Trematode behaviours and the perceptual worlds of parasites

2004 ◽  
Vol 82 (2) ◽  
pp. 292-315 ◽  
Author(s):  
M V.K Sukhdeo ◽  
S C Sukhdeo
Keyword(s):  
Life Histories ◽  
Empirical Studies ◽  
Host Finding ◽  
Free Living ◽  
Theoretical Predictions ◽  
Neuromuscular Systems ◽  
Innate Behaviour ◽  
Complex Patterns ◽  
Patterns And Processes ◽  
Trematode Parasites

There is a great deal of empirical data and theoretical predictions on the patterns and processes of trematode behaviour, particularly in relation to host-finding activities by the free-living stages and site-finding migrations by the parasitic stages within their hosts. Ecological and evolutionary models of trematode life histories often make explicit assumptions about how these organisms must perceive and respond to signals in their worlds as they move from host to host and as they parasitize each host. Nevertheless, it is unclear how natural selection shapes the parasites' behavioural strategies. In addition, at each stage in their life cycle, trematodes are adorned with elaborate sensory organs and possess sophisticated neuromuscular systems, but it is not clear how they use these complex machinery to perceive their worlds. The purpose of this review is to address this question through insights gathered from a century of research on trematode behaviour. Core theoretical assumptions from modern animal behaviour are used to provide the context for this analysis; a key concept is that all animals have unique perceptual worlds that may be inferred from their behaviours. A critical idea is that all animals possess complex patterns of innate behaviour which can be released by extremely specific signals from the environment. The evidence suggests that trematode parasites live in ecologically predictable aquatic and internal host environments where they perceive only small subsets of the total information available from the environment. A general conclusion is that host finding in miracidia and cercaria, and site-finding by trematodes migrating within their definitive hosts, is accomplished through the release of innate patterns of behaviours which are adaptive within the context of conditions in the worm's environment. Examples from empirical studies are used to support the contention that, despite the apparent complexity of their free-living and parasitic environments, the perceptual worlds of trematodes are impoverished, and complex patterns of behaviour may be released by only a few signals in their environment.

scholarly journals Diversity–disturbance relationships: frequency and intensity interact

2012 ◽  
Vol 8 (5) ◽  
pp. 768-771 ◽  
Author(s):  
Alex R. Hall ◽  
Adam D. Miller ◽  
Helen C. Leggett ◽  
Stephen H. Roxburgh ◽  
Angus Buckling ◽  
...  
Keyword(s):  
Species Diversity ◽  
Empirical Evidence ◽  
Empirical Studies ◽  
Ecological Theory ◽  
Intermediate Disturbance Hypothesis ◽  
Intermediate Disturbance ◽  
Disturbance Frequency ◽  
Theoretical Predictions ◽  
Experimental Populations ◽  
Disturbance Hypothesis

An influential ecological theory, the intermediate disturbance hypothesis (IDH), predicts that intermediate levels of disturbance will maximize species diversity. Empirical studies, however, have described a wide variety of diversity–disturbance relationships (DDRs). Using experimental populations of microbes, we show that the form of the DDR depends on an interaction between disturbance frequency and intensity. We find that diversity shows a monotonically increasing, unimodal or flat relationship with disturbance, depending on the values of the disturbance aspects considered. These results confirm recent theoretical predictions, and potentially reconcile the conflicting body of empirical evidence on DDRs.

scholarly journals Trematode parasite cercariae as food in model freshwater trophic interactions

2021 ◽  
Author(s):  
Ben Schultz
Keyword(s):  
Zooplankton Community ◽  
Life Cycles ◽  
Population Abundance ◽  
Trematode Parasite ◽  
Free Living ◽  
Complex Life Cycles ◽  
Future Studies ◽  
High Consumption ◽  
Daphnia Population ◽  
Trematode Parasites

