Tania Jenkins

Functionally and phylogenetically diverse plant communities key to soil biota

Recent studies assessing the role of biological diversity for ecosystem functioning indicate that the diversity of functional traits and the evolutionary history of species in a community, not the number of taxonomic units, ultimately drives the biodiversity--ecosystem-function relationship. Here, we simultaneously assessed the importance of plant functional trait and phylogenetic diversity as predictors of major trophic groups of soil biota (abundance and diversity), six years from the onset of a grassland biodiversity experiment. Plant functional and phylogenetic diversity were generally better predictors of soil biota than the traditionally used species or functional group richness. Functional diversity was a reliable predictor for most biota, with the exception of soil microorganisms, which were better predicted by phylogenetic diversity. These results provide empirical support for the idea that the diversity of plant functional traits and the diversity of evolutionary lineages in a community are important for maintaining higher abundances and diversity of soil communities.

MIGRATORY BEHAVIOR OF BIRDS AFFECTS THEIR COEVOLUTIONARY RELATIONSHIP WITH BLOOD PARASITES

Host traits, such as migratory behavior, could facilitate the dispersal of disease‐causing parasites, potentially leading to the transfer of infections both across geographic areas and between host species. There is, however, little quantitative information on whether variation in such host attributes does indeed affect the evolutionary outcome of host–parasite associations. Here, we employ Leucocytozoon blood parasites of birds, a group of parasites closely related to avian malaria, to study host–parasite coevolution in relation to host behavior using a phylogenetic comparative approach. We reconstruct the molecular phylogenies of both the hosts and parasites and use cophylogenetic tools to assess whether each host–parasite association contributes significantly to the overall congruence between the two phylogenies. We find evidence for a significant fit between host and parasite phylogenies in this system, but show that this is due only to associations between nonmigrant parasites and their hosts. We also show that migrant bird species harbor a greater genetic diversity of parasites compared with nonmigrant species. Taken together, these results suggest that the migratory habits of birds could influence their coevolutionary relationship with their parasites, and that consideration of host traits is important in predicting the outcome of coevolutionary interactions.

Experimental plant communities develop phylogenetically overdispersed abundance distributions during assembly.

The importance of competition between similar species in driving community assembly is much debated. Recently, phylogenetic patterns in species composition have been investigated to help resolve this question: phylogenetic clustering is taken to imply environmental filtering, and phylogenetic overdispersion to indicate limiting similarity between species. We used experimental plant communities with random species compositions and initially even abundance distributions to examine the development of phylogenetic pattern in species abundance distributions. Where composition was held constant by weeding, abundance distributions became overdispersed through time, but only in communities that contained distantly related clades, some with several species (i.e., a mix of closely and distantly related species). Phylogenetic pattern in composition therefore constrained the development of overdispersed abundance distributions, and this might indicate limiting similarity between close relatives and facilitation/complementarity between distant relatives. Comparing the phylogenetic patterns in these communities with those expected from the monoculture abundances of the constituent species revealed that interspecific competition caused the phylogenetic patterns. Opening experimental communities to colonization by all species in the species pool led to convergence in phylogenetic diversity. At convergence, communities were composed of several distantly related but species-rich clades and had overdispersed abundance distributions. This suggests that limiting similarity processes determine which species dominate a community but not which species occur in a community. Crucially, as our study was carried out in experimental communities, we could rule out local evolutionary or dispersal explanations for the patterns and identify ecological processes as the driving force, underlining the advantages of studying these processes in experimental communities. Our results show that phylogenetic relations between species provide a good guide to understanding community structure and add a new perspective to the evidence that niche complementarity is critical in driving community assembly.

Biogeography of avian blood parasites (Leucocytozoon spp.) in two resident hosts across Europe: phylogeographic structuring or the abundance- occupancy relationship?

Relationships between hosts and parasites represent complex co‐evolving systems that can vary both temporally and spatially. This variation may result in different phylogeographic outcomes, ranging from highly geographically structured parasite populations comprised of specialist lineages that are locally abundant but have restricted global occupancy to geographically unstructured parasite populations consisting of widespread parasites. Here, we present results from a large biogeographic study of the Leucocytozoon blood parasites of two nonmigrant bird species, conducted at nine sites across Europe. The aim was to determine whether the parasite lineages of the two hosts were phylogeographically structured across Europe. Employing molecular methods, we found a large diversity of parasites, and although overall prevalence varied greatly, the parasites were not genetically structured. Several measures of local parasite abundance were associated with the number of sites that the lineage occurred in, which is consistent with the macroecological phenomenon of the abundance–occupancy relationship. Taken together, our results show that parasite dispersal is somewhat uncoupled to that of the host in this system: we suggest that broad host and/or vector preference may play an important role in determining the distribution of these parasites and in affecting host–parasite coevolution in this system.

