Physiological adjustments to arid and mesic environments in larks (Alaudidae)

Because deserts are characterized by low food availability, high ambient temperature extremes, and absence of drinking water, one might expect that birds that live in these conditions exhibit a lower basal metabolic rate (BMR), reduced total evaporative water loss (TEWL), and greater ability to cope with high air temperatures than their mesic counterparts. To minimize confounding effects of phylogeny, we compared the physiological performance of four species of larks at ambient temperatures (T(a)'s) ranging from 0 degrees to 50 degrees C: hoopoe larks (Alaemon alaudipes) and Dunn's larks (Eremalauda dunni) live in hot and dry deserts, whereas skylarks (Alauda arvensis) and woodlarks (Lullula arborea) occur in temperate mesic areas. Mass-adjusted BMR and TEWL were indistinguishable between hoopoe lark and Dunn's lark and between skylark and woodlark. When grouping the data of the two desert larks in one set and the data of the two mesic larks in another, desert larks are shown to have 43% lower BMR levels and 27% lower TEWL values than the mesic species. Their body temperatures (T(b)'s) were 1.1 degrees C lower, and the minimal dry heat transfer coefficients (h) were 26% below values for the mesic larks. When T(a) exceeded T(b), the h of hoopoe larks and Dunn's larks was high and indistinguishable from h at 40 degrees C, in contrast to the prediction that h should be decreased to minimize heat gain through conductance, convection, or radiation from the environment when T(a) exceeds T(b).     

Cutaneous and respiratory water loss in larks from arid and mesic environments

Birds from deserts generally have lower total evaporative water loss (TEWL), the sum of cutaneous (CWL) and respiratory water loss (RWL), than species from mesic areas. We investigated the role of CWL and RWL as a function of air temperature (T(a)) in hoopoe larks (Alaemon alaudipes) and Dunn's larks (Eremalauda dunni) from the Arabian Desert and skylarks (Alauda arvensis) and woodlarks (Lullula arborea) from temperate mesic grasslands. The proportional contribution of CWL to TEWL in all larks at moderate T(a) ranged from 50% to 70%. At high T(a) (40 degrees -45 degrees C), larks enhanced CWL by only 45%-78% and relied on an increase in RWL by 676%-2,733% for evaporative cooling. Surface-specific CWL at 25 degrees C was 29% lower in the arid-zone species than in the mesic larks. When acclimated to constant T(a), 15 degrees C-acclimated hoopoe larks increased CWL by 22% compared with 35 degrees C-acclimated birds, but the other species did not change CWL. This study is consistent with the hypothesis that larks from deserts have a reduced CWL at moderate and low T(a) but provided no support for the hypothesis that at high T(a) larks from arid regions rely more on CWL than larks from mesic environments. Interspecific differences in CWL cannot be attributed to acclimation to environmental temperature and are possibly the result of genetic differences due to natural selection or of phenotypically plastic responses to divergent environments during ontogeny.     

Competition between birds and mammals: A comparison of giving-up densities between crested larks and gerbils

We combined the concept of mechanisms of co-existence with the approach of giving-up densities to study inter-taxon competition between seed-eating birds and mammals. We measured feeding behaviour in food patches to define and study the guild of seed-eating vertebrates occupying sandy habitats at Bir Asluj, Negev Desert, Israel. Despite a large number of putatively granivorous rodents and birds at the site, two gerbil species (Allenbys gerbil, Gerbillus allenbyi, and the greater Egyptian gerbil, G. pyramidum) dominated nocturnal foraging, and a single bird species (crested lark, Galerida cristata) contributed all of the daytime foraging. We used giving-up densities to quantify foraging behaviour and foraging efficiencies. A low giving-up density demonstrates the ability of a forager to profitably harvest food at low abundances and to profitably utilize the foraging opportunities left behind by the less efficient forager. Gerbils had lower giving-up densities in the bush than open microhabitat, and lower giving-up densities in the semi-stabilized than stabilized sand habitats. Crested larks showed the opposite: lower giving-up densities in the open than bush, and on the stabilized than semi-stabilized sand habitats. Despite these patterns, gerbils had substantially lower giving-up densities than crested larks in both microhabitats, all sand habitats, and during each month. Several mechanisms may permit the crested lark to co-exist with the gerbils. Larks may be cream skimmers on the high spatial and temporal variability in seed abundances. Larks may rely on insects, fruit or smaller seeds. Or, larks may rely on adjacent rocky habitats.     

