Blue-sided leaf frog (Agalychnis annae)
Photo Credit: Charles J. Sharp
(CC BY-SA 4.0)
Taxonomic Definition
Agalychnis annae is a nocturnal arboreal anuran belonging to the family Phyllomedusidae and the order Anura. Endemic to Costa Rica, its primary distribution is restricted to the Central Valley and the adjacent slopes of the Cordillera de Talamanca and Cordillera Central, where it inhabits premontane moist forests and, increasingly, anthropogenic environments.
Phylogenetic Branches
Agalychnis annae is currently recognized as a monotypic species with no defined subspecies. Phylogenetic placement is best understood through its closest congeners within the genus Agalychnis:
- Agalychnis callidryas: Widespread throughout Central America, this sister taxon shares the characteristic vertical pupil and reticulated palpebrum but differs in flank coloration (blue vs. yellow/white stripes) and iris color (orange/yellow in A. annae vs. red).
- Agalychnis moreletii: A critically endangered montane specialist found from Mexico to El Salvador. It shares high susceptibility to chytridiomycosis with A. annae and occupies a similar ecological niche in highland cloud forests.
- Agalychnis saltator: Known as the mismatch leaf frog, this species represents a divergent lineage within the genus, characterized by distinct behavioral adaptations in reproduction (gliding) not observed in A. annae.
Genomic & Evolutionary Profile
- Divergence: Molecular phylogenetics suggests the genus Agalychnis underwent significant diversification during the Miocene and Pliocene epochs. Agalychnis annae likely diverged from its common ancestor with A. callidryas and A. moreletii approximately 10 to 15 million years ago, driven by the geological uplift of the Central American isthmus.
- Genetics: Like most members of the subfamily Phyllomedusinae, A. annae possesses a diploid chromosome number of 2n = 26.
- Fossil Record: The neotropical anuran fossil record is fragmentary due to the poor preservation potential of delicate amphibian skeletons in humid rainforest environments. Evolutionary history is primarily reconstructed via molecular clock analysis rather than direct lithographic evidence.
Physiological Mechanisms
- Bioactive Cutaneous Secretions: The granular glands in the dorsal skin produce a complex cocktail of bioactive peptides, including bradykinins and tachykinins, which serve as chemical defenses against predation and microbial infection.
- Scotopic Vision: A. annae exhibits high retinal sensitivity suited for low-light environments. The vertical pupil allows for precise regulation of light intake, protecting the retina during diurnal rest while maximizing photon capture during nocturnal activity.
- Water Conservation: Unlike typical hylids, phyllomedusid frogs secrete lipid-based compounds that they spread over their bodies using wiping motions of the limbs. This reduces cutaneous water loss, an adaptation allowing for tolerance of drier conditions during the dry season or in exposed canopy positions.
- Amplexus and Gamete Deposition: This species utilizes axillary amplexus. Females deposit gelatinous egg masses on vegetation overhanging lentic water bodies; upon hatching, tadpoles drop directly into the water column to complete metamorphosis.
Ecological Relevance
Agalychnis annae functions as an arboreal mesopredator, regulating invertebrate populations (Lepidoptera, Diptera, Orthoptera) within the forest canopy. Simultaneously, it serves as a critical prey item for nocturnal snakes (e.g., Leptodeira spp.) and birds. As an amphibian with permeable skin, it acts as a sensitive bio-indicator of environmental health, particularly regarding water quality and the presence of agrochemicals.
Current Scientific Frontiers
Current research focuses heavily on the "urban refuge" paradox observed in Agalychnis annae populations. While the species has faced extirpation in pristine forests due to the pathogenic fungus Batrachochytrium dendrobatidis (Bd), populations persist in the polluted, fragmented habitats of the Greater San José Metropolitan Area. Investigators are analyzing the cutaneous microbiome and peptide profiles of these urban populations to identify potential mechanisms of resistance or tolerance to Bd that are absent in wild-type populations.
Source/Credit: Scientific Frontline
Metazoa Explorer Category page: Metazoa
Metazoa Explorer Index Page: Alphabetical listing
Reference Number: met021626_01
.jpg)