Biogeography of Greater Antillean freshwater fishes, with a review of competing hypotheses.

In biogeography, vicariance and long-distance dispersal are often characterised as competing scenarios. However, they are related concepts, both relying on collective geological, ecological, and phylogenetic evidence. This is illustrated by freshwater fishes, which may immigrate to islands either when freshwater connections are temporarily present and later severed (vicariance), or by unusual means when ocean gaps are crossed (long-distance dispersal). Marine barriers have a strong filtering effect on freshwater fishes, limiting immigrants to those most capable of oceanic dispersal. The roles of vicariance and dispersal are debated for freshwater fishes of the Greater Antilles. We review three active hypotheses [Cretaceous vicariance, Greater Antilles-Aves Ridge (GAARlandia), long-distance dispersal] and propose long-distance dispersal to be an appropriate model due to limited support for freshwater fish use of landspans. Greater Antillean freshwater fishes have six potential source bioregions (defined from faunal similarity): Northern Gulf of México, Western Gulf of México, Maya Terrane, Chortís Block, Eastern Panamá, and Northern South America. Faunas of the Greater Antilles are composed of taxa immigrating from many of these bioregions, but there is strong compositional disharmony between island and mainland fish faunas (>90% of Antillean species are cyprinodontiforms, compared to <10% in Northern Gulf of México and Northern South America, and ≤50% elsewhere), consistent with a hypothesis of long-distance dispersal. Ancestral-area reconstruction analysis indicates there were 16 or 17 immigration events over the last 51 million years, 14 or 15 of these by cyprinodontiforms. Published divergence estimates and evidence available for each immigration event suggests they occurred at different times and by different pathways, possibly with rafts of vegetation discharged from rivers or washed to sea during storms. If so, ocean currents likely provide critical pathways for immigration when flowing from one landmass to another. On the other hand, currents create dispersal barriers when flowing perpendicularly between landmasses. In addition to high salinity tolerance, cyprinodontiforms collectively display a variety of adaptations that could enhance their ability to live with rafts (small body size, viviparity, low metabolism, amphibiousness, diapause, self-fertilisation). These adaptations likely also helped immigrants establish island populations after arrival and to persist long term thereafter. Cichlids may have used a pseudo bridge (Nicaragua Rise) to reach the Greater Antilles. Gars (Lepisosteidae) may have crossed the Straits of Florida to Cuba, a relatively short crossing that is not a barrier to gene flow for several cyprinodontiform immigrants. Indeed, widespread distributions of Quaternary migrants (Cyprinodon, Gambusia, Kryptolebias), within the Greater Antilles and among neighbouring bioregions, imply that long-distance dispersal is not necessarily inhibitory for well-adapted species, even though it appears to be virtually impossible for all other freshwater fishes.

Revised New World bioregions and environmental correlates for vectors of Chagas disease (Hemiptera, Triatominae).

The subfamily Triatominae includes a group of hematophagous insects, vectors of the parasite Trypanosoma cruzi, which is the etiological agent of Chagas disease, also known as American trypanosomiasis. Triatomines occur in the Old and New World and occupy diverse habitats including tropical and temperate areas. Some studies suggest the distributions of triatomines group into three or four regions. This study objectively determined bioregions focused specifically on New World Triatominae, using clustering and ordination analysis. We also identified indicator species by bioregion and investigated relationships among bioregions and environmental variables using redundancy analysis and multivariate regression trees. We delineated seven bioregions specific to Triatominae and linked each with indicator species. This result suggests more biogeographical structure exists than was revealed in earlier studies that were more general, subjective, and based on older taxonomic and distributional information. Precipitation, elevation, and vegetation were important variables in the delimitating bioregions. This implies that more detailed study of how these factors influence triatomine distributions could benefit understanding of how Chagas disease is spread.

Molecular systematics of the North American chub genus Macrhybopsis (Teleostei: Cyprinidae).

