David Rostal - Academia.edu (original) (raw)

Papers by David Rostal

Southeastern Naturalist, Jun 14, 2023

Great Plains Research, 2016

Th e Texas Tortoise covers the life work of Drs. Rose and Judd, who spent much of their scientifi... more Th e Texas Tortoise covers the life work of Drs. Rose and Judd, who spent much of their scientifi c careers studying this ancient survivor. It provides a wealth of information on this species but also warns us of its plight. Included are many blackandwhite fi gures and drawings as well as two sets of excellent color photographs. Th e preface provides insight into the authors’ motivation for undertaking this project. In the introduction, I enjoyed reading the history of the early naturalist Jean Louis Berlandier, aft er whom the tortoise would later be named. In each successive chapter that follows, the authors explain the natural history and biology of the Texas tortoise in a way that readers will enjoy. Chapter 1 not only describes the relationships between the fi ve currently recognized species of North American tortoises but also explains the complexity of determining a genus and species. Chapter 2 follows with an indepth description of the species’ range and habitat. North American tortoises once traveled throughout the Great Plains of North America during the Pleistocene but are now restricted to more southern habitats. We know little about the species in the southern part of its range in Mexico. Following chapters discuss aspects of the Texas tortoise’s biology and allude to areas that need further research or study. Th ese chapters also cover reproduction, sexual size dimorphism, growth, temperature regulation, and population ecology. Th e work concludes with a discussion of conservation and the future of the Texas tortoise, which is experiencing the same declines witnessed for turtles and tortoises around the world. I especially enjoyed the way the authors inserted anecdotes from the past. Th e book provides a thorough coverage of our understanding of the Texas tortoises but occasionally falls short in its current coverage of more recent literature on North American tortoises. Th ere is some redundancy, but it is limited and does not hinder the fl ow of the book. Th at being said, I found its coverage of early foundational papers by early scientists such as Walter Auff enberg to be enlightening. Th e authors in some cases express their strong personal opinions regarding aspects of the biology and conservation of the Texas tortoises, which I appreciated. Many of these classic papers are hard to access today in our modern world of electronic literature. From that standpoint alone it is a book anyone interested in tortoises or turtles will want to have in their library. I have thoroughly enjoyed reading the book and know I will fi nd it an important reference in my personal library. Th e Texas Tortoise is a must for anyone interested in tortoises or herpetology.

Johns Hopkins University Press eBooks, 2014

Southeastern Naturalist, Jun 14, 2023

Southeastern Naturalist, Nov 17, 2022

PeerJ, Jun 14, 2022

Many turtle species have temperature-dependent sex determination (TSD), raising the prospect that... more Many turtle species have temperature-dependent sex determination (TSD), raising the prospect that climate change could impact population dynamics by altering sex ratios. Understanding how climate change will affect populations of animals with TSD requires a reliable and minimally invasive method of identifying the sexes of young individuals. This determination is challenging in many turtles, which often lack conspicuous external sexual dimorphism until years after hatching. Here, we explore four alternatives for sexing three age classes of captive-reared young gopher tortoises (Gopherus polyphemus), a terrestrial turtle of conservation concern native to the southeastern United States: (1) naive testosterone levels, (2) testosterone levels following a follicle stimulating hormone (FSH) challenge, (3) linear morphological measurements, and (4) geometric morphometrics. Unlike some other turtle species, male and female neonatal gopher tortoises have overlapping naive testosterone concentration distributions, justifying more complicated methods. We found that sex of neonates (<7 days old) is best predicted by a ''random forest'' machine learning model with naive testosterone levels and morphological measurements (8% out-of-bag error). Sex of hatchlings (4-8 months old) was predicted with 11% error using a simple threshold on naive testosterone levels, or with 4% error using a simple threshold on post-FSH testosterone levels. Sex of juveniles (approximately 3.5 years old) was perfectly predicted using a simple threshold on naive testosterone levels. Sexing hatchlings at >4 months of age is the easiest and most reliable non-surgical method for sex identification. Given access to a rearing facility and equipment to perform hormone assays, these methods have the potential to supplant laparoscopic surgery as the method of choice for sexing young gopher tortoises.

