MATERNAL ADJUSTMENT OF EGG SIZE ORGANIZES ALTERNATIVE ESCAPE BEHAVIORS,PROMOTING ADAPTIVE PHENOTYPIC INTEGRATION

Numerous integrated traits contribute to any aspect of organismal performance, but favorable trait combinations are difficult to maintain in the face of genetic recombination. We investigated the role of maternal effects in promoting integration of alternative reproductive strategies (～throat colors) with antipredator traits (escape behaviors and dorsal patterns) in the side‐blotched lizard (Uta stansburiana). Previously, we reported that maternally derived estradiol adaptively pairs dorsal patterns with progeny throat colors. Here we show adaptive maternal effects on escape behaviors within each throat color morph. Specifically, yellow‐throated females and all females mated to yellow‐throated sires lay larger eggs. Larger eggs produce stockier offspring, who remain stockier throughout life. Stockiness promotes evasive escape behaviors (e.g., reversals), which are adaptive in barred, yellow‐throated offspring. Orange‐throated females lay smaller eggs, producing leaner hatchlings who perform vertical escape behaviors (e.g., jumping). Vertical behaviors enhance survival in striped, orange‐throated progeny. Escape behavior was not heritable, but was organized by natural or experimental egg size variation. Maternal effects on adaptive phenotypic integration are likely common in polymorphic species, because recombination otherwise breaks apart beneficial trait combinations. Furthermore, our results provide insight into the role of body shape in organizing (and constraining) evolution of integrated reproductive and antipredator strategies.     

The effect of the thermal environment on the ability of hatchling Galapagos land iguanas to avoid predation during dispersal

Summary During the month of February 1979, several hundred hatchling land iguanas (Conolophus pallidus) were observed emerging from their natal burrows in a 2 ha communal nesting area on Isla Santa Fe, Galapagos Islands. During this emergence, as many as nine Galapagos hawks were observed to patrol the nesting area and attack hatchling iguanas.The hypothesis that the ability of hatchling land iguanas to escape predation could be influenced by the interaction of the physiological state of the lizards and the thermal environment was analyzed using (1) empirical data on the effect of body temperature (T _b) on locomotory ability of iguanas and (2) biophysical modeling of the T _b's of hatchlings under natural conditions. This hypothesis was tested by assessing the success of natural hawk attacks on lizards exposed to different thermal environments.During those periods when predicted T _b's of hatchlings were always <32°C, (at which temperatures land iguanas were shown to have less than maximal ability to sprint rapidly) hawks were successful in 67% of the observed attacks. However, when T _b's of hatchlings were always 32° C, hawks were successful on only 19% of observed attacks. During periods when hatchling T _b's could be <32° C or 32–40° C (depending upon which microhabitat the hatchling occupied before the attack), the hawks were successful in 46% of the observed attacks.These data indicate that the physical environment, as mediated through the physiological state of the lizards and to correlated locomotary abilities, significantly affects the ability of hatchling land iguanas to escape predation.     

Thyroxine affects behavioral thermoregulation but not growth rate among populations of the western fence lizard (Sceloporus occidentalis)

