Connecting genomic patterns of local adaptation and niche suitability in teosintes

The central abundance hypothesis predicts that local adaptation is a function of the distance to the centre of a species’ geographic range. To test this hypothesis, we gathered genomic diversity data from 49 populations, 646 individuals and 33,464 SNPs of two wild relatives of maize, the teosintes Zea mays ssp. parviglumis and Zea. mays. ssp. mexicana. We examined the association between the distance to their climatic and geographic centroids and the enrichment of SNPs bearing signals of adaptation. We identified candidate adaptive SNPs in each population by combining neutrality tests and cline analyses. By applying linear regression models, we found that the number of candidate SNPs is positively associated with niche suitability, while genetic diversity is reduced at the limits of the geographic distribution. Our results suggest that overall, populations located at the limit of the species’ niches are adapting locally. We argue that local adaptation to this limit could initiate ecological speciation processes and facilitate adaptation to global change.     

Divergence with gene flow is driven by local adaptation to temperature and soil phosphorus concentration in teosinte subspecies (Zea mays parviglumis and Zea mays mexicana)

Patterns of genomic divergence between hybridizing taxa can be heterogeneous along the genome. Both differential introgression and local adaptation may contribute to this pattern. Here, we analysed two teosinte subspecies, Zea mays ssp. parviglumis and ssp. mexicana, to test whether their divergence has occurred in the face of gene flow and to infer which environmental variables have been important drivers of their ecological differentiation. We generated 9,780 DArTseqTM SNPs for 47 populations, and used an additional data set containing 33,454 MaizeSNP50 SNPs for 49 populations. With these data, we inferred features of demographic history and performed genome wide scans to determine the number of outlier SNPs associated with climate and soil variables. The two data sets indicate that divergence has occurred or been maintained despite continuous gene flow and/or secondary contact. Most of the significant SNP associations were to temperature and to phosphorus concentration in the soil. A large proportion of these candidate SNPs were located in regions of high differentiation that had been identified previously as putative inversions. We therefore propose that genomic differentiation in teosintes has occurred by a process of adaptive divergence, with putative inversions contributing to reduced gene flow between locally adapted populations.     

Chromosomal inversions associated with environmental adaptation in honeybees

Chromosomal inversions can facilitate local adaptation in the presence of gene flow by suppressing recombination between well‐adapted native haplotypes and poorly adapted migrant haplotypes. East African mountain populations of the honeybee Apis mellifera are highly divergent from neighbouring lowland populations at two extended regions in the genome, despite high similarity in the rest of the genome, suggesting that these genomic regions harbour inversions governing local adaptation. Here, we utilize a new highly contiguous assembly of the honeybee genome to characterize these regions. Using whole‐genome sequencing data from 55 highland and lowland bees, we find that the highland haplotypes at both regions are present at high frequencies in three independent highland populations but extremely rare elsewhere. The boundaries of both divergent regions are characterized by regions of high homology with each other positioned in opposite orientations and contain highly repetitive, long inverted repeats with homology to transposable elements. These regions are likely to represent inversion breakpoints that participate in nonallelic homologous recombination. Using long‐read data, we confirm that the lowland samples are contiguous across breakpoint regions. We do not find evidence for disruption of functional sequence by these breakpoints, which suggests that the inversions are likely maintained due to their allelic content conferring local adaptation in highland environments. Finally, we identify a third divergent genomic region, which contains highly divergent segregating haplotypes that also may contain inversion variants under selection. The results add to a growing body of evidence indicating the importance of chromosomal inversions in local adaptation.     

