Structure, Development, and Behaviour of New Strigeatoid Metacercariae from Subtropical Fishes of South America

1969 ◽  
Vol 26 (4) ◽  
pp. 753-786 ◽  
Author(s):  
Lothar Szidat
Keyword(s):  
Life Cycles ◽  
Trematode Species ◽  
South American ◽  
Endocrine Activity ◽  
Specific Memory ◽  
Primitive Species ◽  
History Of ◽  
New Research ◽  
Fish Hosts ◽  
Host Parasite

Eighteen species of metacercariae of the order Strigeatoidea (Trematoda, Digenea) are described from tropical and subtropical freshwater fishes of Argentina. Sixteen of them belong to the superfamily Strigeoidea and two to Clinostomatoidea. Ten are new species, five belong to previously known trematode species, and three are not specifically named.On the basis of the morphology of these metacercariae, probable life cycles and host–parasite relations are discussed. A general conclusion is drawn that the South American trematodes are more primitive than their counterparts from other continents.Different groups of fish hosts are recognized, each with a different history of association with their present environment. Originally marine fishes adapted to life in fresh water with the aid of increased endocrine activity, primarily thyroid activity. The high levels of endocrine secretions affected the parasites of these fishes, causing metacercariae to develop neotenically. The hosts which were originally freshwater appear to exert less influence on their parasites. Their metacercariae have a more or less normal course of development.Attention is drawn to the evolution in behaviour of strigeoid metacercariae. Primitive species infect less protected sites in the host. With progressive evolution, increasingly more protected sites are selected by the parasite. The evolution culminates in infection of the lens of the eye, which offers the best protection to the parasite against destructive influences of the environment.It is suggested that the metacercariae are guided to their selected infection site by an "engram," or a specific memory, developed and fixed in the course of many generations. New research into parasite behaviour is urged.

The effect of trematode parthenitae on the growth of Onoba aculeus, Littorina saxatilis and L. obtusata (Gastropoda: Prosobranchia)

1999 ◽  
Vol 79 (2) ◽  
pp. 273-280 ◽  
Author(s):  
A.M. Gorbushin ◽  
I.A. Levakin
Keyword(s):  
Life History ◽  
White Sea ◽  
Trematode Species ◽  
Snail Species ◽  
Littorina Saxatilis ◽  
Growth Responses ◽  
The White Sea ◽  
Growth Study ◽  
History Of ◽  
Host Parasite

To determine whether modern theories predict snail growth responses to trematode infestation a field growth study of Onoba aculeus, Littorina saxatilis and L. obtusata infected with two closely related Microphallidae trematodes was conducted in the White Sea. In each of the three host–parasite combinations studied trematode infection causes inhibition of snail reproduction. However, contrary to the classical interpretation of the gigantic growth of infected snails as a side effect of parasitic castration, the presented study failed to demonstrate that Microphallus piriformes causes gigantism in Littorina. The infection tended to stunt growth in L. obtusata and had no significant effect on growth rate of L. saxatilis. In contrast, gigantic growth was observed in O. aculeus infected with M. pseudopygmaeus. Considering that both trematode species are very similar biologically, the discrepancy is attributed to differences in the life history of the snail's hosts. Onoba aculeus is a relatively short-lived snail (2.5–3 y). The lifespan of L. saxatilis and L. obtusata is much longer (up to 9–11 y). These findings agree with a previously reported ‘energetic’ hypothesis that predicts growth alterations in accordance with life history variations of the snail species.

Coevolutionary interactions between host life histories and parasite life cycles

Parasitology ◽  
1998 ◽  
Vol 116 (S1) ◽  
pp. S47-S55 ◽  
Author(s):  
J. C. Koella ◽  
P. Agnew ◽  
Y. Michalakis
Keyword(s):  
Life History ◽  
Life Cycle ◽  
Life Histories ◽  
Life History Traits ◽  
Evolutionary Ecology ◽  
Life Cycles ◽  
Microsporidian Parasite ◽  
History Of ◽  
Host Life ◽  
Host Parasite

SummarySeveral recent studies have discussed the interaction of host life-history traits and parasite life cycles. It has been observed that the life-history of a host often changes after infection by a parasite. In some cases, changes of host life-history traits reduce the costs of parasitism and can be interpreted as a form of resistance against the parasite. In other cases, changes of host life-history traits increase the parasite's transmission and can be interpreted as manipulation by the parasite. Alternatively, changes of host's life-history traits can also induce responses in the parasite's life cycle traits. After a brief review of recent studies, we treat in more detail the interaction between the microsporidian parasite Edhazardia aedis and its host, the mosquito Aedes aegypti. We consider the interactions between the host's life-history and parasite's life cycle that help shape the evolutionary ecology of their relationship. In particular, these interactions determine whether the parasite is benign and transmits vertically or is virulent and transmits horizontally.Key words: host-parasite interaction, life-history, life cycle, coevolution.

