Lafayette, LA, United States
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Eme J.,University of North Texas | Elsey R.M.,Rockefeller Wildlife Refuge | Crossley D.A.,University of North Texas
Comparative Biochemistry and Physiology - A Molecular and Integrative Physiology | Year: 2013

We used arterial tyramine injections to study development of sympathetic actions on in vivo heart rate and blood pressure in embryonic, hatching and yearling female American alligators. Tyramine is a pharmacological tool for understanding comparative and developmental sympathetic regulation of cardiovascular function, and this indirect sympathomimetic agent causes endogenous neuronal catecholamine release, increasing blood pressure and heart rate. Arterial tyramine injection in hatchling and yearling alligators caused the typical vertebrate response - rise in heart rate and blood pressure. However, in embryonic alligators, tyramine caused a substantial and immediate bradycardia at both 70% and 90% of embryonic development. This embryonic bradycardia was accompanied by hypotension, followed by a sustained hypertension similar to the hatchling and juvenile responses. Pretreatment with atropine injection (cholinergic receptor blocker) eliminated the embryonic hypotensive bradycardia, and phentolamine pretreatment (α-adrenergic receptor blocker) eliminated the embryonic hypotensive and hypertensive responses but not the bradycardia. In addition, hexamethonium pretreatment (nicotinic receptor blocker) significantly blunted embryos' bradycardic tyramine response. However, pretreatment with 6-hydroxydopamine, a neurotoxin that destroys catecholaminergic terminals, did not eliminate the embryonic bradycardia. Tyramine likely stimulated a unique embryonic response - neurotransmitter release from preganglionic nerve terminals (blocked with hexamethonium) and an acetylcholine mediated bradycardia with a secondary norepinephrine-dependent sustained hypertension. In addition, tyramine appears to stimulate sympathetic nerve terminals directly, which contributed to the overall hypertension in the embryonic, hatchling and yearling animals. Data demonstrated that humoral catecholamine control of cardiovascular function was dominant over the immature parasympathetic nervous system in developing alligator embryos, and suggested that sympathetic and parasympathetic nerve terminals were present and developing in ovo but were not tonically active. © 2013 Elsevier Inc.


Keenan S.W.,Saint Louis University | Keenan S.W.,University of Tennessee at Knoxville | Elsey R.M.,Rockefeller Wildlife Refuge
Integrative and Comparative Biology | Year: 2015

Vertebrates coexist with microorganisms in diverse symbiotic associations that range from beneficial to detrimental to the host. Most research has aimed at deciphering the nature of the composite microbial assemblage's genome, or microbiome, from the gastrointestinal (GI) tract and skin of mammals (i.e., humans). In mammals, the GI tract's microbiome aids digestion, enhances uptake of nutrients, and prevents the establishment of pathogenic microorganisms. However, because the GI tract microbiome of the American alligator (Alligator mississippiensis) is distinct from that of all other vertebrates studied to date, being comprised of Fusobacteria in the lower GI tract with lesser abundances of Firmicutes, Proteobacteria, and Bacteroidetes, the function of these assemblages is largely unknown. This review provides a synthesis of our current understanding of the composition of alligators' microbiomes, highlights the potential role of microbiome members in alligators' health (the good), and presents a brief summary of microorganisms detrimental to alligators' health (the bad) including Salmonella spp. and others. Microbial assemblages of the GI tract have co-evolved with their vertebrate host over geologic time, which means that evolutionary hypotheses can be tested using information about the microbiome. For reptiles and amphibians, the number of taxa studied at present is limited, thereby restricting evolutionary insights. Nevertheless, we present a compilation of our current understanding of reptiles' and amphibians' microbiomes, and highlight future avenues of research (the unknown). As in humans, composition of microbiome assemblages provides a promising tool for assessing hosts' health or disease. By further exploring present-day associations between symbiotic microorganisms in the microbiomes of reptiles and amphibians, we can better identify good (beneficial) and bad (detrimental) microorganisms, and unravel the evolutionary history of the acquisition of microbiomes by these poorly-studied vertebrates. © 2015 The Author.