Free-living parasite stages are important but often overlooked components of ecosystems, especially their role(s) in food webs. Trematode parasites have complex life cycles that include a motile transmission phase, cercariae, that are produced in great quantities within aquatic snail hosts and join the zooplankton community after emerging. Here I examined how cercariae presence affected the population abundance of a common freshwater zooplanktonic animal (Daphnia) when predators were present. I also sought to determine the pathways taken by cercariae-derived carbon within a model freshwater food web by using the stable isotope 13C as a tracer. I found that Daphnia population abundance positively benefitted from cercariae presence when larval dragonfly predators were present, serving as alternate prey. I also found that 13C was an effective tool to track the flow of cercarial carbon, demonstrating high consumption by benthic consumers, as well as the utility of this method for use in future studies.

scholarly journals Growth Impacts of Income Inequality: Empirical Evidence From Nigeria

2019 ◽  
Vol 10 (3) ◽  
pp. 226
Author(s):  
Ademola Obafemi Young
Keyword(s):  
Income Inequality ◽  
Empirical Studies ◽  
Growth Time ◽  
African Countries ◽  
Developed Economies ◽  
Rights Protection ◽  
Property Rights Protection ◽  
Long Run ◽  
Theoretical Predictions ◽  
The Impact

The debate on whether income inequality promotes, restricts, or is independent of economic growth has been widely studied and discussed in development economics discourse. However, a careful reading of this extensive extant and burgeoning literature suggests that, other than the ambivalent nature and the fact that the bulk of these studies relied heavily on cross-section/-country/panel econometric analysis, empirical studies examining the nexus in the context of less developed economies, particularly, African countries, has received less attention, as most of the extant studies predominantly focused on developed economies. This current study, thus, attempts to examine the impact of inequality on growth in Nigeria spanning between the period 1970 and 2018. It also examined the theoretical predictions of some of the distinct transmission channels through which inequality impacts growth. Time series econometrics were applied. The results obtained consistently revealed that inequality hurts long-run growth in Nigeria. Also, the results obtained revealed that inequality in income increases relative redistribution and fertility, but lessens investment, gross enrollment ratio, and property rights protection in Nigeria, which may in turn impede growth.

scholarly journals Evolution of Divergent Life History Strategies in Marine Alphaproteobacteria

mBio ◽  
2013 ◽  
Vol 4 (4) ◽  
Author(s):  
Haiwei Luo ◽  
Miklós Csűros ◽  
Austin L. Hughes ◽  
Mary Ann Moran
Keyword(s):  
Life History ◽  
Life Histories ◽  
Scale Up ◽  
Carbon Mineralization ◽  
Life History Strategies ◽  
Free Living ◽  
Heterotrophic Bacterioplankton ◽  
Evolutionary Origins ◽  
Eukaryotic Phytoplankton ◽  
Microbial Groups

ABSTRACT Marine bacteria in the Roseobacter and SAR11 lineages successfully exploit the ocean habitat, together accounting for ~40% of bacteria in surface waters, yet have divergent life histories that exemplify patch-adapted versus free-living ecological roles. Here, we use a phylogenetic birth-and-death model to understand how genome content supporting different life history strategies evolved in these related alphaproteobacterial taxa, showing that the streamlined genomes of free-living SAR11 were gradually downsized from a common ancestral genome only slightly larger than the extant members (~2,000 genes), while the larger and variably sized genomes of roseobacters evolved along dynamic pathways from a sizeable common ancestor (~8,000 genes). Genome changes in the SAR11 lineage occurred gradually over ~800 million years, whereas Roseobacter genomes underwent more substantial modifications, including major periods of expansion, over ~260 million years. The timing of the first Roseobacter genome expansion was coincident with the predicted radiation of modern marine eukaryotic phytoplankton of sufficient size to create nutrient-enriched microzones and is consistent with present-day ecological associations between these microbial groups. We suggest that diversification of red-lineage phytoplankton is an important driver of divergent life history strategies among the heterotrophic bacterioplankton taxa that dominate the present-day ocean. IMPORTANCE One-half of global primary production occurs in the oceans, and more than half of this is processed by heterotrophic bacterioplankton through the marine microbial food web. The diversity of life history strategies that characterize different bacterioplankton taxa is an important subject, since the locations and mechanisms whereby bacteria interact with seawater organic matter has effects on microbial growth rates, metabolic pathways, and growth efficiencies, and these in turn affect rates of carbon mineralization to the atmosphere and sequestration into the deep sea. Understanding the evolutionary origins of the ecological strategies that underlie biochemical interactions of bacteria with the ocean system, and which scale up to affect globally important biogeochemical processes, will improve understanding of how microbial diversity is maintained and enable useful predictions about microbial response in the future ocean.

scholarly journals The life histories and population dynamics of monogenean gill parasites of Trachurus trachurus (L.)

