A Theory of City Biogeography and the Origin of Urban Species

Many of the choices humans make with regard to infrastructure, urban planning and other phenomena have impacts that will last thousands of years. This can readily be seen in modern cities in which contemporary streets run along street grids that were laid out thousands of years prior or even in which ancient viaducts still play a role. However, rarely do evolutionary biologists explicitly consider the future of life likely to be associated with the decisions we are making today. Here, we consider the evolutionary future of species in cities with a focus on the origin of lineages and species. We do so by adjusting evolutionary predictions from the theory of island biogeography so as to correspond to the unique features of cities as islands. Specifically, the species endemic to cities tend to be associated with the gray habitats in cities. Those habitats tend to be dominated by human bodies, pet bodies and stored food. It is among such species where the origin of new lineages is most likely, although most research on evolution in cities has focused on green habitats. We conclude by considering a range of scenarios for the far future and their implications for the origin of lineages and species.

Origin and evolution of the Haustoriidae (Amphipoda): a eulogy for the Haustoriidira

Haustoriid amphipods have received little recent attention and their systematics and phylogenetics are largely unresolved. Some efforts have been made at classifying the family within the broader Amphipoda, but there is persistent incongruence in its placement among different authors and techniques. Furthermore, there exists no phylogenetic hypothesis of intrafamilial relationships. In this work, we evaluate the competing hypotheses on the phylogenetic position of the Haustoriidae within Amphipoda by examining new and previously published sequences of nearly 100 species across 38 families. We find strong support for the Haustoriidae as basal gammarids, and that other families placed within the parvorder ‘Haustoriidira’ are spread across Amphipoda. The radiation began during the Eocene and may have been driven in North America by the rapid filling of a coastal niche opened by the Chesapeake Bay impact crater. Unlike previous work, we find that the Pacific-endemic genus Eohaustorius is the most basal haustoriid, and that it separated from the rest of the family ~31 Mya. Finally, we provide taxonomic recommendations for relationships within Haustoriidae, including the elevation of a new genus, Cryptohaustorius gen. nov.. We conclude by recommending that the ‘Haustoriidira’ be abandoned.

Morphological differentiation of Peromyscus leucopus and P. maniculatus in East Texas

The white-footed deer mouse (Peromyscus leucopus) and the North American deer mouse (P. maniculatus) are widely distributed throughout North America, often with overlapping distributions. These species are believed to be sympatric east of the Balcones fault zone in Texas, but records from natural history collections indicate that P. maniculatus is not common from this region. Given that these two species are notoriously difficult to differentiate morphologically, it is possible that specimens have been incorrectly identified and that P. maniculatus may be rare or not present in East Texas. This study aims to determine if P. leucopus and P. maniculatus can be differentiated morphologically east of the Balcones fault zone in Texas. Cranial and external characters from genetically identified specimens representing each species were analyzed using traditional and geometric morphometric methods. Morphological analyses revealed that genetically identified specimens of P. leucopus and P. maniculatus from east of the Balcones fault zone could be differentiated using a suite of morphological characters. Many of the specimens of P. leucopus used in this study were originally misidentified, suggesting that P. maniculatus is rare in East Texas.

March Mammal Madness and the power of narrative in science outreach

March Mammal Madness is a science outreach project that, over the course of several weeks in March, reaches hundreds of thousands of people in the United States every year. We combine four approaches to science outreach - gamification, social media platforms, community event(s), and creative products - to run a simulated tournament in which 64 animals compete to become the tournament champion. While the encounters between the animals are hypothetical, the outcomes rely on empirical evidence from the scientific literature. Players select their favored combatants beforehand, and during the tournament scientists translate the academic literature into gripping "play-by-play" narration on social media. To date ~1100 scholarly works, covering almost 400 taxa, have been transformed into science stories. March Mammal Madness is most typically used by high-school educators teaching life sciences, and we estimate that our materials reached ~1% of high-school students in the United States in 2019. Here we document the intentional design, public engagement, and magnitude of reach of the project. We further explain how human psychological and cognitive adaptations for shared experiences, social learning, narrative, and imagery contribute to the widespread use of March Mammal Madness.

Cranial morphology of captive mammals: a meta-analysis

BACKGROUND

Captive facilities such as zoos are uniquely instrumental in conservation efforts. To fulfill their potential as bastions for conservation, zoos must preserve captive populations as appropriate proxies for their wild conspecifics; doing so will help to promote successful reintroduction efforts. Morphological changes within captive populations may be detrimental to the fitness of individual animals because these changes can influence functionality; thus, it is imperative to understand the breadth and depth of morphological changes occurring in captive populations. Here, we conduct a meta-analysis of scientific literature reporting comparisons of cranial measures between captive and wild populations of mammals. We investigate the pervasiveness of cranial differences and whether cranial morphological changes are associated with ecological covariates specific to individual species, such as trophic level, dietary breadth, and home range size.

