Climbing mantella

Climbing Mantella
Conservation status
Least Concern (IUCN 3.1)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Amphibia
Order:	Anura
Family:	Mantellidae
Genus:	Mantella
Species:	M. laevigata
Binomial name
Mantella laevigata Methuen & Hewitt, 1913

The Climbing Mantella (Mantella laevigata) is a species of diurnal poison frog of the genus Mantella that resides in the subtropical regions of northeast Madagascar. Although it spends a significant amount of time in trees or bamboo forests, this frog species is not fully terrestrial and actively seeks areas with a water source.

Like others in the Mantella genus, the Climbing Mantella has aposematically colored skin, which warns predators of its toxic composition. The lipophilic alkaloids, the building blocks of the poison, are derived from dietary arthropods. The Climbing Mantella consumes a variety of small insects, and its diet profile changes dramatically with changing seasons.

The Climbing Mantella engages in unique reproductive behaviors that revolve around arboreal oviposition sites. Males compete with one another over the shallow pools of water where females lay their eggs. Behavioral ecologists are particularly interested in Climbing Mantella’s high degree of parental care.

Description

Considered a small frog, an adult Climbing Mantella measures from 24–30 millimeters and weighs 1.2–2.0 grams. Like other poison frogs, the Climbing Mantella is brightly colored. The anterior portion of its back is bright yellow or pale green. The arms, legs, abdomen, and posterior are black. Its eyes are completely black without any light-colored pigmentation. There are visible blue spots on the arms and legs. Like other frogs, the Climbing Mantella has discs at the tip of its fingers and toes. It also possesses webbed hands and feet. The males are slightly smaller than the females, but it is difficult to identify the frog's sex using physical characteristics. Males are best recognized by their mating calls.

Some other species that resemble this frog are M. betsileo, M. viridis, and M. expectata; however, these frogs are differently colored and often have blue spots on their throats rather than limbs. Unlike the Climbing Mantella, these species have a faint line running along their upper lip.

Habitat and distribution

The Climbing Mantella is found in the northeast coastal region of Madagascar in the lowland rainforests and bamboo groves. This species can be found in several protected areas of Madagascar including,Mananara-Nord National Park, Marojejy National Park, Masoala National Park, Nosy Mangabe Special Reserve, and Betampona Natural Reserve. The favorable humidity level is 80% to 100%. Climbing Mantella can withstand a 17-30 ℃ temperature range, which is relatively large compared to other amphibian species. However, the most suitable temperature level is 20 to 26 ℃.

Conservation

The International Union lists the Climbing Mantella for Conservation of Nature Red List of Threatened Species (IUCN Red List) as Least Concerned in 2016 due to its wide geographical distribution and presumed large population. The IUCN Red List previously listed it as Near Threatened in 2004 and 2008. Other members of the Mantella genus, including M. aurantiaca and M. expectata, have been listed as Endangered or Critically Endangered.

Despite being listed as Least Concerned, the Climbing Mantella population is suspected to be decreasing. Regions of Madagascar outside of protected reserves are at increased risk of deforestation. Greater demand for cattle grazing areas, farmland, and space to build cities may jeopardize the Climbing Mantella’s natural habitat. Currently, the international pet trade levels for this frog species do not present a serious threat to the population. Continued trade regulation of trade is necessary to maintain the local population of Climbing Mantella.

Taxonomy

M. Laevigata belongs to the family of Mantellidae and the genus Mantella. The Mantellidae family is a group of frogs that lives specifically endemically to the islands of Madagascar and Mayotte. Its closest relative is likely to be M. Viridis.

Diet

The Climbing Mantella eats ants, insect larvae, mites, and other insects. Unlike similar frogs from the family Dendrobatidae, the Climbing Mantella is not an ant specialist – its food consumption volume and diet composition vary dramatically based on seasonality. The Climbing Mantella does not prefer a specific type of prey and consumes whatever is readily available in leaf litter.

During the dry season, the Climbing Mantella consumes approximately 44% more in absolute volume compared to the wet season. Ants comprised about 84% of the frog’s diet during the dry season but only 35% during the wet season. Over half of all consumed ants were from the species Pheidole. Thus, although the Climbing Mantella does not specialize in hunting ants, it appears to have a preference to consume one species of ants. Overall, frogs have a more varied diet during the wet season. Wet-season frogs consume significantly more insect larvae, mites, and other insects (including spiders and small beetles) compared to dry season counterparts. The diet changes may arise from different prey availability during seasons rather than specific behavioral changes.

Climbing Mantella tadpoles will consume unfertilized or fertilized eggs of their own species. Tadpoles are only known to consume conspecific eggs, so they do not engage in the cannibalism of other tadpoles and ignore mosquitoes or other small arthropod larvae.

Mating

Group of Climbing Mantella in a bamboo stalk well.