News Article | October 18, 2016
Site: scienceblogs.com

Researchers from the University of Manchester, University of North Texas – Denton, and the Rockefeller Wildlife Refuge – Grand Chenier, Louisiana teamed up to explore the effects of exposure to low oxygen on embryonic American alligators (Alligator mississippiensis). Alligator eggs are often laid in nests where oxygen concentrations can reportedly vary between 11-20% (21% is normal atmospheric levels). This is really important as issues related to embryonic development could continue to affect animals throughout their adult lives as well. The results of the study were recently published in the American Journal of Physiology – Regulatory, Integrative and Comparative Physiology. The researchers found that embryos exposed to low oxygen were smaller and had larger hearts even into their juvenile years. In addition, the mitochondria of juvenile alligators that had been exposed to low oxygen were more efficient at using oxygen. These adaptations may help the animals adjust well to low oxygen environments. In contrast, a recent review article written by Patterson and Zhang suggests that human embryos exposed to low oxygen do not fare as well as alligators. While a period of hypoxia is important in normal development, prolonged exposure of embryos to low oxygen can result abnormal heart structure and function. In fact, it is thought that these embryos may be more prone to heart disease as adults. Sources: Galli GLJ, Crossley J, Elsey R, Dzialowski EM, Shiels HA, Crossley II DA. Developmental Plasticity of Mitochondrial Function in American Alligators, Alligator mississippiensis. American Journal of Physiology – Regulatory, Integrative and Comparative Physiology. In press. doi:10.1152/ajpregu.00107.2016


Lance V.A.,San Diego State University | Elsey R.M.,Rockefeller Wildlife Refuge | Trosclair Iii P.L.,Rockefeller Wildlife Refuge
South American Journal of Herpetology | Year: 2015

Abstract. Very little is known about the attainment of puberty in reptiles. In the American alligator (Alligator mississippiensis) males are assumed to be sexually mature at about 1.8 m in total length, but it is not clear at what size they produce testosterone, spermatozoa and mate successfully. We re-examined this question by studying plasma testosterone levels in blood samples from a large sample of alligators (∼1,500) collected every month of the year and ranging in size from approximately 61 cm (2 ft) to 360 cm (11.5 ft). Testosterone values ranged from 0.05-115.41 ng/mL. All size classes of alligators exhibited a seasonal cycle in testosterone levels, but the concentrations were size-dependent: the larger the alligator the higher the testosterone. In all size-classes testosterone reached a peak in the breeding season (March-May). Mean testosterone in the largest size-class during breeding was 75 ng/mL whereas in the smallest size-class peak testosterone was less than 3 ng/mL. The smallest size-class (59-89 cm) showed an additional rise in testosterone in late summer. The attainment of sexual maturity in alligators appears to be closely associated with growth and is a gradual process lasting several years. Sexually immature alligators show a seasonal pattern of testosterone secretion similar to that of adults, but the values are significantly lower. © 2015 Brazilian Society of Herpetology.


Larsson H.C.,McGill University | Heppleston A.C.,McGill University | Elsey R.M.,Rockefeller Wildlife Refuge
Journal of Experimental Zoology Part B: Molecular and Developmental Evolution | Year: 2010

The three-fingered state of the avian manus poses intriguing questions about the evolution of digit reduction. Although digit reduction in most tetrapods appears to be the product of straightforward digit loss, avian digit reduction may have occurred with a dissociation of digit position from digit identity. The three digits of birds have the ancestral identities of I, II, and III but develop from an early pentadactyl ground state from digital anlage 2, 3, and 4. A series of hypotheses have been proposed in an attempt to explain this disparity, including a recent suggestion that the anteriormost condensation visible in the avian limb bud is in fact a vestigial structure from a hexadactyl ancestral ground state. We investigated this proposal by presenting sets of compatible evolutionary developmental trajectories starting from a hexadactyl state to test hypotheses of digit reduction. The development of skeletogenic mesenchymal condensations in a crocodylian, the closest extant relative to birds, is used to identify any extra precartiloginous digital vestiges. A developmental series of Alligator mississippiensis forelimb buds reveal only five digital anlagen, supports a pentadactyl ground state for the archosaurian manus, and rejects portions of the evolutionary developmental trajectories proposed. This condition lends further support to the contribution of a homeotic transformation during digit reduction in avian ancestry to account for the dissociation between digital identity and developmental position. © 2010 Wiley-Liss, Inc., A Wiley Company.