RESULTS

Cranial measures of skull length, skull width, and the ratio of skull length-to-width differed significantly between many captive and wild populations of mammals reported in the literature. Roughly half of captive populations differed from wild populations in at least one cranial measure, although the degree of changes varied. Carnivorous species with a limited dietary breadth displayed the most consistent changes associated with skull widening. Species with a more generalized diet displayed less morphological changes in captivity.

CONCLUSIONS

Wild and captive populations of mammals differed in cranial morphology, but the nature and magnitude of their cranial differences varied considerably across taxa. Although changes in cranial morphology occur in captivity, specific changes cannot be generalized for all captive mammal populations. The nature of cranial changes in captivity may be specific to particular taxonomic groups; thus, it may be possible to establish expectations across smaller taxonomic units, or even disparate groups that utilize their cranial morphology in a similar way. Given that morphological changes occurring in captive environments like zoos have the potential to limit reintroduction success, our results call for a critical evaluation of current captive husbandry practices to prevent unnecessary morphological changes.

Building Natural History Collections for the Twenty-First Century and Beyond

Natural history collections (NHCs) are important resources for a diverse array of scientific fields. Recent digitization initiatives have broadened the user base of NHCs, and new technological innovations are using materials generated from collections to address novel scientific questions. Simultaneously, NHCs are increasingly imperiled by reductions in funding and resources. Ensuring that NHCs continue to serve as a valuable resource for future generations will require the scientific community to increase their contribution to and acknowledgement of collections. We provide recommendations and guidelines for scientists to support NHCs, focusing particularly on new users that may be unfamiliar with collections. We hope that this perspective will motivate debate on the future of NHCs and the role of the scientific community in maintaining and improving biological collections.

Phylogeography and taxonomic revision of Nelson’s pocket mouse (Chaetodipus nelsoni)

Chaetodipus nelsoni occurs on rocky substrates across the Mexican Altiplano. We investigated phylogeographic diversity within the species using morphologic, karyotypic, and molecular data. Data from nuclear (AFLP) and mitochondrial DNA support three distinct genetic groups with minimal substructuring coincident with biogeographic barriers previously identified in the Chihuahuan Desert and drainage basins of the Altiplano. We examined the morphological and karyotypic data in light of the molecular data. The results support recognition of three species within the currently accepted widespread C. nelsoni: 1) C. nelsoni restricted to a distribution centered on the El Salado River Basin; 2) elevation of C. n. collis to species, with two subspecies: one centered on Trans-Pecos Texas, the other on the Mapimí Basin (new subspecies); and 3) recognition of a new species, C. durangae, centered on the Nazas Basin and upper Río Mezquital drainage.

Red imported fire ant (Solenopsis invicta) aggression influences the behavior of three hard tick species

Few studies have documented the indirect effects of predators on tick behavior. We conducted behavioral assays in the laboratory to quantify the effects of a highly abundant predator, the red imported fire ant (Solenopsis invicta), on three species of ticks endemic to the southern USA: the lone star tick (Amblyomma americanum), the Gulf Coast tick (A. maculatum), and the Cayenne tick (A. mixtum). We documented ant aggression toward ticks (biting, carrying, and stinging) and determined the effects of ants on tick activity. Ticks were significantly less active in the presence of fire ants, and tick activity was negatively associated with ant aggression, but in many cases the effects of fire ants on ticks varied by tick species, stage, and engorgement status. For example, fire ants took half as long (~ 62 s) to become aggressive toward unfed A. americanum adults compared with unfed A. maculatum, and only ~ 8 s to become aggressive toward engorged A. maculatum nymphs. Correspondingly, the activity of unfed A. americanum adults and engorged A. maculatum nymphs was reduced by 67 and 93%, respectively, in the presence of fire ants. This reduction in tick activity translated to less questing by unfed ticks and less time spent walking by engorged nymphs. Our results suggest that fire ants may have important non-consumptive effects on ticks and demonstrate the importance of measuring the indirect effects of predators on tick behavior.