Identification of candidate genes related to highland adaptation from multiple Chinese local chicken breeds by whole genome sequencing analysis

Understanding the genetic mechanism of highland adaptation is of great importance for breeding improvement of Tibetan chickens (TBC). Some studies of TBC have identified some candidate genes and pathways from multiple subgroups, but the related genetic mechanisms remain largely unknown. Different genetic backgrounds and the independent genetic basis of highland adaptation make it difficult to identity the selective region of highland adaptation with all TBC samples. In this study, we conducted pre-analysis in a large-scale population to select a TBC subgroup with the purest and highest level of highland-specific lineage for the further analysis. Finally, the 37 samples from a TBC subgroup and 19 Lahsa White chickens were used to represent the highland group for further analysis with 80 samples from five Chinese local lowland breeds as controls. Population structure analysis revealed that highland adaptation significantly affected population stratification in Chinese local chicken breeds. Genome-wide selection signal analysis identified 201 candidate genes associated with highland adaptation of TBC, and these genes were significantly enriched in calcium signaling, vascular smooth muscle contraction and the cellular response to oxidative stress pathways. Additionally, we identified a narrow 1.76 kb region containing an overlapping region between HBZ and an active enhancer, and our identified region showed a highly significant signal. The highland group selected the haplotype with high activity to improve the oxygen-carrying capacity, thus being adapted to a hypoxic environment. We also found that STX2 was significantly selected in the highland group, thus potentially reducing the oxidative stress caused by hypoxia, and that STX2 exhibited the opposite effects on highland adaptation and reproductive traits. Our findings advance our understanding of extreme environment adaptation of highland chickens, and provide some variants and genes beneficial to TBC genetic breeding improvement.     

The genomic basis of adaptation to high‐altitude habitats in the eastern honey bee (Apis cerana)

The eastern honey bee (Apis cerana) is of central importance for agriculture in Asia. It has adapted to a wide variety of environmental conditions across its native range in southern and eastern Asia, which includes high‐altitude regions. eastern honey bees inhabiting mountains differ morphologically from neighbouring lowland populations and may also exhibit differences in physiology and behaviour. We compared the genomes of 60 eastern honey bees collected from high and low altitudes in Yunnan and Gansu provinces, China, to infer their evolutionary history and to identify candidate genes that may underlie adaptation to high altitude. Using a combination of F_ST‐based statistics, long‐range haplotype tests and population branch statistics, we identified several regions of the genome that appear to have been under positive selection. These candidate regions were strongly enriched for coding sequences and had high haplotype homozygosity and increased divergence specifically in highland bee populations, suggesting they have been subjected to recent selection in high‐altitude habitats. Candidate loci in these genomic regions included genes related to reproduction and feeding behaviour in honey bees. Functional investigation of these candidate loci is necessary to fully understand the mechanisms of adaptation to high‐altitude habitats in the eastern honey bee.     

A Novel Candidate Region for Genetic Adaptation to High Altitude in Andean Populations

Humans living at high altitude (≥2,500 meters above sea level) have acquired unique abilities to survive the associated extreme environmental conditions, including hypoxia, cold temperature, limited food availability and high levels of free radicals and oxidants. Long-term inhabitants of the most elevated regions of the world have undergone extensive physiological and/or genetic changes, particularly in the regulation of respiration and circulation, when compared to lowland populations. Genome scans have identified candidate genes involved in altitude adaption in the Tibetan Plateau and the Ethiopian highlands, in contrast to populations from the Andes, which have not been as intensively investigated. In the present study, we focused on three indigenous populations from Bolivia: two groups of Andean natives, Aymara and Quechua, and the low-altitude control group of Guarani from the Gran Chaco lowlands. Using pooled samples, we identified a number of SNPs exhibiting large allele frequency differences over 900,000 genotyped SNPs. A region in chromosome 10 (within the cytogenetic bands q22.3 and q23.1) was significantly differentiated between highland and lowland groups. We resequenced ~1.5 Mb surrounding the candidate region and identified strong signals of positive selection in the highland populations. A composite of multiple signals like test localized the signal to FAM213A and a related enhancer; the product of this gene acts as an antioxidant to lower oxidative stress and may help to maintain bone mass. The results suggest that positive selection on the enhancer might increase the expression of this antioxidant, and thereby prevent oxidative damage. In addition, the most significant signal in a relative extended haplotype homozygosity analysis was localized to the SFTPD gene, which encodes a surfactant pulmonary-associated protein involved in normal respiration and innate host defense. Our study thus identifies two novel candidate genes and associated pathways that may be involved in high-altitude adaptation in Andean populations.     

