Life-History Variation in the Sagebrush Lizard (Sceloporus graciosus): Phenotypic Plasticity or Local Adaptation?

We performed a laboratory common-environment study to determine the genetic and environmental sources of variation in growth rates of the sagebrush lizard (Sceloporus graciosus). Hatchling lizards were reared from gravid females collected from three study populations along an elevational gradient in southern Utah, USA. Hatchlings were fed ad libidum and were maintained on a 14:10 light:dark cycle, with temperatures at 33°C and 21°C during photophase and scotophase, respectively. Each hatchling was randomly assigned to either a water-supplementation treatment or a control group receiving no supplemental water. Once every five days, the water-supplemented lizards were administered orally a quantity of water equal to 5% of their body mass. Growth was quantified as the total change in body size (length and mass) for 30 d after hatching. Resting metabolic rates of a subset of lizards were measured at hatching and at the end of the study. After adjusting growth for food intake, change in length did not differ between water-supplemented and control lizards, and did not differ among the three populations. Metabolic rates were similar across the study for all treatment groups. Water-supplemented lizards did gain wet mass more rapidly than control lizards; however, the difference in growth between groups was attributed to hydration state, because growth in dry mass did not differ between groups. The effects of water supplementation on growth that were observed by other investigators were likely manifested through changes in thermoregulatory behavior or increased activity

Moistened Seeds Increase Rodent Trap Success

Seed moisture has been shown to influence the rates of seed cache removal by rodents. Although the precise mechanism is not known, this knowledge might prove useful in field applications. We examined whether moistened bait would increase trap success in desert rodent populations. We placed traps 15 m apart in grids within a 500-ha study area and randomly baited traps with either dry or moistened seeds. We found that traps baited with moistened seeds had 34.9% higher success than traps baited with dry seeds (n = 190, Χ2 = 5.389, df = 1, P = 0.020). Our results suggest that application of water to dry seed bait can lead to increased trap success for desert rodents

Spatial Dynamics of Nesting Behavior: Lizards Shift Microhabitats to Construct Nests with Beneficial Thermal Properties

Because temperature affects the growth, development, and survival of embryos,oviparous mothers should discriminate carefully among available nesting sites. We combined a radiotelemetric study of animal movements with a spatial mapping of environmental temperatures to test predictions about the nesting behavior of the eastern fence lizard (Sceloporus undulatus). Females made large excursions from their typical home ranges to construct nests in exposed substrates. These excursions appeared to be related solely to nesting because all females returned to forested habitat immediately afterward. On average, 1% (range ¼ 0–8%, n ¼ 19) of the area used by a female during nesting was contained within the area used before and after nesting. The selection of nesting sites matched predictions based on laboratory studies of embryonic performance; specifically, females nested in extremely open habitat at a mean of 6 cm depth. Spatial mapping of soil temperatures revealed that temperatures of nesting areas exceeded those of areas typically used by females, indicating that females preferred to construct warm nests that speed embryonic growth and development. However, this behavior could reduce the survivorship of females because of the need to rapidly navigate unfamiliar and exposed terrain

Can lizard embryos survive climate warming? Thermal constraints on the physiology of developing Eastern fence lizards

Sublethal stressors will likely mediate an organism’s response to climate change. Mobile animals can change their behavior to maintain temperatures within preferred ranges. However, animals in immobile life stages are particularly vulnerable to warming. For example, lizard embryos experience recurrent thermal stress as they develop in shallow nests with daily temperature fluctuations. Nesting temperatures above 41.5°C can be lethal to Eastern fence lizard (Sceloporus undulatus) embryos. Although that is beyond the range experienced at current nest sites, rapid warming will push nest conditions toward critical limits. Therefore, it is important to examine the effects of sublethal high nest temperatures on developing lizards. We reared S. undulatus embryos under three thermal regimes—one to simulate contemporary nest conditions with a maximum daily temperature (Tmax) of 32.1°C, and two regimes to simulate warming scenarios in which the Tmax was raised to 35.6°C and 39.1°C. We tracked changes in physiology and survival through embryonic development, and we measured growth and metabolic rates of surviving hatchlings. Results showed reduced embryo survival and decreased hatchling growth for lizards reared under sublethal warming, suggesting that thermal constraints on the physiology of developing Eastern fence lizards may limit the persistence of the species under climate warming