Temporal and spatial dynamics of competitive parapatry in chewing lice

We synthesize observations from 1979 to 2016 of a contact zone involving two subspecies of pocket gophers (Thomomys bottae connectens and T. b. opulentus) and their respective chewing lice (Geomydoecus aurei and G. centralis) along the Río Grande Valley in New Mexico, U.S.A., to test predictions about the dynamics of the zone. Historically, the natural flood cycle of the Rio Grande prevented contact between the two subspecies of pocket gophers. Flood control measures completed in the 1930s permitted contact, thus establishing the hybrid zone between the pocket gophers and the contact zone between their lice (without hybridization). Since that time, the pocket gopher hybrid zone has stabilized, whereas the northern chewing louse species has replaced the southern louse species at a consistent rate of ~150 m/year. The 0.2-0.8 width of the replacement zone has remained constant, reflecting the constant rate of chewing louse species turnover on a single gopher and within a local pocket gopher population. In contrast, the full width of the replacement zone (northernmost G. centralis to southernmost G. aurei) has increased annually. By employing a variety of metrics of the species replacement zone, we are better able to understand the dynamics of interactions between and among the chewing lice and their pocket gopher hosts. This research provides an opportunity to observe active species replacement and resulting distributional shifts in a parasitic organism in its natural setting.

Novel Poxvirus in Proliferative Lesions of Wild Rodents in East Central Texas, USA

Northern pygmy mice from 2 localities in East Central Texas, USA, had proliferative epidermal lesions on the tail and feet. Electron microscopy of lesion tissue revealed poxvirus. Phylogenetic analyses indicated the virus differed 35% from its closest relatives, the Chordopoxvirinae. Future research is needed to determine whether this virus could affect human health.

Loss of genetic diversity, recovery and allele surfing in a colonizing parasite, Geomydoecus aurei

Understanding the genetic consequences of changes in species distributions has wide-ranging implications for predicting future outcomes of climate change, for protecting threatened or endangered populations and for understanding the history that has led to current genetic patterns within species. Herein, we examine the genetic consequences of range expansion over a 25-year period in a parasite (Geomydoecus aurei) that is in the process of expanding its geographic range via invasion of a novel host. By sampling the genetics of 1,935 G. aurei lice taken from 64 host individuals collected over this time period using 12 microsatellite markers, we test hypotheses concerning linear spatial expansion, genetic recovery time and allele surfing. We find evidence of decreasing allelic richness (AR) with increasing distance from the source population, supporting a linear, stepping stone model of spatial expansion that emphasizes the effects of repeated bottleneck events during colonization. We provide evidence of post-bottleneck genetic recovery, with average AR of infrapopulations increasing about 30% over the 225-generation span of time observed directly in this study. Our estimates of recovery rate suggest, however, that recovery has plateaued and that this population may not reach genetic diversity levels of the source population without further immigration from the source population. Finally, we employ a grid-based sampling scheme in the region of ongoing population expansion and provide empirical evidence for the power of allele surfing to impart genetic structure on a population, even under conditions of selective neutrality and in a place that lacks strong barriers to gene flow.

Decreased small mammal and on-host tick abundance in association with invasive red imported fire ants (Solenopsis invicta)

Invasive species may impact pathogen transmission by altering the distributions and interactions among native vertebrate reservoir hosts and arthropod vectors. Here, we examined the direct and indirect effects of the red imported fire ant (Solenopsis invicta) on the native tick, small mammal and pathogen community in southeast Texas. Using a replicated large-scale field manipulation study, we show that small mammals were more abundant on treatment plots where S. invicta populations were experimentally reduced. Our analysis of ticks on small mammal hosts demonstrated a threefold increase in the ticks caught per unit effort on treatment relative to control plots, and elevated tick loads (a 27-fold increase) on one common rodent species. We detected only one known human pathogen (Rickettsia parkeri), present in 1.4% of larvae and 6.7% of nymph on-host Amblyomma maculatum samples but with no significant difference between treatment and control plots. Given that host and vector population dynamics are key drivers of pathogen transmission, the reduced small mammal and tick abundance associated with S. invicta may alter pathogen transmission dynamics over broader spatial scales.

Development and Characterization of 12 Novel Polymorphic Microsatellite Loci for the Mammal Chewing Louse Geomydoecus aurei (Insecta: Phthiraptera) and a Comparison of Next-Generation Sequencing Approaches for Use in Parasitology