Male-to-Male Competitions

Males compete with one another for territory. Fighting bouts over territory take the form of wrestling, chasing, and leaping. These conflicts last anywhere from 10 seconds to over 1.5 hours. The resident male, usually the aggressor, typically wins the fight. When not in their own territory, male frogs will infrequently invade the territory of other males, hoping to mate with more females. On rare occasions, the intruder can convince females to mate in a well that he does not claim possession. If the territory resident discovers the intruder, the intruder can either initiate a fighting bout or submissively yield to amplexus. The resident males will not attempt to mate with an unresponsive frog, and the resident will leave the submitted invader after a couple of minutes.

Female-to-Male Interactions

Although it is the only semi-arboreal member of the Mantella genus, the forest environment plays an important role in the Climbing Mantella’s reproductive behavior. Males are highly territorial, claiming a given area of approximately 2 square meters. Each territory contains at least one water-filled well (often found in tree holes or broken bamboo stalks), and the male frogs defend these possible oviposition sites from their rivals. Male Climbing Mantellas choose their wells based on the presence of crane flies, which prey on the eggs, and other frog species. A greater amount of crane flies and other frog species correlates to a less desirable well.

Female frogs will approach male frogs who advertise their territory with a two-tone call made by males. Female frogs are either mute or have weak calls. Upon hearing the mating calls, the female frogs will approach the well occupied by males. The male frog adopts a softer single-note courtship call, and the female frog proceeds to judge the well. The mating calls only attract the female frogs to the male’s territory, and it has no bearing on mate selection. Instead, mate selection from the perspective of the female is entirely based on the quality of the male’s well. Female frogs frequently abandon a male frog after inspecting the location. Thus, well sites are a limiting resource. The most desirable well sites often have eggs from multiple different mating pairs. The Climbing Mantella is the only member of the Mantella genus to engage in phytotelm-breeding.

Parental care

Egg-laying

The Climbing Mantella has the minimum possible clutch size (usually one) and large egg size (3.0-3.5 mm), which are positively correlated with a parental investment in amphibians. Female frogs also lay their eggs at the side of wells or above the water line, exhibiting a form of terrestrial oviposition – another indicator of high parental investment. The Climbing Mantella is the only member of the Mantella genus where parent frogs care for oophagous tadpoles.

Site selection for egg laying

Female Climbing Mantellas engage in trophic egg laying and care for their young by feeding them their unfertilized eggs. When engaging in maternal care, female frogs ignore male mating calls and climb wells alone, depositing their unfertilized eggs at or below the water line in the well. The tadpole that resides in the well will then consume the trophic eggs. It is believed that maternal care is not obligatory, depending more on circumstance and environment than natural behavior.

Territory defense as paternal care

Male territory defense is also considered a form of paternal care. The presence of a male Climbing Mantella dissuades other species of frogs (ex. P. notostica and A. boulengeri) from laying their eggs into the well an individual male has claimed. It is also possible that male frogs discourage land crabs, which have been observed from eating Climbing Mantella eggs, from entering wells. Males also engage in parental care considered to be reproductive parasitism. If a male possesses a desirable well containing one of his offspring, he will always benefit. A male’s reproductive success increases because amplexus either produces another one of his offspring or results in the creation of a new egg that will feed his existing offspring. Thus, males will often take females to wells that already contain their developing eggs or tadpoles. Male frogs actively use some of their offspring as a parental investment to feed their other offspring.

Reproductive parasitism

Both male and female frogs contribute to the tadpole’s sole diet of conspecific eggs. Female frogs will lay unfertilized eggs into wells that contain their offspring. Male frogs exhibit a form of reproductive parasitism by luring female frogs to wells that often contain offspring only belonging to the male. Any fertilized egg resulting from the courtship subsequently serves as food for tadpoles that are only related to the male. Female frogs develop mechanisms to defend themselves against parasitism and avoid laying their eggs in wells containing other tadpoles. In response, tadpoles evolve ways to evade detection by females.

Defense

The evolution of chemical defense in the Climbing Mantella is an exceptional example of convergent evolution. The Dendrobatidae family and Mantella genus developed similar behavioral and physiological adaptations despite sharing their last common ancestor approximately 150 million years ago.

Poisonous lipophilic alkaloids stored in skin glands is the effective defensive chemicals. 41 different potent alkaloids have been found in Climbing Mantella’s skin. Captive frogs lose their toxicity over time, indicating that the Climbing Mantella’s wild diet contains the building blocks needed to construct the alkaloids. Alkaloids are retained in frogs for long periods, and thus the link between seasonality and alkaloid composition is still unclear. While some researchers have found that seasonality plays a significant role in the absence or presence of alkaloids, other studies show that this did not lead to dramatic changes in the Climbing Mantella’s overall alkaloid profile.