Corticosterone, locomotor performance, and metabolism in side-blotched lizards (Uta stansburiana)

Elevated levels of circulating corticosterone commonly occur in response to stressors in wild vertebrates. A rise in corticosterone, usually in animals of subordinate rank, results in a variety of effects on behavior and physiology. Behavioral and physiological responses to short-term increases in corticosterone are well studied. In contrast, the effects of chronic elevated levels of corticosterone are poorly understood, particularly in lizards. Here, we examined the long-term effects of exogenous corticosterone on locomotor performance, resting and active metabolic rate, and hematocrit in male side-blotched lizards Uta stansburiana. Corticosterone implantation resulted in higher levels of stamina relative to sham-surgery controls. In addition, lizards with elevated corticosterone exhibited lower resting metabolic rates relative to controls. Corticosterone had no effect on peak activity metabolism but did result in faster recovery times following exhaustive exercise. We suggest that elevated levels of corticosterone in response to dominance interactions promote enhanced locomotor abilities, perhaps as a flight response to avoid agonistic interactions. Furthermore, stressed lizards are characterized by lower resting metabolic rates, which may serve as strategy to conserve energy stores and enhance survival.     

Climate change trade-offs in the side-blotched lizard (Uta stansburiana): effects of growing-season length and mild temperatures on winter survival

An expanding body of literature has demonstrated that global climate change continues to adversely affect many populations, species, and ecosystems. However, life-history theory also predicts possible benefits from longer growing seasons and less severe winters, particularly for ectotherms. To test the idea that climate change will have benefits as well as costs, I studied the impacts of growing-season length on growth and overwintering conditions on survival time using side-blotched lizards (Uta stansburiana). Experiments in replicate field enclosures revealed that fall growing-season length has a direct effect on overwintering body size. Laboratory experiments revealed that both size and overwintering temperature have direct effects on winter survival time. Larger lizards are more likely to survive longer regardless of winter temperature. Furthermore, animals in colder (but still mild) winter microenvironments are more likely to survive longer than those in warmer winter environments. These results indicate that warmer winters caused by global climate change have the potential to negatively affect ectotherm populations. However, longer growing seasons may offset losses by allowing additional growth and energy storage. Thus, environmental alterations associated with climate change may be simultaneously beneficial and detrimental, and the long-term persistence of certain organisms may depend on the relative strength of their effects.     

Seasonal shifts in clutch size and egg size in the side-blotched lizard,Uta stansburiana Baird and Girard

Summary There is evidence that the side-blotched lizard, Uta stansburiana, and some other organisms of temperate latitudes produce fewer and larger eggs as the reproductive season progresses. There are at least two models that could explain this phenomenon.Proponents of the parental investment model claim that females are selected to increase egg size, at the cost of clutch size, late in the season in order to produce larger and competitively superior hatchlings at a time when food for hatchlings is in low supply and when juvenile density is high. In this model the selective agent is relative scarcity of food available to hatchlings late in the reproductive season, and the adaptive response is production of larger offspring.The alternative explanation (bet-hedging model) proposed in this paper is based on the view that the amount of food available to females for the production of late-season clutches is unpredictable, and that selection has favored conservatively small clutches in the late season to insure that each egg is at least minimally provisioned. Smaller clutches, which occur most frequently late in the season, are more likely to consist of larger eggs, compared to larger clutches, for two reasons. Firstly, unlike birds, oviparous lizards cannot alter parental investment after their eggs are deposited, and therefore, in cases of fractional optimal clutch size, the next lower integral clutch size is selected with the remaining reproductive energy allocated to increased egg size. With other factors constant, eggs of smaller clutches will increase more in size than eggs of larger clutches when excess energy is divided among the eggs of a clutch. Secondly, unanticipated energy that may become available for reproduction during energy-rich years will similarly increase egg size a greater amount if divided among fewer eggs.     

The role of the kisspeptin system in regulation of the reproductive endocrine axis and territorial behavior in male side-blotched lizards (Uta stansburiana)

The neuropeptide kisspeptin and its receptor are essential for activation of the hypothalamic-pituitary-gonadal (HPG) axis and regulating reproduction. While the role of kisspeptin in regulating the HPG axis in mammals has been well established, little is known about the functional ability of kisspeptins to activate the HPG axis and associated behavior in non-mammalian species. Here we experimentally examined the effects of kisspeptin on downstream release of testosterone and associated aggression and display behaviors in the side-blotched lizard (Uta stansburiana). We found that exogenous treatment with kisspeptin resulted in an increase in circulating testosterone levels, castration blocked the kisspeptin-induced increase in testosterone, and testosterone levels in kisspeptin-treated animals were positively related to frequency of aggressive behaviors. This evidence provides a clear link between kisspeptin, testosterone, and aggressive behavior in lizards. Thus, it is likely that kisspeptin plays an important role more broadly in non-mammalian systems in the regulation of reproductive physiology and related behaviors.     

