A synopsis of suggested approaches to address potential competitive interactions between Barred Owls (<Emphasis Type="Italic">Strix varia</Emphasis>) and Spotted Owls (<Emphasis Type="Italic">S. occidentalis</Emphasis>)

The conservation of Spotted Owl (Strix occidentalis) populations has been one of the most controversial and visible issues in United States conservation history. Coincident with declines in Spotted Owl populations over the last three decades has been the invasion of Barred Owls (Strix varia) throughout the range of the Northern Spotted Owl (S. o. caurina) and into the range of the California Spotted Owl (S. o. occidentalis). This invasion has confused the reasons behind recent Spotted Owl declines because anecdotal and correlative information strongly suggests that Barred Owls are a new factor influencing the declines. There is great uncertainty about all aspects of the invasion, and this has sparked discussion about appropriate management and research responses regarding the effects of this invasion on Spotted Owls. We present a set of possible responses to address the issue, and we discuss the relative merits of these with regard to their efficacy given the current state of knowledge. We recommend that research specifically aimed at learning more about the interspecific relationships of these two owls throughout the range of sympatry should begin immediately. Approaches that seem unlikely to be useful in the short-term either because they do not facilitate knowledge acquisition, are relatively costly, or would be technically less feasible, should not be considered viable at this time. We believe the consequences of the invasion are potentially dire for the Spotted Owl and that research and management actions, including the use of adaptive management, are required to inform the near- and long-term decision-making process for conservation of Spotted Owls.     

Geographic variation and genetic structure in Spotted Owls

We examined genetic variation, populationstructure, and definition of conservation unitsin Spotted Owls (Strix occidentalis). Spotted Owls are mostly non-migratory,long-lived, socially monogamous birds that havedecreased population viability due to theiroccupation of highly-fragmented latesuccessional forests in western North America. To investigate potential effects of habitatfragmentation on population structure, we usedrandom amplified polymorphic DNA (RAPD) toexamine genetic variation hierarchicallyamong local breeding areas, subregionalgroups, regional groups, and subspeciesvia sampling of 21 breeding areas (276individuals) among the three subspecies ofSpotted Owls. Data from 11 variable bandssuggest a significant relationship betweengeographic distance among local breeding groupsand genetic distance (Mantel r = 0.53, P< 0.02) although multi-dimensional scaling ofthree significant axes did not identifysignificant grouping at any hierarchical level. Similarly, neighbor-joining clustering ofManhattan distances indicated geographicstructure at all levels and identified MexicanSpotted Owls as a distinct clade. RAPDanalyses did not clearly differentiate NorthernSpotted Owls from California Spotted Owls. Among Northern Spotted Owls, estimates ofpopulation differentiation (F_ST) rangedfrom 0.27 among breeding areas to 0.11 amongregions. Concordantly, within-group agreementvalues estimated via multi-response permutationprocedures of Jaccard's distances ranged from0.22 among local sites to 0.11 among regions. Pairwise comparisons of F_ST andgeographic distance within regions suggestedonly the Klamath region was in equilibrium withrespect to gene flow and genetic drift. Merging nuclear data with recent mitochondrialdata provides support for designation of anEvolutionary Significant Unit for MexicanSpotted Owls and two overlapping ManagementUnits for Northern and California Spotted Owls.     

Breeding dispersal in an isolated population of Spotted Owls Strix occidentalis: evidence for improved reproductive output

