Assessing concurrent patterns of environmental niche and morphological evolution among species of horned lizards (Phrynosoma)

The prediction that variation in species morphology is related to environmental features has long been of interest to ecologists and evolutionary biologists. Many studies have demonstrated strong associations between morphological traits and local habitat characteristics, but few have considered the extent to which morphological traits may be associated with environmental features across broad geographic areas. Here, we use morphological, environmental and phylogenetic data compiled from Phrynosoma species to examine morphological and climatic variation across the geographic ranges of these species in an evolutionary context. We find significant phylogenetic signal in species’ environmental niches, but not in morphological traits. Furthermore, we demonstrate a significant correlation between species’ environmental niches and morphological traits when phylogenetic history is accounted for in the analysis. Our results suggest the importance of climatic variables in influencing morphological variation among species, and have implications for understanding how species distributions are constrained by environmental variation.     

MOLECULAR PHYLOGENETICS AND EVOLUTION OF SEXUAL DICHROMATISM AMONG POPULATIONS OF THE YARROW'S SPINY LIZARD (SCELOPORUS JARROVII)

Understanding evolution of geographic variation in sexually dimorphic traits is critical for understanding the role that sexual selection may play in speciation. We performed a phylogenetic analysis of geographic variation in sexual dichromatism in the Yarrow's spiny lizard (Sceloporus jarrovii), a taxon that exhibits remarkable diversity in male coloration among populations (e.g., black, red, green, yellow, blue, brown). An mtDNA phylogeny based on approximately 880 bp from the 12S ribosomal RNA gene and 890 bp from the ND4 gene was reconstructed for 30 populations of S. jarrovii and eight other species of the torquatus species group using maximum-likelihood and parsimony methods. The phylogeny suggests that S. jarrovii consists of at least five evolutionary species, none of which are sister taxa. Although intraspecific diversity in male coloration is less than indicated by previous taxonomy, two species formerly referred to as S. jarrovii exhibit impressive geographic variation in sexual dichromatism. In one of these species, the phylogeny shows the independent evolution of a distinctive blue color morph in different parts of the species range. This pattern suggests that sexual selection may lead to striking phenotypic divergence among conspecific populations and striking convergence. Results also demonstrate the importance of a phylogenetic perspective in studies of evolutionary processes within nominal species and the problematic nature of “polytypic” species recognized under the biological species concept.     

High mitochondrial diversity in geographically widespread butterflies of Madagascar: A test of the DNA barcoding approach

The standardized use of mitochondrial cytochrome c oxidase subunit I (COI) gene sequences as DNA barcodes has been widely promoted as a high-throughput method for species identification and discovery. Species delimitation has been based on the following criteria: (1) monophyletic association and less frequently (2) a minimum 10× greater divergence between than within species. Divergence estimates, however, can be inflated if sister species pairs are not included and the geographic extent of variation within any given taxon is not sampled comprehensively. This paper addresses both potential biases in DNA divergence estimation by sampling range-wide variation in several morphologically distinct, endemic butterfly species in the genus Heteropsis, some of which are sister taxa. We also explored the extent to which mitochondrial DNA from the barcode region can be used to assess the effects of historical rainforest fragmentation by comparing genetic variation across Heteropsis populations with an unrelated forest-associated taxon Saribia tepahi. Unexpectedly, generalized primers led to the inadvertent amplification of the endosymbiont Wolbachia, undermining the use of universal primers and necessitating the design of genus-specific COI primers alongside a Wolbachia-specific PCR assay. Regardless of the high intra-specific genetic variation observed, most species satisfy DNA barcoding criteria and can be differentiated in the nuclear phylogeny. Nevertheless, two morphologically distinguishable candidate species fail to satisfy the barcoding 10× genetic distance criterion, underlining the difficulties of applying a standard distance threshold to species delimitation. Phylogeographic analysis of COI data suggests that forest fragmentation may have played an important role in the recent evolutionary diversification of these butterflies. Further work on other Malagasy taxa using both mitochondrial and nuclear data will provide better insight into the role of historical habitat fragmentation in species diversification and may potentially contribute to the identification of priority areas for conservation.     

