Ranges Of Southern California Research Articles

The physical soldier caste of an invasive, human-infecting flatworm is morphologically extreme and obligately sterile

We show that the globally invasive, human-infectious flatworm, Haplorchis pumilio, possesses the most physically specialized soldier caste yet documented in trematodes. Soldiers occur in colonies infecting the first intermediate host, the freshwater snail Melanoides tuberculata, and are readily distinguishable from immature and mature reproductive worms. Soldiers possess a pharynx five times absolutely larger than those of immature and mature reproductives, lack a germinal mass, and have a different developmental trajectory than reproductives, indicating that H. pumilio soldiers constitute a reproductively sterile physical caste. Neither immature nor mature reproductives showed aggression in in vitro trials, but soldiers readily attacked heterospecific trematodes that coinfect their host. Ecologically, we calculate that H. pumilio caused ~94% of the competitive deaths in the guild of trematodes infecting its host snail in its invasive range in southern California. Despite being a dominant competitor, H. pumilio soldiers did not attack conspecifics from other colonies. All prior reports documenting division of labor and a trematode soldier caste have involved soldiers that may be able to metamorphose to the reproductive stage and have been from nonhuman-infectious marine species; this study provides clear evidence for an obligately sterile trematode soldier, while extending the phenomenon of a trematode soldier caste to freshwater and to an invasive species of global public health concern.

Taking the Leap: A Binational Translocation Effort to Close the 420-Km Gap in the Baja California Lineage of the California Red-Legged Frog (Rana draytonii)

Conservation translocations, the human-mediated movement and release of a living organism for a conservation benefit, are increasingly recommended in species’ recovery plans as a technique for mitigating population declines or augmenting genetic diversity. However, translocation protocols for species with broad distributions may require regionally specific considerations to increase success, as environmental gradients may pose different constraints on population establishment and persistence in different parts of the range. Here we report on ongoing, genetically informed translocations of a threatened amphibian, California red-legged frog (Rana draytonii), from Baja California, México, to extirpated parts of the range in southern California in the United States, where contemporary stressors related to urbanization, invasive species, and aridification add to the natural environmental challenges already present for amphibians at this ‘warm edge’ of the range. We describe the collaborative binational planning required to jumpstart the effort, the fine-tuning of protocols for collection, transport, headstarting, and release of individuals, and results of multiple translocations, where time will tell whether the successes to date have reached their full potential. The steps outlined in this paper can serve as a template to inform future conservation translocations of imperiled amphibians across the U.S./México border, where the phylogenetics, historical biogeography and future habitat availability of a focal species are blind to political boundaries and critical to guiding recovery actions across the range.

Beyond Ethnography and Beneath the Bedrock Mortars: The Eastern Transverse Ranges of Southern California as Early Holocene Refugia

ABSTRACT Rock Camp (CA-SBR-342) in the San Bernardino Mountains has been regarded as a seasonal Late Prehistoric Complex acorn processing base camp since it was excavated in the 1960s. Reanalysis of its collections and new investigations at the nearby Willow Creek Crossing sites permit reevaluation of archaeological models for the Transverse Ranges of southern California and the adjacent Mojave Desert. Diagnostic artifacts, site structure, and obsidian hydration dating indicate montane Greven Knoll I (9,400-4,000 BP) occupations in inland southern California several millennia earlier than has been previously posited. Moreover, the presence of stemmed points suggests that the Greven Knoll Pattern of the Encinitas Tradition was introduced into the region directly from the Mojave Desert during the onset of the Altithermal. This analysis also serves as a reminder for archaeologists to use ethnohistoric models with caution and to look beyond the obvious.