Next-generation sequencing methodologies open the door for evolutionary studies of wildlife parasites. We used 2 next-generation sequencing approaches to discover microsatellite loci in the pocket gopher chewing louse Geomydoecus aurei for use in population genetic studies. In one approach, we sequenced a library enriched for microsatellite loci; in the other approach, we mined microsatellites from genomic sequences. Following microsatellite discovery, promising loci were tested for amplification and polymorphism in 390 louse individuals from 13 pocket gopher hosts. In total, 12 loci were selected for analysis (6 from each methodology), none of which exhibited evidence of null alleles or heterozygote deficiencies. These 12 loci showed adequate genetic diversity for population-level analyses, with 3-9 alleles per locus with an average H_E per locus ranging from 0.32 to 0.70. Analysis of Molecular Variance (AMOVA) indicated that genetic variation among infrapopulations accounts for a low, but significant, percentage of the overall genetic variation, and individual louse infrapopulations showed F_ST values that were significantly different from zero in the majority of pairwise infrapopulation comparisons, despite all 13 infrapopulations being taken from the same locality. Therefore, these 12 polymorphic markers will be useful at the infrapopulation and population levels for future studies involving G. aurei. This study shows that next-generation sequencing methodologies can successfully be used to efficiently obtain data for a variety of evolutionary questions.

An Assessment of Host Associations, Geographic Distributions, and Genetic Diversity of Avian Chewing Lice (Insecta: Phthiraptera) from Benin

Host associations of highly host-specific chewing lice (Insecta: Phthiraptera) across multiple avian species remains fairly undocumented in the West African country of Benin. Two hundred and seventeen bird specimens collected from multiple localities across Benin and housed at the Texas A&M University Biodiversity Research and Teaching Collections were examined for lice. Lice were identified and genetic data (mitochondrial COI and nuclear EF-1α genes) were obtained and phylogenetically analyzed. In total, we found 15 host associations, 7 of which were new to science. Genetically, most lice from Benin were unique and could represent new species. Based on host associations and unique genetic lineages, we estimate we discovered a minimum of 4 and possibly as many as 8 new chewing louse species. Given the lack of current data on chewing louse species distributions in Benin, this study adds to the knowledge of host associations, geographic distribution, and genetic variability of avian chewing louse species in West Africa.

Effects of 16S rDNA sampling on estimates of the number of endosymbiont lineages in sucking lice

Phylogenetic trees can reveal the origins of endosymbiotic lineages of bacteria and detect patterns of co-evolution with their hosts. Although taxon sampling can greatly affect phylogenetic and co-evolutionary inference, most hypotheses of endosymbiont relationships are based on few available bacterial sequences. Here we examined how different sampling strategies of Gammaproteobacteria sequences affect estimates of the number of endosymbiont lineages in parasitic sucking lice (Insecta: Phthirapatera: Anoplura). We estimated the number of louse endosymbiont lineages using both newly obtained and previously sequenced 16S rDNA bacterial sequences and more than 42,000 16S rDNA sequences from other Gammaproteobacteria. We also performed parametric and nonparametric bootstrapping experiments to examine the effects of phylogenetic error and uncertainty on these estimates. Sampling of 16S rDNA sequences affects the estimates of endosymbiont diversity in sucking lice until we reach a threshold of genetic diversity, the size of which depends on the sampling strategy. Sampling by maximizing the diversity of 16S rDNA sequences is more efficient than randomly sampling available 16S rDNA sequences. Although simulation results validate estimates of multiple endosymbiont lineages in sucking lice, the bootstrap results suggest that the precise number of endosymbiont origins is still uncertain.

Phylogeographic assessment of the northern pygmy mouse, Baiomys taylori

The northern pygmy mouse, Baiomys taylori, occurs throughout the Trans-Mexican Volcanic Belt and southern Altiplano of central Mexico and extends northward in 3 projections into northern Mexico and the United States. We used mitochondrial DNA (from the cytochrome-b and NADH dehydrogenase 2 genes) and morphological data to assess diversity within B. taylori across its geographic range in relation to recognized subspecies and putative physiographic filter-barriers. Our results indicate 5 distinct mitochondrial clades despite little morphological variation across the species’ geographic range. The Sierra Madre Oriental and Sierra Madre Occidental separate clades representing the eastern (Gulf coastal lowlands), central (Altiplano), and Pacific coastal lowlands, which appear to be divided into 3 major mitochondrial clades. Based on a preliminary analysis of cranial morphology, we are able to reject the Balcones Escarpment of Texas as an impediment to the well-documented recent northern expansion of the species, while we are unable to reject a causal role of filter-barriers elsewhere in subspecific differentiation. Revision of subspecific taxonomy must await further genetic sampling, particularly along the western and southeastern portions of the species’ distribution.

