Comparative phylogeography of codistributed aquatic insects in western North America: insights into dispersal and regional patterns of genetic structure

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Invertebrate population genetics across Earth's largest habitat: The deep‐sea floor

Despite the deep sea being the largest habitat on Earth, there are just 77 population genetic studies of invertebrates (115 species) inhabiting non‐chemosynthetic ecosystems on the deep‐sea floor (below 200 m depth). We review and synthesize the results of these papers. Studies reveal levels of genetic diversity comparable to shallow‐water species. Generally, populations at similar depths were well connected over 100s–1,000s km, but studies that sampled across depth ranges reveal population structure at much smaller scales (100s–1,000s m) consistent with isolation by adaptation across environmental gradients, or the existence of physical barriers to connectivity with depth. Few studies were ocean‐wide (under 4%), and 48% were Atlantic‐focused. There is strong emphasis on megafauna and commercial species with research into meiofauna, “ecosystem engineers” and other ecologically important species lacking. Only nine papers account for ~50% of the planet's surface (depths below 3,500 m). Just two species were studied below 5,000 m, a quarter of Earth's seafloor. Most studies used single‐locus mitochondrial genes revealing a common pattern of non‐neutrality, consistent with demographic instability or selective sweeps; similar to deep‐sea hydrothermal vent fauna. The absence of a clear difference between vent and non‐vent could signify that demographic instability is common in the deep sea, or that selective sweeps render single‐locus mitochondrial studies demographically uninformative. The number of population genetics studies to date is miniscule in relation to the size of the deep sea. The paucity of studies constrains meta‐analyses where broad inferences about deep‐sea ecology could be made.     

Three‐dimensional post‐glacial expansion and diversification of an exploited oceanic fish

Vertical divergence in marine organisms is being increasingly documented, yet much remains to be carried out to understand the role of depth in the context of phylogeographic reconstruction and the identification of management units. An ideal study system to address this issue is the beaked redfish, Sebastes mentella – one of four species of ‘redfish’ occurring in the North Atlantic – which is known for a widely distributed ‘shallow‐pelagic’ oceanic type inhabiting waters between 250 and 550 m, and a more localized ‘deep‐pelagic’ population dwelling between 550 and 800 m, in the oceanic habitat of the Irminger Sea. Here, we investigate the extent of population structure in relation to both depth and geographic spread of oceanic beaked redfish throughout most of its distribution range. By sequencing the mitochondrial control region of 261 redfish collected over a decadal interval, and combining 160 rhodopsin coding nuclear sequences and previously genotyped microsatellite data, we map the existence of two strongly divergent evolutionary lineages with significantly different distribution patterns and historical demography, and whose genetic variance is mostly explained by depth. Combined genetic data, analysed via independent approaches, are consistent with a Late Pleistocene lineage split, where segregation by depth probably resulted from the interplay of climatic and oceanographic processes with life history and behavioural traits. The ongoing process of diversification in North Atlantic S. mentella may serve as an ‘hourglass’ to understand speciation and adaptive radiation in Sebastes and in other marine taxa distributed across a depth gradient.     

Is reproductive strategy a key factor in understanding the evolutionary history of Southern Ocean Asteroidea (Echinodermata)?