Substance P-like immunoreactivity in the parietal eye visual system of the lizard Uta stansburiana

Summary We examined the parietal eye visual system of the iguanid lizard Uta stansburiana for the presence of substance P-like immunoreactivity by use of both immunofluorescence and peroxidase-antiperoxidase techniques. In the parietal eye no substance P-containing somata were found; however, its plexiform layer contained small (ca. 1 m diam) immunoreactive fibers. These fibers apparently originate outside the parietal eye. Immunoreactive fibers also were found in the parietal nerve, the dorsal sac, and the leptomeninx of the pineal gland. No labeled somata were observed in any of these regions in either normal or colchicine treated animals. Previously we demonstrated that a system of centrifugal fibers to the parietal eye originates from neurons in the dorsal sac (Engbretson et al. 1981). The apparent absence of substance P-containing neurons in the dorsal sac suggests that the substance P-containing fibers in the parietal eye are not the previously observed centrifugal fibers. The source of the substance P-containing fibers in the parietal eye is unknown. The pars dorsolateralis of the left medial habenular nucleus receives a dense substance P-positive projection. No such projection was seen in the right habenula. Simultaneous visualization of the terminals of ganglion cells of the parietal eye (labeled with orthograde intraaxonally transported horseradish peroxidase) and substance P-like immunofluorescence showed that the locus of habenular immunoreactivity is distinct from the projection field of the parietal eye. Thus the substance P-positive terminals in the habenula do not originate in the parietal eye. Transection of the parietal nerve confirmed this conclusion.     

Tail injuries increase the risk of mortality in free-living lizards (Uta stansburiana)

Summary Caudal autotomy is an effective anti-predator mechanism used by many lizard species. Fitness benefits of surviving a predatory attack are obvious, although lizards that autotomize their tails may be at greater risk during subsequent encounters with predators than lizards with complete tails. In previous laboratory studies, tail-less lizards were more vulnerable to capture by predators, but little is known about the relative survival of tailed versus tail-less lizards in nature. This study reports on significant associations between naturally incurred tail injuries and the subsequent risk of mortality in 7 populations of the lizard Uta stansburiana. I used standard mark-recapture techniques to document survival and quantified tail injuries by estimating tail completeness. I then used sampled randomization tests to compare intitial tail completeness values of surviving versus non-surviving lizards. I evaluated overall patterns by comparising the means of tail completeness values of survivors versus non-survivors among mark-recapture sequences. Lizards with incomplete tails suffered higher mortality in the field, although this was not true for every comparison considered (i.e., for every mark-recapture sequence analyzed), and the overall trend was much stronger for adult males than for either adult females or juveniles. Higher mortality among lizards with incomplete tails is presumably a consequence of increased vulnerability to capture by predators. Vulnerability to predation of tail-injured lizards may be confounded by reduced social status in this species, because social subordination can result in the occupation of an inferior home range.     

Chromosome number in the lizard genus Uta (family Iguanidae)

A chromosome number of 34 (12 macro- and 22 microchromosomes) was found to be characteristic of the bone marrow in 47 animals including males from the species Uta antiquus, and both males and females from the following species and subspecies: Uta stansburiana stansburiana, Uta stansburiana stejnegeri, Uta stansburiana elegans, Uta stansburiana klauberi, Uta stansburiana mannophorus, Uta nolascensis, Uta palmeri, and Uta squamata. — Diploid chromosome numbers of 34 and haploid numbers of 17 were found in the nine testis smears examined. — The presence of a large number of hypodiploid figures in the bone marrow smears is attributed to cell fragmentation and the problem of distinguishing the small microchromosomes. — Series of polyploid figures whose chromosome numbers increased in arithmetic rather than geometric progressions were observed in the testis dry smears. Possible alternatives for the origin of these figures are presented. — Problems encountered in the use of chromosome number as a taxonomic character are discussed.Supported in part by Research Grants GB-366 and GB-5416 from the National Science Foundation, and GM-15361 from the United States Public Health Service.     