Breeding dispersal among territorial species is of interest to population biologists because leaving a territory carries fundamental risks to the dispersing individuals, and this may not outweigh the costs of maintaining the territory. Most studies of breeding dispersal have focused on species inhabiting spatially open populations, in which undetected emigration could impart a negative bias to estimates of dispersal. We studied breeding dispersal in an isolated (spatially closed) population of California Spotted Owl Strix occidentalis occidentalis in southern California for 12 years to assess factors that might correlate with breeding dispersal. Twenty‐nine per cent (n = 47) of territorial females and 19% (n = 35) of territorial males dispersed at least once during the study. Annually, 0–13% of the territorial females and 0–12% of the territorial males dispersed. Among a set of a priori and post hoc models related to breeding dispersal, the top a priori model indicated that birds having higher reproductive output relative to the population average were less likely to disperse. A post hoc model based on an index of territory quality was ranked higher than the top a priori model and indicated that birds occupying higher quality territories were less likely to disperse. These two models were correlated and represented short‐ and long‐term reproductive performance, respectively. Birds that dispersed also failed to fledge young in the year prior to dispersal, but the failure to fledge young did not, by itself, explain dispersal. Because Spotted Owls are long‐lived, they may ultimately improve their reproduction by dispersing given that they would have future opportunities to breed over the long term. Birds whose mates are likely to have died tended to improve their reproductive success, whereas the relationship between reproductive success of birds that divorced was less clear. Substantial variation in breeding dispersal was unexplained by our analysis so it is likely that the motivation to disperse was a complex process in this population.     

Blood parasites in owls with conservation implications for the Spotted Owl (Strix occidentalis)

The three subspecies of Spotted Owl (Northern, Strix occidentalis caurina; California, S. o. occidentalis; and Mexican, S. o. lucida) are all threatened by habitat loss and range expansion of the Barred Owl (S. varia). An unaddressed threat is whether Barred Owls could be a source of novel strains of disease such as avian malaria (Plasmodium spp.) or other blood parasites potentially harmful for Spotted Owls. Although Barred Owls commonly harbor Plasmodium infections, these parasites have not been documented in the Spotted Owl. We screened 111 Spotted Owls, 44 Barred Owls, and 387 owls of nine other species for haemosporidian parasites (Leucocytozoon, Plasmodium, and Haemoproteus spp.). California Spotted Owls had the greatest number of simultaneous multi-species infections (44%). Additionally, sequencing results revealed that the Northern and California Spotted Owl subspecies together had the highest number of Leucocytozoon parasite lineages (n = 17) and unique lineages (n = 12). This high level of sequence diversity is significant because only one Leucocytozoon species (L. danilewskyi) has been accepted as valid among all owls, suggesting that L. danilewskyi is a cryptic species. Furthermore, a Plasmodium parasite was documented in a Northern Spotted Owl for the first time. West Coast Barred Owls had a lower prevalence of infection (15%) when compared to sympatric Spotted Owls (S. o. caurina 52%, S. o. occidentalis 79%) and Barred Owls from the historic range (61%). Consequently, Barred Owls on the West Coast may have a competitive advantage over the potentially immune compromised Spotted Owls.     

Stable isotopes reveal unexpected relationships between fire history and the diet of Spotted Owls

Although the effects of shifting fire regimes on bird populations have been recognized as important to ecology and conservation, the consequences of fire for trophic interactions of avian species – and raptors in particular – remain relatively unknown. Here, we found that within national parks with long‐standing (40+ years) fire management programmes, California Spotted Owls Strix occidentalis occidentalis consumed predominantly Woodrats Neotoma spp. and Pocket Gophers Thomomys spp.; however, in contrast to our predictions, when their territories experienced more extensive and frequent fire, Spotted Owls consumed proportionally more Flying Squirrels Glaucomys oregonensis. We hypothesize this finding could have been driven by either changes to prey abundance following fires (e.g. increases in flying squirrels) or changes to prey availability (e.g. shifts in forest structure or flying squirrel spatial distribution that increased predation upon them by owls). Our work thus demonstrates that fire may have unexpected consequences for the trophic interactions of raptor species and provides valuable information for the conservation of Spotted Owls in fire‐prone forest landscapes.     