Life traits such as reproductive strategy can be determining factors of species evolutionary history and explain the resulting diversity patterns. This can be investigated using phylogeographic analyses of genetic units. In this work, the genetic structure of five asteroid genera with contrasting reproductive strategies (brooding: Diplasterias, Notasterias and Lysasterias versus broadcasting: Psilaster and Bathybiaster) was investigated in the Southern Ocean. Over 1,400 mtDNA cytochrome C oxidase subunit I (COI) sequences were analysed using five species delineation methods (ABGD, ASAP, mPTP, sGMYC and mGMYC), two phylogenetic reconstructions (ML and BA), and molecular clock calibrations, in order to examine the weight of reproductive strategy in the observed differences among phylogeographic patterns. We hypothesised that brooding species would show higher levels of genetic diversity and species richness along with a clearer geographic structuring than broadcasting species. In contrast, genetic diversity and species richness were not found to be significantly different between brooders and broadcasters, but broadcasters are less spatially structured than brooders supporting our initial hypothesis and suggesting more complex evolutionary histories associated to this reproductive strategy. Broadcasters' phylogeography can be explained by different scenarios including deep‐sea colonisation routes, bipolarity or cosmopolitanism, and sub‐Antarctic emergence for the genus Bathybiaster; Antarctic‐ New Zealand faunal exchanges across the Polar Front for the genus Psilaster. Brooders' phylogeography could support the previously formulated hypothesis of a past trans‐Antarctic seaway established between the Ross and the Weddell seas during the Plio‐Pleistocene. Our results also show, for the first time, that the Weddell Sea is populated by a mixed asteroid fauna originating from both the East and West Antarctic.     

Phylogeography and Demographic History of Chinese Black-Spotted Frog Populations (<Emphasis Type="Italic">Pelophylax nigromaculata</Emphasis>): Evidence for Independent Refugia Expansion and Secondary Contact

Background  

Pleistocene glaciations had considerable impact on phylogeographic patterns within and among closely related species of many vertebrates. Compared to Europe and North America, research on the phylogeography of vertebrates in East Asia, particularly in China, remains limited. The black-spotted frog (Pelophylax nigromaculata) is a widespread species in East Asia. The wide distribution of this species in China makes it an ideal model for the study of palaeoclimatic effects on vertebrates in East Asia. Our previous studies of P. nigromaculata revealed significant subdivisions between the northeast China populations and populations in other regions of the mainland. In the present study, we aim to see whether the deepest splits among lineages and perhaps subsequent genealogical divisions are temporally consistent with a Pleistocene origin and whether clade geographic distributions, with insight into expansion patterns, are similarly spatially consistent with this model.     

Asymmetric oceanographic processes mediate connectivity and population genetic structure,as revealed by RADseq,in a highly dispersive marine invertebrate (Parastichopus californicus)

Marine populations are typically characterized by weak genetic differentiation due to the potential for long‐distance dispersal favouring high levels of gene flow. However, strong directional advection of water masses or retentive hydrodynamic forces can influence the degree of genetic exchange among marine populations. To determine the oceanographic drivers of genetic structure in a highly dispersive marine invertebrate, the giant California sea cucumber (Parastichopus californicus), we first tested for the presence of genetic discontinuities along the coast of North America in the northeastern Pacific Ocean. Then, we tested two hypotheses regarding spatial processes influencing population structure: (i) isolation by distance (IBD: genetic structure is explained by geographic distance) and (ii) isolation by resistance (IBR: genetic structure is driven by ocean circulation). Using RADseq, we genotyped 717 individuals from 24 sampling locations across 2,719 neutral SNPs to assess the degree of population differentiation and integrated estimates of genetic variation with inferred connectivity probabilities from a biophysical model of larval dispersal mediated by ocean currents. We identified two clusters separating north and south regions, as well as significant, albeit weak, substructure within regions (F_ST = 0.002, p = .001). After modelling the asymmetric nature of ocean currents, we demonstrated that local oceanography (IBR) was a better predictor of genetic variation (R² = .49) than geographic distance (IBD) (R² = .18), and directional processes played an important role in shaping fine‐scale structure. Our study contributes to the growing body of literature identifying significant population structure in marine systems and has important implications for the spatial management of P. californicus and other exploited marine species.     

