Does the ostrich (Struthio camelus) coprodeum have the electrophysiological properties and microstructure of other birds?

The ostrich is unique among birds in having complete separation of urine and faeces. The coprodeal epithelium is thus during dehydration exposed to a fluid 500 mOsm hyperosmotic to plasma. We have investigated whether the coprodeum is adapted like a mammalian bladder. The coprodeal epithelium was studied by electrophysiology in the Ussing chamber, and the anatomy by light microscopy and scanning electron microscopy. ELECTROPHYSIOLOGY: The short-circuit current (SCC) and open circuit electrical potential difference were recorded. The change induced by 0.1 mmol mucosal amiloride was recorded. An average basal SCC of 162+/-29 microA/cm(2) was observed, and a resistance of 297+/-34 Omega cm(2) calculated. These values are as observed in other avian coprodea. The resistance is much lower than in mammalian bladders (10000 Omega cm(2)). The amiloride-sensitive SCC, equal to net sodium absorption, was approximately 5 micromol/cm(2)h as observed in other avian species. ANATOMY: The mucosal membrane is composed of broad irregular folds with very short intestinal glands containing an unusually high proportion of goblet cells. CONCLUSION: The ostrich coprodeum is not adapted like a mammalian bladder. The abundance of goblet cells results in a copious secretion of mucus that establishes a thick unstirred layer giving effective osmotic protection.     

Phylogenetic reconstruction of parental-care systems in the ancestors of birds

Due to the controversy surrounding incipient avian parental care, ancestral parental care systems were reconstructed in a phylogeny including major extant amniote lineages. Using two different resolutions for the basal avian branches, transitions between the states no care, female care, biparental care and male care were inferred for the most basal branches of the tree. Uniparental female care was inferred for the lineage to birds and crocodiles. Using a phylogeny where ratites and tinamous branch off early and an ordered character-state assumption, a transition to biparental care was inferred for the ancestor of birds. This ancestor could be any organism along the lineage leading from the crocodile-bird split up to modern birds, not necessarily the original bird. We discuss the support for alternative avian phylogenies and the homology in parental care between crocodiles and birds. We suggest that the phylogenetic pattern should be used as a starting point for a more detailed analysis of parental care systems in birds and their relatives.     

Adaptive strategies for post-renal handling of urine in birds

Birds are a diverse vertebrate class in terms of diet and habitat, but they share several common physiological features, including the use of uric acid as the major nitrogenous waste product and the lack of a urinary bladder. Instead, ureteral urine refluxes from the urodeum into the more proximal coprodeum and portions of the hindgut (colon or rectum and ceca). This presents a potential problem in that hyperosmotic ureteral urine in contact with the permeable epithelia of these tissues would counteract renal osmotic work. This review describes and provides examples of different strategies used by avian species to balance renal and post-renal changes in urine composition. The strategies described include: 1. a "reptilian" mode, with moderate renal concentrating ability, but high rates of post-renal salt and water resorption; 2. the "mammalian" strategy, in which the coprodeum effectively functions like a mammalian urinary bladder, preserving the osmotic concentrating work of the kidney; 3. an interaction strategy, in which post-renal transport processes are hormonally regulated in order to optimize renal function under varying conditions of salt or water stress; 4. the salt gland strategy seen in marine or estuarine birds with functional salt glands, in which post-renal transport mechanisms are used to conserve urinary water and to recycle excess NaCl to the nasal salt glands. Finally, we also describe some features of an as-yet unstudied group of birds, the birds of prey. At least some species in this group are relatively good renal concentrators, and would be predicted to have post-renal mechanisms to preserve this work. This new synthesis illustrates the marked diversity of adaptive mechanisms used by avian species to maintain osmotic homeostasis.     

Relating neuromuscular control to functional anatomy of limb muscles in extant archosaurs