The North American fish genus Macrhybopsis (Teleostei: Cyprinidae) as presently conceived comprises 12 species and occurs in much of interior eastern North America. Variation in the mitochondrial ND2 gene and the nuclear S7 intron 1 reveal conflicting gene-tree relationships for deeper nodes, which are assumed to represent past introgression and heterospecific mitochondrial fixation. The results support monophyly for the wide-ranging M. aestivalis complex with successive sister relationships to M. gelida, M. meeki, and M. storeriana. The current species-level taxonomy of Macrhybopsis is generally supported. Species status is supported for the morphologically distinct M. australis and M. tetranema, both of which are genetically introgressed by M. hyostoma. The results agree with previous suggestions that the wide-ranging M. hyostoma harbors cryptic species. Similar crypticity is indicated for the poorly sampled M. storeriana; a sample from the Pearl River shows 8% ND2 divergence from two Mississippi River populations. Within the M. aestivalis complex, there are only two examples of geographic overlap among mtDNA phylogroups. One involves co-occurrence of the highly divergent M. marconis and M. cf. hyostoma, and the other is the detection of the apparently anthropogenic occurrence of mitochondrial DNA from a Red River form, either M. cf. hyostoma or M. australis, in the Cimarron River of the Arkansas River basin.

Biogeography of "Cyprinella lutrensis": intensive genetic sampling from the Pecos River 'melting pot' reveals a dynamic history and phylogenetic complexity.

Thorough sampling is necessary to delineate lineage diversity for polytypic "species" such as Cyprinella lutrensis. We conducted extensive mtDNA sampling (cytochrome b and ND4) from the Pecos River, Rio Grande, and South Canadian River, New Mexico. Our study emphasized the Pecos River due to its complex geological history and potential to harbor multiple lineages. We used geometric-morphometric, morphometric, and meristic analyses to test for phenotypic divergence and combined nucDNA with mtDNA to test for cytonuclear disequilibrium and combined our sequences with published data to conduct a phylogenetic re-assessment of the entire C. lutrensis clade. We detected five co-occurring mtDNA lineages in the Pecos River, but no evidence for cytonuclear disequilibrium or phenotypic divergence. Recognized species were interspersed amongst divergent lineages of "C. lutrensis". Allopatric divergence among drainages isolated in the Late Miocene and Pliocene apparently produced several recognized species and major divisions within "C. lutrensis". Pleistocene re-expansion and subsequent re-fragmentation of a centralized lineage founded younger, divergent lineages throughout the Rio Grande basin and Edwards Plateau. There is also evidence of recent introductions to the Rio Grande, Pecos and South Canadian Rivers. Nonetheless, deeply divergent lineages have coexisted since the Pleistocene.

Fish faunal provinces of the conterminous United States of America reflect historical geography and familial composition.

Although the conterminous USA has a long history of ichthyological exploration, the description of biogeographical provinces has been ad hoc. In this study we quantitatively determined fish faunal provinces and interpreted them in the context of the geological history of North America. We also evaluated influences of major river basin occupancy and contemporary environmental factors on provincial patterns. Our data set comprised 794 native fishes, which we used to generate a presence and absence matrix for U.S. Geological Survey (USGS) four-digit hydrologic units. Three nested data sets were analysed separately: primary freshwater families, continental freshwater families (including primary and secondary families) and all freshwater families (including primary, secondary and peripheral families). We used clustering analysis to delimit faunal breaks and one-way analysis of similarity (ANOSIM) to determine significance among clusters (i.e. provinces). We used an indicator-species analysis to identify species that contributed most to province delineations and a similarity-percentage (SIMPER) analysis to describe the relative influence of representatives from each category (i.e. primary, secondary, peripheral) on provincial boundaries. Lastly, we used a parsimony redundancy analysis to determine the roles of historical (i.e. major river basin) and contemporary environmental factors in shaping provinces. Analysis of the nested data sets revealed lessening provincial structure with inclusion of more families. There were 10 primary freshwater provinces, 9 continental freshwater provinces and 7 all freshwater provinces. Major basin occupancy, but not contemporary environmental factors, explained substantial variance in faunal similarities among provinces. However, provincial boundaries did not conform strictly to modern river basins, but reflected river-drainage connections of the Quaternary. Provinces represent broad-scale patterns of endemism and provide a starting point for future studies. Relative malleability of province boundaries in the continental interior highlights this region as biogeographically diverse and dynamic. Interior-core provinces of this region (Central Gulf Coastal Plains, Northern Interior) have not been recognized previously and warrant further study.

