Woodrat Species Research Articles

Asymmetric mate preference and reproductive interference mediate climate-induced changes in mate availability in a small mammal hybrid zone.

Range expansion and contraction are among the most common biotic responses to changing environmental conditions, yet much is to be learned about the mechanisms that underlie range-edge population dynamics, especially when those areas are points of secondary contact between closely related species. Here, we present field-measured parentage data that document the reproductive outcomes of changes in mate availability at a secondary contact zone between two species of woodrat in the genus Neotoma. Changes in mate availability resulted from drought-driven differential survival between the species and their hybrids. As the availability of conspecific mates declined, rates of hybridization increased, leading to the accumulation of admixed individuals in the zone of contact. Patterns of reproductive success in the wild appear to be the result of a combination of both pre-mating isolation and post-zygotic selection resulting from genomic incompatibilities between the parental lineages. Evidence of asymmetric mate preference between the parental lineages came from both skewed reproductive output in the field and laboratory preference trials. Moreover, partial genomic incompatibility was evident from the near-zero reproductive success of F1 males and because nearly all surviving hybrids had one pure parent. Nonetheless, high reproductive success of F1 females and backcrossing in both parental directions allow for introgression between the parental species. These findings reveal how climate change may alter evolutionary outcomes for species at the edge of their ranges through an interplay of behavioral, demographic, and genetic mechanisms.

Rodents consuming the same toxic diet harbor a unique functional core microbiome

Gut microbiota are intrinsic to an herbivorous lifestyle, but very little is known about how plant secondary compounds (PSCs), which are often toxic, influence these symbiotic partners. Here we interrogated the possibility of unique functional core microbiomes in populations of two species of woodrat (Neotoma lepida and bryanti) that have independently converged to feed on the same toxic diet (creosote bush; Larrea tridentata) and compared them to populations that do not feed on creosote bush. Leveraging this natural experiment, we collected samples across a large geographic region in the U.S. desert southwest from 20 populations (~ 150 individuals) with differential ingestion of creosote bush and analyzed three gut regions (foregut, cecum, hindgut) using16S sequencing and shotgun metagenomics. In each gut region sampled, we found a distinctive set of microbes in individuals feeding on creosote bush that were more abundant than other ASVs, enriched in creosote feeding woodrats, and occurred more frequently than would be predicted by chance. Creosote core members were from microbial families e.g., Eggerthellaceae, known to metabolize plant secondary compounds and three of the identified core KEGG orthologs (4-hydroxybenzoate decarboxylase, benzoyl-CoA reductase subunit B, and 2-pyrone-4, 6-dicarboxylate lactonase) coded for enzymes that play important roles in metabolism of plant secondary compounds. The results support the hypothesis that the ingestion of creosote bush sculpts the microbiome across all major gut regions to select for functional characteristics associated with the degradation of the PSCs in this unique diet.

Metabolomic evidence of independent biotransformation pathways for terpenes in two specialist mammalian herbivores (genus Neotoma).

Herbivory is common in mammals, yet our understanding of detoxification processes used by mammals to biotransform plant secondary compounds (PSCs) is limited. Specialist herbivores are thought to have evolved detoxification mechanisms that rely more heavily on energetically cheap Phase I biotransformation reactions to process high levels of PSCs in their diets. We explored this hypothesis by comparing the urinary metabolite patterns of two specialist herbivores (genus Neotoma). Neotoma stephensi is an obligate specialist on one-seeded juniper (Juniperus monosperma). Neotoma lepida is a generalist forager across its range, yet populations in the Great Basin specialize on Utah juniper (J. osteosperma). While both juniper species have high levels of terpenes, the terpene profiles and quantities differ between the two. Individuals from both woodrat species were fed diets of each juniper in a cross-over design. Urine, collected over a 24-h period, was extracted and analyzed in an untargeted metabolomics approach using both GC-MS and HPLC-MS/MS. The obligate specialist N. stephensi excreted a unique pattern of Phase I metabolites when fed its native juniper, while N. lepida excreted a unique pattern of Phase II metabolites when fed its native juniper. Both woodrat species utilized the Phase II metabolic pathway of glucuronidation more heavily when consuming the more chemically diverse J. osteosperma, and N. stephensi utilized less glucuronidation than N. lepida when consuming J. monosperma. These results are consistent with the hypothesis that obligate specialists may have evolved unique and efficient biotransformation mechanisms for dealing with PSCs in their diet.

