holocrine
Holocrine (from Ancient Greek ὅλος; ''hólos'', “whole, entire” + κρῑ́νω; ''krī́nō'', “to separate”) is a term used to classify the mode of secretion in exocrine glands in the study of histology. Holocrine secretions are ...
secretory gland found on the inside of the thighs of certain lizard
Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia al ...
s and amphisbaenians which releases pheromone
A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...
s to attract mates or mark territory. In certain species only the male has these pores and in other species, both sexes have them, with the male's being larger. Femoral pores appear as a series of pits or holes within a row of scales on the ventral portion of the animal's thigh.
Femoral pores are present in all genera
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial ...
in the families Cordylidae, Crotaphytidae, Hoplocercidae, Iguanidae
The Iguanidae is a family of lizards composed of the iguanas, chuckwallas, and their prehistoric relatives, including the widespread green iguana.
Taxonomy
Iguanidae is thought to be the sister group to the collared lizards (family Crotaph ...
, Phrynosomatidae
The Phrynosomatidae are a diverse family of lizards, sometimes classified as a subfamily (Phrynosomatinae), found from Panama to the extreme south of Canada. Many members of the group are adapted to life in hot, sandy deserts, although the spin ...
, and Xantusiidae. They are absent in all genera in the Anguidae
Anguidae refers to a large and diverse family of lizards native to the Northern Hemisphere. Common characteristics of this group include a reduced supratemporal arch, striations on the medial faces of tooth crowns, osteoderms, and a lateral fold ...
, Chamaeleonidae, Dibamidae, Helodermatidae, Scincidae, Xenosauridae
Xenosauridae is a family of anguimorph lizards whose only living representative is the genus ''Xenosaurus'', which is native to Central America. Xenosauridae also includes the extinct genera '' Exostinus'' and '' Restes''. Also known as knob-scal ...
, and Varanidae families. They are present in other lizards and amphisbaenians quite variably, some geckoes, '' Phelsuma'', for example have these pores, others in the same family do not.
In the desert iguana (''Dipsosaurus dorsalis''), the waxy lipid
Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids incl ...
s released from the femoral pores absorb ultraviolet
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiati ...
(UV) wavelengths making them visible to species which can detect UV light. According to tests performed on the Green iguana, the variation in the chemicals released by the femoral pores can help to determine age, sex, and individual identity of the animal in question. Male leopard geckos (''Eublepharis macularius''), actually taste the secretions by flicking their tongues, if a male determines the other gecko in question is a male, the two will fight.
In certain species such as geckoes, the females lack femoral pores altogether. In most families of lizards that have femoral pores, notably the iguanids, both sexes have femoral pores, but the males tend to be much larger than females of the same size and age. In these instances they are used as a marker for sexual dimorphism
Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most an ...
.
The number of femoral pores varies considerably among species. For example, the number of pores in male lizards of the family Lacertidae can range between zero (e.g. '' Meroles anchietae'') and 32 (e.g. '' Gallotia galloti'') per limb. Also, shrub-climbing species tend to have fewer femoral pores than species inhabiting other substrates (such as sandy and rocky substrate), suggesting a role of the environment on the evolution of the chemical signaling apparatus in lacertid lizards.
References
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Reptile anatomy