The Journal of Wildlife Management, 2021

ABSTRACTLong‐term datasets are required to understand the response of long‐lived organisms (e.g.,... more ABSTRACTLong‐term datasets are required to understand the response of long‐lived organisms (e.g., gopher tortoises [Gopherus polyphemus]) to management actions, such as prescribed burns. Our objective was to estimate the effects of prescribed burning on gopher tortoise population dynamics over decadal time frames at Fort Stewart Army Reserve, southeastern Georgia, USA. We captured and marked adult tortoises from 1994–2020. In addition, since the early 1990s, managers at Fort Stewart collected spatial records of prescribed burns; thus, we could compare demography of the population to prescribed burning. We used a Bayesian hierarchical model (open population Jolly‐Seber model) to estimate population parameters (emigration and survival, immigration and recruitment, and adult abundance) and their relationships with years since burn. We observed opposing responses to years since burn at 2 sites: abundance and the probability of staying (survival plus not emigrating) increased within 1 si...

Presented at Meeting of American Society of Ichthyologists and Herpetologist

General and Comparative Endocrinology, 2016

Anthropogenic stressors such as habitat loss are a global problem for wildlife. Coastal developme... more Anthropogenic stressors such as habitat loss are a global problem for wildlife. Coastal development in the United States has replaced estuary shorelines with hard erosion barriers. In Barnegat Bay, New Jersey, the diamondback terrapin (Malaclemys terrapin) encounters these barriers when approaching upland beaches for nesting. To determine the effects of shoreline barriers on this threatened species' nesting abilities, we measured adrenocortical response (i.e., stress response) by comparing natural corticosterone and testosterone levels of 91 terrapins following in situ exposure to either an experimentally blocked, or open nesting beach. In addition, we exposed 15 individuals, from various nesting beaches, to handling stress to identify acute corticosterone secretion, finding a significant increase over 60 min to 8 ng/ml. Corticosterone did not reach this level in terrapins exposed to barriers. Corticosterone and testosterone levels were not significantly higher among terrapins exposed to barriers compared to those at open reference beaches. This lack of a stress response suggests that terrapins do not physiologically respond to barriers when they approach nesting beaches and thus are not stressed. This may be due to an adaptive trait to help female turtles complete the nesting process despite the natural stresses inherent to coming on land. Our study suggests that this lack of stress response is also applied to non-natural, human made nesting barriers. If terrapins are not physiologically capable of adapting to shoreline barriers, future erosion control structures could support terrapin nesting with periodic upland access points. This endocrinological study provides a more quantitative approach to guiding management of anthropogenic stressors upon wildlife.

This talk was given during the Southeast Regional Meeting of the Society for Integrative and Comp... more This talk was given during the Southeast Regional Meeting of the Society for Integrative and Comparative Biology

The effects of testosterone (T) on territorial lizards have been studied extensively; however, th... more The effects of testosterone (T) on territorial lizards have been studied extensively; however, the effects of T on non-territorial lizards have not. In territorial lizards, T has been suggested as a possible mediator of seasonal increases in whole-animal performance capacities (i.e. sprint speed and bite force), which are important factors in maintaining territories and winning male-male competitions. Previous work in our lab has shown that in Aspidoscelis sexlineata, a common non-territorial lizard, bite force, locomotor performance (measured as the max. time until exhaustion), and T are each greatest during the breeding season; thereby suggesting that T also mediates seasonal increases in performance for this species. Furthermore, T implants have been shown to successfully elevate circulating T levels in A. sexlineata. However, the T implants failed to increase whole-animal performance capacities, and hence suggest a training effect. The current study will test the effects of training on locomotor performance capacities and morphology (i.e. locomotor muscle size & composition). Thirty adult male A. sexlineata were assigned to one of three treatment groups: T implant + training, empty implant + training, and empty implant without training. Training consisted of 3 performance measures: treadmill endurance, burst speed, and maximal exertion. At the end of the study, changes in muscle size, muscle fiber size, or fiber-type composition were assessed for multiple hindlimb muscles using histochemical analyses to determine the influence of treatment group (T, training regime). This research will further isolate the role of T and training on the morphological factors affecting seasonal locomotor performance in non-territorial species

