Skin gland concentrations adapted to different evolutionary pressures in the head and posterior regions of the caecilian Siphonops annulatus

Abstract

Amphibian skin is rich in mucous glands and poison glands, secreting substances important for gas exchange and playing a fundamental role in chemical defense against predators and microorganisms. In the caecilian Siphonops annulatus (Mikan, 1920) we observed a concentration of enlarged mucous glands in the head region. In the posterior region of the body a similar concentration is made up of enlarged poison glands. These accumulations of glands structurally resemble the macroglands previously reported in anurans and salamanders. The skin glands in these regions are each surrounded by collagen walls forming a honeycomb-like structure. The collagen network in the head region firmly attaches to tiny pits in the bones of the skull. The two extremities of the body produce different secretions, containing exclusive molecules. Considering the fossorial lifestyle of caecilians, it seems evident that the secretions of the head and caudal region serve different functions. The anterior macrogland of mucous glands, rich in mucous/lipid secretion, in conjunction with the funnel-shaped head, may act to lubricate the body and penetrate the soil, thus facilitating locomotion underground. The blunt posterior end bearing an internalized macrogland of poison glands in the dermis may act in chemical defense and/or by blocking invasion of tunnels.

Light and transmission electron microscopic structure of skin glands and dermal scales of a caecilian amphibian Gegeneophis ramaswamii, with a note on antimicrobial property of skin gland secretion

“…No protein was detected in them. Jared et al () reported the granular and mucous glands in Siphonops annulatus . The organization of granular glands in G ramaswamii are similar to those described in other caecilian species.…”

“…The caecilian species (irrespective of sex, n = 5, mean length 385 ± SD 29 mm) were maintained in a terrarium in our lab. Crude skin secretions from all specimens were collected according to the method of Jared et al (). The specimens were washed with Milli‐Q water (Millipore, USA) in a petri plate to remove the soil contaminants.…”

Life history and reproduction of the neotropical caecilian Siphonops annulatus (Amphibia, Gymnophiona, Siphonopidae), with special emphasis on parental care

“…Soil‐dwelling caecilians are head‐first burrowers. Numerous cutaneous mucous glands spread across the entire surface of Siphonops annulatus presumably provide lubrication during burrowing, reducing friction (Gabe, ) and enabling these animals to “dive” underground (Jared et al., , ). Additionally, mucous gland secretions lubricate the walls of established tunnels contributing to their smooth, shiny and sometimes moist surface.…”

“…Jared, Navas, & Toledo, ; Junqueira, Jared, & Antoniazzi, ; Kupfer, Nabhitabhata, & Himstedt, , ). Similarly to other amphibians, the caecilians have glands in the skin that are responsible for the secretion of toxins for defence, but also mucus that, besides their use in respiration, have an important role in burrowing locomotion (Jared et al., ). Nonetheless, caecilians are noted for their diversity of reproductive modes (e.g.…”

Skin glands of an aquatic salamander vary in size and distribution and release antimicrobial secretions effective against chytrid fungal pathogens

“…While mucous glands of A. tridactylum were most abundant in the head, the consistent size of mucous glands across the entire body suggests that these glands lack specialization and serve more general roles in Amphiuma. Because amphiumid salamanders are fossorial, the lubricative secretions of cephalically located mucous glands may facilitate head-first burrowing activities by providing protection from abrasive skin damage (Breckenridge and Murugapillai, 1974;Jared et al, 2018).…”