Sperm quality, secondary sexual characters and parasitism in roach (Rutilus rutilus L.)

According to sperm competition models, a male spawning in a disfavoured role should have spermatozoa with higher velocity but shorter longevity compared with a male spawning in a favoured role. Moreover, immunosuppressive androgens are needed to produce both secondary sexual characters and sperm cells. The 'sperm protection' hypothesis suggests that the immunosuppressive action of androgens has evolved to protect haploid spermatozoa, which are antigenic, from autoimmune attacks. Therefore, a male with high sexual ornamentation may be more susceptible to diseases but may possess better quality ejaculate than his less ornamented rival. We studied sexual ornamentation (breeding tubercles), ejaculation quality (sperm concentration, longevity and spermatozoal velocity) and intensity of parasitism in the cyprinid, Rutilus rutilus . Sperm longevity and spermatozoal velocity were positively correlated. Males having elaborated sexual ornamentation had longer-lived sperm and more Myxobolus mülleri parasites in the liver compared with males with low ornamentation. However, no difference was found between males with different degrees of ornamentation with respect to sperm concentration, spermatozoal velocity or other parasites. Since the highly ornamented males had higher sperm longevity, the present results are partly consistent with the predictions of the sperm competition models and the 'sperm protection' hypothesis.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 81 , 111–117.     

Selection often overrides the effects of random processes in island populations of Philaenus spumarius (Homoptera)

The influence of various evolutionary factors on the populations of the colour polymorphic meadow spittlebug, Philaenus spumarius (Homoptera), was investigated on islands in the Gulf of Finland. Long-term (30-year) investigations showed that the populations can survive through very narrow bottlenecks, but after strong reduction in the size of a population, random genetic drift may remove alleles or change allele frequencies. One of the factors sustaining the presence of almost all the colour polymorphism alleles in almost all the populations is gene flow. Migration seems to be largely by air and by the sea surface (anemohydrochoric). On one rocky island, gene flow was able to carry the top dominant allele, p^T, to a number of scattered plant stands. However, it was not powerful enough to alter the differences in allele frequencies between populations living on the same island in meadows of different types 3 m or 12 m from each other. It is highly probable that the factor operating is meadow-specific selection. Its action appears to be based on the ecological character of the meadow. In the different meadows, the coverages of the food plants of the spittlebug are dissimilar. Differences in plant assemblages are possibly of importance in maintaining the meadow-specific allele frequencies in the spittlebug populations.     

Breeding-related seasonal changes in immunocompetence, health state and condition of the cyprinid fish, Rutilus rutilus, L.

Seasonal changes in immunocompetence are predicted by the hypothesized trade-off between reproduction and self-maintenance, whereby immune function is a measure of self-maintenance and reproductive effort is seasonally dependent. We examined seasonal patterns in immunological, haematological and body condition parameters for male and female freshwater fish. In two different populations, the relative size of the spleen and the chemotaxic migration activity of head kidney granulocytes decreased immediately before and after spawning, respectively. Those decreases were accompanied by an increase in haematocrit values shortly before and after spawning in both populations and a decrease in the relative body weight in one population, possibly due to physiological stress caused by increased activity during the spawning period. Breeding-related changes in other measures studied (phagocytosis activity of head kidney granulocytes, blood IgM concentration, white cell count and red cell count) were absent or inconsistent. Some of the results are in line with the idea of a trade-off between reproduction and immune defence. The present data suggest that the differential responses of the immune system may have different temporal patterns, which should be taken into account in immunoecological studies.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 78 , 117−127.     

Echo-sounding can discriminate between fish and macroinvertebrates in fresh water