Lipids of the stratum corneum vary with cutaneous water loss among larks along a temperature-moisture gradient

We explored the relationship between lipids of the stratum corneum (SC), the barrier to water-vapor diffusion of the skin, and cutaneous water loss (CWL) of species of free-living larks along a temperature-moisture gradient. Our results showed that free fatty acids, cholesterol, and ceramides were the major constituents of SC in larks from different environments including the Netherlands, a mesic environment; Iran, a semiarid region; and several areas in Saudi Arabia, a hot dry desert. We found that CWL was reduced among larks inhabiting deserts, but our data did not support the hypothesis that birds from desert environments have larger quantities of lipids per unit dry mass of the SC than larks from more mesic environments. Instead, larks in arid environments had a higher proportion of ceramides, especially the more polar fractions 4-6, and a smaller proportion of free fatty acids in their SC, an adjustment that apparently reduced their CWL. Subtle changes in the ratios of lipid classes can apparently alter the movement of water vapor through the skin. We hypothesize that desert birds have higher proportions of ceramides in their SC and lower proportions of free fatty acids because this combination allows the lipid lamellae to exist in a more highly ordered crystalline phase and consequently creates a tighter barrier to water-vapor diffusion.     

Thermoregulation in the Angolan free-tailed bat Mops condylurus: A small mammal that uses hot roosts.

The Angolan free-tailed bat (Mops condylurus) uses roosts that often exceed 40 degrees C, an ambient temperature (Ta) that is lethal to many microchiropterans. We measured the physiological responses of this species at Ta's from 15 degrees to 45 degrees C. Torpor was commonly employed during the day at the lower Ta, but the bats generally remained euthermic at night, with a mean body temperature (Tb) of 35.2 degrees C. Metabolic rate reflected the pattern of Tb, increasing with falling Ta at night but decreasing during the day. Metabolic rate and evaporative losses were lower in torpid than in euthermic bats. Body temperature increased at each Ta >35 degrees C and was 43 degrees C at Ta of 45 degrees C. At Ta of 40 degrees C bats increased dry thermal conductance and evaporative heat loss compared to lower Ta. At 45 degrees C dry thermal conductance was lower than at 40 degrees C and evaporative heat loss was 132% of metabolic heat production. At high Ta there was only a slight increase in metabolic rate despite the employment of evaporative cooling mechanisms and an increase in Tb. Collectively our results suggest that M. condylurus is well suited to tolerate high Ta, and this may enable it to exploit thermally challenging roost sites and to colonise habitats and exploit food sources where less stressful roosts are limiting.     

Seasonal metabolic flexibility is correlated with microclimate variation in horned larks and house sparrows

Maximum and minimum metabolic rates in birds are flexible traits and such flexibility can be advantageous in variable climates. The climatic variability hypothesis (CVH) posits that more variable climates should result in greater metabolic flexibility for geographically distinct populations. Whether the CVH applies to sympatric species occupying microclimates differing in variability is unknown. Microclimates of open habitats are likely more variable than those of sheltered habitats. If the CVH extends to microclimates, we expect birds from open habitats to show greater flexibility than those from sheltered habitats. To test this extension of the CVH, we compared seasonal variation in microclimates and metabolic rates for sympatric horned larks Eremophila alpestris, which occupy open habitats, and house sparrows Passer domesticus, which occupy sheltered habitats. We measured operative temperature (T_e, an integrative measure of the thermal environment), summit metabolic rate (M_sum, maximal cold-induced metabolic rate), and basal metabolic rate (BMR, minimal maintenance metabolic rate) in summer and winter. For both winter and summer, daily minimum T_e was similar between open and sheltered habitats but maximum T_e was higher for open habitats. Winter microclimates, however, were colder for open than for sheltered habitats after accounting for convective differences. Both species increased M_sum in winter, but seasonal M_sum flexibility was greater for larks (43%) than for sparrows (31%). Winter increases in BMR were 92.5% and 11% for larks and sparrows, respectively, with only the former attaining statistical significance. Moreover, species * season interactions in general linear models for whole-organism metabolic rates were significant for BMR and showed a similar, although not significant, pattern for M_sum, with greater seasonal metabolic flexibility in horned larks than in house sparrows. These results suggest that extending the CVH to sympatric bird species occupying different microclimates may be valid.     

