Relative roles of Neogene vicariance and Quaternary climate change on the historical diversification of bunchgrass lizards (Sceloporus scalaris group) in Mexico

Neogene vicariance during the Miocene and Pliocene and Quaternary climate change have synergistically driven diversification in Mexican highland taxa. We investigated the impacts of these processes on genetic diversification in the widely distributed bunchgrass lizards in the Sceloporus scalaris group. We searched for correlations between timing in diversification and timing of (1) a period of marked volcanism across the Trans-Mexican Volcanic Belt in central Mexico 3-7.5 million years ago (Ma) and (2) a transition to larger glacial-interglacial cycles during the mid-Pleistocene. From our phylogenetic analyses of mitochondrial DNA we identified two major clades that contained 13 strongly supported lineages. One clade contained lineages from the two northern sierras of Mexico, and the other clade included lineages associated with the Trans-Mexican Volcanic Belt and Central Mexican Plateau. Results provided support for Neogene divergences within the S. scalaris group in response to uplift of the Trans-Mexican Volcanic Belt, a pattern observed in several co-distributed taxa, and suggested that Quaternary climate change likely had little effect on diversification between lineages. Uplift of the Trans-Mexican Volcanic Belt during specific time periods appears to have strongly impacted diversification in Mexican highland taxa.     

Gill‐derived glands in species of Astyanax (Teleostei: Characidae)

The presence of a gill‐derived gland is herein reported for the first time in males of species of Astyanax and related genera; they are described through histological cuts and SEM. The gill‐derived glands described for the Characidae, when fully developed, present a similar structure in different species. The main external feature of gill‐derived glands is the fusion of anteriormost gill filaments on the ventral branch of first gill arch. This fusion is caused by squamous stratified epithelial tissue that covers adjacent filaments, forming a series of chambers. In the region where the gill‐derived gland develops, the secondary lamellae of the gill filaments are much reduced or completely atrophied being characterized by the presence of glandular cells forming nests.     

Comparative ultrastructural investigations of the pineal organ of the blind cave fish,Anoptichthys jordani,and its ancestor,the eyed river fish,Astyanax mexicanus

A comparative ultrastructural study has been made of the pineal organ in specimens of two closely related populations of the characid fish, Astyanaz mexicanus. The specimens of one population are living in the river, under natural light conditions. The specimens of the other population, originally described as Anoptichthys jordani, are living in a completely dark cave. In specimens of both populations the pineal organ consists of a spindle shaped end-vesicle, connected to the diencephalic roof by a slender stalk. The pineal tissue is compact and consists predominantly of glia-like supporting cells and sensory cells resembling the photoreceptor cells of the lateral vertebrate eye. Phagocytotic microglia-like cells can be found in close contact with the outer segments of the sensory cells. Nerve cells are located in the neighbourhood of neuropil formations, in which synaptic contacts are established between sensory cells and nerve cells. From these nerve cells fibers are emerging, forming the pineal tract that runs down the pineal stalk towards the diencephalon. On the basis of the ultrastructure described by other authors it is concluded that the pineal organ in specimens of the river population of Astyanax mexicanus resembles the pineal organ of other fish species. In specimens of the river population, reared under normal light-dark conditions for 3, 9 or 18 months, conspicuous morphological changes have not been detected in the presumably light-sensitive outer segments of the sensory cells or in other parts of the pineal tissue. In specimens of the cave populations, reared under identical conditions, an age-dependent, gradual regression of the regular outer segment organization of the pineal sensory cells takes place. In other parts of the pineal tissue, only small morphological changes can be observed. In specimens of the cave population, reared in constant darkness, the regression of the pineal outer segment organization begins earlier and is obvious. It is postulated that the gradual age-dependent regression of the regular organization of the outer segments in the pineal organ of cave specimens of Astyanax mexicanus is genetically determined and indicates a regressive evolution of the pineal light sensitivity. The expression of the regressive traits is dependent on the environmental light conditions.     