Faulting and Folding of the Transgressive Surface Offshore Ventura Records Deformational Events in the Holocene

Identifying the offshore thrust faults of the Western Transverse Ranges that could produce large earthquakes and seafloor uplift is essential to assess potential geohazards for the region. The Western Transverse Ranges in southern California are an E-W trending fold-and-thrust system that extends offshore west of Ventura. Using a high-resolution seismic CHIRP dataset, we have identified the Last Glacial Transgressive Surface (LGTS) and two Holocene seismostratigraphic units. Deformation of the LGTS, together with onlapping packages that exhibit divergence and rotation across the active structures, provide evidence for three to four deformational events with vertical uplifts ranging from 1 to 10 m. Based on the depth of the LGTS and the Holocene sediment thickness, age estimates for the deformational events reveal a good correlation with the onshore paleoseismological results for the Ventura-Pitas Point fault and the Ventura-Avenue anticline. The observed deformation along the offshore segments of the Ventura-Pitas Point fault and Ventura-Avenue anticline trend diminishes toward the west. Farther north, the deformation along the offshore Red Mountain anticline also diminishes to the west with the shortening stepping north onto the Mesa-Rincon Creek fault system. These observations suggest that offshore deformation along the fault-fold structures moving westward is systematically stepping to the north toward the hinterland. The decrease in the amount of deformation along the frontal structures towards the west corresponds to an increase in deformation along the hinterland fold systems, which could result from a connection of the fault strands at depth. A connection at depth of the northward dipping thrusts to a regional master detachment may explain the apparent jump of the deformation moving west, from the Ventura-Pitas Point fault and the Ventura-Avenue anticline to the Red Mountain anticline, and then, from the Red Mountain anticline to the Mesa-Rincon Creek fold system. Finally, considering the maximum vertical uplift estimated for events on these structures (max ∼10 m), along with the potential of a common master detachment that may rupture in concert, this system could generate a large magnitude earthquake (>Mw 7.0) and a consequent tsunami.

Modeling Partially Surveyed Point Process Data: Inferring Spatial Point Intensity of Geomagnetic Anomalies

Many former military training sites contain unexploded ordnance (UXO) and require environmental remediation. For the first phase of UXO remediation, locations of geomagnetic anomalies are recorded over a subregion of the study area to infer the spatial intensity of anomalies and identify high concentration areas. The data resulting from this sampling process contain locations of anomalies across narrow regions that are surveyed; however, the surveyed regions only constitute a small proportion of the entire study area. Existing methods for analysis require selecting a window size to transform the partially surveyed point pattern to a point-referenced dataset. To model the partially surveyed point pattern and infer intensity of anomalies at unsurveyed regions, we propose a Bayesian spatial Poisson process model with a Dirichlet process mixture as the inhomogeneous intensity function. A data augmentation step is used to impute anomalies in unsurveyed locations and reconstruct clusters of anomalies that span surveyed and unsurveyed regions. To verify that data augmentation reconstructs the underlying structure of the data, we demonstrate fitting the model to simulated data, using both the full study area and two different sampled subregions. Finally, we fit the model to data collected at the Victorville Precision Bombing range in southern California to estimate the intensity surface in anomalies per acre. Supplementary materials accompanying this paper appear online.

Movement and habitat selection of the western spadefoot (Spea hammondii) in southern California.

Agricultural activity, urban development and habitat alteration have caused the disappearance of the western spadefoot (Spea hammondii) from 80% of its geographic range in southern California. Despite the western spadefoot's continuing decline, little research has been conducted on its natural history. The home range of adult spadefoots is unknown, and their use of upland habitat is poorly understood. Both factors are important for the long-term conservation of the species because adult spadefoots spend the majority of their lives away from breeding pools in self-excavated burrows. Between January 2012 and January 2013, we surgically implanted radio transmitters in 15 spadefoots at two locations and recorded their movements and habitat use. The mean distance moved between burrow locations was 18 m (SD ± 24.1 m, range1-204 m). The mean distance of burrows from the breeding pools was 40 m (SD ± 37.42 m, range 1-262 m). Rain was a significant predictor of spadefoot movement, with more rain predicting higher probability of movement and larger distances moved. At remote sensing scale (1 m) spadefoots selected grassland habitat for their burrow locations. At the microsite scale (< 1 m) spadefoots strongly selected duff over grass or shrub cover. Spadefoots burrowed in friable, sandy/loam soil with significantly less clay than random pseudoabsence points. This research enhances our understanding of a little-studied species and will contribute to the development of effective management plans for the western spadefoot.

