BIOL170 L7: Anuran Reproduction

External Fertilization

The mode of reproduction in most species of Anura where fertilization occurs outside the female's body.

Internal Fertilization

The mode of reproduction in Ascaphus and Leiopelma, where fertilization occurs inside the female's body.

Two families that exhibit internal fertilization

Ascaphus and Leiopelma

Amplexus

The mating position of frogs and toads, with two main types (inguinal and axillary) and four other variations.

Inguinal Amplexus

The mating position where the male grabs the female around the waist during mating, seen only in archaeobatrachia.

Axillary Amplexus

The mating position where the male grabs the female behind the forelimb (shoulder) during mating, seen in all neobatrachia.

Oviposition Sites

Various locations where frogs lay their eggs, including lakes, ponds, streams, hoof prints, bromeliads, tree holes, leaves, rocks, and under soil or retained on the body.

Foam Nests

Oviposition method seen in Leptodactylidae, Rhacophoridae, and Myobatrachidae, where eggs are deposited in foam nests

*Example of convergent evolution, because these three are all distant families

Bare Clutches

Oviposition method where eggs are deposited in various arrangements in the exposed environment

Bare Clutches of Bufonidae “True Frogs”

Deposit their eggs in strings

Bare Clutches of Alytidae

Male carries their eggs on their lower back/near butt

Bare Clutches of Ranidae + Eleutherodactylidae

Eggs are placed in random clusters

Bare Clutches of Hylidae

Eggs are laid in strings that are wrapped around branches

Bare Clutches of Centrolenidae

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

Family that carry tadpoles on their back (1)

Dendrobatidae

Families that keep eggs on their back (2)

Alytidae + Hemiphractidae

Family that lodges eggs into their back (1)

Pipidae

Parental Guarding

Reproductive strategy seen in Leiopelmatidae, Centrolenidae, and Microhylidae, where male parents guard the eggs or tadpoles.

How Anurans Avoiding Aquatic Predators

Some groups of frogs have removed or reduced the water stage from reproduction to protect their offspring from aquatic predators.

Specific Adaptations to Avoid Aquatic Predators (4)

(1) Carrying egg + tadpoles on their back

(2) Putting eggs + tadpoles in places with few predators (like temporary ponds, bromeliads, hollow nuts)

(3) Delay putting tadpoles into water until they are older

(4) Don’t have tadpoles at all —> direct development

Direct Development

Reproductive strategy where frogs skip the tadpole stage and develop directly from eggs carried inside the female frog

Advantages of Having Tadpoles (3)

(1) Don’t have to be large enough to accommodate an egg yolk to support offspring

(2) Can have more offspring; increases their chances of survival

(3) No need to exhibit as much parental care

Egg Size-Clutch Size Tradeoff

Frogs cannot have lots of very big eggs without radically changing body size (can only have one or other)

# of offspring with tadpoles vs. direct development

Frogs with tadpoles can produce 100s or 1000s of tadpoles

Direct development frogs can only produce a few dozen

Biogeographical Distribution of Direct Development vs. Frogs with Tadpoles

Direct development frogs are usually found in humid areas (near Equator)

Frogs with tadpoles are usually found in arid areas

Oviposition Methods of Hemiphractidae

Eggs are guarded in a pouch on the back

Oviposition Methods of Myobatrachidae

Myobatrachidae rheobatrachus: eggs deposited in the stomach

Myobatrachidae assa: tadpoles are kept in side hip pocket

Oviposition Methods of Rhinodermatidae

Eggs are kept in the throat pouch

Unique Loss of Paternity with Polyandry

The phenomenon where many males mate with a single female frog, often found in species that breed in water bodies.

Reproductive Patterns of Evolution study looked at 3 things…

(1) Evolution of Egg Phase

(2) Evolution of Tadpole’s Source of Nutrition

(3) Protection Method: egg v. larvae v. direct development

Exotrophic Larvae

Tadpoles that obtain their food from external sources.

Endotrophic Larvae

Tadpoles that rely solely on the yolk sac as their source of nutrition.

Most Common Evolved Protection Method

Unprotected eggs + larvae evolving to protected eggs + larvae or protected eggs only

*No species went from protected offspring/direct development to unprotected offspring

Most Common Evolved Nutrition Method

Go from exotrophic tadpoles to endotrophic tadpoles/direct development

Most Common Evolved Egg Phase

Aquatic egg —> Terrestrial eggs —(about 1/2)—> direct development

* No frogs went from direct development —> aquatic/terrestrial eggs