Numerous studies have examined the effects of testosterone on behavior in territorial lizards, bu... more Numerous studies have examined the effects of testosterone on behavior in territorial lizards, but few have explored the role of testosterone (T) in non-territorial species. Here, we experimentally manipulated T levels in Aspdidoscelis sexlineatus, a common non-territorial lizard. During the breeding season, males exhibit mate guarding, and will follow a female for several days after copulation. Male-to-male interactions during the breeding season involve chasing and occasionally escalate into fights with biting. Therefore, high bite force and high endurance capacity should be advantageous to retain exclusive access to females and ensure paternity. In territorial lizards, T levels peak with the breeding season and several studies have cited T as a possible mediator of the seasonal increases in performance (e.g. bite force and locomotor performance). Fluctuating T levels have been observed in A. sexlineatus; however, the role that T plays in the performance of A. sexlineatus or other mate guarding species remains unknown. For this study, male racerunners were captured and blood samples were drawn immediately to quantify T levels. Lizards were then returned to the lab where locomotor performance (endurance), bite force, and morphological data were collected. Following performance trials, lizards received silastic T implants. Lizards were housed in the lab for four weeks where locomotor endurance and bite force performance were measured biweekly. Additionally, a blood sample was collected every two weeks to monitor T levels. This research will quantify the morphological and physiological factors affecting performance in A. sexlineatus and provide valuable data concerning how T affects alternative mating systems

Choice Reviews Online, Feb 24, 2015

Herpetological Monographs, 2016

Abstract: The conservation of large, long-lived turtle species can be a challenging issue becaus... more Abstract: The conservation of large, long-lived turtle species can be a challenging issue because their life-history strategies make populations sensitive to changes in adult survivorship and populations may be difficult to sample. The Alligator Snapping Turtle (Macrochelys temminckii) is a large freshwater turtle species occurring in North America for which commercial harvest has severely reduced populations throughout the species range. Given recent population declines and a general deficit of demographic knowledge for Macrochelys, we conducted a mark–recapture study of M. temminckii from 1997–2013 in Spring Creek, Georgia, USA. We made 166 captures of 75 individuals using baited hoop-net traps and skin-diving searches. The observed and estimated population structure described the adult sex ratio as even and adults as more abundant than juveniles. Apparent survival was higher for adult males (0.98) and females (0.95) than for juveniles (0.86), and we estimated a population density of 13–14 turtles/stream kilometer. The survival estimates for adult M. temminckii are among the highest of all freshwater turtle species reported in the literature. We used the empirical demographic parameters described here and a literature review to build an updated population model for M. temminckii; the model estimated a finite rate of population increase consistent with a growing population (λ = 1.036) at Spring Creek, and population viability analysis found the population growing over the next 50 yr in 100% of simulations. Application of our model to published survival estimates from two impacted western populations indicated a declining population (λ = 0.563) with a high risk of extirpation in Oklahoma and a population with a slow rate of decline (λ = 0.978) but approaching stability in Arkansas. Simulations identified combinations of survival values which generate viable populations and also characterized population structure resulting from viable scenarios. This is the first study to document a stable and viable population of Macrochelys. We suggest that the population parameters described at Spring Creek are the best approximation of reference demographic conditions for Macrochelys to date, and this study provides a general framework applicable for large, long-lived, endangered turtle species for which demographic data are unavailable.

Herpetological Monographs, 1994

... Extensive observations of the behavior of the tortoises in these pens were carried out from A... more ... Extensive observations of the behavior of the tortoises in these pens were carried out from April-September, 1992, by Niblick et al. (1994). ... Female solicitation of particular males and avoid-ance of others has been observed in captive desert tortoises (Niblick et al., 1994). ...

General and Comparative Endocrinology, 2001

To characterize seasonal changes in thyroid function in a terrestrial reptile, thyroid hormones w... more To characterize seasonal changes in thyroid function in a terrestrial reptile, thyroid hormones were measured over a period of 2 years in desert tortoises, Gopherus agassizii, maintained at the Desert Tortoise Conservation Center in Las Vegas, Nevada. In all samples, triiodothyronine was nondetectable (less than 0.1 ng/ml). Thyroxine (T(4)) exhibited distinct cycles in both sexes, being lowest during hibernation and rising toward the time of emergence. Females exhibited only one peak in T(4), during the early spring. In males, T(4) levels peaked in early spring and again in late summer. The desert tortoise has distinct activity patterns that include increased feeding, mating, and locomotor activity in the early spring and increased mating and combat in the late summer. In an experiment to determine whether food intake influences T(4), food was withheld for 2 weeks. Compared to continuously fed controls, T(4) declined significantly in unfed tortoises, but increased significantly within 36 h of refeeding, indicating that thyroid activity is responsive to nutrient intake. The second seasonal peak of T(4) only in males suggests that male reproductive activity in late summer is associated with thyroid activation. To evaluate this possibility, adult, subadult, and juvenile males were sampled during the months of the second seasonal peak in T(4). Although all three age groups showed similar foraging and thermoregulatory behaviors, T(4) peaked in July only in the reproductively active adults, which also exhibited significantly higher testosterone levels. Elevated T(4) in desert tortoises is thus associated with periods of increased feeding and reproductive activity, supporting a role for thyroid hormones in these energy-demanding activities.