Sympatric divergence and clinal variation in multiple coloration traits of Ficedula flycatchers

Geographic variation in phenotypes plays a key role in fundamental evolutionary processes such as local adaptation, population differentiation and speciation, but the selective forces behind it are rarely known. We found support for the hypothesis that geographic variation in plumage traits of the pied flycatcher Ficedula hypoleuca is explained by character displacement with the collared flycatcher Ficedula albicollis in the contact zone. The plumage traits of the pied flycatcher differed strongly from the more conspicuous collared flycatcher in a sympatric area but increased in conspicuousness with increasing distance to there. Phenotypic differentiation (P_ST) was higher than that in neutral genetic markers (F_ST), and the effect of geographic distance remained when statistically controlling for neutral genetic differentiation. This suggests that a cline created by character displacement and gene flow explains phenotypic variation across the distribution of this species. The different plumage traits of the pied flycatcher are strongly to moderately correlated, indicating that they evolve non‐independently from each other. The flycatchers provide an example of plumage patterns diverging in two species that differ in several aspects of appearance. The divergence in sympatry and convergence in allopatry in these birds provide a possibility to study the evolutionary mechanisms behind the highly divergent avian plumage patterns.     

Giant sex chromosomes retained within the Portuguese lineage of the field vole (<Emphasis Type="Italic">Microtus agrestis</Emphasis>)

The field vole (Microtus agrestis) is characterised by extremely large blocks of heterochromatin on both the X and Y chromosome. Some other Microtus also have blocks of heterochromatin on their sex chromosomes but not as extensive and always of independent origin from the heterochromatic expansion found in M. agrestis. Coupled with evidence of geographic variation in large heterochromatic blocks within other species (e.g. in the western hedgehog Erinaceus europaeus), it might be expected that field voles would show substantial variation in size and disposition of the sex chromosome heterochromatin. In fact, only minor variation has been described up to now. Those studies conducted previously were largely on field voles from central and northern Europe. Here, we describe the karyotype of field voles from Portugal, of interest because recent molecular studies have shown field voles from western Iberia to be a separate evolutionary unit that might be considered a cryptic species, distinct from populations further to the east. The two Portuguese field voles (one female, one male) that we examined also had essentially the same karyotype as seen in other field voles, including the giant sex chromosomes, but with small differences in the structure of the Y chromosome from that described previously. The finding that field voles throughout Europe show relatively little variation in their giant sex chromosomes is consistent with molecular data which suggest a recent origin for this complex of species/near-species.     

Subspecies delineation amid phenotypic,geographic and genetic discordance in a songbird

Understanding the processes that drive divergence within and among species is a long‐standing goal in evolutionary biology. Traditional approaches to assessing differentiation rely on phenotypes to identify intra‐ and interspecific variation, but many species express subtle morphological gradients in which boundaries among forms are unclear. This intraspecific variation may be driven by differential adaptation to local conditions and may thereby reflect the evolutionary potential within a species. Here, we combine genetic and morphological data to evaluate intraspecific variation within the Nelson's (Ammodramus nelsoni) and salt marsh (Ammodramus caudacutus) sparrow complex, a group with populations that span considerable geographic distributions and a habitat gradient. We evaluated genetic structure among and within five putative subspecies of A. nelsoni and A. caudacutus using a reduced‐representation sequencing approach to generate a panel of 1929 SNPs among 69 individuals. Although we detected morphological differences among some groups, individuals sorted along a continuous phenotypic gradient. In contrast, the genetic data identified three distinct clusters corresponding to populations that inhabit coastal salt marsh, interior freshwater marsh and coastal brackish–water marsh habitats. These patterns support the current species‐level recognition but do not match the subspecies‐level taxonomy within each species—a finding which may have important conservation implications. We identified loci exhibiting patterns of elevated divergence among and within these species, indicating a role for local selective pressures in driving patterns of differentiation across the complex. We conclude that this evidence for adaptive variation among subspecies warrants the consideration of evolutionary potential and genetic novelty when identifying conservation units for this group.     

