Morphology of the cloaca in the estuarine crocodile, Crocodylus porosus, and its plastic response to salinity

Glans inflation morphology and female cloaca copulatory interactions of the male American alligator phallus†

The phallic glans of the American alligator (Alligator mississippiensis) is the distal termination of the semen-conducting sulcus spermaticus and during copulation has the closest, most intimate mechanical interactions with the female urodeum, the middle cloacal chamber that contains the opening to the vaginal passages and oviducts. However, the details of this interface leading to insemination and gamete uptake are unclear. Here, we: (1) histologically characterize the underlying tissue types and morphologically quantify the shape changes associated with glans inflation into the copulatory conformation, (2) digitally reconstruct from MRI the 3D shape of functional tissue compartments, and (3) diffusible iodine-based contrast-enhanced computed tomography image the copulatory fit between male phallus and female cloaca. We discuss these results in relation to tissue type material properties, the transfer on intromittent forces, establishing potential copulatory lock, inflated glans volume scaling with body mass/length, the mechanics of semen targeting and insemination, and potential female cryptic choice impacting multiple clutch paternity. In part, this study further clarifies the phallic morphological variation observed among crocodylians and begins to investigate the role(s) these divergent male forms play during copulation interacting with female cloacal forms to increase reproductive success.

Crocodylian conservation and evolution insights from an anatomical and histological examination of phalli from male false gharial (Tomistoma schlegelii)

As wild population threats for the endangered false gharial (Tomistoma schlegelii) persist, conservation breeding programs, including developing semen collection techniques for subsequent artificial insemination, are becoming important species conservation measures. Developing reproductive biology understanding of a species is important to developing best practices and hopefully maximizing reproductive successes. However, information on crocodylians functional copulatory anatomy in general is lacking. To that end, zoological facilities and conservation centres have the exceptional opportunity to contribute new understandings that may not otherwise be attainable regarding crocodylian reproductive anatomy, particularly during routine physical examinations or post-mortem necropsies. Therefore, to better understand T. schlegelii reproductive biology, to contribute knowledge in support of zoo breeding conservation efforts and to contribute to what is known overall about crocodylian reproduction, we investigated phallic anatomy of adult male Tomistoma from two zoological populations, the St. Louis Zoo, USA and Sungai Dusun Wildlife Reserve, Peninsular Malaysia. Here, we present the gross anatomical features and histological analysis of underlying tissue-level details in pursuit of a better understanding of copulatory function and associated gamete transfer mechanisms. While much of the overall Tomistoma phallic morphology and inferred function corresponds to that of other crocodylian species and speaks to conserved aspects of functional anatomy across taxa, species-specific aspects of glans and glans tip morphology are also identified. These novelties are discussed in a general function and overall broader evolutionary contexts.

Correlation between increased postpubertal phallic growth and the initiation of cranial sexual dimorphisms in male Morelet's crocodile

While puberty is an animal commonality, little is known of its timing or process in crocodylians. Males copulate with an intromittent phallus that has a distinct glans morphology which directly interacts with the female cloaca, putatively effecting effective semen transfer and ultimately increased fecundity. Here we present, during the Morelet's crocodile lifecycle, a well-defined body length (65 cm snout-vent length) inflection point that marks a subsequent increase of phallic glans growth rates. Putatively, this postpubescent growth produces a copulatory-effective phallus. While not as robust of a trend as snout-vent length, this growth inflection concomitantly begins with a body condition index (CI = BM/SVL³ ) between 2.0 and 2.5 and is most distinct above a CI of 2.5. Also, in males, this 65 cm size threshold also aligns with the initiation of more robust growth in caniniform alveoli associated with prominent maxillary and mandibular teeth. This inflection was not observed in females, thus marking a sexual dimorphism that begins to present with the onset of puberty. This bodily manifestation of puberty other than those changes observed in the reproductive tracts is a novel observation for crocodylians and lays a foundation for further study among species of how changing endocrine signaling within sexually maturing males may also influence a broader range of secondary sex characteristics.