Electromyography (EMG) is used to understand muscle activity patterns in animals. Understanding how much variation exists in muscle activity patterns in homologous muscles across animal clades during similar behaviours is important for evaluating the evolution of muscle functions and neuromuscular control. We compared muscle activity across a range of archosaurian species and appendicular muscles, including how these EMG patterns varied across ontogeny and phylogeny, to reconstruct the evolutionary history of archosaurian muscle activation during locomotion. EMG electrodes were implanted into the muscles of turkeys, pheasants, quail, guineafowl, emus (three age classes), tinamous and juvenile Nile crocodiles across 13 different appendicular muscles. Subjects walked and ran at a range of speeds both overground and on treadmills during EMG recordings. Anatomically similar muscles such as the lateral gastrocnemius exhibited similar EMG patterns at similar relative speeds across all birds. In the crocodiles, the EMG signals closely matched previously published data for alligators. The timing of lateral gastrocnemius activation was relatively later within a stride cycle for crocodiles compared to birds. This difference may relate to the coordinated knee extension and ankle plantarflexion timing across the swing-stance transition in Crocodylia, unlike in birds where there is knee flexion and ankle dorsiflexion across swing-stance. No significant effects were found across the species for ontogeny, or between treadmill and overground locomotion. Our findings strengthen the inference that some muscle EMG patterns remained conservative throughout Archosauria: for example, digital flexors retained similar stance phase activity and M. pectoralis remained an ‘anti-gravity’ muscle. However, some avian hindlimb muscles evolved divergent activations in tandem with functional changes such as bipedalism and more crouched postures, especially M. iliotrochantericus caudalis switching from swing to stance phase activity and M. iliofibularis adding a novel stance phase burst of activity.     

Ultrastructure and electrolyte transport of the epithelium of coprodeum,colon and the proctodeal diverticulum of Rhea americana

The structure and function of the lower intestinal tract of Rhea americana were characterized to evaluate the evolutionary relationship to other struthioniform and avian species. In 5 rheas the gross anatomy and the light and transmission electron microscopy were studied in parallel to in vitro electrophysiological measurements of ion transport. The mucosa in the colon was amplified with villi, often branched, and in the coprodeum with folds. In both tissues the epithelium was a monolayer composed of columnar absorptive cells, goblet cells and mitochondria-rich cells. Colon and coprodeum appeared to produce large amounts of mucus. The proctodeal diverticulum was rich in lymphoid tissue arranged into lobuli bursales, and it was concluded that this structure is a modified bursa of Fabricius. The sparse interlobular epithelium of the diverticulum resembled that of colon and coprodeum. Baseline short circuit currents (I_SC) averaged 114.5 ±13.8 µA/cm² in colon, 193.1 ± 30.3 µA/cm² in coprodeum and 60.4 ± 9.1 µA/cm² in the diverticulum. Amiloride sensitive Na⁺-transport amounted to 31, 88 and 38% of the baseline I_SC in these three tissues, respectively. In all tissues, there was also a modest, theophylline activated chloride secretion response, and ouabain, the Na⁺/K⁺-ATPase inhibitor, abolished most of the I_SC. The transepithelial resistance (TER) of the diverticulum was much higher than the other tissues. Upon dissection, urate from ureteral urine was observed in the lower third of the colon and to a lesser extent in the proctodeal diverticulum, indicating retrograde peristalsis of the urine. Thus, unlike the ostrich, there is no sphincter separating colon and coprodeum. On the other hand, a thick mucus layer was seen overlying the mucosa in both colon and coprodeum, as in the ostrich. This may help to prevent osmotic water loss, despite the presence of hyperosmotic urine (up to 800 mOsm) in the lower intestine. Both morphological and electrophysiological data from the rhea support the hypothesis that the rhea lower intestine contributes to post-renal modification of ureteral urine and to the regulation of osmotic balance, as also seen in domestic fowl and other avian species. The proctodeal diverticulum functions mainly as an immune organ, with only limited transport capability.     

An analogue computer simulation of cloacal resorption of salt and water from ureteral urine in birds

The transmural flow of NaCl and water occurring during the retrograde flow of ureteral urine into the coprodeum and large intestine of birds has been simulated by analogue computation. The purpose was to estimate whether a fraction of the urine (water) which in the dehydrated state is hyperosmotic to plasma can, in spite of this, be absorbed from the narrow space between the epithelium and the central faeces core. The values of urine flow, urine osmolality, osmotic permeability, net NaCl absorption rate, and solute-linked water flow determined by in vivo perfusion studies in the domestic fowl were used in the calculation. The cloacal sojourn of ureteral urine was found to result in a net water gain but at the expense of a hyperosmotic NaCl absorption. The model was further used to evaluate the quantitative influence of the system's parameters upon the fractional water absorption. This was found very sensitive to the urine osmolality, moderately sensitive to the urine flow and NaCl absorption rate and almost unaffected by the osmotic permeability of the coprodeum and large intestine within a reasonable physiological range. The change of the epithelial transport parameters from the normally hydrated to the dehydrated state resulted in a marked increase in water absorption.     