We investigated whether thyroxine influences hatchling growth rate of the western fence lizard (Sceloporus occidentalis) throught its effects on thermoregulatory behaviors. We reared control and thyroxine-injected hatchlings from three populations of S. occidentalis that differ in growth rate in a thermal gradient. We also measured the daily changes in body temperature and activity level (proportion of time spent out of retreat sites) of control and thyroxine-injected lizards. Previous studies have shown that within and among population differences in growth rate of the western fence lizard are correlated with the maintenance of high activity levels (proportion of time spent outside of retreat sites) and high body temperatures throughout the day. Growth rate was not influenced by injections of thyroxine. However, injections of thyroxine did elevate average daily body temperature and daily activity. Although administration of thyroxine uniformly increased the probability of activity throughout the day, it did not appear to alter the daily changes in activity. Previous studies have shown that the slower-growing hatchlings from northern populations exhibit a decline in activity during the later part of the thermal cycle, whereas the faster growing southern hatchlings maintain the same level of high activity throughout the thermal cycle. The decline in activity of northern populations was not prevented by thyroxine injection used in our current study. Northern lizards receiving exogenous thyroxine were still less active later in the day compared to early in the day, even though activity level throughout the day was elevated. Thus, the effects of thyroxine on temperature regulation observed in our study (general increase in activity level) appear to be unrelated to those aspects of temperature regulation (e.g., daily changes in behavioral thermoregulation) that are correlated with among population differences in growth rate. We also raised hatchlings in a cycling thermal regime (forced thermal cycle of 34°C:15°C, 12L:12D) where behavioral thermoregulation is not possible. The growth rate of lizards forced to cycle between 34°C:15°C on a daily basis was significantly lower than those lizards allowed to behaviorally thermoregulate, further underscoring the importance of the circadian pattern of thermoregulation for growth.Abbreviations GR growth rate - MR metabolic rate - SMR standard metabolic rate - SVL snout-vent length - T₄ thyroxine - T _b body temperature - T _e environmental temperature     

Comparative thermal ecology of two lizards

Summary In a habitat judged to be energetically costly for thermoregulation, mean body temperatures (MBT's) ofAnolis sagrei are significantly higher than those ofA. distichus. As indexed by the slope of the regression of body temperatures (T _b ) on substrate temperature (T _s ),A. sagrei is more dependent upon environmental temperatures thanA. distichus.In a habitat judged to be less costly for thermoregulation and where interspecific competition for perch sites may be less, MBT's ofA. sagrei are significantly higher, proportionally more lizards occupy sunny perches, and the slope of the regression of T _b on T _s is significantly less, than for conspecifics in the costly habitat.As indexed by length-specific fat body weights, well-nourished lizards in the costly habitat have T _b 's which are independent of environmental temperature; T _b 's of poorly-nourished lizards are highly dependent upon environmental temperature. This relationship does not hold for lizards in the low-cost habitat.These results corroborate the hypothesis that energetic costs are important in controlling the extent to which lizards thermoregulate. In high-cost habitats lizards thermoregulate less precisely than in low-cost habitats. Lizards that exploit the habitat as if it were highly productive thermoregulate more precisely than lizards that exploit the environment as if it were of low productivity.     

The effects of thermal biology and refuge availability on the restricted distribution of an alpine lizard

Aim In an effort to disentangle the ecological processes that confine ectotherms to alpine environments, we studied the thermoregulatory and microhabitat selection behaviours of the rock lizard Iberolacerta cyreni, which is endemic to some mountains of central Spain, and of the wall lizard Podarcis muralis, which is a potential competitor of rock lizards. Location We chose three areas in the Sierra de Guadarrama (central Spain) that differed in their thermal quality [mean deviation of environmental operative temperatures from the lizards’ preferred thermal range (PTR)] and refuge availability: a pine forest (1770 m a.s.l.) in which P. muralis was the only species found, and two mixed shrub and rock sites (1770 and 1900 m a.s.l.) where both species were present. Methods In the field we collected data on refuge availability, sun exposure, body temperature (T_b) and operative temperature (T_e). Thus, we estimated the thermal habitat quality of the areas sampled and the thermoregulation accuracy and effectiveness of both species. Results The pine forest had the lowest thermal quality and refuge availability. The lower‐elevation shrub site offered the best thermal quality, but refuges were much scarcer than at the higher‐elevation site. Both species thermoregulated accurately, because mean deviations of body temperature (T_b) from PTR were considerably smaller than those of T_e. Podarcis muralis had higher T_b values than did I. cyreni, which had similar T_b values at both shrub sites, whereas P. muralis had lower T_b values at higher elevation. Overall, the thermoregulatory effectiveness (extent to which T_b values are closer to the PTR than are T_e values) of both species was similar, but whereas I. cyreni thermoregulated more efficiently at higher elevation, the opposite was true for P. muralis. At the lower‐elevation shrub site, I. cyreni remained closer to refuges than did P. muralis. Main conclusions Our results suggest that the pine forest belt might prevent the expansion of rock lizards towards lower elevations as a result of its low thermal quality and scarcity of refuges, that the thermoregulatory effectiveness of rock lizards in alpine environments depends more on refuge availability than on thermal habitat quality, and that competition with wall lizards is unlikely to explain either the distribution or the thermoregulatory effectiveness of rock lizards.     