General and Comparative Endocrinology, 2009

Ultrasonography has been used effectively to study reproduction in a variety of reptile species, ... more Ultrasonography has been used effectively to study reproduction in a variety of reptile species, but its application to crocodilians has been relatively limited. We present results from a study testing the efficacy of using ultrasonography to monitor reproduction in the American alligator, Alligator mississippiensis. Ultrasound results were then compared with plasma hormone levels. A total of 124 females were examined during March, April, May, and early June (2001-2003). Ultrasound results were validated on a series of reproductive females (n=14) necropsied for other studies. Previtellogenic follicles, vitellogenic follicles, recently shelled eggs, fully developed well-calcified eggs, and atretic follicles were readily discernible with ultrasound in mature females. Reproductive structures were observed in 57 females of which 43 were actively reproductive, while 14 were non-reproductive, but contained large atretic follicles from prior years. Oviducts were discernible in females with eggs. Ovarian state was also correlated with hormone levels. These results are in agreement with previous studies that showed that 50% or less of the adult female alligator population is reproductively active in a given year. Ultrasonography can be used to make an accurate assessment of reproductive condition in wild alligator populations.

Endangered Species Research, 2008

In an attempt to better understand the reproductive cycle of adult male loggerhead sea turtles, s... more In an attempt to better understand the reproductive cycle of adult male loggerhead sea turtles, several techniques were used to assess their reproductive activity, including plastron-softness analysis, ultrasonography, laparoscopy, testicular biopsy samples, and measuring testosterone levels. Stress levels were evaluated on a subset of turtles by measuring testosterone and corticosterone concentrations after capture and before release. A total of 40 adult males were captured in the Port Canaveral shipping channel in April of 2006 and 2007. Four turtles were classified as reproductively inactive based on laparoscopic examination, histology of the testes, and testosterone levels. The relative area of plastron softness was significantly lower for the inactive males compared to the active males. Ultrasonography proved to be a promising tool, as we were able to visualize both the testes and epididymides on the turtles examined. Furthermore, we found no statistical difference in epididymal duct diameters measured by ultrasonography and during laparoscopy, suggesting that ultrasonography could be used successfully as a substitute for laparoscopic surgery. Finally, testosterone levels separated into 2 distinct groups, with concentrations of the inactive males below 5 ng ml-1 , and concentrations of the active males reaching 188 ng ml-1. We conclude that in order to reduce stress levels due to capture and handling, especially during laparoscopy, ultrasonography and plastron analysis could be used together as a way to determine the reproductive activity of adult males in the field. The results from this study also suggest that not all adult males participate in mating activity each year.

General and Comparative Endocrinology, 2001

The reproductive endocrinology of nesting leatherback turtles (Dermochelys coriacea) was studied ... more The reproductive endocrinology of nesting leatherback turtles (Dermochelys coriacea) was studied during the 1996-1997 and 1997-1998 nesting seasons at Los Baulas National Park, Playa Grande, Costa Rica. Blood samples were collected from nesting females throughout the season. Females were observed to nest up to 10 times during the nesting season. Plasma steroids were measured by radioimmunoassay and total plasma calcium was measured by flame atomic absorption spectrophotometry. Plasma testosterone and plasma estradiol levels declined throughout the nesting cycle of the female. Testosterone declined from a mean of 10.18 +/- 0.77 ng/ml at the beginning of the nesting cycle to 1.73 +/- 0.34 ng/ml at the end of the nesting cycle. Estradiol declined in a similar manner, ranging from a mean of 190.95 +/- 16.80 pg/ml at the beginning of the nesting cycle to 76.52 +/- 12.66 pg/ml at the end of the nesting cycle. Plasma progesterone and total calcium levels were relatively constant throughout the nesting cycle. Lack of fluctuation of total calcium levels, ranging from a mean high of 97.46 +/- 11.37 microg/ml to a mean low of 64.85 +/- 11.20 microg/ml, further suggests that vitellogenesis is complete prior to the arrival of the female at the nesting beach. Clutch size (both yolked and yolkless eggs) did not vary over the course of the nesting cycle.