Sympatric rodents in a desert shrubland differ in arthropod consumption

The foraging ecology of sympatric mammals within xeric habitats is poorly understood. In this study, we surveyed the diets of two sympatric woodrat species, Neotoma bryanti, N. lepida and their hybrids in a desert shrubland during the dry season using stable isotope analyses of hair and arthropod DNA metabarcoding of feces. We found that woodrats regardless of their ancestry fed on similar plants during the same season across multiple years. However, stable isotope analyses and arthropod metabarcoding were consistent with greater arthropod ingestion by N. bryanti compared to N. lepida or hybrids. These results suggest that while the diets of these sympatric woodrats largely overlap during the dry season in terms of the plant components, they differ in terms of arthropod ingestion. This arthropod feeding may serve to reduce interspecific competition or act as dietary supplementation during nutritionally challenging periods. These results demonstrate that integrating DNA metabarcoding approaches with stable isotope tracers enables a more rigorous evaluation of animal foraging behavior.

Toxin tolerance across landscapes: Ecological exposure not a prerequisite.

Little is known about the tolerances of mammalian herbivores to plant specialized metabolites across landscapes.We investigated the tolerances of two species of herbivorous woodrats, Neotoma lepida (desert woodrat) and Neotoma bryanti (Bryant's woodrat) to creosote bush (Larrea tridentata), a widely distributed shrub with a highly toxic resin. Woodrats were sampled from 13 locations both with and without creosote bush across a 900 km transect in the US southwest. We tested whether these woodrat populations consume creosote bush using plant metabarcoding of feces and quantified their tolerance to creosote bush through feeding trials using chow amended with creosote resin.Toxin tolerance was analyzed in the context of population structure across collection sites with microsatellite analyses. Genetic differentiation among woodrats collected from different locations was minimal within either species. Tolerance differed substantially between the two species, with N. lepida persisting 20% longer than N. bryanti in feeding trials with creosote resin. Furthermore, in both species, tolerance to creosote resin was similar among woodrats near or within creosote bush habitat. In both species, woodrats collected greater than 25 km from creosote had markedly lower tolerances to creosote resin compared to animals from within the range of creosote bush.The results imply that mammalian herbivores are adapted to the specialized metabolites of plants in their diet, and that this tolerance can extend several kilometers outside of the range of dietary items. That is, direct ecological exposure to the specialized chemistry of particular plant species is not a prerequisite for tolerance to these compounds. These findings lay the groundwork for additional studies to investigate the genetic mechanisms underlying toxin tolerance and to identify how these mechanisms are maintained across landscape-level scales in mammalian herbivores.

Mammalian cytochrome P450 biodiversity: Physiological importance, function, and protein and genomic structures of cytochromes P4502B in multiple species of woodrats with different dietary preferences.

The vast diversity of cytochrome P450 enzymes in mammals has been proposed to result in large measure from plant-animal warfare, whereby evolution of chemical defenses such as phenolics and terpenoids in plants led to duplication and divergence of P450 genes in herbivores. Over evolutionary time, natural selection is predicted to have produced P450s with high affinity and enhanced metabolism of substrates that are ingested regularly by herbivores. Interestingly, however, almost all knowledge of the interactions of mammalian P450 enzymes with substrates stems from studies of the metabolism of drugs and model compounds rather than studies on wild mammalian herbivores and their respective PSMs. A question of particular interest centers on the role of individual P450 enzymes in the ability of certain herbivores to specialize on plants that are lethal to most other species, including those from the same genus as the specialists. We tackled this intricate problem using a tractable natural system (herbivorous woodrats, genus Neotoma) focusing on comparisons of the specialist N. stephensi, the facultative specialist N. lepida, and the generalist N. albigula, and employing a cross-disciplinary approach involving ecology, biochemistry, pharmacology, structural biology, and genomics. Based on multiple findings suggesting the importance of CYP2B enzymes for ingestion of juniper and a major constituent, α-pinene, we characterized the structure, function and activity of several CYP2B enzymes in woodrats with different dietary habits. Results to date suggest that differences in CYP2B gene copy number may contribute to differential tolerance of PSMs among woodrat species, although additional work is warranted to firmly link gene copy number to juniper tolerance.