Natural variation for fertile triploid F1 hybrid formation in allohexaploid wheat speciation

The tempo, mode, and geography of allopolyploid speciation are influenced by natural variation in the ability of parental species to express postzygotic reproductive phenotypes that affect hybrid fertility. To shed light on the impact of such natural variations, we used allohexaploid Triticum aestivum wheats’ evolution as a model and analyzed the geographic and phylogenetic distributions of Aegilops tauschii (diploid progenitor) accessions involved in the expression of abnormality and fertility in triploid F₁ hybrids with Triticum turgidum (tetraploid progenitor). Artificial-cross experiments and chloroplast-DNA-based evolutionary analyses showed that hybrid-abnormality-causing accessions had limited geographic and phylogenetic distributions, indicative that postzygotic hybridization barriers are underdeveloped between these species. In contrast, accessions that are involved with fertile triploid F₁ hybrid formation have wide geographic and phylogenetic distributions, indicative of a deep evolutionary origin. Wide-spread hybrid-fertilizing accessions support the theory that T. aestivum speciation occurred at multiple sites within the species range of Ae. tauschii, in which existing conditions enabled natural hybridization with T. turgidum. Implications of our findings on how natural variation in the ability of Ae. tauschii to express those postzygotic reproductive phenotypes diversified and contributed to the speciation of T. aestivum are discussed. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

GEOGRAPHIC VARIATION AND PHENOTYPIC PLASTICITY OF NUMBER OF TRUNK VERTEBRAE IN SLENDER SALAMANDERS,BATRACHOSEPS (CAUDATA: PLETHODONTIDAE)

To understand the evolutionary significance of geographic variation, one must identify the factors that generate phenotypic differences among populations. I examined the causes of geographic variation in and evolutionary history of number of trunk vertebrae in slender salamanders, Batrachoseps (Caudata: Plethodontidae). Number of trunk vertebrae varies at many taxonomic levels within Batrachoseps. Parallel clines in number occur along an environmental gradient in three lineages in the Coast Ranges of California. These parallel clines may signal either adaptation or a shared phenotypically plastic response to the environmental gradient. By raising eggs from 10 populations representing four species of Batrachoseps, I demonstrated that number of trunk vertebrae can be altered by the developmental temperature; however, the degree of plasticity is insufficient to account for geographic variation. Thus, the geographic variation results largely from genetic variation. Number of trunk vertebrae covaries with body size and shape in diverse vertebrate taxa, including Batrachoseps. I hypothesize that selection for different degrees of elongation, possibly related to fossoriality, has led to the extensive evolution of number of trunk vertebrae in Batrachoseps. Analysis of intrapopulational variation revealed sexual dimorphism in both body shape and number of trunk vertebrae, but no correlation between these variables in either sex. Females are more elongate than males, a pattern that has been attributed to fecundity selection in other taxa. Patterns of covariation among different classes of vertebrae suggest that some intrapopulational variation in number results from changes in vertebral identity rather than changes in segmentation.     

Geographic Variation in Note Composition and Use of chick‐a‐dee Calls of Carolina Chickadees (Poecile carolinensis)

The aim of this study was to determine whether geographic variation exists in the composition of note types in the chick‐a‐dee call of Carolina chickadees. This determination is of interest for two reasons: earlier studies with a related species suggested minimal geographic variation in note composition, and geographic variation in social signals may represent important developmental or selection processes shaping signal use. Carolina chickadees were recorded in a naturalistic observation study in west‐central Indiana. Chick‐a‐dee calls were analyzed and compared to calls from an eastern Tennessee population that had been described in a previously published study (Auk, 125, 2008, 896). Despite much similarity in the basic rules by which notes are organized to compose calls, there were several significant differences in how calls of the two populations were structured. Furthermore, birds from Indiana used their chick‐a‐dee calls in certain contexts in different ways compared to birds from Tennessee. These findings suggest interesting population‐level variation in this call system, and future research should be able to determine whether these differences are driven by evolutionary, ecological, or developmental factors, or some combination of these factors.     

