Femoral gland

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Femoral glands are prominent here on the ventral side of the hindlimbs of Mantidactylus grandidieri. Mantidactylus grandidieri.jpg
Femoral glands are prominent here on the ventral side of the hindlimbs of Mantidactylus grandidieri .

The femoral gland is a specialised gland found in some male frogs that plays a role in chemical communication and reproductive signalling. Particularly prominent within the frog family Mantellidae, these glands are located on the underside of the hindlimbs, usually on the inner thighs or shanks. Femoral glands can be identified by their swollen appearance and distinct colouration, which differ from the surrounding skin. Femoral glands are classified into four distinct morphological types, varying from minute granular structures to conspicuous patches characterised by large granules and prominent central indentations.

Contents

Femoral glands in certain frogs, particularly in the subfamily Mantellinae, are implicated in reproductive signalling and species recognition, affecting behaviours like oviposition. These glands, which develop early in species like Nyctibatrachus major , are subject to hormonal and environmental influences. Unlike the amplexus (sexual clasp) observed in other anuran frogs, Mantellinae males employ these glands in a unique, loose mating clasp. The volatile organic compounds secreted by the glands serve a chemical communication role that influences mating behaviour. Research indicates that compounds from femoral glands in mantellid frogs can specifically activate olfactory neurons, responsible for detecting and transmitting odour signals to the brain. Structural variations in the femoral glands assist in the taxonomic differentiation of some frog species and genera.

Characteristics

Mantidactylus salegy01.jpg
Mantidactylus webbi04.jpg
Gephyromantis salegy (top) and Gephyromantis webbi have "Type 2" femoral glands, which are typical of most other Gephyromantis species. [1]

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]

In addition to their prevalence in the family Mantellidae, femoral glands are also found in some species in several frog genera: Indirana (family Ranixalidae), Nyctibatrachus (Nyctibatrachidae), Petropedetes (Petropedetidae), and Phrynobatrachus (Phrynobatrachidae). [3]

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 convergent evolution, with their independent appearance across different clades of ranoid frogs likely due to the expansion and specialization of granular glands in the skin of the ventral shank. [6] The Dutch herpetologist Blommers-Schlösser regarded these glands as an ancestral trait within the Mantellidae, supporting a phylogenetic standpoint that views the family as a descendant of the early rhacophorid lineage. [3]

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. [7] Gland secretions may influence female behaviour, potentially stimulating oviposition and aiding intra-species recognition. [8] The variation of the femoral glands in the species Nyctibatrachus major may reflect hormonal regulation akin to thumb pad elaboration, a common secondary sex characteristic in male frogs. The size and function of femoral glands in N. major show seasonality and a correlation with reproductive activity, paralleling the strict seasonal changes in the Western Ghats environment. The presence of femoral glands in males of this species with small snout–vent lengths indicates that the development of these glands begins at a relatively early stage. [9]

The role of femoral glands in facilitating amplexus (the mating clasp) among hill-stream anurans such as N. major has been proposed. [9] While these glands do not seem to be involved in the typical amplexus seen in Ranidae and Rhacophoridae, they are related to a more relaxed form of mating embrace. In this unique mating behaviour, observed solely in Mantellinae, males may drape their thighs over the female's head and shoulders if arboreal, or clasp the female briefly and loosely around the waist if terrestrial, with the mating grasp lasting only from a few seconds to minutes. [3]

Biochemical diversity

Blommersia nataliae (10.3897-zookeys.994.57012) Figure 2.jpg
Blommersia transmarina (10.3897-zookeys.994.57012) Figure 3.jpg
Dorsolateral (top) and ventral (botton) views of Blommersia nataliae (left), and the closely related B. transmarina (right). The colour and shape of the femoral glands help to distinguish these species.

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, [13] the French herpetologist François Mocquard in 1909 first proposed using the presence and structure of the femoral gland as a taxonomic character in distinguishing species in genus Mantidactylus. [8] This character has since been recognised for its utility as a trait in classifying amphibian species, [6] and modern species descriptions often give morphometric parameters such as FGL (femoral gland length), FGW (femoral gland width), FGD (distance between femoral glands on opposite thighs). [7]

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]

Related Research Articles

<span class="mw-page-title-main">Mantellidae</span> Family of amphibians

The Mantellidae are a family of the order Anura. These frogs are endemic to the islands of Madagascar and Mayotte.

