Sexual size dimorphism and phylogeny in North American minnows

Sexual size dimorphism (SSD) is predicted to vary across mating systems. A previous study examined a model of SSD in fishes as it relates to three mating system variables: probability of sperm competition, male territorial guarding, and male-male contest. I tested the ability of these variables to predict SSD in North American freshwater minnows, after controlling for phylogenetic effects by an independent contrasts method. Across 58 species only male territorial guarding was significandy related to SSD in a stepwise multiple regression. When tested for 26 genera and subgenera, both male territorial guarding and male-male contest were significant in the model. The concentrated-changes test revealed that character changes in SSD (from males the same size or smaller than females, to males larger than females) were more concentrated on branches with presence of male guarding (similar results were found for changes in SSD and presence of sperm competition), at the species and genus levels. Both comparative approaches demonstrated that male guarding and male-male contest variables are linked to SSD in minnows.     

Incongruent gene trees, complex evolutionary processes, and the phylogeny of a group of North American minnows (Hybognathus Agassiz 1855)

Hybognathus is a putatively monophyletic group of North American minnows containing seven extant species. Although much is known about the taxonomy, biology, and life history of Hybognathus species, their phylogenetic relations with each other remain unclear. We address this problem with partial sequences of mitochondrial cytochrome-b, 16S rRNA, and ND4 mtDNA genes and nuclear growth hormone (GH) and S7 introns from representatives of all Hybognathus species and four outgroup taxa. Phylogenetic analyses of these data corroborated previous studies on the monophyly of seven recognized species of Hybognathus, and indicated weak support for monophyly of the genus. Topological tests, however, revealed significant (all P < 0.001) conflict among molecular data sets. Ad hoc removal of taxa from topologies and subsequent testing indicated that incongruence was localized to two specific ingroup taxa (H. hayi and H. regius) and suggested that the conflict is a function of underlying processes that have generated the observed phylogenetic patterns. Hybridization (ancestral), which is commonplace in cyprinids, may best explain topological disagreements among datasets; however, retention of ancestral polymorphism and natural selection remain as alternative hypotheses. Our results highlight methodological and topological problems associated with estimating interspecific phylogenies from multiple genes.     

Identification and species characterization of some North American minnows by electrophoresis

The LDH and MDH phenotypes of Notropis comutus, Nocomis biguttatus, Pimephales promelas, P. notatus, Rhinichthys atratulus and Semotilus atromaculatus show no apparent intraspecific variation. All species with the exception of Notropis comutus and Rhinichthys atratulus possess unique MDH phenotypes. Those two species can be readily differentiated on the basis of their LDH phenotypes. This represents a rapid, simple, inexpensive technique for an unambiguous separation and identification of otherwise similar, closely related species.     

Niche breadth and range area in North American trees

Identifying factors affecting species distribution is a longstanding goal in ecology and evolution that is accentuated by our need to anticipate climate change impacts. We sought to test whether any phylogenetic effect can be detected in either the environmental characteristics or range attributes of North American trees, and to explore the existence of a general interspecific pattern in the environmental factors influencing species range size. To do so we tested prevailing hypotheses relating climatic and edaphic characteristics to species range size in the North American arboflora (n = 598), using spatial null models to test for the relevance of observed patterns. We found that interspecific variation in the range area of North American trees is strongly related to the environmental regimes characteristic of the species range. Linear models and phylogenetic regressions involving six environmental characteristics explained 83% of the variance in species range area, and affirmed a positive relationship between niche breadth and range size. Tree species that can tolerate a larger variability in local climatic conditions, deal with harsher edaphic conditions, and weak levels of environmental energy tend to have larger range area; this can account for the greater geographic range of species at higher latitudes, the Rapoport effect. There is a significant phylogenetic signal for both range area and limits in North American trees, and for climatic limits, but not for energy or edaphic characteristics associated with species range. These findings highlight the possibility that species with small geographic ranges may be more sensitive to the effects of climate change.     