Testing Local Adaptation in a Natural Great Tit-Malaria System: An Experimental Approach

Finding out whether Plasmodium spp. are coevolving with their vertebrate hosts is of both theoretical and applied interest and can influence our understanding of the effects and dynamics of malaria infection. In this study, we tested for local adaptation as a signature of coevolution between malaria blood parasites, Plasmodium spp. and its host, the great tit, Parus major. We conducted a reciprocal transplant experiment of birds in the field, where we exposed birds from two populations to Plasmodium parasites. This experimental set-up also provided a unique opportunity to study the natural history of malaria infection in the wild and to assess the effects of primary malaria infection on juvenile birds. We present three main findings: i) there was no support for local adaptation; ii) there was a male-biased infection rate; iii) infection occurred towards the end of the summer and differed between sites. There were also site-specific effects of malaria infection on the hosts. Taken together, we present one of the few experimental studies of parasite-host local adaptation in a natural malaria system, and our results shed light on the effects of avian malaria infection in the wild.

Host shift and cospeciation rate estimation from co-phylogenies

Host shifts can cause novel infectious diseases, and is a key process in diversification. Disentangling the effects of host shift vs. those of cospeciation is non-trivial as both can result in phylogenic congruence. We develop a new framework based on network analysis and Approximate Bayesian Computation to quantify host shift and cospeciation rates in host-parasite systems. Our method enables estimation of the expected time to the next host shift or cospeciation event. We then apply it to avian haemosporidian parasite systems and to the pocket gophers-chewing lice system, and demonstrate that both host shift and cospeciation can be reliably estimated by our method. We confirm that host shifts have shaped the evolutionary history of avian haemosporidian parasites and have played a minor role in the gopher-chewing lice system. Our method is promising for predicting the rate of potential host shifts and thus the emergence of novel infectious diseases.

Avian malaria and bird humoral immune response

BackgroundPlasmodium parasites are known to impose fitness costs on their vertebrate hosts. Some of these costs are due to the activation of the immune response, which may divert resources away from self-maintenance. Plasmodium parasites may also immuno-deplete their hosts. Thus, infected individuals may be less able to mount an immune response to a new pathogen than uninfected ones. However, this has been poorly investigated.MethodsThe effect of Plasmodium infection on bird humoral immune response when encountering a novel antigen was tested. A laboratory experiment was conducted on canaries (Serinus canaria) experimentally infected with Plasmodium relictum (lineage SGS1) under controlled conditions. Birds were immune challenged with an intra-pectoral injection of a novel non-pathogenic antigen (keyhole limpet haemocyanin, KLH). One week later they were challenged again. The immune responses to the primary and to the secondary contacts were quantified as anti-KLH antibody production via enzyme-linked immunosorbent assay (ELISA).ResultsThere was no significant difference in antibody production between uninfected and Plasmodium infected birds at both primary and secondary contact. However, Plasmodium parasite intensity in the blood increased after the primary contact with the antigen.ConclusionsThere was no effect of Plasmodium infection on the magnitude of the humoral immune response. However, there was a cost of mounting an immune response in infected individuals as parasitaemia increased after the immune challenge, suggesting a trade-off between current control of chronic Plasmodium infection and investment against a new immune challenge.

Prevalence and diversity of haemosporidian parasites in the yellow-rumped warbler hybrid zone

Abstract Parasites can play a role in speciation, by exerting different selection pressures on different host lineages, leading to reproductive barriers in regions of possible interbreeding. Hybrid zones therefore offer an ideal system to study the effect of parasites on speciation. Here, we study a hybrid zone in the foothills of the Rocky Mountains where two yellow‐rumped warbler subspecies, Setophaga coronata coronata and S. c. auduboni, interbreed. There is partial reproductive isolation between them, but no evidence of strong assortative mating within the hybrid zone, suggesting the existence of a postzygotic selection against hybrids. Here, we test whether haemosporidian parasites might play a role in selecting against hybrids between S. c. coronata and S. c. auduboni. We screened birds from five transects across the hybrid zone for three phylogenetic groupings of avian haemosporidians Plasmodium, Haemoproteus and Leucocytozoon parasites and quantified intensity of infection. Contrary to our prediction, hybrids did not have higher haemosporidian parasite prevalence. Variation in Haemoproteus prevalence was best explained by an interaction between a birds’ hybrid index and elevation, while the probability of infection with Leucocytozoon parasites was only influenced by elevation. We also found no significant difference in the diversity of haemosporidian lineages between the warbler subspecies and their hybrids. Finally, intensity of infection by Haemoproteus increased significantly with elevation, but was not significantly linked to birds’ hybrid index. In conclusion, our data suggest that haemosporidian parasites do not seem to play a major role in selecting against hybrids in this system.