Phylogeographical structure in the subterranean tuco-tuco Ctenomys talarum (Rodentia: Ctenomyidae): contrasting the demographic consequences of regional and habitat-specific histories

In this work we examined the phylogeography of the South American subterranean herbivorous rodent Ctenomys talarum (Talas tuco-tuco) using mitochondrial DNA (mtDNA) control region (D-loop) sequences, and we assessed the geographical genetic structure of this species in comparison with that of subterranean Ctenomys australis, which we have shown previously to be parapatric to C. talarum and to also live in a coastal sand dune habitat. A significant apportionment of the genetic variance among regional groups indicated that putative geographical barriers, such as rivers, substantially affected the pattern of genetic structure in C. talarum. Furthermore, genetic differentiation is consistent with a simple model of isolation by distance, possibly evidencing equilibrium between gene flow and local genetic drift. In contrast, C. australis showed limited hierarchical partitioning of genetic variation and departed from an isolation-by-distance pattern. Mismatch distributions and tests of neutrality suggest contrasting histories of these two species: C. talarum appears to be characterized by demographic stability and no significant departures from neutrality, whereas C. australis has undergone a recent demographic expansion and/or departures from strict neutrality in its mtDNA.     

Energy and distribution in subterranean rodents: sympatry between two species of the genus Ctenomys

The low basal metabolic rate (BMR) observed in subterranean rodents, compared to that of surface-dwelling species of comparable size, has been proposed to be an adaptation to underground life. Two main hypotheses have been proposed to explain this finding, the cost of burrowing and the thermal stress. The former states that the low BMR is due to the high cost of extending the tunnel system whereas the other relates it to the possibility of overheating in burrows where evaporative and convective heat exchange are restricted. Additionally, both hypotheses related the energetics of subterranean rodent with spatial distribution. The genus Ctenomys is an excellent model to evaluate the cost of burrowing or thermal stress, since they are widely distributed, with members differing markedly in body mass. The aim of this study was to assess digging and basal energetics in two Ctenomys species that live in sympatry in a coastal grassland, but differ in their microspatial distribution by soil preference. We used the obtained energetic data to test both energy-distribution hypotheses. We measured BMR and digging metabolic rate (DMR) through open flow respirometry in two species exposed to soft and hard soils. In brief, DMR in Ctenomys talarum (100-170 g), as in Ctenomys australis (250-600 g), was unaffected by soil hardness. Within thermoneutral zone of each species, DMR/RMR quotient was lower in the smaller species. Our data did not support the thermal stress hypothesis, but the cost of burrowing hypothesis was not rejected. Other alternative hypotheses are proposed to explain the distribution of C. talarum and C. australis.     

New Karyotypes and Some Considerations about the Chromosomal Diversification of Ctenomys minutus (Rodentia: Ctenomyidae) on the Coastal Plain of the Brazilian State of Rio Grande do Sul

The dominant mammals occupying the subterranean niche in South America are rodents of the genus Ctenomys, which form a large group of 56 species with chromosome numbers ranging from 2n= 10 to 70. In southern Brazil, Ctenomys minutus is the species with the widest geographic distribution, inhabiting sandy fields and dunes extending from Jaguaruna beach in the state of Santa Catarina to the town of São José do Norte in the state of Rio Grande do Sul. Eleven karyotypes (2n= 42; 2n= 46a; 2n= 46b; 2n= 47a; 2n= 47b; 2n= 48a; 2n= 48b; 2n= 49a; 2n= 49b; 2n= 50a and 2n= 50b) were described for this species and zones of hybridization are also known. A sample of 51 C. minutus specimens was collected from five sampling sites about 20 km apart along the coastal plain of Rio Grande do Sul between the municipalities of Tavares (31°23′S 51°09′W) and São José do Norte (31°52′S 51°54′W). We were able to extend the known geographic distribution of C. minutus by 90 km, from Tavares southwards to São José do Norte. During our study we found five karyotypes (2n= 46b, 47b, 48b, 49b and 50b), four of which (2n= 47b, 48b, 49b and 50b) have not previously been described for this species.     