A thermal denaturation study of genomic DNAs from North American minnows (Cyprinidae: Teleostei)

Base compositions and differential melting rate profiles of genomic DNAs from twenty species of North American cyprinid fishes were generated via thermal denaturation. Base pair composition expressed as % GC values ranged among the twenty species from 36.1–41.3%. This range is considerably broader than that observed at comparable taxonomic levels in other vertebrate groups. Both the range and average difference in base pair composition between species in the diverse and rapidly evolving genus Notropis were considerably greater than those between species in other North American cyprinid genera. This may indicate that genomic changes at the level of base pair composition are frequent and possibly important events in cyprinid evolution. Compositional heterogeneity and asymmetry values among the twenty species were uniform and low, respectively, suggesting that most of the species lacked DNA components in their genomes which differed substantially from their main-band DNAs in base pair composition. The melting rate profiles revealed a prominent and distinct heavy or GC-rich DNA component in the genomes of three species belonging to the subgenus Cyprinella of Notropis. These and other data suggest that the heavy melting component may reflect a large, comparatively GC-rich family of highly repeated or satellite DNA sequences common to all three genomes.     

Genome size variation in North American minnows (Cyprinidae). II. Variation among 20 species

Genome sizes (nuclear DNA contents) from 200 individuals representing 20 species of North American cyprinid fishes (minnows) were examined spectrophotometrically. The distributions of DNA values of individuals within populations of the 20 species were essentially continuous and normal; the distribution of DNA values among species was continuous and overlapping. These observations suggest that changes in DNA quantity in cyprinids are small in amount, involve both gains and losses of DNA, and are cumulative and independent in effect. Significant heterogeneity in mean genome size occurs both between individuals within populations of species and among species. The former averages maximally around 6% of the cyprinid genome and is nearly the same as the amount of DNA theoretically needed for the entire cyprinid structural gene component. The majority of the DNA content variation among the 20 species is distributed above the level of individuals within populations. Comparisons of average genome size difference or distance between individuals drawn from different levels of taxonomic organization indicate that considerably greater divergence in genome size has occurred in the extremely speciose cyprinid genus Notropis as compared with other North American cyprinid genera. This may suggest that genome size change is concentrated in speciation episodes. Finally, no associations were found between interspecific variation in genome size and five life-history characters. This suggests that much of the variation in genome size within and among the 20 species may be phenotypically inconsequential.     

Palynological insights of the eastern Asian and eastern North American disjunct genus Symplocarpus (Araceae)

Symplocarpus L. (Araceae) is a disjunct genus including S. foetidus (L.) Nutt. var. latissimus (Makino) S. Hara, S. nipponicus Makino, and S. nabekuraensis Otsuka & K. Inoue in temperate eastern Asia; S. egorovii N. S. Pavlova & V. A. Nechaev in the Russian far east; and S. foetidus (L.) Nutt. in temperate northeastern North America. For the first time, pollen morphology of Symplocarpus was investigated by light and scanning electron microscopes. Symplocarpus foetidus var. latissimus and S. foetidus had reticulate surfaces and rounded (obtuse), long, equatorial axis tips, whereas S. nipponicus had microreticulate surfaces and acute tips. Symplocarpus foetidus in North America had larger pollen grains than S. foetidus var. latissimus in eastern Asia. Thus, based on pollen characteristics, S. foetidus var. latissimus is more closely related to S. foetidus than to S. nipponicus. Other lines of evidence, such as molecular phylogenetic studies and phenology, support the phylogenetic relationships among these species proposed in this study. The slightly modified acetolysis procedure conducted in this paper is a promising application to study weak exine or exineless pollen grains.     