Molecular systematics and historical biogeography of the Nocomis biguttatus species group (Teleostei: Cyprinidae): nuclear and mitochondrial introgression and a cryptic Ozark species.

The Nocomis biguttatus species group ranges widely across North America from the Red River in Oklahoma and Arkansas north to Minnesota and east-west from Wyoming to Ontario. The group includes three traditionally recognized allopatric species: the wide-ranging N. biguttatus and two geographically more restricted species, N. asper from the western Ozarks (Arkansas River system) and two disjunct locations in the Red River system, and N. effusus from the Green, Cumberland, and lower Tennessee rivers. Separate analyses of the mitochondrial cytb gene and two nuclear genes (S7 intron 1 and a portion of the gene for growth hormone, GH), each resolved a cryptic species previously treated as N. biguttatus from the southern Ozarks (White River). Relationships among the four species were unresolved because of conflicts between cytb and S7 and a lack of resolution for GH. A previously indicated N. biguttatus-N. effusus sister-relationship appears to reflect past hybridization and mtDNA capture by N. effusus. Nocomis biguttatus includes four primary cytb clades with unresolved inter-relationships. A Northern Ozarks-Great Plains-Upper Midwest Clade and an Ohio River-Eastern Great Lakes Clade presumably represent late Quaternary dispersal from glacial refugia in, respectively, the northern Ozarks and an unglaciated portion of the Ohio River system. Other clades include one from the Meramec River and a Black River-St. Francis River Clade. There was evidence in N. effusus for a phylogeographic break between the lower Tennessee River and the Green-Cumberland basins. Geographic structure is weak in N. asper, indicating relatively recent contact between now disjunct populations in the Arkansas and Red river basins. The Blue River population of N. asper appears to reflect late Pleistocene or Holocene hybridization and genetic swamping of a resident native population of N. biguttatus by an invading population of N. asper. This postulates past occurrence of N. biguttatus far south of its present range.

Genetic effective size, N(e), tracks density in a small freshwater cyprinid, Pecos bluntnose shiner (Notropis simus pecosensis).

Genetic monitoring tracks changes in measures of diversity including allelic richness, heterozygosity and genetic effective size over time, and has emerged as an important tool for understanding evolutionary consequences of population management. One proposed application of genetic monitoring has been to estimate abundance and its trajectory through time. Here, genetic monitoring was conducted across five consecutive year for the Pecos bluntnose shiner, a federally threatened minnow. Temporal changes in allele frequencies at seven microsatellite DNA loci were used to estimate variance effective size (N(eV)) across adjacent years in the time series. Likewise, effective size was computed using the linkage disequilibrium method (N(eD)) for each sample. Estimates of N(e) were then compared to estimates of adult fish density obtained from traditional demographic monitoring. For Pecos bluntnose shiner, density (catch-per-unit-effort), N(eV) and N(eD) were positively associated across this time series. Results for Pecos bluntnose shiner were compared to a related and ecologically similar species, the Rio Grande silvery minnow. In this species, density and N(eV) were negatively associated, which suggested decoupling of abundance and effective size trajectories. Conversely, density and N(eD) were positively associated. For Rio Grande silvery minnow, discrepancies among estimates of N(e) and their relationships with adult fish density could be related to effects of high variance in reproductive success in the wild and/or effects of supplementation of the wild population with captive-bred and reared fish. The efficacy of N(e) as a predictor of density and abundance may depend on intrinsic population dynamics of the species and how these dynamics are influenced by the landscape features, management protocols and other factors.