Southeastern Naturalist, Jun 14, 2023

Great Plains Research, 2016

Th e Texas Tortoise covers the life work of Drs. Rose and Judd, who spent much of their scientifi... more Th e Texas Tortoise covers the life work of Drs. Rose and Judd, who spent much of their scientifi c careers studying this ancient survivor. It provides a wealth of information on this species but also warns us of its plight. Included are many blackandwhite fi gures and drawings as well as two sets of excellent color photographs. Th e preface provides insight into the authors’ motivation for undertaking this project. In the introduction, I enjoyed reading the history of the early naturalist Jean Louis Berlandier, aft er whom the tortoise would later be named. In each successive chapter that follows, the authors explain the natural history and biology of the Texas tortoise in a way that readers will enjoy. Chapter 1 not only describes the relationships between the fi ve currently recognized species of North American tortoises but also explains the complexity of determining a genus and species. Chapter 2 follows with an indepth description of the species’ range and habitat. North American tortoises once traveled throughout the Great Plains of North America during the Pleistocene but are now restricted to more southern habitats. We know little about the species in the southern part of its range in Mexico. Following chapters discuss aspects of the Texas tortoise’s biology and allude to areas that need further research or study. Th ese chapters also cover reproduction, sexual size dimorphism, growth, temperature regulation, and population ecology. Th e work concludes with a discussion of conservation and the future of the Texas tortoise, which is experiencing the same declines witnessed for turtles and tortoises around the world. I especially enjoyed the way the authors inserted anecdotes from the past. Th e book provides a thorough coverage of our understanding of the Texas tortoises but occasionally falls short in its current coverage of more recent literature on North American tortoises. Th ere is some redundancy, but it is limited and does not hinder the fl ow of the book. Th at being said, I found its coverage of early foundational papers by early scientists such as Walter Auff enberg to be enlightening. Th e authors in some cases express their strong personal opinions regarding aspects of the biology and conservation of the Texas tortoises, which I appreciated. Many of these classic papers are hard to access today in our modern world of electronic literature. From that standpoint alone it is a book anyone interested in tortoises or turtles will want to have in their library. I have thoroughly enjoyed reading the book and know I will fi nd it an important reference in my personal library. Th e Texas Tortoise is a must for anyone interested in tortoises or herpetology.

Johns Hopkins University Press eBooks, 2014

Southeastern Naturalist, Jun 14, 2023

Southeastern Naturalist, Nov 17, 2022

PeerJ, Jun 14, 2022

Many turtle species have temperature-dependent sex determination (TSD), raising the prospect that... more Many turtle species have temperature-dependent sex determination (TSD), raising the prospect that climate change could impact population dynamics by altering sex ratios. Understanding how climate change will affect populations of animals with TSD requires a reliable and minimally invasive method of identifying the sexes of young individuals. This determination is challenging in many turtles, which often lack conspicuous external sexual dimorphism until years after hatching. Here, we explore four alternatives for sexing three age classes of captive-reared young gopher tortoises (Gopherus polyphemus), a terrestrial turtle of conservation concern native to the southeastern United States: (1) naive testosterone levels, (2) testosterone levels following a follicle stimulating hormone (FSH) challenge, (3) linear morphological measurements, and (4) geometric morphometrics. Unlike some other turtle species, male and female neonatal gopher tortoises have overlapping naive testosterone concentration distributions, justifying more complicated methods. We found that sex of neonates (<7 days old) is best predicted by a ''random forest'' machine learning model with naive testosterone levels and morphological measurements (8% out-of-bag error). Sex of hatchlings (4-8 months old) was predicted with 11% error using a simple threshold on naive testosterone levels, or with 4% error using a simple threshold on post-FSH testosterone levels. Sex of juveniles (approximately 3.5 years old) was perfectly predicted using a simple threshold on naive testosterone levels. Sexing hatchlings at >4 months of age is the easiest and most reliable non-surgical method for sex identification. Given access to a rearing facility and equipment to perform hormone assays, these methods have the potential to supplant laparoscopic surgery as the method of choice for sexing young gopher tortoises.

