Variation in resource exploitation along an altitudinal gradient: the willow psyllids (Cacopsylla spp.) on Salix lapponum

Three congeneric species of Salix -fedding psyllid Cacospsylla spp. Occur along an altitudinal gradient (988 1222 m. a.s.l.) in southern Norway. The 27-km transect covered the local altitudinal range of the three species. Each species showed a different characteristic altitudinal distribution: C. propinqua occurred over the entire altitudinal range of the transect C. palmeni was restricted to higher altitude and C brunneipennis occurred manly at lower altitudes. This pattern of local altitudinal distribution mirrored the broader geographical distributions of these psyllids along latitudinal gradients. All three species developed on willow catkins, but also made use of leaves. Species differed in their use of leaves with >10% of sampled individuals of C. brunncipennis or C. Palmeni developing on leaves compared with up to 80% in C. propinqua. The proportion of C. propinqua nymphs developing on catkins increased with altitude and was also related to the temporal and spatial availability of catkins but was not a result of competitive displacement from catkins. Nitrogen concentration of host plants did not affect the proportions of C propinqua on leaves or catkins and was not related to adult size or psyllid density on catkins. Patterns or resource use are discussed in relation to differences in the distribution and abundance of the three species along the transect.     

The effects of chilling and forcing temperatures on spring synchrony between larch casebearer and tamarack

1. Spring phenological synchrony can be important for tree-insect interactions. Depending on the magnitude and direction of phenological shifts, overwintering insects could be affected in many ways, for example, facing starvation or having to contend with increased chemical or physical defences of host trees. If temperature has different influences on the phenology of trees and insects, climate change can alter spring phenological synchrony.
2. In this experiment, we exposed tamarack seedlings and larch case bearer larvae from Minnesota, USA, to a variety of chilling and forcing temperatures and measured spring phenology (twig bud break and larval activation). We additionally measured case bearer performance on seedlings that were exposed to different forcing × chilling levels, tracking larval survivorship to adulthood.
3. Warmer forcing enhanced larval activation and bud break, but larval development slowed down past 21°C. Higher chilling temperatures accelerated bud break, but the effect was inconclusive for larvae. There was no chilling × forcing interaction for either species. Spring activity accelerated more quickly with increases in temperature for larvae than for seedlings, resulting in increased phenological synchrony at warmer temperatures. Activation rates for overwintering larvae were highest at 27°C, while survivorship to adulthood following spring activation was highest at 21°C. At temperatures at or beyond 27°C, no larvae reached adulthood.
4. Warmer winters and springs will likely initially increase spring synchrony between tamarack and larch case bearer, exposing larvae to younger, potentially more nutritious foliage, but extremely warm spring temperatures may decrease survivorship of larvae to adulthood.

     

Host plant growth characteristics as determinants of abundance and phenology in jumping plant-lice on downy willow

1. Salix lapponum host plants at an upper altitudinal site differed significantly in size, structural density, phenology, growth performance, and spatial isolation from those growing at a lower site. 2. Plant differences were paralleled by significant differences in psyllid population density and phenology parameters, with psyllid population density, percentage of catkins occupied, and phenological development relatively lower or retarded at the upper site. Population densities at the upper site, nevertheless, remained high. 3. Plant measurements were good predictors of insect density, often explaining up to 73% of the variance in abundance among plants at a given site. 4. Sets of four plant characters identified by best subsets regression were better predictors of psyllid density and development than single factors, although differences were often not great and the combinations of characters selected by multiple regression sometimes differed from the best single predictors. 5. Best single predictors of psyllid density on catkins were measurements of plant size, particularly height, length, and basal stem diameter. Shoot density and catkin phenology were occasionally important but plant isolation and prior growth performance were less important. 6. By contrast with density, age structure of the psyllid population was predicted best from plant phenological measurements, notably catkin phenology.     

