Holopainen, I. J., Tonn, W. M. & Paszkowski, C. A. 1997: Tales of two fish: the dichotomous biology of crucian carp (Carassius carassius (L.)) in northern Europe. — Ann. Zool. Fennici 34: 1–22.
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Lambin, X. & Mathers, C. 1997: Dissipation of kin discrimination in Orkney voles, Microtus arvalis orcadensis: a laboratory study. — Ann. Zool. Fennici 34: 23–30.
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Öst, M. & Kilpi, M. 1997: A recent change in size distribution of blue mussels (Mytilus edulis) in the western part of the Gulf of Finland. — Ann. Zool. Fennici 34: 31–36.
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Taskinen, T., Mäkelä, T. & Valtonen, E. T. 1997: Exploitation of Anodonta piscinalis (Bivalvia) by trematodes: parasite tactics and host longevity. — Ann. Zool. Fennici 34: 37–46.
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Valtonen, E. T. & Gibson, D. I. 1997: Aspects of the biology of diplostomid metacercarial (Digenea) populations occurring in fishes in different localities of northern Finland. — Ann. Zool. Fennici 34: 47–59.
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Eeva, T., Lehikoinen, E. & Sunell, C. 1997: The quality of pied flycatcher (Ficedula hypoleuca) and great tit (Parus major) females in an air pollution gradient — Ann. Zool. Fennici 34: 61–71.
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Holopainen, I. J., Tonn, W. M. & Paszkowski, C. A. 1997: Tales of two fish: the dichotomous biology of crucian carp (Carassius carassius (L.)) in northern Europe. — Ann. Zool. Fennici 34: 1–22.
Crucian carp, a common Eurasian cyprinid fish, shows striking dichotomies in several aspects of its physiology and ecology, at both the individual and population levels. These dichotomies consistently reflect the communities and ecosystems in which they occur, contrasting crucian carp that occur in “monocultures” (single-species fish assemblages) in ponds with those occurring in multi-species assemblages, primarily in lakes. Dichotomies also occur in the physiological state of individuals between summer and winter. All these dichotomies, involving differences in morphology and population structure, population dynamics and life history, reflect in an integrative way the adaptive strengths and limitations of a unique species. In numerous northern ponds, dense monocultures of crucian carp are sealed in by thick ice and snow to live more than six months in dark, anoxic waters at near freezing temperatures. In summer, these populations experience temperatures of up to 30°C during a relatively brief period of vigorous growth and repeated bouts of reproduction in almost continuous daylight. Crucians in lakes experience a more benign abiotic environment and, with densities that can be orders of magnitude lower than those in ponds, are likely unaffected by intraspecific interactions. However, co-occurring species present a challenging biotic environment. Crucian carp is exceptionally vulnerable to predation and populations persist via three kinds of refugia. Aided by extreme physiological adaptations, crucian carp can be the sole piscine inhabitant of seasonally harsh but productive small ponds, the refugium habitat , where they form dense monocultures of stunted individuals. The structural complexity offered by dense beds of macrophytes in productive larger lakes, the other common habitat (habitat refugium ) of crucian carp, ensures survival of a few offspring, even in the presence of piscivores. The risk of predation still remains high for crucians until a certain length (and/or body depth), the size refugium , is attained. Crucian carp’s unique anoxia tolerance, accompanied by many exceptional structural and functional features, and the species’ suitability for laboratory studies, has recently raised crucian carp to a status of a physiological model species like its relative, the goldfish. Moreover, the dichotomy found in the structure of natural populations has made crucian carp an attractive model for ecological studies in competititon and predation. Crucian carp’s resistance to adverse environmental conditions further suggests promising economical use in aquaculture to produce hybrids endowed with higher survival capacity than common carp.
Lambin, X. & Mathers, C. 1997: Dissipation of kin discrimination in Orkney voles, Microtus arvalis orcadensis: a laboratory study. — Ann. Zool. Fennici 34: 23–30.
Field experiments testing the roles of relatedness in vole demography make different assumptions on the ability of voles to recognize their unfamiliar kin and this may have contributed to their contrasting outcomes. We measured the rate of dissipation of discrimination between related male and between related female Orkney voles (Microtus arvalis orcadensis) after increasing periods of separation to test these assumptions. Females showed a decreasing preference for the odour of their sisters as familiarity for new cage-mates increased and an increasing preference for their new cage-mates as familiarity increased. In contrast, males showed no such changes in their avoidance of their brothers following separation. Dissipation of kin-discrimination by Orkney voles in absence of reinforcement by familiarity is therefore rapid and familiarity established in adult life seemingly has the same impact on preference between females as relatedness.
Öst, M. & Kilpi, M. 1997: A recent change in size distribution of blue mussels (Mytilus edulis) in the western part of the Gulf of Finland. — Ann. Zool. Fennici 34: 31–36.
We sampled blue mussels (Mytilus edulis) in 1992–1996 from mussel beds that common eiders (Somateria mollissima) preferentially use during foraging in the Hanko archipelago, Finland. We also compared our data with an earlier study carried out in the same area. We found a consistent trend towards decreasing mussel size; the proportion of larger mussels in the population has decreased significantly. Since blue mussels are an essential part of the Baltic ecosystem, a shift in mean mussel size may have important consequences. A decrease in salinity during the last few decades may be the ultimate reason for the observed changes, as salinity affects growth, maximum size and reproduction of mussels. We also suggest that selective eider predation may be of local importance.