Early evolutionary differentiation of morphological variation in the mandible of South American caviomorph rodents (Rodentia, Caviomorpha)

Caviomorphs are a clade of South American rodents recorded at least since the early Oligocene (> 31.5 Ma) that exhibit ample eco-morphological variation. It has been proposed that phylogenetic structure is more important than ecological factors for understanding mandibular shape variation in this clade. This was interpreted as a result of the long-standing evolutionary history of caviomorphs and the early divergence of major lineages. In this work, we test this hypothesis through the analysis of morphological variation in the mandible of living and extinct species and compare this information with that obtained through comparative phylogenetic analyses. Our results support the hypothesis of early origin of mandibular variation; moreover, they suggest the conservation of early differentiated morphologies, which could indicate the existence of constrained evolutionary diversification.     

Introgressive hybridization between two species of waterstriders (Hemiptera: Gerridae: Limnoporus): geographical structure and temporal change of a hybrid zone

Where the distribution ranges of the waterstriders Limnoporus notabilis and L. dissortis meet in western Canada, extensive hybridization and introgression occurs. Multivariate ordination analyses of genetic and morphometric data by principal component analysis revealed that a single axis separating the two parent species could account for nearly all the variation in both data sets. Maps of principal component scores for both data sets revealed geographical patterns of variation reflecting specific topographic features in the region. Comparisons of morphometric data from some of the samples collected in the 1980s and from the same sites revisited in the 1990s revealed substantial changes. An ‘island’ of dissortis‐like populations inside the range of L. notabilis in interior British Columbia expanded, and a marked local protrusion of notabilis‐like phenotypes into the range of L. dissortis on the east slope of the Rocky Mountains diminished during the decade between collections. We conclude that introgressive hybridization between these two species of waterstriders is a spatially complex and highly dynamic process.     

Distribution patterns of the small mammals (Insectivora and Rodentia) in a transitional zone between the Eurosiberian and the Mediterranean regions

To determine, by means of quantitative analyses, the distribution patterns of the insectivores and rodents in Catalonia using physiographical regions as Operative Geographical Units (OGUs). Catalonia (north‐eastern Iberian Peninsula). Based on the presence/absence of twenty‐five small mammals in thirteen physiographical regions, which were used as OGUs, the following aspects were studied: (a) identification of biotic boundaries; (b) determination of chorological association of species; (c) climatic characterization of the biotic regions and the chorotypes. Groups of biotic regions and species were established, and their statistical significance was tested. The possible effect of several climatic factors on these groupings was studied using discriminant analyses. A significant biotic boundary was found to separate the central and eastern Pyrenees from the remaining physiographical regions. The climatic variables that defined this boundary were related to the severity and the availability of environmental energy. Four chorotypes were identified. One chorotype was constituted by Pyrenean or Pre‐Pyrenean species, an association determined by their mid‐European requirements; another chorotype was formed by Eurosiberian species, but showed a variable degree of tolerance to Mediterranean conditions; a third chorotype included species with a wide distribution that are Mediterranean, anthropic, generalist or have very specific habitats; and finally the fourth chorotype was constituted by a strictly Mediterranean species. The climatic factors that accounted for the distribution of these chorotypes were the mean July temperature and the mean annual precipitation. We conclude that the axial zone of the Pyrenees, except the coastal portion, determines two biotic regions in Catalonia. As for the classification of species, using quantitative techniques for the first time, we offer a new biogeographicalal configuration for the small mammals in this temperate‐Mediterranean transition.     

Thermoregulation in three species of Afrotropical subterranean mole-rats (Rodentia: Bathyergidae) from Zambia and Angola and scaling within the genus Cryptomys

