A species assemblage approach to comparative phylogeography of birds in southern Australia

We present a novel approach to investigating the divergence history of biomes and their component species using single-locus data prior to investing in multilocus data. We use coalescent-based hierarchical approximate Bayesian computation (HABC) methods (MsBayes) to estimate the number and timing of discrete divergences across a putative barrier and to assign species to their appropriate period of co-divergence. We then apply a coalescent-based full Bayesian model of divergence (IMa) to suites of species shown to have simultaneously diverged. The full Bayesian model results in reduced credibility intervals around divergence times and allows other parameters associated with divergence to be summarized across species assemblages. We apply this approach to 10 bird species that are wholly or patchily discontinuous in semi-arid habitats between Australia's southwest (SW) and southeast (SE) mesic zones. There was substantial support for up to three discrete periods of divergence. HABC indicates that two species wholly restricted to more mesic habitats diverged earliest, between 594,382 and 3,417,699 years ago, three species from semi-arid habitats diverged between 0 and 1,508,049 years ago, and four diverged more recently, between 0 and 396,843 years ago. Eight species were assigned to three periods of co-divergence with confidence. For full Bayesian analyses, we accounted for uncertainty in the two remaining species by analyzing all possible suites of species. Estimates of divergence times from full Bayesian divergence models ranged between 429,105 and 2,006,355; 67,172 and 663,837; and 24,607 and 171,085 for the earliest, middle, and most recent periods of co-divergence, respectively. This single-locus approach uses the power of multitaxa coalescent analyses as an efficient means of generating a foundation for further, targeted research using multilocus and genomic tools applied to an understudied biome.     

Comparative phylogeography as an integrative approach to historical biogeography

Phylogeography has become a powerful approach for elucidating contemporary geographical patterns of evolutionary subdivision within species and species complexes. A recent extension of this approach is the comparison of phylogeographic patterns of multiple co-distributed taxonomic groups, or 'comparative phylogeography.' Recent comparative phylogeographic studies have revealed pervasive and previously unrecognized biogeographic patterns which suggest that vicariance has played a more important role in the historical development of modern biotic assemblages than current taxonomy would indicate. Despite the utility of comparative phylogeography for uncovering such 'cryptic vicariance', this approach has yet to be embraced by some researchers as a valuable complement to other approaches to historical biogeography. We address here some of the common misconceptions surrounding comparative phylogeography, provide an example of this approach based on the boreal mammal fauna of North America, and argue that together with other approaches, comparative phylogeography can contribute importantly to our understanding of the relationship between earth history and biotic diversification.     

Statistical inferences in phylogeography

In conventional phylogeographic studies, historical demographic processes are elucidated from the geographical distribution of individuals represented on an inferred gene tree. However, the interpretation of gene trees in this context can be difficult as the same demographic/geographical process can randomly lead to multiple different genealogies. Likewise, the same gene trees can arise under different demographic models. This problem has led to the emergence of many statistical methods for making phylogeographic inferences. A popular phylogeographic approach based on nested clade analysis is challenged by the fact that a certain amount of the interpretation of the data is left to the subjective choices of the user, and it has been argued that the method performs poorly in simulation studies. More rigorous statistical methods based on coalescence theory have been developed. However, these methods may also be challenged by computational problems or poor model choice. In this review, we will describe the development of statistical methods in phylogeographic analysis, and discuss some of the challenges facing these methods.     

An information-theoretical approach to a system of interacting elements

The maximum-entropy principle in information theory is generalized to include the interaction between elements of the system. A complex relation between the probabilities of the events is derived using a familiar technique in statistical mechanics. The relation is explicitly discussed for the case of bilinear interaction and only two events. Quite noteworthy is the existense in the system of a kind of “phase transition” similar to ferromagnetism. The result is applied to the mass behaviour. It is shown that the cooperative mass behaviour such as boom and fashion may be interpreted as a phase transition which would occur below certain “informational temperature”.     

An informational approach to sensory adaptation

Summary Concepts from information theory can enhance our understanding of perceptual processes by providing a unified picture of the process of perception. A single equation is shown to embrace adaptation phenomena, stimulus-response relations, and differential thresholds. Sensory adaptation is regarded as representing a gain in information by the receptor. It is calculated that for constant stimuli in the form of step inputs, insects and arachnids obtain approximately the same amount of information per stimulus from their respective environments as do human beings.     