EVOLUTIONARY PATTERNS OF THE THERMAL SENSITIVITY OF SPRINT SPEED IN ANOLIS LIZARDS

I present evidence that the thermal sensitivity of sprint speed of Anolis lizards has evolved to match the activity body temperatures (T_b) experienced by local populations in nature. Anolis lizards from a range of altitudes in Costa Rica have limited thermoregulatory abilities and consequently have field T_b that differ substantially in median and interquartile distance (a measure of variability). Experimentally determined maximal sprint temperatures (T_b at which lizards run fastest) were positively correlated with median field T_b, and performance breadths (ranges of T_b over which lizards run well) were correlated with the variability (interquartile distance) of field T_b in the species I examined. Such correlations would be expected if the thermal sensitivity of sprint speed and field T_b had evolved together to improve the sprint performance of lizards in nature. Integration of laboratory and field studies indicates that several species of Anolis regularly experience impaired sprint speeds in the field, despite apparent evolutionary modification of their thermal physiologies. However, this impairment would have been more severe if the thermal sensitivities of sprint speed had not evolved. Data from other groups of lizards indicate that the thermal sensitivity of sprint speed has not evolved to match T_b of local populations (Hertz et al., 1983; Crowley, 1985). These lizards experience less variable T_b and less impairment of sprint speeds in the field than do the anoles. Thus, selection for modification of the thermal sensitivity of sprint speed might have been stronger for anoles than for other groups of lizards.     

Miami heat: Urban heat islands influence the thermal suitability of habitats for ectotherms

The urban heat island effect, where urban areas exhibit higher temperatures than less‐developed suburban and natural habitats, occurs in cities across the globe and is well understood from a physical perspective and at broad spatial scales. However, very little is known about how thermal variation caused by urbanization influences the ability of organisms to live in cities. Ectotherms are sensitive to environmental changes that affect thermal conditions, and therefore, increased urban temperatures may pose significant challenges to thermoregulation and alter temperature‐dependent activity. To evaluate whether these changes to the thermal environment affect the persistence and dispersal of ectothermic species in urban areas, we studied two species of Anolis lizards (Anolis cristatellus and Anolis sagrei) introduced to Miami‐Dade County, FL, USA, where they occur in both urban and natural habitats. We calculated canopy openness and measured operative temperature (T_e), which estimates the distribution of body temperatures in a non‐thermoregulating population, in four urban and four natural sites. We also captured lizards throughout the day and recorded their internal body temperature (T_b). We found that urban areas had more open canopies and higher T_e compared to natural habitats. Laboratory trials showed that A. cristatellus preferred lower temperatures than A. sagrei. Urban sites currently occupied by each species appear to lower thermoregulatory costs for both species, but only A. sagreihad field T_b that were more often within their preferred temperature range in urban habitats compared to natural areas. Furthermore, based on available T_e within each species' preferred temperature range, urban sites with only A. sagrei appear less suitable for A. cristatellus, whereas natural sites with only A. cristatellus are less suitable for A. sagrei. These results highlight how the thermal properties of urban areas contribute to patterns of persistence and dispersal, particularly relevant for studying species invasions worldwide.     

