María José Ruiz-López

Genetic evidence for multiple introduction events of raccoons (Procyon lotor) in Spain

The common raccoon (Procyon lotor) is endemic to Central and North America, although non-native populations have become established around the world. In Spain, growing evidence of the introduction of raccoons has been reported across the country in the last decade, especially in Central Spain where the largest population is thought to occur. We used mitochondrial and microsatellite DNA data to investigate the genetics of invasive raccoons in Central Spain and to infer: the number of introduction events, the number of founders and the genetic variability of the introduced populations compared to a native population. We found that at least two introduction events have occurred along the Jarama and Henares Rivers in Central Spain, which currently constitute two genetically differentiated subpopulations. In both localities the number of effective founders from a native population was estimated as 2–4 individuals. These newly founded populations have expanded and show evidence of incipient contact and reproduction between them. This may allow for an increase in the genetic variability and adaptive potential of the population(s), possibly increasing the difficulty of controlling this invasive species. Our results reveal the ability to longitudinally monitor the genetics of the raccoon range expansion and emphasize the urgent need to control the pet trade of potentially invasive species.

The Effect and Relative Importance of Neutral Genetic Diversity for Predicting Parasitism Varies across Parasite Taxa

Understanding factors that determine heterogeneity in levels of parasitism across individuals is a major challenge in disease ecology. It is known that genetic makeup plays an important role in infection likelihood, but the mechanism remains unclear as does its relative importance when compared to other factors. We analyzed relationships between genetic diversity and macroparasites in outbred, free-ranging populations of raccoons (Procyon lotor). We measured heterozygosity at 14 microsatellite loci and modeled the effects of both multi-locus and single-locus heterozygosity on parasitism using an information theoretic approach and including non-genetic factors that are known to influence the likelihood of parasitism. The association of genetic diversity and parasitism, as well as the relative importance of genetic diversity, differed by parasitic group. Endoparasite species richness was better predicted by a model that included genetic diversity, with the more heterozygous hosts harboring fewer endoparasite species. Genetic diversity was also important in predicting abundance of replete ticks (Dermacentor variabilis). This association fit a curvilinear trend, with hosts that had either high or low levels of heterozygosity harboring fewer parasites than those with intermediate levels. In contrast, genetic diversity was not important in predicting abundance of non-replete ticks and lice (Trichodectes octomaculatus). No strong single-locus effects were observed for either endoparasites or replete ticks. Our results suggest that in outbred populations multi-locus diversity might be important for coping with parasitism. The differences in the relationships between heterozygosity and parasitism for the different parasites suggest that the role of genetic diversity varies with parasite-mediated selective pressures.

The interplay between clumped resources, social aggregation, and genetic relatedness in the raccoon

The extent to which individuals within a population live in groups is often variable, as group formation is most likely to occur when the benefits of group-living outweigh the costs. The distribution of resources can underpin the likelihood of group formation by altering costs associated with individuals aggregating. By influencing the extent of group-living, resources may also influence relatedness patterns. To address this, we examined relatedness in raccoons (Procyon lotor) by combining spatial and genetic data in an experimental framework wherein resources were manipulated. We tested for differences in patterns of genetic relatedness among 12 sites subject to three treatments: no supplemental food; supplemental food added in a dispersed, non-predictable fashion; and clumped, predictable food supplements resulting in aggregations. We measured mean relatedness for >500 raccoons using blood and hair samples genotyped at 14 nuclear microsatellites and tested for differences between sites and sexes. For two sites, we radio-tracked raccoons and calculated volume of intersection (VI) values, which measure the probability of co-occurrence between individuals’ home ranges, and calculated the relationship between VI and relatedness. Telemetry data indicated that raccoons exposed to clumped food shifted their home ranges, in turn perturbing patterns of relatedness between individuals, especially among females. This was exhibited through a positive association between VI and relatedness for females at the site with dispersed food, which was not observed among males or at the site with clumped food. At the landscape level, sites differed significantly in mean relatedness, but there were no clear patterns that corresponded to treatments. Overall, our observations support expectations of the resource dispersion hypothesis, wherein individuals modify ranges to include clumped resources if the costs of tolerating other individuals are low.