Gonadotropin hormone modulation of testosterone, immune function, performance, and behavioral trade-offs among male morphs of the lizard Uta stansburiana

Sexual selection predicts that trade-offs maintain trait variation in alternative reproductive strategies. Experiments often focus on testosterone (T), but the gonadotropins follicle-stimulating hormone and luteinizing hormone may provide a clearer understanding of the pleiotropic relationships among traits. We assess the activational role of gonadotropins on T and corticosterone regulation in traits expressed by polymorphic male side-blotched lizards Uta stansburiana. Gonadotropins are found to enhance and suppress multiple physiological, morphological, and behavioral traits independently, as well as indirectly via T, and we demonstrate selective trade-offs between reproduction and survival. The OBY locus, a genetic marker in our model vertebrate mating system, allows characterization of the interaction between genotype and hormone treatment on male traits. Our results suggest that oo, ob, and bb males are near their physiological and behavioral capacity for reproductive success, whereas yy and by males are maintained below their physiological maximum. Both by and yy morphs show trait plasticity, and we demonstrate that gonadotropins are likely proximate effectors that govern not only trait differences between alternative mating strategies but also morph plasticity. Gonadotropins clearly represent an important mechanism maintaining variation in physiological, morphological, and behavioral traits, as well as potentially maintaining the immunosuppression costs of male sexual signals.     

Duration of attachment by mites and ticks on the iguanid lizards Sceloporus graciosus and Uta stansburiana.

Duration of attachment was determined for the mites Neotrombicula californica and Geckobiella texana and the tick Ixodes pacificus on the iguanid lizards Sceloporus graciosus and Uta stansburiana from southern California. Neotrombicula californica infestations lasted approximately 1 wk. Attachment of Ixodes pacificus larvae and nymphs lasted approximately 8 days on S. graciosus and 16 days on U. stansburiana. Geckobiella texana remained attached to S. graciosus for 5 days and to U. stansburiana for 28 days.     

The effects of tail loss on survival, growth, reproduction, and sex ratio of offspring in the lizard Uta stansburiana in the field

Tail autotomy is a defense against predators used by many lizard species but is associated with various costs, most of which have been measured only in the laboratory. We conducted a field experiment in which we induced tail autotomy to approximately half (58%) of a marked sample (n=326) of Uta stansburiana from western Texas in the fall, and left the other half with intact tails. The following spring we determined survival, measured growth, and brought females to the laboratory to allow them to oviposit their eggs, which we incubated until hatching. Based on past studies, we anticipated inferior survival, growth, and reproduction following tail autotomy. We also predicted that females with tail loss would be energetically compromised and would alter the sex ratio of their offspring toward more daughters (as predicted by the Trivers-Willard hypothesis). Tailless lizards experienced significantly reduced survivorship, but those that survived grew the same as their tailed counterparts. Tailed and tailless females produced clutches equivalent in number of eggs and total mass. Whereas tailed females showed a significant positive relationship between average egg mass and snout-vent length, tailless females did not. Contrary to our expectations, tailless females produced heavier hatchlings than tailed ones, and sex ratios of hatchlings were equivalent for tailed and tailless females. In this population, tail loss in subadults leads to an increased risk of death, but apparently does not impose an energetic handicap such that later growth and reproduction suffer. We suggest that because tailless females are faced with decreased reproductive value, they respond by growing as much and laying as many eggs of the same mass as tailed females, despite the fact that they are also regenerating the tail. In addition, they somehow produce larger hatchlings than tailed females. Nevertheless, tailless females probably end up with lower overall lifetime fitness than tailed females, and tail loss thus induces the conditional reproductive strategy ”make the best of a bad situation”. Because tailless females produce larger, not smaller, hatchlings, they do not produce more daughters as predicted; i.e., we found no evidence for the Trivers-Willard effect following tail autotomy. Received: 29 November 1998 / Accepted: 17 September 1999     

Life‐history differences across latitude in common side‐blotched lizards (Uta stansburiana)

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Predictions of response to selection caused by angling in a wild population of Atlantic salmon (Salmo salar)