Different traits predict competitive effect versus response by Bromus madritensis in its native and invaded ranges

Community assembly and coexistence theories predict that both fitness and plant functional traits should influence competitive interactions between native and invasive species. The evolution of the increased competitive ability hypothesis predicts that species will grow larger (a measure of fitness) in their invaded than native range; hence we hypothesized that species might exert greater competitive effects in their invaded range, lessening the importance of functional traits for competitive outcomes. In a greenhouse experiment we compared traits and competitive interactions between Bromus madritensis (an annual grass) and resident species from its native range in Spain, and its invaded range in Southern California. As predicted, B. madritensis collected in California grew larger and had a greater competitive effect on resident species than B. madritensis collected in Spain. However, residents from California also suppressed the growth of B. madritensis more than species from its native range in Spain. Competitive interaction strengths were predicted by different suites of traits in the native versus invaded range of B. madritensis; surprisingly, however, size of the resident species (fitness), did not predict variation in competitive interactions. This study shows that different suites of traits may aid in identifying those native species likely to strongly compete with invaders, versus those that will be competitively suppressed by invaders, with important implications for the design of restoration efforts aimed at promoting native species growth and preventing invasion. More generally, our study shows that fitness differences may not be as important as traits when predicting competitive outcomes in this system.

Steady 10Be‐derived paleoerosion rates across the Plio‐Pleistocene climate transition, Fish Creek‐Vallecito basin, California

Rates of erosion over time provide a valuable tool for gauging tectonic and climatic drivers of landscape evolution. Here we measure 10Be archived in quartz sediment from the Fish Creek‐Vallecito basin to resolve a time series of catchment‐averaged erosion rates and to test the hypothesis that aridity and increased climate variation after approximately 3 Ma led to an increase in erosion rates in this semiarid, ice‐free setting. The Fish Creek‐Vallecito basin, located east of the Peninsular Ranges in Southern California, is an ideal setting to derive a Plio‐Pleistocene paleoerosion rate record. The basin has a rapid sediment accumulation rate, a detailed magnetostratigraphic age record, and its stratigraphy has been exposed through recent, rapid uplift and erosion. A well‐defined source region of uniform lithology and low erosion rate provides a high, reproducible 10Be signal. We find that paleoerosion rates were remarkably consistent between 1 and 4 Ma, averaging 38 ± 24 m/Myr (2σ). Modern catchment‐averaged erosion rates are similar to the paleoerosion rates. The uniformity of erosion over the past 4 Myr indicates that the landscape was not significantly affected by late Pliocene global climate change, nor was it affected by a local long‐term increase in aridity.

Population genetic structure and ancestry of steelhead/rainbow trout (Oncorhynchus mykiss) at the extreme southern edge of their range in North America

Steelhead (Oncorhynchus mykiss) populations have declined dramatically in many parts of their range in North America, most critically in Southern California, where these anadromous trout are now classified as ‘Endangered’ under the United States Endangered Species Act. The widespread introduction of hatchery rainbow trout, the domesticated freshwater resident form of the species O. mykiss, is one factor threatening the long-term persistence of native steelhead and other trout populations. To identify where native fish of coastal steelhead lineage remained, we performed a population genetic analysis of microsatellite and SNP genotypes from O. mykiss populations at the extreme southern end of their range in Southern California, USA and Baja California, Mexico. In the northern part of this region, nearly all populations appeared to be primarily descendants of native coastal steelhead. However, in the southern, more urbanized part of this region, the majority of the sampled populations were derived primarily from hatchery trout, indicating either complete replacement of native fish or a strong signal of introgression overlaying native ancestry. Nevertheless, these genetically introgressed populations represent potentially critical genetic resources for the continued persistence of viable networks of O. mykiss populations, given the limited native ancestry uncovered in this region and the importance of genetic variation in adaptation. This study elucidates the geographic distribution of native trout populations in this region, and serves as a baseline for evaluating the impacts of hatchery trout on native O. mykiss populations and the success of steelhead conservation and recovery efforts.