An information-theoretical measure of taxonomic diversity

Traditional diversity indices are computed from the abundances of species present and are insensitive to taxonomic differences between species. However, a community in which most species belong to the same genus is intuitively less diverse than another community with a similar number of species distributed more evenly between genera. In this paper, we propose an information-theoretical measure of taxonomic diversity that reflects both the abundances and taxonomic distinctness of the species. Unlike previous measures of taxonomic diversity, such as Rao's quadratic entropy, in this new measure the analyzed taxonomic properties are associated with the single species instead of species pairs.     

Statistical phylogeography

While studies of phylogeography and speciation in the past have largely focused on the documentation or detection of significant patterns of population genetic structure, the emerging field of statistical phylogeography aims to infer the history and processes underlying that structure, and to provide objective, rather than ad hoc explanations. Methods for parameter estimation are now commonly used to make inferences about demographic past. Although these approaches are well developed statistically, they typically pay little attention to geographical history. In contrast, methods that seek to reconstruct phylogeographic history are able to consider many alternative geographical scenarios, but are primarily nonstatistical, making inferences about particular biological processes without explicit reference to stochastically derived expectations. We advocate the merging of these two traditions so that statistical phylogeographic methods can provide an accurate representation of the past, consider a diverse array of processes, and yet yield a statistical estimate of that history. We discuss various conceptual issues associated with statistical phylogeographic inferences, considering especially the stochasticity of population genetic processes and assessing the confidence of phylogeographic conclusions. To this end, we present some empirical examples that utilize a statistical phylogeographic approach, and then by contrasting results from a coalescent-based approach to those from Templeton's nested cladistic analysis (NCA), we illustrate the importance of assessing error. Because NCA does not assess error in its inferences about historical processes or contemporary gene flow, we performed a small-scale study using simulated data to examine how our conclusions might be affected by such unconsidered errors. NCA did not identify the processes used to simulate the data, confusing among deterministic processes and the stochastic sorting of gene lineages. There is as yet insufficient justification of NCA's ability to accurately infer or distinguish among alternative processes. We close with a discussion of some unresolved problems of current statistical phylogeographic methods to propose areas in need of future development.     

Comparative phylogeography of unglaciated eastern North America

Regional phylogeographical studies involving co-distributed animal and plant species have been conducted for several areas, most notably for Europe and the Pacific Northwest of North America. Until recently, phylogeographical studies in unglaciated eastern North America have been largely limited to animals. As more studies emerge for diverse lineages (including plants), it seems timely to assess the phylogeography across this region: (i) comparing and contrasting the patterns seen in plants and animals; (ii) assessing the extent of pseudocongruence; and (iii) discussing the potential applications of regional phylogeography to issues in ecology, such as response to climatic change. Unglaciated eastern North America is a large, geologically and topographically complex area with the species examined having diverse distributions. Nonetheless, some recurrent patterns emerge: (i) maritime - Atlantic vs. Gulf Coast; (ii) Apalachicola River discontinuity; (iii) Tombigbee River discontinuity; (iv) the Appalachian Mountain discontinuity; (v) the Mississippi River discontinuity; and (vi) the Apalachicola River and Mississippi River discontinuities. Although initially documented in animals, most of these patterns are also apparent in plants, providing support for phylogeographical generalizations. These patterns may generally be attributable to isolation and differentiation during Pleistocene glaciation, but in some cases may be older (Pliocene). Molecular studies sometimes agree with longstanding hypotheses of glacial refugia, but also suggest additional possible refugia, such as the southern Appalachian Mountains and areas close to the Laurentide Ice Sheet. Many species exhibit distinct patterns that reflect the unique, rather than the shared, aspects of species' phylogeographical histories. Furthermore, similar modern phylogeographical patterns can result from different underlying causal factors operating at different times (i.e. pseudocongruence). One underemphasized component of pseudocongruence may result from the efforts of researchers to categorize patterns visually - similar patterns may, in fact, not fully coincide, and inferring agreement may obscure the actual patterns and lead to erroneous conclusions. Our modelling analyses indicate no clear spatial patterning and support the hypothesis that phylogeographical structure in diverse temperate taxa is complex and was not shaped by just a few barriers.     

