Phylogenetic relationships of Mexican minnows of the genus Notropis (Actinopterygii, Cyprinidae)

We conducted phylogenetic analyses based on complete mitochondrial cytochrome b gene sequences among southern and central Mexican cyprinid species, included in the genera Notropis and Hybopsis. In addition 15 northern species of the genera Notropis and Hybopsis were included in the analyses in order to place the Mexican species into a larger phylogenetic framework. The phylogenetic relationships supported the existence of five major clades: (1) including species of the subgenus Alburnops of the genus Notropis plus N. shumardi; (2) species of the subgenus Notropis; (3) species of the genus Hybopsis; (4) species of the N. texanus + N. volucellus species group of the genus Notropis; (5) Mexican endemic species of the genus Notropis plus the genus Yuriria. Previous phylogenetic inferences based on morphological characters resolved the Mexican minnows analysed as N. sallaei, N. calientis, N. boucardi and Y. alta, non‐monophyletic. According to our cytochrome b evidence all Mexican minnows of the genera Notropis and Yuriria formed a monophyletic group with respect to the northern species of the genera Notropis and Hybopsis. Within the Mexican clade, three well‐supported clades were identified: the first included the closely related species N. moralesi and N. boucardi, which occur in three independent drainages of south Mexico; the second consisted of two different lineages, N. imeldae and an undescribed species of Notropis, inhabiting two independent drainages of south Mexico; the third comprised two central Mexican Notropis species (N. calientis and N. sallaei) and the Y. alta populations. Based on this study and pending a more extensive taxonomic revision of the genus Notropis, we adopt the conservative criterion of considering all Notropis species from southern and central Mexico examined, including Y. alta, as belonging to the genus Notropis. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 80 , 323–337.     

Reconciling gene trees of eastern North American minnows

Most eastern North American cyprinid fishes belong to a clade known as the "open posterior myodome" (OPM) minnows, but phylogenetic relationships within this clade have been difficult to ascertain. Previous attempts to resolve relationships among the generally benthic "chubs" and the more pelagic "shiners", that constitute the majority of OPM minnows, have led to highly discordant phylogenetic hypotheses. To further examine relationships among the OPM minnows, we utilized both a concatenated Bayesian approach and a coalescent-based species tree method to analyze data from six protein coding nuclear loci (Enc1, Ptr, Ryr3, Sh3px3, Tbr1, and Zic1), as well as the mitochondrial locus (Cytb). We focused our analyses on the chub-like genus Phenacobius, a group that has drifted topologically between other benthic chubs and the more pelagic shiners, and also included exemplar taxa from 11 other OPM lineages. Individual gene trees were highly discordant regarding relationships within Phenacobius and across the OPM clade. The concatenated Bayesian analysis and coalescent-based species tree reconstruction recovered slightly different phylogenetic topologies. Additionally, the posterior support values for clades using the coalescent-based approach were consistently lower than the concatenated analysis. However, Phenacobius was resolved as monophyletic and as the sister lineage to Erimystax regardless of the combined data approach taken. Furthermore, Phenacobius+Erimystax was recovered as more closely related to the shiners we examined than to other chubs. Relationships within Phenacobius varied depending on the combined phylogenetic method utilized. Our results highlight the importance of multi-locus, coalescent-based approaches for resolving the phylogeny of diverse clades like the eastern North American OPM minnows.     

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.     

Southern Mexican minnows of the genus Notropis (Actinopterygii, Cyprinidae): genetic variation, phylogenetic relationships and biogeographical implications

Allozyme analyses were performed to determine patterns of genetic variation and phylogenetic relationships within the genus Notropis in southern Mexico. Products of 28 gene loci were resolved in 24 geographic samples belonging to four putative species. These species represent the southern limit of the Cyprinidae in North America. Five loci were found monomorphic and 11 were diagnostic among species when the outgroup, Phoxinus phoxinus, was not taken into account. Four groups were identified, but these do not correspond perfectly to the four nominal species. Notropis sallaei was identified by allozyme analyses being the most basal among southern Mexican Notropis and the most genetically divergent. Notropis imeldae, was also diagnosed on the basis of allozymic variation, however a population sample representing the Balsas drainage was genetically divergent and is considered as an undescribed new species (N. n. sp.). No genetic differences were found between the samples of N. boucardi and N. moralesi. Therefore, we recommend that N. moralesi should be considered as a junior synonym of N. boucardi. A broad geographic sampling strategy was employed across all the distribution range of N. boucardi representing rivers from three different drainages, which cover both Mexican slopes. The slight divergence found among the headwater populations of N. boucardi permitted us to predict a model of paleohydrographic relationships of these three drainages. Two alternative hypotheses are postulated to explain the current distribution pattern of populations of N. boucardi in southern Mexico.     

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.     

Geographic variation in thermal tolerance of a widespread minnow Notropis lutrensis of the North American mid-west

Eighteen populations of Notropis lutrensis , representing all of the major river systems occupied by this species across an 1100km north-south span of its range, showed no significant differences in mean critical thermal maximum (CTM), although general north-south differences in climatic temperatures exist. There were no clinal trends in CTMs, and CTMs were unrelated to stream size or any other discernible feature of the local habitats. Previous research has shown that N. lutrensis can adapt rapidly to an artificially altered thermal regime. The present results suggest that even though a species may have potentially 'labile' thermal physiology, it may nonetheless be 'static' or evolutionarily conservative in such characters when natural populations are examined empirically.     

