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.     

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     

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.