The geographic and seasonal dimensions of habitat use in Galerida larks: implications for species coexistence and range limits

In this paper, we investigated the patterns of habitat use in three sibling species of larks: the Thekla lark Galerida theklae which is sympatric with either of two parapatric species of crested larks (G. macrorhyncha replacing G. cristata in arid areas of Morocco). Specifically, we addressed the following questions: 1) do species show niche conservatism in space (France vs Morocco) and time (breeding vs winter period)? 2) Does habitat use change at different interspecific densities? 3) Which factors drive the narrow range limit between G. cristata and G. macrorhyncha? We found that G. theklae was strongly associated with sloping and rocky (rugged) habitats in comparison with crested larks, but habitat use was not entirely consistent in space and time. Evidences for ecological displacement were mitigated. In the only habitat shared by G. cristata and G. theklae in France (vineyards surrounded by low shrubland), we observed a one‐third increase of G. theklae from nearby garrigues in winter, which coincided with a significant decrease of G. cristata after we controlled for density changes in non‐shared habitats. However, in Morocco, the use of rugged habitats by G. theklae was not affected by the prevalence of G. cristata or G. macrorhyncha in surrounding areas, at least at the spatial scales investigated. Our results suggest that interspecific competition plays a role in the parapatric distribution of G. cristata and G. macrorhyncha, because: 1) the alternative of a recent contact receives little support; 2) transition between species coincides with aridity gradients but not with topographic barriers or a sharp ecotone; 3) G. cristata also occurs in arid areas wherein G. macrorhyncha is rare or absent. Overall, our results add support to the view that a better integration of biotic interactions and spatio‐temporal variations in ecological niches might increase the predictive power of ecological niche models.     

Immune indexes of larks from desert and temperate regions show weak associations with life history but stronger links to environmental variation in microbial abundance

Abstract Immune defense may vary as a result of trade-offs with other life-history traits or in parallel with variation in antigen levels in the environment. We studied lark species (Alaudidae) in the Arabian Desert and temperate Netherlands to test opposing predictions from these two hypotheses. Based on their slower pace of life, the trade-off hypothesis predicts relatively stronger immune defenses in desert larks compared with temperate larks. However, as predicted by the antigen exposure hypothesis, reduced microbial abundances in deserts should result in desert-living larks having relatively weaker immune defenses. We quantified host-independent and host-dependent microbial abundances of culturable microbes in ambient air and from the surfaces of birds. We measured components of immunity by quantifying concentrations of the acute-phase protein haptoglobin, natural antibody-mediated agglutination titers, complement-mediated lysis titers, and the microbicidal ability of whole blood. Desert-living larks were exposed to significantly lower concentrations of airborne microbes than temperate larks, and densities of some bird-associated microbes were also lower in desert species. Haptoglobin concentrations and lysis titers were also significantly lower in desert-living larks, but other immune indexes did not differ. Thus, contrary to the trade-off hypothesis, we found little evidence that a slow pace of life predicted increased immunological investment. In contrast, and in support of the antigen exposure hypothesis, associations between microbial exposure and some immune indexes were apparent. Measures of antigen exposure, including assessment of host-independent and host-dependent microbial assemblages, can provide novel insights into the mechanisms underlying immunological variation.     

Temperature regulation following nickel intoxication in the mouse: effect of ambient temperature

1. The purpose of this study was to examine the interaction between ambient temperature (Ta) and the effects of nickel chloride on the thermoregulatory system of the mouse. 2. Male mice of the BALB/c strain were injected with nickel chloride at dosages of 0, 0.1, 1.0, 2.5, 5.0 and 10.0 mg/kg intraperitoneally and placed in an environmental chamber set at a Ta of either 10, 20, 30 or 35 degrees C for 60 min. Colonic temperature was then measured after one hour of exposure at a given Ta. 3. The thermoregulatory effects of nickel chloride were highly dependent on Ta. Nickel chloride had no effect on body temperature at Ta's of 30 and 35 degrees C. 4. 10 mg/kg dosage of nickel chloride caused a significant reduction in colonic temperature at a Ta of 20 degrees C. At a Ta of 10 degrees C the 5 and 10 mg/kg dosages of nickel chloride caused a significant lowering of body temperature. 5. Using segmented linear regression techniques it was shown that the threshold dose of nickel chloride for causing hypothermia was 9.6 and 3.3 mg/kg at Ta's of 20 and 10 degrees C, respectively. 6. This study has shown that two stressors, low Ta and nickel chloride intoxication, when applied independently have no effect on body temperature; however, when applied simultaneously, they have a significant toxic effect on thermoregulation.     