Suburbs in transition: new approaches to suburban history

Urban History ◽  
2007 ◽  
Vol 34 (2) ◽  
pp. 317-337 ◽  
Author(s):  
RUTH MCMANUS ◽  
PHILIP J. ETHINGTON
Keyword(s):  
Twentieth Century ◽  
Research Agenda ◽  
Life Cycles ◽  
Suburban History ◽  
History Of ◽  
Late Twentieth ◽  
New Perspective ◽  
New Research ◽  
Late Twentieth Century ◽  
Scholarly Attention

The history of suburbs has received so much scholarly attention in recent decades that it is time to take stock of what has been established, in order to discern aspects of suburbs that are still unknown. To date, the main lines of inquiry have been dedicated to the origins, growth, diverse typologies, culture and politics of suburbs, as well as to newer topics such as the gendered nature of suburban space. The vast majority of these studies have been about particular times and places. The authors propose a new perspective on the study of suburbs, one which will begin to investigate the transformations of suburbs after they have been established. Taking the entire era from the mid-nineteenth century through to the late twentieth century as a whole, it is argued that suburbs should be subjected to a longitudinal analysis, examining their development in the context of metropolises that usually enveloped them within a generation or two of their founding. It is proposed that investigation of these ‘transitions’ should be undertaken in parallel with the changes that occur in the life-cycles of their residents. It is suggested that an exploration of the interaction of these factors will open a broad new research agenda for suburban history as a subfield of urban history.

scholarly journals Anatomy, Embryology and Life Cycle of Lophophytum, a Root-Holoparasitic Plant

2021 ◽  
Author(s):  
Hector Arnaldo Sato ◽  
Ana Maria Gonzalez
Keyword(s):  
Life Cycle ◽  
Fruit Development ◽  
Embryo Sac ◽  
Life Cycles ◽  
South American ◽  
Evolutionary Trend ◽  
Stems And Leaves ◽  
Holoparasitic Plant ◽  
Host Parasite

The most extreme manifestation of parasitism occurs in holoparasites, plants that are totally achlorophyllous. Among them, the genus Lophophytum (Balanophoraceae) is characterized by an aberrant vegetative body called a tuber, devoid of stems and leaves. The genus is exclusively South American, comprising five taxa, which parasitize the roots of trees or shrubs. This review focuses on the Argentine species of the genus: L. leandri and L. mirabile subsp. bolivianum. Topics covered include: morphology and anatomy of the vegetative body and host–parasite connection; structure, anatomy and development of the staminate and pistillate flowers; sporogenesis and gametogenesis, embryo sac inversion; endospermogenesis, embryogenesis and fruit development. The evolutionary trend in the gynoecium and embryo sac of the Balanophoraceae is also discussed to reflect the variability. Finally, observations were made on the synchronization of the life cycles of the parasites and hosts to infer possible ways by which parasitism has evolved, until now unknown.

Helminth parasites of South American fishes: current status and characterization as a model for studies of biodiversity

2016 ◽  
Vol 91 (2) ◽  
pp. 150-164 ◽  
Author(s):  
J.L. Luque ◽  
F.B. Pereira ◽  
P.V. Alves ◽  
M.E. Oliva ◽  
J.T. Timi
Keyword(s):  
South America ◽  
Life Cycles ◽  
Fish Parasites ◽  
Current Status ◽  
South American ◽  
Helminth Parasites ◽  
Research Groups ◽  
Ecological Data ◽  
Host Parasite ◽  
Diverse Groups