Hybridization of cultivated Vitis vinifera with wild V. californica and V. girdiana in California

Hybridization of introduced domesticates and closely related natives is well documented in annual crops. The widespread introduction of the domesticated grapevine, Vitis vinifera, into California where it overlaps with two native congenerics, with which it is interfertile, provides opportunity to investigate hybridization between woody perennials. Although geographically widespread, the introduction over the past two centuries has been limited to a few elite clonal cultivars, providing a unique opportunity to study the effects of hybridization on the native species. The amount of hybridization with V. vinifera and the genetic diversity of wild‐growing Vitis californica and Vitis girdiana were examined using nineteen microsatellite markers. STRUCTURE analysis was used to define hybrid and introgressed individuals and to analyze genetic structure of the native species. FAMOZ software was used to identify which V. vinifera cultivars served as parents of F₁ hybrids. The three species were clearly distinguished by STRUCTURE analysis. Thirty percent of 119 V. californica vines were hybrids. The domesticated parent was identified for 16 F₁ hybrid vines; the original California cultivar, ‘Mission’, was the parent of eight. Backcrosses were also found, showing introgression into subsequent generations. Similar results were obtained for a small sample of V. girdiana. Removing hybrids greatly reduced the genetic variation of the presumed pure species, among which there was essentially no genetic structure. Limited genetic variability indicates the California natives may be threatened by genetic erosion. The discovery of F₁ hybrids of ‘Mission’, a cultivar not grown in the areas for ~100 years, suggests long generation times for wild vines that, often, grow into expansive liana and propagate by layering, all factors that limit recruitment in populations already disjunct by habitat lose. Hermaphroditic flowers and fruit that is more attractive to birds may favor the production of backcross seed and establishment of introgressed individuals.     

Genetic structure, introgression, and a narrow hybrid zone between northern and California spotted owls (Strix occidentalis)

The northern spotted owl (Strix occidentalis caurina) is a threatened subspecies and the California spotted owl (Strix occidentalis occidentalis) is a subspecies of special concern in the western United States. Concern for their continued viability has arisen because of habitat loss caused by timber harvesting. The taxonomic status of the northern subspecies has been the subject of continuing controversy. We investigated the phylogeographical and population genetic structure of northern and California spotted owls with special reference to their region of contact. Mitochondrial DNA (mtDNA) control region sequences confirmed the existence of two well-differentiated lineages connected by a narrow hybrid zone in a region of low population density in north central California. Maximum-likelihood estimates indicated bidirectional gene flow between the lineages but limited introgression outside the region of contact. The lengths of both the mtDNA hybrid zone and the reduced density patch were similar and slightly exceeded estimates of natal dispersal distances. This suggests that the two subspecies were in secondary contact in a hybrid zone trapped by a population density trough. Consequently, the zone of interaction is expected to be geographically stable. We discovered a third, rare clade of haplotypes, which we interpreted to be a result of incomplete lineage sorting; those haplotypes result in a paraphyletic northern spotted owl with respect to the California spotted owl. A congeneric species, the barred owl (Strix varia), occasionally hybridizes with spotted owls; our results indicated an upper bound for the frequency of barred owl mtDNA haplotypes in northern spotted owl populations of 3%.     

Hybridization between two parapatric ranid frog species in the northern Sierra Nevada,California, USA

Contact zones between species provide a unique opportunity to test whether taxa can hybridize or not. Cross‐breeding or hybridization between closely related taxa can promote gene flow (introgression) between species, adaptation, or even speciation. Though hybridization events may be short‐lived and difficult to detect in the field, genetic data can provide information about the level of introgression between closely related taxa. Hybridization can promote introgression between species, which may be an important evolutionary mechanism for either homogenization (reversing initial divergence between species) or reproductive isolation (potentially leading to speciation). Here, we used thousands of genetic markers from nuclear DNA to detect hybridization between two parapatric frog species (Rana boylii and Rana sierrae) in the Sierra Nevada of California. Based on principal components analysis, admixture, and analysis of heterozygosity at species diagnostic SNPs, we detected two F1 hybrid individuals in the Feather River basin, as well as a weak signal of introgression and gene flow between the frog species compared with frog populations from two other adjacent watersheds. This study provides the first documentation of hybridization and introgression between these two species, which are of conservation concern.     