Cryptic speciation along a bathymetric gradient

The deep ocean supports a highly diverse and mostly endemic fauna, yet little is known about how or where new species form in this remote ecosystem. How speciation occurs is especially intriguing in the deep sea because few obvious barriers exist that would disrupt gene flow. Geographic and bathymetric patterns of genetic variation can provide key insights into how and where new species form. We quantified the population genetic structure of a protobranch bivalve, Neilonella salicensis, along a depth gradient (2200–3800 m) in the western North Atlantic using both nuclear (28S and calmodulin intron) and mitochondrial (cytochrome c oxidase subunit I) loci. A sharp genetic break occurred for each locus between populations above 2800 m and below 3200 m, defining two distinct clades with no nuclear or mitochondrial haplotypes shared between depth regimes. Bayesian phylogenetic analyses provided strong support for two clades, separated by depth, within N. salicensis. Although no morphological divergence was apparent, we suggest that the depth‐related population genetic and phylogenetic divergence is indicative of a cryptic species. The frequent occurrence of various stages of divergence associated with species formation along bathymetric gradients suggests that depth, and the environmental gradients that attend changes in depth, probably play a fundamental role in the diversification of marine organisms, especially in deep water. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 897–913.     

The puzzling phylogeography of the haplochromine cichlid fish Astatotilapia burtoni

Astatotilapia burtoni is a member of the “modern haplochromines,” the most species‐rich lineage within the family of cichlid fishes. Although the species has been in use as research model in various fields of research since almost seven decades, including developmental biology, neurobiology, genetics and genomics, and behavioral biology, little is known about its spatial distribution and phylogeography. Here, we examine the population structure and phylogeographic history of A. burtoni throughout its entire distribution range in the Lake Tanganyika basin. In addition, we include several A. burtoni laboratory strains to trace back their origin from wild populations. To this end, we reconstruct phylogenetic relationships based on sequences of the mitochondrial DNA (mtDNA) control region (d‐loop) as well as thousands of genomewide single nucleotide polymorphisms (SNPs) derived from restriction‐associated DNA sequencing. Our analyses reveal high population structure and deep divergence among several lineages, however, with discordant nuclear and mtDNA phylogenetic inferences. Whereas the SNP‐based phylogenetic hypothesis uncovers an unexpectedly deep split in A. burtoni, separating the populations in the southern part of the Lake Tanganyika basin from those in the northern part, analyses of the mtDNA control region suggest deep divergence between populations from the southwestern shoreline and populations from the northern and southeastern shorelines of Lake Tanganyika. This phylogeographic pattern and mitochondrial haplotype sharing between populations from the very North and the very South of Lake Tanganyika can only partly be explained by introgression linked to lake‐level fluctuations leading to past contact zones between otherwise isolated populations and large‐scale migration events.     

Recent phylogeographic structure in a widespread ‘weedy’ Neotropical tree species,Cordia alliodora (Boraginaceae)

Aim Although hundreds of tree species have broad geographic ranges in the Neotropics, little is known about how such widespread species attained disjunct distributions around mountain, ocean and xeric barriers. Here, we examine the phylogeographic structure of a widespread and economically important tree, Cordia alliodora, to: (1) test the roles of vicariance and dispersal in establishing major range disjunctions, (2) determine which geographic regions and/or habitats contain the highest levels of genetic diversity, and (3) infer the geographic origin of the species. Location Twenty‐five countries in Central and South America, and the West Indies. Methods Chloroplast simple sequence repeats (cpSSR; eight loci) were assayed in 67 populations (240 individuals) sampled from the full geographic range of C. alliodora. Chloroplast (trnH–psbA) and nuclear (internal transcribed spacer, ITS) DNA sequences were sampled from a geographically representative subset. Genetic structure was determined with samova , structure and haplotype networks. Analysis of molecular variance (AMOVA) and rarefaction analyses were used to compare regional haplotype diversity and differentiation. Results Although the ITS region was polymorphic it revealed limited phylogeographic structure, and trnH–psbA was monomorphic. However, structure analysis of cpSSR variation recovered three broad demes spanning Central America (Deme 1), the Greater Antilles and the Chocó (Deme 2), and the Lesser Antilles and cis‐Andean South America (Deme 3). samova showed two predominant demes (Deme 1 + 2 and Deme 3). The greatest haplotype diversity was detected east of the Andes, while significantly more genetic variation was partitioned among trans‐Andean populations. Populations experiencing high precipitation seasonality (dry ecotype) had greater levels of genetic variation. Main conclusions Cordia alliodora displayed weak cis‐ and trans‐Andean phylogeographic structure based on DNA sequence data, indicative of historical dispersal around this barrier and genetic exchange across its broad range. The cpSSR data revealed phylogeographic structure corresponding to three biogeographic zones. Patterns of genetic diversity are indicative of an origin in the seasonally dry habitats of South America. Therefore, C. alliodora fits the disperser hypothesis for widespread Neotropical species. Dispersal is evident in the West Indies and the northern Andean cordilleras. The dry ecotype harbours genetic variation that is likely to represent the source for the establishment of populations under future warmer and drier climatic scenarios.     