Phylogeography of colour polymorphism in the coral reef fish Pseudochromis fuscus, from Papua New Guinea and the Great Barrier Reef

Body colour has played a significant role in the evolution of coral reef fishes, but the phylogenetic level at which colour variation is expressed and the evolutionary processes driving the development and persistence of different colour patterns are often poorly understood. The aim of this study was to examine the genetic relationships between multiple colour morphs of Pseudochromis fuscus (family Pseudochromidae), both within and among geographic locations. Pseudochromis fuscus is currently described as a single species, but exhibits at least six discrete colour morphs throughout its range. In this study, P. fuscus from Papua New Guinea (PNG) and the Great Barrier Reef (GBR), Australia, formed three genetically distinct clades based on mitochondrial DNA (control region) sequence data: (1) yellow and brown morphs from the GBR and southern PNG, as well as an orange morph from southern PNG; (2) a pink morph from southern PNG; and (3) all three morphs (pink, orange and grey) found in Kimbe Bay, northern PNG. The three groups showed deep levels of divergence (d=14.6–25.4%), suggesting that P. fuscus is a complex of polychromatic species, rather than a single widespread species with many different colour morphs. Population genetic analyses indicate that the three clades have experienced unique evolutionary histories, possibly from differential effects of sea level fluctuations, barriers to gene flow and historical biogeography.     

Is geographic variation within species related to macroevolutionary patterns between species?

The relationship between microevolution and macroevolution is a central topic in evolutionary biology. An aspect of this relationship that remains very poorly studied in modern evolutionary biology is the relationship between within‐species geographic variation and among‐species patterns of trait variation. Here, we tested the relationship between climate and morphology among and within species in the salamander genus Plethodon. We focus on a discrete colour polymorphism (presence and absence of a red dorsal stripe) that appears to be related to climatic distributions in a common, wide‐ranging species (Plethodon cinereus). We find that this trait has been variable among (and possibly within) species for >40 million years. Furthermore, we find a strong relationship among species between climatic variation and within‐species morph frequencies. These between‐species patterns are similar (but not identical) to those in the broadly distributed Plethodon cinereus. Surprisingly, there are no significant climate–morphology relationships within most other polymorphic species, despite the strong between‐species patterns. Overall, our study provides an initial exploration of how within‐species geographic variation and large‐scale macroevolutionary patterns of trait variation may be related.     

Müllerian mimicry of a quantitative trait despite contrasting levels of genomic divergence and selection

Hybrid zones, where distinct populations meet and interbreed, give insight into how differences between populations are maintained despite gene flow. Studying clines in genetic loci and adaptive traits across hybrid zones is a powerful method for understanding how selection drives differentiation within a single species, but can also be used to compare parallel divergence in different species responding to a common selective pressure. Here, we study parallel divergence of wing colouration in the butterflies Heliconius erato and H. melpomene, which are distantly related Müllerian mimics which show parallel geographic variation in both discrete variation in pigmentation, and quantitative variation in structural colour. Using geographic cline analysis, we show that clines in these traits are positioned in roughly the same geographic region for both species, which is consistent with direct selection for mimicry. However, the width of the clines varies markedly between species. This difference is explained in part by variation in the strength of selection acting on colour traits within each species, but may also be influenced by differences in the dispersal rate and total strength of selection against hybrids between the species. Genotyping‐by‐sequencing also revealed weaker population structure in H. melpomene, suggesting the hybrid zones may have evolved differently in each species, which may also contribute to the patterns of phenotypic divergence in this system. Overall, we conclude that multiple factors are needed to explain patterns of clinal variation within and between these species, although mimicry has probably played a central role.     