Habitat preferences for Long-eared Owls Asio otus and Little Owls Athene noctua in semi-arid environments at three spatial scales

Capsule There is a relationship between owl numbers and the availability of the agri-forest patchwork.

Aims To model habitat preferences at three different scales of two predators largely neglected within the framework of Environmental Impact Assessment (EIA) studies.

Methods We studied habitat preferences of Long-eared Owls and Little Owls by comparing habitat composition around 28 and 78 occupied territories respectively with 55 non-occupied territories in Alicante (eastern Spain). Generalized linear models were used to examine patterns of habitat preference at three different spatial scales: nest-site, home range and landscape.

Results At the nest-site scale, Long-eared Owls preferred wooded areas with few paved roads while Little Owls preferred arid plantations. Furthermore, the probability of finding an occupied territory increased with the proximity of another occupied territory in the surroundings. The home range scale models mirror the feeding requirements of the owls. Thus, Long-eared Owls occupied areas with high percentages of forest, arid plantations, edges between these two land uses, short distances between nests, with presence of conspecifics and little human disturbance. Little Owls occupied arid plantations with high availability of linear structures and the proximity of villages. At the landscape scale, Long-eared Owls eluded extensive forests, and Little Owls preferred arid plantations.

Conclusions We suggest a hierarchical process of habitat selection for both owls regarding fitting trophic resources at the broadest scales and adequate sites for breeding and roosting at the smallest scale. EIA studies must consider that protecting small areas around single nests may not be an efficient conservation option compared with preserving clusters of territories for both species.     

Habitat Use and Selection by California Spotted Owls in a Postfire Landscape

ABSTRACT Forest fire is often considered a primary threat to California spotted owls (Strix occidentalis occidentalis) because fire has the potential to rapidly alter owl habitat. We examined effects of fire on 7 radiomarked California spotted owls from 4 territories by quantifying use of habitat for nesting, roosting, and foraging according to severity of burn in and near a 610-km²fire in the southern Sierra Nevada, California, USA, 4 years after fire. Three nests were located in mixed-conifer forests, 2 in areas of moderate-severity burn, and one in an area of low-severity burn, and one nest was located in an unburned area of mixed-conifer-hardwood forest. For roosting during the breeding season, spotted owls selected low-severity burned forest and avoided moderate- and high-severity burned areas; unburned forest was used in proportion with availability. Within 1 km of the center of their foraging areas, spotted owls selected all severities of burned forest and avoided unburned forest. Beyond 1.5 km, there were no discernable differences in use patterns among burn severities. Most owls foraged in high-severity burned forest more than in all other burn categories; high-severity burned forests had greater basal area of snags and higher shrub and herbaceous cover, parameters thought to be associated with increased abundance or accessibility of prey. We recommend that burned forests within 1.5 km of nests or roosts of California spotted owls not be salvage-logged until long-term effects of fire on spotted owls and their prey are understood more fully.     

Using Detection Dogs to Conduct Simultaneous Surveys of Northern Spotted (Strix occidentalis caurina) and Barred Owls (Strix varia)