The Journal of Wildlife Management, 2021

ABSTRACTLong‐term datasets are required to understand the response of long‐lived organisms (e.g.,... more ABSTRACTLong‐term datasets are required to understand the response of long‐lived organisms (e.g., gopher tortoises [Gopherus polyphemus]) to management actions, such as prescribed burns. Our objective was to estimate the effects of prescribed burning on gopher tortoise population dynamics over decadal time frames at Fort Stewart Army Reserve, southeastern Georgia, USA. We captured and marked adult tortoises from 1994–2020. In addition, since the early 1990s, managers at Fort Stewart collected spatial records of prescribed burns; thus, we could compare demography of the population to prescribed burning. We used a Bayesian hierarchical model (open population Jolly‐Seber model) to estimate population parameters (emigration and survival, immigration and recruitment, and adult abundance) and their relationships with years since burn. We observed opposing responses to years since burn at 2 sites: abundance and the probability of staying (survival plus not emigrating) increased within 1 si...

Presented at Meeting of American Society of Ichthyologists and Herpetologist

General and Comparative Endocrinology, 2016

Anthropogenic stressors such as habitat loss are a global problem for wildlife. Coastal developme... more Anthropogenic stressors such as habitat loss are a global problem for wildlife. Coastal development in the United States has replaced estuary shorelines with hard erosion barriers. In Barnegat Bay, New Jersey, the diamondback terrapin (Malaclemys terrapin) encounters these barriers when approaching upland beaches for nesting. To determine the effects of shoreline barriers on this threatened species' nesting abilities, we measured adrenocortical response (i.e., stress response) by comparing natural corticosterone and testosterone levels of 91 terrapins following in situ exposure to either an experimentally blocked, or open nesting beach. In addition, we exposed 15 individuals, from various nesting beaches, to handling stress to identify acute corticosterone secretion, finding a significant increase over 60 min to 8 ng/ml. Corticosterone did not reach this level in terrapins exposed to barriers. Corticosterone and testosterone levels were not significantly higher among terrapins exposed to barriers compared to those at open reference beaches. This lack of a stress response suggests that terrapins do not physiologically respond to barriers when they approach nesting beaches and thus are not stressed. This may be due to an adaptive trait to help female turtles complete the nesting process despite the natural stresses inherent to coming on land. Our study suggests that this lack of stress response is also applied to non-natural, human made nesting barriers. If terrapins are not physiologically capable of adapting to shoreline barriers, future erosion control structures could support terrapin nesting with periodic upland access points. This endocrinological study provides a more quantitative approach to guiding management of anthropogenic stressors upon wildlife.

This talk was given during the Southeast Regional Meeting of the Society for Integrative and Comp... more This talk was given during the Southeast Regional Meeting of the Society for Integrative and Comparative Biology

The effects of testosterone (T) on territorial lizards have been studied extensively; however, th... more The effects of testosterone (T) on territorial lizards have been studied extensively; however, the effects of T on non-territorial lizards have not. In territorial lizards, T has been suggested as a possible mediator of seasonal increases in whole-animal performance capacities (i.e. sprint speed and bite force), which are important factors in maintaining territories and winning male-male competitions. Previous work in our lab has shown that in Aspidoscelis sexlineata, a common non-territorial lizard, bite force, locomotor performance (measured as the max. time until exhaustion), and T are each greatest during the breeding season; thereby suggesting that T also mediates seasonal increases in performance for this species. Furthermore, T implants have been shown to successfully elevate circulating T levels in A. sexlineata. However, the T implants failed to increase whole-animal performance capacities, and hence suggest a training effect. The current study will test the effects of training on locomotor performance capacities and morphology (i.e. locomotor muscle size & composition). Thirty adult male A. sexlineata were assigned to one of three treatment groups: T implant + training, empty implant + training, and empty implant without training. Training consisted of 3 performance measures: treadmill endurance, burst speed, and maximal exertion. At the end of the study, changes in muscle size, muscle fiber size, or fiber-type composition were assessed for multiple hindlimb muscles using histochemical analyses to determine the influence of treatment group (T, training regime). This research will further isolate the role of T and training on the morphological factors affecting seasonal locomotor performance in non-territorial species

