The water-absorption region of ventral skin of several semiterrestrial and aquatic anuran amphibians identified by aquaporins

Abstract

Regions of specialization for water absorption across the skin of Bufonid and Ranid anurans were identified by immunohistochemistry and Western blot analysis, using antibodies raised against arginine vasotocin (AVT)-stimulated aquaporins (AQPs) that are specific to absorbing regions of Hyla japonica. In Bufo marinus, labeling for Hyla urinary bladder-type AQP (AQP-h2), which is also localized in the urinary bladder, occurred in the ventral surface of the hindlimb, pelvic, and pectoral regions. AQP-h2 was not detected in any skin regions of Rana catesbeiana, Rana japonica, or Rana nigromaculata. Hyla ventral skin-type AQP (AQP-h3), which is found in the ventral skin but not the bladder of H. japonica, was localized in the hindlimb, pelvic, and pectoral skins of Bufo marinus, in addition to AQP-h2. AQP-h3 was also localized in ventral skin of the hindlimb of all three Rana species and also in the pelvic region of R. catesbiana. Messenger RNA for AQP-x3, a homolog of AQP-h3, could be identified by RT-PCR from the hindlimb, pectoral, and pelvic regions of the ventral skin of Xenopus laevis, although AVT had no effect on water permeability. In contrast, 10 Ϫ8 M AVT-stimulated water permeability and translocation of AQP-h2 and AQP-h3 into the apical membrane of epithelial cells in regions of the skin of species where they had been localized by immunohistochemistry and Western blot analysis. Finally, water permeability of the hindlimb skin of B. marinus and all the Rana species was stimulated by hydrins 1 and 2 to a similar level as seen for AVT. The present data demonstrate species differences in the occurrence, distribution, and regulation of AQPs in regions of skin specialized for rapid water absorption that can be associated with habitat and also phylogeny. hindlimb skin; arginine vasotocin; immunohistochemistry; water permeability; frogs MANY ADULT ANURAN AMPHIBIANS do not drink through their mouth. Rather, they absorb water across their skin and form dilute urine that is stored in their urinary bladder and can be reabsorbed when foraging away from a hydration source (4, 5). Hillman et al. (14) refer to this water balance strategy as semiterrestrial to distinguish it from terrestrial species that are completely independent of water. The semiterrestrial classification applies to tree frogs in the family Hylidae and toads in the family Bufonidae that have been traditionally classified as arboreal and terrestrial, respectively, in that both have large urinary bladder capacity and specializations for rapidly rehydrating when water is available. Specifically, they utilize an area of skin in the posteroventral region of the body that is specialized for rapid water absorption from shallow water sources or moist substrates. This region, termed the pelvic patch or seat patch, extends laterally to the ventral surface of the hindlimbs and shows a pattern of elevations and grooves termed verrucae hydrophilicae (14). The seat patch is also an area where capillaries form intimate contact with the basement membrane that underli...

The Lineage-Specific Evolution of Aquaporin Gene Clusters Facilitated Tetrapod Terrestrial Adaptation

“…These observations also confirmed that canonical AQP2 is not encoded in the genome of the Western-clawed frog [24] or its congener the African clawed frog. The Bayesian analyes show that the wholly aquatic Western-clawed frog has two paralogs of AQP5 , a canonical form ( AQP5 , formerly annotated as AQP-x5 , [28]) and a related paralog ( AQP5L , formerly annotated as AQP2 ) encoded between two AQP6 genes, the urinary bladder-type ( AQP6ub ) and the ventral skin type ( AQP6vs ) formerly identified as (h2-like and h3-like) type-a2 anuran specific aquaporins [23], [24], [32]. Amongst other Anura the Bayesian data provide statistical support for three paralogs of AQP6 (see Table S2), the urinary bladder type ( AQP6ub ) and two paralogs ( AQP6vs1 , -6vs2 ) that mediate cutaneous hydration through the ventral skin of semi-aquatic and semi-terrestrial anurans [33], [35].…”

Geographic variation in adult and embryonic desiccation tolerance in a terrestrial-breeding frog

“…There is also evidence that skin thickness is associated with habitat aridity at the species level (Toledo and Jared 1993), with species from drier areas producing a thicker epidermis which reduces dehydration rates whilst also impeding water uptake. Further, aquaporins (water channel proteins) embedded within the pelvic patch (Kubota et al 2006) can influence rehydration rates in anurans, and variation in the density and type of aquaporins among species has been interpreted as an adaptation of frogs to their respective hydric environment (Suzuki et al 2007;Ogushi et al 2010). It is currently unknown whether similar patterns of morphological or physiological differences in the skin properties exist at the population level, and we encourage future studies to explore the underlying mechanisms that drive intraspecific differences in dehydration and rehydration rates across hydric gradients.…”

The effect of three anaesthetic protocols on the stress response in cane toads (Rhinella marina)

“…In Bufo sp . the inguinal area has the highest capacity for transcutaneus absorption (Ogushi et al. 2010), so the volume of water used to induce the animals was enough to submerge a third of their height.…”

“…In Bufo sp. the inguinal area has the highest capacity for transcutaneus absorption (Ogushi et al 2010), so the volume of water used to induce the animals was enough to submerge a third of their height. Furthermore maintaining the animals in a low volume of water facilitated the introduction of a sponge or a piece of fabric to the container enabling the head to be kept clear of the water once the righting reflex was abolished.…”