Thermoregulation in the meerkat (Suricata suricatta Schreber, 1776)

Tre of the suricates exhibits a marked diurnal rhythm (mean Tre at night 36.3 +/- 0.6 degrees C and 38.3 +/- 0.5 degrees C during the day). Oxygen consumption is lowest at Ta 30-32.5 degrees C (mean 0.365 +/- 0.022 ml O2 g-1 hr-1); this is 42% below the value expected from body mass. At Ta below the TNZ, oxygen uptake rises rapidly, minimal thermal conductance (0.040 ml O2 g-1 h-1 degrees C-1) being 18% above the mass-specific level. Lowest heart rates occur at Ta 30 degrees C (mean 109.6 +/- 9.8 beats min-1) and oxygen pulse is minimal at Ta 30-35 degrees C with 40-45 microliter O2 beat-1. At Ta 15-32.5 degrees C total evaporative water loss is between 0.46-0.63 ml H2O kg-1 hr-1 and increases markedly during heat stress (to a mean of 5.35 ml H2O kg-1 hr-1 at Ta 40 degrees C). This rise of TEWL is mainly attributable to the onset of panting at Ta above 35 degrees C.     

Phenotypic variation in Galerida larks in Morocco: the role of history and natural selection

The relative influences of history, natural selection and hybridization in shaping phenotypic variation in closely related taxa is a crucial issue in current evolutionary biology. In this study, we used as a model two sibling but paradoxically highly variable species of larks (Galerida theklae and Galerida cristata) of Morocco to separate the impacts of these evolutionary forces. In the former species, variation is manifested mainly in colouration, while in the latter, variation also encompasses bill size and shape. Mitochondrial and nuclear DNA sequencing were used to identify the historical relationships among the subspecies and species. According to our analyses, G. cristata and G. theklae diverged about 3.7 million years ago (Ma), and we found no evidence for a role of hybridization in maintaining their similarity. In G. theklae, there was no further subdivision, while in G. cristata two major mtDNA groups were identified (divergence approximately 1.1 Ma). These two lineages are parapatric and regroup, respectively, the three short-billed subspecies [G. (cristata) cristata] and the two long-billed subspecies [G. (cristata) randonii]. Patterns of morphological variation were then contrasted to this pattern of neutral relationships: we found that G. (c.) cristata was morphologically more similar to G. theklae than to G. (c.) randonii. Overall, these results point towards the prominent role of (i) natural selection and/or phenotypic plasticity in adapting the plumage to local conditions and (ii) natural selection in combination with historical isolation in driving the divergence in size and bill morphology in the crested larks.     

Ventilatory accommodation of oxygen demand and respiratory water loss in kangaroos from mesic and arid environments, the eastern grey kangaroo (Macropus giganteus) and the red kangaroo (Macropus rufus)

We studied ventilation in kangaroos from mesic and arid environments, the eastern grey kangaroo (Macropus giganteus) and the red kangaroo (Macropus rufus), respectively, within the range of ambient temperatures (T(a)) from -5 degrees to 45 degrees C. At thermoneutral temperatures (Ta=25 degrees C), there were no differences between the species in respiratory frequency, tidal volume, total ventilation, or oxygen extraction. The ventilatory patterns of the kangaroos were markedly different from those predicted from the allometric equation derived for placentals. The kangaroos had low respiratory frequencies and higher tidal volumes, even when adjustment was made for their lower basal metabolism. At Ta>25 degrees C, ventilation was increased in the kangaroos to facilitate respiratory water loss, with percent oxygen extraction being markedly lowered. Ventilation was via the nares; the mouth was closed. Differences in ventilation between the two species occurred at higher temperatures, and at 45 degrees C were associated with differences in respiratory evaporative heat loss, with that of M. giganteus being higher. Panting in kangaroos occurred as a graded increase in respiratory frequency, during which tidal volume was lowered. When panting, the desert red kangaroo had larger tidal volumes and lower respiratory frequencies at equivalent T(a) than the eastern grey kangaroo, which generally inhabits mesic forests. The inference made from this pattern is that the red kangaroo has the potential to increase respiratory evaporative heat loss to a greater level.     

