Femoral gland
The femoral gland is a specialised
Femoral glands in certain frogs, particularly in the subfamily
Characteristics
Femoral glands can be identified by their swollen appearance and distinct colouration, which typically differ from the surrounding skin. In the family Mantellidae, four structural types of femoral glands have been documented, ranging from tiny granules to well-defined patches with large granules and central depressions:[2]
- Type 1: A patch of densely packed small granules without defined edges, specific to Guibemantis species, with G. liber having more distinct edges. Towards the edges of the gland patch they are increasingly arranged in small rosette-like groups—with five to seven granules surrounding one central granule.
- Type 2: A single group of moderate-sized granules forming an .
- Type 3: A prominent, rounded structure with a central depression surrounded by large granules and a secondary group of smaller granules, reduced in M. brevipalmatus, occurring in the genus Brygoomantis and subgenera Ochthomantis, Hylobatrachus, and Chonomantis.
- Type 4: Similar to type 3 but lacking the secondary group of granules, seen in the genus Mantidactylus.
In addition to their prevalence in the family Mantellidae, femoral glands are also found in some species in several frog genera:
Function and evolution
Femoral glands in mantelline frogs are used by males for secreting chemical compounds important in territory marking and attracting mates.[4] Some of these chemicals display double bond isomerism, meaning the molecules, while similar in composition, differ in the arrangement of their double bonds. This difference in structure, as seen in molecules like the gephyromantolide A (a macrocyclic lactone) from Gephyromantis boulengeri compared to its counterpart in Hyperolius cinnamomeoventris, results in distinct chemical signals for each species. This specificity in chemical messaging aids in mating and species recognition, reducing mating between different species by using different isomers. This kind of molecular specificity, while not exclusive to amphibians, is less common in the animal kingdom and has been predominantly observed in insects. It helps ensure accurate mate identification during courtship.[5]
The emergence of femoral glands in amphibians is attributed to
Reproductive significance
During mating, the femoral glands' placement on the male's ventral surface of the thigh suggests that they may contact the female's dorsal skin, implicating the glands in reproductive signalling.
The role of femoral glands in facilitating
Biochemical diversity
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Research has uncovered a vast diversity of volatile compounds that are produced in the femoral glands across many species within the subfamily Mantellinae, indicating a complex chemical communication system not directly correlated with gland size or prominence.[4] For instance, in the Madagascar-native frog Mantidactylus betsileanus, macrolide compounds produced by the femoral glands stimulate female attraction and generally heighten activity in both genders.[10][11] A suspected pheromone from M. betsileanus, the macrolide phoracantholide J, has the ability to activate specific smell-sensitive sensory neurons in the olfactory region of the brain. Meanwhile, it appears not to affect the secondary smelling system, known as the vomeronasal organ. This separation of functions is a specialised trait that has developed alongside the presence of femoral glands in mantellid frogs.[12]
History and taxonomic utility
In 1909,
The distinct count of granules in the femoral gland serves as a key feature to distinguish species within the subgenus Laurentomantis. Gephyromantis marokoroko, for example, is easily identified by its eight prominent granules in each femoral gland, setting it apart from other species in the subgenus.[14] In contrast, a 2011 taxonomic review of the genus Nyctibatrachus determined the presence of male femoral glands to be an unreliable characteristic for diagnosis due to their inconsistent seasonal prominence.[15]
References
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- S2CID 44069685.
- ^ .
- ^ .
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- ^ .
- ^ a b Glaw, F.; Vences, M. (2011). "Description of a new frog species of Gephyromantis (subgenus Laurentomantis) with tibial glands from Madagascar (Amphibia, Mantellidae)" (PDF). Spixiana. 34 (1): 121–127.
- ^ a b Blommers-Schlösser, R.M.A. (1979). "Biosystematics of the Malagasy frogs. I. Mantellinae (Ranidae)" (PDF). Beaufortia. 352: 1–77.
- ^ a b Krishnamurthy, S.V.; Katre, Shakuntala; Reddy, S. Ravichandra (1992). "Structure of femoral gland and habitat features of an endemic anuran, Nyctibatrachus major (Boulenger)". Journal of the Indian Institute of Science. 72: 385–393.
- PMID 22266641.
- PMID 24004086.
- PMID 27084295.
- ^ Mocquard, François (1909). "Synopsis des families, genres et espèces de Reptiles ecailleux et des Batraciens de Madagascar" [Synopsis of the families, genera, and species of scaly Reptiles and Amphibians of Madagascar]. Nouvelles archives du Muséum d'histoire naturelle (in French). 5: 1–106.
- .
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