Allen V.,Royal Veterinary College University of London | Elsey R.M.,Rockefeller Wildlife Refuge | Jones N.,Royal Veterinary College University of London | Wright J.,Royal Veterinary College University of London | Hutchinson J.R.,Royal Veterinary College University of London
Journal of Anatomy | Year: 2010

Crocodylians exhibit a fascinating diversity of terrestrial gaits and limb motions that remain poorly described and are of great importance to understanding their natural history and evolution. Their musculoskeletal anatomy is pivotal to this diversity and yet only qualitative studies of muscle-tendon unit anatomy exist. The relative masses and internal architecture (fascicle lengths and physiological cross-sectional areas) of muscles of the pectoral and pelvic limbs of American alligators (Alligator mississippiensis Daudin 1801) were recorded for an ontogenetic series of wild specimens (n = 15, body masses from 0.5 to 60 kg). The data were analysed by reduced major axis regression to determine scaling relationships with body mass. Physiological cross-sectional areas and therefore muscle force-generating capacity were found to be greater in the extensor (anti-gravity) muscles of the pelvic limb than in the pectoral limb, reflecting how crocodylians differ from mammals in having greater loading of the hindlimbs than the forelimbs. Muscle masses and architecture were generally found to scale isometrically with body mass, suggesting an ontogenetic decrease in terrestrial athleticism. This concurs with the findings of previous studies showing ontogenetic decreases in limb bone length and the general scaling principle of a decline of strength: weight ratios with increasing size in animals. Exceptions to isometric scaling found included positive allometry in fascicle length for extensor musculature of both limbs, suggesting an ontogenetic increase in working range interpreted as increasing postural variability - in particular the major hip extensors - the interpretation of which is complicated by previous described ontogenetic increase of moment arms for these muscles. © 2010 The Authors. Journal compilation © 2010 Anatomical Society of Great Britain and Ireland.


Selman W.,University of Southern Mississippi | Selman W.,Rockefeller Wildlife Refuge
Herpetological Conservation and Biology | Year: 2012

Graptemys flavimaculata (Yellow-blotched Sawback) is a small, highly aquatic turtle that is endemic to rivers and large creeks of the Pascagoula River system of southeastern Mississippi, USA. Little is known about geographic variation in population structure, shape morphology, and sexual size dimorphism (SSD) throughout the drainage. I captured and measured G. flavimaculata from three sites in 2005 and 2006. I analyzed female head width at two of these sites in 2008. Results indicate that body size and population structure vary across a geographic gradient; turtles from the Pascagoula River site were generally larger (both body mass and plastron length) relative to two upstream sites on two tributaries, the Leaf and Chickasawhay rivers. Additionally, body shape in females varied among populations, with Pascagoula River females having a more domed shape than upstream sites where turtles have a more streamlined shape. There was little difference in male shapes among sites. Female-biased SSD typified all three populations with SSD being less pronounced in the two upstream sites. Female head width was significantly different across sites (Pascagoula > Leaf), while there was no difference among sites for male claw length. Presumably, synergistic factors influence population structure, shape morphology, and sexual size dimorphism in Graptemys flavimaculata including: 1) food availability; 2) presence of competitors; 3) thermal environment; 4) presence of alligators; and 5) fluvial conditions. © 2012. Will Selman. All Rights Reserved.