Recurrent sublethal warming reduces embryonic survival, inhibits juvenile growth, and alters species distribution projections under climate change

The capacity to tolerate climate change often varies across ontogeny in organisms with complex life cycles. Recently developed species distribution models incorporate traits across life stages; however, these life-cycle models primarily evaluate effects of lethal change. Here, we examine impacts of recurrent sublethal warming on development and survival in ecological projections of climate change. We reared lizard embryos in the laboratory under temperature cycles that simulated contemporary conditions and warming scenarios. We also artificially warmed natural nests to mimic laboratory treatments. In both cases, recurrent sublethal warming decreased embryonic survival and hatchling sizes. Incorporating survivorship results into a mechanistic species distribution model reduced annual survival by up to 24% compared to models that did not incorporate sublethal warming. Contrary to models without sublethal effects, our model suggests that modest increases in developmental temperatures influence species ranges due to effects on survivorship

High-resolution Niche Models via a Correlative Approach: Comparing and Combining Correlative and Process-based Information

Correlative and process-based approaches to describing the ecological niche in a spatially explicit fashion have often been compared in an adversarial framework. We sought to compare niche models developed via classic (correlative only), niche (process-based information), and hybridized (correlative augmented with process-based derived information) approaches, with the goal of determining if the added effort of process-based model development yielded better model fit. Correlative data layers (i.e., habitat models) included vegetation community types, Euclidean distance statistics, neighborhood analyses, and topographically-derived information. Mechanistic data layers were estimates of thermal suitability derived from field-collected datasets and biophysical calculations, and estimates of prey biomass interpolated from monitoring stations. We applied these models at high resolution (1 m × 1 m pixel size) to habitat occupied by a population of Texas horned lizards (Phrynosoma cornutum) located in central Oklahoma. Results suggested that our treatment of process-based information offered dramatically better identification of suitable habitat when compared to correlative information, but that these results were likely due to low variability of niche variable pixel values. Niche layers nearly perfectly predicted lizard locations; the interpretation of these results suggest that lizards occupy habitat based on thermal suitability over the duration of a field season. Given the low variability observed in thermal suitability layers, we question the ecological reality of these predictions. Correlative models may accurately describe the niche at small spatial scales, and may suffice in situations where time and financial resources are limiting constraints on project goals. Process-based information continues to be an important part of the niche, and may offer additional predictive accuracy via correlative approaches when included in an ecologically meaningful context

Plasticity reveals hidden resistance to extinction under climate change in the global hotspot of salamander diversity

Extinction rates are predicted to rise exponentially under climate warming, but many of these predictions ignore physiological and behavioral plasticity that might buffer species from extinction. We evaluated the potential for physiological acclimatization and behavioral avoidance of poor climatic conditions to lower extinction risk under climate change in the global hotspot of salamander diversity, a region currently predicted to lose most of the salamander habitat due to warming. Our approach integrated experimental physiology and behavior into a mechanistic species distribution model to predict extinction risk based on an individual’s capacity to maintain energy balance with and without plasticity. We assessed the sensitivity of extinction risk to body size, behavioral strategies, limitations on energy intake, and physiological acclimatization of water loss and metabolic rate. The field and laboratory experiments indicated that salamanders readily acclimatize water loss rates and metabolic rates in ways that could maintain positive energy balance. Projections with plasticity reduced extinction risk by 72% under climate warming, especially in the core of their range. Further analyses revealed that juveniles might experience the greatest physiological stress under climate warming, but we identified specific physiological adaptations or plastic responses that could minimize the lethal physiological stress imposed on juveniles. We conclude that incorporating plasticity fundamentally alters ecological predictions under climate change by reducing extinction risk in the hotspot of salamander diversity

Isopods Failed to Acclimate Their Thermal Sensitivity of Locomotor Performance During Predictable or Stochastic Cooling