El ratón pigmeo norteño, Baiomys taylori, se distribuye a través del Eje Volcánico Transmexicano y la parte sur del Altiplano del centro de México y se extiende hacia el norte de México y los Estados Unidos en tres direcciones. Utilizamos ADN mitocondrial (del citocromo-b y del gen NADH deshidrogenasa) y datos morfológicos para evaluar la diversidad dentro de B. taylori a través de su rango geográfico en relación con las subespecies reconocidas y las supuestas barreras-filtro fisiográficas. Nuestros resultados indican 5 clados mitocondriales distintos a pesar de la escasa variación morfológica a lo largo de su rango geográfico. La Sierra Madre Oriental y la Sierra Madre Occidental separan los clados representantes de las tierras bajas del este (tierras bajas del Golfo), del centro (Altiplano), y las tierras bajas del Pacífico, que parecen estar divididas en 3 clados mitocondriales principales. Basados en un análisis preliminar de la morfología craneal, pudimos rechazar el Escarpe de Balcones de Texas como un impedimento a la bien documentada expansión norteña de la especie, mientras que no fue posible rechazar el rol causal de las otras barreras-filtro en la diferenciación subespecífica. La revisión de la taxonomía subespecífica deberá esperar un mayor muestreo genético, en particular a lo largo de las porciones oeste y sureste de la distribución de la especie.

Populations at risk: conservation genetics of kangaroo mice (Microdipodops) of the Great Basin Desert

The Great Basin Desert of western North America has experienced frequent habitat alterations due to a complex biogeographic history and recent anthropogenic impacts, with the more recent alterations likely resulting in the decline of native fauna and flora. Dark (Microdipodops megacephalus) and pallid (M. pallidus) kangaroo mice are ecological specialists found within the Great Basin Desert and are potentially ideal organisms for assessing ecosystem health and inferring the biogeographic history of this vulnerable region. Herein, newly acquired nuclear-encoded microsatellite loci were utilized to assess patterns of variation within and among spatially discrete groups of kangaroo mice and to evaluate gene flow, demographic trends, and genetic integrity. Results confirm that there are at least three genetically distinct units within M. megacephalus and two such units within M. pallidus. The three units of M. megacephalus appear to have different demographic histories, with effectively no gene flow among them since their divergence. Similarly, the two units of M. pallidus also appear to have experienced different demographic histories, with effectively no gene exchange. Contemporary effective population sizes of all groups within Microdipodops appear to be low (<500), suggesting that each genetic lineage may have difficulty coping with changing environmental pressures and hence may be at risk of extirpation. Results of this study indicate that each Microdipodops group should be recognized, and therefore managed, as a separate unit in an effort to conserve these highly specialized taxa that contribute to the diversity of the Great Basin Desert ecosystem. The Great Basin Desert of western North America has experienced frequent habitat alterations due to a complex biogeographic history and recent anthropogenic impacts, with the more recent alterations likely resulting in the decline of native fauna and flora. Herein, newly acquired nuclear-encoded microsatellite loci were utilized to assess patterns of variation within and among spatially discrete groups of the dark (Microdipodops megacephalus) and pallid (M. pallidus) kangaroo mouse, and to evaluate gene flow, demographic trends, and genetic integrity. Results of this study indicate that each Microdipodops group should be recognized, and therefore managed, as a separate unit in an effort to conserve these highly specialized taxa that contribute to the diversity of the Great Basin Desert ecosystem (photo credit J. C. Hafner).

River barriers and cryptic biodiversity in an evolutionary museum

The Riverine Barriers Hypothesis (RBH) posits that tropical rivers can be effective barriers to gene flow, based on observations that range boundaries often coincide with river barriers. Over the last 160 years, the RBH has received attention from various perspectives, with a particular focus on vertebrates in the Amazon Basin. To our knowledge, no molecular assessment of the RBH has been conducted on birds in the Afrotropics, despite its rich avifauna and many Afrotropical bird species being widely distributed across numerous watersheds and basins. Here, we provide the first genetic evidence that an Afrotropical river has served as a barrier for birds and for their lice, based on four understory bird species collected from sites north and south of the Congo River. Our results indicate near-contemporaneous, Pleistocene lineage diversification across the Congo River in these species. Our results further indicate differing levels of genetic variation in bird lice; the extent of this variation appears linked to the life-history of both the host and the louse. Extensive cryptic diversity likely is being harbored in Afrotropical forests, in both understory birds and their lice. Therefore, these forests may not be "museums" of old lineages. Rather, substantial evolutionary diversification may have occurred in Afrotropical forests throughout the Pleistocene, supporting the Pleistocene Forest Refuge Hypothesis. Strong genetic variation in birds and their lice within a small part of the Congo Basin forest indicates that we may have grossly underestimated diversity in the Afrotropics, making these forests home of substantial biodiversity in need of conservation.