Genetic divergence between cave and surface populations of Astyanax in Mexico (Characidae,Teleostei)

A study of genetic diversity at microsatellite loci and the mitochondrial DNA (mtDNA) cytochrome b gene was carried out to assess genetic relationships among four Mexican cave (Pachon, Sabinos, Tinaja, Chica) and four surface populations of Astyanax fasciatus (Characidae) from northeast Mexico and the Yucatan. With the exception of Chica, the cave populations were all characterized by extremely low microsatellite variability, which most likely resulted from bottleneck events. Population analyses of the microsatellite data indicated no measurable levels of gene flow between all cave and surface populations (F(ST) > 0.0707). Phylogenetic analyses of mtDNA data showed that only two cave populations - Sabinos and Tinaja - group together to the exclusion of surface populations. From the microsatellite data these cave populations cluster with the Pachon cave fish population. The mtDNA thus appears to have been replaced in Pachon because of introgressive hybridization. It is likely that these three cave populations have descended from a surface ancestor in common with current surface populations, rather than evolving recently from one of the extant surface populations. Like Pachon, the Chica population clustered with the surface populations according to mtDNA data, but was not clearly associated with either the surface or the other cave populations according to the microsatellite data. Our data indicate that the Chica population evolved recently from a surface population, and subsequently hybridized with a phylogenetically older cave population. In conclusion, both the microsatellite and mtDNA data suggest multiple origins of cave populations and the Chica and Sabinos/Tinaja/Pachon were founded after at least two independent invasions from surface populations.     

Cytogenetic characterization of a supernumerary chromosome segment and of B-chromosomes in Astyanax scabripinnis (Teleostei, Characidae)

The chromosome complement of a local population of Astyanax scabripinnis in Brazil was investigated with emphasis on the study of the heterochromatin attached to the A-chromosomes and present in the macro B-chromosome. Analysis after C-banding, silver and CMA₃ staining, incorporation of 5-bromo-2′-deoxyuridine and chromosome digestion with nine restriction endonucleases revealed that the heterochromatin in the B-chromosomes was different from that found in the A-chromosomes. A polymorphism due to the presence of a supernumerary heterochromatic chromosome segment was observed in the population investigated. Some aspects related to the origin of the heterochromatin polymorphism in Astyanax scabripinnis are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetics and hybridization in surface and cave Astyanax (Teleostei): a comparison of regressive and constructive traits

Change in ecological conditions, as seen in surface and cave populations of Astyanax (Teleostei), has caused the divergent evolution of a large number of traits like eyes, coloration, taste, lateral line, and different kinds of behaviour like schooling, sleep or feeding posture. Because of the interfertility of surface and cave forms these fish are an exceptional object to study the morphological and genetic basis of the evolution of such complex regressive and constructive traits. Classical crossing analyses and genomic studies are contributing to growing understanding. Both kinds of traits mostly rely on multiple genetic bases and the phenotypic manifestation in the various crosses is similar. The gene effect underlying the phenotypic manifestation may exhibit an exponential increase at differing amounts in the various traits and crosses. Missing or presence of such genetic interaction helps determine whether the variability of eyes or pigmentation exhibited by Astyanax cave fish populations like Micos, is due to a more recent origin or to secondary hybridization with the surface fish. Neither crossing analysis nor QTL mapping revealed that eye reduction is pleiotropically antagonistically related to the increase of taste buds or lateral line sense. Independent inheritance of traits suggests that Astyanax cave fish are subjected to mosaic evolution.     

Comparative phylogeography of livebearing fishes in the genera Poeciliopsis and Poecilia (Poeciliidae: Cyprinodontiformes) in central Mexico

Aim To test the hypothesis that the vicariant event responsible for north–south divergences in two clades of the fish genus Poeciliopsis Regan was also responsible for north–south divergences in the fish Poecilia butleri Jordan. Location Central Mexico. Methods Parsimony, distance, maximum likelihood and Bayesian phylogenetic analyses of a mitochondrial gene. Molecular clock test and Bayesian analyses of divergence time. Results We report concordant phylogeographical patterns between two clades in the genus Poeciliopsis (i.e. the other formed by P. latidens Garman and P. fasciata Meek, and the other formed by P. presidionis Jordan and P. turneri Miller) and the clade of Poecilia butleri, with northern and southern individuals within each clade grouping into separate lineages. There is also evidence for slower substitution rates in Poecilia compared with Poeciliopsis. After taking into account these substitution rate discrepancies with Bayesian relaxed molecular clock analyses, north–south divergences in Poecilia butleri were equivalent to those reported for Poeciliopsis latidens‐fasciata and P. presidionis‐turneri. Main conclusions The same Plio‐Pleistocene vicariant event associated with geological activity of the Trans‐Mexican Volcanic Belt (TMVB) appears to have caused divergence in three different freshwater fish lineages. This study is an example of how comparative phylogeography can strengthen inferences about vicariant events in regions of high biological diversity and complex geological history such as the TMVB.     

