No description available.

No description available.

Plagiorchis elegans is a typical digenean parasite that cycles through aquatic molluscs and insects as intermediate hosts. During emergence of P. elegans cercariae, infected snails moved to the top of the water column where they remained immobile for 2-3h. Consequently, the cercariae formed a dense cloud which dispersed slowly. The infectivity of cercariae was $<$20% upon emergence and peaked at 76% 4-6h later. This delay in reaching maximum infectivity may be an adaptation to prevent superinfection and the associated mortality of insect hosts. Cercariae transformed into metacercariae after penetrating Aedes aegypti larvae, the experimental insect host. Overall development of metacercariae, and excystment of infective metacercariae in vitro, was temperature dependent. However, there was an initial 8-hour period of obligatory host-parasite contact that was temperature independent. This may represent a period of major nutrient acquisition since young metacercariae were more active metabolically than older metacercariae, as measured by the in vitro uptake of $ sp3$H-glucosamine and $ sp3$H-leucine. Mosquitoes may have mechanisms to reduce losses of larvae to parasites. Oviposition by adult A. aegypti was reduced in waters that had previously contained P. elegans-infected larvae. We propose that this selective oviposition was due to the production of an oviposition deterrent compound produced by parasitized larvae that serves to reduce oviposition in sites detrimental to larval development.

No description available.

No description available.

No description available.

Salmincola edwardsii is an ectoparasitic copepod typically found on the gills of brook trout (Salvelinus fontinalis). Laboratory experiments were conducted to determine: (i) the effects of temperature and photoperiod on early life cycle events, and (ii) the rate of larval development to adult. Egg incubation time, duration of copepodid swimming activity and copepodid survival time all decreased with increasing temperature. Different photoperiods had no effect. Hatching duration and hatching success were not influenced by either temperature or photoperiod. Copepodids remained alive and active for up to 16 days at 8$ sp circ$ and 5 days at 20$ sp circ$C. Adult male copepods were observed at 3 to 8 days after host exposure. They lived for up to 3 days. Adult females became permanently attached to hosts between 11 and 16 days post-infection.

The presence of parasites in a population has an impact on mate choice and has substantial evolutionary significance. A relatively unexplored aspect of this dynamic is whether or not the presence of parasites increases the likelihood of hybridization events, which also have a significant role in ecological adaptation. One explanation of increased hybridization in some areas and not others is that stress from parasites results in selection for an increase of novel genotypes. Two swordtail species Xiphophorus birchmanni and Xiphophorus malinche maintain an active hybrid zone. The patterns of hybridization are unique in that they do not match up directly with expectations. We set out to test whether or not individuals can sense, using chemical cues, whether conspecifics in their immediate vicinity have high parasite loads and also whether this has an effect on mating and association behavior toward both conspecific and hybrid mates. Our hypothesis being that females will have greater association times with hybrid/heterospecific mates if conscpecifics are heavily parasitized. We found that females exposed to parasitized males had a weaker preference for conspecific odor than those exposed to unparasitized males, both relative to a water control and relative to hybrids. The empirical investigation described above is coupled with a historical and philosophical discussion of some of the issues surrounding the acceptance and understanding of the concept of hybridization. This discussion takes as its major themes: an analysis of the role that social views have on the formation of scientific hypothesis; the lag between epochal change in the scientific community and the assimilation of the consequences into social beliefs; the survival of hierarchical and teleological thinking in our concept of species and purity; and the failures of contemporary evolutionary theory to provide satisfactory explanations about the meaning and upshot of hybridization. Two specific misconceptions about hybridization are addressed. First, that hybridization clashes with the belief in kinds/types/species having separate and pure identities. Secondly, the teleological view that reads purpose into nature and places all instances of variation on a hierarchical scale; the top and bottom of which are determined by estimated closeness to the predetermined perfection of a type. < <

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The role of semiochemicals in the behaviour and biology of <I>Lepeophtheirus salmonis</I> was investigated using a range of techniques. The potential use of semiochemicals in the behavioural ecology of mobile stages was examined using longitudinal monitoring and experimental manipulation of laboratory reared single cohort populations. The chronic and long term effects of separation from the host were also investigated using similar populations. The nature and chemosensory capability of the sense system of the parasite was assessed through morphological and ultrastructural studies. Finally, the nature of potential chemical stimuli during initial copepodid settlement, pair formation and mating, and host re-attachment of mobile stages, was examined using both <I>in vitro</I> and <I>in vivo</I> techniques. Longitudinal monitoring of populations created a model for mobile development and the timing and processes of pair formation and mating. There was evidence of a hierarchy of pair formation between female stages, periods of strong mate competition between males, and many factors within the processes were defined. Survival off the host was strongly related to the developmental stage and/or size of the louse; with adult females surviving for the longest and preadult I males for the shortest periods. The ability of adult males to re-attach and subsequently persist on the host was significantly reduced after only 72 hours of separation. Very few potential chemosensory setae were found on the appendages examined, the exception to this being the antennule. Two distinct populations of setae on the distal (14 setae) and proximal (27 setae) articles of the antennule demonstrated a wide range of morphology. The internal organisation, innervation and ultrastructure of these antennular setae was examined in detail. The setae could be divided into at least 6 distinct categories, when the internal data were combined with the external morphology.