Changes in hemoglobin function and isoform expression during embryonic development in the American alligator, Alligator mississippiensis

In the developing embryos of egg-laying vertebrates, O2 flux takes place across a fixed surface area of the eggshell and the chorioallantoic membrane. In the case of crocodilians, the developing embryo may experience a decrease in O2 flux when the nest becomes hypoxic, which may cause compensatory adjustments in blood O2 transport. However, whether the switch from embryonic to adult hemoglobin isoforms (isoHb) plays some role in these adjustments is unknown. Here, we provide a detailed characterization of the developmental switch of isoHb synthesis in the American alligator, Alligator mississippiensis. We examined the in vitro functional properties and subunit composition of purified alligator isoHbs expressed during embryonic developmental stages in normoxia and hypoxia (10% O2). We found distinct patterns of isoHb expression in alligator embryos at different stages of development, but these patterns were not affected by hypoxia. Specifically, alligator embryos expressed two main isoHbs, HbI, prevalent at early developmental stages, with a high O2 affinity and high ATP sensitivity, and HbII, prevalent at later stages and identical to the adult protein, with a low O2 affinity and high CO2 sensitivity. These results indicate that whole blood O2 affinity is mainly regulated by ATP in the early embryo and by CO2 and bicarbonate from the late embryo until adult life, but the developmental regulation of isoHb expression is not affected by hypoxia exposure.

Mapping Micro-Level Decision-Making for Alligator Management in North Carolina

Human-carnivore interactions represent a grand challenge to conservation decision-making and legitimacy across all levels of governance. Human populations continue to encroach upon and devastate carnivore habitats and populations, intensifying interactions between a variety of biodiversity interests and beneficiaries. As a result, carnivores most intensely impact those living in their midst, demanding increased attention by local decision makers, who are often best suited to catering to the needs of communities most affected. Their views and desires can serve as a forerunner of public trust and acceptance of policies created. However, due to the complexity of decisions about carnivores, these actors are often overlooked in the formal decision process. To address this need, we applied multi-criteria decision analysis (MCDA) to a case study of American alligator (Alligator mississippiensis) conservation in 10 coastal North Carolina counties to identify and postulate legitimate outcomes. We surveyed 25 local decision makers who are or may be responsible for management decisions concerning the American alligator and asked them to evaluate and indicate the level of importance of salient alligator management elements. Results indicate that decision makers strongly favored the wildlife and social factors when making alligator management decisions, as well as the criteria human well-being, attitudes toward alligators, education programs, and storm mitigation. Respondents favored highly managed and balanced management alternatives to maximize preferred criteria and achieve legitimate alligator management at the local level. These results demonstrate that local decision makers are capable of identifying what is important to alligator management decisions, and can provide an insightful look at trade-offs that need to or could be made to achieve optimal alligator outcomes. We conclude that local decision makers should become more involved in shaping carnivore outcomes to enhance legitimacy of alligator policy and help achieve conservation targets. Future research will need to further expand understandings of local decision makers' decision-making process in other carnivore contexts. Researchers will want to consider using and refining decision analysis to cut through the complexity of carnivore conservation decision-making that exists across wide geopolitical expanses.

Variations in the cerebrospinal fluid dynamics of the American alligator (Alligator mississippiensis)

Background Studies of mammalian CSF dynamics have been focused on three things: paravascular flow, pressure and pulsatility, and “bulk” flow; and three (respective) potential motive forces have been identified: vasomotor, cardiac, and ventilatory. There are unresolved questions in each area, and few links between the different areas. The American alligator (Alligator mississippiensis) has pronounced plasticity in its ventilatory and cardiovascular systems. This study was designed to test the hypothesis that the greater cardiovascular and ventilatory plasticity of A. mississippiensis would result in more variation within the CSF dynamics of this species. Methods Pressure transducers were surgically implanted into the cranial subarachnoid space of 12 sub-adult alligators; CSF pressure and pulsatility were monitored along with EKG and the exhalatory gases. In four of the alligators a second pressure transducer was implanted into the spinal subarachnoid space. In five of the alligators the CSF was labeled with artificial microspheres and Doppler ultrasonography used to quantify aspects of the spinal CSF flow. Results Both temporal and frequency analyses of the CSF pulsations showed highly variable contributions of both the cardiac and ventilatory cycles. Unlike the mammalian condition, the CSF pressure pulsations in the alligator are often of long (~ 3 s) duration, and similar duration CSF unidirectional flow pulses were recorded along the spinal cord. Reduction of the duration of the CSF pulsations, as during tachycardia, can lead to a “summation” of the pulsations. There appears to be a minimum duration (~ 1 s) of isolated CSF pulsations. Simultaneous recordings of cranial and spinal CSF pressures reveal a 200 ms delay in the propagation of the pressure pulse from the cranium to the vertebral canal. Conclusions Most of the CSF flow dynamics recorded from the alligators, are similar to what has been reported from studies of the human CSF. It is hypothesized that the link between ventilatory mechanics and CSF pulsations in the alligator is mediated by displacement of the spinal dura. The results of the study suggest that understanding the CSF dynamics of Alligator may provide unique insights into the evolutionary origins and functional regulation of the human CSF dynamics.