Speciation and anagenesis in the genus Cyprinella of Mexico (Teleostei: Cyprinidae): a case study of Model III allopatric speciation

Allozyme variation at 42 presumptive gene lociis presented for members of the C. formosa species group. This group iscorroborated as a monophyletic assemblage whosecommon ancestor occupied pluvial Lake Palomasof the Guzman Basin. With increasingaridity during the Pleistocene this basin andassociated populations of this commonancestor were fragmented into several lineagesthat diverged independently of oneanother. The pattern of relationships andlevels of anagenetic change observed inindependent lineages for this clade are notconsistent with expectations of the mostcommon modes of speciation, Model I large-scalevicariance or Model II peripheralisolation. Rather, divergence in these fishlineages is consistent with the rarely observedModel III allopatric speciation. Consistentwith predictions of this model, thephylogenetic pattern recovered revealspolychotomous relationships (a hard polytomy)and varied rates of anagenetic change acrossexamined lineages.     

Behavior in an ‘intermediate’ population of the subterranean-dwelling characid Astyanax fasciatus

Synopsis A population of the characid Astyanax fasciatus was found living at the outflow of a subterranean source of water. Field observations revealed differences in behavior when compared with river populations. Affinity of this fish for the subterranean cavity was evidenced by behavior and distribution of individuals. Fish almost always carried bait into the subterranean cavity prior to feeding and also went into the cavity at night. Three factors may influence the affinity for the subterranean source of water: 1) protection against aerial predation, 2) the advantage to fishes of hovering in shade, 3) sheltering for reproduction. These observations suggest that cave colonization may take place actively rather than accidentaly, that behavioral changes may preceed morphological ones during initial stages of cave entry, and that behavioral adaptations may occur quite rapidly.     

Re-evaluation of morphological and chloroplast DNA variation in Juniperus osteosperma Hook and Juniperus occidentalis Torr. Little (Cupressaceae) and their putative hybrids

Relationships between variation in cpDNA and morphology were examined to test the hypothesis of hybridization between Juniperus osteosperma and Juniperus occidentalis. Principal components analysis of 11 taxonomically-important characters distinguished individuals collected from eastern Nevada and Utah from those of southern Oregon. In contrast, many individuals collected from sympatric populations in western Nevada were morphologically intermediate to these two groups. Comparative sequencing of the trnS-trnG intergenic spacer and restriction site analysis of a trnL-trnF PCR product revealed nine haplotypes, and examination of haplotype-morphology associations allowed identification of species-specific genetic markers as well as those that transcend species limits. The confinement of morphological intermediacy and transcendent haplotypes to zones of sympatry, the discovery of haplotypes characteristic of one species in the morphological background of the other, and determination that the character intermediacy encountered is of the type expected under interspecific gene flow are marshaled in support of introgressive hybridization between J. osteosperma and J. occidentalis.     

Accentuated polymorphism of heterochromatin and nucleolar organizer regions in Astyanax scabripinnis (Pisces, Characidae): tools for understanding karyotypic evolution

Astyanax scabripinnis has been considered a species complex because it presents high karyotypic and morphological variability among its populations. In this work, individuals of two A. scabripinnis populations from different streams in the same hydrographic basin were analyzed through C‐banding and AgNOR. Although they present distinct diploid numbers, they show meta and submetacentric chromosome groups highly conserved (numerically and morphologically). Other chromosomal characteristics are also shared by both populations, as the pattern of constitutive heterochromatin distribution (large blocks in the telomeric regions of subtelocentric and acrocentric chromosomes) and some nucleolar chromosomes. Inter‐individual variations both in the number and size of heterochromatic blocks, and in the number and localization of NORs were verified in the studied populations, characterizing them as polymorphics for these regions. The mechanisms involved in the dispersion of heterochromatin and NORs through the karyotypes, as well as the possible events related to the generation of polymorphism of those regions are discussed. Furthermore, relationships between these populations and within the context of the scabripinnis complex are also approached. This revised version was published online in July 2006 with corrections to the Cover Date.     

