Testing the Mating System Model of Parasite Complex Life Cycle Evolution Reveals Demographically Driven Mixed Mating.

AbstractMany parasite species use multiple host species to complete development; however, empirical tests of models that seek to understand factors impacting evolutionary changes or maintenance of host number in parasite life cycles are scarce. Specifically, one model incorporating parasite mating systems that posits that multihost life cycles are an adaptation to prevent inbreeding in hermaphroditic parasites and thus preclude inbreeding depression remains untested. The model assumes that loss of a host results in parasite inbreeding and predicts that host loss can evolve only if there is no parasite inbreeding depression.

Characterization of 21 microsatellite loci for the precocious, grass-shrimp trematode Alloglossidium renale.

We developed microsatellite markers to use in studying the population genetics of the trematode Alloglossidium renale, a fluke with a precocious life cycle where sexual maturation occurs in a grass shrimp. Among 21 tested loci in a Mississippi population sample, 14 were polymorphic, 12 of which significantly deviated from Hardy-Weinberg Equilibrium (HWE). We estimated identity disequilibrium (ID) to confirm whether the deviations from HWE were due to significant amounts of selfing or due to technical factors.

Population genomics of helminth parasites.

Next generation sequencing technologies have facilitated a shift from a few targeted loci in population genetic studies to whole genome approaches. Here, we review the types of questions and inferences regarding the population biology and evolution of parasitic helminths being addressed within the field of population genomics. Topics include parabiome, hybridization, population structure, loci under selection and linkage mapping.

TREMATODE CLONE ABUNDANCE DISTRIBUTIONS: AN ECO-EVOLUTIONARY LINK BETWEEN PARASITE TRANSMISSION AND PARASITE MATING SYSTEMS.

Most trematodes and some cestodes have obligate life history features that include an asexual developmental stage that can produce genetically-identical individuals (clonemates) followed by an adult stage with sexual reproduction. These life history features can influence the evolutionary mechanism of inbreeding in parasites, especially among self-compatible hermaphroditic endoparasites whose mating opportunities are restricted to within hosts. As clonemate mating in hermaphroditic species produces a genetic inbreeding signature identical to that of self-mating, it is important to understand how clonemates are transmitted through their life stages.

QUANTIFYING BILATERAL INFECTION PATTERNS IN THE TREMATODE ALLOGLOSSIDIUM RENALE.

Within-host distributions of parasites can have relevance to parasite competition, parasite mating, transmission, and host health. We examined the within-host distribution of the adult trematode Alloglossidium renale infecting the paired antennal glands of grass shrimp. There are 4 possible parasite distributions for infections of paired organs: random, uniform, biased aggregation to 1 particular organ (e.

Clonemate cotransmission supports a role for kin selection in a puppeteer parasite.

Host manipulation by parasites is a fascinating evolutionary outcome, but adaptive scenarios that often accompany even iconic examples in this popular field of study are speculative. Kin selection has been invoked as a means of explaining the evolution of an altruistic-based, host-manipulating behavior caused by larvae of the lancet fluke in ants. Specifically, cotransmission of larval clonemates from a snail first host to an ant second host is presumed to lead to a puppeteer parasite in the ant's brain that has clonemates in the ant abdomen.

Recognizing the Causes of Parasite Morphological Variation to Resolve the Status of a Cryptogenic Pentastome.

Exotic species can threaten biodiversity by introducing parasites to native hosts. Thus, it is critical to identify if the same parasite species infects both native and exotic hosts. However, developmental- or environmental-induced morphological variation may render species identification ambiguous.

Little to no inbreeding depression in a tapeworm with mixed mating.

Meta-studies on hermaphrodites have found a negative relationship between primary selfing rates and levels of inbreeding depression (ID) and, thus, generally support purging in inbred systems. However, in plants, high among-taxa variance in ID results in no difference in the mean ID between outcrossing and mixed-mating taxa. Selective interference likely explains high ID among mixed-mating taxa, whereas low levels of ID among mixed-mating taxa are not as stressed.

Hurdles in the evolutionary epidemiology of : Pseudogenes, incongruence between taxonomy and DNA sequence variants, and cryptic lineages.

, the rat lungworm, is a zoonotic pathogen that is one of the leading causes of eosinophilic meningitis worldwide. This parasite is regarded as an emerging pathogen with a global range expansion out of southeastern Asia post-WWII. To date, molecular systematic/phylogeographic studies on have mainly used two mitochondrial (mtDNA) markers, (1) and (), where the focus has largely been descriptive in terms of reporting local patterns of haplotype variants.

Resolving evolutionary changes in parasite life cycle complexity: Molecular phylogeny of the trematode genus Alloglossidium indicates more than one origin of precociousness.

The evolutionary causes and consequences of changes in complex life cycles are of central importance in parasitology. However, data remain limited because in part, knowledge on phylogenetic relationships among species that differ in life cycle patterns remains scarce. We present a molecular phylogeny of the trematode genus Alloglossidium, which contains several species that display precocious (a.

Role of parasite transmission in promoting inbreeding: II. Pedigree reconstruction reveals sib-transmission and consequent kin-mating.

Even though parasitic flatworms are one of the most species-rich groups of hermaphroditic organisms, we know virtually nothing of their mating systems (selfing or kin-mating rates) in nature. Hence, we lack an understanding of the role of inbreeding in parasite evolution. The natural mating systems of parasitic flatworms have remained elusive due to the inherent difficulty in generating progeny-array data in many parasite systems.

Role of parasite transmission in promoting inbreeding: I. Infection intensities drive individual parasite selfing rates.

