WILD 3580 1st Edition Lecture 25 Outline of Last Lecture I Courtship II Delayed Fertilization III Viparity IV Extended Parental Investment V Sex Determination Outline of Current Lecture I Sex Determination II Parthenogenesis III Thermoregulation Current Lecture I Sex Determination Genotypic sex determination sex of the offspring is determined at fertilization o Heterogametic different sex chromosomes Temperature dependent sex determination TSD sex is determined by temperature during incubation Crocodilians many turtles and some lizards Not in snakes o General Mechanism average temperature during the middle third thermos sensitive period of embryonic development When gonads are developing 3 major patterns 1 Males produced at cooler temperatures females at warmer temperature turtles Pivotal temperature 50 50 sex ratio These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute 2 Females produced at lower temperatures males at higher temperatures most lizards and crocodilians Opposite relationship 3 Females are produced at low and high temperatures males are produced at intermediate temperatures some lizards some turtles and some crocodilians II III o Greater reproductive success more advantageous for temperature dependent sex determination o Favor because it will differentiate sex determination Parthenogenesis Reproduction from an unfertilized egg o Populations consist entirely of females Offspring are clones of the female Outbreeding depression through hybridization Alter the distribution of chromosomes females have diploid gametes 40 species of squamates mostly lizards ex Whiptail lizardsAspidoscelis o Pseudocopulation behavior same behavioral display typical of males and females Thermoregulation Temperature control Reptiles are ectothermic body temperature is controlled through behavior Depends on 2 factors 1 Ambient temperatures 2 Behavior o Behavioral thermoregulation Basking positioning body to optimize solar radiation Body positioning in relation to the sun Flattening the body to increase surface area Change color lighter reflects darker absorbs Hypothalamus is the part of the brain that functions as the thermostat Can control behavior and physiology Optimal temperature for a reptile depends on many factors o Examples Digestion higher temperatures Q10 effect chemical reactions double with each 10 degrees Celsius increase in temperature
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