Genomic Shifts,Phenotypic Clines,and Fitness Costs Associated With Cold Tolerance in the Asian Tiger Mosquito

Climatic variation is a key driver of genetic differentiation and phenotypic traits evolution, and local adaptation to temperature is expected in widespread species. We investigated phenotypic and genomic changes in the native range of the Asian tiger mosquito, Aedes albopictus. We first refine the phylogeographic structure based on genome-wide regions (1,901 double-digest restriction-site associated DNA single nucleotide polymophisms [ddRAD SNPs]) from 41 populations. We then explore the patterns of cold adaptation using phenotypic traits measured in common garden (wing size and cold tolerance) and genotype–temperature associations at targeted candidate regions (51,706 exon-capture SNPs) from nine populations. We confirm the existence of three evolutionary lineages including clades A (Malaysia, Thailand, Cambodia, and Laos), B (China and Okinawa), and C (South Korea and Japan). We identified temperature-associated differentiation in 15 out of 221 candidate regions but none in ddRAD regions, supporting the role of directional selection in detected genes. These include genes involved in lipid metabolism and a circadian clock gene. Most outlier SNPs are differently fixed between clades A and C, whereas clade B has an intermediate pattern. Females are larger at higher latitude yet produce no more eggs, which might favor the storage of energetic reserves in colder climate. Nondiapausing eggs from temperate populations survive better to cold exposure than those from tropical populations, suggesting they are protected from freezing damages but this cold tolerance has a fitness cost in terms of egg viability. Altogether, our results provide strong evidence for the thermal adaptation of A. albopictus across its wide temperature range.     

Different trends of neighboring populations of Lesser Kestrel: Effects of climate and other environmental conditions

The sensitivity of population trends to the climate and environment is generally considered a species-specific trait. However, evidence that populations may show different responses to the climate and environmental conditions is growing. Whether this differential sensitivity may arise even among neighboring populations remains elusive. We compared the trends of two neighboring populations of the Lesser Kestrel Falco naumanni, using data from a 12-year survey of 158 colonies in Sicily, Italy; the two populations inhabiting a lowland and an highland area, respectively. Population trends were modeled through the TRIM algorithms implemented in R (package rtrim). A reversed U-shaped population trend was observed in the lowland, while the highland population showed oscillations around a stable trend. Sahel rainfall 2 years before each annual survey significantly affected population variation in the lowland, while rainfall in March and an index of primary productivity in the breeding areas affected population variation in the highland. This suggests that the population in the lowland may be limited mainly by winter survival in Sahel, because the lowland may be an optimal breeding area for this species. In contrast, the highland population, which occupies a different part of the climatic niche of the species, may be limited mainly by reproductive output, because rainfall in March and the primary productivity in May could represent prey availability immediately before and during the breeding months. Overall, our findings suggest that population-specific environmental sensitivity might occur even over small (<100 km) geographical scales, highlighting the need for population-specific conservation strategies.     

Genetic diversity within and among populations of Diprion pini (Hym., Diprionidae) determined by random amplified polymorphic DNA-polymerase chain reaction of haploid males