State and federal actions to conserve northern spotted owl (Strix occidentalis caurina) habitat are largely initiated by establishing habitat occupancy. Northern spotted owl occupancy is typically assessed by eliciting their response to simulated conspecific vocalizations. However, proximity of barred owls (Strix varia)-a significant threat to northern spotted owls-can suppress northern spotted owl responsiveness to vocalization surveys and hence their probability of detection. We developed a survey method to simultaneously detect both species that does not require vocalization. Detection dogs (Canis familiaris) located owl pellets accumulated under roost sites, within search areas selected using habitat association maps. We compared success of detection dog surveys to vocalization surveys slightly modified from the U.S. Fish and Wildlife Service's Draft 2010 Survey Protocol. Seventeen 2 km ×2 km polygons were each surveyed multiple times in an area where northern spotted owls were known to nest prior to 1997 and barred owl density was thought to be low. Mitochondrial DNA was used to confirm species from pellets detected by dogs. Spotted owl and barred owl detection probabilities were significantly higher for dog than vocalization surveys. For spotted owls, this difference increased with number of site visits. Cumulative detection probabilities of northern spotted owls were 29% after session 1, 62% after session 2, and 87% after session 3 for dog surveys, compared to 25% after session 1, increasing to 59% by session 6 for vocalization surveys. Mean detection probability for barred owls was 20.1% for dog surveys and 7.3% for vocal surveys. Results suggest that detection dog surveys can complement vocalization surveys by providing a reliable method for establishing occupancy of both northern spotted and barred owl without requiring owl vocalization. This helps meet objectives of Recovery Actions 24 and 25 of the Revised Recovery Plan for the Northern Spotted Owl.     

Mitochondrial DNA reveals the genealogical history of the snake-eyed lizards (Ophisops elegans and O. occidentalis) (Sauria: Lacertidae)

The snake-eyed lizards of the genus Ophisops (Lacertidae) have been through a series of taxonomical revisions, but still their phylogenetic relationships remain uncertain. In the present study we estimate the phylogeographic structure of O. elegans across its distributional range and we evaluate the relationships between O. elegans and the sympatric, in North Africa, species O. occidentalis, using partial mtDNA sequences (16S rRNA, COI, and cyt b). All phylogenetic analyses produced topologically identical trees where extant populations of O. elegans and O. occidentalis were found polyphyletic. Taking into account all the potential causes of polyphyly (introgressive hybridization, incomplete lineage sorting, and imperfect taxonomy) we suggest the inaccurate taxonomy as the most likely explanation for the observed pattern. Our results stress the need for re-evaluation of the current taxonomical status of these species and their subspecies. Furthermore, our biogeographic analyses and the estimated time of divergences suggest a late Miocene diversification within these species, where the present distribution of O. elegans and O. occidentalis was the result of several dispersal and vicariant events, which are associated with climatic oscillations (the late Miocene aridification of Asia and northern Africa) and paleogeographic barriers of late Miocene and Pliocene period.     

Introgression between invasive and native blue mussels (genus Mytilus) in the central California hybrid zone

The ecological and genetic factors determining the extent of introgression between species in secondary contact zones remain poorly understood. Here, we investigate the relative importance of isolating barriers and the demographic expansion of invasive Mytilus galloprovincialis on the magnitude and the direction of introgression with the native Mytilus trossulus in a hybrid zone in central California. We use double‐digest restriction‐site‐associated DNA sequencing (ddRADseq) to genotype 1337 randomly selected single nucleotide polymorphisms and accurately distinguish early and advanced generation hybrids for the first time in the central California Mytilus spp. hybrid zone. Weak levels of introgression were observed in both directions but were slightly more prevalent from the native M. trossulus into the invasive M. galloprovincialis. Few early and advanced backcrossed individuals were observed across the hybrid zone confirming the presence of strong barriers to interbreeding. Heterogeneous patterns of admixture across the zone of contact were consistent with the colonization history of M. galloprovincialis with more extensive introgression in northern localities furthest away from the putative site of introduction in southern California. These observations reinforce the importance of dynamic spatial and demographic expansions in determining patterns of introgression between close congeners, even in those with high dispersal potential and well‐developed reproductive barriers. Our results suggest that the threat posed by invasive M. galloprovincialis is more ecological than genetic as it has displaced, and continues to displace the native M. trossulus from much of central and southern California.     