Most organisms experience environments that vary continuously over time, yet researchers generally study phenotypic responses to abrupt and sustained changes in environmental conditions. Gradual environmental changes, whether predictable or stochastic, might affect organisms differently than do abrupt changes. To explore this possibility, we exposed terrestrial isopods (Porcellio scaber) collected from a highly seasonal environment to four thermal treatments: (1) a constant 20 degrees C; (2) a constant 10 degrees C; (3) a steady decline from 20 degrees to 10 degrees C; and (4) a stochastic decline from 20 degrees to 10 degrees C that mimicked natural conditions during autumn. After 45 days, we measured thermal sensitivities of running speed and thermal tolerances (critical thermal maximum and chill-coma recovery time). Contrary to our expectation, thermal treatments did not affect the thermal sensitivity of locomotion; isopods from all treatments ran fastest at 33 degrees to 34 degrees C and achieved more than 80% of their maximal speed over a range of 10 degrees to 11 degrees C. Isopods exposed to a stochastic decline in temperature tolerated cold the best, and isopods exposed to a constant temperature of 20 degrees C tolerated cold the worst. No significant variation in heat tolerance was observed among groups. Therefore, thermal sensitivity and heat tolerance failed to acclimate to any type of thermal change, whereas cold tolerance acclimated more during stochastic change than it did during abrupt change

Integrating physiology into correlative models can alter projections of habitat suitability under climate change for a threatened amphibian

Rapid global change has increased interest in developing ways to identify suitable refu-gia for species of conservation concern. Correlative and mechanistic species distribu-tion models (SDMs) represent two approaches to generate spatially-explicit estimates of climate vulnerability. Correlative SDMs generate distributions using statistical associations between environmental variables and species presence data. In contrast, mechanistic SDMs use physiological traits and tolerances to identify areas that meet the conditions required for growth, survival and reproduction. Correlative approaches assume modeled environmental variables influence species distributions directly or indirectly; however, the mechanisms underlying these associations are rarely verified empirically. We compared habitat suitability predictions between a correlative-only SDM, a mechanistic SDM and a correlative framework that incorporated mechanis-tic layers (‘hybrid models’). Our comparison focused on green salamanders Aneides aeneus, a priority amphibian threatened by climate change throughout their disjunct range. We developed mechanistic SDMs using experiments to measure the thermal sensitivity of resistance to water loss (ri) and metabolism. Under current climate con-ditions, correlative-only, hybrid and mechanistic SDMs predicted similar overlap in habitat suitability; however, mechanistic SDMs predicted habitat suitability to extend into regions without green salamanders but known to harbor many lungless salaman-ders. Under future warming scenarios, habitat suitability depended on climate sce-nario and SDM type. Correlative and hybrid models predicted a 42% reduction or 260% increase in area considered to be suitable depending on the climate scenario. In mechanistic SDMs, energetically suitable habitat declined with both climate scenarios and was driven by the thermal sensitivity of ri. Our study indicates that correlative-only and hybrid approaches produce similar predictions of habitat suitability; however, discrepancies can arise for species that do not occupy their entire fundamental niche, which may hold consequences of conservation planning of threatened species

Sibling sex, but not androgens, shapes phenotypes in perinatal common marmosets (\u3ci\u3eCallithrix jacchus\u3c/i\u3e)

When offspring share a womb, interactions among fetuses can impart lasting impressions on phenotypic outcomes. Such intrauterine interactions often are mediated by sex steroids (estrogens and androgens) produced by the developing fetuses. In many mammals, intrauterine interactions between brothers and sisters lead to masculinization of females, which can induce fitness consequences. Many litter-bearing primates, though, seem to escape androgen-mediated litter effects, begging why? Here, we investigated how the sex composition (i.e., same- or mixed-sex) of litters influences perinatal outcomes in the common marmoset monkey (Callithrix jacchus), using a combination of physiological, morphological, and behavioural assays. We hypothesized that androgens from male fetuses would mediate developmental differences across litter types. We found that newborns (24–36 hours old) from same- and mixed-sex litters were indistinguishable by urinary androgen profiles, birth weights, morphometrics, and behaviour. However, monkeys born into same- and mixed-sex litters exhibited subtle morphological and neurobehavioral differences later in the perinatal period, independent of their androgen profiles. Our findings suggest that while androgens from male fetuses likely do not organize their siblings’ phenotypes, perinatal stimuli may initiate divergent developmental trajectories among siblings, which, in turn, promotes inter-individual variability within families