To better understand the evolutionary radiation of the Simulium arcticum complex of black flies (Diptera: Simuliidae), we compared the geographic distributions of present-day larvae to their ...sex-chromosome diversity. We used the 5 known data sets including collections and sex-chromosome analysis from 307 geographic locations of 31 taxa of approximately 20,000 larvae from throughout the geographic range of distribution of the complex, from Alaska, western Canada, and the western United States to southern California, Arizona, and New Mexico. Siblings (reproductively isolated in sympatry) have considerably larger geographic distributions than do cytotypes (not reproductively isolated in sympatry), suggesting that the former may have been in existence longer than the latter. Simulium negativum (the oldest member of the complex), S. brevicercum (standard noninverted sex chromosomes), S. saxosum (sex determination on the X chromosome), and S. arcticum s. s. (IIL-3) share geographic distributions with all other siblings. Notably, 21 of 22 cytotypes share geographic distributions within those of siblings. Cytotypes are almost always discovered within the geographic distributions of siblings, suggesting that the former might be arising sympatrically.
An updated checklist of 50 species of mosquitoes found in Montana is presented and includes 2 new records (Aedes niphadopsis and Anopheles walkeri) that can be added to the 2005 state list by Darsie ...and Ward. The results of a statewide mosquito surveillance program, conducted annually from 2004 to 2015, facilitated the establishment of an abundance rating of the species in the state and expanded the known geographic range for Coquillettidia perturbans, Ae. nigromaculis, and Culiseta minnesotae.
The populations of many amphibian species, in widely scattered habitats, appear to be in severe decline; other amphibians show no such declines. There is no known single cause for the declines, but ...their widespread distribution suggests involvement of global agents-increased UV-B radiation, for example. We addressed the hypothesis that differential sensitivity among species to UV radiation contributes to these population declines. We focused on species-specific differences in the abilities of eggs to repair UV radiation damage to DNA and differential hatching success of embryos exposed to solar radiation at natural oviposition sites. Quantitative comparisons of activities of a key UV-damage-specific repair enzyme, photolyase, among oocytes and eggs from 10 amphibian species were reproducibly characteristic for a given species but varied >80-fold among the species. Levels of photolyase generally correlated with expected exposure of eggs to sunlight. Among the frog and toad species studied, the highest activity was shown by the Pacific treefrog (Hyla regilla), whose populations are not known to be in decline. The Western toad (Bufo boreas) and the Cascades frog (Rana cascadae), whose populations have declined markedly, showed significantly lower photolyase levels. In field experiments, the hatching success of embryos exposed to UV radiation was significantly greater in H. regilla than in R. cascadae and B. boreas. Moreover, in R. cascadae and B. boreas, hatching success was greater in regimes shielded from UV radiation compared with regimes that allowed UV radiation. These observations are thus consistent with the UV-sensitivity hypothesis.
Numerous reports suggest that populations of amphibians from a wide variety of locations are experiencing population declines and/or range reductions. In some cases, unusually high egg mortality has ...been reported. Field experiments have been used with increasing frequency to investigate ultraviolet radiation as one of the potential factors contributing to these declines. Results from field experiments illustrate that hatching success of eggs is hampered by ultraviolet radiation in a number of species, while other species appear to be unaffected. Continued mortality in early life-history stages may ultimately contribute to a population decline. Although UV-B radiation may not contribute to the popu declines of all species, it may play a role in the population decline of some species, especially those that lay eggs in open shallow water subjected to solar radiation and in those that have a poor ability to repair UV-induced DNA damage.
We use microsatellite loci to examine genetic structure of the Florida scrub lizard (Sceloporus woodi) and test for the effects of landscape variables at the scale of neighboring patches. We evaluate ...ecological metrics of connectivity with genetics data, which to our knowledge is the first application of these particular metrics to landscape-level genetics studies in Florida scrub. Florida scrub is a highly threatened ecosystem in which habitat patches are remnants of a previously widespread xeric landscape. Analysis of mitochondrial DNA (mtDNA) has shown that landscape structure influenced the evolutionary history of the Florida scrub lizard (S. woodi) across its range. Our results concur with these mtDNA studies in documenting divergence between xeric ridge systems and also demonstrate divergence at very local scales. Both least-cost distance and pairwise isolation (a metric used in ecological studies that includes patch size, quality and a modified isolation index) were better predictors of genetic distance than Euclidean distance, indicating that mesic and hydric habitat influence spatial patterns in genetic variation. Our results support the need for focusing on spatial distribution of scrub habitat at the scale of neighboring patches, as well as regionally, in conservation management and restoration. Also, our study points to the value of integrating landscape ecology metrics into landscape genetics.