A new role for joint mobility in reconstructing vertebrate locomotor evolution

Reconstructions of movement in extinct animals are critical to our understanding of major transformations in vertebrate locomotor evolution. Estimates of joint range of motion (ROM) have long been used to exclude anatomically impossible joint poses from hypothesized gait cycles. Here we demonstrate how comparative ROM data can be harnessed in a different way to better constrain locomotor reconstructions. As a case study, we measured nearly 600,000 poses from the hindlimb joints of the Helmeted Guineafowl and American alligator, which represent an extant phylogenetic bracket for the archosaurian ancestor and its pseudosuchian (crocodilian line) and ornithodiran (bird line) descendants. We then used joint mobility mapping to search for a consistent relationship between full potential joint mobility and the subset of joint poses used during locomotion. We found that walking and running poses are predictably located within full mobility, revealing additional constraints for reconstructions of extinct archosaurs. The inferential framework that we develop here can be expanded to identify ROM-based constraints for other animals and, in turn, will help to unravel the history of vertebrate locomotor evolution.

Anatomical and histological analyses reveal that tail repair is coupled with regrowth in wild-caught, juvenile American alligators (Alligator mississippiensis)

Reptiles are the only amniotes that maintain the capacity to regenerate appendages. This study presents the first anatomical and histological evidence of tail repair with regrowth in an archosaur, the American alligator. The regrown alligator tails constituted approximately 6–18% of the total body length and were morphologically distinct from original tail segments. Gross dissection, radiographs, and magnetic resonance imaging revealed that caudal vertebrae were replaced by a ventrally-positioned, unsegmented endoskeleton. This contrasts with lepidosaurs, where the regenerated tail is radially organized around a central endoskeleton. Furthermore, the regrown alligator tail lacked skeletal muscle and instead consisted of fibrous connective tissue composed of type I and type III collagen fibers. The overproduction of connective tissue shares features with mammalian wound healing or fibrosis. The lack of skeletal muscle contrasts with lizards, but shares similarities with regenerated tails in the tuatara and regenerated limbs in Xenopus adult frogs, which have a cartilaginous endoskeleton surrounded by connective tissue, but lack skeletal muscle. Overall, this study of wild-caught, juvenile American alligator tails identifies a distinct pattern of wound repair in mammals while exhibiting features in common with regeneration in lepidosaurs and amphibia.

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.

New early Pleistocene Alligator (Eusuchia: Crocodylia) from Florida bridges a gap in Alligator evolution

The American Alligator (Alligator mississippiensis) is one of two species of Alligator in the modern world. It is only distantly related to the other extant species (A. sinensis), with much closer relatives known from the geologic past of North America. A disparity exists, though, in the fossil record between A. mississippiensis and its close relative, the late Miocene (?)—early Pliocene A. mefferdi. While A. mississippiensis is known from the mid-Pleistocene and later, few Alligator remains were known from the earliest Pleistocene of North America until the discovery of the Haile 7C and 7G early Pleistocene (Blancan Land Mammal Age) sites from Alachua County, Florida. The Haile alligators exhibit a suite of characters from both A. mississippiensis and A. mefferdi, displaying intermediate morphology in time. The Haile alligators are distinct from either of the aforementioned taxa, and a new species, Alligator hailensis is suggested, bridging an important gap in the evolution of the American Alligator.