Effects of photoperiod and raised winter temperatures on egg development and timing of oviposition in the willow psyllid Cacopsylla moscovita

Nymphal development of Cacopsylla moscovita (And.) (Homoptera: Psylloidea) takes place only on female catkins of Salix repens L. and close phenological synchrony is crucial because development times of catkins and nymphs are similar. Eggs are laid on catkins as soon as they develop and close synchrony between oviposition and budburst maximizes time available for nymphal development. Sampling adult C. moscovita in the field revealed little synchrony between egg development and budburst, with over 60% of females containing mature eggs four weeks before catkins first appeared. In the laboratory, egg development was influenced by both temperature and photoperiod. At 10°C, egg development occurred approximately one month earlier than at 5°C and two weeks earlier than in the field. Adult survival in the laboratory was substantially reduced at increased temperature, with only 20% of adults surviving longer than two weeks at 10°C, compared with over 95% at 5°C. Body condition (weight corrected for size) of males and females decreased significantly in the field over winter. However, body condition of females levelled off before budburst, coincident with egg development implying that females had resumed feeding. We discuss our results in relation to regulation of phenological synchrony between oviposition and catkin appearance.     

Anatomy of an outbreak: the biology and population dynamics of a Cardiaspina psyllid species in an endangered woodland ecosystem

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Progressive restriction of host plant exploitation along a climatic gradient: the willow psyllid Cacopsylla groenlandica in Greenland

1. Host plant selection by the endemic willow psyllid Cacopsylla groenlandica was studied at eight sites in three locations along a N–S climatic gradient in west Greenland.
2. C. groenlandica oviposited and developed on four willow species: Salix glauca, S. arctophila, S. uva-ursi and S. herbacea. Development took place on female catkins of all species and on leaf shoots of S. glauca .
3. At sites in southern Greenland, C. groenlandica fully utilized all four willow species. However, there was progressive reduction of host plant species and tissues exploited as latitude increased, such that towards the northern limit of its range the psyllid became highly specialized, feeding only on female catkins of S. glauca , despite the presence of alternative hosts. Where plant growth was tightly constrained within a restricted growing season, the demands of synchronizing with more than one species may have become too great, resulting in specialization on a single host.
4. The probable mechanisms producing specialization were between-species differences in host plant phenology, linked to variation in the growing season, set against the partially non-overlapping geographical distribution patterns of the host willows.
5. A small degree of phenological asynchrony between host plants can be advantageous for the insect. Under favourable conditions the reproductive season can be extended by using a series of host plants with staggered phenologies. Some 'early' hosts also create predator-free space. However, as asynchrony increases, the advantages disappear as the insect becomes unable to exploit the full range of host options.
6. The importance of host plant synchrony in the life histories of arctic insects is discussed.     

Carabid life-cycle strategies and climate change: a study on an altitude transect

Abstract.

• 1 There was little overlap in the species composition of carabid beetle assemblages sampled below 450 m and above 800 m on an altitude transect and the first axis of a DECORANA ordination was closely correlated with altitude (r₁₁= 0.93, P < 0.001), probably reflecting the differing temperature requirements of different species.
• 2 Life-cycle strategies of two low-altitude species, found predominantly below 600 m, and two species caught above 600 m a.s.l., have been determined, using mandible wear to identify whether the females breed in the calendar year that they emerge as adults or in the year following.
• 3 Nebria salina has an annual cycle at 630 m. Pterostichus madidus and Calathus fuscipes were both biennial at altitudes above 300 m although predominantly annual at low altitude. N.gyllenhali was biennial above 600 m and it is not known whether it is able to switch to an annual cycle at low altitude.
• 4 Both N.salina and N.gyllenhali ceased activity soon after emergence, an adaptation which preserves their mandibles from wear.
• 5 At altitudes of 305 m and 430 m, P.madidus and C.fuscipes entered the breeding season with 33% and 56% reduction in mandible tip length, possibly reducing their reproductive output.
• 6 The necessity for relatively sharp mandibles on entry into the breeding season may restrict the capacity of carabids to respond to a temperature change by switching from annual to biennial cycles, and vice versa, adding support to the suggestion that carabids are more likely to respond to climate change by shifting distributions than by physiological adaptation.

     

Seed traits and germination behaviour of four Sardinian populations of Helichrysum microphyllum subsp. tyrrhenicum (Asteraceae) along an altitudinal gradient