A rangewide herbarium‐derived dataset indicates high levels of gene flow in black cherry (Prunus serotina)

Isolation by Distance (IBD) is a genetic pattern in which populations geographically closer to one another are more genetically similar to each other than populations which are farther apart. Black cherry (Prunus serotina Ehrh.) (Rosaceae) is a forest tree species widespread in eastern North America, and found sporadically in the southwestern United States, Mexico, and Guatemala. IBD has been studied in relatively few North American plant taxa, and no study has rigorously sampled across the range of such a widespread species. In this study, IBD and overall genetic structure were assessed in eastern black cherry (P. serotina Ehrh. var. serotina), the widespread variety of eastern North America. Eastern North America. Prunus serotina Ehrh. var. serotina (Rosaceae). Dense sampling across the entire range of eastern black cherry was made possible by genotyping 15 microsatellite loci in 439 herbarium samples from all portions of the range. Mantel tests and STRUCTURE analyses were performed to evaluate the hypothesis of IBD and genetic structure. Mantel tests demonstrated significant but weak IBD, while STRUCTURE analyses revealed no clear geographic pattern of genetic groups. The modest geographic/genetic structure across the eastern black cherry range suggests widespread gene flow in this taxon. This is consistent with P. serotina's status as a disturbance‐associated species. Further studies should similarly evaluate IBD in species characteristic of low‐disturbance forests.     

Phylogeographic inference using Bayesian model comparison across a fragmented chorus frog species complex

Fragmented species complexes provide an interesting system for investigating biogeographic history and the present distribution of genetic variation. Recent advances in sequencing technology and statistical phylogeography enable the collection and rigorous analysis of large multilocus data sets, but designing studies that produce meaningful phylogeographic inferences remains challenging. We implemented a Bayesian model comparison approach to investigate previous biogeographic hypotheses while simultaneously inferring the presence of genetic structure in a chorus frog species complex. The Illinois chorus frog (Pseudacris illinoensis), originally described as a subspecies of the broadly distributed Strecker's chorus frog (Pseudacris streckeri), occurs in small, disjunct regions associated with scarce sand prairie habitats that have been impacted by human development. We used high‐throughput sequencing to develop and collect a multitiered genetic data set comprised of three different marker types (23 anonymous nuclear sequence loci, four mitochondrial genes and 14 microsatellite loci) designed to address questions across different evolutionary timescales. Phylogenetic analyses uncovered a deep divergence between populations in the Edwards Plateau of central Texas and all other P. streckeri/P. illinoensis populations, but suggest the disjunct distribution of P. illinoensis occurred more recently. Our best‐supported migration model is consistent with the hypothesis that central Texas represented a refugium from which populations expanded via multiple routes. This model also indicates that disjunct northern and southern regions of P. illinoensis should be considered genetically distinct management units. Our study provides an evolutionary context for future studies and conservation efforts in P. illinoensis and demonstrates the utility of model‐based approaches for phylogeographic inference.     