AbstractThe South American subcontinent supports one of the world's most diverse and commercially very important ichthyofauna. In this context, the study of South American fish parasites is of increased relevance in understanding their key roles in ecosystems, regulating the abundance or density of host populations, stabilizing food webs and structuring host communities. It is hard to estimate the number of fish parasites in South America. The number of fish species studied for parasites is still low (less than 10%), although the total number of host–parasite associations (HPAs) found in the present study was 3971. Monogeneans, with 835 species (1123 HPAs, 28.5%), and trematodes, with 662 species (1127 HPAs, 30.9%), are the more diverse groups. Data gathered from the literature are useful to roughly estimate species richness of helminths from South American fish, even though there are some associated problems: the reliability of information depends on accurate species identification; the lack of knowledge about life cycles; the increasing number of discoveries of cryptic species and the geographically biased number of studies. Therefore, the closest true estimations of species diversity and distribution will rely on further studies combining both molecular and morphological approaches with ecological data such as host specificity, geographical distribution and life-cycle data. Research on biodiversity of fish parasites in South America is influenced by problems such as funding, taxonomic impediments and dispersion of research groups. Increasing collaboration, interchange and research networks in the context of globalization will enable a promising future for fish parasitology in South America.

The First Americans: The Current Debate

2016 ◽  
Vol 46 (4) ◽  
pp. 543-561 ◽  
Author(s):  
Herbert S. Klein
Keyword(s):  
Early History ◽  
Western Hemisphere ◽  
Archaeological Sites ◽  
Current Debate ◽  
South American ◽  
Genetic Studies ◽  
The Past ◽  
History Of ◽  
First Americans ◽  
New Research

Scholars from multiple disciplines generally agree about new models for the origin and dating of migration to the Western Hemisphere, replacing the rigid Clovis-first model that had dominated texts for the past fifty years. This new research has not resolved all of the questions relating to this migration; serious controversies still exist. But the development of the new field of genetic studies and the recent opening of major South American archaeological sites has resolved many older debates and has provided a far more nuanced and complex early history of mankind in the Western Hemisphere than existed before.

FBI and Religion

2017 ◽  
Keyword(s):  
Religious Orientation ◽  
Religious Communities ◽  
Academic Scholarship ◽  
History Of ◽  
Interdisciplinary Assessment ◽  
Civic Religion ◽  
New Research ◽  
The Relationship ◽  
The Way

This volume is an interdisciplinary assessment of the relationship between religion and the FBI. We recount the history of the FBI’s engagement with multiple religious communities and with aspects of public or “civic” religion such as morality and respectability. The book presents new research to explain roughly the history of the FBI’s interaction with religion over approximately one century, from the pre-Hoover period to the post-9/11 era. Along the way, the book explores vexed issues that go beyond the particulars of the FBI’s history—the juxtaposition of “religion” and “cult,” the ways in which race can shape the public’s perceptions of religion (and vica versa), the challenges of mediating between a religious orientation and a secular one, and the role and limits of academic scholarship as a way of addressing the differing worldviews of the FBI and some of the religious communities it encounters.

Clause Structure and Word Order in the History of German

2018 ◽  
Keyword(s):  
Word Order ◽  
Left Periphery ◽  
Structural Factors ◽  
Clause Structure ◽  
Verb Second ◽  
Verb Forms ◽  
History Of ◽  
New Research ◽  
The Right ◽  
Theoretical Analyses

Over roughly the last decade, there has been a notable rise in new research on historical German syntax in a generative perspective. This volume presents a state-of-the-art survey of this thriving new line of research by leading scholars in the field, combining it with new insights into the syntax of historical German. It is the first comprehensive and concise generative historical syntax of German covering numerous central aspects of clause structure and word order, tracing them throughout various historical stages. Each chapter combines a solid empirical basis and valid descriptive generalizations with reference also to the more traditional topological model of the German clause with a detailed discussion of theoretical analyses couched in the generative framework. The volume is divided into three parts according to the main parts of the clause: the left periphery dealing with verbal placement and the filling of the prefield (verb second, verb first, verb third orders) as well as adverbial connectives; the middle field including discussion of pronominal syntax, order of full NPs and the history of negation; and the right periphery with chapters on basic word order (OV/VO), prosodic and information-structural factors, and the verbal complex including the development of periphrastic verb forms and the phenomena of IPP (infinitivus pro participio) and ACI (accusativus cum infinitivo). This book thus provides a convenient overview of current research on the major issues concerning historical German clause structure both for scholars interested in more traditional description and for those interested in formal accounts of diachronic syntax.

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