Abstract: Based on haploid males, random amplified polymorphic DNA (RAPD) markers were used to study genetic variation within and among four French populations and one Finnish outgroup population of the common pine sawfly, Diprion pini (L.), representing a severe European forest pest associated with mass outbreaks. Taking into account that all multilocus haplotypes were detected, a total of 140 individuals were completely discriminated by means of 17 polymorphic markers (present or absent), which were amplified from nine selected random-decamer primers. All populations shared the same genetic types, but pronounced population-specific frequency distributions were found, indicating that on average 84% of the present genetic variation exists within populations and the remaining smaller part counts for interpopulational variation. The haplotype differentiation registered was able to distinguish between the class of lowland populations and the class of highland populations. Reproductive isolation and therefore limited altitudinal gene flow, indicated in case of a French highland population by an enlarged number of fixed markers, and hitchhiking effects with respect to selective processes at certain loci following local adaptation and speciation are discussed to explain the population structures found. A possible selection is indicated by five markers, showing significantly different frequency distributions between the class of highland populations and the class of lowland populations.     

Phylogeography of silver‐studded blue,Plebejus subsolanus (Lepidoptera: Lycaenidae), in the central mountainous regions of Japan

The silver‐studded blue, Plebejus subsolanus, is widely distributed in the Russian Altai mountains, northeastern China, the Korean Peninsula, and the Japanese archipelago. In Japan, the species is distributed across wide elevation ranges from the lowlands of Hokkaido to the subalpine zone of Honshu. Current subspecies classification in Japan is as follows: ssp. iburiensis, occurring in lowland grasslands in Hokkaido; ssp. yaginus in lower mountain grasslands in Honshu; and ssp. yarigadakeanus in higher mountain grasslands in Honshu. The habitat of this species has been markedly reduced due to recent habitat destruction and land‐use changes. Here, we undertook phylogeographic analyses of two subspecies, ssp. yaginus and yarigadakeanus in the central mountainous regions of Japan, based on two mitochondrial gene sequences, in order to collect information for establishing effective conservation strategies. From 57 samples from the four mountain ranges, we obtained a haplotype network comprised of 12 haplotypes. Because of the haplotype network topology, the geographic distribution of haplotypes and the correspondence of haplotype divergence to subspecies taxonomy, we provisionally divided the haplotypes into three haplogroups: YR1 and YR2, which comprised ssp. yarigadakeanus, and YG, which comprised ssp. yaginus. Mitochondrial DNA genetic differentiation generally agreed with morphological subspecies classification. The haplotype network suggested that ssp. yarigadakeanus populations had multiple origins, and the subspecies character of “bright blue of the male's wings” was assumed to have evolved independently in each subalpine meadow. We found that P. subsolanus was genetically differentiated depending upon the elevation at each mountain region, suggesting that each haplogroup should be a conservation unit.     

BEHAVIORAL DIFFERENTIATION IN OVIPOSITION ACTIVITY IN DROSOPHILA BUZZATII FROM HIGHLAND AND LOWLAND POPULATIONS IN ARGENTINA: PLASTICITY OR THERMAL ADAPTATION?

Highland populations of several Drosophila species in Argentina were active early in the afternoon in the field as opposed to populations from a much warmer lowland site, where flies were mainly active in the early evening prior to sunset. For one of these species, Drosophila buzzatii, we tested for a genetic component of activity differences by carrying out crosses within and between populations and measuring oviposition activity of the progeny in the laboratory. We found that activity in the highland population exceeded that in the lowland one during the midafternoon, whereas activity in the lowland population exceeded that in the highland one prior to the beginning of the dark period. Oviposition activity for the period corresponding to the field observations was regressed on the proportion of the genome derived from the highland population. This variable significantly predicted oviposition activity between 1400 and 1600 and between 2000 and 2200 h. Activity of both reciprocal crosses was intermediate and not significantly different from each other, suggesting that nuclear genetic, rather than cytoplasmic factors contribute to differences in oviposition activity between the populations. Two morphological, one genetic, and one stress resistance trait were also scored to examine whether temperature differences between environments were associated with other differences between populations. Wing length of wild-caught and laboratory-reared flies from the highland population significantly exceeded that in the lowland. Thorax length of laboratory-reared flies from the highland population also significantly exceeded that from the lowland. Chromosomal inversion frequencies differed significantly between the two populations with a fivefold reduction in the frequency of arrangement 2st in the highland as compared to the lowland population. This arrangement is known for its negative dose effect on size, and thus, the highland population has experienced a genetic change, perhaps as a result of adaptation to the colder environment, where body size and the frequency of arrangement 2st have changed in concert. Finally, a heat knockdown test revealed that the lowland population was significantly more resistant to high temperature than the highland one. In conclusion, we suggest that temperature has been an important selective agent causing adaptive differentiation between these two populations. We also suggest that the activity rhythms of the two populations have diverged as a consequence of behavioral evolution, that is, through avoidance of stressful temperatures as a mean of thermal adaptation.     