Realized climatic niches of deciduous trees: comparing western Eurasia and eastern North America

Aim  Assessment of cross-continental similarities and differences in climatic limiting values for deciduous tree species and of the possible deterministic influence of past and present climatic differences on the modern tree flora in two regions.
Location  The deciduous forest regions of western Eurasia and eastern North America.
Methods  Based on species distribution data (range maps) and climate site data, the realized climatic niches of 137 deciduous tree species from the two regions were quantified using climatic envelopes. To compare these envelopes on the two continents, a hierarchical cluster analysis was performed, and principal components analysis was used to check cluster consistency.
Results  Significant differences do exist for upper limits of winter temperatures and for lower limits of summer temperatures between Western Eurasia and eastern North America. Lower limits for the annual water balance also appear different, suggesting that the deciduous trees may be more drought-tolerant in western Eurasia than in eastern North America. Climatic range types generated by the cluster analysis can be characterized, according to the distribution of the species, as boreal-temperate, northern temperate, temperate, southern temperate, and Appalachian. Five of the eight clusters contain trees from both regions, but three groups consist only of American species that have no European counterparts.
Main conclusions  Differences in temperature limitations can be explained by location on the east versus west side of the continents and by the almost complete lack of warm moist areas in western Eurasia. The difference in drought tolerance, on the other hand, is more likely to be the product of a deterministic sorting process that occurred during the Plio-Pleistocene.     

Chromosome observations on some eastern North American Eleocharis (Cyperaceae)

Chromosome numbers are reported forEleocharis obtusa var.ellipsoidalis (2n = 10),E. obtusa var.peasei (2n =10),E. engelmannii (2n =10),E. olivacea f.olivacea (2n = 20),E. olivacea f.reductiseta (2n = 20),E. flavescens (2n = 30),E. tenuis var.verrucosa (2n = 20),E. tenuis var.tenuis (2n = 24),E. tenuis var.pseudoptera (2n = 39), a possible hybrid betweenE. tenuis var.pseudoptera and var.tenuis (2n = ca. 34 & 68),E. intermedia (2n = 22),E. tuberculosa (2n = 30),E. smallii (2n = 36), andE. ambigens (2n = 46). Noticeable chromosome size differences inE. tenuis, E. smallii, andE. ambigens are consistent with size differences previously reported by other authors. Variable meiotic pairing configurations were observed inE. flavescens, E. intermedia, andE. tenuis. Chromosome data help verify taxonomic relationships of some taxa and indicate the need for further investigation of others.     

Inferring species networks from gene trees in high-polyploid North American and Hawaiian violets (Viola, Violaceae)

The phylogenies of allopolyploids take the shape of networks and cannot be adequately represented as bifurcating trees. Especially for high polyploids (i.e., organisms with more than six sets of nuclear chromosomes), the signatures of gene homoeolog loss, deep coalescence, and polyploidy may become confounded, with the result that gene trees may be congruent with more than one species network. Herein, we obtained the most parsimonious species network by objective comparison of competing scenarios involving polyploidization and homoeolog loss in a high-polyploid lineage of violets (Viola, Violaceae) mostly or entirely restricted to North America, Central America, or Hawaii. We amplified homoeologs of the low-copy nuclear gene, glucose-6-phosphate isomerase (GPI), by single-molecule polymerase chain reaction (PCR) and the chloroplast trnL-F region by conventional PCR for 51 species and subspecies. Topological incongruence among GPI homoeolog subclades, owing to deep coalescence and two instances of putative loss (or lack of detection) of homoeologs, were reconciled by applying the maximum tree topology for each subclade. The most parsimonious species network and the fossil-based calibration of the homoeolog tree favored monophyly of the high polyploids, which has resulted from allodecaploidization 9-14 Ma, involving sympatric ancestors from the extant Viola sections Chamaemelanium (diploid), Plagiostigma (paleotetraploid), and Viola (paleotetraploid). Although two of the high-polyploid lineages (Boreali-Americanae, Pedatae) remained decaploid, recurrent polyploidization with tetraploids of section Plagiostigma within the last 5 Ma has resulted in two 14-ploid lineages (Mexicanae, Nosphinium) and one 18-ploid lineage (Langsdorffianae). This implies a more complex phylogenetic and biogeographic origin of the Hawaiian violets (Nosphinium) than that previously inferred from rDNA data and illustrates the necessity of considering polyploidy in phylogenetic and biogeographic reconstruction.     