Cophylogeny on a fine scale: Geomydoecus chewing lice and their pocket gopher hosts, Pappogeomys bulleri

Many species of pocket gophers and their ectoparasitic chewing lice have broadly congruent phylogenies, indicating a history of frequent codivergence. For a variety of reasons, phylogenies of codiverging hosts and parasites are expected to be less congruent for more recently diverged taxa. This study is the first of its scale in the pocket gopher and chewing louse system, with its focus entirely on comparisons among populations within a single species of host and 3 chewing louse species in the Geomydoecus bulleri species complex. We examined mitochondrial DNA from a total of 46 specimens of Geomydoecus lice collected from 11 populations of the pocket gopher host, Pappogeomys bulleri. We also examined nuclear DNA from a subset of these chewing lice. Louse phylogenies were compared with a published pocket gopher phylogeny. Contrary to expectations, we observed a statistically significant degree of parallel cladogenesis in these closely related hosts and their parasites. We also observed a higher rate of evolution in chewing louse lineages than in their corresponding pocket gopher hosts. In addition, we found that 1 louse species (Geomydoecus burti) may not be a valid species, that subspecies within G. bulleri are not reciprocally monophyletic, and that morphological and genetic evidence support recognition of a new species of louse, Geomydoecus pricei.

Palaeoclimatic events, dispersal and migratory losses along the Afro-European axis as drivers of biogeographic distribution in Sylvia warblers

BACKGROUND

The Old World warbler genus Sylvia has been used extensively as a model system in a variety of ecological, genetic, and morphological studies. The genus is comprised of about 25 species, and 70% of these species have distributions at or near the Mediterranean Sea. This distribution pattern suggests a possible role for the Messinian Salinity Crisis (from 5.96-5.33 Ma) as a driving force in lineage diversification. Other species distributions suggest that Late Miocene to Pliocene Afro-tropical forest dynamics have also been important in the evolution of Sylvia lineages. Using a molecular phylogenetic hypothesis and other methods, we seek to develop a biogeographic hypothesis for Sylvia and to explicitly assess the roles of these climate-driven events.

RESULTS

We present the first strongly supported molecular phylogeny for Sylvia. With one exception, species fall into one of three strongly supported clades: one small clade of species distributed mainly in Africa and Europe, one large clade of species distributed mainly in Africa and Asia, and another large clade with primarily a circum-Mediterranean distribution. Asia is reconstructed as the ancestral area for Sylvia. Long-distance migration is reconstructed as the ancestral character state for the genus, and sedentary behavior subsequently evolved seven times.

CONCLUSION

Molecular clock calibration suggests that Sylvia arose in the early Miocene and diverged into three main clades by 12.6 Ma. Divergence estimates indicate that the Messinian Salinity Crisis had a minor impact on Sylvia. Instead, over-water dispersals, repeated loss of long-distance migration, and palaeo-climatic events in Africa played primary roles in Sylvia divergence and distribution.

Multiple lineages of lice pass through the K-Pg boundary

For modern lineages of birds and mammals, few fossils have been found that predate the Cretaceous-Palaeogene (K-Pg) boundary. However, molecular studies using fossil calibrations have shown that many of these lineages existed at that time. Both birds and mammals are parasitized by obligate ectoparasitic lice (Insecta: Phthiraptera), which have shared a long coevolutionary history with their hosts. Evaluating whether many lineages of lice passed through the K-Pg boundary would provide insight into the radiation of their hosts. Using molecular dating techniques, we demonstrate that the major louse suborders began to radiate before the K-Pg boundary. These data lend support to a Cretaceous diversification of many modern bird and mammal lineages.

Origin of clothing lice indicates early clothing use by anatomically modern humans in Africa

Clothing use is an important modern behavior that contributed to the successful expansion of humans into higher latitudes and cold climates. Previous research suggests that clothing use originated anywhere between 40,000 and 3 Ma, though there is little direct archaeological, fossil, or genetic evidence to support more specific estimates. Since clothing lice evolved from head louse ancestors once humans adopted clothing, dating the emergence of clothing lice may provide more specific estimates of the origin of clothing use. Here, we use a Bayesian coalescent modeling approach to estimate that clothing lice diverged from head louse ancestors at least by 83,000 and possibly as early as 170,000 years ago. Our analysis suggests that the use of clothing likely originated with anatomically modern humans in Africa and reinforces a broad trend of modern human developments in Africa during the Middle to Late Pleistocene.