Selman W.,Rockefeller Wildlife Refuge | Jawor J.M.,University of Southern Mississippi | Qualls C.P.,University of Southern Mississippi
Copeia | Year: 2012

Currently, little is known about the seasonal variation of corticosterone (CORT) levels, either baseline or stress response, within freshwater turtles. We conducted a seasonal CORT study with a species of freshwater turtle, Graptemys flavimaculata (Yellow-blotched Sawback; family Emydidae), that is endemic to the Pascagoula River system of southeastern Mississippi. Graptemys flavimaculata is commonly observed while basking on deadwood snags, with us using basking traps and dip nets as active capture methods. We caught both male (n = 60) and female (n = 49) turtles during the months of April-October during 2007 and 2008. Immediately after capture, we collected an initial blood sample, confined the turtle for 35 minutes, and then took a second blood sample. Competitive binding radioimmunoassays were done to determine CORT levels. Time zero CORT levels for both sexes were generally lower than previously reported levels for other turtle species, likely due to the trapping methods used. By time 35 min, CORT levels were significantly elevated relative to initial levels. We did not detect seasonal differences in time zero CORT levels for males or females. However, seasonal differences in time 35 CORT levels for males were detected, with higher levels observed during summer months (July, August) relative to spring (April) and fall (October) months. Seasonal differences were also detected in time 35 CORT levels of females, with lower levels observed during July (nesting season) relative to September. This study provides novel information and insight into the differences in seasonal physiological demands for this species, and aquatic turtle species in general, while also providing probable connections of physiology to seasonal life history events. © 2012 by the American Society of Ichthyologists and Herpetologists.


Elsey R.M.,Rockefeller Wildlife Refuge | Trosclair P.L.,Rockefeller Wildlife Refuge
Southeastern Naturalist | Year: 2016

Coastal marshes of Louisiana provide nesting habitat for Alligator mississippiensis (American Alligator). Helicopters are typically used to locate Alligator nests in remote interior marshes. We tested the use of an unmanned aerial vehicle (UAV) to detect Alligator nests on Rockefeller Wildlife Refuge in Grand Chenier, LA. Three brief flights with a combined search time of approximately 25 minutes and 9 seconds were conducted in a single afternoon, covering 28.2 ha. While in the field, we observed 6 Alligator nests with the UAV, and later review of video imagery recorded allowed us to detect an additional 6 Alligator nests. The use of UAVs may be a useful tool for detecting Alligator nests.


Selman W.,Rockefeller Wildlife Refuge | Hess Jr. T.J.,Rockefeller Wildlife Refuge | Salyers B.,Rockefeller Wildlife Refuge | Salyers C.,Rockefeller Wildlife Refuge
Southeastern Naturalist | Year: 2012

Translocation of wildlife is a valuable tool for managers to alleviate impacts of human/wildlife conflicts, habitat fragmentation, and small population sizes. Pelecanus occidentalis (Brown Pelican) were previously successfully translocated into Louisiana in 19601980s and had rebounded significantly prior to the Deepwater Horizon Oil Spill in April 2010. The Deepwater Horizon Oil Spill had a dramatic impact on southeastern Louisiana, including the people, wildlife, and coastal habitats of the region. We translocated 182 oil-rehabilitated Brown Pelicans from southeastern Louisiana to an area non-impacted by the oil spill in southwestern Louisiana (Rabbit Island, Cameron Parish). Daily surveys were conducted at the island for six weeks and documented mortality, movements, integration with local pelican flocks, persistence of pelicans at the island, and the role of supplemental feeding. We documented no mortality of rehabilitated birds and found that translocated Brown Pelicans readily integrated with local pelican flocks. Supplemental feeding likely contributed to the persistence of pelicans at Rabbit Island from weeks 1 to 4. By weeks 4 to 6, many local and translocated pelicans moved away from the island, likely due to a combination of natural and human-induced factors. After the initial stages of the translocation, we tentatively suggest that the program was a success and propose recommendations for future translocation attempts with Brown Pelicans.

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