BIOL170 L7: Anuran Reproduction

Reproductive Diversity in Anura

  • Modes of Reproduction (2)

    • External Fertilization: most species

    • Internal Fertilization: only Ascaphus and Leiopelma

      • Leiopelma put their cloaca together to fertilize inside the female

  • Amplexus (2 main + 4 others) [**Amplexus: the mating position of frogs and toads]

    • Inguinal amplexus: male grabs female around the waist when mating

      • Seen only in archaeobatrachia

    • Axillary amplexus: male grabs female behind forelimb (shoulder) when mating

      • Seen in all neobatrachia

    • Other 4 (don’t think you need to memorize)

      • Straddle (male over female head)

        • Effective because male has hormones that he wants the female to smell

      • Glued (small male adhered to larger female)

      • Cloacal apposition (butts towards each other)

      • Cephalic (grabs the head)

  • Oviposition Sites: lakes, ponds, streams, hoof prints, bromeliads (type of plant), tree holes, leaves, rocks, under soil or retained on the body

  • Oviposition Methods

    • Foam Nests: seen in Leptodactylidae, Rhacophoridae, Myobatrachidae

      • Example of convergent evolution, because these are all distant families

    • Bare Clutches (6)

      • Bufonidae “True Frogs”: eggs are deposited in strings

      • Alytidae (archaeobatrachian): male carries the egg on its lower back/near butt

      • Ranidae + Eleutherodactylidae: random clusters

      • Hylidae: strings that are wrapped around branches

      • Centrolenidae: eggs are laid on leaves above water; so that when tadpoles eventually pop out, they fall into the water below

    • Carry tadpoles on back: seen in Dendrobatidae

    • Keep eggs on back: seen in Alytidae and Hemiphractidae

    • Lodge eggs in back: seen in Pipidae

  • Parental Guarding: seen in Leiopelmatidae, Centrolenidae, and Microhylidae

  • Uncommon Strategies

    • Hemiphractidae: eggs are guarded in a pouch on back

    • Myobatrachidae

      • Rheobatrachus: eggs deposited in the stomach

      • Assa: tadpoles are kept in side hip pocket

    • Rhinodermatidae: eggs are kept in the throat pouch

Reproductive Strategies

  • Avoiding Aquatic Predators

    • Why some groups of frogs have (partially) removed the water stage from reproduction

      • Tadpoles have a high mortality rate, especially against fish

      • Tadpoles can escape dragonflies because they can detach their tails once caught

    • Specific Adaptations

      • Carrying eggs and/or tadpoles on back

      • Putting eggs and tadpoles in places with few predators

        • e.g. Temporary ponds, bromeliads (type of plant), hollow nuts

      • Delay putting tadpoles into water until they are older

      • Don’t have tadpoles at all —> direct development

  • Advantages of Having Tadpoles [ **Evolutionary Trade-Off: egg size + egg number]

    • Direct developing frogs…

      1. Must be large enough to accommodate a sizable egg yolk

        • All energy for a developing frog must come from an egg yolk (no additional energy input from environment or mother)

      2. Can only have a few offspring (because of energy needed to invest in offspring)3

      3. Are more likely to exhibit parental care

    • **Egg size-clutch size tradeoff: cannot have lots of very big eggs without radically changing body size (can only have one or other)

      • Frogs with tadpoles can produce 100s or 1000s of eggs per clutch

        • But less chance of survival because of aquatic predators + risk of ponds drying

      • Direct developing frogs can only produce a few dozen eggs

    • **Costs and benefits of (aquatic vs. terrestrial development) or (direct development vs. tadpoles) differ depending on environment

      • Direct development frogs are usually found in humid areas

      • Frogs with tadpoles are usually found in arid areas

  • Unique Loss of Paternity with Polyandry

    • Many males mate with a single female frog

    • Often found in species that breed in water bodies

    • Terrestrial species tend to have hidden amplexus (?)

      • Hidden in the nest

      • pg. 31

Reproductive Patterns of Evolution Study (3)

  • Egg Phase

    • Most common path: aquatic egg —> terrestrial eggs —(about 1/2)—> direct development

    • 0 species went from direct development —> aquatic / terrestrial eggs

  • Tadpole’s Source of Nutrition

    • Exotrophic larvae: food source comes from outside

    • Endotrophic larvae: only food source is the yolk sac

    • Most common path: exotrophic —> endotrophic / direct development

    • 0 species went from endotrophic —> direct development

    • Almost no species went from endotrophic / direct development —> exotrophic

  • Protection Method: egg v. larvae v. direct development

    • Most common path: unprotected eggs + larvae —> protected eggs + larvae / protected eggs only

    • No species went from protected eggs + larvae / direct development —> unprotected eggs