1. Recreational angling activities in wild populations of Atlantic salmon may induce a selection pressure towards a reduction in body size and length if the angling season coincides with the return of the largest sea age fish class. 2. Using estimates of heritability for growth traits and estimates of the selection pressure from angling operating on growth, we predicted the response to selection expected to occur in a wild population of Atlantic salmon. 3. The dataset used here comprised individuals from two consecutive generations (parents and offspring) from the River Bidasoa (NW Spain). Offspring were assigned to parents using six highly polymorphic microsatellite loci. Use of restricted maximum likelihood methodology and the animal model allowed us to estimate the heritability for body length and body weight as well as their genetic correlation. 4. Estimated heritabilities (0.32 ± 0.12 for length and 0.32 ± 0.11 for weight) and selection pressure caused by angling were used to obtain predictions of response to selection because of angling. Our results suggested a decline of 1.9 mm in body length and 103.3 g in body weight per generation because of angling pressure. 5. The results derived from this study suggest that the angling season should be annually delayed in order to avoid selective angling of the multi‐year class and further reductions in body weight and length.     

Size and scaling of sexually-selected traits in the lizard, Uta palmeri

Differences between the sexes in overall body size and in the size of other morphological traits, relative to overall body size, are common in many animals. In this study, patterns of growth and scaling of sexually dimorphic tratis are assessedin a lilzard and then used to sugest general developmental mechanisms responsible for sexual size dimorphism (SSD). Adult make Uta palmeri lizards are larger than adult females inoverall body size (snout-vent length, SVL), body mass, jaw length head width, and head depth. Two general growth processes produce this adult SSD. First, juvenile males have greater annual SVL growth rates than do juvenile females, contributing to adult SSD because males will be larger than females in any trait positively correlated with SVL. Secondly, males and females differ in age-related changes in growth of the three head size traits, relative to growth in SVL. Comparing slopes from reduced major axis regressions of each trait on SVL reveals that the sexes do not differ in the scaling of these traits as juveniles, but as adults males have greater slopes than adult females, indicating ontogenetic differences in scaling of these traits in males. Two other topics in SSD are addressed with these data. First, comparing these data on scaling to those of an earlier analysis that used ordinary least squares regression reveals that conclusions about underlying mechanisms in an analysis of scaling can be altered by the choice of a regression model. Secondly, these data indicate that postmaturational differences in scaling contribute to adult sexual size differences, contrary to an earlier study. Shine (1990) found that for many ectotherms, which continue to grow after sexual maturation, post-maturational events contribute little to sexual differences in overall body size. Results for U. palmeri suggest that these findings may only hold for measures of overall body size (e.g. SVL) and may not generalize to traits that exhibit sex difference in scaling.     

Severe inbreeding depression in a wild wolf (Canis lupus) population

The difficulty of obtaining pedigrees for wild populations has hampered the possibility of demonstrating inbreeding depression in nature. In a small, naturally restored, wild population of grey wolves in Scandinavia, founded in 1983, we constructed a pedigree for 24 of the 28 breeding pairs established in the period 1983-2002. Ancestry for the breeding animals was determined through a combination of field data (snow tracking and radio telemetry) and DNA microsatellite analysis. The population was founded by only three individuals. The inbreeding coefficient F varied between 0.00 and 0.41 for wolves born during the study period. The number of surviving pups per litter during their first winter after birth was strongly correlated with inbreeding coefficients of pups (R2=0.39, p<0.001). This inbreeding depression was recalculated to match standard estimates of lethal equivalents (2B), corresponding to 6.04 (2.58-9.48, 95% CI) litter-size-reducing equivalents in this wolf population.     

Interspecific odour discrimination by a lizard (Eumeces laticeps)

When presented with odours on cotton swabs, adult borad-headed skinks (Eumeces laticeps) of both sexes flicked their tongues at much higher rates to conspecific odour stimuli than to those of their most closely related congeners, E. fasciatus and E. inexpectatus, during 60-s exposures to cloacal odours from lizards of the opposite sex. A successive discrimination design was used in which each lizard responded to five different odour treatments in a random sequence. In addition to the three lizard odours, water was used as a measure of baseline tongue protrusion rates and a cologne was used as a pungency control. There were no significant differences among the four non-conspecific odour treatments in numbers of tongue flicks elicited, but the skinks emitted significantly greater numbers of tongue flicks to conspecific cloacal odours than to any of the other stimuli. It is hypothesized that E. laticeps produces a pheromone which may function for species identification. Although it is tempting to speculate that the pheromone may serve as a pre-mating mechanism for maintaining reproductive isolation from syntopic congeners, insufficient information is avialable to draw firm conclusions regarding such a function.