The heat-acclimated pigeon: an ideal physiological model for a desert bird

Acclimation of rock pigeon (Columba livia) to high ambient temperature (Ta) 50 degrees C from the time of hatching resulted in a well-developed cutaneous evaporative cooling mechanism (CECM), which became the dominant mechanism for heat dissipation. After the age of 15 days and in adults, acclimated pigeons exposed to 48-60 degrees C Ta could regulate normal body temperature (Tb) without employing either panting or gular fluttering. Respiration rate varied between 36 +/- 12 (SD) and 35 +/- 14 breaths/min at moderate and at extreme high Ta's, respectively. During thermal stress (42, 45, and 47 degrees C) imposed in a metabolic chamber, nonpanting pigeons' heat balance was achieved by adjusting low-level heat production (46.2 +/- 6.8 W/m2) and by use of an efficient CECM that dissipated 145% of the metabolic heat. Tb was regulated between 40.7 +/- 0.5 and 41.8 +/- 0.4 degrees C over a wide range of Ta's (20-56 degrees C). The respiratory evaporative cooling mechanism (RECM) was effective since hatching. The CECM developed approximately 24 h later during the ontogeny of the altricial nestling pigeon. This trait, which exists in many bird species and may be a recent development, possibly evolved as an adaptation to hot environments. In the present study we have brought evidence for a multitrait physiological adaptation that takes preeminence in adjusting the processes involved in maintaining heat balance. This integrative complex creates a powerful, efficient tool for contending with the most extreme thermal conditions.     

Body temperature and oxygen uptake in the kinkajou (Potos flavus, Schreber), a nocturnal tropical carnivore.

Two kinkajous (Potos flavus, Procyonidae) showed marked nycthemeral variations in their rectal temperature. The mean Tr at night was 38.1 +/- 0.4 degrees C SD and 36.0 +/- 0.6 degrees C SD while resting during the day. Body temperature and O2-consumption were measured at ambient temperatures from 5-35 degrees C. With one exception at 35 degrees C, hypo- or hyperthermia was never observed. At air temperatures above 30 degrees C the bears reacted with behavioural responses. O2-consumption was minimal at Ta's from 23-30 degrees C. The mean basal metabolic rate was 0.316 ml O2 g-1 h-1 which is only 65% of the expected value according to the Kleiber formula. Below 23 degrees C heat production followed the equation : y (ml O2 g-1 h-1) = 0.727--0.018 Ta. The minimal thermal conductance was 90% of the predicted value according to the formula : C (ml O2 g-1 h-1 degrees C-1) = 1.02 W-0.505 (HERREID & KESSEL, 1967). Kinkajous are another distinct exception to the mouse to elephant curve.     

Unappreciated tolerance to high ambient temperatures in a widely distributed desert rodent, Dipodomys merriami

A long-held assertion has been that nocturnality is an escape mechanism for many nocturnal desert rodents because of limited tolerances to heat. To test this claim, we used a treadmill to examine the tolerances to high ambient temperatures (T(a)'s) of one subspecies of desert rodent, Merriam's kangaroo rat, Dipodomys merriami merriami, from contrasting environments. We simultaneously measured body temperature (T(b)), evaporative water loss, and metabolic rates at an ecologically relevant speed (0.6 km h(-1)) at different ambient temperatures (Ta=25 degrees -42.5 degrees C). We hypothesized that kangaroo rats from a more xeric site would have greater abilities to remain active and maintain stable T(b) than those from a more mesic site, but mesic- and xeric-site animals had comparable tolerances and were active until Tb=42 degrees C. At Ta=42.5 degrees C, however, T(b) of mesic-site animals increased more quickly than in xeric-site animals. Although most animals could not run more than 18 min at Ta=42.5 degrees C, most could run at Ta=40 degrees C for at least 30 min. Benefits of nocturnality for this species may reside more in purposes of water conservation and avoidance of predation and less on the direct regulation of T(b), as T(b) is more labile than commonly thought.     

Ecological and evolutionary physiology of desert birds: a progress report

The adaptive significance of mechanisms of energy and water conservation among species of desert rodents, which avoid temperature extremes by remaining within a burrow during the day, is well established. Conventional wisdom holds that arid-zone birds, diurnal organisms that endure the brunt of their environment, occupy these desert climates because of the possession of physiological design features common to all within the class Aves. We review studies that show that desert birds may have evolved specific features to deal with hot desert conditions including: a reduced basal metabolic rate (BMR) and field metabolic rate (FMR), and lower total evaporative water loss (TEWL) and water turnover (WTO).Previous work on the comparative physiology of desert birds relied primarily on information gathered on species from the deserts of the southwestern U.S., which are semi-arid habitats of recent geologic origin. We include data on species from Old World deserts, which are geologically older than those in the New World, and place physiological responses along an aridity axis that includes mesic, semi-arid, arid, and hyperarid environments.The physiological differences between desert and mesic birds that we have identified using the comparative method could arise as a result of acclimation to different environments, of genetic change mediated by selection, or both. We present data on the flexibility of BMR and TEWL in Hoopoe Larks that suggest that phenotypic adjustments in these variables can be substantial. Finally, we suggest that linkages between the physiology of individual organism and its life-history are fundamental to the understanding of life-history evolution.     