Seed size and shade-tolerance: a comparative analysis of North American temperate trees

Large seed size is a trait associated with plant species of mature, closed habitats, and is thought to supply an ample nutrient reserve necessary for seedling establishment. While this relationship has been shown for annuals and short-lived perennials, it is poorly documented for trees. A comparative method was used to determine whether North American temperate tree species which typically establish in shady conditions have larger seeds than those requiring more open conditions. Both angiosperms (hardwoods) and gymnosperms (conifers) were involved in the study. A significant relationship was found between large seed mass and shade-tolerance for angiosperms, but not for gymnosperms. These contrasting results seem to relate to unique evolutionary opportunities or constraints in different taxa. The absence of a relationship for gymnosperms is discussed in terms of character traits which might prevent seed size selection in response to shade. The finding for angiosperms underlines the importance of the regeneration niche in promoting coexistence among temperate hardwood species through seed size differentiation. Received: 18 March 1997 / Accepted: 26 November 1997     

Spawning performance in North American minnows: direct evidence of the occurrence of multiple clutches in the genus Notropis

Pairs of laboratory–reared F₁, and F₂ males and females of Notropis leedsi were observed in aquaria. Analyses of spawning histories and ovum diameter histograms showing the pattern of ovum development demonstrated that females produced multiple clutches of eggs. Each clutch is comprised of oocytes which undergo synchronous development and are oviposited within a relatively short period of time. Examinations of collections from streams in Florida and Georgia showed that N. leedsi has a spawning season which lasts at least from May to September. Because the pattern of ovum development in wild-caught females was the same as that observed in laboratory females, we believe that our laboratory observations demonstrate processes which occur in the natural environment. A total of 193 spawning intervals was observed in 34 pairs kept at 22–26°C in the laboratory. The interspawning intervals ranged from 3 to 10 days, with a mean of 4.6 days and a mode of 4 days. The clutches ranged in size from 26 to 28 ova for females of 36.7–52.5 mm standard length.     

Anaerobic oral flora in the North American black bear (Ursus americanus) in eastern North Carolina

Microbial flora can provide insight into the ecology and natural history of wildlife in addition to improving understanding of health risks. This study examines the anaerobic oral flora of hunter killed black bears (Ursus americanus) in eastern North Carolina. Oral swabs from the buccal and lingual supragingival tooth surfaces of the first and second mandibular and maxillary molars of 22 black bears were inoculated onto Brucella Blood Agar plates supplemented with hemin and vitamin K after transport from the field using reduced oxoid nutrient broth. Sixteen anaerobic bacterial species, representing nine genera were identified using the RapID ANA II Micromethod Kit system and a number of organisms grown that could not be identified with the system. The most frequently identified anaerobes were Peptostreptococcus prevotii, Streptococcus constellatus, and Porphyromonas gingivalis. The diversity in the anaerobic oral flora of black bear in eastern North Carolina suggests the importance of including these organisms in basic health risk assessment protocols and suggests a potential tool for assessment of bear/habitat interactions.     