Land masses and oceanic currents drive population structure of Heritiera littoralis,a widespread mangrove in the Indo‐West Pacific

Phylogeographic forces driving evolution of sea‐dispersed plants are often influenced by regional and species characteristics, although not yet deciphered at a large spatial scale for many taxa like the mangrove species Heritiera littoralis. This study aimed to assess geographic distribution of genetic variation of this widespread mangrove in the Indo‐West Pacific region and identify the phylogeographic factors influencing its present‐day distribution. Analysis of five chloroplast DNA fragments’ sequences from 37 populations revealed low genetic diversity at the population level and strong genetic structure of H. littoralis in this region. The estimated divergence times between the major genetic lineages indicated that glacial level changes during the Pleistocene epoch induced strong genetic differentiation across the Indian and Pacific Oceans. In comparison to the strong genetic break imposed by the Sunda Shelf toward splitting the lineages of the Indian and Pacific Oceans, the genetic differentiation between Indo‐Malesia and Australasia was not so prominent. Long‐distance dispersal ability of H. littoralis propagules helped the species to attain transoceanic distribution not only across South East Asia and Australia, but also across the Indian Ocean to East Africa. However, oceanic circulation pattern in the South China Sea was found to act as a barrier creating further intraoceanic genetic differentiation. Overall, phylogeographic analysis in this study revealed that glacial vicariance had profound influence on population differentiation in H. littoralis and caused low genetic diversity except for the refugia populations near the equator which might have persisted through glacial maxima. With increasing loss of suitable habitats due to anthropogenic activities, these findings therefore emphasize the urgent need for conservation actions for all populations throughout the distribution range of H. littoralis.     

Spatial scales of genetic structure and gene flow in Calochortus albus (Liliaceae)

Calochortus (Liliaceae) displays high species richness, restriction of many individual taxa to narrow ranges, geographic coherence of individual clades, and parallel adaptive radiations in different regions. Here we test the first part of a hypothesis that all of these patterns may reflect gene flow at small geographic scales. We use amplified fragment length polymorphism variation to quantify the geographic scales of spatial genetic structure and apparent gene flow in Calochortus albus, a widespread member of the genus, at Henry Coe State Park in the Coast Ranges south of San Francisco Bay. Analyses of 254 mapped individuals spaced 0.001–14.4 km apart show a highly significant decline in genetic identity with ln distance, implying a root‐mean‐square distance of gene flow σ of 5–43 m. STRUCTURE analysis implies the existence of 2–4 clusters over the study area, with frequent reversals among clusters over short distances (<200 m) and a relatively high frequency of admixture within individuals at most sampling sites. While the intensity of spatial genetic structure in C. albus is weak, as measured by the Sp statistic, that appears to reflect low genetic identity of adjacent plants, which might reflect repeated colonizations at small spatial scales or density‐dependent mortality of individual genotypes by natural enemies. Small spatial scales of gene flow and spatial genetic structure should permit, under a variety of conditions, genetic differentiation within species at such scales, setting the stage ultimately for speciation and adaptive radiation as such scales as well.     

Genetic and epigenetic insight into morphospecies in a reef coral

Incongruence between conventional and molecular systematics has left the delineation of many species unresolved. Reef‐building corals are no exception, with phenotypic plasticity among the most plausible explanations for alternative morphospecies. As potential molecular signatures of phenotypic plasticity, epigenetic processes may contribute to our understanding of morphospecies. We compared genetic and epigenetic variation in Caribbean branching Porites spp., testing the hypothesis that epigenetics—specifically, differential patterns of DNA methylation—play a role in alternative morphotypes of a group whose taxonomic status has been questioned. We used reduced representation genome sequencing to analyse over 1,000 single nucleotide polymorphisms and CpG sites in 27 samples of Porites spp. exhibiting a range of morphotypes from a variety of habitats in Belize. We found stronger evidence for genetic rather than epigenetic structuring, identifying three well‐defined genetic groups. One of these groups exhibited significantly thicker branches, and branch thickness was a better predictor of genetic groups than depth, habitat or symbiont type. In contrast, no clear epigenetic patterns emerged with respect to phenotypic or habitat variables. While there was a weak positive correlation between pairwise genetic and epigenetic distance, two pairs of putative clones exhibited substantial epigenetic differences, suggesting a strong environmental effect. We speculate that epigenetic patterns are a complex mosaic reflecting diverse environmental histories superimposed over a relatively small heritable component. Given the role of genetics in branching Porites spp. morphospecies we were able to detect with genomewide sequencing, use of such techniques throughout the geographic range of these corals may help settle their phylogeny.     

