Sexual selection in amphibians involves sexual selection processes in amphibians, including frogs, salamanders and newts. 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 and other complex behaviours to attract mates. The fittest males will have the deepest croaks and the best territories, with females making their mate choices at least partly based on the males depth of croaking. This has led to sexual dimorphism, with females being larger than males in 90% of species, males in 10% and males fighting for groups of females. There is a direct competition between males to win the attention of the females in salamanders and newts, with elaborate courtship displays to keep the females attention long enough to get her interested in choosing him to mate with. Some species store sperm through long breeding seasons, as the extra time may allow for interactions with rival sperm.
Selection in salamanders
Important aspects of courtship displays include male alert posture, approach and pursuit, the marking of the substrate trail, and tail undulations. Once a male has the attention of the female, he may release pheromones, which are used for individual recognition, mate recognition, and mate choice decisions, and generally increase female receptivity towards the male's spermatophore and improve his chances of reproductive success with her. In the red-legged salamander (Plethodon shermani), males directly apply pheromones onto the female's nares. In the aquatic smooth newt (Lissotriton vulgaris), the pheromones are delivered indirectly; the male wafts them towards the female with his tail. 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. In the newt species of the Italian crested newt (Triturus carnifex), males that possessed large mid-dorsal body crests were more favorable to the females looking to mate. Female choice is the final step in the males attempt to reproduce; if the female does not find the male's traits desirable, reproduction will not be successful. As it is in most species, body size is an important and most common desired trait amongst females. Body size is indicative of fitness and/or genetic quality; and because it is easily observable, it can be an indicator for how a female will pick her mate. A larger body size positively correlates to higher paternity; thus larger males are more successful in siring more offspring than smaller males. Male salamanders also prefer larger females because they produce more ova than smaller females. In sexual coercion, a form of male sexual intimidation which includes forced copulations, repeated mating attempts with the same female, and punishing resisting females. males forcibly mate with females; an example is the red-backed salamander (Plethodon cinereus). It has also been proposed as a third form of sexual selection, along with intersexual selection and intrasexual selection, even though prevailing scientific opinion is that sexual coercion is a manifestation of sexual conflict, stemming out of the natural discord between males and females. In some species of salamanders, females that are territorial and aggressive also intimidate males. Plethodon cinereus females aggressively punish males who are exhibiting social polygyny. Males have been shown to punish females that partake in mating polyandry, forcing them into mating monogamously. Populations of salamanders tend to be heavily male-biased, which results in a higher number of males vying for access to the lesser number of females. Males will use different tactics in an effort to keep other males away from the female of interest and ensure their own paternity and reproductive success, such as sexual defense, which is used to steal other males spermatophore, which may have already deposited into the female, and sexual interference, when a male pushes the female away from another courting male, such as sperm capping, whereby a competing male lays his spermatophore directly on top of those previously deposited by another male. Females also participate in sexual interference: a rival female places herself between the courting male and the female he is courting, and attempts to engage the male in their own courtship dance, a tactic for avoiding sperm competition. The male removes the sperm from a female who had mated with a previous male: many species of salamanders will remove the spermatophore from the previous male and insert his own; thus, ensuring his paternity. Sperm storage is a method by which females can control the sperm that fertilizes their eggs. Female salamanders and newts, most notably Triturus vulgaris, possess sperm-storage glands called spermathecae in the walls of their cloacae. Sperm storage has evolved independently to control reproduction in response to the environment. Females have the ability to store multiple spermatophores until they are needed for fertilization. Sperm storage leads to the post-copulatory sexual selection process of cryptic female choice, which occurs when a female removes the deposited sperm or favors one set of spermatophore over another, during or after copulation. Spermatophores are composed of a cap containing the spermatozoa and a gelatinous support arrangement which fastens the spermatophore to a substrate. Spermatophores are very central to reproductive success; therefore, they are handled carefully. Mating success has a direct correlation to favorable phenotypic traits such as tail loss, adult body size, and age.
Vocal signaling in frogs
The vocalizations that male frogs use to call for females are crucial for reproductive success in frogs. Initially, male frogs produce advertisement calls, considered a pre-mating isolating mechanism because females use them to isolate conspecific males, as cited in which convey information about species, sexual readiness, and size, with females moving towards the call they find most attractive. In Hyla versicolor, females favor long calls rather than short calls while in Dendropsophus microcephalus they are attracted to short and high rate calling.
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