Fluvial geomorphology of a boulder-bed, debris-flow — Dominated channel in an active tectonic environment

Numerous streams, with a drainage area of a few square kilometers, draining the south flank of the Santa Ynez Range in Southern California are characterized by steep boulder-bed, debris-flow-dominated channels. Rattlesnake Creek is a good example. Approximately 90% of the stored sediment in the stream valley is stable debris flow deposits found in debris flow terraces and levees adjacent to the channel. The remaining 10% of stored sediment resides in the active channel, where the channel morphology is dominated by large boulders (1 to 4+m in diameter) derived from debris flows or rock fall that, along with bedrock outcrops, form rock or boulder transverse ribs with frequent step-pools.The dominant channel pool morphology is the step-pool, which accounts for most of the pools and approximately 30% of relief (drop in elevation) through the study reaches. Less common pool types identified in the study reaches include forced pools that result from convergence of flow with scour between LBREs (large boulder roughness elements) and bedrock outcrop along the channel at near bankfull discharge.The LBREs and boulders in step-pools armor the channel and are primary controls on channel morphology and gradient. Rock strength is a secondary control on channel morphology, location, and abundance of pools.We hypothesize that step-pools, when inundated with sand and fine gravel from a disturbance (such as wildfire) during a flow event, fill near bankfull stage and scour on falling stage below bankfull when unit stream power is a maximum over the step. Thus, as with forced pools, step-pool maintenance depends on a specific pattern of discharge and process. The process of scour during falling stage reestablishes step-pools during moderate flows, following disturbance.

Insights into the establishment of the Manila clam on a tidal flat at the southern end of an introduced range in Southern California, USA.

Coastal ecosystem modifications have contributed to the spread of introduced species through alterations of historic disturbance regimes and resource availability, and increased propagule pressure. Frequency of occurrence of the Manila clam (Venerupis phillipinarum, Veneridae) in Southern California estuaries has increased from absent or sparse to common since the mid-1990s. Potential invasion vectors include seafood sales and aquaculture, and spread from established northern populations over decades. The clam’s post-settlement habitat preferences are, however, uncertain in this region. Our project aimed to identify factors associated with established patches of the clam within a bay toward the southern end of this introduced range. During summer 2013, we sampled 10 tidal flat sites in Mission Bay, San Diego; each containing an area with and without hard structure (e.g., riprap, boulders). We measured likely environmental influences (e.g., sediment variables, distance to ocean). Manila clam densities across the bay were most strongly associated with site, where highest densities were located in the northern and/or back halves of the bay; and weakly correlated with lower porewater salinities. Within sites, Manila clam density was enhanced in the presence of hard structure in most sites. Prevailing currents and salinity regimes likely contribute to bay wide distributions, while hard structures may provide suitable microhabitats (refuge from predators and physical stress) and larval entrapment within sites. Results provide insights into decisions about future shoreline management efforts. Finally, we identify directions for future study to better understand and therefore predict patterns of establishment of the Manila clam in the southern portion of its introduced range.

Cryptic divergence and revised species taxonomy within the Great Basin pocket mouse,Perognathus parvus(Peale, 1848), species group

The Great Basin pocket mouse, Perognathus parvus, inhabits temperate shrub-steppe and arid grassland biomes throughout the Columbia Plateau, Great Basin, and adjacent regions of western North America. We used both mitochondrial DNA (mtDNA) and nuclear DNA (nDNA) sequences to address phylogenetic and biogeographic structure within the P. parvus species group. Phylogenetic and biogeographic analyses divide haplotypes from the mtDNA cytochrome oxidase subunit 3 (COIII) gene into largely allopatric northern versus southern lineages (clades), with divergences of up to 18.8%. The southern mtDNA clade also includes at least 1 of the 2 recently extant populations of the white-eared pocket mouse, P. alticolus—an endangered species with a restricted range in southern California. The northern mtDNA clade is further subdivided into several additional lineages with divergences as high as 8.8%, whereas the southern clade has no divergence greater than 1.2%. The deeper mtDNA gene tree structure was recovered by use of nDNA exon sequences from the interphotoreceptor retinoid-binding protein (IRBP) and recombination activating gene 2 (RAG2) gene regions, supporting a “gene tree–species tree” congruence. We estimated through molecular clock analyses that the northern and southern clades likely diverged within a late Miocene time frame. The limited available karyological evidence is consistent with a genome-wide divergence between northern and southern clades—thus, is consistent with recognition of each as a separate species. Conversely, our morphometric analysis revealed a high level of morphological conservatism without detectable diagnostic differences, rendering them as “cryptic” species. We revised species-level taxonomy, designating 2 neotypes given apparent loss of original type specimens. We postulate that barriers associated with Columbia Plateau, Snake River Plain, and Great Basin physiographic evolution, during a Neogene time frame, resulted in persistent geographic isolation driving divergence between the northern and southern clades.