1. Acoustic scattering from fish and macroinvertebrates was studied in a boreal Finnish lake at three echosounder frequencies (38, 120 and 200 kHz). Split-beam transducers with partly overlapping 7° beams were employed. Acoustic, fish and invertebrate sampling were undertaken simultaneously. Vertical gradients of temperature and oxygen concentration were measured during the exercise.
2. At all frequencies, a narrow scattering layer coincided with the thermocline. At 38 kHz, fish were detected well with practically no reverberation from invertebrates while 200 kHz detected both fish and invertebrates.
3. Minor differences in the magnitude of acoustic scattering from fish were found between frequencies and between depth layers, but scattering at different frequencies was correlated at all depths. Acoustic scattering and fish density indices from trawl catches, consisting mostly of smelt ( Osmerus eperlanus ) (97%) and vendace ( Coregonus albula ) (3%), were significantly correlated.
4. Acoustic scattering from invertebrates increased with sound frequency. Correlation analysis suggested that the invertebrate scattering was mostly induced by Chaoborus flavicans . A low frequency is recommended for estimating fish abundance without bias from reverberation induced by invertebrate scattering. Although fish and invertebrates can also be successfully discriminated at a single frequency by thresholding and cross filtering, the combination of a low and a high frequency is a more robust tool for effective fish-invertebrate discrimination.     

Apomictic Parthenogenesis and the Pattern of the Environment

Advantages of obligatory apomixis are modeled, and curculionidweevils are used as examples. It is suggested that the allegedtwofold number of female offspring in relation to sexual parentalsshould not be exaggerated. Instead, specific circumstances facilitatingthe origin of especially heterotic genotypes capable of apomixisshould be sought; crosses between differentiated (long-isolated)populations (preferably followed by a population flush) seempromising. Optimal strategies in temporally heterogeneous environmentsare studied, and situations favoringsexual reproduction bothin fine-grained and coarse-gained environments seem common (apomictsare capable only for individual adaptability, but sexual populationsmay track even one-generation changes by evolving). In apomicts,diapause determination and other seasonal constraints need specificattention, as they may interfere with geographical dispersal,and only life-cycles of one or more years seem possible. Inrich biotic communities, which evolve continuously, evolutionaryrigidity of apomicts may lead to their extinction. This showsthat the dichotomy between immediate and long-term advantagesof apomixis needs revision; if the number of generations neededfor competitive exclusion between asexual and sexual organismsis relatively high, the greater evolutionary potential of sexualpopulations must be considered (there are directional changesboth in the physical and biotic environments). Apomixis thenseems most advantageous in low-competitive, early successionhabitats which are recurrent and change relatively slowly (increasedcolonization ability of apomicts is here advantageous). Also,apomixis may succeed in spatially coarse-grained environmentin stable patches small enough to exclude high-competitive communityat the site. Then reduced vagility (loss of flight) may facilitatethe origin of apomixi     

Visual conditions and habitat shape the coloration of the Eurasian perch (Perca fluviatilis L.): a trade‐off between camouflage and communication?

In theory, selection for effective camouflage (i.e. dull coloration) in fish should be strongest when the conditions for visual predation are most favourable, such as in structurally simple pelagic habitats. By contrast, in more sheltered (e.g. littoral) habitats, selection may favour effective intra‐specific communication (i.e. bright coloration) (at the expense of crypsis). Poor transparency, as in highly humic waters, should constrain colour adaptations. We investigated phenotypic variation in body coloration of Eurasian perch (Perca fluviatilis L.) in littoral and pelagic habitats of four humic boreal lakes. Perch from the most transparent lake had the lightest and less coloured belly and perch were more colourful in the littoral habitats than in the pelagic areas, with the pattern being clearest in the most transparent lake. In addition, perch in the most transparent lake exhibited sexual dichromatism, with males having a more colourful belly than the females, whereas no indications of sexual dichromatism were found in more humic lakes. Moreover, in the most transparent lake, the condition of fish correlated with bright belly coloration in the littoral, but with dull belly coloration in the pelagic habitat. The results obtained in the present study suggest that selection on perch coloration may differ between lakes as a result of visual properties of the water, and within lakes as a result of divergent selection for camouflage and communication in pelagic and littoral habitats. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 47–59.     

Seasonal Onset and Disappearance of Diurnal Rhythmicity in Melatonin Secretion in Female Reindeer

