Ecological changes affect pathogen epidemiology and evolution and may trigger the emergence of novel diseases. Aquaculture radically alters the ecology of fish and their pathogens. Here we show an ...increase in the occurrence of the bacterial fish disease Flavobacterium columnare in salmon fingerlings at a fish farm in northern Finland over 23 years. We hypothesize that this emergence was owing to evolutionary changes in bacterial virulence. We base this argument on several observations. First, the emergence was associated with increased severity of symptoms. Second, F. columnare strains vary in virulence, with more lethal strains inducing more severe symptoms prior to death. Third, more virulent strains have greater infectivity, higher tissue-degrading capacity and higher growth rates. Fourth, pathogen strains co-occur, so that strains compete. Fifth, F. columnare can transmit efficiently from dead fish, and maintain infectivity in sterilized water for months, strongly reducing the fitness cost of host death likely experienced by the pathogen in nature. Moreover, this saprophytic infectiousness means that chemotherapy strongly select for strains that rapidly kill their hosts: dead fish remain infectious; treated fish do not. Finally, high stocking densities of homogeneous subsets of fish greatly enhance transmission opportunities. We suggest that fish farms provide an environment that promotes the circulation of more virulent strains of F. columnare. This effect is intensified by the recent increases in summer water temperature. More generally, we predict that intensive fish farming will lead to the evolution of more virulent pathogens.
We describe an unusually high infection rate of Gyrodactylus salaris Malmberg in juvenile Atlantic salmon Salmo salar L. of Baltic Sea origin, which are generally believed to be more resistant to G. ...salaris than East Atlantic salmon populations. Based on analyses of mitochondrial (complete cytochrome oxidase 1 CO1 gene, 1548 bp) and nuclear (ADNAM1, 435 bp; internal transcribed spacer ITS rDNA region, 1232 bp) DNA fragments, the closest relatives of the characterized Estonian G. salaris strain were parasites found off the Swedish west coast and in Raasakka hatchery, Iijoki (Baltic Sea, Finland). Analyses of 14 microsatellite loci of the host S. salarrevealed that approximately 40% of studied fish were triploids. We subsequently identified triploid Atlantic salmon of Baltic origin as more susceptible to G. salaris infection than their diploid counterparts, possibly due to compromised complement-dependent immune pathways in triploid salmon. This is in accordance with earlier studies that have shown elevated susceptibility of triploids to various viral or bacterial pathogens, and represents one of the first reports of increased susceptibility of triploid salmonid fish to an ectoparasite. However, further experimental work is needed to determine whether triploid Atlantic salmon is generally more susceptible to G. salaris compared to their diploid counterparts, irrespective of the particular triploidization method and population of origin.
A broad-range bacterial PCR method with universal 16S rDNA targeting primers and bacterial cultivation was used to identify the putative pathogen in flavobacterial outbreaks. Restriction fragment ...length polymorphism (PCR-RFLP) analysis and sequencing of the partial 16S rDNA PCR products of 10 skin samples and 10 representative isolates derived from the same fish specimens revealed differences between direct molecular and cultivation-based analysis. Flavobacterium columnare-like sequences dominated in the direct molecular analysis in most cases, whereas most of the isolates belonged to a phylogenetically heterogeneous group of flavobacteria clustering with F. hibernum. F. columnare was isolated in only 1 outbreak. The possible explanations for the different results may be attributable to difficulties in the plate cultivation procedure of external flavobacterial samples. During plate cultivation, the dominating Flavobacterium species can be masked by saprophytic species of the same genus or other genera, or the growth of flavobacteria can be completely inhibited by antagonistic bacteria such as Pseudomonas. Direct analysis of the prevailing 16S rDNA sequences avoids the problems with cultivation and may thus be preferable for the diagnosis of flavobacterial diseases. When isolating flavobacteria from external samples, serial dilution of the sample before plating can improve the results.
Inbreeding depression and male fitness in black grouse Höglund, Jacob; Piertney, Stuart B; Alatalo, Rauno V ...
Proceedings of the Royal Society. B, Biological sciences,
04/2002, Letnik:
269, Številka:
1492
Journal Article
Recenzirano
Odprti dostop
The male lifetime lekking performance was studied, and related to inbreeding-outbreeding in a wild population of black grouse (Tetrao tetrix) in central Finland between 1989 and 1995. Inbreeding was ...measured as the mean heterozygosity and mean d2 of 15 microsatellite loci. We found a significantly positive relationship between mean d2 and lifetime copulation success (LCS), while the relationship between heterozygosity and LCS was close to significant. We also found that males that never obtained a lek territory had significantly lower mean heterozygosity than males that were observed on a territory at least during one mating season in their life. Furthermore, among males that were successful in obtaining a lek territory, LCS and mean d2 were highest for those males that held central territories. We suggest that inbred males have a disadvantage (or outbred males have an advantage) in the competition for territories that may explain the relationships with LCS and inbreeding. Furthermore, the fact that mean d2 was positively correlated with LCS whereas heterozygosity was not when we restricted the analysis to territorial males, suggests that mean d2 provides more information about levels of inbreeding-outbreeding than heterozygosity alone, and potentially highlights the effects of heterosis. To our knowledge, this is the first time that measures of inbreeding and lifetime fitness have been linked in a non-isolated population. This is important in establishing that the relationships found in previous studies are not artefacts of low gene flow created by limited dispersal but a general feature of wild vertebrate populations.