Multilocus phylogeny of Crenicichla (Teleostei: Cichlidae), with biogeography of the C. lacustris group: species flocks as a model for sympatric speciation in rivers

First multilocus analysis of the largest Neotropical cichlid genus Crenicichla combining mitochondrial (cytb, ND2, 16S) and nuclear (S7 intron 1) genes and comprising 602 sequences of 169 specimens yields a robust phylogenetic hypothesis. The best marker in the combined analysis is the ND2 gene which contributes throughout the whole range of hierarchical levels in the tree and shows weak effects of saturation at the 3rd codon position. The 16S locus exerts almost no influence on the inferred phylogeny. The nuclear S7 intron 1 resolves mainly deeper nodes. Crenicichla is split into two main clades: (1) Teleocichla, the Crenicichla wallacii group, and the Crenicichla lugubris-Crenicichla saxatilis groups (“the TWLuS clade”); (2) the Crenicichla reticulata group and the Crenicichla lacustris group-Crenicichla macrophthalma (“the RMLa clade”). Our study confirms the monophyly of the C. lacustris species group with very high support. The biogeographic reconstruction of the C. lacustris group using dispersal-vicariance analysis underlines the importance of ancient barriers between the middle and upper Paraná River (the Guaíra Falls) and between the middle and upper Uruguay River (the Moconá Falls). Our phylogeny recovers two endemic species flocks within the C. lacustris group, the Crenicichla missioneira species flock and the herein discovered Crenicichla mandelburgeri species flock from the Uruguay and Paraná/Iguazú Rivers, respectively. We discuss putative sympatric diversification of trophic traits (morphology of jaws and lips, dentition) and propose these species flocks as models for studying sympatric speciation in complex riverine systems. The possible role of hybridization as a mechanism of speciation is mentioned with a recorded example (Crenicichla scottii).     

Progenitor-derivative speciation in Pozoa (Apiaceae, Azorelloideae) of the southern Andes

Background and Aims

Studies examining patterns and processes of speciation in South America are fewer than in North America and Europe. One of the least well documented processes has been progenitor–derivative speciation. A particularly instructive example occurs in the southern Andes in the genus Pozoa (Apiaceae, Azorelloideae), which consists of only two diploid outcrossing species, the widespread P. coriacea and the geographically and ecologically restricted P. volcanica. This paper tests the hypothesis that the latter species originated from the former through local geographical and ecological isolation by progenitor–derivative speciation.

Methods

DNA sequences were analysed from Pozoa and the related South American genera Asteriscium, Eremocharis and Gymnophyton from non-coding regions of the plastid genome, ndhF-rpl32 and rpl32-trnL, plus incorporation of previously reported rpl16 intron and trnD-trnT intergenic spacer sequences. Amplified fragment length polymorphism (AFLP) data from 105 individuals in 21 populations throughout the entire range of distribution of the genus were used for estimation of genetic diversity, divergence and SplitsTree network analysis. Ecological factors, including habitat and associated species, were also examined.

Key Results

Pozoa coriacea is more similar genetically to the outgroup genera, Asteriscium and Eremocharis, than is P. volcanica. At the population level, only P. volcanica is monophyletic, whereas P. coriacea is paraphyletic. Analyses of genetic differentiation among populations and genetic divergence and diversity of the species show highest values in P. coriacea and clear reductions in P. volcanica. Pozoa coriacea occurs in several types of high elevation habitats, whereas P. volcanica is found only in newly formed open volcanic ash zones.

Conclusions

All facts support that Pozoa represents a good example of progenitor–derivative speciation in the Andes of southern South America.     

Morphological Differentiation and Possible Origin of B Chromosomes in Natural Brazilian Population of Astyanax Scabripinnis (PISCES, CHARACIDAE)

Specimens of Astyanax scabripinnisfrom three different altitudes (1920, 1800 and 700?m) along the Ribeirão Grande stream in the Campos do Jordão region (São Paulo State, Brazil) were investigated. The same diploid number, 2n?=?50, was detected in the three populations, with the following karyotypic constitution: 6M, 22SM, 10ST and 12A. The populations located at 1920 and 1800?m altitude presented a high incidence of B chromosomes varying in number (0–2), shape (meta- and submetacentrics), size (large and small) and sex-related frequency (they were more frequent among females). The two morphologically variant B chromosomes probably evolved from a metacentric macrochromosome, which is the most commonly observed B chromosome in several A. scabripinnispopulations.     

Molecular genetic and quantitative trait divergence associated with recent homoploid hybrid speciation: a study of Senecio squalidus (Asteraceae)

Hybridization is increasingly seen as a trigger for rapid evolution and speciation. To quantify and qualify divergence associated with recent homoploid hybrid speciation, we compared quantitative trait (QT) and molecular genetic variation between the homoploid hybrid species Senecio squalidus and its parental species, S. aethnensis and S. chrysanthemifolius, and also their naturally occurring Sicilian hybrids. S. squalidus originated and became invasive in the United Kingdom following the introduction of hybrid plants from Mount Etna, Sicily, about 300 years ago. We recorded considerable molecular genetic differentiation between S. squalidus and its parents and their Sicilian hybrids in terms of both reduced genetic diversity and altered allele frequencies, potentially due to the genetic bottleneck associated with introduction to the United Kingdom. S. squalidus is also distinct from its parents and Sicilian hybrids for QTs, but less so than for molecular genetic markers. We suggest that this is due to resilience of polygenic QTs to changes in allele frequency or lack of selection for hybrid niche divergence in geographic isolation. While S. squalidus is intermediate or parental-like for most QTs, some trangressively distinct traits were observed, which might indicate emerging local adaptation in its invasive range. This study emphasizes the important contribution of founder events and geographic isolation to successful homoploid hybrid speciation.     