Taskinen, T., Mäkelä, T. & Valtonen, E. T. 1997: Exploitation of Anodonta piscinalis (Bivalvia) by trematodes: parasite tactics and host longevity. — Ann. Zool. Fennici 34: 37–46.
In a long-lived molluscan host, trematode adaptations that minimize the risk of parasite-induced host mortality may evolve because the residual reproductive value of a parasite would not be limited by a short life-span of the host. Two features of the host exploitation (site selection and timing of the reproductive period) were examined for the bucephalid trematodes Rhipidocotyle fennica and R. campanula in their first intermediate host Anodonta piscinalis which is a long-lived freshwater clam. The gonad, assumed to be less critical for survival of the host, was the organ most frequently parasitized by both of the parasite species. Except for the kidney in the case of R. campanula, the prevalence of infection was low in organs that were expected to be important for host survival (kidney, gills, digestive gland). We also made a literature survey on the site selection of larval trematodes of aquatic molluscs in general. We found that the longer the life-span of the host, the higher the proportion of trematode-mollusc associations where the gonad is the main site of infection. Infected A. piscinalis do not reproduce due to parasitic castration but the uninfected individuals develop their offspring, presumably, during the period of most abundant resources in the seasonally fluctuating environment. Therefore, if the parasites adjust their cercarial production to the same period as the uninfected clams they should minimize mortality caused by an energetic stress for the host. We found the reproductive period of R. fennica to co-occur with that of the host, while the cercarial production of R. campanula started 2 weeks earlier than the host reproduction. In summary, R. fennica followed a “damage avoidance tactic” but R. campanula to a lesser extent.
Valtonen, E. T. & Gibson, D. I. 1997: Aspects of the biology of diplostomid metacercarial (Digenea) populations occurring in fishes in different localities of northern Finland. — Ann. Zool. Fennici 34: 47–59.
Diplostomid metacercariae were found at a high prevalence and in large numbers in the eyes of a wide variety of fish species from widely differing freshwater and brackish water environments in northern Finland. These parasites were found to infect the following: 21 of 25 fish species, some of which were marine, studied in the oligohaline, brackish waters of the Bothnian Bay, Baltic Sea; all nine fish species studied from a large, oligotrophic lake in NE Finland (Yli-Kitka); and all five studied fish species in a small, hypereutrophic lake (Kuivasjärvi). Diplostomids in the lens of the fishes of the Bothnian Bay, studied during two periods extending over seven years, suggest the presence of a stable and predictable system, despite the extremely narrow transmission window between the first (snail) and second (fish) intermediate hosts. Diplostomids in the lens of fishes from the Bothnian Bay and Lake Kuivasjärvi predominated (> 50% infection in 14 of 21 species) over those from the vitreous body of the eye in most cases, but were much lower (< 18%) in Lake Yli-Kitka. The situation in the vitreous body was quite the reverse, since diplostomids in this site predominated over those in the lens in fishes of Lake Yli-Kitka (> 80% prevalences in five of nine fish species). This difference is considered to be dependent on differences in the piscivorous bird fauna. The fact that diplostomid metacercariae accumulated in the fish, together with the lack of any real seasonal variation, confirms the longevity of these larvae in their fish intermediate hosts. Thus metacercariae form a reservoir which is mainly responsible for the maintenance of diplostomid suprapopulations in these northern latitudes.
Eeva, T., Lehikoinen, E. & Sunell, C. 1997: The quality of pied flycatcher (Ficedula hypoleuca) and great tit (Parus major) females in an air pollution gradient. — Ann. Zool. Fennici 34: 61–71.
We studied whether pied flycatcher (Ficedula hypoleuca) and great tit (Parus major) females differed in quality between polluted and unpolluted habitats. Comparing female condition between incubation and nestling periods, we aimed at testing whether biometric differences in F. hypoleuca females were caused by assortative settlement (i.e. intraspecific competition) or as a consequence of breeding in environments exposed to different levels of pollution stress. Body mass, wing length, fat reserves, age distribution, timing of breeding and breeding density of females were measured along an air pollution gradient from a copper smelter in SW Finland in 1991–1994. We found few differences in female quality which could be explained by assortative settling. Females were of the same size in all areas. At nestling time P. major females were heaviest in a moderately polluted area. However, females in the most polluted area were not lighter than those in background areas. Female fat reserves in both species were smaller in the polluted area in one cold breeding season. This suggests that natural (weather) and human induced (pollution) stress factors affected female condition additively. The proportion of young F. hypoleuca females was slightly higher in the polluted area than elsewhere. P. major females started laying earlier near the factory complex than farther away. F. hypoleuca females laid later in the polluted area in early breeding seasons but in late seasons laying started simultaneously everywhere. Especially F. hypoleuca bred more sparsely in the polluted area. Observed differences in the condition of F. hypoleuca females along the pollution gradient emerged mainly in the course of breeding.