Edalorhina perezi

Perez’s snouted frog, Edalorhina perezi, is in the genus Edalorhina and family Leptodactylidae. The only two species in this genus are E. perezi and E. nasuta. Previous studies addressing phylogeny have mostly focusing on morphological, behavioral and karyotypical differences. An earlier morphological and behavioral study considered Edalorhina to be most closely related to the families Lithodytes and Physalaemus as all of them construct foam nests.[5] In a later cytogenetics study, the analysis of all 22 chromosomes of this frog also suggested the close relationship between Edalorhina and Physalaemus, while Pleurodema is relatively less related to Edalorhina.[8] However, the precise phylogenetic relationships of Edalorhina are still under a debate.[8][5][9]

Studies have shown that there are large variations in Perez’s snouted frog’s morphology.[2][5] An early study conducted by Dunn in 1949 examined 52 specimens and revealed dissimilarity in vomerine teeth and dorsal skin structure.[5] The study classified this species into three morphs: perezi, plicifrons and buckleyi. The Perezi type has a dermal ridge between the eyes and vomerine teeth, but it lacks longitudinal warts on the back. Plicifrons, on the other hand, has longitudinal warts, but lacks vomerine teeth and dermal ridge. Buckleyi looks similar to Plicifrons, but it has vomerine teeth. Dunn also noticed that certain appearances are more common in distinct areas of the species' range. For example, 86.6% of the specimens from Ecuador are perezi type, while in the Peruvian specimens this type only accounts for 62.5%. There are also other obvious geographical differences, such as absence of vomerine teeth and the development of a wart on the snout tip.[4] A later study in 1990 by Duellman dug deeper into this topic by looking into dorsal skin structure and ventral color pattern. The dorsal patterns were classified into five categories based on smoothness, and each geographical area was dominated by populations of a specific type of pattern. The ventral color was also classified into five groups based on the pattern of black and white patches. The range of each group is highly correlated with the distribution of river systems, which include Rio Purus, Rio Madre de Dios, Rio Ucayali, and Rio Tapiche. One explanation for why populations of Perez’s snout frog differ so much from each other is historical climatic-ecological changes. During Pleistocene, the rivers coming down from Andes carried a greater volume of melting galcier water than today, thus isolating the frogs into different basins and causing these populations to evolve independently. The present-day pattern categories also correspond to geographical segregation in history.[2]

Perez’s snouted frog is commonly found in the upper Amazon Basin in Ecuador and Peru. Its sister species E. nasuta has a much smaller range and is only found in Peru. Some populations of E. perezi are also documented in southern Colombia and Brazil. They range from basins that are only 200m in elevation to 1100m on the eastern slopes of the Andes Mountains. They are a diurnal and terrestrial frog species. Typical habitats are forest floors covered with leaf litter in lowland tropical rainforests.[2] They are well adapted to both primary and secondary forests.[5]

Perez's snouted frog is a "sit-and-wait" predator that relies on its cryptic coloration to hide from prey.[10] This allows the frog to prey on mobile arthropods such as cockroaches, spiders, and crickets in the leaf litter. It is thought E. perezi only feeds a few times per day.

Tadpoles primarily feed on detritus in the bottom of the pools where they hatch, although there have been reports of tadpoles cannibalizing eggs and other larvae.[11]

Perez’s snouted frogs breed opportunistically, usually right after a storm. During amplexus, females usually carry males to the edge of the pool, where they build foam nests together. Water is important for nest making so females always drink water before amplexus. The female is attracted by male's advertisement call and moves towards the calling male. During mating season, the frog is equally active during the day and night. Amplexus can last as long as six days, but the actual mating only takes place for four to six hours. The female first releases a signal for foam nest construction by arching its back. Then, the male immediately puts its feet near the female’s cloacal region and forms a collecting basket, where fertilization occurs. After this, the male raises its legs to water level and starts to beat the female’s foam secretion with the purpose of smoothing the surface. The beating lasts about 10–12 seconds with about 45 beats. After 45 seconds the female does the back-arching signal again, and the whole set of movements repeat. The construction of a foam nest usually takes 30 to 60 minutes.[7]

Female Perez’s snouted frogs breed every four weeks under laboratory conditions.[12][13] Females lay 30-154 small unpigmented eggs, 2.1 mm in diameter, in a foam nest about 60mm.[2] The foam nest protects eggs and early tadpoles. In ideal conditions foam can protect tadpoles in dry pools for up to 13 days, with 50% survival up to 10 days. However, to complete larval development, at least two weeks in water is needed. Thus, in a neotropical forest with stable temperature but seasonal rainfall, the uncertainty of precipitation has a strong influence on the frog’s reproductive success.[12]

Perez’s snouted frog prefer treefall pools (holes at the roots of large fallen trees), either temporal or permanent, to lay their eggs. These kind of treefall holes are a common nesting site for many other tree frogs and poison-dart frogs. A three-year study done by Murphy demonstrated the risk-sensitive oviposition strategy of Perez’s snouted frogs.[12] The three major risks for Perez’s snouted frog offspring are desiccation, insect predation, and intraspecific competition. For the two external risks, desiccation and predation, there is always a trade-off because predation risk is lower in temporal pools, but the temporary pools can potentially be completely dry. A mark-recapture experiment proved that adults actively select pools that benefit their offspring most based on these three factors. Their decisions are very flexible as they vary across both temporal and spatial scales, instead of being fixed and passively triggered by seasonal changes. In the early rainy season, females normally choose persistent pools, but they switch to ephemeral pools later in the season. This trend is reflected both by change in nest placement and tadpole density in each type of pool across time. The reasoning behind this phenomenon is that rainfall in the transitional period is highly uncertain, so persistent pools provide more stable environment. Later in the season, rainfall becomes more consistent and persistent pools build up insect predators and higher densities of tadpoles, which makes temporal pools relatively better with a lower predation risk and less intense food competition. Female egg-laying position choice is not affected by male calling sites. After mating, females can carry the male to her favorite egg-laying site.[12][13]

Tadpoles start to develop cryptic brown colorations three weeks after hatching, which persist through adulthoods.[7] An interesting predator defense display of the Perez’s snouted frog is deimatic behavior using their macroglands. Macroglands are also called inguinal or lumbar glands, which are accumulations of serous glands in the sacral region. Although not all species in the family Leiuperinae have this structure, it is commonly found in the Leiperines, Edalorhina, Engystomops, Physalaemus, and Pleurodema families. When a Perez’s snouted frog is frightened, it will face away from the predator and elevate its sacral region to suddenly expose macroglands, which display hidden flash coloration resembling a pair of huge eyes belonging to a large animal.[9]