• Helichrysum microphyllum subsp. tyrrhenicum (Asteraceae) is an endemic taxon of Sardinia and Corsica, where it grows at different altitudes. The objective of this study was to investigate the seed traits and germination behaviour of four Sardinian populations of this taxon located at different altitudes.
• Seed traits were evaluated, and germination tests were carried out by incubating seeds at a range of constant (5–30 °C) and alternating (25/10 °C) temperatures. The dry after‐ripening (DAR) pre‐treatment was also applied by storing seed in dry conditions for 3 months at 25 °C. Seed traits and germination behaviour data were statistically analysed to identify if there was a correlation with altitude.
• Differences in seed size, area and mass among populations were recorded, however, no relationship was found with altitude. High germination percentages were obtained in all populations, both in untreated and DAR seeds, and were positively affected by alternating temperatures. The final germination percentage and time required to reach 50% final germination (T₅₀) showed no relationship with altitude.
• The differences in seed traits and germination detected among the studied populations of H. microphyllum subsp. tyrrhenicum were not correlated with altitude. This study provides new and important knowledge for this taxon. H. microphyllum subsp. tyrrhenicum is characterised by high germination percentages and low T₅₀ values and does not seem to require any dormancy‐breaking treatment. This species represents a high‐potential native plant species that should be considered within environmental management plans.

     

Effects of carrot psyllid (Trioza apicalis) feeding on carrot yield and content of sugars and phenolic compounds

Carrot psyllid, Trioza apicalis, is a serious pest of carrot in Northern Europe, as it can significantly damage young carrot seedlings in a period as short as 3 days. This study was conducted to investigate effects of carrot psyllid feeding at different plant growth stages on carrot yield and to assess changes in content of sugars, phenolics and related compounds in carrot roots resulting from the psyllid feeding. In addition, reflectance of carrot leaves was measured to assess the intensity of discolouration in damaged leaves. Results showed that carrot yield was significantly reduced by a 3‐day carrot psyllid feeding period when the seedlings were exposed to psyllids at 1‐ or 2‐leaf stage. However, at 4‐leaf stage feeding by one carrot psyllid did not reduce yield. Sucrose concentration in the damaged roots was significantly decreased, whereas concentrations of some phenolic compounds were significantly increased. The reflectance of leaves of damaged carrots differed significantly from those of undamaged control leaves. These observations indicate that carrot psyllid damage has potential to lower not only the carrot yield, but also the carrot crop quality. No phytoplasma was detected in the carrots exposed to psyllids, but recently, T. apicalis has been associated with ‘Candidatus Liberibacter solanacearum’. The role of carrot psyllid feeding and the psyllid‐associated bacterium in the damage formation are discussed.     

Effects of the fungus Isaria fumosorosea (Hypocreales: Cordycipitaceae) on reduced feeding and mortality of the Asian citrus psyllid,Diaphorina citri (Hemiptera: Psyllidae)

The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae), is an important citrus pest primarily because it transmits bacteria putatively responsible for huanglongbing, a serious disease of citrus. We present a study on the effects of blastospore and conidial formulations of Isaria fumosorosea Wize on feeding rates and mortality of adult psyllids in laboratory bioassays. Information on quantities of honeydew droplets was used to make inferences on feeding rates. Psyllids treated with the blastospore formulation of I. fumosorosea produced fewer honeydew droplets compared to the conidial treatment and control beginning within the first 24 h after treatment. The highest daily mean number of droplets thereafter never exceeded 2.4 drops compared to 4 and 8 for the conidial treatment and control, respectively. The mean number (±SEM) of honeydew droplets produced per psyllid per day over 7 days was significantly higher in the control (5.5±0.5) compared to the blastospore treatment; however, there were no significant differences between the treatments. Psyllids treated with the conidial formulation of the pathogen showed no significant reduction in feeding activity until 4 days after treatment. One and 2 day's post-exposure, mortality of psyllids in the blastospore treatment ranged from 8 to 25% compared to 0% in the conidial and control treatments. By 7 days post-exposure, psyllid mortality reached 100% under both fungal treatments compared to none in the controls. This study documented that adult psyllids infected by I. fumosorosea (PFR 97) produce less honeydew than healthy psyllids and suggests that they may feed less, which could potentially reduce the spread of huanglongbing.     