Thermal biology,microhabitat selection,and conservation of the insular lizard Podarcis hispanica atrata

Summary We studied aspects of the thermal biology and microhabitat selection of the endangered lizard Podarcis hispanica atrata during autumn in the field and laboratory. Body temperatures (T _b ) of active lizards were within a narrow range, were largely independent of ambient temperatures, and exhibited little diel variation. Activity T _b s largely coincided with the selected temperatures maintained in a laboratory thermogradient and with T _b s that maximize running performance. Alternation of basking with other activities and shuttling between sun and shade were obvious aspects of thermoregulatory behaviour. Lizards shifted microhabitat use throughout the day. During early morning and late afternoon, basking lizards were restricted to rocky sites surrounded by shrubs. Near midday lizards used a wider array of microhabitats, and many moved in open grassy sites. Juveniles maintained lower activity T _b s, had lower selected temperatures, and basked less frequently than the adults. Juveniles occupied open grassy patches more often than the adults. We discuss the relevance of our results for the conservation of this extremely rare lizard and the management of its habitats.     

Support for the thermal coadaptation hypothesis from the growth rates of Sceloporus jarrovii lizards

The thermal coadaptation hypothesis posits that ectotherms thermoregulate behaviorally to maintain body temperatures (T_b) that maximize performance, such as net energy gain. Huey's (1982) energetics model describes how food availability and T_b interact to affect net energy gain. We tested the thermal coadaptation hypothesis and Huey's energetics model with growth rates of juvenile Yarrow's spiny lizards (Sceloporus jarrovii). We compared the preferred (selected) T_b range (T_sel) of lizards in high and low energy states to their optimal temperature (T_o) for growth over nine weeks, and determined whether the T_o for growth depended on food availability. We also measured the same lizards’ resting metabolic rate at five T_bs to test the energetics model assumptions that metabolic cost increases exponentially with T_b and does not differ between energy states. The T_sel of lizards on both diets overlapped with the T_o for growth. The assumptions of the energetics model were verified, but the T_o for net energy gain did not depend on food availability. Therefore, we found support for the thermal coadaptation hypothesis. We did not find support for the energetics model, but this may have been due to low statistical power.     

Heritability of resistance to oxidative stress in early life

Oxidative stress has recently been suggested to play an important role in life‐history evolution, but little is known about natural variation and heritability of this physiological trait. Here, we explore phenotypic variation in resistance to oxidative stress of cross‐fostered yellow‐legged gull (Larus cachinnans) chicks. Resistance to oxidative stress was not related to plasma antioxidants at hatching, which are mostly derived from maternal investment into eggs. Common environmental effects on phenotypic variation in resistance to oxidative stress were not significant. Heritability was relatively low and nonsignificant in hatchlings, but interestingly, the chicks of age 8 days showed high and significant heritability (h² = 0.59). Our results suggest that resistance to oxidative stress is determined mainly by the genotype as chicks grow. Further work is required to explore the genetic role of oxidative stress in life‐history evolution.     

Behavioural thermoregulation by the endangered crocodile lizard (Shinisaurus crocodilurus) in captivity

Understanding the factors that may affect behavioural thermoregulation of endangered reptiles is important for their conservation because thermoregulation determines body temperatures and in turn physiological functions of these ectotherms. Here we measured seasonal variation in operative environmental temperature (T_e), body temperature (T_b), and microhabitat use of endangered crocodile lizards (Shinisaurus crocodilurus) from a captive population, within open and shaded enclosures, to understand how they respond to thermally challenging environments. T_e was higher in open enclosures than in shaded enclosures. The T_b of lizards differed between the open and shaded enclosures in summer and autumn, but not in spring. In summer, crocodile lizards stayed in the water to avoid overheating, whereas in autumn, crocodile lizards perched on branches seeking optimal thermal environments. Crocodile lizards showed higher thermoregulatory effectiveness in open enclosures (with low thermal quality) than in shaded enclosures. Our study suggests that the crocodile lizard is capable of behavioural thermoregulation via microhabitat selection, although overall, it is not an effective thermoregulator. Therefore, maintaining diverse thermal environments in natural habitats for behavioural thermoregulation is an essential measure to conserve this endangered species both in the field and captivity.     