The thermoregulatory characteristics of three species of Cryptomys from Zambia and Angola are examined and, together with published data on four other species of Cryptomys from southern Africa, used to determine whether scaling occurs in this genus of subterranean rodents. The thermoregulatory properties of acclimated giant Zambian mole-rats, Cryptomys mechowi ( =267 g), Angolan mole-rats, Cryptomys bocagei ( =94 g) and Zambian common mole-rats Cryptomys hottentotus amatus ( =77 g) are as follows. Mean resting metabolic rates (RMRs) within the respective thermoneutral zones were 0.60±0.08 cm³ O₂ g^-1 h^-1 (n=12) for C. mechowi; 0.74±0.06 cm³ O₂ g^-1 h^-1 (n=8) for C. bocagei and 0.63±0.06 cm³O₂ g^-1 h^-1 (n=21) for C. h. amatus. The thermoneutral zones (TNZs) of all three species are narrow: 29–30°C for C. mechowi; 31.5–32.5°C for C. bocagei and 28–32° C for C. h. amatus. The increase in mean RMR at the lowest temperatures tested (15° C for C. mechowi, 18° C for C. bocagei and C. h. amatus) was 2.35, 2.2 and 3.82 times their RMR in the TNZ respectively. Body temperatures are low, 34±0.53° C (n=24) for C. mechowi, 33.7±0.32° C (n=20) for C. bocagei and 33.8±0.43° C (n=40) for C. h amatus. At the lower limit of thermoneutrality, conductances are 0.09±0.01 cm³ O₂ g^-1 h^-1 °C^-1 (n=30) in C. mechowi; 0.12±0.01 cm³ O₂ g^-1 h^-1 °C^-1 (n=20) in C. bocagei and 0.12±0.03 cm³ O₂ g^-1 h^-1 °C^-1 (n=32) in C. h. amatus. The range in mean body mass among the seven species of Cryptomys examined for scaling was 60 g (C. darlingi) to 267 g (C. mechowi). There is no clear relationship between RMR within the TNZ and body mass. The resultant relationship is represented by the power curve RMR=2.45 mass^-0.259.     

Phylogenetic relationships among species of Stilestrongylus Freitas, Lent and Almeida, 1937 (Trichostrongyloidea: Heligmonellidae: Nippostrongylinae), parasites of myomorph rodents (Rodentia: Muridae) in the Neotropics

The phylogenetic relationships of 14 species of Stilestrongylus were analyzed using the comparative morphology of 21 characters. We obtained 2 shortest trees of 50 steps, with a consistency index of 0.540 and 25 apomorphic character states. Ingroup monophyly was supported on these trees by 2 and 3 synapomorphies, respectively, and the ingroup was defined by the following characters: greater number of ventral ridges relative to the number of ridges dorsally, asymmetric bursa, and externodorsal rays differing in size. Sister-group relationships among Stilestrongylus and the other genera designated as outgroups are relatively consistent with those postulated by Durette-Desset's in a classification of the Nippostrongylinae. The ancestor of the species groups comprising Hassalstrongylus, Guerrerostrongylus, and Stilestrongylus originated and diversified in murids in the Neotropical region. Species of Hassalstrongylus occur in rodents between southeastern North America and the eastern part of South America (Brazil and Argentina), whereas species of Guerrerostrongylus and Stilestrongylus diversified exclusively in rodents in the Neotropics.     

Phylogeny and temporal diversification of Calomys (Rodentia, Sigmodontinae): implications for the biogeography of an endemic genus of the open/dry biomes of South America

A thorough analysis of character evolution and biogeography of a group is only possible with a comprehensive sampling of its diversity. The sigmodontine genus Calomys is particularly interesting for the study of neotropical biogeography as it occurs exclusively in the dry and grassland biomes: Cerrado, Caatinga, Chaco, Pampas, Venezuelan Llanos, Puna, and a diversity of dry forests biomes. Although Brazil encompasses a large part of the geographic distribution of the genus and at least three endemic species, the last published phylogeny of Calomys included only two specimens (both representing the same species) from a single locality in this country. In the present paper we add complete cytochrome b sequences of Brazilian karyomorphs to previously published sequences in order to provide a phylogenetic hypothesis including most of the genus diversity. The main objectives of this study were to clarify taxonomic issues related to Brazilian karyomorphs and to study the diversification processes of the genus by analyzing its biogeography in combination with cladogenesis dates estimated with a molecular clock. The phylogeny indicates that at least six different species inhabit the Brazilian territory, one of them still undescribed. Date estimates indicate that two sequential basal splits, the first separating Andean from lowland species and the second isolating species north and south of the Amazonia, took place in the Pliocene between 3 and 4 Ma. A large-bodied and speciose clade of lowland species associated with dry forests and ecotones of the core Cerrado and Chaco areas with adjacent biomes diversified in the Pleistocene. This indicates the importance of safeguarding ecotones and the Cerrado at a time where this biome is being rapidly destroyed.     