A test of the sympatric host race formation hypothesis in Neodiprion (Hymenoptera: Diprionidae)

Theory suggests that sympatric speciation is possible; however, its prevalence in nature remains unknown. Because Neodiprion sawflies are host specialists and mate on their hosts, sympatric speciation via host shifts may be common in this genus. Here, we test this hypothesis using near-complete taxonomic sampling of a species group, comprehensive geographical and ecological data, and multiple comparative methods. Host-use data suggest that host shifts contributed to the evolution of reproductive isolation in Neodiprion and previous work has shown that gene flow accompanied divergence. However, geographical data provide surprisingly little support for the hypothesis that host shifts occurred in sympatry. While these data do not rule out sympatric host race formation in Neodiprion, they suggest that this speciation mode is uncommon in the genus and possibly in nature.     

Evolutionary history of frogfishes (Teleostei: Lophiiformes: Antennariidae): a molecular approach

Fishes of the family Antennariidae (order Lophiiformes) are primarily shallow-water benthic forms found in nearly all tropical and subtropical oceans and seas of the world, with some taxa extending into temperate waters. Despite an earlier attempt based on morphology, no previous hypothesis of intergeneric relationships of the Antennariidae exists. To resolve phylogenetic relationships within the Antennariidae, and to test the validity of species groups within Antennarius, DNA sequences from the mitochondrial 16S and cytochrome oxidase c subunit 1 (COI) genes, and nuclear recombination activating gene 2 (RAG2), for 25 described and four undescribed antennariid species, representing 10 of 12 known genera and one undescribed genus, were unambiguously aligned and analyzed using Bayesian and maximum likelihood methods. The markers were partitioned and analyzed for substitution saturation and only the third codon position of COI (COI-3) was found to have reached saturation. However, analysis of both datasets, one with the saturated data and one without, differed only slightly. All molecular analyses recovered two major clades, one comprised of Fowlerichthys, Antennarius, Histrio, and Antennatus; and another containing Rhycherus, Antennariidae gen. et sp. nov., Kuiterichthys, Phyllophryne, Echinophryne, Tathicarpus, Lophiocharon, and Histiophryne. Evidence is presented to illustrate a correlation between phylogeny, geographic distribution, and reproductive life history. The results of these analyses provide the first hypothesis of evolutionary relationships within the Antennariidae.     

Rhabditophanes schneideri (Rhabditida) phoretic on a cave pseudoscorpion

Information of phoretic nematode-pseudoscorpion associations and cases of parasitism on five European species of pseudoscorpions was summarized by Cur?ic et al. [Curci?, B.P.M., Dimitrijevi?, R.N., Makarov, S.E., Luci?, L.R., Curci?, S.B., 1996. Further report on nematode-pseudoscorpion associations. Acta arachnol. 45, 43-46; Curci?, B.P.M., Sudhaus, W., Dimitrijevi?, R.N., Tomi?, V.T., Curci?, S.B., 2004. Phoresy of Rhabditophanes schneideri (Bütschli) (Rhabditida: Alloionematidae) on pseudoscorpions (Arachnida: Pseudoscorpiones). Nematology 6 (3), 313-317]. An examination of a sample of the cavernicolous pseudoscorpion Neobisium rajkodimitrijevici (Curci? and Tomi?, 2006) (comprising a holotype male and a paratype tritonymph) from a cave in Eastern Serbia revealed this false scorpion to be a nematode carrier; the present paper reports this finding and extends our knowledge of phoresy of Rhabditophanes on pseudoscorpions. This is the first time that the rhabditid R. schneideri (Bütschli, 1873) has been noted in association with a cavernicolous pseudoscorpion. There must be some patchily distributed micro-habitats in caves where saprobiotic nematodes and small arthropods can complete their life-cycles, for example something like deposits of bat guano. The transportation of Rhabditophanes J3 by pseudoscorpions indicate that Neobisium specimens often visit these micro-habitats to find their prey.