Multigenerational backcrossing and introgression between two woodrat species at an abrupt ecological transition.

When organisms experience secondary contact after allopatric divergence, genomic regions can introgress differentially depending on their relationships with adaptation, reproductive isolation, recombination, and drift. Analyses of genome-wide patterns of divergence and introgression could provide insight into the outcomes of hybridization and the potential relationship between allopatric divergence and reproductive isolation. Here, we generate population genetic data (26,262 SNPs; 353 individuals) using a reduced-representation sequencing approach to quantify patterns of ancestry, differentiation, and introgression between a pair of ecologically distinct mammals-the desert woodrat (N. lepida) and Bryant's woodrat (N. bryanti)-that hybridize at a sharp ecotone in southern California. Individual ancestry estimates confirmed that hybrids were rare in this bimodal hybrid zone, and entirely consisted of a few F1 individuals and a broad range of multigenerational backcrosses. Genomic cline analyses indicated more than half of loci had elevated introgression from one genomic background into the other. However, introgression was not associated with relative or absolute measures of divergence, and loci with extreme values for both were not typically found near detoxification enzymes previously implicated in dietary specialization for woodrats. The decoupling of differentiation and introgression suggests that processes other than adaptation, such as drift, may underlie the extreme clines at this contact zone.

Differences in dietary composition and preference maintained despite gene flow across a woodrat hybrid zone.

Ecotones, characterized by adjacent yet distinct biotic communities, provide natural laboratories in which to investigate how environmental selection influences the ecology and evolution of organisms. For wild herbivores, differential plant availability across sharp ecotones may be an important source of dietary‐based selection.We studied small herbivore diet composition across a sharp ecotone where two species of woodrat, Neotoma bryanti and N. lepida, come into secondary contact with one another and hybridize. We quantified woodrat dietary preference through trnL metabarcoding of field‐collected fecal pellets and experimental choice trials. Despite gene flow, parental N. bryanti and N. lepida maintain distinct diets across this fine spatial scale, and across temporal scales that span both wet and dry conditions. Neotoma bryanti maintained a more diverse diet, with Frangula californica (California coffeeberry) making up a large portion of its diet. Neotoma lepida maintains a less diverse diet, with Prunus fasciculata (desert almond) comprising more than half of its diet. Both F. californica and P. fasciculata are known to produce potentially toxic plant secondary compounds (PSCs), which should deter herbivory, yet these plants have relatively high nutritional value as measured by crude protein content. Neotoma bryanti and N. lepida consumed F. californica and P. fasciculata, respectively, in greater abundance than these plants are available on the landscape—indicating dietary selection. Finally, experimental preference trials revealed that N. bryanti exhibited a preference for F. californica, while N. lepida exhibited a relatively stronger preference for P. fasciculata. We find that N. bryanti exhibit a generalist herbivore strategy relative to N. lepida, which exhibit a more specialized feeding strategy in this study system.Our results suggest that woodrats respond to fine‐scale environmental differences in plant availability that may require different metabolic strategies in order to balance nutrient acquisition while minimizing exposure to potentially toxic PSCs.

A New Species of Eimeria (Apicomplexa: Eimeriidae) from Eastern Woodrat, Neotoma floridana (Rodentia: Cricetidae), from Arkansas, USA, and a Summation of Eimerians from North American Woodrats.