Sequential evolution of Euphilotes (Lycaenidae: Scolitantidini) on their plant host Eriogonum (Polygonaceae: Eriogonoideae)

The relationship between the butterfly genus Euphilotes and their host plant genus Eriogonum in western North America is suggested to be one of sequential evolution rather than coevolution. Eriogonum, a genus of nearly 250 species, probably had a Miocene origin, but has had its modern distribution significantly influenced by recent Pleistocene glaciation. The evolution of Euphilotes, as a distinct genus of four sibling species, apparently postdates the establishment and recent proliferation of Eriogonum. Successful speciation in Euphilotes has been accomplished mainly through modifications in genitalia of those butterflies using a single species of Eriogonum. The subsequent proliferation of Euphilotes subspecies has been the result of host switching coupled with geographic isolation onto individual species of Eriogonum acting as restricted biogeographic islands. In the first instance, direct evolutionary competition for a limited resource (one species of Eriogonum) leads to partitioning of that resource by the butterflies whose entire life cycle is associated with that plant species. In the second instance, host switching and isolation have permitted establishment of minor subspecies without significant interaction with other subspecies of the same species. In instances where interspecific subspecies competition exists, resource partitioning, coupled with more pronounced genetic isolation, seem to have occurred resulting in more readily distinct subspecies. We speculate that the success of subspeciation in Euphilotes is dependent upon the numeric size and geographic extent of the host species. Euphilotes subspecies on plants of restricted distributions are themselves seemingly limited in their evolutionary potential as the most dynamic evolution of Euphilotes subspecies is that associated with widespread and variable Eriogonum species. In all instances, the tempo and mode of evolution in Euphilotes appears to be sequential as it follows and is seemingly dependent upon what has already occurred in Eriogonum.     

Phylogeography of the Chionodraco genus (Perciformes, Channichthydae) in the Southern Ocean

Antarctic fish of the suborder Notothenioidei represent one of the most notable examples of adaptive radiation in the marine environment. The evolutionary relationships between and within the eight families of this suborder have been well established by numerous studies, whereas the microevolutionary processes of notothenioid species remain largely unexplored. In the present paper we investigated the evolutionary relationships between three closely related species of the genus Chionodraco (family Channichthyidae), namely Chionodraco hamatus, Chionodraco rastrospinosus, and Chionodraco myersi by analysing portions of the mitochondrial genome (D-loop and 16S rRNA). The taxonomic status of C. hamatus and C. rastrospinosus as separate species has been questioned because of the limited number of key morphological characters that distinguish these two taxa. Our results, based on the analysis of several specimens belonging to both morphological groups revealed a small genetic differentiation among haplotypes, however, a clear separation between the two nominal species emerged since all individuals of each of the two taxa clustered together in distinct monophyletic groups. C. myersi appeared more distantly related in the phylogenetic analysis. For one species, C. hamatus, sampling was carried out at three different geographic locations in the area of the Ross Sea and Weddell Sea. The results showed that the partition of the genetic variation within this species is not compatible with the hypothesis of panmixia as gene flow between populations was significantly reduced.     

Geographic and molecular variation in a natural plant transgene

A PCR based survey of Festuca ovina plants from populations around the southern part of the Baltic Sea demonstrates both geographic and molecular variation in the enzyme gene PgiC2, horizontally transferred from a Poa-species. Our results show that PgiC2—a natural functional nuclear transgene—is not a local ephemeral phenomenon but is present in a very large number of individuals. We find also that its frequency is geographically variable and that it appears in more than one molecular form. The chloroplast variation in the region does not indicate any distinct subdivision due to different colonization routes after the last glaciation. Our data illustrate the geographic and molecular variation that may occur in natural populations with a polymorphic, unfixed transgene affected by diverse kinds of mutational and evolutionary processes.     

Geographic host use variability and host range evolutionary dynamics in the phytophagous insect <Emphasis Type="Italic">Apagomerella versicolor</Emphasis> (Cerambycidae)