<span class="mw-page-title-main">Mantellinae</span> Subfamily of amphibians

Mantellinae is a subfamily of frogs in the family Mantellidae. These frogs are native to Madagascar and Mayotte. The species vary in size from under 25 mm to over 100 mm. The subfamily is most famous for the genus Mantella, which contains species that superficially resemble poison dart frogs of the tropical Americas, and have converged on similar aposematic colouration and toxins. As of 2 May 2016, there are 128 described species in this subfamily, but several more are described each year.

<i>Mantidactylus</i> Genus of amphibians

Mantidactylus is a frog genus in the mantellid subfamily Mantellinae. This genus is restricted to Madagascar. The genus is divided into several subgenera that form monophyletic genetic clusters and are ecologically similar.

<i>Aglyptodactylus</i> Genus of amphibians

Aglyptodactylus is a genus of frogs in the family Mantellidae. These frogs, sometimes known as the Madagascar jumping frogs, are endemic to Madagascar. Systematic revisions of the groups were published in 1998 and 2015. Six species are currently recognized.

<i>Boophis</i> Genus of amphibians

Boophis is the only genus in the mantellid frog subfamily Boophinae. They are commonly known as bright-eyed or skeleton frogs. They show typical 'tree frog' traits, and are a good example of convergent evolution with morphologically similar species in the families Hylidae and Rhacophoridae, among others. This genus can only be found on Madagascar and Mayotte Island (Comoros).

<i>Spinomantis aglavei</i> Species of frog

Spinomantis aglavei is a species of frog in the mantellid subfamily Mantellinae, endemic to Madagascar.

<i>Mantidactylus albofrenatus</i> Species of frog

Mantidactylus albofrenatus is a species of frog in the family Mantellidae. It is endemic to eastern Madagascar near An'Ala and Andasibe. Common name eastern Madagascar frog has been proposed for it.

<i>Guibemantis albolineatus</i> Species of frog

Guibemantis albolineatus, also known as the white-lined Madagascar frog, is a species of frog in the family Mantellidae. It is endemic to Madagascar. It is known from the southeastern part of the island. However, there is some confusion between this species and Guibemantis bicalcaratus, as well as possibly undescribed species, making its actual distribution unclear.

Wakea madinika is a species of frogs in the mantellid subfamily Mantellinae. It is the only species in the monotypic genus Wakea. It is endemic to Madagascar.

<i>Boehmantis</i> Genus of amphibians

Boehmantis is a genus of frogs in the mantellid subfamily Mantellinae. It is monotypic, being represented by a single species, Boehmantis microtympanum. The genus is endemic to Madagascar.

<i>Spinomantis peraccae</i> Species of frog

Spinomantis peraccae is a species of frog in the mantellid subfamily Mantellinae. It is endemic to Madagascar and widely distributed in the northern, eastern, and central parts of the island. The specific epithet honours Italian herpetologist Mario Giacinto Peracca. Common name Peracca's Madagascar frog has been coined for it.

<i>Gephyromantis tschenki</i> Species of amphibian

Gephyromantis tschenki, commonly known as Tschenk's Madagascar frog, is a species of frogs in the family Mantellidae. It is endemic to Madagascar. Its natural habitats are subtropical or tropical moist lowland forests, subtropical or tropical moist montane forests, and rivers. It is threatened by habitat loss.

<i>Gephyromantis</i> Genus of amphibians

Gephyromantis is a frog genus in the mantellid subfamily Mantellinae. This genus is restricted to Madagascar. At present it contains 45 species divided into six subgenera.

<i>Spinomantis</i> Genus of amphibians

Spinomantis is a frog genus in the mantellid subfamily Mantellinae. This genus is restricted to Madagascar. At present it contains 13 species. They are arboreal or terrestrial frogs and occur in or along small streams. Most species are nocturnal.

<i>Guibemantis</i> Genus of amphibians

Guibemantis is a frog genus in the mantellid subfamily Mantellinae. This genus is restricted to Madagascar. At present it contains 16 species divided into two subgenera.

Tsingymantis is a monotypic genus of frogs in the family Mantellidae. The sole species is Tsingymantis antitra.

<i>Spinomantis bertini</i> Species of frog

Spinomantis bertini is a species of frog in the mantellid subfamily Mantellinae, endemic to Madagascar.

<i>Spinomantis fimbriatus</i> Species of frog

Spinomantis fimbriatus is a species of frog in the Mantellid subfamily Mantellinae, endemic to Madagascar.

<i>Spinomantis massi</i> Species of frog

Spinomantis massi is a species of frog in the mantellid subfamily Mantellinae. It is endemic to the humid forests of northwestern Madagascar.

<i>Spinomantis guibei</i> Species of frog

Spinomantis guibei is a species of frog in the Mantellid subfamily Mantellinae, endemic to Madagascar.