North American woodrats or packrats (genus Neotoma) are excellent hosts of coccidians and several species remain to be reported as hosts. Eleven species of Eimeria have been previously described from Neotoma spp. However, it has been nearly 35years, since the last eimerian (E. ladronensis Reduker and Duszynski, 1985) was described from any woodrat species. Six adult eastern woodrats, Neotoma floridana (Ord, 1818) were collected with Sherman live traps from Blue Haze Vista, Polk County, Arkansas, USA. Fecal specimens or rectal contents were examined for coccidia. Measurements were taken on 30 sporulated oöcysts and photographs were taken using brightfield optics. One (17%) eastern woodrat was found to be passing oocysts of Eimeria machardyi n. sp. as well as three (50%) with Eimeria albigulae Levine, Ivens, and Kruidenier, 1957, and two (33%) with Eimeria glauceae Wheat and Ernst, 1974. We provide a description of a new species of Eimeria from eastern woodrats, Neotoma floridana, the first photomicrograph of E. glauceae, and additional information on E. albigulae. A summation of the eimerians of North American woodrats is also provided. Nine of 13 (69%) species of packrats north of México have now been reported to harbor 12 species of eimerians. Additional surveys of Neotoma spp. which have not yet been reported as hosts, particularly those from México and Central America, should yield more eimerians and distributional records as well as the possibility of discovery of new species.

Terpenes May Serve as Feeding Deterrents and Foraging Cues for Mammalian Herbivores.

Terpenes, volatile plant secondary compounds produced by woody plants, have historically been thought to act as feeding deterrents for mammalian herbivores. However, three species of woodrats, Neotoma stephensi, N. lepida, and N. albigula, regularly consume juniper, which is high in terpenes, and N. stephensi and N. lepida are considered juniper specialists. By investigating the terpene profiles in Juniperus monosperma and J. osteosperma, which are browsed or avoided by woodrats in the field, and recording the caching and consumption of juniper foliage by woodrats in the lab, we have evidence that terpenes may serve as feeding and/or foraging cues. The obligate specialist N. stephensi chose to forage on trees higher in p-cymene and preferred to consume juniper rather than caching it in a laboratory setting. These observations provide evidence that terpenes serve as a feeding cue and that the obligate specialist's physiological mechanism for metabolizing the terpenes present in juniper may negate the need for caching. The facultative specialist N. lepida chose to forage on trees lower in four terpenes and cached more juniper than the obligate specialist N. stephensi, providing evidence that terpenes serve as a feeding deterrent for N. lepida and that this woodrat species relies on behavioral mechanisms to minimize terpene intake. The generalist N. albigula foraged on trees with higher terpenes levels but consumed the least amount of juniper in the lab and preferred to cache juniper rather than consume it, evidence that terpenes act as foraging but not feeding cues in the generalist. Our findings suggest that volatile plant secondary compounds can act as feeding and/or foraging cues and not just feeding deterrents in mammalian herbivores.

Metagenomic sequencing provides insights into microbial detoxification in the guts of small mammalian herbivores (Neotoma spp.).

Microbial detoxification of plant toxins influences the use of plants as food sources by herbivores. Stephen's woodrats (Neotoma stephensi) specialize on juniper, which is defended by oxalate, phenolics and monoterpenes, while closely related N. albigula specialize on cactus, which only contains oxalate. Woodrats maintain two gut chambers harboring dense microbial communities: a foregut chamber proximal to the major site of toxin absorption, and a cecal chamber in their hindgut. We performed several experiments to investigate the location and nature of microbial detoxification in the woodrat gut. First, we measured toxin concentrations across gut chambers of N. stephensi. Compared to food material, oxalate concentrations were immediately lower in the foregut, while concentrations of terpenes remained high in the foregut, and were lowest in the cecal chamber. We conducted metagenomic sequencing of the foregut chambers of both woodrat species and cecal chambers of N. stephensi to compare microbial functions. We found that most genes associated with detoxification were more abundant in the cecal chambers of N. stephensi. However, some genes associated with degradation of oxalate and phenolic compounds were more abundant in the foregut chambers. Thus, microbial detoxification may take place in various chambers depending on the class of chemical compound.

Role of cytochrome P450 2B sequence variation and gene copy number in facilitating dietary specialization in mammalian herbivores.