Multiple Paternity In the American Dog Tick, Dermacentor variabilis (Acari: Ixodidae)

Abstract: The reproductive strategies and variation in reproductive success of ticks are poorly understood. We determined variation in multiple paternity in the American dog tick Dermancentor variabilis. In total, 48 blood-engorged female ticks and 22 male companion ticks were collected from 13 raccoon (Procyon lotor) hosts. In the laboratory, 56.3% of blood-engorged females laid eggs, of which 37.0% hatched or showed signs of development. We examined the presence of multiple paternity in the ensuing clutches by genotyping groups of eggs and larvae at 5 microsatellite loci and subtracting the known maternal alleles, thereby identifying male-contributed alleles. Seventy-five percent of the clutches presented multiple paternity, with a mode of 2 fathers siring the clutch. Males associated with the females on the host always sired some offspring. In 1 case, a male was the sire of clutches derived from 2 females, indicating both polygyny and polyandry may occur for this species. These results, combined with those of several other recent studies, suggest that multiple paternity might be frequent for ixodid ticks.

Genomic Resources Notes Accepted 1 December 2014 – 31 January 2015

This article documents the public availability of (i) transcriptome sequence data and assembly for the rostrum dace (Leuciscus burdigalensis) naturally infected by a copepod ectoparasite (Tracheliastes polycolpus) and (ii) SNPs identified and validated from RAD sequencing for the Ugandan red colobus (Procolobus rufomitratus tephrosceles) using RAD sequencing.

Major Histocompatibility Complex, demographic, and environmental predictors of antibody presence in a free-ranging mammal

Major Histocompatibility Complex (MHC) variability plays a key role in pathogen resistance, but its relative importance compared to environmental and demographic factors that also influence resistance is unknown. We analyzed the MHC II DRB exon 2 for 165 raccoons (Procyon lotor) in Missouri (USA). For each animal we also determined the presence of immunoglobulin G (IgG) and immunoglobulin M (IgM) antibodies to two highly virulent pathogens, canine distemper virus (CDV) and parvovirus. We investigated the role of MHC polymorphism and other demographic and environmental factors previously associated with predicting seroconversion. In addition, using an experimental approach, we studied the relative importance of resource availability and contact rates. We found important associations between IgG antibody presence and several MHC alleles and supertypes but not between IgM antibody presence and MHC. No effect of individual MHC diversity was found. For CDV, supertype S8, one allele within S8 (Prlo-DRB(∗)222), and a second allele (Prlo-DRB(∗)204) were positively associated with being IgG+, while supertype S4 and one allele within the supertype (Prlo-DRB(∗)210) were negatively associated with being IgG+. Age, year, and increased food availability were also positively associated with being IgG+, but allele Prlo-DRB(∗)222 was a stronger predictor. For parvovirus, only one MHC allele was negatively associated with being IgG+ and age and site were stronger predictors of seroconversion. Our results show that negative-frequency dependent selection is likely acting on the raccoon MHC and that while the role of MHC in relation to other factors depends on the pathogen of interest, it may be one of the most important factors predicting successful immune response.

Cis-Regulatory Evolution in a Wild Primate: Infection-Associated Genetic Variation Drives Differential Expression of MHC-DQA1 In-Vitro

Few studies have combined genetic association analyses with functional characterization of infection‐associated SNPs in natural populations of nonhuman primates. Here, we investigate the relationship between host genetic variation, parasitism and natural selection in a population of red colobus (Procolobus rufomitratus tephrosceles) in Kibale National Park, Uganda. We collected parasitological, cellular and genomic data to test the following hypotheses: (i) MHC‐DQA1 regulatory genetic variation is associated with control of whipworm (Trichuris) infection in a natural population of red colobus; (ii) infection‐associated SNPs are functional in driving differential gene expression in vitro; and (iii) balancing selection has shaped patterns of variation in the MHC‐DQA1 promoter. We identified two SNPs in the MHC‐DQA1 promoter, both in transcription factor binding sites, and both of which are associated with decreased control of Trichuris infection. We characterized the function of both SNPs by testing differences in gene expression between the two alleles of each SNP in two mammalian cell lines. Alleles of one of the SNPs drove differential gene expression in both cell lines, while the other SNP drove differences in expression in one of the cell lines. Additionally, we found evidence of balancing selection acting on the MHC‐DQA1 promoter, including extensive trans‐species polymorphisms between red colobus and other primates, and an excess of intermediate‐frequency alleles relative to genome‐wide, coding and noncoding RADseq data. Our data suggest that balancing selection provides adaptive regulatory flexibility that outweighs the consequences of increased parasite infection intensity in heterozygotes.