Wolbachia modifies thermal preference in Drosophila melanogaster

Environmental variation can have profound and direct effects on fitness, fecundity, and host–symbiont interactions. Replication rates of microbes within arthropod hosts, for example, are correlated with incubation temperature but less is known about the influence of host–symbiont dynamics on environmental preference. Hence, we conducted thermal preference (T_p) assays and tested if infection status and genetic variation in endosymbiont bacterium Wolbachia affected temperature choice of Drosophila melanogaster. We demonstrate that isogenic flies infected with Wolbachia preferred lower temperatures compared with uninfected Drosophila. Moreover, T_p varied with respect to three investigated Wolbachia variants (wMel, wMelCS, and wMelPop). While uninfected individuals preferred 24.4°C, we found significant shifts of −1.2°C in wMel- and −4°C in flies infected either with wMelCS or wMelPop. We, therefore, postulate that Wolbachia-associated T_p variation within a host species might represent a behavioural accommodation to host–symbiont interactions and trigger behavioural self-medication and bacterial titre regulation by the host.     

Analysis of the genetic behavior of some starch properties in indica rice ( Oryza sativa L.): thermal properties,gel texture,swelling volume

Starch comprises about 90% of milled rice, so that the eating and cooking quality of rice is mainly affected by the starch properties. In the present paper, we analyzed the genetical behavior of gelatinization temperature tested by differential scanning calorimetry (DSC), gel texture, and the swelling volume (SV) of indica rice with an incomplete cross of 4×8 parents. A genetic model which can dissect the effects of triploid seed, the cytoplasm, and the maternal plant on the endosperm traits was used. The results indicated that peak temperature (T_p), conclusion temperature (T_c) and enthalpy (ΔH) were controlled by three types of genetic effects: seed direct (endosperm) effects, cytoplasmic effects and maternal effects. No cytoplasmic effects for the onset temperature (T_o), hardness and SV, and no maternal effects for cohesiveness were found. The additive variances (V _A +V _Am ) were larger than the dominance variances (V _D +V _Dm ) for all the traits except for T_c, which suggested that selection could be applied for the starch properties in early generations. The total narrow-sense heritability for each parameter was over 60%, indicating that selection advances were predictable in the early generations for these traits. Received: 17 February 2001 / Accepted: 17 May 2001     

Thermal sensitivity of growth rate in hatchling Sceloporus lizards: environmental,behavioral and genetic aspects

Summary To investigate the physiological, behavioral, and genetic contributions to growth rate, we studied the thermal sensitivity of growth rate in hatchlings of the iguanid lizards Sceloporus occidentalis and S. graciosus in the laboratory. We used a cycling thermal regime patterned after thermal environments found in nature. Growth rates increased with duration of access to radiant heat. Thus, variation in the thermal environment can cause phenotypic variation in growth rate and hence body size. The two species differed in both the magnitude and thermal sensitivity of growth rate, and these differences were associated with differences in behavioral thermoregulation. Thus, growth is determined interactively by both behavior and physiology. We found evidence of among-family variation in the growth rates of S. occidentalis, suggesting that growth rate has the genetic potential to evolve. In S. occidentalis, both growth rate and egg size affected body size of hatchlings at several weeks of age. In turn, hatchling size may affect fitness: for example, larger S. occidentalis hatchlings had higher sprint speeds and may therefore be more adept at capturing prey or evading predators. Our results demonstrate that growth rate has genetic, behavioral, and physiological components, and that the resulting effects on body size may have important consequences for ecological performance e.g., sprint speed.     