Theory postulates that dietary specialization in mammalian herbivores is enabled by a specialized set of liver enzymes that process the high concentrations of similar plant secondary metabolites (PSMs) in the diets of specialists. To investigate whether qualitative and quantitative differences in detoxification mechanisms distinguish dietary specialists from generalists, we compared the sequence diversity and gene copy number of detoxification enzymes in two woodrat species: a generalist, the white-throated woodrat (Neotoma albigula) and a juniper specialist, Stephens' woodrat (N.stephensi). We focused on enzymes in the cytochrome P450 subfamily 2B (CYP2B), because previous research suggests this subfamily plays a key role in the processing of PSMs. For both woodrat species, we obtained and sequenced CYP2B cDNA, generated CYP2B phylogenies, estimated CYP2B gene copy number and created a homology model of the active site. We found that the specialist possessed on average ~5 more CYP2B gene copies than the generalist, but the specialist's CYP2B sequences were less diverse. Phylogenetic analysis of putative CYP2B homologs resolved woodrat species as reciprocally monophyletic and suggested evolutionary convergence of distinct homologs on similar key amino acid residues in both species. Homology modelling of the CYP2B enzyme suggests that interspecific differences in substrate preference and function likely result from amino acid differences in the enzyme active site. The characteristics of CYP2B in the specialist, that is greater gene copy number coupled with less sequence variation, are consistent with specialization to a narrow range of dietary toxins.

Differential Effects of Climate on Survival Rates Drive Hybrid Zone Movement

Climate change has been implicated as driving shifts of hybridizing species' range limits [1, 2]. Whether and how much hybrid zones move depends on the relative fitness of hybridzing species under changing conditions [3, 4]. However, fitness is rarely linked to both climatic conditions and movement of hybrid zones, such that the relationship between climate change and hybrid zone dynamics remains tenuous [5]. Here we report how interactions between climate (seasonal precipitation) and competitor densities result in steep differentials in survival, which in turndrive hybrid zone movement for two woodrat species (Neotoma fuscipes and N.macrotis) in central California, USA. Using 6 years of capture-mark-recapture data, we found that the smaller-bodied species, N.macrotis, and hybrids had survival advantages over the larger-bodied N.fuscipes in the contact region during dry winters and wet springs. This pattern of differential survival, with N.macrotis having a consistent advantage over N.fuscipes during our study period, matched the spatial dynamics of the hybrid zone, which moved steadily north into N.fuscipes territory, with its estimated center moving ∼150m north in 6 years. Our findings provide a unique demonstration of range movements emerging from a complex interplay between climate and competition. Although all studysite areas experienced the same climatic conditions, competitive effects created a complex spatial pattern of survival differentials, which in turn influenced hybrid zone movement. Characterization of fitness differentials derived from replicated demographic studies of contact regions between competitors should greatly improve our ability to understand and forecast climate-driven range dynamics.

The Woodrat Gut Microbiota as an Experimental System for Understanding Microbial Metabolism of Dietary Toxins.

The microbial communities inhabiting the alimentary tracts of mammals, particularly those of herbivores, are estimated to be one of the densest microbial reservoirs on Earth. The significance of these gut microbes in influencing the physiology, ecology and evolution of their hosts is only beginning to be realized. To understand the microbiome of herbivores with a focus on nutritional ecology, while evaluating the roles of host evolution and environment in sculpting microbial diversity, we have developed an experimental system consisting of the microbial communities of several species of herbivorous woodrats (genus Neotoma) that naturally feed on a variety of dietary toxins. We designed this system to investigate the long-standing, but experimentally neglected hypothesis that ingestion of toxic diets by herbivores is facilitated by the gut microbiota. Like several other rodent species, the woodrat stomach has a sacculated, non-gastric foregut portion. We have documented a dense and diverse community of microbes in the woodrat foregut, with several genera potentially capable of degrading dietary toxins and/or playing a role in stimulating hepatic detoxification enzymes of the host. The biodiversity of these gut microbes appears to be a function of host evolution, ecological experience and diet, such that dietary toxins increase microbial diversity in hosts with experience with these toxins while novel toxins depress microbial diversity. These microbial communities are critical to the ingestion of a toxic diet as reducing the microbial community with antibiotics impairs the host’s ability to feed on dietary toxins. Furthermore, the detoxification capacity of gut microbes can be transferred from Neotoma both intra and interspecifically to naïve animals that lack ecological and evolutionary history with these toxins. In addition to advancing our knowledge of complex host-microbes interactions, this system holds promise for identifying microbes that could be useful in the treatment of diseases in humans and domestic animals.