Widespread hybridization between the Greater Spotted Eagle Aquila clanga and the Lesser Spotted Eagle Aquila pomarina (Aves: Accipitriformes) in Europe

Hybridization is a significant threat for endangered species and could potentially even lead to their extinction. This concern applies to the globally vulnerable Greater Spotted Eagle Aquila clanga, a species that co‐occurs, and potentially interbreeds, with the more common Lesser Spotted Eagle Aquila pomarina in a vast area of Eastern Europe. We applied single nucleotide polymorphism (SNP) and microsatellite markers in order to study hybridization and introgression in 14 European spotted eagle populations. We detected hybridization and/or introgression in all studied sympatric populations. In most regions, hybridization took place prevalently between A. pomarina males and A. clanga females, with introgression to the more common A. pomarina. However, such a pattern was not as obvious in regions where A. clanga is still numerous. In the course of 16 years of genetic monitoring of a mixed population in Estonia, we observed the abandonment of A. clanga breeding territories and the replacement of A. clanga pairs by A. pomarina, whereby on several occasions hybridization was an intermediate step before the disappearance of A. clanga. Although the total number of Estonian A. clanga × A. pomarina pairs was twice as high as that of A. clanga pairs, the number of pairs recorded yearly were approximately equal, which suggests a higher turnover rate in interbreeding pairs. This study shows that interspecific introgressive hybridization occurs rather frequently in a hybrid zone at least 1700‐km wide: it poses an additional threat for the vulnerable A. clanga, and may contribute to the extinction of its populations. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 725–736.     

Annual climate in Mexican Spotted Owl habitat in the Sacramento Mountains,New Mexico: implications for responding to climate change

Global climate change presents a growing conservation threat, but our understanding of the effects of climate change remains limited for most species. We evaluated the annual climate cycle for threatened Mexican Spotted Owls (Strix occidentalis lucida) in high-elevation mixed-conifer forests in the Sacramento Mountains of New Mexico from 2005 to 2010. We used data from a network of weather stations in Mexican Spotted Owl habitat to describe annual temperature cycles, and precipitation data from a National Weather Service weather station to describe the annual precipitation cycle. We coupled these data with equations from the literature to estimate annual cycles in resting metabolic rate and evaporative water loss, and evaluated the potential effects of a warming climate on these parameters. Annual weather was characterized by cold, dry winters, warmer and dry springs, warm and wet summers, and cool and relatively wet falls. Ambient temperature never exceeded the upper critical temperature for Mexican Spotted Owls (35.2°C), but > 90% of 663,422 hourly temperature observations were below the lower critical temperature (18.2°C). Thus, heat stress was not predicted to occur, but owls likely expended energy on thermoregulation at low temperatures. Resting energy use peaked during winter (December–February) and was lowest when owls would be feeding young (May–August). In contrast, evaporative water loss peaked from June to August, when precipitation also peaked. Mexican Spotted Owls generally appeared well-adapted to the current climate cycle in our montane study area, but late winter (February–March) may be a critical period in terms of energy requirements, and late spring (April–May) may be critical in terms of water relationships. Predicted changes in temperature through 2099 would result in reductions in predicted energy use by Mexican Spotted Owls, but increases in predicted water use. Water relationships may become increasingly important for Mexican Spotted Owls in the face of climate change, especially in warmer and drier areas. In forested areas, retaining patches of older forest with high canopy cover in cool, mesic sites may provide continued benefits to Mexican Spotted Owls under climate change.     