1962 ◽  
Vol 42 (3) ◽  
pp. 587-600 ◽  
Author(s):  
J. Llewellyn
Keyword(s):  
Coastal Waters ◽  
Life Histories ◽  
Feeding Habits ◽  
Limiting Factor ◽  
Trachurus Trachurus ◽  
Free Living ◽  
Sea Bottom ◽  
Second Year ◽  
Post Spawning ◽  
Gill Parasites

Gastrocotyle trachuri and Pseudaxine trachuri infect young Trachurus trachurus at Plymouth as soon as the 3- or 4-month-old adolescent fishes descend to the sea bottom in October. The parasites normally mature in 3 or 4 months, but, exceptionally, in about 1 month, and the life-span is normally no longer than 1 year. Trachurus specimens at the beginning of their second year pick up a largely new infection of parasites.G. trachuri and P. trachuri are much less frequent on 2- and 3-year-old specimens of Trachurus and probably occur only very rarely on still older fishes, the limiting factor being not an age-immunity but a post-spawning migration of the host from the concentration of free-living infective stages of the parasites in coastal waters.The parasites have adapted themselves to a seasonal change in the feeding habits of Trachurus by ceasing to produce larvae in anticipation of the summer disappearance of scad from the sea bottom in pursuit of pelagic food-organisms.

The life histories of north-temperate populations of the crayfish Cambarus robustus and Cambarus bartoni

1985 ◽  
Vol 63 (10) ◽  
pp. 2313-2322 ◽  
Author(s):  
Premysl Hamr ◽  
Michael Berrill
Keyword(s):  
Life History ◽  
Life Histories ◽  
Carapace Length ◽  
Late Summer ◽  
Temperate Climate ◽  
Free Living ◽  
Southern Ontario ◽  
The Third ◽  
Early Fall ◽  
First Time

The life histories of the crayfish Cambarus robustus and Cambarus bartoni were studied in the Kawartha Lakes region of southern Ontario. There were marked differences in their breeding and molting cycles compared with the familiar pattern of the Orconectes species of this region. Egg extrusion occurred later (July in C. robustus, June in C. bartoni), and juveniles therefore did not become free living until late summer or early fall. With little growing time in their first summer, they measured only 5–10 mm in carapace length (CPL) before growth ceased for the winter. At the end of their second summer the still immature crayfish measured 17–26 mm CPL in C. robustus and 13–20 mm CPL in C. bartoni. Maturity was therefore not attained until the end of the third summer, when most C. robustus matured at 34–45 mm CPL and C. bartoni at 25–30 mm CPL. The majority of individuals apparently reproduced for the first time during their fourth summer; a few apparently survived into another summer, reaching carapace lengths greater than 50 mm in C. robustus and 30 mm in C. bartoni. In males of both species, form 1 and form 2 occur throughout the summer. Although lacking the synchrony of Orconectes species, breeding and molting activities are still confined to the period between April and October. The timing of the life-history events observed in these two Cambarus species may be adaptations to seasonal stresses of the swift water environments that these species inhabit as well as to the relative harshness of the northern temperate climate.