Speciation along a shared evolutionary trajectory.

Groups of organisms—whether multiple species or populations of a single species—can differ in several non-exclusive ways. For example, groups may have diverged phenotypically, genetically, or in the evolutionary responses available to them. We tested for the latter of these—response divergence—between 2 species of woodrats: Neotoma fuscipes and Neotoma macrotis. Based on random skewers analyses we found that, despite being well differentiated both phenotypically and genetically, N. fuscipes and N. macrotis appear to be diverging along a shared evolutionary trajectory (r° = 0.895, P = 0.114). Because these species are currently in secondary contact, their phenotypic evolution being along a shared evolutionary axis has important implications. In particular, that their response to selection arising from interspecific interactions will be constrained along the same evolutionary trajectory may reduce the potential for reinforcing selection to maintain species boundaries.

Using the Specialization Framework to Determine Degree of Dietary Specialization in a Herbivorous Woodrat

To be considered a dietary specialist, mammalian herbivores must consume large quantities of a plant species considered "difficult" with respect to nutrient or toxin content, and possess specialized adaptations to deal with plant defensive compounds or low nutritional content. Populations of Neotoma lepida in the Great Basin consume Juniperus osteosperma, a plant heavily defended by terpenes, but a detailed dietary analysis of this population is lacking. Therefore, we investigated the extent of dietary specialization in this species in comparison with the better-studied specialist species, N. stephensi. Microhistological analysis of feces from N. lepida revealed that greater than 90% of their diet in nature was comprised of juniper. In laboratory tolerance trials, N. lepida tolerated a diet of 80% J. osteosperma, similar to that observed for N. stephensi. There was no difference in the abilities of N. lepida and N. stephensi to metabolize hexobarbital, a proxy compound for terpene metabolism. In preference tests of native and non-native juniper species, N. lepida did not exhibit a preference for its native or co-occurring juniper, J. osteosperma, over the non-native species, J. monosperma, whereas N. stephensi preferred its native or co-occurring juniper J. monosperma over non-native J. osteosperma. Behavioral and habitat differences between these woodrat species lead to the categorization of N. stephensi as an obligate juniper specialist with a small range that overlaps that of its preferred food, J. monosperma, and N. lepida as a facultative juniper specialist with a large range, and only a portion of its distribution containing populations that feed extensively on J. osteosperma.

Hybridization and asymmetric introgression across a narrow zone of contact betweenNeotoma fuscipesandN. macrotis(Rodentia: Cricetidae)

When lineages diverge in allopatry and come into secondary contact, we have a unique opportunity to examine the degree to which they have become reproductively isolated from one another and the mechanisms that contribute to rates of interspecific gene flow. If hybridization and introgression have occurred in the past or are ongoing, examining patterns of variation in differentially inherited genetic markers can provide insight into underlying mechanisms determining interspecific reproductive interactions. We investigated genetic variation in a recently discovered contact zone between two species of woodrats (Neotoma fuscipes and N. macrotis) in central coastal California. Previous studies have found evidence of historic hybridization between these species, but an active site of sympatry had yet to be discovered. Here, we describe the first known area of sympatry between the two species and present evidence of ongoing hybridization at this site. We intensively sampled throughout the narrow area of interspecific contact and continuously into the adjacent areas where each taxon existed largely in isolation of the other. We genotyped 851 individuals sampled in a single year at 15 nuclear microsatellite loci and sequenced a portion of the cytochrome b gene in a subset of these to examine patterns of introgression. We find that the area of sympatry is less than 1 km in length, but hybridization appeared to be fairly common, with 15% of the woodrats being of hybrid origin. At least some hybrids are fertile because introgression was evident. However, introgression appeared to be asymmetric with backcrosses toward N. macrotis being more common, a pattern we suspect is due in part to directional mate choice related to differential body size. This study adds to our growing understanding of the nature of species boundaries, especially between lineages that are far along the continuum towards speciation. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 115, 162–172.