In laboratory experiments the swimming behaviour of the ectoparasite Argulus foliaceus and its infection rates on juvenile perch (Perca fluviatilis) and roach (Rutilus rutilus) were examined. The ...highest infection rate and a preference for perch juveniles were obtained in darkness, the lowest infection rate and a lack of preference in the light, when aquaria with glass walls (high reflectivity) were used. In the light, when aquaria were lined with black plastic (low reflectivity) an intermediate level of infection for perch and the highest for roach was recorded. Under such conditions roach were significantly more heavily infected than perch; an attack rate 4 times greater was recorded for brighter (more reflective) roach juveniles than for perch. Within the aquaria with a low reflective interior parasites swam 4.4 times slower and were observed predominantly in the central area, while in the highly reflective aquaria fast swimming A. foliaceus were recorded mainly near the walls. The primary role of visual stimuli for the host search behavior of A. foliaceus in the light is suggested. Parasites can effectively use such stimuli only in the low reflective surroundings. Highly reflective glass aquarium walls produce numerous secondary local light sources, which cause fast, erratic parasite movements and prevent the efficient location of potential hosts.
'Good genes' models assume that females can use a signal such as mating effort to assess a male's lifetime fitness. Inferring long-term performance from short-term behavioural observations can be ...unreliable, and repeated sampling may be needed for more accurate assessment of males. Additionally, if sexual advertisement is viewed as a life-history trait subject to trade-offs, reliable comparison of mates should yield information on all life-history components rather than on one trait value in one season. We show that in the lekking black grouse (Tetrao tetrix), a male's success is best explained by assuming that females are informed of the past history of males up to the beginning of the study (eight years). Much of this extremely lasting 'memory' can be attributed to females observing long-term outcomes of male-male competition: current territory position is the only momentarily observable variable that has high power in predicting female choice, and it correlates to a male's past lekking effort on a cumulative lifetime scale. We conclude that females can use territory position as a signal that conveys information of a male's lifetime performance that combines lekking effort and longevity. Females may thus overcome the problem of male allocations varying in time, without the need to pay costs associated with repeated sampling.
The evolution of social behaviour has puzzled biologists since Darwin. Since Hamilton's theoretical work in the 1960s it has been realized that social behaviour may evolve through the effects of ...kinship. By helping relatives, an individual may pass on its genes despite negative effects on its own reproduction. Leks are groups of males that females visit primarily to mate. The selective advantage for males to join such social groups has been given much recent attention, but no clear picture has yet emerged. Here we show, using microsatellite analysis, that males but not females of a lekking bird (the black grouse, Tetrao tetrix) are genetically structured at the lek level. We interpret this structuring to be the effects of strong natal philopatry in males. This has the consequence that males on any specific lek should be more related than expected by chance as indicated by our genetic data. Our results thus suggest that kin selection is a factor that needs to be considered in the evolution and maintenance of the lek mating system in black grouse and sheds new light on models of lek evolution.
We studied supra-orbital combs in lekking black grouse (Tetrao tetrix) in relation to sexual selection at five leks in Finland 1991-1998 and four leks in Sweden 1992-1995. Comb size was estimated in ...two ways: by observing its natural size in the field at different behaviors (“observed comb size”), and by measuring the comb size from captured birds (“measured comb size”). The size of combs is highly variable, and individuals can change it within seconds. Males express their larger combs during display, as compared to other behaviors. Observed mean comb sizes were larger on leks with a higher number of males and a higher number of copulations. Measured and observed comb sizes and copulatory success did not significantly correlate when all males where analyzed, but a positive and significant relationship between observed comb size and copulatory success was found within males that achieved copulations. Measured comb length correlated positively with the amount of testosterone. While females were present on the lek, displaying and successful males showed the largest observed comb size. When we compared observed comb size during fighting between successful and unsuccessful males and correlated comb size of pairs of fighting males with their fighting activity, no significant differences in comb size were found. The result that comb size correlated significantly with an increase in testosterone level and that larger comb size, within successful males, predicted higher copulatory success suggests that combs may be a cue for females to assess male quality. The lack of a significant relationship between observed comb size and fighting behavior suggests that comb size either has minor importance in male-male signaling on the lek or that males may express similar-sized combs during fighting to avoid serious fights and thus risk of comb injuries.
Variation in female behaviour has only recently received attention in studies of sexual selection. It has been suggested that females may invest differentially in their offspring in relation to the ...quality of their mate. This may lead to females that mate with high-quality and/or attractive males laying larger clutches. Females may also differ in their ability to choose between males. For example, females in good physical condition may make better choices. If physical condition and clutch size are positively correlated, this hypothesis could also produce a relationship between male attractiveness and female clutch size. We found, in lekking black grouse,Tetrao tetrix, that females mated to the highest ranked males laid the largest clutches. Furthermore we found, regardless of female age, a positive relationship between a measure of female condition and male rank but not between female condition and her clutch size. In addition, females in good condition visited a larger number of different male territories, and old females produced the largest clutches. Our results suggest two mechanisms to explain our findings. First, females in good physical condition tend to mate with the top males, suggesting an assortative mating pattern. Second, females mating with the highest ranked males lay larger clutches as a consequence of their choice. In general, our result calls for caution in evaluating studies that look at the consequences of mate choice. It may be that differences in female quality produce effects that may be wrongly interpreted as male quality effects.
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