The genetic basis of population fecundity prediction across multiple field populations of Nilaparvata lugens

Identifying the molecular markers for complex quantitative traits in natural populations promises to provide novel insight into genetic mechanisms of adaptation and to aid in forecasting population dynamics. In this study, we investigated single nucleotide polymorphisms (SNPs) using candidate gene approach from high‐ and low‐fecundity populations of the brown planthopper (BPH) Nilaparvata lugens Stål (Hemiptera: Delphacidae) divergently selected for fecundity. We also tested whether the population fecundity can be predicted by a few SNPs. Seven genes (ACE, fizzy, HMGCR, LpR, Sxl, Vg and VgR) were inspected for SNPs in N. lugens, which is a serious insect pest of rice. By direct sequencing of the complementary DNA and promoter sequences of these candidate genes, 1033 SNPs were discovered within high‐ and low‐fecundity BPH populations. A panel of 121 candidate SNPs were selected and genotyped in 215 individuals from 2 laboratory populations (HFP and LFP) and 3 field populations (GZP, SGP and ZSP). Prior to association tests, population structure and linkage disequilibrium (LD) among the 3 field populations were analysed. The association results showed that 7 SNPs were significantly associated with population fecundity in BPH. These significant SNPs were used for constructing general liner models with stepwise regression. The best predictive model was composed of 2 SNPs (ACE_‐862 and VgR_‐816) with very good fitting degree. We found that 29% of the phenotypic variation in fecundity could be accounted for by only two markers. Using two laboratory populations and a complete independent field population, the predictive accuracy was 84.35–92.39%. The predictive model provides an efficient molecular method to predict BPH fecundity of field populations and provides novel insights for insect population management.     

RACIAL EVOLUTION IN ELEUSINE CORACANA SSP. CORACANA (FINGER MILLET)

Eleusine coracana ssp. coracana (finger millet, eleusine) is widely distributed in Africa and India as a cereal. The crop is cultivated in diverse eco-geographical areas. Over this range of distribution, eleusine displays high variability in vegetative, floral and seed morphology. The intent of this study is to establish correlations between morphology and distribution, and to determine the intraspecific taxonomy of the crop. Three eco-geographical races were determined: (1) an African highland race which is cultivated in the East African highlands, (2) a lowland race which is grown in the lowlands of Africa and South India, and (3) an Indian race with its center of distribution in Northeast India. In addition to these basic races, an Indian highland type was identified. The African highland race is the most primitive from which the lowland race evolved. The latter race was subsequently introduced to southern India where a secondary center of diversity became established. The Indian race originated from the lowland race, while the North Indian highland type can be derived from either or both of the two basic races in India. This study indicated that natural selection played a major role in the evolution of the crop. Artificial selection, although significant, was restricted within the limits imposed on it by the ultimate adaptation of the races to their environments.     

