Sexual selection in amphibians
Prolonged breeders, the majority of frog species, have breeding seasons at regular intervals where male-male competition occurs with males arriving at the waters edge first in large number and producing a wide range of vocalizations, with variations in depth of calls the speed of calls[1] and other complex behaviours to attract mates.
[3] Important aspects of courtship displays include male alert posture, approach and pursuit, the marking of the substrate trail, and tail undulations.
[5] In the aquatic smooth newt (Lissotriton vulgaris), the pheromones are delivered indirectly; the male wafts them towards the female with his tail.
[6] In some species, it has been shown that the size a larger, more elaborate male's tail has played a role in the female's decision to mate.
Female salamanders and newts, most notably Triturus vulgaris, possess sperm-storage glands called spermathecae in the walls of their cloacae.
Mating success has a direct correlation to favorable phenotypic traits such as tail loss, adult body size, and age.
[22] Initially, male frogs produce advertisement calls, considered a pre-mating isolating mechanism because females use them to isolate conspecific males,[23] as cited in[24] which convey information about species, sexual readiness, and size,[24] with females moving towards the call they find most attractive.
[27] as cited by[24] Since anurans are highly sensitive to motion, females use conspicuous movements to communicate interest.
[28] A female frog may also send vocal signals of her own to males, motivating copulation and competitive behaviors.
[29] Female Iberian midwife toads (Alytes cisternasii) use courtship calls to distinguish themselves from other male competitors.
[30] The Emei music frog (Babina daunchina) female calling stimulates male movement towards sound or phonotaxis.
Dendropsophus microcephalus, a small tree frog, will produce 100 notes per minute for several hours, requiring up to 25 times more oxygen.
The Madagascar bright eyed frog (Boophis madagascariensis) is able to produce 28 different types of aggressive calls by modifying pulse rate and notes.
Eavesdroppers will intercept these increased signals and begin to call for the female in a more aggressive manner,[24] which generally leads to escalated conflicts.
[39] It can also inform frogs when the competition has become too intense, where it can reduce or stop calling altogether and move to a different location outside of the chorus.
[42] In Bibron's toadlet (Pseudophryne bibronii), females spread out their eggs across the nests of two to eight males, with those who exhibited higher levels of polyandrous behavior having higher mean offspring survivorship, showing that insurance against nest failure and dispersal of mortality risk is related to the evolution of polyandry.
[49] as cited by[41] However, data suggest that this male mechanism only operates in superfamily Dentrobatoidea,[41] possibly due to alternative mating techniques that reduce selection pressure on body size.
[41] Initial observation of mating in the green poison-dart frog Dendrobates auratus shows convincing evidence of sex-role reversal.
Small female clutch size, female-female competition, and large parental care investment by males are characteristic of sexual role reversal.
Summers[52] weakens the sexual role reversal hypothesis and strengthens the case parental quality selection.