The reindeer (Rangifer tarandus tarandus) is a semidomesticatedholarctic ruminant subject to economic activity. Our researchwas carried out in Northern Finland, at latitude 69°10'N,where the daily light-dark rhythm has a polar pattern: constantdarkness starts on November 26th and lasts about 10 weeks, whilethe polar day of about 10 weeks starts on May 15th. We had previouslyfound distinct daily rhythms in reindeer melatonin secretionin autumn, winter and spring but not at all in summer. Herewe determine how the daily melatonin pattern develops afterthe period of polar day and how it disappears at the beginningof that period. Melatonin showed increased concentrations verysoon after the first sunset. Thereafter the daily pattern developedgradually and was fully developed around the autumn equinox.Its shape was asymmetric and the maximum amplitude occurrednear the end of the dark period. The disappearance of this dailypattern in spring was also gradual. The maximal concentrationsdepended on ambient illumination, especially the duration ofthe dark period. In spring the reindeer appeared to be moresensitive to light than in autumn. Additionally illuminationof the same magnitude suppressed serum melatonin levels moreeffectively before midnight than afterwards, which is in accordancewith the asymmetric secretion pattern. Melatonin secretion wasalways suppressed when the ambient illumination exceeded 1,0001x. The pattern of melatonin secretion in reindeer is differentfrom those described earlier and hence the reindeer may serveas a model for melatonin secretion at high latitudes. We suggestthat, in addition to the duration of the melatonin secretion,changes in amplitude are also of importance in the reindeer.     

Lagged effects of North Atlantic Oscillation on spittlebug Philaenus spumarius (Homoptera) abundance and survival

The North Atlantic Oscillation (NAO) is a large‐scale pattern of climate variability that has been shown to have important ecological effects on a wide spectrum of taxa. Studies on terrestrial invertebrates are, however, lacking. We studied climate‐connected causes of changes in population sizes in island populations of the spittlebug Philaenus spumarius (L.) (Homoptera). Three populations living in meadows on small Baltic Sea islands were investigated during the years 1970–2005 in Tvärminne archipelago, southern Finland. A separate analysis was done on the effects of NAO and local climate variables on spittlebug survival in 1969–1978, for which survival data existed for two islands. We studied survival at two stages of the life cycle: growth rate from females to next year's instars (probably mostly related to overwintering egg survival), and survival from third instar stage to adult. The latter is connected to mortality caused by desiccation of plants and spittle masses. Higher winter NAO values were consistently associated with smaller population sizes on all three islands. Local climate variables entering the most parsimonious autoregressive models of population abundance were April and May mean temperature, May precipitation, an index of May humidity, and mean temperature of the coldest month of the previous winter. High winter NAO values had a clear negative effect on late instar survival in 1969–1978. Even May–June humidity and mean temperature of the coldest month were associated with late instar survival. The climate variables studied (including NAO) had no effect on the growth rate from females to next year's instars. NAO probably affected the populations primarily in late spring. Cold and snowy winters contribute to later snow melt and greater spring humidity in the meadows. We show that winter NAO has a considerable lagged effect on April and May temperature; even this second lagged effect contributes to differences in humidity. The lagged effect of the winter NAO to spring temperatures covers a large area in northern Europe and has been relatively stationary for 100 years at least in the Baltic area.     

Climatic effects on litter decomposition from arctic tundra to tropical rainforest

Climatic effects on the decomposition rates of various litter types in different environments must be known to predict how climatic changes would affect key functions of terrestrial ecosystems, such as nutrient and carbon cycling and plant growth. We developed regression models of the climatic effects on the first‐year mass loss of Scots pine needle litter in boreal and temperate forests across Europe (34 sites), and tested the applicability of these models for other litter types in different ecosystems from arctic tundra to tropical rainforest in Canada (average three year mass loss of 11 litter types at 18 sites), the USA and Central America (four litter types at 26 sites). A temperature variable (annual mean temperature, effective temperature sum or its logarithm) combined with a summer drought indicator (precipitation minus potential evapotranspiration between May and September) explained the first‐year mass loss of the Scots pine needle litter across Europe with a higher R² value than actual evapotranspiration (0.68–0.74 vs. 0.51) and with less systematic error for any sub‐region. The model with temperature sum and the summer drought indicator appeared best suited to the other litter types and environments. It predicted the climatic effects on the decomposition rates in North and Central America with least systematic error and highest R² values (0.72–0.80). Compared with Europe, the decomposition rate was significantly less sensitive to annual mean temperature in Canada, and to changes in actual evapotranspiration in the USA and Central America. A simple model distinguishing temperature and drought effects was able to explain the majority of climatic effects on the decomposition rates of the various litter types tested in the varying environments over the large geographical areas. Actual evapotranspiration summarizing the temperature and drought effects was not as general climatic predictor of the decomposition rate.