Evolutionary history of mammalian sucking lice (Phthiraptera: Anoplura)

Background

Sucking lice (Phthiraptera: Anoplura) are obligate, permanent ectoparasites of eutherian mammals, parasitizing members of 12 of the 29 recognized mammalian orders and approximately 20% of all mammalian species. These host specific, blood-sucking insects are morphologically adapted for life on mammals: they are wingless, dorso-ventrally flattened, possess tibio-tarsal claws for clinging to host hair, and have piercing mouthparts for feeding. Although there are more than 540 described species of Anoplura and despite the potential economical and medical implications of sucking louse infestations, this study represents the first attempt to examine higher-level anopluran relationships using molecular data. In this study, we use molecular data to reconstruct the evolutionary history of 65 sucking louse taxa with phylogenetic analyses and compare the results to findings based on morphological data. We also estimate divergence times among anopluran taxa and compare our results to host (mammal) relationships.

Results

This study represents the first phylogenetic hypothesis of sucking louse relationships using molecular data and we find significant conflict between phylogenies constructed using molecular and morphological data. We also find that multiple families and genera of sucking lice are not monophyletic and that extensive taxonomic revision will be necessary for this group. Based on our divergence dating analyses, sucking lice diversified in the late Cretaceous, approximately 77 Ma, and soon after the Cretaceous-Paleogene boundary (ca. 65 Ma) these lice proliferated rapidly to parasitize multiple mammalian orders and families.

Conclusions

The diversification time of sucking lice approximately 77 Ma is in agreement with mammalian evolutionary history: all modern mammal orders are hypothesized to have diverged by 75 Ma thus providing suitable habitat for the colonization and radiation of sucking lice. Despite the concordant timing of diversification events early in the association between anoplurans and mammals, there is substantial conflict between the host and parasite phylogenies. This conflict is likely the result of a complex history of host switching and extinction events that occurred throughout the evolutionary association between sucking lice and their mammalian hosts. It is unlikely that there are any ectoparasite groups (including lice) that tracked the early and rapid radiation of eutherian mammals.

Mutational meltdown in primary endosymbionts: selection limits Muller's ratchet

Background

Primary bacterial endosymbionts of insects (p-endosymbionts) are thought to be undergoing the process of Muller's ratchet where they accrue slightly deleterious mutations due to genetic drift in small populations with negligible recombination rates. If this process were to go unchecked over time, theory predicts mutational meltdown and eventual extinction. Although genome degradation is common among p-endosymbionts, we do not observe widespread p-endosymbiont extinction, suggesting that Muller's ratchet may be slowed or even stopped over time. For example, selection may act to slow the effects of Muller's ratchet by removing slightly deleterious mutations before they go to fixation thereby causing a decrease in nucleotide substitutions rates in older p-endosymbiont lineages.

Methodology/Principal Findings

To determine whether selection is slowing the effects of Muller's ratchet, we determined the age of the Candidatus Riesia/sucking louse assemblage and analyzed the nucleotide substitution rates of several p-endosymbiont lineages that differ in the length of time that they have been associated with their insect hosts. We find that Riesia is the youngest p-endosymbiont known to date, and has been associated with its louse hosts for only 13–25 My. Further, it is the fastest evolving p-endosymbiont with substitution rates of 19–34% per 50 My. When comparing Riesia to other insect p-endosymbionts, we find that nucleotide substitution rates decrease dramatically as the age of endosymbiosis increases.

Conclusions/Significance

A decrease in nucleotide substitution rates over time suggests that selection may be limiting the effects of Muller's ratchet by removing individuals with the highest mutational loads and decreasing the rate at which new mutations become fixed. This countering effect of selection could slow the overall rate of endosymbiont extinction.

Geographic distributions and origins of human head lice (Pediculus humanus capitis) based on mitochondrial data

Human head lice (Pediculus humanus capitis) are subdivided into 3 deeply divergent mitochondrial clades (Clades A, B, and C), each having unique geographical distributions. Determining the evolutionary history and geographic distribution of these mitochondrial clades can elucidate the evolutionary history of the lice as well as their human hosts. Previous data suggest that lice belonging to mitochondrial Clade B may have originated in North America or Asia; however, geographic sampling and sample sizes have been limited. With newly collected lice, we calculate the relative frequency, geographic distribution, and genetic diversity of louse mitochondrial clades to determine the geographic origin of lice belonging to Clade B. In agreement with previous studies, genetic diversity data support a North American origin of Clade B lice. It is likely that lice belonging to this mitochondrial clade recently migrated to other geographic localities, e.g., Europe and Australia, and, if not already present, may disperse further to occupy all geographic regions.