Environmental Proteomics of the Mussel Mytilus: Implications for Tolerance to Stress and Change in Limits of Biogeographic Ranges in Response to Climate Change

Climate change will affect temperature extremes and averages, and hyposaline conditions in coastal areas due to extreme precipitation events and oceanic pH. How climate change will push species close to, or beyond, their physiological tolerance limits as well as change the limits of their biogeographic ranges can probably be investigated best in species that have already responded to climate change and whose distribution ranges are currently in flux. Blue mussels provide such a study system, with the invading warm-adapted Mediterranean Mytilus galloprovincialis having replaced the native more cold-adapted Mytilus trossulus from the southern part of its range in southern California over the past century, possibly due to climate change. However, freshwater input may prevent the latter species from expanding further north. We used a proteomics approach to characterize the responses of the two congeners to acute heat stress, chronic thermal acclimation, and hyposaline stress. In addition, we investigated the proteomic changes in response to decreasing seawater pH in another bivalve, the eastern oyster Crassostrea virginica. The results suggest that reactive oxygen species (ROS) are a common costressor during environmental stress, including oceanic acidification, and possibly cause modifications of cytoskeletal elements. All stressors disrupted protein homeostasis, indicated by the induction of molecular chaperones and, in the case of acute heat stress, proteasome isoforms, possibly due both to protein denaturation directly by the stressor and to the production of ROS. Acute stress by heat and hyposalinity changed several small G-proteins implicated in cytoskeletal modifications and vesicular transport, respectively. Changes in abundance of proteins involved in energy metabolism and ROS scavenging further suggest a possible trade-off during acute and chronic stress from heat and cold between ROS-generating NADH-producing pathways and ROS-scavenging NADPH-producing pathways, especially through the reaction of NADPH-dependent isocitrate dehydrogenase and the pentose-phosphate pathway. Some of the proteomic changes may not constitute de novo protein synthesis but rather shifts in abundance of isoforms differing in posttranslational modifications, specifically acetylation by a NAD-dependent deacetylase (sirtuin). Interspecific differences suggest that these processes set physiological tolerance limits and thereby contribute to recent biogeographic shifts in range, possibly caused by climate change.

Reappearance of the Vanishing Wild Buckwheat: A Status Review of Eriogonum evanidum (Polygonaceae)

Abstract Eriogonum evanidum Reveal is an annual herb in the buckwheat family that is endemic to southern California, USA and northern Baja California, Mexico. It was described by James Reveal in 2004 and was determined to be extinct due to the lack of recent observations and accessioned specimen collections. During field surveys conducted in 2007 and 2008 this species was rediscovered across its known range in southern California. Three of 10 historic occurrences that were presumed extirpated were located. One new occurrence was documented in the vicinity of Holcomb Valley, San Bernardino Mountains, CA. Location and habitat information are provided and the current conservation status of this species is discussed.

Vagrant Western Red-shouldered Hawks: Origins, Natal Dispersal Patterns, and Survival

We report the results of a 40-year study of the western Red-shouldered Hawk (Buteo lineatus elegans) involving the banding of 2742 nestlings in southern California from 1970 to 2009 (this study) plus 127 nestlings banded in other California studies (1956–2008) and the analyses of 119 records of subsequent recovery from the Bird Banding Laboratory (1957–2009). Of the Red-shouldered Hawks recovered, 109 (91.6%) moved <100 km (short-distance dispersers), while 10 (8.4%) moved >100 km (long-distance dispersers). Three (2.5%), all long-distance dispersers, were vagrants (recovered outside the species' range of residency), and were found 374 to 843 km northeast and south of their banding locations in the Mojave, Great Basin, and Vizcaino deserts. The distribution of directions of short-distance dispersal was bipolar, closely corresponding with the northwest—southeast orientation of the species' range in southern California, while that of long-distance dispersers was mainly to the north. One of 10 long-distance dispersers, a nonvagrant, survived well into the age of breeding (103.0 months), whereas eight of the other nine perished before 14.5 months. The implications of vagrancy for conservation of this resident subspecies are that a relatively small source area can contribute genetic material over a vastly larger receiving area but rarely does so because of high mortality rates. Nonetheless, the movements of vagrants we documented provide evidence for the species' potential to populate new landscapes in response to changing environmental conditions and to maintain genetic heterogeneity within existing populations.