Phylogenetic interrelationships of living and extinct Tinamidae,volant palaeognathous birds from the New World

Tinamous, one of the earliest diverging living avian lineages, consists of a Neotropical clade of palaeognathous birds with a fossil record limited to the early Miocene–Quaternary of southern South America. Here, we conduct a comprehensive, morphology‐based phylogenetic study of the interrelationships among extinct and living species of tinamous. Morphological data of fossil species are included in a matrix of 157 osteological and myological characters of 56 terminal taxa. The monophyly of most recognized genera is supported by the results of the analysis. The cladistic analysis also recovers the traditional subdivision between those tinamous specialized for open areas (Nothurinae) and those inhabiting forested environments (Tinaminae). Temporal calibration of the resultant phylogeny indicates that such a basal divergence had already taken place in the early Miocene, some 17 million years ago. The placement of the fossil species within the open‐area (Nothurinae) and the forest‐dwelling (Tinaminae) tinamous is also consistent with the palaeoenvironmental conditions inferred from the associated fauna. © 2014 The Linnean Society of London     

The development of the bladder trigone, the center of the anti-reflux mechanism

The urinary tract is an outflow system that conducts urine from the kidneys to the bladder via the ureters that propel urine to the bladder via peristalsis. Once in the bladder, the ureteral valve, a mechanism that is not well understood, prevents backflow of urine to the kidney that can cause severe damage and induce end-stage renal disease. The upper and lower urinary tract compartments form independently, connecting at mid-gestation when the ureters move from their primary insertion site in the Wolffian ducts to the trigone, a muscular structure comprising the bladder floor just above the urethra. Precise connections between the ureters and the trigone are crucial for proper function of the ureteral valve mechanism; however, the developmental events underlying these connections and trigone formation are not well understood. According to established models, the trigone develops independently of the bladder, from the ureters, Wolffian ducts or a combination of both; however, these models have not been tested experimentally. Using the Cre-lox recombination system in lineage studies in mice, we find, unexpectedly, that the trigone is formed mostly from bladder smooth muscle with a more minor contribution from the ureter, and that trigone formation depends at least in part on intercalation of ureteral and bladder muscle. These studies suggest that urinary tract development occurs differently than previously thought, providing new insights into the mechanisms underlying normal and abnormal development.     

Congruent Avian Phylogenies Inferred from Mitochondrial and Nuclear DNA Sequences

Recent molecular studies addressing the phylogenetic relationships of avian orders have had conflicting results. While studies using nuclear DNA sequences tend to support traditional taxonomic views, also supported by morphological data [(paleognaths (galloanseres (all other birds)))], with songbirds forming a clade within Neoaves (all other birds), analyses with complete mtDNA genomes have resulted in topologies that place songbirds as one of the earliest-diverging avian lineages. Considering that over half of the extant bird species are songbirds, these different results have very different implications for our understanding of avian evolution. We analyzed data sets comprising nearly 4 kb of mitochondrial DNA (mtDNA) (complete 12S, ND1, ND2, and cytochrome b) plus 600 bp of the nuclear gene c-mos for 15 birds that were chosen to represent all major avian clades and to minimize potential long-branch attraction problems; we used a partition-specific maximum likelihood approach. Our results show congruence with respect to the ingroup among phylogenies obtained with mtDNA and the nuclear gene c-mos, separately or combined. The data sets support a traditional avian taxonomy, with paleognaths (ratites and tinamous) occupying a basal position and with songbirds more derived and forming a monophyletic group. We also show that, for mtDNA studies, turtles may be a better outgroup for birds than crocodilians because of their slower rate of sequence evolution.     

Spatial, temporal, and species variation in prevalence of influenza A viruses in wild migratory birds