Among parasitic organisms, inbreeding has been implicated as a potential driver of host-parasite co-evolution, drug-resistance evolution and parasite diversification. Yet, fundamental topics about how parasite life histories impact inbreeding remain to be addressed. In particular, there are no direct selfing-rate estimates for hermaphroditic parasites in nature.

Cryptic lineage diversity in the zoonotic pathogen Angiostrongylus cantonensis.

Delimitation of species is still a necessity among parasitic pathogens especially where morphological characters provide limited discernibility. Identification of cryptic lineages (independently evolving lineages that are morphologically similar) is critical as there could be lineage-specific traits that are of epidemiological importance. Angiostrongylus cantonensis is a zoonotic pathogen that can cause eosinophilic meningitis in humans.

Characterization of nine microsatellite loci for Dicrocoelium dendriticum, an emerging liver fluke of ungulates in North America, and their use to detect clonemates and random mating.

This study characterizes polymorphic microsatellite loci from adults of the liver fluke Dicrocoelium dendriticum sampled from a population of sympatric beef cattle and wapiti in a region of emergence in southern Alberta, Canada. We also scrutinized the markers to validate their use in studying the population genetics of this complex life cycle parasite. Among the nine loci described, four deviated significantly from Hardy Weinberg Equilibrium (HWE) due to technical artefacts.

Species mtDNA genetic diversity explained by infrapopulation size in a host-symbiont system.

Understanding what shapes variation in genetic diversity among species remains a major challenge in evolutionary ecology, and it has been seldom studied in parasites and other host-symbiont systems. Here, we studied mtDNA variation in a host-symbiont non-model system: 418 individual feather mites from 17 feather mite species living on 17 different passerine bird species. We explored how a surrogate of census size, the median infrapopulation size (i.

Physiological Status Drives Metabolic Rate in Mediterranean Geckos Infected with Pentastomes.

Negative effects of parasites on their hosts are well documented, but the proximate mechanisms by which parasites reduce their host's fitness are poorly understood. For example, it has been suggested that parasites might be energetically demanding. However, a recent meta-analysis suggests that they have statistically insignificant effects on host resting metabolic rate (RMR).

Evolutionary consequence of a change in life cycle complexity: A link between precocious development and evolution toward female-biased sex allocation in a hermaphroditic parasite.

The evolutionary consequences of changes in the complex life cycles of parasites are not limited to the traits that directly affect transmission. For instance, mating systems that are altered due to precocious sexual maturation in what is typically regarded as an intermediate host may impact opportunities for outcrossing. In turn, reproductive traits may evolve to optimize sex allocation.

Does a facultative precocious life cycle predispose the marine trematode Proctoeces cf. lintoni to inbreeding and genetic differentiation among host species?

Intraspecific variability in parasite life cycle complexity (number of hosts and species of hosts in the life cycle) may have an impact how parasite genetic variation is partitioned among individual parasites, host individuals or host species within a given area. Among digenean trematodes, a three-host life cycle is common. However, a few species are precocious and may reach sexual maturity in what is typically regarded as the second intermediate host.

Alloglossidium floridense n. sp. (Digenea: Macroderoididae) from a spring run in North Central Florida.

A new species of Alloglossidium is described from the intestines of 2 madtom species (Noturus leptacanthus and Noturus gyrinus) that were collected from the run of a small, unnamed spring system that drains into the Santa Fe River, Florida. Alloglossidium floridense n. sp.

Testing local-scale panmixia provides insights into the cryptic ecology, evolution, and epidemiology of metazoan animal parasites.

When every individual has an equal chance of mating with other individuals, the population is classified as panmictic. Amongst metazoan parasites of animals, local-scale panmixia can be disrupted due to not only non-random mating, but also non-random transmission among individual hosts of a single host population or non-random transmission among sympatric host species. Population genetics theory and analyses can be used to test the null hypothesis of panmixia and thus, allow one to draw inferences about parasite population dynamics that are difficult to observe directly.

Host genetics and population structure effects on parasitic disease.

Host genetic factors exert significant influences on differential susceptibility to many infectious diseases. In addition, population structure of both host and parasite may influence disease distribution patterns. In this study, we assess the effects of population structure on infectious disease in two populations in which host genetic factors influencing susceptibility to parasitic disease have been extensively studied.

Ascariasis in people and pigs: new inferences from DNA analysis of worm populations.

Ascaris is a large parasitic roundworm (nematode) of the small intestine of humans and pigs. These roundworms cause the socioeconomically important disease, ascariasis. For the past 20 years, molecular markers have been used in studies on Ascaris and ascariasis, and added valuable information to the understanding of these roundworms.

Testing Mendelian inheritance from field-collected parasites: Revealing duplicated loci enables correct inference of reproductive mode and mating system.

Cryptic aspects of parasite population biology, e.g., mating systems, are increasingly being inferred from polymorphic and co-dominant genetic markers such as microsatellite loci.

More than meets the eye: detecting cryptic microgeographic population structure in a parasite with a complex life cycle.

Nonrandom recruitment of parasites among hosts can lead to genetic differentiation among hosts and mating dynamics that promote inbreeding. It has been hypothesized that strictly aquatic parasites with intermediate hosts will behave as panmictic populations among hosts because ample opportunity exists for random mixing of unrelated individuals during transmission to the definitive host. A previous allozyme study on the marine trematode Lecithochirium fusiforme did not support this hypothesis; in that, there was genetic differentiation among, and significant heterozygote deficiencies within, definitive hosts.