Gerald F. Shields

REPRODUCTIVE STATUS AND CONTINUITY OF TAXA OF THE SIMULIUM ARCTICUM COMPLEX (DIPTERA: SIMULIIDAE) AT THE CLEARWATER RIVER, MONTANA (2007, 2008, AND 2009)

ABSTRACT. We made 27 collections over nine years at the Clearwater River and conducted preliminary cytogenetic analysis on 232 individuals of the Simulium arcticum complex there. Based on these preliminary findings, we analyzed an additional 1825 larvae from Clearwater collections in 2007, 2008, and 2009 to investigate the reproductive statuses of the two prevalent taxa of the complex there and to determine whether cytogenetic diversity and frequency of types were similar from year to year. We describe a cytotype new to science and a potentially derivative cytotype of S. arcticum sensu stricto. We also determine that these two taxa are present in similar frequencies from year to year and are in genetic equilibrium, suggesting that they are not reproductively isolated. This study constitutes the fourth positive test of our Geographic Distribution/Taxon Age hypothesis.

THE EFFECT OF ELEVATION ON THE DISTRIBUTION OF SIBLING SPECIES IN THE SIMULIUM ARCTICUM COMPLEX (DIPTERA: SIMULIIDAE)

Abstract At least 5 sibling species and an additional 11 cytotypes of the Simulium arcticum complex occur in Montana. Consequently, this speciose complex might allow study of environmental correlates with genetic differentiation. We used conventional methods of collection and cytogenetic analysis to study 1128 male larvae of the Simulium arcticum complex at 15 sites within 5 drainages in western Montana to test the hypothesis that distribution of siblings is associated with elevation. We sampled at the mouth, at the headwaters, and at an intermediate site to span the range of elevations within each drainage. We restricted our analyses to the most abundant taxa of the S. arcticum complex within our study area and observed a statistically significant presence of S. apricarium at low-elevation sites. Simulium arcticum IIL-18 appeared more frequently than expected at high elevation sites. Simulium brevicercum and S. arcticum sensu strictu appeared to be distributed randomly. We suggest potential causal reasons for these distributions including differential use of habitats along these elevational gradients.

The speciation continuum: Population structure, gene flow, and maternal ancestry in the Simulium arcticum complex (Diptera: Simuliidae)

Comparative analyses of populations at different stages of divergence can yield insights into the process of speciation. We assess population structure, gene flow, and maternal ancestry at five locations containing sympatric members of the Simulium arcticum complex at different stages of chromosome divergence. We analyze both nuclear and mitochondrial DNA markers, including 11 microsatellite loci, as well as COI, COII, cytb, and ND4 gene sequences. Simulium negativum, representing the later stages of divergence, shows both nuclear and mitochondrial differentiation when compared with allopatric and sympatric chromosomal forms, as well as both low contemporary and historical gene flow in sympatry. At intermediate stages of chromosome divergence, populations differ at nuclear, but not mitochondrial, loci in allopatry and sympatry. In one comparison of intermediate stage chromosomal forms (S. arcticum sensu stricto and S. apricarium), populations demonstrate low contemporary, but higher historical, gene flow in sympatry. In a second sympatric comparison (S. arcticum s. s. and S. brevicercum), both contemporary and historical gene flow are high. All analyses of sympatric populations at the earliest stages of chromosome divergence demonstrate panmixia; yet, some nuclear differentiation in allopatry is apparent. These findings suggest that molecular divergence is tracking chromosome divergence along a chromosomally-defined continuum of speciation in black flies.

Colonization history and taxonomy of moose Alces alces in southeastern Alaska inferred from mtDNA variation

Abstract We assessed phylogeographic history of moose Alces alces in southeastern Alaska, USA, by determining their genetic affinity to surrounding populations thereby clarifying their origin and uncertain taxonomic status. Moose from central and southern regions of the southeastern Alaska panhandle were characterized by two mitochondrial haplotypes that were highly divergent from those in the remainder of the state; overlap with other haplotypes occurred only in the northernmost area of the panhandle. Moose inhabiting areas of British Columbia, Canada, immediately adjacent to Alaskas panhandle showed high haplotype diversity. A small proportion of those moose shared haplotypes with moose in southeastern and interior Alaska, but most possessed haplotypes that were restricted to that region. Association between geographic distribution and phylogenetic structure of haplotypes indicated spatial separation of moose lineages in the past. Our results indicate that there were two separate entries of moose into the region during colonization, likely from different geographic areas. Coastal populations of moose living south of 58°45′N latitude in southeastern Alaska should be classified as A. a. andersoni rather than as A. a. gigas. Behavioural and morphological differences between A. a. gigas and other forest-dwelling subspecies in North America indicate a need to examine moose management strategies and objectives in southeastern Alaska.

Resolving evolutionary relationships in closely related nonmodel organisms: a case study using chromosomally distinct members of a black fly species complex

Coalescent‐based analyses have been recommended for species delimitation and tree reconstruction. Yet, despite recent advances in molecular methods, acquiring sufficient genetic data often precludes coalescent‐based analyses in nonmodel organisms. We show that these methods are accessible to questions in nonmodel systems. Specifically, we use coalescent‐based analyses to investigate evolutionary independence and relationships among chromosomally distinct members (sibling species) of a black fly (Diptera: Simuliidae) species complex. Our dataset consists of nuclear DNA (nuDNA) and mitochondrial DNA (mtDNA) markers – the former developed using the black fly transcriptome and available genomes from model relatives. We show that individual gene trees exhibit considerable discordance among one another and reveal little about potential species limits. Consistent species tree topologies are obtained from analyses of nuDNA, both with and without the inclusion of mtDNA data. Nodes on the tree receive robust support with the addition of mtDNA. Coalescent‐based species validation approaches recognize all sibling species. However, unlike species tree analyses, the addition of mtDNA data does not improve or alter the results. Thus, analyses of nuDNA alone can validate sibling species. Contrary to these results, population genetic patterns of neutral diversity, within‐locus recombination, and linkage disequilibrium suggest that sibling species represent a single species with high levels of nucleotide polymorphism, large effective population sizes, and extensive gene flow. Demographic patterns inferred from neutrality tests integrate seemingly disparate results by showing signatures of gene flow among structured populations that are expanding in size. Thus, admixture associated with geographic range expansions may be assimilating sibling species into a single genetic lineage.

Differential Development of Male and Female Larvae of a Black Fly Complex (Diptera: Simuliidae)

Abstract  Some adult female black flies (Diptera: Simuliidae) bite humans and can be pests in high numbers. In areas of high black fly abundance, larvicide-based suppression programs reduce the emergence of adults from rivers and streams. However, little is known about whether either of the sexes develops or emerges first. Descriptions of sexual development might help control managers decide when application of pesticides is most effective. For the past 14 yr the cytogenetic diversity within the Simulium arcticum (Malloch) complex of black flies in the Pacific Northwest has been studied and described. These descriptions have been accompanied by an “on-slide” identification of the gonads and, thus, the sex of individual larvae. Consequently, a very large data set is available to describe sex ratios during larval development and determine if either sex develops before the other. The sex of >11,000 larvae from 161 collections from 41 geographic locations has been monitored. Larvae having white histoblasts we...