Amplified fragment length polymorphisms and sequence data in the phylogenetic analysis of polyploids: multiple origins of Veronica cymbalaria (Plantaginaceae)

The origin of polyploid Veronica cymbalaria (Plantaginaceae) was investigated using DNA sequence data and amplified fragment length polymorphism (AFLP) fingerprints to reveal the parentage of this taxon. The use of AFLP fingerprints in phylogenetic analysis is problematic and various methods have therefore been compared. DNA sequence data (for the internal transcribed spacer (ITS) region and the plastid trnL-F region (trnL intron, 3'exon, and trnL-F spacer)) and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis of the ITS region suggested a reliable hypothesis for the evolution of the V. cymbalaria complex. This hypothesis allowed evaluation of the effect of different distance measures (Jaccard and Nei-Li) in phenetic, character-state weighted parsimony, and Bayesian analyses of AFLP markers. The study establishes that tetraploid V. cymbalaria originated at least twice in the eastern Mediterranean, with one parent differing in the two separate origins. Hexaploid V. cymbalaria originated even more often. The results illustrate that even subtle differences in the analyses of AFLP markers can lead to drastically different conclusions. The study reveals multiple origins of a Mediterranean polyploid species. Furthermore, it demonstrates that the analysis of a complex marker system such as AFLP fingerprints using only one type of analysis can easily be misleading.     

Phylogenetics of the woodrat genus Neotoma (Rodentia: Muridae): implications for the evolution of phenotypic variation in male external genitalia

Interspecific morphological variation in animal genitalia has long attracted the attention of evolutionary biologists because of the role genital form may play in the generation and/or maintenance of species boundaries. Here we examine the origin and evolution of genital variation in rodents of the muroid genus Neotoma. We test the hypothesis that a relatively rare genital form has evolved only once in Neotoma. We use four mitochondrial and four nuclear markers to evaluate this hypothesis by establishing a phylogenetic framework in which to examine genital evolution. We find intron seven of the beta-fibrinogen gene to be a highly informative nuclear marker for the levels of differentiation that characterize Neotoma with this locus evolving at a rate slower than cytochrome b but faster than 12S. We estimate phylogenetic relationships within Neotoma using both maximum parsimony and maximum likelihood-based Bayesian methods. Our Bayesian and parsimony reconstructions differ in significant ways, but we show that our parsimony analysis may be influenced by long-branch attraction. Furthermore, our estimate of Neotoma phylogeny remains consistent across various data partitioning strategies in the Bayesian analyses. Using ancestral state reconstruction, we find support for the monophyly of taxa that possess the relatively rare genital form. However, we also find support for the independent evolution of the common genital form and discuss possible underlying developmental shifts that may have contributed to our observed patterns of morphological evolution.     

Phylogeographical and speciation patterns in subterranean worm lizards of the genus Blanus (Amphisbaenia: Blanidae)

The peculiar lifestyle of subterranean reptiles must determine their modes of speciation and diversification. To further understand the evolutionary biology of subterranean reptiles, we studied the phylogeny of worm lizards of the genus Blanus and the phylogeography of its Iberian representatives. We used mitochondrial (ND4 and 16S rRNA) and nuclear (anonymous) partial gene sequences to resolve phylogenetic relationships within Blanus. The Eastern Mediterranean Blanus strauchi was recovered as sister group of Western Mediterranean species. Iberian and North African Blanus were recovered as reciprocally monophyletic groups. The same genes were used to determine phylogeography of 47 populations of Blanus cinereus. Mitochondrial and nuclear sequence data recovered two highly supported Iberian clades. Parapatry and high sequence divergences between them suggest that these clades may represent independent taxonomic units. A molecular clock was calibrated considering that the split between Iberian and North African Blanus was due to the re-opening of the Betic Strait in the Upper Tortonian (8-9 million years ago). Differentiation between the two Iberian clades was estimated to date back to 5.2 million years ago. The Central Iberian clade included five mitochondrial haplotype lineages (A-E). Geographical ranges of two of them broadly overlap in the central Iberian plateau. After testing alternative hypotheses, the most likely explanation for this striking phylogeographical pattern involves recent dispersal of one of the lineages (C) over the geographical range of the other (B). The inferred recent dispersal of this fossorial reptile is explained in terms of demographic advantages associated to underground lifestyle.     