Parental effects on embryonic viability and growth in Arctic charr Salvelinus alpinus at two incubation temperatures

The parental influences on three progeny traits (survival to eyed‐embryo stage, post‐hatching body length and yolk‐sac volume) of Arctic charr Salvelinus alpinus were studied under two thermal conditions (2 and 7° C) using a factorial mating design. The higher temperature resulted in elevated mortality rates and less advanced development at hatching. Survival was mostly attributable to maternal effects at both temperatures, but the variation among families was dependent on egg size only at the low temperature. No additive genetic variation (or pure sire effect) could be observed, whereas the non‐additive genetic effects (parental combination) contributed to offspring viability at 2° C. In contrast, any observable genetic variance in survival was lost at 7° C, most likely due to the increased environmental variance. Irrespective of temperature, dam and sire–dam interaction contributed significantly to the phenotypic variation in both larval length and yolk size. A significant proportion of the variation in larval length was also due to the sire effect at 2° C. Maternal effects were mediated partly through egg size, but as a whole, they decreased in importance at the high temperature, enabling a concomitant increase in non‐additive genetic effects. For larval length, however, the additive component, like maternal effects, decreased at 7° C. The present results suggest that an exposure to thermal stress during incubation can modify the genetic architecture of early developmental traits in S. alpinus and presumably constrain their short‐term adaptive potential and evolvability by increasing the amount of environmentally induced variation.     

The effect of photoperiod on temperature selection in the European green lizard,Lacerta viridis

Summary Voluntary body temperature selection of unrestrained Lacerta viridis revealed consistant photoperiod entrained diel patterns. Each daily cycle was characterized by an elevation in body temperature (T _b) to a high level plateau which declined at the onset of scotophase to a low level; both of which were maintained within narrow ranges.Under natural photoperiod in fall, lizards responded to shorter days by sinking low level T _b's and expanding the duration of these low levels until no rhythmicity was shown. Subsequent exposure to long day, LD 16:8, induced self-arousal and a slightly altered diel T _b selection with significantly higher T _b's being chosen at both the elevated and lower daily levels. Changes in the relations of diel T _b selection due to shift in photoperiod, suggest that photoperiod acts as a seasonal indicator for thermal adaptation.This research was carried out in partial fulfillment of a diploma degree at the J.W.G. University, Frankfurt/Main     

Modelling exposure to selected temperature during pregnancy: the limitations of squamate viviparity in a cool-climate environment

Behavioural thermoregulation is important for the success of cool‐climate lizards, and a basis of the cold‐climate hypothesis for the evolution of viviparity in squamate reptiles. The temperature (T_sel) selected by pregnant females in a thermal gradient is considered to be optimal for embryonic development; however, exposure to T_sel throughout pregnancy has been difficult to estimate in small‐bodied lizards as temperature‐sensitive telemetry is impractical. In addition, the value of maternal thermophily during pregnancy is controversial: some studies have shown elevated T_sel, whereas others have found lowered T_sel or no change during pregnancy. We estimated indirectly the overall exposure to T_sel during the 4–5 months of pregnancy of the cool‐climate, sub‐alpine species Oligosoma maccanni (McCann's skink, 3–6 g) from southern New Zealand. The thermal environment available to skinks was modelled using temperature loggers inside validated copper models in basking and retreat sites. Pregnant skinks were able to achieve mean T_sel (28.9 °C) in the field very infrequently (4–15% of each month during the final 4 months of pregnancy). In field thermoregulatory studies, pregnant females did not bask more frequently and did not show altered field body temperature compared with non‐pregnant adults, suggesting that all skinks (whether pregnant or not) thermoregulate maximally whenever conditions allow. Further research on cool‐climate lizards should address the significance for offspring phenotypes of low and variable exposure to T_sel during pregnancy, as well as the significance of temperatures for embryos in maternal bodies (viviparity) versus nest sites (oviparity) arising from differences in maternal body size. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 96 , 541–552.     