Short feeding period of carrot psyllid (Trioza apicalis) females at early growth stages of carrot reduces yield and causes leaf discolouration

Overwintered adult carrot psyllids [Trioza apicalis Förster (Homoptera: Psylloidea: Triozidae)] damage carrot [(Daucus carota ssp. sativum L.) (Apiaceae)] seedlings by phloem feeding on the leaves. The aim of this study was to investigate the carrot root and shoot growth in relation to carrot psyllid density during early growth stages. One, two, or three carrot psyllids were allowed to feed on carrot seedlings for 3 days. Leaf damage was measured at the 8‐leaf stage, and root, leaf fresh weight, and number of true leaves were measured at harvest. Both the age of the carrot seedling at infestation and the psyllid density had a significant effect on leaf damage at the 8‐leaf stage: seedlings damaged at the cotyledon stage exhibited more leaf damage than seedlings damaged at the 1‐leaf stage. A higher psyllid density significantly reduced the carrot root weight at harvest. The significant interaction of psyllid density with seedling age indicates that differently aged carrot seedlings responded differently to feeding: one psyllid feeding for 3 days at the cotyledon stage caused a significant yield loss, whereas three psyllids were needed to cause the same impact at the 1‐leaf stage. Carrot leaf weight at harvest was not reduced by carrot psyllid feeding: leaves recovered from the damage but roots did not. Our results confirm the farmers’ observations that a trap replacement period of 1 week for carrot psyllid monitoring is too long, especially at the cotyledon stage. Severe leaf discolouration on damaged carrots was observed at harvest. The possible reasons for this discolouration, such as toxin excreted in psyllid saliva or plant pathogenic mycoplasma infection, are discussed.     

Direct and indirect effects of weather variability in a specialist butterfly

1. Climate change poses serious threats to the long‐term persistence of many animal and plant populations. Species having specific niche requirements, or characterised by highly co‐evolved interactions, will face the greatest challenges. An example is represented by Maculinea alcon (Denis & Schiffermüller), a monophagous and univoltine butterfly species, which lays eggs only on larval host plants which occur inparticular phenological conditions. 2. The present 2‐year study focused on two M. alcon populations, both located at the southern boundaries of the species, but facing different climatic conditions (360 m, low altitude versus 860 m, high altitude). Population vulnerability with respect to direct and indirect effects of climate change was analysed, focusing on two important aspects of butterfly biology, i.e. the flight activity of adults and the degree of synchrony in the larval plant–insect interactions. 3. It was observed that, when positive temperature anomalies are reached, the temperature can exert detrimental effects on adults' activity. At a low altitude, in a hotter than usual year, a temperature threshold was recorded (around 32 °C), above which the activity of butterflies is inhibited. In contrast, at a high altitude, temperature increases maintain the opportunity to enhance butterfly activity. Altitudinal differences were also observed in the phenology of the two interacting species, which generate stronger asynchrony at low altitudes. 4. High‐ and low‐altitude populations represent different conservation units: a global increase in temperature would pose a serious threat to the lowland populations, whereas high‐altitude populations would gain a greater role in assuring the persistence of M. alcon at its southern boundaries.     

Altitudinal variation in life cycle syndromes of California populations of the grasshopper,Melanoplus sanguinipes (F.)

Summary Life cycles of California populations of the grasshopper, Melanoplus sanguinipes, varied along an altitudinal gradient. Temperature records indicate a longer season at low altitude on the coast, based on computation of degree days available for development, even though summer air temperatures are cooler than at high altitude; this is a result of warm soil temperatures. At high and low altitudes there was a high proportion of diapause eggs oviposited, while intermediate proportions of diapause eggs occurred at mid altitudes. The low altitude, and especially sea level, populations diapaused at all stages of embryonic development, while at high altitudes most diapause occurred in the late stages just before hatch. Diapause was more intense at high altitudes. One result of diapause differences was delayed hatching in the sea level population. Nymphal development and development of adults to age at first reproduction were both accelerated at high altitude relative to sea level. At lower temperatures (27° C) there was a tendency for short days to accelerate development of sea level nymphs, but not high altitude nymphs. In both sea level and high altitude grasshoppers, short days accelerated maturation of adults to onset of oviposition at warm temperature (33° C); there was little reproduction at 27° C. Population differences for all traits studied appear to be largely genetic with some maternal effects possible. We interpret diapause variation at low and mid altitudes to be responses to environmental uncertainty and variations in development rates to be adaptations to prevailing season lengths.     