Numerous studies have examined the effects of testosterone on behavior in territorial lizards, bu... more Numerous studies have examined the effects of testosterone on behavior in territorial lizards, but few have explored the role of testosterone (T) in non-territorial species. Here, we experimentally manipulated T levels in Aspdidoscelis sexlineatus, a common non-territorial lizard. During the breeding season, males exhibit mate guarding, and will follow a female for several days after copulation. Male-to-male interactions during the breeding season involve chasing and occasionally escalate into fights with biting. Therefore, high bite force and high endurance capacity should be advantageous to retain exclusive access to females and ensure paternity. In territorial lizards, T levels peak with the breeding season and several studies have cited T as a possible mediator of the seasonal increases in performance (e.g. bite force and locomotor performance). Fluctuating T levels have been observed in A. sexlineatus; however, the role that T plays in the performance of A. sexlineatus or other mate guarding species remains unknown. For this study, male racerunners were captured and blood samples were drawn immediately to quantify T levels. Lizards were then returned to the lab where locomotor performance (endurance), bite force, and morphological data were collected. Following performance trials, lizards received silastic T implants. Lizards were housed in the lab for four weeks where locomotor endurance and bite force performance were measured biweekly. Additionally, a blood sample was collected every two weeks to monitor T levels. This research will quantify the morphological and physiological factors affecting performance in A. sexlineatus and provide valuable data concerning how T affects alternative mating systems

Choice Reviews Online, Feb 24, 2015

Herpetological Monographs, 2016

Abstract: The conservation of large, long-lived turtle species can be a challenging issue becaus... more Abstract: The conservation of large, long-lived turtle species can be a challenging issue because their life-history strategies make populations sensitive to changes in adult survivorship and populations may be difficult to sample. The Alligator Snapping Turtle (Macrochelys temminckii) is a large freshwater turtle species occurring in North America for which commercial harvest has severely reduced populations throughout the species range. Given recent population declines and a general deficit of demographic knowledge for Macrochelys, we conducted a mark–recapture study of M. temminckii from 1997–2013 in Spring Creek, Georgia, USA. We made 166 captures of 75 individuals using baited hoop-net traps and skin-diving searches. The observed and estimated population structure described the adult sex ratio as even and adults as more abundant than juveniles. Apparent survival was higher for adult males (0.98) and females (0.95) than for juveniles (0.86), and we estimated a population density of 13–14 turtles/stream kilometer. The survival estimates for adult M. temminckii are among the highest of all freshwater turtle species reported in the literature. We used the empirical demographic parameters described here and a literature review to build an updated population model for M. temminckii; the model estimated a finite rate of population increase consistent with a growing population (λ = 1.036) at Spring Creek, and population viability analysis found the population growing over the next 50 yr in 100% of simulations. Application of our model to published survival estimates from two impacted western populations indicated a declining population (λ = 0.563) with a high risk of extirpation in Oklahoma and a population with a slow rate of decline (λ = 0.978) but approaching stability in Arkansas. Simulations identified combinations of survival values which generate viable populations and also characterized population structure resulting from viable scenarios. This is the first study to document a stable and viable population of Macrochelys. We suggest that the population parameters described at Spring Creek are the best approximation of reference demographic conditions for Macrochelys to date, and this study provides a general framework applicable for large, long-lived, endangered turtle species for which demographic data are unavailable.

Herpetological Monographs, 1994

... Extensive observations of the behavior of the tortoises in these pens were carried out from A... more ... Extensive observations of the behavior of the tortoises in these pens were carried out from April-September, 1992, by Niblick et al. (1994). ... Female solicitation of particular males and avoid-ance of others has been observed in captive desert tortoises (Niblick et al., 1994). ...

General and Comparative Endocrinology, 2001

To characterize seasonal changes in thyroid function in a terrestrial reptile, thyroid hormones w... more To characterize seasonal changes in thyroid function in a terrestrial reptile, thyroid hormones were measured over a period of 2 years in desert tortoises, Gopherus agassizii, maintained at the Desert Tortoise Conservation Center in Las Vegas, Nevada. In all samples, triiodothyronine was nondetectable (less than 0.1 ng/ml). Thyroxine (T(4)) exhibited distinct cycles in both sexes, being lowest during hibernation and rising toward the time of emergence. Females exhibited only one peak in T(4), during the early spring. In males, T(4) levels peaked in early spring and again in late summer. The desert tortoise has distinct activity patterns that include increased feeding, mating, and locomotor activity in the early spring and increased mating and combat in the late summer. In an experiment to determine whether food intake influences T(4), food was withheld for 2 weeks. Compared to continuously fed controls, T(4) declined significantly in unfed tortoises, but increased significantly within 36 h of refeeding, indicating that thyroid activity is responsive to nutrient intake. The second seasonal peak of T(4) only in males suggests that male reproductive activity in late summer is associated with thyroid activation. To evaluate this possibility, adult, subadult, and juvenile males were sampled during the months of the second seasonal peak in T(4). Although all three age groups showed similar foraging and thermoregulatory behaviors, T(4) peaked in July only in the reproductively active adults, which also exhibited significantly higher testosterone levels. Elevated T(4) in desert tortoises is thus associated with periods of increased feeding and reproductive activity, supporting a role for thyroid hormones in these energy-demanding activities.