Conservation genetics of evolutionary lineages of the endangered mountain yellow-legged frog, Rana muscosa (Amphibia: Ranidae), in southern California

Severe population declines led to the listing of southern California Rana muscosa (Ranidae) as endangered in 2002. Nine small populations inhabit watersheds in three isolated mountain ranges, the San Gabriel, San Bernardino and San Jacinto. One population from the Dark Canyon tributary in the San Jacinto Mountains has been used to establish a captive breeding population at the San Diego Zoo Institute for Conservation Research. Because these populations may still be declining, it is critical to gather information on how genetic variation is structured in these populations and what historical inter-population connectivity existed between populations. Additionally, it is not clear whether these populations are rapidly losing genetic diversity due to population bottlenecks. Using mitochondrial and microsatellite data, we examine patterns of genetic variation in southern California and one of the last remaining populations of R. muscosa in the southern Sierra Nevada. We find low levels of genetic variation within each population and evidence of genetic bottlenecks. Additionally, substantial population structure is evident, suggesting a high degree of historical isolation within and between mountain ranges. Based on estimates from a multi-population isolation with migration analysis, these populations diversified during glacial episodes of the Pleistocene, with little gene flow during population divergence. Our data demonstrate that unique evolutionary lineages of R. muscosa occupy each mountain range in southern California and should be managed separately. The captive breeding program at Dark Canyon is promising, although mitigating the loss of neutral genetic diversity relative to the natural population might require additional breeding frogs.

Faulting Parameters of Earthquakes (4.1 &lt;= ML &lt;= 5.3) in the Peninsular Ranges of Baja California, Mexico

Seismic moment ( M ) is a parameter related to the physical process that takes place at the source (Aki 1966; Aki and Richards 1980). Sometimes it is possible to calculate M from the constant spectral amplitude level at low frequencies, but in other cases this is not possible. For instance, for M > 4.0 earthquakes (recorded at short distances), it is difficult to determine the flat portion of the spectrum due to instrumental limitations. For these cases, waveform modeling is an alternative way to evaluate M . In addition to determining this source parameter, it is also possible to obtain the faulting geometry and the depth of the hypocenter through waveform modeling. In the Peninsular Ranges of Baja California (PRBC), few studies have been conducted to determine earthquake faulting parameters. Some examples are the studies of Nava and Brune (1983) (1975 ML 5.1 earthquake) and Gonzalez (1987) (1985 ML 5.0 earthquake). However, studies of the seismic source have not been attempted for earthquakes of lower magnitude ( M < 5). We computed the faulting parameters of five small-to-moderate earthquakes that occurred between 1991 and 1996 in the PRBC, via waveform modeling of broadband seismograms recorded at regional distances (180 to 245 km). Our modeling was important in constraining the fault plane orientation obtained from first-motion polarities recorded for those earthquakes. In this modeling, we considered epicenter-to-station paths of the Peninsular Ranges of southern California and Baja California tectonic regions. Historically, moderate size earthquakes (5 ≤ M ≤ 7) have occurred in the PRBC, mainly along the San Miguel fault. Examples of these earthquakes are the 1954 earthquakes ( M 6.0 and 6.4; Leeds 1979) and the 1956 earthquakes ( ML 6.8, 6.4 and 6.3; Shor and Roberts 1958). Castro (1983) used synthetic seismograms to calculate the seismic …

Phylogeography of a stream-dwelling frog ( Pseudacris cadaverina) in southern California