Population genomic footprints of selection and associations with climate in natural populations of Arabidopsis halleri from the Alps

Natural genetic variation is essential for the adaptation of organisms to their local environment and to changing environmental conditions. Here, we examine genomewide patterns of nucleotide variation in natural populations of the outcrossing herb Arabidopsis halleri and associations with climatic variation among populations in the Alps. Using a pooled population sequencing (Pool‐Seq) approach, we discovered more than two million SNPs in five natural populations and identified highly differentiated genomic regions and SNPs using F_ST‐based analyses. We tested only the most strongly differentiated SNPs for associations with a nonredundant set of environmental factors using partial Mantel tests to identify topo‐climatic factors that may underlie the observed footprints of selection. Possible functions of genes showing signatures of selection were identified by Gene Ontology analysis. We found 175 genes to be highly associated with one or more of the five tested topo‐climatic factors. Of these, 23.4% had unknown functions. Genetic variation in four candidate genes was strongly associated with site water balance and solar radiation, and functional annotations were congruent with these environmental factors. Our results provide a genomewide perspective on the distribution of adaptive genetic variation in natural plant populations from a highly diverse and heterogeneous alpine environment.     

Seasonal effects and fine‐scale population dynamics of Aedes taeniorhynchus,a major disease vector in the Galapagos Islands

Characterization of the fine‐scale population dynamics of the mosquito Aedes taeniorhynchus is needed to improve our understanding of its role as a disease vector in the Galapagos Islands. We used microsatellite data to assess the genetic structure of coastal and highland mosquito populations and patterns of gene flow between the two habitats through time on Santa Cruz Island. In addition, we assessed possible associations of mosquito abundance and genetic diversity with environmental variables. The coastal and highland mosquito populations were highly differentiated from each other all year round, with some gene flow detected only during periods of increased precipitation. The results support the hypothesis that selection arising from ecological differences between habitats is driving adaptation and divergence in A. taeniorhynchus, and maintaining long‐term genetic differentiation of the populations against gene flow. The highland and lowland populations may constitute an example of incipient speciation in progress. Highland populations were characterized by lower observed heterozygosity and allelic richness, suggesting a founder effect and/or lower breeding site availability in the highlands. A lack of reduction in genetic diversity over time in highland populations suggests that they survive dry periods as dormant eggs. Association between mosquito abundance and precipitation was strong in the highlands, whereas tide height was the main factor affecting mosquito abundance on the coast. Our findings suggests differences in the infection dynamics of mosquito‐borne parasites in the highlands compared to the coast, and a higher risk of mosquito‐driven disease spread across these habitats during periods of increased precipitation.     

Large-scale identification and characterization of genetic variants in asthma candidate genes

Asthma is a chronic inflammatory disorder of the airways, and a number of genetic loci are associated with the disease. Candidate gene association studies have been regarded as effective tools to study complex traits. Knowledge of the sequence variation and structure of the candidate genes is required for association studies. Thus, we investigated the genetic variants of 32 asthma candidate genes selected by colocalization of positional and functional candidate genes. We screened all exons and promoter regions of those genes using 12 healthy individuals and 12 asthma patients and identified a total of 418 single nucleotide polymorphisms (SNPs), including 270 known SNPs and 148 novel SNPs. Levels of nucleotide diversity varied from gene to gene (0.72×10⁻⁴–14.53×10⁻⁴), but the average nucleotide diversity between coding SNPs (cSNPs) and noncoding SNPs was roughly equivalent (4.63×10⁻⁴ vs 4.69×10⁻⁴). However, nucleotide diversity of cSNPs was strongly correlated to codon degeneracy. Nucleotide diversity was much higher at fourfold degenerate sites than at nondegenerate sites (9.42×10⁻⁴ vs 3.14×10⁻⁴). Gene-based haplotype analysis of asthma-associated genes in this study revealed that common haplotypes (frequency >5%) represented 90.5% of chromosomes, and they could be uniquely identified with five or fewer haplotype-tagging SNPs per gene. Therefore, our results may have important implications for the selection of asthma candidate genes and SNP markers for comprehensive association studies using large sample populations.     