References

  1. ↑ Scherz, Mark D.; Hawlitschek, Oliver; Razafindraibe, Jary H.; Megson, Steven; Ratsoavina, FanomezanaMihaja; Rakotoarison, Andolalao; Bletz, Molly C.; Glaw, Frank; Vences, Miguel (2018). "A distinctive new frog species (Anura, Mantellidae) supports the biogeographic linkage of two montane rainforest massifs in northern Madagascar". Zoosystematics and Evolution. 94 (2): 247–261. doi: 10.3897/zse.94.21037 .
  2. ↑ Glaw, Frank; Vences, Miguel; Gossmann, Viola (2000). "A new species of Mantidactylus (subgenus Guibemantis) from Madagascar, with a comparative survey of internal femoral gland structure in the genus (Amphibia: Ranidae: Mantellinae)". Journal of Natural History. 34 (7): 1135–1154. doi:10.1080/00222930050020140. S2CID   44069685.
  3. 1 2 3 Blommers-Schlösser, Rose M.A. (1993). "Systematic relationships of the Mantellinae Laurent 1946 (Anura Ranoidea)". Ethology Ecology & Evolution. 5 (2): 199–218. doi:10.1080/08927014.1993.9523105.
  4. 1 2 Nowack, C.; Peram, P.S.; Wenzel, S.; Rakotoarison, A.; Glaw, F.; Poth, D.; Schulz, S.; Vences, M. (2017). "Volatile compound secretion coincides with modifications of the olfactory organ in mantellid frogs". Journal of Zoology. 303 (1): 72–81. doi:10.1111/jzo.12467.
  5. ↑ Kuhn, Johanna; Schulz, Stefan (2022). "Cinnamomeoventrolide – double bond regioisomerism in frog semiochemicals". Journal of Chemical Ecology. 48 (5–6): 531–545. doi:10.1007/s10886-022-01370-6. PMC   9375755 . PMID   35804278.
  6. 1 2 Vences, Miguel; Wahl-Boos, Gabriele; Hoegg, Simone; Glaw, Frank; Spinelli Oliveira, Elisabeth; Meyer, Axel; Perry, Steven (2007). "Molecular systematics of mantelline frogs from Madagascar and the evolution of their femoral glands". Biological Journal of the Linnean Society. 92 (3): 529–539. doi:10.1111/j.1095-8312.2007.00859.x.
  7. 1 2 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.
  8. 1 2 Blommers-Schlösser, R.M.A. (1979). "Biosystematics of the Malagasy frogs. I. Mantellinae (Ranidae)" (PDF). Beaufortia. 352: 1–77.
  9. 1 2 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.
  10. ↑ Poth, Dennis; Wollenberg, Katharina C.; Vences, Miguel; Schulz, Stefan (2012). "Volatile amphibian pheromones: macrolides from mantellid frogs from Madagascar". Angewandte Chemie International Edition. 51 (9): 2187–2190. doi:10.1002/anie.201106592. PMID   22266641.
  11. ↑ Poth, Dennis; Peram, Pardha Saradhi; Vences, Miguel; Schulz, Stefan (2013). "Macrolides and alcohols as scent gland constituents of the Madagascan Frog Mantidactylus femoralis and their intraspecific diversity". Journal of Natural Products. 76 (9): 1548–1558. doi:10.1021/np400131q. PMID   24004086.
  12. ↑ Nowack, Christine; Vences, Miguel (2016). "Ontogenetic development of the derived olfactory system of the mantellid frog Mantidactylus betsileanus". The Anatomical Record. 299 (7): 943–950. doi: 10.1002/ar.23351 . PMID   27084295.
  13. ↑ 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.
  14. ↑ Hutter, Carl R.; Andriampenomanana, Zo F.; Andrianasolo, Ginah Tsiorisoa; Cobb, Kerry A.; Razafindraibe, Jary H.; Abraham, Robin K.; Lambert, Shea M. (2021). "A fantastic new species of secretive forest frog discovered from forest fragments near Andasibe, Madagascar". Zoosystematics and Evolution. 97 (2): 483–495. doi: 10.3897/zse.97.73630 .
  15. ↑ Biju, S.D.; Bocxlaer, Ines Van; Mahony, Stephen; Dinesh, K.P.; Radhakrishnan, C.; Zachariah, Anil; Giri, Varad; Bossuyt, Franky (2011). "A taxonomic review of the night frog genus Nyctibatrachus Boulenger, 1882 in the Western Ghats, India (Anura: Nyctibatrachidae) with description of twelve new species". Zootaxa . 3029 (1): 49–52. doi: 10.11646/zootaxa.3029.1.1 .
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