Effects of beta-endorphin on body temperature in mice at different ambient temperatures

The effect of intracerebroventricular injection of beta-endorphin (beta-END) on body temperature of mice was studied at ambient temperatures (Ta) of 10 degrees, 20 degrees and 31 degrees C. Doses between 0.1 and 10.0 microgram/mouse were studied. The lower (less than 1 microgram) doses of beta-END produced a hyperthermia at all Ta's studied. The higher doses of beta-END produced hyper- or hypothermia depending on the Ta. The subcutaneous injection of naloxone (1 mg/kg) antagonized the high dose hypothermic effects, but not the hyperthermic effect of beta-END. These data suggest that there may be different receptors and/or sites of action for high and low doses of beta-END.     

Desaturation of exhaled air in camels

We have found that camels can reduce the water loss due to evaporation from the respiratory tract in two ways: (1) by decreasing the temperature of the exhaled air and (2) by removal of water vapour from this air, resulting in the exhalation of air at less than 100% relative humidity (r.h.). Camels were kept under desert conditions and deprived of drinking water. In the daytime the exhaled air was at or near body core temperature, while in the cooler night exhaled air wat at or near ambient air temperature. In the daytime the exhaled air was fully saturated, but at night its humidity might fall to approximately 75% r.h. The combination of cooling and desaturation can provide a saving of water of 60% relative to exhalation of saturated air at body temperature. The mechanism responsible for cooling of the exhaled air is a simple heat exchange between the respiratory air and the surfaces of the nasal passageways. On inhalation these surfaces are cooled by the air passing over them, and on exhalation heat from the exhaled air is given off to these cooler surfaces. The mechanism responsible for desaturation of the air appears to depend on the hygroscopic properties of the nasal surfaces when the camel is dehydrated. The surfaces give off water vapour during inhalation and take up water from the respiratory air during exhalation. We have used a simple mechanical model to demonstrate the effectiveness of this mechanism.     

Climate-driven diversification in two widespread Galerida larks

Background

The major impact of Plio-Pleistocene climatic oscillations on the current genetic structure of many species is widely recognised but their importance in driving speciation remains a matter of controversies. In addition, since most studies focused on Europe and North America, the influence of many other biogeographic barriers such as the Sahara remains poorly understood. In this paper, climate-driven diversification was investigated by using a comparative phylogeographic approach in combination with phenotypic data in two avian species groups distributed on both sides of the deserts belt of Africa and Asia. In particular, we tested whether: 1) vicariance diversification events are concomitant with past climatic events; and 2) current ecological factors (using climate and competition as proxies) contribute to phenotypic divergence between allopatric populations.

Results

Mitochondrial and nuclear sequence data indicated that the crested and Thekla lark species groups diverged in the early Pliocene and that subsequent speciation events were congruent with major late Pliocene and Pleistocene climatic events. In particular, steep increase in aridity in Africa near 2.8 and 1.7 million years ago were coincident with two north-south vicariance speciation events mediated by the Sahara. Subsequent glacial cycles of the last million years seem to have shaped patterns of genetic variation within the two widespread species (G. cristata and G. theklae). The Sahara appears to have allowed dispersal from the tropical areas during climatic optima but to have isolated populations north and south of it during more arid phases. Phenotypic variation did not correlate with the history of populations, but was strongly influenced by current ecological conditions. In particular, our results suggested that (i) desert-adapted plumage evolved at least three times and (ii) variation in body size was mainly driven by interspecific competition, but the response to competition was stronger in more arid areas.

Conclusion

Climatic fluctuations of the Plio-Pleistocene strongly impacted diversification patterns in the Galerida larks. Firstly, we found that cladogenesis coincides with major climatic changes, and the Sahara appears to have played a key role in driving speciation events. Secondly, we found that morphology and plumage were strongly determined by ecological factors (interspecific competition, climate) following vicariance.