Sex-linked chromosomal inversions in black flies (Diptera:Simuliidae) are important in the process of species differentiation. These inversions occur early in the differentiation process before DNA ...monophyly of sibling species. Nine sibling species and an additional 22 cytotypes have been described for the Simulium arcticum complex. An unresolved question is whether these chromosome types spread throughout a river corridor or from one corridor to another. We determined the sex-linked chromosomal configuration of ∼7300 male larvae of the S. arcticum complex at 46 collection sites in 14 different drainages and asked whether flies in the same river corridor are chromosomally more similar than are flies of different corridors. This research could identify factors important in divergence. Flies within the same river corridor were chromosomally more similar than were flies between different corridors. Comparisons between sites suggest that river distance and Euclidian distance are associated negatively with chromosomal type similarity, but river distance showed the highest similarity comparisons for any given distance. The chromosomes of flies at sites ≤50 km apart were more similar than were the chromosomes of flies at sites >50 km apart. Flies among different river corridors were less similar chromosomally even when these sites were closer in Euclidian distance than in river distance. Flies were chromosomally most similar in streams of equivalent size, particularly if those streams were <25 km apart in river distance. Most sibling species had considerable chromosomal similarities in large, medium, and small streams as measured by proportional abundance. However, some cytotypes appeared to be restricted to large rivers, whereas other cytotypes were restricted to medium-sized streams.
Understanding how patchy landscapes affect the distribution and abundance of species is a central issue in applied ecology. We examined the effects of landscape structure on the distribution of the ...Florida scrub lizard (Sceloporus woodi) in naturally fragmented habitat. Scrub lizards were absent from 89 of 132 patches, and their distribution was explained in multifactor models by two landscape variables: patch size and patch isolation. Mark-recapture studies of S. woodi and experimental displacement trials indicate that this species exhibits low vagility within a patch and that movement through dense habitat, which often characterizes the landscape matrix, is restricted. Poor dispersal ability relative to the degree of isolation of patches in this landscape may account for large gaps in its distribution. To examine the applicability of the scrub lizard model to other species, we applied the model to a sympatric lizard, the six-lined race-runner (Cnemidophorus sexlineatus), which is similar in body size, food habits, and habitat requirements. The race-runner was more widely distributed than the Florida scrub lizard within our scrub landscape, and the model failed to predict its distribution. This differing response to landscape structure by a similar species is likely due to the greater dispersal ability of C. sexlineatus. Our results, and similar studies of other scrub organisms, indicate that each species may have a unique response to habitat fragmentation. The design and management of effective preserves for Florida scrub will require a multiscaled, multispecies approach that reflects the differences in the dispersal abilities, area requirements, and habitat preferences of the species to be preserved.
Habitat destruction and fragmentation are often cited as primary causes for declines in reptile and amphibian populations. Smaller habitat patches constrain population size resulting in increased ...extinction risk caused by stochastic processes. However, patch size also may affect populations in a deterministic manner. We used mark and recapture techniques to examine effects of patch size on demographics of the Florida Scrub Lizard (Sceloporus woodi). We examined populations in eight scrub habitat patches that differed in size but were similar with respect to other habitat characteristics. Abundance, survivorship, and recruitment were positively associated with patch size for both sexes. Individual growth rate increased with patch size for males but was negatively associated with patch size for females. Although our data indicate that patch size strongly affects demographics of scrub lizards, mechanisms responsible for these patterns are unknown. We discuss conservation implications of area-sensitive demography for local and regional populations. In particular, we suggest caution when constructing metapopulation models that assume homogenous survival and fecundity rates for all patches regardless of patch size.
Previous research has shown that amphibian species have differential sensitivity to ultravioletâB (UVâB) radiation. In some anuran species, ambient levels of UVâB cause mortality in embryonic ...stages and hatching success is significantly reduced. Projected increases in UVâB may affect an increasing number of species. The adverse effects of UVâB may eventually be manifested at the population level and may ultimately contribute to population declines. Using field experiments, we investigated the effects of ambient UVâB on salamander (Ambystoma gracile) embryos developing at natural oviposition sites. We show that the hatching success of eggs of A. gracile shielded from UVâB is significantly higher than those not shielded from UVâB.
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