Recent phylogeographic studies of animal taxa in California have revealed common geographic patterns of evolutionary divergence and genetic diversity that are generally attributable to landscape influences. However, there remains a paucity of knowledge on the evolution of freshwater taxa in southern California. Here, we investigate phylogeographic patterns in a stream-dwelling frog ( Pseudacris cadaverina). Two hundred and twenty-one individuals were collected from 46 populations across the species’ range in southern California. Using 1100 bp of sequence data from cytochrome b and tRNA-Glu, we conducted phylogenetic analyses, analysis of molecular variance, and nested clade phylogeographic analysis to gain insight into the factors contributing to the distribution of genetic diversity in P. cadaverina. We tested for evidence of two putative phylogeographic breaks and tested hypotheses that genetic diversity in this species is partitioned into (1) major watersheds, (2) mountain ranges, and (3) coastal and desert regions. Our results suggest that the eastern Transverse Ranges are the center of origin for extant P. cadaverina lineages and that the observed genetic structure in this species was established during the Pleistocene Epoch. There is strong support for three major haplotype groups and a Transverse Range break in P. cadaverina that is concordant with breaks found in numerous other taxa. The distribution of genetic diversity in P. cadaverina is due in large part to the separation of populations into different major watersheds and mountain ranges. Gene flow appears to be generally limited among disjunct populations throughout the region and some desert populations have been isolated by historical habitat fragmentation.

Lithospheric evolution of the Pacific–North American Plate Boundary considered in three dimensions

Tomographic images developed using the combined seismic networks of California and Nevada provide a three-dimensional view into Neogene Pacific–North American plate boundary evolution. Images reveal structures similar in size and spatial distribution to the large-scale structures observed at the surface. A prominent linear anomaly in the mantle is imaged beneath the western foothills to a depth of 70–90 km. Called the Sierran Foothill Anomaly (SFA), this 1–2% high-velocity structure extends the length of the physiographic Sierra Nevada Mountains. Much of the velocity increase is thermal in origin, with a first episode of cooling during the same late-Cretaceous to Paleogene low-angle subduction that affected most of western North America. Post-Laramide resumption of subduction continued chilling the western SFA. Small thrust earthquakes at the contact between the Juan de Fuca slab and the SFA indicate that the contact is still relatively cold to depths approaching 90 km. We propose that this chilled lithospheric section as responsible for the block-like integrity of the core of the Sierra Nevada. The Peninsular Ranges in southern California have also maintained a high degree of integrity, at least until recent times, because they shared a similar batholithic generation and Laramide chilling as the Sierra Nevada. The tomographic image includes other large-scale features. West of the SFA is a low-velocity region interpreted as upwelling mantle filling the window behind the NW-translating Juan de Fuca slab. This low-velocity feature appears to be offset by the San Andreas fault, which would indicate transform relations extend into the mantle. Compression and shortening between the Peninsular Ranges and the Sierra Nevada blocks began when the transform boundary shifted east of the Peninsular Ranges and Baja California around 5.5 Ma. High-velocity structures in the upper mantle developed beneath the Transverse Ranges and the Southern Great Valley (SGV) to accommodate crustal shortening. Alternative explanations for the SGV Anomaly are explored by comparing the volume of proximal sources to the volume of the sinking SGV Anomaly. No local source such as convective overturning of Sierran block eclogitic roots seems adequate to provide the volume needed to explain the anomaly as a purely local feature. Surface and subsurface views of the plate margin are complimentary, but consistent, and each contributes to resolving problems not accessible to the other.

Patterns of Genetic Variation Between the Checkered Skippers &lt;I&gt;Pyrgus communis&lt;/I&gt; and &lt;I&gt;Pyrgus albescens&lt;/I&gt; (Lepidoptera: Hesperiidae)

We examined patterns of genetic variation between the transcontinental species Pyrgus communis (Grote) and Pyrgus albescens Plotz (Hesperiidae) to examine whether patterns of molecular variation are congruent with the taxonomy. Sequence data from mitochondrial DNA and nuclear DNA failed to distinguish the two taxa. Although substantial genetic variation is explained by the two nominal taxa, more variation is explained by geography. Specifically, our molecular data indicate that the Transverse Ranges of southern California and the Sierra Nevada are important features affecting patterns of genetic variation. The possibility of recent divergence and secondary contact is discussed. Although P. communis and P. albescens do not adhere to a phylogenetic species concept, diagnostic morphological and distributional differences exist between the two entities that merit consideration regarding their taxonomic status.