Biogeography and host‐related factors trump parasite life history: limited congruence among the genetic structures of specific ectoparasitic lice and their rodent hosts

Parasites and hosts interact across both micro‐ and macroevolutionary scales where congruence among their phylogeographic and phylogenetic structures may be observed. Within southern Africa, the four‐striped mouse genus, Rhabdomys, is parasitized by the ectoparasitic sucking louse, Polyplax arvicanthis. Molecular data recently suggested the presence of two cryptic species within P. arvicanthis that are sympatrically distributed across the distributions of four putative Rhabdomys species. We tested the hypotheses of phylogeographic congruence and cophylogeny among the two parasite lineages and the four host taxa, utilizing mitochondrial and nuclear sequence data. Despite the documented host‐specificity of P. arvicanthis, limited phylogeographic correspondence and nonsignificant cophylogeny was observed. Instead, the parasite–host evolutionary history is characterized by limited codivergence and several duplication, sorting and host‐switching events. Despite the elevated mutational rates found for P. arvicanthis, the spatial genetic structure was not more pronounced in the parasite lineages compared with the hosts. These findings may be partly attributed to larger effective population sizes of the parasite lineages, the vagility and social behaviour of Rhabdomys, and the lack of host‐specificity observed in areas of host sympatry. Further, the patterns of genetic divergence within parasite and host lineages may also be largely attributed to historical biogeographic changes (expansion‐contraction cycles). It is thus evident that the association between P. arvicanthis and Rhabdomys has been shaped by the synergistic effects of parasite traits, host‐related factors and biogeography over evolutionary time.     

Genetic diversity of Cedrela fissilis (Meliaceae) in the Brazilian Atlantic Forest reveals a complex phylogeographic history driven by Quaternary climatic fluctuations

Quaternary climatic fluctuations have shaped the geographic distribution of lineages, potentially affecting the demography, genetic structure, and patterns of genetic diversity of extant species. Different phylogeographic scenarios have been proposed for plants in neotropical cloud forests during the Last Glacial Maximum based on paleoecological data: the dry refugia hypothesis (DRH) and the moist forest hypothesis. We specifically focus on the Brazilian Atlantic Forest (BAF) range of Cedrela fissilis (Meliaceae), sampling 410 specimens from 50 localities. Our study combines analyses of the genetic diversity, phylogeographic patterns, and past geographic distributions with a particular focus on highland populations. We identified 283 alleles across the 11 microsatellite loci, ranging from 18 to 33 alleles per locus, distributed across five genetic groups. Most populations of C. fissilis from the BAF exhibited a diffuse genetic structure, reflected in low pairwise F_ST values, which could be the consequence of high gene flow. In addition, the plastid data showed a connection between the western, southern, and eastern populations in the North‐East of Brazil, but no association between genetic data and elevation was observed. Habitat suitability projections over the past 140 000 years showed less fragmentation relative to the present, indicating a higher connectivity and gene flow. Our results provide support for both the moist forest as well as the DRH, suggesting that most likely, a mixture of these processes has acted through space and time.     