Matching loci surveyed to questions asked in phylogeography

Although mitochondrial DNA (mtDNA) has long been used for assessing genetic variation within and between populations, its workhorse role in phylogeography has been criticized owing to its single-locus nature. The only choice for testing mtDNA results is to survey nuclear loci, which brings into contrast the difference in locus effective size and coalescence times. Thus, it remains unclear how erroneous mtDNA-based estimates of species history might be, especially for evolutionary events in the recent past. To test the robustness of mtDNA and nuclear sequences in phylogeography, we provide one of the largest paired comparisons of summary statistics and demographic parameters estimated from mitochondrial, five Z-linked and 10 autosomal genes of 30 avian species co-distributed in the Caucasus and Europe. The results suggest that mtDNA is robust in estimating inter-population divergence but not in intra-population diversity, which is sensitive to population size change. Here, we provide empirical evidence showing that mtDNA was more likely to detect population divergence than any other single locus owing to its smaller N_e and thus faster coalescent time. Therefore, at least in birds, numerous studies that have based their inferences of phylogeographic patterns solely on mtDNA should not be readily dismissed.     

分子生物学技术在昆虫系统发育地理学研究中的应用

文章对分子生物学技术在系统发育地理学上的应用和研究进展进行综述。介绍mtDNA和ITS等使用最频繁的分子标记,其研究方法最好是测序加上RAPD,RFLP分析,同工酶电泳,SSCP和DSCP中的1种以上或几种方法的组合,数据分析最好是2种方法共同使用,从而确保结果的准确性。     

The joint allele frequency spectrum of multiple populations: a coalescent theory approach

The allele frequency spectrum is a series of statistics that describe genetic polymorphism, and is commonly used for inferring population genetic parameters and detecting natural selection. Population genetic theory on the allele frequency spectrum for a single population has been well studied using both coalescent theory and diffusion equations. Recently, the theory was extended to the joint allele frequency spectrum (JAFS) for three populations using diffusion equations and was shown to be very useful in inferring human demographic history. In this paper, I show that the JAFS can be analytically derived with coalescent theory for a basic model of two isolated populations and then extended to multiple populations and various complex scenarios, such as those involving population growth and bottleneck, migration, and positive selection. Simulation study is used to demonstrate the accuracy and applicability of the theoretical model. The coalescent theory-based approach for the JAFS can characterize the demographic history with comprehensive statistical models as the diffusion approach does, and in addition gains several novel advantages: the computational complexity of calculating the JAFS with coalescent theory is reduced, and thus it is feasible to analytically obtain the JAFS for multiple populations; the hitchhiking effect can be efficiently modeled in coalescent theory, enabling the development of methodologies for detecting selection via multi-population polymorphism data. As an alternative to the diffusion approximation approach, the coalescent theory for the JAFS also provides a foundation for population genetic inference with the advent of large-scale genomic polymorphism data.     

Mitochondrial DNA phylogeography of European hedgehogs

European hedgehog populations belonging to Erinaceus europaeus and E . concolor have been investigated by mitochondrial DNA analysis. A 383 bp fragment of the cytochrome b gene has been sequenced and maximum parsimony and neighbour-joining trees of Tamura–Nei genetic distance values have been constructed. Similar topologies have been produced by both methods, showing a deep divergence between E . europaeus and E . concolor and a further subdivision of each species into a western and an eastern clade. A comparison with previously published allozyme data is made, and concordant and discordant patterns are discussed. The influence of Pleistocene glaciations on the observed pattern of divergence is inferred.     

An integrative approach to delimiting species in a rare but widespread mycoheterotrophic orchid

In the spirit of recent calls for species delimitation studies to become more pluralistic, incorporating multiple sources of evidence, we adopted an integrative, phylogeographic approach to delimiting species and evolutionarily significant units (ESUs) in the Corallorhiza striata species complex. This rare, North American, mycoheterotrophic orchid has been a taxonomic challenge regarding species boundaries, displaying complex patterns of variation and reduced vegetative morphology. We employed plastid DNA, nuclear DNA and morphometrics, treating the C. striata complex as a case study for integrative species delimitation. We found evidence for the differentiation of the endangered C. bentleyi (eastern USA) + C. striata var. involuta (Mexico) from the remaining C. striata (= C. striata s.s.; USA, Canada, Mexico). Corallorhiza striata involuta and C. bentleyi, disjunct by thousands of kilometres (Mexico‐Appalachia), were genetically identical but morphologically distinct. Evidence suggests the C. striata complex represents three species: C. bentleyi, C. involuta and a widespread C. striata s.s under operational criteria of diagnosability and common allele pools. In contrast, Bayesian coalescent estimation delimited four species, but more informative loci and a resultant species tree will be needed to place higher confidence in future analyses. Three distinct groupings were identified within C. striata s.s., corresponding to C. striata striata, C. striata vreelandii, and Californian accessions, but these were not delimited as species because of occupying a common allele pool. Each comprises an ESU, warranting conservation considerations. This study represents perhaps the most geographically comprehensive example of integrative species delimitation for any orchid and any mycoheterotroph.     