Rapid diversification in the North American minnow genus Nocomis

Diversification rates among stream fishes are likely governed by geographical factors that impact connectivity among and between stream systems. Herein we investigate rates of diversification within species of River Chubs, Nocomis, a monophyletic group of stream fishes distributed throughout the drainage basins of the Mississippi River, Atlantic Slope and Gulf Coast. We used nucleotide sequences of two protein-coding nuclear genes (IRBP and rhodopsin) and one mitochondrial gene (cytochrome b) to generate a phylogenetic hypothesis of population-level relationships within and among species. Results of molecular analyses suggest that morphological and meristic treatments of Nocomis have underestimated species diversity within the group. Tree-based Bayesian methods and diversification statistics were implemented to model the rate of evolutionary change along lineages and estimate divergence dates among phylogroups. Significantly elevated rates of cladogenesis are observed among coastally distributed populations 2-3 million years before present. This period was dominated by dramatic sea level fluctuations that suggest a period of climatic instability. Climatic instability and other factors may have driven the burst of rapid diversification observed in Nocomis. Results generated in this study reinforce faunistic and geologic arguments for the hypothesized existence of extinct rivers, such as White's River and the Appalachian River.     

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.     

The occurrence of synchrony in the North American fireflyPhotinus carolinus (Coleoptera: Lampyridae)

Synchronous flashing has been described for some Southeast Asian fireflies but has rarely been reported in North American fireflies. Our field observations indicated thatPhotinus carolinus flash synchronously. The flash pattern of individualP. carolinus was characterized by a burst of five to eight flashes over a period of approximately 4 s. These flash bursts were repeated about every 12 s. Groups of fireflies comprised individuals exhibiting this species-specific flash pattern. Remarkably, members of the group flashed synchronously: Flash bursts started and stopped at the same time and the flashes among individuals occurred at the same time as well. We used low-light level videography to examine this behavior in caged groups of (3 or 10) fireflies for synchronic flashing. The occurrence of concurrent rhythmic group flashing satisfies the criteria for synchrony as defined by Buck (1988). The intermittent nature of the bursts of flashes shown byP. carolinus makes this a discontinuous synchrony. The mechanisms underlying discontinuous synchrony are not known.     

The reproductive biology, age and growth of the North American cyprinid, Notropis longirostris (Hay)

Notropis longirostris (Hay), the longnose shiner, in Catahoula Creek, Jourdan River drainage, Hancock County, Mississippi, was studied from May 1970 to May 1972. In 1971 reproduction occurred from late March into October, as indicated by gross examination of testes, breeding tubercles and breeding colour in males, and ovarian weights, measurements of ova, and gross examination of ovaries in females. Gross examination of ovaries in 1970 also indicated an extended reproductive season. Generally no significant differences from a 1 : 1 sex ratio or in the size of males and females in collections taken during the reproductive season were indicated. Males and females matured about the same size. Most females were sexually mature when 29–30 mm SL. The smallest female with mature ova was 28 mm; however, the majority of females did not have mature ova until 31–33 mm. The number of mature ova produced prior to spawning ranged from 15 to 129 for females 30.8–44 mm SL. There were significant differences in the number of mature ova with time, two peaks being indicated: the first in late March and April at the beginning of the reproductive period and the second in early July about the middle of the season. This conclusion is also supported by ovarian weight measurements and length frequency histograms. The mean diameters of mature ova ranged from 0.70–1.05 mm, averaging 0.90 mm, and were not significantly correlated with length. Most fish live about 1–1.5 years and do not live through two winters, indicating an annual turnover in the population. Maximum size was about 48 mm SL. Specific characteristics of the life history pattern of N. longirostris are discussed in relation to ecological conditions of the habitat.     

The Relationship of Spawning Mode to Conservation of North American Minnows (Cyprinidae)

Approximately 20% of North American minnows are considered imperiled. The factors responsible for imperilment in this group are complex, but the relationship of spawning mode to conservation of North American minnows has not been explored. I provide a summary of the spawning modes of imperiled North American minnows, discuss patterns between these modes and conservation status, and predict the spawning modes for several poorly-known imperiled species. Of the 46 species of North American minnows that are imperiled, spawning modes are known for only 13 species. All spawning modes are represented in the imperiled group of minnows except mound-building and egg-clustering, and with the exception of crevice-spawners and pit-ridge-builders, the percentage of imperiled minnows in each category of spawning mode is roughly proportional to the percentage of minnows in that category overall. Species with complex spawning modes, such as mound-building, pit-building and egg-clustering, are among the most common fishes in North American streams. This pattern suggests that there is a relationship between parental care and success (lack of imperilment) in minnows. Spawning mode is an important consideration in the formulation of recovery plans and proactive conservation efforts.     

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.     

The occurrence of nitro-toxins in North American astragalus (Fabaceae)

Leaves from herbarium specimens of 505 species and varieties of North AmericanAstragalus were examined for the presence of organic nitro-toxins. The relative concentration of these nitro compounds was determined for the 263 nitro-containing species and varieties. Chemotaxonomic relationships existed among many species so that the presence, molecular configuration, and concentration of the nitro-toxins in the species examined could be used to predict the occurrence of these toxins in other taxa. Geographic differences were also noted for varieties of one species,A. robbinsii (Oakes) A. Gray.     

North American face flies Old World origins: mitochondrial evidence

Analysis of a 513 base sequence of mitochondrial cytochrome oxidase I gene in Musca autumnalis De Geer (Diptera: Muscidae) from the U.S.A., England, Russia and Kazakhstan confirms that North American flies originated in Western Europe. Flies from the U.S.A., England and southern Russia shared most of their mitochondrial diversities, but face flies from Kazakhstan were substantially dissimilar, suggesting highly restricted gene flow and a species complex within the Palearctic.