Distinct successional patterns and processes of free‐living and particle‐attached bacterial communities throughout a phytoplankton bloom

2020 ◽  
Vol 65 (8) ◽  
pp. 1363-1375 ◽  
Author(s):  
Huimin Xu ◽  
Dayong Zhao ◽  
Jin Zeng ◽  
Congcong Jiao ◽  
Zhongbo Yu ◽  
...  
Keyword(s):  
Bacterial Communities ◽  
Phytoplankton Bloom ◽  
Free Living ◽  
Patterns And Processes

scholarly journals Do glucocorticoids predict fitness? Linking environmental conditions, corticosterone and reproductive success in the blue tit, Cyanistes caeruleus

2017 ◽  
Vol 4 (10) ◽  
pp. 170875 ◽  
Author(s):  
L. J. Henderson ◽  
N. P. Evans ◽  
B. J. Heidinger ◽  
K. A. Herborn ◽  
K. E. Arnold
Keyword(s):  
Reproductive Success ◽  
Environmental Conditions ◽  
Empirical Studies ◽  
Blue Tit ◽  
Cyanistes Caeruleus ◽  
Free Living ◽  
Brood Rearing ◽  
Fledging Success ◽  
Harsh Conditions ◽  
Blue Tits

Glucocorticoids, including corticosterone (CORT), have been suggested to provide a physiological link between ecological conditions and fitness. Specifically, CORT, which is elevated in response to harsh conditions, is predicted to be correlated with reduced fitness. Yet, empirical studies show that CORT can be non-significantly, positively and negatively linked with fitness. Divergent environmental conditions between years or study systems may influence whether CORT is linked to fitness. To test this, we monitored free-living blue tits ( Cyanistes caeruleus ) during breeding over 3 years. We quantified foraging conditions during brood rearing, and examined whether they were correlated with parental baseline CORT and reproductive success. We then tested whether CORT predicted fitness. Elevated parental CORT was associated with lower temperatures, greater rainfall and lower territory-scale oak density. Whereas asynchrony with the caterpillar food peak was correlated with reduced nestling mass and fledging success, but not parental CORT. Only low temperatures were associated with both reduced nestling mass and elevated parental CORT. Despite this, parents with elevated CORT had lighter offspring in all years. Contrarily, in 2009 parental CORT was positively correlated with the number fledged. The absence of a direct link between the foraging conditions that reduce nestling quality and elevate parental CORT suggests that parental CORT may provide a holistic measure of conditions where parents are working harder to meet the demands of developing young. As the positive correlation between parental CORT and fledging success differed between years, this suggests that contrasting conditions between years can influence correlations between parental CORT and fitness. Ultimately, as CORT concentrations are intrinsically variable and linked to the prevalent conditions, studies that incorporate environmental harshness will improve our understanding of evolutionary endocrinology.

scholarly journals Mutual information reveals variation in temperature-dependent sex determination in response to environmental fluctuation, lifespan and selection

2008 ◽  
Vol 275 (1650) ◽  
pp. 2441-2448 ◽  
Author(s):  
Lisa E Schwanz ◽  
Stephen R Proulx
Keyword(s):  
Mutual Information ◽  
Sex Determination ◽  
Life Histories ◽  
Reaction Norm ◽  
Population Based ◽  
Reaction Norms ◽  
Temperature Dependent ◽  
Environmental Fluctuation ◽  
Functional Aspects ◽  
Theoretical Predictions

Quantifying the degree to which sex determination depends on the environment can yield insight into the evolution, ecological dynamics, and functional aspects of sex determination. In temperature-dependent sex determination (TSD), theory often predicts a complete dependence of sex on temperature, with a switch-like reaction norm. However, empirical data suggest more shallow relationships between sex and temperature. Here, we demonstrate the usefulness of an index, mutual information (MI), to reflect the degree of temperature dependence in sex. MI depends on both the shape of a reaction norm and the natural temperature variation, thus providing a measure of TSD that is ecologically dependent. We demonstrate that increased lifespan and decreased environmental fluctuation predict reaction norms with high MI (switch-like). However, mutation and weaker selection on sex-specific performance reduce average MI in a population, suggesting that mutation–selection balance can resolve some of the conflict between theoretical predictions of individual-based optimality and population-based empirical results. The MI index allows clear comparison of TSD across life histories and habitats and reveals functional similarities between reaction norms that may appear different. The model provides testable predictions for TSD across populations, namely that MI should increase with lifespan and decrease with historical environmental fluctuations.

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