Comparative phylogeography of Nearctic and Palearctic fishes

Combining phylogeographic data from mitochondrial DNA (mtDNA) of Nearctic and Palearctic freshwater and anadromous fishes, we used a comparative approach to assess the influence of historical events on evolutionary patterns and processes in regional fish faunas. Specifically, we (i) determined whether regional faunas differentially affected by Pleistocene glaciations show predictable differences in phylogeographic patterns; (ii) evaluated how processes of divergence and speciation have been influenced by such differential responses; and (iii) assessed the general contribution of phylogeographic studies to conservation issues. Comparisons among case studies revealed fundamental differences in phylogeographic patterns among regional faunas. Tree topologies were typically deeper for species from nonglaciated regions compared to northern species, whereas species with partially glaciated ranges were intermediate in their characteristics. Phylogeographic patterns were strikingly similar among southern species, whereas species in glaciated areas showed reduced concordance. The extent and locations of secondary contact among mtDNA lineages varied greatly among northern species, resulting in reduced intraspecific concordance of genetic markers for some northern species. Regression analysis of phylogeographic data for 42 species revealed significant latitudinal shifts in intraspecific genetic diversity. Both relative nucleotide diversity and estimates of evolutionary effective population size showed significant breakpoints matching the median latitude for the southern limit of the Pleistocene glaciations. Similarly, analysis of clade depth of phylogenetically distinct lineages vs. area occupied showed that evolutionary dispersal rates of species from glaciated and nonglaciated regions differed by two orders of magnitude. A negative relationship was also found between sequence divergence among sister species as a function of their median distributional latitude, indicating that recent bursts of speciation events have occurred in deglaciated habitats. Phylogeographic evidence for parallel evolution of sympatric northern species pairs in postglacial times suggested that differentiation of cospecific morphotypes may be driven by ecological release. Altogether, these results demonstrate that comparative phylogeography can be used to evaluate not only phylogeographic patterns but also evolutionary processes. As well as having significant implications for conservation programs, this approach enables new avenues of research for examining the regional, historical, and ecological factors involved in shaping intraspecific genetic diversity.     

Prospects for nuclear gene phylogeography

In phylogeography, an empirical focus on gene lineages enables the history of population processes to be inferred from the simultaneous analysis of temporal and spatial patterns. Rapidly evolving cytoplasmic DNA has been the empirical workhorse propelling the success of this nascent field. Now, as more sophisticated historical models are being tested, there is a growing need for phylogeography to expand from a largely marker-specific discipline to a more general analytical approach that can be applied across independent loci. Recent results using nuclear haplotypes to study phylogeography indicate that the anticipated technical and biological hurdles can be overcome in many taxa to achieve phylogeographical comparisons across unlinked loci. Although many challenges remain, a more complete understanding of the historical, demographic and selective processes shaping phylogeographical patterns is emerging.     

A vectorized method of importance sampling with applications to models of mutation and migration

An importance-sampling method is presented for computing the likelihood of the configuration of population genetic data under general assumptions about population history and transitions among states. The configuration of the data is the number of chromosomes sampled that are in each of a finite set of states. Transitions among states are governed by a Markov chain with transition probabilities dependent on one or more parameters. The method assumes that the joint distribution of coalescence times of the underlying gene genealogy is independent of the genetic state of each lineage. Given a set of coalescence times, the probability that a pair of lineages is chosen to coalesce in each replicate is proportional to the contribution that the coalescence event makes to the probability of the data. This method can be applied to gene genealogies generated by the neutral coalescent process and to genealogies generated by other processes, such as a linear birth-death process which provides a good approximation to the dynamics of low-frequency alleles. Two applications are described. In the first, the fit of allele frequencies at two microsatellite loci sampled in a Sardinian population to the one-step mutation model is tested. The one-step model is rejected for one locus but not for the other. The second application is to low-frequency alleles in a geographically subdivided population. The geographic location is the allelic state, and the alleles are assumed to be sufficiently rare that their dynamics can be approximated by a linear birth-death process in which the birth and death rates are independent of geographic location. The analysis of eight low-frequency allozyme alleles found in the glaucous-winged gull, Larus glaucescens, illustrates how geographically restricted dispersal can be detected.