Although extensive data exist on avian influenza in wild birds in North America, limited information is available from elsewhere, including Europe. Here, molecular diagnostic tools were employed for high-throughput surveillance of migratory birds, as an alternative to classical labor-intensive methods of virus isolation in eggs. This study included 36,809 samples from 323 bird species belonging to 18 orders, of which only 25 species of three orders were positive for influenza A virus. Information on species, locations, and timing is provided for all samples tested. Seven previously unknown host species for avian influenza virus were identified: barnacle goose, bean goose, brent goose, pink-footed goose, bewick's swan, common gull, and guillemot. Dabbling ducks were more frequently infected than other ducks and Anseriformes; this distinction was probably related to bird behavior rather than population sizes. Waders did not appear to play a role in the epidemiology of avian influenza in Europe, in contrast to the Americas. The high virus prevalence in ducks in Europe in spring as compared with North America could explain the differences in virus-host ecology between these continents. Most influenza A virus subtypes were detected in ducks, but H13 and H16 subtypes were detected primarily in gulls. Viruses of subtype H6 were more promiscuous in host range than other subtypes. Temporal and spatial variation in influenza virus prevalence in wild birds was observed, with influenza A virus prevalence varying by sampling location; this is probably related to migration patterns from northeast to southwest and a higher prevalence farther north along the flyways. We discuss the ecology and epidemiology of avian influenza A virus in wild birds in relation to host ecology and compare our results with published studies. These data are useful for designing new surveillance programs and are particularly relevant due to increased interest in avian influenza in wild birds.     

Clutch predation in great tinamous Tinamus major and implications for the evolution of egg color

Egg camouflage has been found to reduce predation in several ground‐nesting species. Therefore, the evolution of eggs that lack camouflage in ground nesting birds is puzzling. Even though clutch predation in the tropics is high, tinamous are the only tropical ground‐nesting birds that do not build a nest and do not lay cryptic eggs. I studied predation of great tinamou clutches in a lowland tropical forest and found that risk of predation was higher during incubation when the eggs are covered by the parent, than during laying when they are exposed, suggesting that predators primarily use cues from the incubating males to locate the clutch and not cues from the eggs. Clutch size had no effect on predation rate, even though larger clutches are more conspicuous to a human observer. Predation by visual cues is likely reduced during incubation by the camouflaged plumage and high nest attendance of males. If most predators use cues from the incubating male and not the eggs to locate clutches, then conspicuous egg color may have evolved in great tinamous as an intra‐specific signal. I evaluate hypotheses that may explain the maintenance of conspicuous egg color in tinamous.     

Relationships between bird species and tree species assemblages in forested habitats of eastern North America

Aim We examined the relative influence of geographical location, habitat structure (physiognomy), and dominant plant species composition (floristics) on avian habitat relationships over a large spatial extent. Although it has been predicted that avian distributions are more likely to covary with physiognomy than with floristics at coarse scales, we sought to determine, more specifically, whether there remained a significant association between gradients in assemblages of bird species and dominant plant species within a general biome type, after statistically controlling for structural variation and geographical location of sampling sites. Location Our sample consisted of a subset of North American Breeding Bird Census survey sites that covered most of the range of eastern forests, from Florida to Nova Scotia, and west to Minnesota and North Dakota (up to c. 2500 km between sites). Methods We restricted our analyses to the single year (1981) that provided the largest sample of sites (47) for which vegetation data were available within ± 2 years of the avian surveys. We examined the relationship between avian community composition and tree species composition over this series of forested plots. Data were divided into four sets: (1) bird species abundances, (2) tree species abundances, (3) physiognomic or structural variables and (4) geographical location (latitude and longitude). We performed separate detrended correspondence analysis ordinations of birds and trees, before and after statistically partialling out covariation associated with structural variables and geographical location. To gauge the relationship between the two sets of species we correlated site scores resulting from separate ordinations. We also compared continental‐scale patterns of variation in bird and tree assemblages to understand possible mechanisms controlling species distribution at that scale. Results Both bird and tree communities yielded strong gradients, with first‐axis eigenvalues from 0.75 to 0.97. All gradients were relatively long (> 4.0), implying complete turnover in species composition. However, geographical location accounted for < 10% of the total variation associated with any ordination. Prior to partialling out covariation resulting from location and physiognomy, bird species ordinations were strongly correlated with tree species ordinations. The strength of association was reduced after partialling, but one bird and one tree axis remained significantly correlated. There was a significant species–area effect for birds, but not for trees. Main conclusions There was a significant relationship between bird species assemblages and tree species assemblages in the eastern forests of North America. Even after partialling out covariation associated with spatial location and forest physiognomy, there remained a significant correlation between major axes from bird and tree ordinations, consistent with the hypothesis that floristic variation is likely to be important in organizing assemblages of birds within a general biome type, albeit over a much larger spatial extent than originally predicted. Forest tree species ordinations differed from bird species ordinations in several ways: trees had a higher rate of turnover along underlying environmental gradients; trees appeared more patchily distributed than birds at this scale; and tree species were more spaced out along the underlying ecological gradients, with less overlap. By understanding the relationship between bird assemblages and forest floristics, we might better understand how avian communities are likely to change if tree species distributions are altered as a result of climatic changes.     