The Genomic Architecture of Adaptation to Larval Malnutrition Points to a Trade-off with Adult Starvation Resistance in Drosophila

Periods of nutrient shortage impose strong selection on animal populations. Experimental studies of genetic adaptation to nutrient shortage largely focus on resistance to acute starvation at adult stage; it is not clear how conclusions drawn from these studies extrapolate to other forms of nutritional stress. We studied the genomic signature of adaptation to chronic juvenile malnutrition in six populations of Drosophila melanogaster evolved for 150 generations on an extremely nutrient-poor larval diet. Comparison with control populations evolved on standard food revealed repeatable genomic differentiation between the two set of population, involving >3,000 candidate SNPs forming >100 independently evolving clusters. The candidate genomic regions were enriched in genes implicated in hormone, carbohydrate, and lipid metabolism, including some with known effects on fitness-related life-history traits. Rather than being close to fixation, a substantial fraction of candidate SNPs segregated at intermediate allele frequencies in all malnutrition-adapted populations. This, together with patterns of among-population variation in allele frequencies and estimates of Tajima’s D, suggests that the poor diet results in balancing selection on some genomic regions. Our candidate genes for tolerance to larval malnutrition showed a high overlap with genes previously implicated in acute starvation resistance. However, adaptation to larval malnutrition in our study was associated with reduced tolerance to acute adult starvation. Thus, rather than reflecting synergy, the shared genomic architecture appears to mediate an evolutionary trade-off between tolerances to these two forms of nutritional stress.     

Sex-specific migration patterns in Central Asian populations, revealed by analysis of Y-chromosome short tandem repeats and mtDNA.

Eight Y-linked short-tandem-repeat polymorphisms (DYS19, DYS388, DYS389I, DYS389II, DYS390, DYS391, DYS392, and DYS393) were analyzed in four populations of Central Asia, comprising two lowland samples-Uighurs and lowland Kirghiz-and two highland samples-namely, the Kazakhs (altitude 2,500 m above sea level) and highland Kirghiz (altitude 3,200 m above sea level). The results were compared with mtDNA sequence data on the same individuals, to study possible differences in male versus female genetic-variation patterns in these Central Asian populations. Analysis of molecular variance (AMOVA) showed a very high degree of genetic differentiation among the populations tested, in discordance with the results obtained with mtDNA sequences, which showed high homogeneity. Moreover, a dramatic reduction of the haplotype genetic diversity was observed in the villages at high altitude, especially in the highland Kirghiz, when compared with the villages at low altitude, which suggests a male founder effect in the settlement of high-altitude lands. Nonetheless, mtDNA genetic diversity in these highland populations is equivalent to that in the lowland populations. The present results suggest a very different migration pattern in males versus females, in an extended historical frame, with a higher migration rate for females.     

The role of selection and historical factors in driving population differentiation along an elevational gradient in an island bird

Adaptation to local environmental conditions and the range dynamics of populations can influence evolutionary divergence along environmental gradients. Thus, it is important to investigate patterns of both phenotypic and genetic variations among populations to reveal the respective roles of these two types of factors in driving population differentiation. Here, we test for evidence of phenotypic and genetic structure across populations of a passerine bird (Zosterops borbonicus) distributed along a steep elevational gradient on the island of Réunion. Using 11 microsatellite loci screened in 401 individuals from 18 localities distributed along the gradient, we found that genetic differentiation occurred at two spatial levels: (i) between two main population groups corresponding to highland and lowland areas, respectively, and (ii) within each of these two groups. In contrast, several morphological traits varied gradually along the gradient. Comparison of neutral genetic differentiation (F_ST) and phenotypic differentiation (P_ST) showed that P_ST largely exceeds F_ST at several morphological traits, which is consistent with a role for local adaptation in driving morphological divergence along the gradient. Overall, our results revealed an area of secondary contact midway up the gradient between two major, cryptic, population groups likely diverged in allopatry. Remarkably, local adaptation has shaped phenotypic differentiation irrespective of population history, resulting in different patterns of variation along the elevational gradient. Our findings underscore the importance of understanding both historical and selective factors when trying to explain variation along environmental gradients.