Phylogenetic relationships between tuna species of the genus Thunnus (Scombridae: Teleostei): Inconsistent implications from morphology,nuclear and mitochondrial genomes

In order to infer phylogenetic relationships between tuna species of the genus Thunnus, partial sequences of the mitochondrial cytochrome b and ATPase genes were determined in all eight species. Supplemental restriction analysis on the nuclear rRNA gene was also carried out. Pacific northern bluefin tuna (Thunnus thynnus orientalis) was found to have mtDNA distinct from that of the Atlantic subspecies (T. t. thynnus) but very similar to that from the species albacore (T. alaluga). In contrast, no differentiation in nuclear genome was observed between the Atlantic and Pacific northern bluefin tunas. The Atlantic northern bluefin and southern bluefin tunas possessed mtDNA sequences very similar to species of yellowfin tuna group and not so similar to albacore and bigeye tunas which were morphologically assigned to the bluefin tuna group. The molecular data indicate that (1) mtDNA from albacore has been incorporated into the Pacific population of northern bluefin tuna and has extensively displaced the original mtDNA, and (2) albacore is the earliest offshoot, followed by bigeye tuna in this genus, which is inconsistent with the phylogenetic relationships between these tuna species inferred from morphology. Correspondence to: S. Chow     

A study of genetic distances and variability in several species pf the gemis Ctenomys (Rodentia: Octodontidae) with special references to a probable causal role of chromosomes in speciation

Genetic variability measured by allozymic electrophoresis has been studied in several species of the subterranean rodent genus Ctenomys (Octodontidae). The study was carried out with the main purpose of analysing a special group known as the 'Corrientes group' which inhabits the province of Corrientes in Argentina. The members of the group are, with high probability, isolated reproductively due to their karyotypic differences diploid numbers are between 42 and 70). To evaluate whether the chromosomal differences were the causes of speciation or if they arose a posteriori, we compared the level of the genetic distance among taxa within the orrientes group with all those measured between intraspecific populations in Ctenomys . The results indicate that the distances among the populations of the Corrientes group are at or below the level of those measured among traspecific populations in Ctenomys . Thus, it is unlikely that genetic differentiation triggered speciation. It is shown that this low level of genetic differentiation is not in contradiction with the high levels expected for species originating from one of the possible mechanisms of chromosomal speciation named, chromosomal transilience. Although for geographical reasons it seems obviousthat gene flow is precluded among the members of the Corrientes group, the Slatkin method for estimating Nm values was also used. Because high values of Nm exist but no isolation by distance could be detected, it is suggested that reproductive and geographical isolation are very ecent. Finally, analysis of population variability suggests that the high levels of heterozygosity observed (a) can be explained by the population structure, and (b) are within the range of expected values if bottlenecks have occurred in the recent history of the Corrientes group. As a general conclusion, the results indicate that in the Corrientes group the genetic data support a putative causal role for chromosomes in speciation.     

Egg chamber production, egg protection and clutch size among fungivorus beetles of the genus Eumicrota (Coleoptera: Staphylinidae) and their evolutionary implications