Possible epithelial sodium channels visualized by freeze-fracture

The coprodeum is a very efficient Na⁺-retaining epithelium. Coprodeum from birds on a high Na⁺ diet has virtually no ion transport, while an Amiloride-sensitive Na⁺ absorption of 10–12 μ equiv·cm^?2·h^?1 is induced in the coprodeal epithelium from birds on a low Na⁺ diet. Both measurements of the Na⁺ influx and Na⁺-diffusion potentials across the luminal cell membrane have revealed a selective opening of this membrane to Na⁺ in birds on a low Na⁺ diet. Freeze-fracture P faces of the luminal membrane in coprodea taken from birds on a low Na⁺ diet have rod-shaped particles, $\text{100 × 240}\text{A}\text{?}$, in more than 20% of the principal cells. Rod-shaped particles appear in less than 1% of these cells in coprodea from high Na⁺-diet birds. Thus a low Na⁺ diet induces rod-shaped particles in the luminal cell membrane of the hen coprodeum. These new particles may function as Na⁺-channels mediating the increased Na⁺-influx across the apical cell membrane.     

Evolutionary shifts in the melanin‐based color system of birds

Melanin pigments contained in organelles (melanosomes) impart earthy colors to feathers. Such melanin‐based colors are distributed across birds and thought to be the ancestral color‐producing mechanism in birds. However, we have had limited data on melanin‐based color and melanosome diversity in Palaeognathae, which includes the flighted tinamous and large‐bodied, flightless ratites and is the sister taxon to all other extant birds. Here, we use scanning electron microscopy and spectrophotometry to assess melanosome morphology and quantify reflected color for 19 species within this clade. We find that brown colors in ratites are uniquely associated with elongated melanosomes nearly identical in shape to those associated with black colors. Melanosome and color diversity in large‐bodied ratites is limited relative to other birds (including flightless penguins) and smaller bodied basal maniraptoran dinosaur outgroups of Aves, whereas tinamous show a wider range of melanosome forms similar to neognaths. The repeated occurrence of novel melanosome forms in the nonmonophyletic ratites suggests that melanin‐based color tracks changes in body size, physiology, or other life history traits associated with flight loss, but not feather morphology. We further anticipate these findings will be useful for future color reconstructions in extinct species, as variation in melanosome shape may potentially be linked to a more nuanced palette of melanin‐based colors.     

The anatomy of the middle ear of the tinamiformes (Aves: Tinamidae)

The morphology of the middle ear region including the basicranium and quadrate of tinamous is compared among ratites and flying birds belonging to the Procellariiformes, Sphenisciformes, Pelecaniformes, and Ciconiiforms. The middle ears of tinamous and ratites share a number of important characters including absence of a separate foramen for the glossopharyngeal nerve; eustachian tube, carotid artery, and stapedial artery encased in bone; and a metotic process with vascular canals or notches. Outgroup analysis confirms these characters as synapomorphies. These data support the position that the Tinami and Ratiti form a monophyletic assemblage.     

New nuclear evidence for the oldest divergence among neognath birds: the phylogenetic utility of ZENK (i)

To date, there is little consensus concerning the phylogenetic relationships among neognath orders, which include all extant birds except ratites and tinamous. Different data sets, both molecular and morphologic, have yielded radically different and often unresolved ordinal topologies, especially within the neoaves clade. This lack of resolution and ongoing conflict indicates a need for additional phylogenetic characters to be applied to the question of higher-level avian phylogeny. In this study, sequences of a single-copy nuclear gene, ZENK, were used to reconstruct an ordinal-level phylogeny of neognath birds. Strong support was indicated for the oldest divergence within Neognathae; the chicken- and duck-like birds formed a clade that was sister to all other modern birds. In addition, many families of traditional taxonomic orders clustered together in the ZENK tree, indicating the gene's general phylogenetic reliability. However, within the neoaves clade, there was little support for relationships among orders, which is a result similar to all other recent molecular studies of higher-level avian phylogeny. This similarity among studies suggests the possibility of a rapid radiation of the major neoaves lineages. Despite the ongoing lack of neoaves resolution, ZENK's sequence divergence and base composition patterns indicate its general utility as a new phylogenetic marker for higher-level avian systematics.     

