic heat production (endothermy) Producing Metabolic Heat E.g. The leatherback turtle (Dermochelys coriacea) In leatherbacks, heat is generated through muscular activity Retained by insulative thick, oil-filled skin Can maintain body temperatures of 25oC in 8oC seawater and range into cold northern seas. Producing Metabolic Heat E.g. Pythons Females use the heat produced by muscle contractions to incubate their eggs Metabolic rate during brooding 20 x that of nonbrooding females Eggs are maintained at ~30° C Gaining and losing heat Direct solar radiation Reflected solar radiation Convection Metabolic Heat Evaporation Infrared Loss Conduction Infrared Gain Convection Heat exchange between a solid and a fluid medium (air or water) Involves differing amount of contact with fluid flows, especially, wind Side blotched lizard, Uta stansburiana Gaining and losing heat Direct solar radiation Reflected solar radiation Convection Metabolic Heat Evaporation Infrared Loss Conduction Infrared Gain Conduction Exchange from solid to solid Managed mainly through posture shifts that change the degree of body contact with substrate Conduction is especially important for fossorial species Nocturnal species Gaining and losing heat Direct solar radiation Reflected solar radiation Convection Metabolic Heat Evaporation Infrared Loss Conduction Infrared Gain Evaporative Cooling Water passed across skin, vaporizes on surface Conversion of water from liquid to gaseous phase involves a large loss of heat. Last step is convection of water vapor. E.g., in reptiles: panting, salivation, urination on limbs and body. Evaporative Cooling: A major issue for amphibians Skin is so permeable that high water loss is continuous. Limits the thermal regulatory ability of amphibians. Only a few have any physiological control over evaporative heat loss, e.g., some arboreal tree frogs (e.g., Phylomedusa spp). Evaporative Cooling: E.g. Green frogs (Rana clamitans) and Bull frogs (Rana catesbeiana) Evaporative Cooling: Phyllomedusa spp. Secretes wax that seals itself up – when very high temperatures are achieved, then wax melts and evaporative cooling ensues Reptile Skin and thermoregulation Highly impermeable skin, permits direct exposure to sunlight without excessive water loss Hence temperature control is much more common in reptiles Wood Turtle, J.C. Mitchell Western Pond Turtle, G. Hodgson 2011 Year of the Turtle Alligator Snapping Turtle, J.C. Mitchell Bog Turtle, J. Hall Spotted Turtle, G. Lipps Green Sea Turtle, J.D. Willson Chicken Turtle hatchling, J.C. Mitchell Gopher Tortoise, D. Stevenson Showcase of projects Themed events Products In press Sponsored by: Partners in Amphibian and Reptile Conservation www.parcplace.org PARC seeks: Your involvement! Projects to showcase Events to co-sponsor Ideas to make the year a success Spiny Softshell Turtle, J. Hall Contacts: Dede Olson, National PARC Co-Chair, [email protected] Priya Nanjappa, PARC State Agencies Coordinator, [email protected] Diamondback Terrapin, J.D. Willson Eastern Box Turtle, J.D. Willson River Cooter, J.D. Willson Species numbers Notes: ~5900 amphibians? Notes: ~300 species of turtles Current number of amphibian species: 6,723 (Sep 28, 2010) amphibiaweb.org Last week IUCN representative: 334 species in modern times, of which 9 species have become extinct since 1500 AD, leaving 325 species extant. The point is orders of magnitude… Graptemys gibbonsi Pearl River Map Turtle: Thermoregulation – Dealing with the cold Dormancy - a response to temperature extremes, especially cold. Most species seek hibernation areas where environmental temperatures will not fall below freezing. Thermally stable areas are caves, wetlands, soil. Especially common is use of bottoms of lakes and streams Water at maximum density at 4oc, so resting on or in bottom protects against temperatures <4oc Respire dermally, occasionally activate Hibernation on land Must stay below frostline -- slowly dig gradually deeper to avoid it (e.g., box turtles Terrapene carolina) Ambystoma salamanders migrate down, then up, seasonally. Freezing! Freezing is usually lethal Extracellular water freezes first, creating osmotic imbalance and drawing water out of cells. Blocked fluid circulation prevents gas exchange, nutrient uptake, etc. Physical damage Freeze resistance Allow body temp to drop below 0oC, and hope that nucleation process that causes freezing doesn’t take place. E.g. hatchling Chrysemys picta Advanced Freeze Tolerance Locally there are a number of freeze-tolerant species Pseudacris crucifer, Hyla versicolor, Rana sylvatica, Terrapene carolina Cryoprotectants… Build up high concentrations of sugars or sugar alcohols inside cells (glucose or glycerol, made from glycogen) Builds up osmolarity within cells which i) prevents freezing and ii) equalizes osmolar differential when ice forms outside cells To conclude… Direct solar radiation Reflected solar radiation Convection Metabolic Heat Evaporation Infrared Loss Conduction Infrared Gain The future: Climate change and herps? Putting the Heat on Tropical Animals, Tewkesbury et al. Upcoming events… Exam I – Oct. 5 Week of 10/11 Individual presentation topics due in lab to Meredith: (1) title, (2) short description (3-5 sentences), (3) list of 510 relevant citations, (4) first page of 5 of those citations. TOPIC ABSTRACT, ANNOTATED BIBLIOGRAPHY AND PRESENTATION Abstract Written synopsis (10-15 sentences), typed, single-spaced. Annotated Bibliography reference list used provide a few sentences about each article’s usefulness to your topic at least five quality references Presentation 7-minute oral presentation (with 3 minutes for questions) In lab, end of the semester. Topics? 10/7 Individual presentation topics due in lab Third eye in the tuatara Phylogenetic position of turtles Climate change and tropical lizards Road-kill and turtles…biologically important? Color morph variation in redbacks The tegu skin trade Lizard foot structure to facilitate running Gecko toes and nanotechnology Basking to control chytrid infections Sea turtle recovery in the se United States Bullfrogs as invasives elsewhere Etc. Temperature relations (end)