Influence of altitude on local adaptation in upland tree species from central Argentina

• Steep climatic gradients boost morphological and physiological adjustments in plants, with consequences on performance. The three principal woody species of the Sierras Grandes Mountains of central Argentina have marked differences in sapling performance along their altitudinal distribution. We hypothesize that the steep gradient of climatic conditions across the species’ altitudinal distribution promotes trait differences between populations of different altitudes that are inherited by the following generation.
• Seeds from different altitudes were exposed to three temperature regimes to assess differential germination responses. Saplings were then transplanted to a greenhouse to assess possible variations in attributes and performance after 18 months.
• The three species showed differences in germination responses to temperature among altitudes and/or in sapling attributes and performance. In Maytenus boaria and Escallonia cordobensis, germination success was higher under high temperatures for the highest‐altitude, whereas lower temperatures boosted germination of the lowest altitudes. Polylepis australis showed no differences in germination among temperature treatments. In the greenhouse, saplings of the three species from intermediate altitudes showed high performance, whereas the upper and lower populations seemed to be adjusted to tolerating more stressful conditions (i.e., lower temperatures at the upper end and water stress at the lower end), showing lower performance toward both altitudinal limits.
• These patterns agree with those described for saplings growing under field conditions, suggesting adjustments in response to environmental changes undergone by populations along the altitudinal range. The marked adjustments of populations to the local environment suggest a potentially high impact of climatic change on species distribution.

     

Discrimination among host plants (Leucaena species and accessions) by the psyllid pest Heteropsylla cubana and implications for understanding resistance

Abstract 1 The herbivorous bug Heteropsylla cubana Crawford (Homoptera: Psyllidae) is a pest of the cattle fodder crop Leucaena (Leguminosae: Mimosoideae). The interaction between the psyllid and three varieties of its Leucaena host plant was investigated in relation to the apparent resistance of some Leucaena varieties (Leucaena leucocephala, Leucaena pallida and their hybrids) to attack. 2 Field trials demonstrated that adult psyllids distinguished among the different varieties of Leucaena over a distance, and were attracted to L. leucocephala in significantly higher numbers than to L. pallida or to the hybrid. Pesticide treatment increased the attractiveness of Leucaena plants, even of those deemed to be psyllid resistant. Numbers of psyllid eggs and nymphs, sampled in the field, reflect the arrival rates of adults at the three plant varieties. 3 Wavelength reflectance data of the three Leucaena varieties were not significantly different from one another, suggesting that psyllids cannot discriminate among the three plants using brightness or wavelength cues. There was a differential release of caryophyllene among the three varieties. Release of caryophyllene in L. leucocephala and the hybrid appeared to be influenced by environmental conditions. 4 Experiments demonstrated that caryophyllene (at least on its own) did not influence the behaviour of leucaena psyllids in relation to leucaena plants. 5 The results suggest that host plant volatiles cannot be dismissed as significant in the interaction between the leucaena psyllid and its Leucaena host plants. Further avenues for investigation are recommended and these are related to novel ways of understanding resistance in insect plant inter‐relationships.     

Layers of nocturnal insect migrants at high-altitude: the influence of atmospheric conditions on their formation

• 1 Radar studies of nocturnal insect migration have often found that the migrants tend to form well‐defined horizontal layers at a particular altitude.
• 2 In previous short‐term studies, nocturnal layers were usually observed to occur at the same altitude as certain meteorological features, most notably at the altitudes of temperature inversion tops or nocturnal wind jets.
• 3 Statistical analyses are presented of 4 years of data that compared the presence, sharpness and duration of nocturnal layer profiles, observed using continuously‐operating entomological radar, with meteorological variables at typical layer altitudes over the U.K.
• 4 Analysis of these large datasets demonstrated that temperature was the foremost meteorological factor that was persistently associated with the presence and formation of longer‐lasting and sharper layers of migrating insects over southern U.K.

     

Phenology of Festuca pallescens in relation to topography in north-western Patagonia

Abstract. The phenological changes in populations of Festuca pallescens (St. Yves) Parodi at different topographic positions and exposure along an altitudinal gradient (600 - 1100 m) were investigated during two growing seasons in northwestern Patagonia. Stepwise multiple regression analysis was used to describe the relationship between phenology and environment during the entire growing season. Analysis of variance was also performed at each sample date to detect significant environmental factors influencing phenology at different sites. The sum of maximum air temperatures was identified as the environmental variable best correlated with the seasonal variation of phenological events of Festuca pallescens over the period of two growing seasons, explaining 93.2 % of the total variance. Significant differences between sites were observed at each sample date. Main effects of altitude and topographic position and two-way interactions between altitude and topographic position, and topographic position and exposure were also detected as significant. Phenology was delayed at increased altitude. Differences in phenology between topographic sites at the same altitude were not detected during the entire growing season and were only observed in the reproductive phase. At this time, the phenology was significantly delayed at high topographic positions on the slopes as compared with low and mid positions. At high altitudes in the valley (950 m a. s. 1.), where steep slopes and humid conditions prevail, phenology was delayed on western exposures and low positions. The results adequately summarize and quantify the effect of spatial and temporal environmental variation on the phenological development of Festuca pallescens in northwestern Patagonia.     