Phylogeography and ecological niche modeling unravel the evolutionary history of the African green toad,Bufotes boulengeri boulengeri (Amphibia: Bufonidae), through the Quaternary

Recent integration of ecological niche models in phylogeographic studies is improving our understanding of the processes structuring genetic variation across landscapes. Previous studies on the amphibian Bufotes boulengeri boulengeri uncovered a surprisingly weak intraspecific differentiation across the Maghreb region. We widely sampled this species from Morocco to Egypt and sequenced one nuclear and three mitochondrial (mtDNA) genes to determine the level of genetic variability across its geographic range. We evaluated these data with ecological niche modeling to reveal its evolutionary history in response to climate change during the Quaternary. Our results highlight some mtDNA phylogeographic structure within this species, with one haplogroup endemic to coastal Morocco, and one haplogroup widely distributed throughout North Africa. No or little genetic differentiation is observed between isolated populations from the Hoggar Mountains, the Sabha district and the islands of Kerkennah and Lampedusa, compared to others populations. This can be explained by the expansion of the distribution range of B. b. boulengeri during glacial periods. This might have facilitated the species’ dispersal and subsequent gene flow between most North African localities.     

Metapopulation patterns of additive and nonadditive genetic variance in the sea bass (Dicentrarchus labrax)

Describing and explaining the geographic within‐species variation in phenotypes (“phenogeography”) in the sea over a species distribution range is central to our understanding of a variety of eco‐evolutionary topics. However, phenogeographic studies that have a large potential to investigate adaptive variation are overcome by phylogeographic studies, still mainly focusing on neutral markers. How genotypic and phenotypic data could covary over large geographic scales remains poorly understood in marine species. We crossed 75 noninbred sires (five origins) and 26 dams (two origins; each side of a hybrid zone) in a factorial diallel cross in order to investigate geographic variation for early survival and sex ratio in the metapopulation of the European sea bass (Dicentrarchus labrax), a highly prized marine fish species. Full‐sib families (N = 1,950) were produced and reared in a common environment. Parentage assignment of 7,200 individuals was performed with seven microsatellite markers. Generalized linear models showed significant additive effects for both traits and pleiotropy between traits. A significant nonadditive genetic effect was detected. Different expression of traits and distinct relative performances were found for reciprocal crosses involving populations located on each side of the main hybrid zone located at the Almeria‐Oran front, illustrating asymmetric reproductive isolation. The poor fitness performance observed for the Western Mediterranean population of sea bass is discussed as it represents the main source of seed hatchery production, but also because it potentially illustrates nonadaptive introgression and maladaptation.     

Mitochondrial genomes reveal the global phylogeography and dispersal routes of the migratory locust

The migratory locust, Locusta migratoria, is the most widely distributed grasshopper species in the world. However, its global genetic structure and phylogeographic relationships have not been investigated. In this study, we explored the worldwide genetic structure and phylogeography of the locust populations based on the sequence information of 65 complete mitochondrial genomes and three mitochondrial genes of 263 individuals from 53 sampling sites. Although this locust can migrate over long distances, our results revealed high genetic differentiation among the geographic populations. The populations can be divided into two different lineages: the Northern lineage, which includes individuals from the temperate regions of the Eurasian continent, and the Southern lineage, which includes individuals from Africa, southern Europe, the Arabian region, India, southern China, South‐east Asia and Australia. An analysis of population genetic diversity indicated that the locust species originated from Africa. Ancestral populations likely separated into Northern and Southern lineages 895 000 years ago by vicariance events associated with Pleistocene glaciations. These two lineages evolved in allopatry and occupied their current distributions in the world via distinct southern and northern dispersal routes. Genetic differences, caused by the long‐term independent diversification of the two lineages, along with other factors, such as geographic barriers and temperature limitations, may play important roles in maintaining the present phylogeographic patterns. Our phylogeographic evidence challenged the long‐held view of multiple subspecies in the locust species and tentatively divided it into two subspecies, L. m. migratoria and L. m. migratorioides.