Transcript C. caretta
Conservation and Ecology of Marine Reptiles MARE 490 Dr. Turner Summer 2011 Reproduction Occurs within 3 general contraints 1. Nesting must occur during condition which are conducive to adult activity 2. Nesting must occur during conditions that favor embryo development & survival 3. Hatchlings must emerge into conditions that are conducive to their survival Exhibition All sea turtles exhibit: 1. Iteroperous reproduction (except Ridley’s) 2. Stereotyped nesting behavior 3. Laying relative large numbers of eggs 4. Strong nesting site fidelity Exhibition Semelparous organisms produce all of their offspring over one relatively short period in a single reproductive event. Exhibition Iteroperous organisms produce their offspring in a series of separate events, which means that they have to save some of their resources to survive between reproductive events. Adult Cycle All species migrate (at least short distance) from forage to mating areas - ♂ back to foraging areas - ♀ to nesting beaches Cheloniids – reproduce on or near beaches Adult Cycle Generalize Sea Turtle Life Cycle Distribution Foraging areas widely distributed - cold temperate (leatherback) to tropical Nesting areas typically tropical – subtropical D. coriacea, C. mydas, N. depressus, E. imbricata, L. kempi, L. olivacea mainland or island beaches between Tropics of Cancer & Capricorn C. caretta – temperate - subtropical Reproductive Statistics Maturity: > 10 years Beach: deep, loose sand above high tide Philopatry: (regional decrimination) b/w forage & nesting; most <1000 km, +2600 km May not return to specific beach of birth but return to specific region Nest site fidelity: subsequent nesting 0-5 km Periodicity: 1-9 years; - L. kempi & ♂ C. caretta annually??? Reproductive Statistics Mating Activity Precopulatory behaviors: head bobbing, position in water column, head-head bumps, nuzzling, biting, movement of flipper, dinner ♂ mounts ♀, uses enlarged claws on fore & hind flippers to hold carapace Curls long tail to bring cloacea into contact In captivity coupled > 10hrs; ↑ Coupling = ↑ Fertility Nesting Activity General Requirements of Nesting Beaches: 1. Accessible from the sea 2. High enough to prevent water inundation e.g. – tides, water table 3. Substrate facilitates gas diffusion 4. Substrate must prevent collapse of egg chamber during construction e.g. – moist & fine-grained Typically: ↓ salinity, ↑ humidity, ↑ ventilation Nesting Activity Time of Nesting: most at night Time required to complete nesting process: L. olivacea & L. kempi: 1 hr E. imbricata, N. depressus: 1-1.5 hr C. caretta: 1-2 hr D. coriacea: 1.5 hr C. mydas: 2-3 hr Extreme durations Hawksbill: 45 min Green: 7 hrs Nesting Process General nesting process similar in all species Pattern contains: 1. Emerging from surf 2. Ascending the beach 3. Excavating the body pit 4. Digging the egg chamber 5. Oviposition 6. Filling the egg chamber 7. Filling the body pit 8. Return to the sea Stages of Nesting Behavior Reproductive Characteristics All species: Lay several clutches during a nesting season Lay white, spherical cleidoic eggs with flexible calcareous shells Size of eggs differs between clutches and among species Size of eggs, # & # of clutches represent result of adaptive survival compromise Reproductive Characteristics Embryos! Fertility is marine turtles typically high >95% measured by hatching success Factors that can influences success: Nutrition Health Stressors Human impacts Tightness of underwear Embryos! When a ♀ sea turtle arrives on the nesting beach – carrying the full component of follicles to supply yolks for all the eggs laid that season Follicles increase in size slightly due to H2O absorption Embryos! Embryos! Chorion - outermost membrane around the embryo Albumen – egg white; protein rich Allantois – collects waste; exchanges gases Chorioallantois – gas exchange Hatchlings! Hatch after 6 – 13 weeks of incubation depending upon temperature Weigh < 50% of oviposition weight Large eggs produce large hatchlings The Hatch! Embryos use caruncle to cut through the amniotic & chlorio-allantoic membranes Shell ruptured, amniotic fluid drains Reduction in volume allows the space required for the hatchlings to wriggle to the surface – “Social Facilitation” Social Facilitation The upward digging activity of the hatchlings that is stimulated by the activity of the other hatchlings – usually from the bottom of the chamber Typically emerge at night – circumvent two major problems with diurnal emergence: 1. Lethal temperature 2. Predators Hatching Success! Clutches of sea turtle eggs typically have high hatching success > 80% Reduction of hatching success caused by: 1. Predation 2. Environmental change 3. Microbial infection Hatchling Protection Focus on conservation protection for reducing turtles divides into two categories: 1. Protection of the animals 2. Protection of their habitat This requires: 1. Protection of eggs 2. Protection of nests 3. Protection of foraging areas 4. Protection of mating areas Temperature Effects Incubation time is directly influenced by nest temperature Thermal tolerance range (TTR) for development of sea turtle embryos incubated at a constant temperature appear to fall between 25-27°C & 33-35°C Temperature Effects Temperature Effects Temperature-dependent sex determination – produces ♀ at warm temps, ♂ at cool temps Sensitive period for sex determination takes place during middle third of incubation Threshold temperature for the transition of producing one sex to the other is 28-30°C Temperature Effects Temperature Effects Temperature Effects Emergence & Sea Finding After emerging, hatchlings crawl toward the sea; sea-finding behavior occurs reliable in daylight or at night in a variety of conditions - cues hatchlings use are primarily visual Emergence & Sea Finding Cues hatchlings use are primarily visual Emergence & Sea Finding Sensitivity to directional light can be described by a specific “cone of acceptance” which indicates how much of the world a hatchling measures at any one instant Light Effects Artificial light a problem Not tied to full moon Focused on light sources at the horizon – sources high in the sky (moon, streetlights) often don’t have a direct effect Wave Effects As hatchlings complete their crawl across the beach and enter the surf, they are lifted off the sand by incoming waves When their flippers no longer contact sand they being swimming vigorously Orientation Mechanisms Three types of cues: visual, wave & magnetic orientation Chemical Imprinting The chemical imprinting hypothesis for sea turtles proposes that hatchling turtles imprint on chemical cues unique to their natal beach and use this information years later as adults to return to the same beach for nesting & mating Little evidence to support or refute