General and Comparative Endocrinology, 2009

Ultrasonography has been used effectively to study reproduction in a variety of reptile species, ... more Ultrasonography has been used effectively to study reproduction in a variety of reptile species, but its application to crocodilians has been relatively limited. We present results from a study testing the efficacy of using ultrasonography to monitor reproduction in the American alligator, Alligator mississippiensis. Ultrasound results were then compared with plasma hormone levels. A total of 124 females were examined during March, April, May, and early June (2001-2003). Ultrasound results were validated on a series of reproductive females (n=14) necropsied for other studies. Previtellogenic follicles, vitellogenic follicles, recently shelled eggs, fully developed well-calcified eggs, and atretic follicles were readily discernible with ultrasound in mature females. Reproductive structures were observed in 57 females of which 43 were actively reproductive, while 14 were non-reproductive, but contained large atretic follicles from prior years. Oviducts were discernible in females with eggs. Ovarian state was also correlated with hormone levels. These results are in agreement with previous studies that showed that 50% or less of the adult female alligator population is reproductively active in a given year. Ultrasonography can be used to make an accurate assessment of reproductive condition in wild alligator populations.

Endangered Species Research, 2008

In an attempt to better understand the reproductive cycle of adult male loggerhead sea turtles, s... more In an attempt to better understand the reproductive cycle of adult male loggerhead sea turtles, several techniques were used to assess their reproductive activity, including plastron-softness analysis, ultrasonography, laparoscopy, testicular biopsy samples, and measuring testosterone levels. Stress levels were evaluated on a subset of turtles by measuring testosterone and corticosterone concentrations after capture and before release. A total of 40 adult males were captured in the Port Canaveral shipping channel in April of 2006 and 2007. Four turtles were classified as reproductively inactive based on laparoscopic examination, histology of the testes, and testosterone levels. The relative area of plastron softness was significantly lower for the inactive males compared to the active males. Ultrasonography proved to be a promising tool, as we were able to visualize both the testes and epididymides on the turtles examined. Furthermore, we found no statistical difference in epididymal duct diameters measured by ultrasonography and during laparoscopy, suggesting that ultrasonography could be used successfully as a substitute for laparoscopic surgery. Finally, testosterone levels separated into 2 distinct groups, with concentrations of the inactive males below 5 ng ml-1 , and concentrations of the active males reaching 188 ng ml-1. We conclude that in order to reduce stress levels due to capture and handling, especially during laparoscopy, ultrasonography and plastron analysis could be used together as a way to determine the reproductive activity of adult males in the field. The results from this study also suggest that not all adult males participate in mating activity each year.

General and Comparative Endocrinology, 2001

The reproductive endocrinology of nesting leatherback turtles (Dermochelys coriacea) was studied ... more The reproductive endocrinology of nesting leatherback turtles (Dermochelys coriacea) was studied during the 1996-1997 and 1997-1998 nesting seasons at Los Baulas National Park, Playa Grande, Costa Rica. Blood samples were collected from nesting females throughout the season. Females were observed to nest up to 10 times during the nesting season. Plasma steroids were measured by radioimmunoassay and total plasma calcium was measured by flame atomic absorption spectrophotometry. Plasma testosterone and plasma estradiol levels declined throughout the nesting cycle of the female. Testosterone declined from a mean of 10.18 +/- 0.77 ng/ml at the beginning of the nesting cycle to 1.73 +/- 0.34 ng/ml at the end of the nesting cycle. Estradiol declined in a similar manner, ranging from a mean of 190.95 +/- 16.80 pg/ml at the beginning of the nesting cycle to 76.52 +/- 12.66 pg/ml at the end of the nesting cycle. Plasma progesterone and total calcium levels were relatively constant throughout the nesting cycle. Lack of fluctuation of total calcium levels, ranging from a mean high of 97.46 +/- 11.37 microg/ml to a mean low of 64.85 +/- 11.20 microg/ml, further suggests that vitellogenesis is complete prior to the arrival of the female at the nesting beach. Clutch size (both yolked and yolkless eggs) did not vary over the course of the nesting cycle.