PHYLOGEOGRAPHY OF SPOTTED OWL (STRIX OCCIDENTALIS) POPULATIONS BASED ON MITOCHONDRIAL DNA SEQUENCES: GENE FLOW,GENETIC STRUCTURE,AND A NOVEL BIOGEOGRAPHIC PATTERN

Mitochondrial DNA control region sequences of spotted owls (Strix occidentalis) allowed us to investigate gene flow, genetic structure, and biogeographic relationships among these forest-dwelling birds of western North America Estimates of gene flow based on genetic partitioning and the phylogeography of haplotypes indicate substantial dispersal within three long-recognized subspecies. However, patterns of individual phyletic relationships indicate a historical absence of gene flow among the subspecies, which are essentially monophyletic. The pattern of haplotype coalescence enabled us to identify the approximate timing and direction of a recent episode of gene flow from the Sierra Nevada to the northern coastal ranges. The three subspecies comprise phylogenetic species, and the northern spotted owl (S. o. caurina) is sister to a clade of California (S. o. occidentalis) plus Mexican spotted owls (S o lucida); this represents a novel biogeographic pattern within birds. The California spotted owl had substantially lower nucleotide diversity than the other two subspecies; this result is inconsistent with present patterns of population density A causal explanation requires postulating a severe bottleneck or a selective sweep, either of which was confined to only one geographic region.     

Phenotypic evolution in high‐elevation populations of western fence lizards (Sceloporus occidentalis) in the Sierra Nevada Mountains

Adaptive divergence in response to variable habitats, climates, and altitude is often accentuated along elevation gradients. We investigate phenotypic evolution in body size and coloration in the western fence lizard (Sceloporus occidentalis Baird & Girard, 1852) across elevation gradients in Yosemite National Park, California, situated in the Sierra Nevada mountains of Western North America. High‐elevation populations occurring above 2100 m a.s.l. are recognized as a separate subspecies (Sceloporus occidentalis taylori Camp, 1916), with a distinctive phenotype characterized by a large body size and extensive blue ventral pigmentation. We sampled S. occidentalis from across elevation gradients in Yosemite National Park, California, and collected phenotypic data (body size and ventral coloration measurements; 410 specimens) and mitochondrial DNA sequence data (complete NADH1 gene; 969 bp, 181 specimens) to infer phylogenetic relationships, and examine the genetic and phenotypic diversity among populations. Populations of S. occidentalis in Yosemite National Park follow Bergmann's rule and exhibit larger body sizes in colder, high‐elevation environments. The high‐elevation subspecies S. o. taylori is not monophyletic, and the mitochondrial DNA genealogy supports a model of convergent phenotypic evolution among high‐elevation populations belonging to different river drainages. The hypothesis that separate populations of S. occidentalis expanded up river drainages after the recession of glaciers is supported by population demographic analyses, and suggest that Bergmann's clines can evolve rapidly along elevation gradients. The distinctive high‐elevation phenotype that is attributable to S. o. taylori has evolved independently several times, and includes adaptive phenotypic changes associated with increases in body size and ventral coloration. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 630–641.     

Following the rivers: historical reconstruction of California voles Microtus californicus (Rodentia: Cricetidae) in the deserts of eastern California

The California vole, Microtus californicus, restricted to habitat patches where water is available nearly year‐round, is a remnant of the mesic history of the southern Great Basin and Mojave deserts of eastern California. The history of voles in this region is a model for species‐edge population dynamics through periods of climatic change. We sampled voles from the eastern deserts of California and examined variation in the mitochondrial cytb gene, three nuclear intron regions, and across 12 nuclear microsatellite markers. Samples are allocated to two mitochondrial clades: one associated with southern California and the other with central and northern California. The limited mtDNA structure largely recovers the geographical distribution, replicated by both nuclear introns and microsatellites. The most remote population, Microtus californicus scirpensis at Tecopa near Death Valley, was the most distinct. This population shares microsatellite alleles with both mtDNA clades, and both its northern clade nuclear introns and southern clade mtDNA sequences support a hybrid origin for this endangered population. The overall patterns support two major invasions into the desert through an ancient system of riparian corridors along streams and lake margins during the latter part of the Pleistocene followed by local in situ divergence subsequent to late Pleistocene and Holocene drying events. Changes in current water resource use could easily remove California voles from parts of the desert landscape.