Thermal ecology of the Australian agamid Pogona barbata

This study compares the thermal ecology of male bearded dragon lizards (Pogona barbata) from south-east Queensland across two seasons: summer (1994–1995) and autumn (1995). Seasonal patterns of body temperature (T _b) were explored in terms of changes in the physical properties of the thermal environment and thermoregulatory effort. To quantify thermoregulatory effort, we compared behavioral and physiological variables recorded for observed lizards with those estimated for a thermoconforming lizard. The study lizards' field T _bs varied seasonally (summer: grand daily mean (GDM) 34.6 ± 0.6°C, autumn: GDM 27.5 ± 0.3°C) as did maximum and minimum available operative temperatures (summer: GDM T _max 42.1 ± 1.7°C, T _min 32.2 ± 1.0°C, autumn: GDM T _max 31.7 ± 1.2°C, T _min 26.4 ± 0.5°C). Interestingly, the range of temperatures that lizards selected in a gradient (selected range) did not change seasonally. However, P. barbata thermoregulated more extensively and more accurately in summer than in autumn; lizards generally displayed behaviors affecting heat load nonrandomly in summer and randomly in autumn, leading to the GDM of the mean deviations of lizards' field T _bs from their selected ranges being only 2.1 ± 0.5°C in summer, compared to 4.4 ± 0.5°C in autumn. This seasonal difference was not a consequence of different heat availability in the two seasons, because the seasonally available ranges of operative temperatures rarely precluded lizards from attaining field T _bs within their selected range, should that have been the goal. Rather, thermal microhabitat distribution and social behavior appear to have had an important influence on seasonal levels of thermoregulatory effort. Received: 28 April 1997 / Accepted: 29 December 1997     

CONDITION, GENOTYPE-BY-ENVIRONMENT INTERACTION, AND CORRELATIONAL SELECTION IN LIZARD LIFE-HISTORY MORPHS

Abstract We compared reproductive allocation and variation in condition and survivorship of two heritable female throat color morphs (orange and yellow) in a free‐living population of side‐blotched lizards (Uta stansburiana). Using path analysis and structural equation modeling, we investigated how variation in the social environment affected clutch size and egg mass and two condition traits (postlaying mass, immunological condition) and how these traits in turn affected female field survival. In the presence of many neighbors, both morphs increased their clutch sizes, although these effects were only significant in yellow females. In addition, yellow females increased their egg mass in the presence of many orange neighbors. Orange females surrounded by many orange neighbors showed sign of stress in the form of immunosuppression, whereas this effect was less pronounced in yellow females. The morphs also differed in the impact of variation in clutch size and egg mass on both condition traits. Finally, female morphotype and immune responsiveness affected fitness interactively, and hence these two traits showed signs of fitness epistasis: Selection gradients on this trait were opposite in sign in the two morphs. The correlational selection gradient (_{γthroatxantibody response}) between female throat color and antibody responsiveness was ‐0.365. Our data thus reveal important interactive effects such as genotype‐by‐environment interaction toward the social environment and morph‐specific trade‐offs as well as the occurrence of correlational selection. We discuss the use of naturally occurring and conspicuous genetic polymorphisms in field studies of selection and life‐history allocation.     

Seasonal effects on metabolism and thermoregulation abilities of the Red-winged Starling (Onychognathus morio)

Basal metabolic rate (BMR) of birds is beginning to be viewed as a highly flexible physiological trait influenced by environmental fluctuations, and in particular changes in ambient temperatures (T_a). Southern Africa is characterized by an unpredictable environment with daily and seasonal variation. This study sought to evaluate the effects of seasonal changes in T_a on mass-specific resting metabolic rate (RMR), BMR and body temperature (T_b) of Red-winged Starlings (Onychognathus morio). They have a broad distribution, from Ethiopia to the Cape in South Africa and are medium-sized frugivorous birds. Metabolic rate (VO₂) and T_b were measured in wild caught Red-winged Starlings after a period of summer and winter acclimatization in outdoor aviaries. RMR and BMR were significantly higher in winter than summer. Body mass of Starlings was significantly higher in winter compared with summer. The increased RMR and BMR in winter indicate improved ability to cope with cold and maintenance of a high T_b. These results show that the metabolism of Red-winged Starlings are not constant, but exhibit a pronounced seasonal phenotypic flexibility with maintenance of a high T_b.