Identifying factors determining the altitudinal distribution of the invasive pest leafminers Liriomyza huidobrensis and Liriomyza sativae

Abiotic and biotic factors that change with altitude can influence the distribution of herbivorous insects. We examined factors influencing the distribution of the generalist leafminers Liriomyza sativae Blanchard and Liriomyza huidobrensis Blanchard (Diptera: Agromyzidae), two pests of agricultural crops, in the tropical Dieng mountainous area of Central Java, Indonesia. Liriomyza huidobrensis predominated at altitudes above 700 m a.s.l. and was the only species collected above 1 400 m a.s.l. In contrast, L. sativae predominated below 600 m a.s.l. and was not found above 1 200 m where the average temperature was 20.7 °C. Parasitoid diversity decreased with altitude, but parasitism did not change. The distribution of neither species was affected by parasitoids; L. huidobrensis predominant at high altitudes was preferred by Opius parasitoids common at these altitudes. Intra‐ and interspecific competition was detected in laboratory experiments where larval density was high, but led to coexistence rather than species displacement. No competition was detected in a field experiment when larval density was low. However, L. sativae failed to reproduce at the highest altitude, whereas L. huidobrensis established at all altitudes. Host composition varied with altitude and one host (faba beans) preferred by L. huidobrensis was common at high altitudes. By relating published data on the performance of the leafminer species to altitudinal temperature changes, we were partly successful in predicting the altitude at which the dominant species switched. Temperature plays an overriding influence on the altitudinal distribution of leafminers.     

Secondary Endosymbionts of Psyllids Have Been Acquired Multiple Times

Previous studies have established that psyllids (Hemiptera, Psylloidea) contain primary endosymbionts, designated as Carsonella ruddii, which cospeciate with the psyllid host. This association appears to be the consequence of a single infection of a psyllid ancestor with a bacterium. Some psyllids may have additional secondary (S-) endosymbionts. We have cloned and sequenced the 16S–23S ribosomal RNA genes of seven representative psyllid S-endosymbionts. Comparison of the S-endosymbiont phylogenetic trees with those of C. ruddii indicates a lack of congruence, a finding consistent with multiple infections of psyllids with different precursors of the S-endosymbionts and/or possible horizontal transmission. Additional comparisons indicate that the S-endosymbionts are related to members of the Enterobacteriaceae as well as to several other endosymbionts and insect-associated bacteria. Received: 2 May 2000 / Accepted: 8 June 2000     

The lizard Psammodromus algirus (Squamata: Lacertidae) is darker at high altitudes

Altitudinal gradients offer a good opportunity to study organisms' adaptations to clinal environmental variables. Regarding altitude, the most influential variables on organisms are temperature and ultraviolet (UV) solar radiation, the first decreasing and the second increasing with altitude. Both variables affect ectotherms' biology, as ectotherms depend on environmental temperature for thermoregulation, frequently being heliotherms. Here, we studied dorsal coloration in the lizard Psammodromus algirus (Linnaeus, 1758) along a wide altitudinal gradient (2200 m) in Sierra Nevada (south‐east Spain). We hypothesize that the skin will be darker with altitude, i.e. in environments with lower temperatures and higher UV radiation intensity. Results show that individual dorsal colorations became darker at high altitude. We propose two non‐mutually exclusive explanations for this result: (1) darker dorsal surface would favour faster warming at high altitudes, where temperature is lower, and (2) darker dorsal surface would protect against UV radiation, stronger at high altitudes. We found significant relationships between both temperature and UV radiation and population dorsal darkness, giving mixed support for the two explanations. Moreover, dorsal hue was positively correlated with substrate hue, suggesting that hue evolved to maximize crypsis. Our study therefore suggests that geographical variation in dorsal coloration in this lizard is adaptive, and darkness coloration might have evolved in response to adverse conditions (low temperature and high UV radiation) at high altitudes. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 112 , 132–141.