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Estimates of trematode diversity are inaccurate due to unrecognized cryptic species and phenotypic plasticity within species. Integrative taxonomy (genetics, morphology and host use) increases the clarity of species delineation and improves knowledge of parasite biology. In this study, we used this approach to resolve taxonomic issues and test hypotheses of cryptic species in a genus of trematode, Quinqueserialis. Specimens from throughout North America were field collected from hosts and obtained from museums. We found three morphologically distinct groups and successfully sequenced specimens from two of these groups. DNA sequencing at the 28S and CO1 gene regions revealed that two of the three groups were genetically distinct. One genetic group included two morphological clusters demonstrating host-induced phenotypic plasticity within Quinqueserialis quinqueserialis. The other unique genetic group is a novel species, Quinqueserialis kinsellai n. sp., which is described herein. Our study illustrates the importance of integrating multiple sources of evidence when investigating trematode diversity to account for the influence of cryptic species or phenotypic plasticity. However, further sampling is needed to understand Quinqueserialis spp. diversity as some species have no genetic information associated with them.

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.k.a., progenetic) life cycles (i.e., maturation in what is typically regarded as an intermediate host). The molecular phylogeny contrasts with previous morphological and life-history based phylogenetic hypotheses. In particular, a precocious life cycle wherein leeches are used as final hosts evolved early in the history of the genus. Among the remaining species, which are a separate clade, a three-host life cycle using ictalurid catfishes is ancestral. Furthermore, there are at least two additional independent evolutionary events that lead to a precocious life cycle where a catfish host is lost and a crustacean is used as a final host. We conclude with a discussion on how existing hypotheses on the evolution of precociousness, and parasite life cycle complexity in general, may or may not relate to the patterns observed in genus Alloglossidium., (Copyright © 2018 Elsevier Inc. All rights reserved.)

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. Here, we test the hypothesis that sex allocation evolved toward a more female-biased function in populations of the hermaphroditic digenean trematode Alloglossidium progeneticum that can precociously reproduce in their second hosts. In these precocious populations, parasites are forced to self-fertilize as they remain encysted in their second hosts. In contrast, parasites in obligate three-host populations have more opportunities to outcross in their third host. We found strong support that in populations with precocious development, allocation to male resources was greatly reduced. We also identified a potential phenotypically plastic response in a body size sex allocation relationship that may be driven by the competition for mates. These results emphasize how changes in life cycle patterns that alter mating systems can impact the evolution of reproductive traits in parasites., (© 2015 The Author(s). Evolution © 2015 The Society for the Study of Evolution.)

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. is morphologically very similar to other nonprecocious Alloglossidium spp. that use ictalurids as definitive hosts, but can be distinguished by a combination of its smaller overall size (length and width), large eggs in relation to its small body size, position of the vitellaria, ovary shape, and position of the ovary in relation to the cirrus sac. A comparison of nuclear rDNA sequences (spanning partial 18s, complete ITS1, 5.8s, ITS2, and partial 28s regions) showed that A. floridense n. sp. diverged by 0.70-3.17% from the other 4, nonprecocious species that infect ictalurids (Alloglossidium corti, Alloglossidium fonti, Alloglossidium geminum, and Alloglossidium kenti). The new species of Alloglossidium, described herein, is the first of the genus to be reported from Florida and the first to be recorded from N. leptacanthus . In light of the subtle morphological differences among the nonprecocious species that infect ictalurids, we discuss how previous descriptions of species traits that are not supported with genetic data are difficult to interpret because of the possible past nonrecognition of distinct species.

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. We provide an outline that addresses 3 tiered questions when testing parasite panmixia on local scales: is there greater than 1 parasite population/species, is there genetic subdivision amongst infrapopulations within a host population, and is there asexual reproduction or a non-random mating system? In this review, we highlight the evolutionary significance of non-panmixia on local scales and the genetic patterns that have been used to identify the different factors that may cause or explain deviations from panmixia on a local scale. We also discuss how tests of local-scale panmixia can provide a means to infer parasite population dynamics and epidemiology of medically relevant parasites.