Timing the eastern Asian-eastern North American floristic disjunction: molecular clock corroborates paleontological estimates

Sequence data of the chloroplast gene rbcL were used to estimate the time of the well-known eastern Asian-eastern North American floristic disjunction. Sequence divergence of rbcL was examined for 22 species of 11 genera (Campsis, Caulophyllum, Cornus, Decumaria, Liriodendron, Menispermum, Mitchella, Pachysandra, Penthorum, Podophyllum, and Phryma) representing a diverse array of flowering plants occurring disjunctly in eastern Asia and eastern North America. Divergence times of putative disjunct species pairs were estimated from synonymous substitutions, using rbcL molecular clocks calibrated for Cornus. Relative rate tests were performed to assess rate constancy of rbcL evolution among lineages. Corrections of estimates of divergence times for each species pair were made based on rate differences of rbcL between Cornus and other species pairs. Results of these analyses indicate that the time of divergence of species pairs examined ranges from 12.56 +/- 4.30 million years to recent (<0.31 million years), with most within the last 10 million years (in the late Miocene and Pliocene). These results suggest that the isolation of most morphologically similar disjunct species in eastern Asia and eastern North America occurred during the global climatic cooling period that took place throughout the late Tertiary and Quaternary. This estimate is closely correlated with paleontological evidence and in agreement with the hypothesis that considers the eastern Asian-eastern North American floristic disjunction to be the result of the range restriction of a once more or less continuously distributed mixed mesophytic forest of the Northern Hemisphere that occurred during the late Tertiary and Quaternary. This implies that in most taxa the disjunction may have resulted from vicariance events. However, long-distance dispersal may explain the disjunct distribution of taxa with low divergence, such as Menispermum.     

Beta-globin gene cluster haplotypes in two North American indigenous populations

Haplotypes derived from five polymorphic restriction sites were determined in 50 Carrier-Sekani and 70 Mvskoke chromosomes, and the results were integrated with those previously obtained for 11 South American Indian populations. Eleven haplotypes were identified in the Mvskokes, while five were observed in the Carrier-Sekani. As in South American natives, haplotype 2 (+----) and 6 (-++ -+) were the most prevalent among the Mvskoke (46% and 30%, respectively). In the Carrier-Sekani, haplotype 2 was also the most common, but haplotype 5 (-+ -++) was somewhat more frequent (18%) than 6 (12%). High heterozygosities, as well as genetic differentiation, were observed among these two North American and two other South American groups (Mapuche and Xavante). They could be due to non-Indian admixture in the Mvskoke and Mapuche, but the findings in the other two populations require some other type of explanation.     

Cuspidatispora xiphiago gen. et sp. nov. from an eastern North American creek

An interesting aquatic ascomycete was found that appeared to possess characteristics of some members of the Sordariales. Subsequent sequencing of the 28S large subunit rDNA and β-tubulin genes confirmed the morphological data by placing it in the Sordariales but failed to provide support for placing this species in any recognized genus. Therefore, a new genus, Cuspidatispora, is erected to accommodate Cuspidatispora xiphiago, which is described as a new species based on a combination of morphological and molecular data. Cuspidatispora xiphiago is unique in possessing a central, melanized ascomal wall layer and apiosporous ascospores with a pronounced apical wall extension.     

Revisiting projected shifts in the climate envelopes of North American trees using updated general circulation models

Global climate models are constantly being upgraded, but it is often not clear what these changes have on climate change impact projections. We used difference maps to directly compare downscaled projections of temperature and precipitation across North America for two versions (or generations) of three different Atmospheric‐Ocean General Circulation Models (AOGCM)s. We found that AOGCM versions differed in their projections for the end of the current century by up to 4 °C for annual mean temperature and 60% for annual precipitation. To place these changes in an ecological context, we reanalyzed our work on shifts in tree climate envelopes (CEs) using the newer‐generation AOGCM projections. Based on the updated AOGCMs, by the 2071–2100 period, tree CEs shifted up to 2.4 degrees further north or 2.6 degrees further south (depending on the AOGCM) and were about 10% larger in size. Despite considerable differences between versions of a given AOGCM, projections made by the newer version of each AOGCM were in general agreement, suggesting convergence across the three models studied here. Assessing the AOGCM outputs in this way provides insight into the magnitude and importance of change associated with AOGCM upgrades as they continue to evolve through time.