Evolution of biparental care in tropical frogs

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The evolution of biparental care in tropical frogs is the evolution of the behaviour of a parental care system in frogs in which both the mother and father raise their offspring.

Contents

Evolution

Many tropical frogs have developed a parental care system where both the mother and father partake in raising their offspring. The evolution of biparental care, which is the joint effort of both parents, is a topic that is still under investigation. Biparentalism arose in some species of tropical frogs as a result of ecological conditions, the differences between the sexes, and their natural tendencies.

Male parental care could have served as the basis for the development of biparental care. Phylogenetic evidence shows that male parental care is the ancestral strategy in Dendrobates . [1] Currently there are Dendrobates species, such as D. ventrimaculatus and D. fantasticus , that exhibit biparental care. [1] The trend of using males to guard or brood eggs for biparental care or paternal care can be understood from the perspective of the female. After oviposition, or when the eggs are laid, the females need to replenish their bodies that have been dedicated to nurturing the eggs before they can mate again. [2] Brooding by the females would delay the opportunity to mate by about two to four weeks. [2] Since this outcome would cause many males to compete for a few females that are able to mate, the males are favored for the brooding. [2]

Environment

The environment can have a substantial impact on the uses of parental care. Not all tropical frogs have the ability to lay their eggs plainly on land or plants. Tropical frogs can choose from a variety of water sources, such as lakes, streams, and small puddles. There is greater risk involved with reproducing in bigger bodies of water because of the higher likelihood of fish and other aquatic predators being there. [3] Instead, frogs can choose to place eggs in phytotelmata. [3] However, there is a trade-off that comes with electing a smaller water source. Not much sunlight reaches these locations, so algae and other food sources cannot grow to feed the inhabitants. [4] Tropical frogs must use alternative methods of feeding their tadpole offspring. In the case of using phytotelmata, it is very difficult for one parent to guard and feed his or her offspring in possibly several different places. Roles performed by both parents provide a great advantage to the offspring. [4] As seen in the Amazon rainforest, the different size of the bodies of water chosen for breeding correlates with the amount of biparental care in two very similar species of the genus Ranitomeya. [3] Ranitomeya imitator favors smaller pools and uses biparental care. [3] Conversely, Ranitomeya variabilis utilizes larger bodies of water for breeding and only males take part in parental care. [3] The ecologic aspects of a species habitat can have significant impacts on the type of parental care exhibited.

Competition

Trophic egg feeding plays a key role in the ability of frogs to breed in smaller bodies of water that lack food sources. [3] Many species of tropical frogs have an inherent nature of cannibalism, such as Dendrobates vanzolinii , that allow their tadpoles to utilize the eggs for nourishment. [4] With a male guarding the eggs, an intermediate step to developing biparental care may have been using the eggs from a mating with another female to feed existing tadpoles. [1] Males could direct where the eggs should be positioned, and then he could move them into the water that holds his tadpole offspring. [1] This polygynous relationship puts a cost on the female because she loses eggs to benefit offspring that are not her own. [1] It is possible that the female could counter this effect by participating in biparental care with her mate. [1] Also, since there may be a lack of males, females could benefit from attacking other clutches that her mate might have fertilized. [5] Eliminating competition of a female's offspring might result in higher survival of those she is trying to protect. Females have been seen eating other females' eggs in captivity by certain species, such as Dendrobates auratus . [5] This intrasexual competition among the females might have been another important driving force for bringing about biparental care. Multiple factors contributed to the evolution of biparental care in some species of tropical frogs.

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Poison dart frog is the common name of a group of frogs in the family Dendrobatidae which are native to tropical Central and South America. These species are diurnal and often have brightly colored bodies. This bright coloration is correlated with the toxicity of the species, making them aposematic. Some species of the family Dendrobatidae exhibit extremely bright coloration along with high toxicity — a feature derived from their diet of ants, mites and termites— while species which eat a much larger variety of prey have cryptic coloration with minimal to no amount of observed toxicity. Many species of this family are threatened due to human infrastructure encroaching on their habitats.

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Ranitomeya variabilis, formerly known as Dendrodates variabilis, is a species of small poison dart frog distributed in northern Peru, along the eastern slope of Andes in the upper Rio Huallaga drainage basin. Its common name, Zimmerman's poison frog, is named after Elke Zimmermann, a German zoologist who described the morph of this species and differentiated it from D. ventrimaculatus. The species was formerly considered to be synonymous with Ranitomeya ventrimaculata.

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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.

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Vertebrate maternal behavior is a form of parental care that is specifically given to young animals by their mother in order to ensure the survival of the young. Parental care is a form of altruism, which means that the behaviors involved often require a sacrifice that could put their own survival at risk. This encompasses behaviors that aid in the evolutionary success of the offspring and parental investment, which is a measure of expenditure exerted by the parent in an attempt to provide evolutionary benefits to the offspring. Therefore, it is a measure of the benefits versus costs of engaging in the parental behaviors. Behaviors commonly exhibited by the maternal parent include feeding, either by lactating or gathering food, grooming young, and keeping the young warm. Another important aspect of parental care is whether the care is provided to the offspring by each parent in a relatively equal manner, or whether it is provided predominantly or entirely by one parent. There are several species that exhibit biparental care, where behaviors and/or investment in the offspring is divided equally amongst the parents. This parenting strategy is common in birds. However, even in species who exhibit biparental care, the maternal role is essential since the females are responsible for the incubation and/or delivery of the young.

References

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  2. 1 2 3 Weygoldt, P. 1987. Evolution of parental care in dart poison frogs. Journal of Zoological Systematics and Evolutionary Research 25(1):51-67.
  3. 1 2 3 4 5 6 Brown, J. L., Morales, V., and Summers, K.. 2010. A Key Ecological Trait Drove the Evolution of Biparental Care and Monogamy in an Amphibian. The American Naturalist 175(4):436-446.
  4. 1 2 3 Caldwell, J. P., and de Oliveira, V.. 1999. Determinants of Biparental Care in the Spotted Poison Frog (Dendrobates vanzolinii). Copeia 1999(3):565-575.
  5. 1 2 Wells, K.D. 1978. Courtship and Parental Behavior in a Panamanian Poison-Arrow Frog (Dendrobates auratus). Herpetologica 34(2):148-155.