Observations of members of the staphylinid genus Eumicrota show that they breed on a variety of relatively persistent gilled mushrooms (Pleurotus, Hohenbuehelia) , relatively fleshy polypores (Fauolus, Phaeolus) and similar fungi (Climacodon, Hydnellum, Phanerochaete) , and a few more woody polypores (Daedaleopszs). Behaviour features of members of Eumicrota associated with these mushrooms include: construction of an egg chamber by the female; female guarding and care of eggs; and fidelity of the female to the egg chamber before, during, and after hatching. Such energetic investment by the female results in increased survival and hatching of eggs by preventing egg predation by conspecific larvae and adults, and by preventing fungal hyphae from growing over the eggs. This behaviour differs significantly from that of related genera (Phanerota, Gyrophaena) which live and breed on more ephemeral gilled mushrooms. This is especially noticable in comparison with members of the genus Gyrophaena which are exclusively limited to those mushrooms. Members of Gyrophaena do not form an egg chamber or guard their eggs (though some cover their eggs with a layer of fungal frass), adults leave the mushroom soon after larvae hatch, and females lay significantly fewer eggs per clutch (Gyrophaena mean = 4.94, N= 18; Eumicrota mean = 11.78, N = 23; P < 0.05). It is hypothesized that these differences in behaviour of closely related genera reflect life cycle strategies evolved in response to host fungi which differ in persistence and predictability. Comparison of known behavioural features among lineages of gyrophaenine staphylinid beetles did not resolve the phylogenetic patterns of evolution of these life history features, primarily because of lack of comparative data for some groups.     

Phylogenetic species delimitation in ectomycorrhizal fungi and implications for barcoding: the case of the Tricholoma scalpturatum complex (Basidiomycota)

Population studies have revealed that the fungal ectomycorrhizal morphospecies Tricholoma scalpturatum consists of at least two genetically distinct groups that occur sympatrically in several geographical areas. This discovery prompted us to examine species boundaries and relationships between members formerly assigned to T. scalpturatum and allied taxa using phylogenetic analyses. Sequence data were obtained from three nuclear DNA regions [internal transcribed spacer (ITS), gpd and tef], from 101 carpophores collected over a large geographical range in Western Europe, and some reference sequences from public databases. The ITS was also tested for its applicability as DNA barcode for species delimitation. Four highly supported phylogenetic clades were detected. The two previously detected genetic groups of T. scalpturatum were assigned to the phylospecies Tricholoma argyraceum and T. scalpturatum. The two remaining clades were referred to as Tricholoma cingulatum and Tricholoma inocybeoides. Unexpectedly, T. cingulatum showed an accelerated rate of evolution that we attributed to narrow host specialization. This study also reveals recombinant ITS sequences in T. inocybeoides, suggesting a hybrid origin. The ITS was a useful tool for the determination of species boundaries: the mean value of intraspecific genetic distances in the entire ITS region (including 5.8S rDNA) was <0.2%, whereas interspecific divergence estimates ranged from 1.78% to 4.22%. Apart from giving insights into the evolution of the T. scalpturatum complex, this study contributes to the establishment of a library of taxonomically verified voucher specimens, an a posteriori correlation between phenotype and genotype, and DNA barcoding of ectomycorrhizal fungi.     

The role of chromosomal rearrangements and geographical barriers in the divergence of lineages in a South American subterranean rodent (Rodentia: Ctenomyidae: Ctenomys minutus)

Identifying factors and the extent of their roles in the differentiation of populations is of great importance for understanding the evolutionary process in which a species is involved. Ctenomys minutus is a highly karyotype–polymorphic subterranean rodent, with diploid numbers ranging from 42 to 50 and autosomal arm numbers (ANs) ranging from 68 to 80, comprising a total of 45 karyotypes described so far. This species inhabits the southern Brazilian coastal plain, which has a complex geological history, with several potential geographical barriers acting on different time scales. We assessed the geographical genetic structure of C. minutus, examining 340 individuals over the entire distributional range and using information from chromosomal rearrangements, mitochondrial DNA (mtDNA) sequences and 14 microsatellite loci. The mtDNA results revealed seven main haplogroups, with the most recent common ancestors dating from the Pleistocene, whereas clustering methods defined 12 populations. Some boundaries of mtDNA haplogroups and population clusters can be associated with potential geographical barriers to gene flow. The isolation-by-distance pattern also has an important role in fine-scale genetic differentiation, which is strengthened by the narrowness of the coastal plain and by common features of subterranean rodents (that is, small fragmented populations and low dispersal rates), which limit gene flow among populations. A step-by-step mechanism of chromosomal evolution can be suggested for this species, mainly associated with the metapopulation structure, genetic drift and the geographical features of the southern Brazilian coastal plain. However, chromosomal variations have no or very little role in the diversification of C. minutus populations.