Multigene analysis of phylogenetic relationships and divergence times of primate sucking lice (Phthiraptera: Anoplura)

Cospeciation between hosts and parasites offers a unique opportunity to use information from parasites to infer events in host evolutionary history. Although lice (Insecta: Phthiraptera) are known to cospeciate with their hosts and have frequently served as important markers to infer host evolutionary history, most molecular studies are based on only one or two markers. Resulting phylogenies may, therefore, represent gene histories (rather than species histories), and analyses of multiple molecular markers are needed to increase confidence in the results of phylogenetic analyses. Herein, we phylogenetically examine nine molecular markers in primate sucking lice (Phthiraptera: Anoplura) and we use these markers to estimate divergence times among louse lineages. Individual and combined analyses of these nine markers are, for the most part, congruent, supporting relationships hypothesized in previous studies. Only one marker, the nuclear protein-coding gene Histone 3, has a significantly different tree topology compared to the other markers. The disparate evolutionary history of this marker, however, has no significant effect on topology or nodal support in the combined phylogenetic analyses. Therefore, phylogenetic results from the combined data set likely represent a solid hypothesis of species relationships. Additionally, we find that simultaneous use of multiple markers and calibration points provides the most reliable estimates of louse divergence times, in agreement with previous studies estimating divergences among species. Estimates of phylogenies and divergence times also allow us to verify the results of [Reed, D.L., Light, J.E., Allen, J.M., Kirchman, J.J., 2007. Pair of lice lost or parasites regained: the evolutionary history of anthropoid primate lice. BMC Biol. 5, 7.]; there was probable contact between gorilla and archaic hominids roughly 3 Ma resulting in a host switch of Pthirus lice from gorillas to archaic hominids. Thus, these results provide further evidence that data from cospeciating organisms can yield important information about the evolutionary history of their hosts.

What's in a name: the taxonomic status of human head and body lice

Human head lice (Anoplura: Pediculidae: Pediculus) are pandemic, parasitizing countless school children worldwide due to the evolution of insecticide resistance, and human body (clothing) lice are responsible for the deaths of millions as a result of vectoring several deadly bacterial pathogens. Despite the obvious impact these lice have had on their human hosts, it is unclear whether head and body lice represent two morphological forms of a single species or two distinct species. To assess the taxonomic status of head and body lice, we provide a synthesis of publicly available molecular data in GenBank, and we compare phylogenetic and population genetic methods using the most diverse geographic and molecular sampling presently available. Our analyses find reticulated networks, gene flow, and a lack of reciprocal monophyly, all of which indicate that head and body lice do not represent genetically distinct evolutionary units. Based on these findings, as well as inconsistencies of morphological, behavioral, and ecological variability between head and body lice, we contend that no known species concept would recognize these louse morphotypes as separate species. We recommend recognizing head and body lice as morphotypes of a single species, Pediculus humanus, until compelling new data and analyses (preferably analyses of fast evolving nuclear markers in a coalescent framework) indicate otherwise.

Pair of lice lost or parasites regained: the evolutionary history of anthropoid primate lice

BACKGROUND

The parasitic sucking lice of primates are known to have undergone at least 25 million years of coevolution with their hosts. For example, chimpanzee lice and human head/body lice last shared a common ancestor roughly six million years ago, a divergence that is contemporaneous with their hosts. In an assemblage where lice are often highly host specific, humans host two different genera of lice, one that is shared with chimpanzees and another that is shared with gorillas. In this study, we reconstruct the evolutionary history of primate lice and infer the historical events that explain the current distribution of these lice on their primate hosts.

RESULTS

Phylogenetic and cophylogenetic analyses suggest that the louse genera Pediculus and Pthirus are each monophyletic, and are sister taxa to one another. The age of the most recent common ancestor of the two Pediculus species studied matches the age predicted by host divergence (ca. 6 million years), whereas the age of the ancestor of Pthirus does not. The two species of Pthirus (Pthirus gorillae and Pthirus pubis) last shared a common ancestor ca. 3-4 million years ago, which is considerably younger than the divergence between their hosts (gorillas and humans, respectively), of approximately 7 million years ago.

CONCLUSION

Reconciliation analysis determines that there are two alternative explanations that account for the current distribution of anthropoid primate lice. The more parsimonious of the two solutions suggests that a Pthirus species switched from gorillas to humans. This analysis assumes that the divergence between Pediculus and Pthirus was contemporaneous with the split (i.e., a node of cospeciation) between gorillas and the lineage leading to chimpanzees and humans. Divergence date estimates, however, show that the nodes in the host and parasite trees are not contemporaneous. Rather, the shared coevolutionary history of the anthropoid primates and their lice contains a mixture of evolutionary events including cospeciation, parasite duplication, parasite extinction, and host switching. Based on these data, the coevolutionary history of primates and their lice has been anything but parsimonious.