The high diversity of phytophagous insects has been explained by the tendency of the group towards specialization; however, generalism may be advantageous in some environments. The cerambycid Apagomerella versicolor exhibits intraspecific geographical variation in host use. In northern Argentina it is highly specialized on the herb Pluchea sagittalis (Asteraceae), while in central and southern areas it uses seven Asteraceae species. To study host species geographical variation from ecological and evolutionary perspectives, we investigated field host availability and use across a wide latitudinal range, and performed laboratory studies on insect oviposition preference and larval performance and mitochondrial DNA (mtDNA) variation in a phylogeographical framework. Geographic variation in host use was unrelated to host availability but was highly associated with laboratory oviposition preference, larval performance, and mtDNA variation. Genetic studies revealed three geographic races of A. versicolor with gene flow restriction and recent geographic expansion. Trophic generalism and oligophagy within A. versicolor seem to have evolved as adaptations to seasonal and spatial unavailability of the preferred host P. sagittalis in cooler areas of the species’ geographic range. No single genotype is successful in all environments; specialization may be advantageous in environments with uniform temporal and spatial host availability, while being a trophic generalist may provide an adaptive advantage in host-constrained environments.     

New variation and biosystematic patterns detected by allozyme and morphological comparisons inLimnanthes sect.Reflexae (Limnanthaceae)

Sixty-one populations ofLimnanthes sect.Reflexae were surveyed for variation at 19 allozyme loci and reassessed for their morphological diversity and biosystematic relationships. Cluster analysis of allozyme data at individual population level provided evidence for a fairly good fit with the earlier systematic work on this genus but both morphological and allozyme data together defined some new clusters as well as exceptional entities. For example, only var.rosea of the fourL. douglasii varieties described byMason (1952) on the basis of geographical distribution, flower color and leaf morphology, remained as a distinct entity; the others were realigned along new geographic boundaries.L. striata appeared to have two well-developed subgroups, one of which was closely related to theL. douglasii complex. Further ecogeographic and hybridization studies are needed to fully describe these new phenetic findings in the context of phylogenetic inference. SectionInflexae was readily distinguished from sect.Reflexae by several diagnostic loci, thus supporting the validity of this division. Interspecific variation levels and population differentiation inLimnanthes were high when compared to other plant taxa, possibly indicating highly dynamic evolutionary processes for which variable habitats and extreme subdivision within species have been suggested as explanations.     

MULTIPLE ORIGINS OF SELF-COMPATIBILITY IN LINANTHUS SECTION LEPTOSIPHON (POLEMONIACEAE): PHYLOGENETIC EVIDENCE FROM INTERNAL-TRANSCRIBED-SPACER SEQUENCE DATA

Phylogenetic reconstruction based on sequence variation in the internal transcribed spacer (ITS) region of rDNA was used to investigate the evolutionary dynamics of homomorphic self-incompatibility in Linanthus section Leptosiphon (Polemoniaceae), a group of annual plant species. Hand-pollination experiments revealed that five species were self-incompatible and four were self-compatible. Optimization of breeding systems onto the tree resulting from maximum-likelihood analysis, with no assumptions made about the ancestral condition, indicated that self-incompatibility has been lost four times in this section. An alternative tree rearrangement conforming to the hypothesis of three losses of self-incompatibility did not have a significantly lower likelihood than the maximum-likelihood tree as determined by a paired-sites test, but all rearrangements resulting in fewer than three losses were statistically rejected. Linanthus bicolor, a selfing species, was found to be polyphyletic, with populations from different geographic regions occurring in three well-supported clades. Morphological similarity in these distinct lineages is likely to have resulted from convergent evolution of traits associated with self-fertilization. Selection for reproductive assurance is hypothesized to have played an important role in the recurrent transformations from self-incompatibility to selfing in this group of annual species.     

Genetic differentiation,gene flow and the origin of infestations of the medfly,Ceratitis capitata

The genetic structure of natural populations of the economically important dipteran species Ceratitis capitatawas analysed using both biochemical and molecular markers. This revealed considerable genetic variation in populations from different geographic regions. The nature of this variation suggests that the evolutionary history of the species involved the spread of individuals from the ancestral African populations through Europe and, more recently, to Latin America, Hawaii and Australia. The observed variation can be explained by various evolutionary forces acting differentially in the different geographic areas, including genetic drift, bottleneck effects, selection and gene flow. The analysis of the intrinsic variability of the medfly's genome and the genetic relationships among populations of this pest is a prerequisite for any control programme.