Reproduction Meeting the physiological requirements of development oxygen food waste removal calcium Direct / Indirect development Metamorphosis Plasticity of life stage
Q: How might all female (= parthenogenetic) species have originated? Whiptail lizard (Cnemidophorus) uniparens. aromatase testosterone estradiol dihydrotestosterone reductase Wennstrom and Crews 1995
ESD = environmental sex determination (behavior = BSD) Q: How might behavior influence the HPG axis? Godwin et al. 2003 Simultaneous hermaphrodites Hamlet bass, Hypoplectrus
Sequential hermaphroditism based on sex ratios / social encounters = ESD (behavior) Angelfish: Centropyge potteri ovary BSD can override other methods of sex determination African reed frog Hyperolius viridiflavus testis
Evolution of sex-determining mechanisms in tetrapods Mammalia Q: What does the distribution of sex-determining methods in vertebrates suggest about their evolution?
Sex determination in lizards Using phylogeny to reconstruct transitions in sex determination TSD GSD XX XY ZZ ZW Q: What is the take-home message? Q: What are possible sources of error? Pokorna and Kratochvil 2009
Parity modes Oviparity Viviparity Eggs are laid and develop outside the mother; passive interaction with environment Nutritional modes Lecithotrophy Eggs develop inside the mother and young are born live; active interaction with environment Matrotrophy Nutrition from stored yolk (originally from mother) Nutrition from current maternal physiology
LO Q: What parity and nutritional modes are likely ancestral in vertebrates? Meeting the physiological needs of the developing lecithotrophic oviparous vertebrate: oxygen food waste removal calcium Greatest physiological danger?
Different strategies in lecithitrophic oviparity LO Number of eggs laid Amount of yolk in each egg Q: How can reproductive success be enhanced when few eggs are laid?
LO Diverse parental care options in (lecithotrophic oviparous) frogs marsupial frog Surinam toad gastric-brooding frog Rheobactrachus silus 8-week incubation! Inhibition of gastric secretion in Bufo by water from Rheobatrachus tadpoles, Tyler et al. 1983
Amniotic eggs solve the water problem LO membranes yolk sac amnion chorion allantois shell.but introduce others: Q: How are the physiological needs of the developing baby met in amniotic lecithotrophic oviparous vertebrates? oxygen food waste removal calcium
LO Calcium stores mobilized for the developing amniote: hypothetical ancestor bullsnake alligator Q: What evolutionary changes might supply of calcium from the shell rule out?
Q: what increase in egg volume do you predict for a doubling of egg length? LO Q: what physiological problems might occur in species with large eggs as a result of these dimensions? Q: what physiological problems might occur as the baby grows within a single egg? Eggs breathe by diffusion slope = 0.456 Rahn et al. 1979 Q: which egg shell cross section is from the larger egg? Ar et al. 1976
Q: What physiological processes does retention of the baby within the mother s body complicate? LV Osteichthyes Coelacanth Latimeria chalumnae Amphibia Alpine salamander Salamandra atra Chondrichthyes Dogfish shark Squalus acanthias Anatomical adaptations for the evolution of lecithotrophic viviparity
Tomida et al. 2012 LV
Matrotrophic oviparity MO Although the initial growth and development of most multi- cellular animals depends on the provision of yolk, there are many varied contrivances by which animals provide additional or alternative investment in their offspring. Kupfer et al. 2006 monotremes marsupials eutherians spiny echidna Monotremes are mammals with: eggs minimal yolk incubatorium lactation Echidna movie Hughes 1993 Behringer et al. 2006
MO Parental investment by skin-feeding in oviparous matrotrophic caecilian amphibians Kupfer et al. 2006, supplemental movie 1 http://www.nature.com/nature/ journal/v440/n7086/suppinfo/ nature04403.html
Q: How does matrotrophic viviparity differ from matrotrophic oviparity? How are nutrients transferred to the baby? MV Matrotrophic viviparity in anamniotes trophonemata southern stingray oophagy sand tiger shark trophotaenia goodeid teleosts oviducalphagy scolecomorphid caecilians yolk sac placentation Sharpnose shark
Placental (matrotrophic) viviparity in amniotes How are physiological needs met? oxygen food waste calcium MV choriovitelline placenta marsupials chorioallantoic placenta eutherians
MV Placentation has evolved at least 100 times in squamate reptiles.. Placental structure is highly variable..but never in birds or crocodylians Q: Might different methods of storing calcium for the baby explain this pattern?
Eutherian mammals have chorioallantoic placentation MV Marsupial mammals have transient yolk sac placentation
Direct vs. indirect development Q: What are potential selective advantages of metamorphosis?
Gudernatsch experiment, 1912
hypothalamus Metamorphosis in vertebrates is controlled by the HPT axis pituitary gland thyroid gland T 4 - thyroxine T 3 - tri-iodothyronine
Responses to thyroid hormones during amphibian metamorphosis Growth of adult tissues Remodeling Cell death of larval tissues Biochemical respecification Switch from ammoneotelism to ureotelism
Plasticity of life stage in amphibians 1) Loss of the adult body form (sexual maturity occurs in the juvenile body form) Axolotl, Ambystoma mexicanum Mudpuppy, Necturus maculosus Q: how might paedomorphosis have evolved in amphibians? Q: how might metamorphosis be induced in paedomorphic amphibians?
Plasticity of life stage in amphibians + thyroid hormones + thyroid hormones Q: how might you explain the different responses of the two salamanders to the experimental application of thyroid hormones? Safi et al. 2004 Prahlad and Delanney 1965