Alginate increases water stability whilst maintaining diet digestibility in farmed saltwater crocodiles ()

Saltwater crocodile () farming in Papua New Guinea is an emerging industry that supplies high-quality skins to the fashion industry. Crocodiles are semiaquatic and fed high-quality feed made from extrudated animal byproducts (i.e., forced through a die at low pressure but not heat treated); however, it disintegrates on contact with water, and this leads to low utilization. Alginate is used extensively in food and pharmaceutical processes because it quickly forms a gel at room temperature; however, its effects on nutrient availability are equivocal, and its utility in crocodile diets is unknown. Extrudated chicken byproduct-based crocodile diets were formulated (as-fed) with and without 1.7 and 3.3% Na alginate with either CaCl or CaCO to cross-link. After immersion in water at 30°C for 24 h, feed retained on a 0.5-mm screen was measured to determine DM retention (DMR). Regardless of inclusion level, alginate addition resulted in a 13-fold increase in DMR ( < 0.05) when CaCO was used as a Ca source; however, CaCl use resulted in a much lower DMR. In a digestibility trial, 10 juvenile crocodiles (2.2 to 2.4 yr of age; 1.2 to 1.9 kg BW) were chosen from farm-raised stocks and fed extrudated chicken byproduct-based diets with and without 1.5% Na alginate and 1.9% CaCO. Animals fed 2% BW for 12 d and with excreta collected the last 5 d were slaughtered and had digesta sampled from the ileum. There were no differences in apparent ileal digestibilities of any AA, N (65.0 vs. 55.8%, SE = 12.2%), and OM (46.8 vs. 39.6%, SE = 12.8%) between diets with and without alginate, respectively. Total-tract digestibilities of OM (69.8 vs. 39.2%, SE = 9.1%) and energy (72.2 vs. 44.4%, SE = 8.3%), however, were greater in alginate-containing diets ( < 0.05). Our study showed that alginate addition to crocodile feed improved its stability in water and did not impair nutrient digestion. Application of these findings should greatly decrease feed wastage, which ultimately will benefit Papua New Guinea by simultaneously increasing economic returns and decreasing environmental impacts.

Human-caused habitat fragmentation can drive rapid divergence of male genitalia

The aim of this study rests on three premises: (i) humans are altering ecosystems worldwide, (ii) environmental variation often influences the strength and nature of sexual selection, and (iii) sexual selection is largely responsible for rapid and divergent evolution of male genitalia. While each of these assertions has strong empirical support, no study has yet investigated their logical conclusion that human impacts on the environment might commonly drive rapid diversification of male genital morphology. We tested whether anthropogenic habitat fragmentation has resulted in rapid changes in the size, allometry, shape, and meristics of male genitalia in three native species of livebearing fishes (genus: Gambusia) inhabiting tidal creeks across six Bahamian islands. We found that genital shape and allometry consistently and repeatedly diverged in fragmented systems across all species and islands. Using a model selection framework, we identified three ecological consequences of fragmentation that apparently underlie observed morphological patterns: decreased predatory fish density, increased conspecific density, and reduced salinity. Our results demonstrate that human modifications to the environment can drive rapid and predictable divergence in male genitalia. Given the ubiquity of anthropogenic impacts on the environment, future research should evaluate the generality of our findings and potential consequences for reproductive isolation.

Location of the ureteral openings in the cloacas of tinamous, some ratite birds, and crocodilians: a primitive character

Cloacas of 67 avian species, of both sexes, from various habitats and differing dietary habits, were examined macro- and microscopically to investigate possible variation in the location of the ureteral openings. Differing from most birds studied, in adult male Rhea americana and several tinamous species the ureters were found to open into the coprodeum. In these species the urodeum receives only the vas deferens or oviduct. Similarly, in crocodiles Caiman crocodilus yacare, but not in lizards Tropidurus montanus and snakes Crotalus durissus terrificus, the ureters empty into the coprodeum. This similarity between ancient birds (ratites and tinamous) and crocodiles may indicate a primitive character linking reptiles and birds. This unusual position of the ureteral orifice can represent an adaptation to facilitate urine collection into the coprodeum and large intestine. Another possibility is that this variation in ureter position is a male reproductive strategy to avoid the mixture of urine and semen in the cloaca. There were no evident correlations between the location of the ureteral openings and the birds' habitat, diet, or histology of the coprodeal mucosa. The occurrence of a phallus in eight species of birds was detected, as well as a peculiar vascularization related to the coprodeal epithelium of anseriformes. Together, these data add to the scarce information about the morphophysiology of the avian cloaca, and also contribute to clarify avian phylogenetic linkages.