Squamates

• examples of squamates


  lizard, skink, gecko, ignuanids, lacertids
• viviparity


  give birth to live young, 20% of squamates, covergently evolved 100x
• 3 forms of viviparity in squamates


  lecithotrophic, matrotrophy, placentotropy
• lecithotrophic


  foetus gets all nutrients from yolk when ovulated but embryo retained in utero
• matrotrophy


  minimal nutrient transfer to primarily lecithotrophic embryos (horned lizard, all boas)
• placentrotrophy


  active and passive transfer of nutrients and oxygen from mother to foetus, transfer of waste products from foetus to maternal blood supply (south american skink)
• oviparity


  egg-laying, no trophic interaction between parent and offspring. all nutrients required in egg when ovulated
• costs and benefits of ovi vs vivi


  context dependent and phylogenetically constrained
• cold climate hypothesis (viviparity)


  indirect reference that it is costly due to its association with colder climates yet viviparous squamates (boas and geckos) found in tropics
• costs of viviparity


  costs to female pregnancy, condition while pregnant, increased predation, limited number of clutches per year, reduced female performance, energetic costs
• benefits of viviparity


  female in control of offspring development, internal incubation is faster and more steady development, higher hatching success in offspring, reduced cost of predation on nest, improved neonate survival, temperature regulation
• costs of oviparity


  vulnerable to environmental factors, increased infanticide/decreased neonatal survival, limited range expansion for mother
• benefits of oviparity


  high reproductive output, lower maternal energetic investment, reduced risk of maternal predation