Parasite prevalence and community diversity in sympatric and allopatric populations of two woodrat species (Sigmodontinae: Neotoma) in central California.

Patterns of host-parasite association may vary across the landscape in part because of host and parasite diversity, divergence, local ecology, or interactions among these factors. In central coastal California, we quantified parasite prevalence, infection intensity, and diversity in two sister species of woodrats (Neotoma fuscipes and Neotoma macrotis) where the species co-occur (sympatry) and where each species exists alone (allopatry). In feces from 50 adults we identified seven taxa: the protozoans Eimeria, Giardia, and Cryptosporidium, the nematodes Trichuris, Aspicularis, and Eucoleus, and a cestode in the family Anoplocephalidae. Gastrointestinal parasite infection intensity and diversity were higher in males than in females, a difference that was most pronounced in the more aggressive N. fuscipes. Both species had lower infection intensity in sympatry than in allopatry and in sympatry the two species did not differ in infection intensity in total but did maintain distinct parasite communities. Taken together, our findings suggest that host evolutionary differences, including perhaps species-specific patterns of aggressive behavior, as well as local ecology, influence the likelihood of infection by these endoparasite taxa.

Multilocus Characterization of a Woodrat (Genus Neotoma) Hybrid Zone

In order to investigate hybridization between 2 species of woodrats, Neotoma floridana and Neotoma micropus, 103 specimens were collected, in March of 1988, from a known area of sympatry, and compared with reference collections from areas of allopatry. Ten genetic markers, consisting of 7 microsatellite loci, 1 mitochondrial gene (cytochrome-b [Cytb]), and 2 nuclear introns (intron 2 of the vertebrate alcohol dehydrogenase gene [Adh1-I2] and intron 7 of the beta-fibrinogen gene [Fgb-I7]) were used to develop a composite genotype for each individual and for detection of hybridization. Six individuals were identified as pure parental N. micropus, 96 as hybrids, and 1 as pure parental N. floridana Hybrids were formed primarily through matings between complex genotypes, resulting in a high prevalence of individuals classified as backcrosses. The ratio of hybrid classes, population substructure, and presence of significant linkage disequilibrium within the zone of contact could not reject either the hybrid superiority or hybrid equilibrium model as responsible for maintenance of this hybrid zone. The collection date of this dataset (1988) provided not only a point in time assessment of the hybrid zone but also provided opportunities for future comparisons of temporal datasets with the purpose of examining hybrid zone characteristics over multiple generations.

Captivity results in disparate loss of gut microbial diversity in closely related hosts.

The gastrointestinal tracts of animals contain diverse communities of microbes that provide a number of services to their hosts. There is recent concern that these communities may be lost as animals enter captive breeding programmes, due to changes in diet and/or exposure to environmental sources. However, empirical evidence documenting the effects of captivity and captive birth on gut communities is lacking. We conducted three studies to advance our knowledge in this area. First, we compared changes in microbial diversity of the gut communities of two species of woodrats (Neotoma albigula, a dietary generalist, and Neotoma stephensi, which specializes on juniper) before and after 6-9 months in captivity. Second, we investigated whether reintroduction of the natural diet of N. stephensi could restore microbial diversity. Third, we compared the microbial communities between offspring born in captivity and their mothers. We found that the dietary specialist, N. stephensi, lost a greater proportion of its native gut microbiota and overall diversity in response to captivity compared with N. albigula. Addition of the natural diet increased the proportion of the original microbiota but did not restore overall diversity in N. stephensi. Offspring of N. albigula more closely resembled their mothers compared with offspring-mother pairs of N. stephensi. This research suggests that the microbiota of dietary specialists may be more susceptible to captivity. Furthermore, this work highlights the need for further studies investigating the mechanisms underlying how loss of microbial diversity may vary between hosts and what an acceptable level of diversity loss may be to a host. This knowledge will aid conservation biologists in designing captive breeding programmes effective at maintaining microbial diversity. Sequence Accession Numbers: NCBI's Sequence Read Archive (SRA) - SRP033616.