The early history of modern birds inferred from DNA sequences of nuclear and mitochondrial ribosomal genes

The traditional view of avian evolution places ratites and tinamous at the base of the phylogenetic tree of modern birds (Neornithes). In contrast, most recent molecular studies suggest that neognathous perching birds (Passeriformes) compose the oldest lineage of modern birds. Here, we report significant molecular support for the traditional view of neognath monophyly based on sequence analyses of nuclear and mitochondrial DNA (4.4 kb) from every modern avian order. Phylogenetic analyses further show that the ducks and gallinaceous birds are each other's closest relatives and together form the basal lineage of neognathous birds. To investigate why other molecular studies sampling fewer orders have reached different conclusions regarding neognath monophyly, we performed jackknife analyses on our mitochondrial data. Those analyses indicated taxon-sampling effects when basal galloanserine birds were included in combination with sparse taxon sampling. Our phylogenetic results suggest that the earliest neornithines were heavy-bodied, ground-dwelling, nonmarine birds. This inference, coupled with a fossil bias toward marine environments, provides a possible explanation for the large gap in the early fossil record of birds.     

Multiple nuclear genes and retroposons support vicariance and dispersal of the palaeognaths,and an Early Cretaceous origin of modern birds

The origin and timing of the diversification of modern birds remains controversial, primarily because phylogenetic relationships are incompletely resolved and uncertainty persists in molecular estimates of lineage ages. Here, we present a species tree for the major palaeognath lineages using 27 nuclear genes and 27 archaic retroposon insertions. We show that rheas are sister to the kiwis, emu and cassowaries, and confirm ratite paraphyly because tinamous are sister to moas. Divergence dating using 10 genes with broader taxon sampling, including emu, cassowary, ostrich, five kiwis, two rheas, three tinamous, three extinct moas and 15 neognath lineages, suggests that three vicariant events and possibly two dispersals are required to explain their historical biogeography. The age of crown group birds was estimated at 131 Ma (95% highest posterior density 122–138 Ma), similar to previous molecular estimates. Problems associated with gene tree discordance and incomplete lineage sorting in birds will require much larger gene sets to increase species tree accuracy and improve error in divergence times. The relatively rapid branching within neoaves pre-dates the extinction of dinosaurs, suggesting that the genesis of the radiation within this diverse clade of birds was not in response to the Cretaceous–Paleogene extinction event.     

Morphology and putative function of the colon and cloaca of marine and freshwater snakes

Among tetrapods, evidence for postrenal modification of the urine by the distal digestive tract (including the colon and cloaca) is highly variable. Birds and bladderless reptiles are of interest because the colon and cloaca represent the only sites from which water and ions can be reclaimed from the urine secreted by the kidney. For animals occupying desiccating environments (e.g., deserts and marine environments), postrenal modification of the urine may directly contribute to the maintenance of hypo‐osmotic body fluids. We compared the morphology and distribution of key proteins in the colon, cloaca, and urogenital ducts of watersnakes from marine (Nerodia clarkii clarkii) and freshwater (Nerodia fasciata) habitats. Specifically, we examined the epithelia of each tissue for evidence of mucus production by examining the distribution of mucopolysaccharides, and for evidence of water/ion regulation by examining the distribution of Na⁺/K⁺‐ATPase (NKA), Na⁺/K⁺/Cl^? cotransporter (NKCC), and aquaporin 3 (AQP3). NKCC localized to the basolateral epithelium of the colon, urodeal sphincter, and proctodeum, consistent with a role in secretion of Na⁺, Cl^?, and K⁺ from the tissue, but NKA was not detected in the colon or any compartment of the cloaca. Interestingly, NKA was detected in the basolateral epithelium of the ureters, suggesting the urothelium may play a role in active ion transport. AQP3 was detected in the ureters and coprodeal complex, consistent with a role in urinary and fecal dehydration or, potentially, in the production of the watery component of the mucus secreted by the coprodeal complex. Since no differences in general cloacal morphology, production of mucus, or the distribution of ion transporters/water channels were detected between the two species, cloacal osmoregulation may either be regulated by proteins not examined in this study or may not be responsible for the differential success of N. c. clarkii and N. fasciata in marine habitats. J. Morphol. 2011. © 2011 Wiley Periodicals, Inc.