Low Spring Temperatures Research Articles

CDNA-AFLP analysis on transcripts associated with bolting in

Premature bolting, caused by low temperature in spring and summer cultivation in low land and high land respectively, leads to reduction of the yield and quality of the harvested products in Chinese cabbage. Therefore, exploring genes involved in vernalization response is important to the improvement of Chinese cabbage varieties. Here, one extremely early bolting line (DH-54) and one extremely late bolting line (DH-43) were employed, and the cDNA-AFLP approach was used to identify key components involved in the low-temperature required vernalization response. Of 256 primer recombinations screened, a total of 191 differential expressed transcript-derived fragments (TDFs) were identified, and 82 TDFs were sequenced. BLAST and alignments showed that 52 candidate TDFs shared high levels of similarity with genes of known function, 22 TDFs of unknown function and 8 novel ESTs. The TDFs of known function were involved in genes encoding enzymes working in metabolism, proteins related to stress and defense, signal transduction, and transcription regulation, etc.

Production of high yielding red raspberry long canes in a Northern climate

Techniques for the production of raspberry long canes with high yield potential were studied on a research station and in two commercial nurseries in South Norway. Potted ‘Glen Ample’ plants were grown in the open and in polyethylene greenhouses during two seasons in order to optimize cultural practices. Dates of propagation and transfer to the production sites were varied. Following cold storage from December to early June, the canes were tipped (cut) at 160 cm height and grown in open plastic tunnels in the fruiting season for the evaluation of growth and yield performance. Remarkable berry yields of 1.5–3.8 kg per plant (cane) were regularly achieved. When grown in the open, later starts than June 1 (June 15 and July 1) successively reduced yields. On the other hand, an earlier start involves risks of growth cessation due to low spring temperature. When grown in greenhouses, high yields were still possible when plants were transferred from propagation conditions as late as July 1, although optimal yields of nearly 4 kg per plant were obtained with transfer on June 15. In a year with unusually high summer temperatures, the yields of canes produced in the open and in greenhouses did not vary significantly, whereas in the second year with normal summer temperatures, canes produced in greenhouses consistently out-yielded those produced in the open by about 1 kg per cane. Regression analyses revealed that high yields were associated with fruiting cane architecture traits such as cane height, number and length of laterals, and a low proportion of dormant buds. The single most important component was lateral length which alone accounted for 82% of the yield variation. Since lateral lengths increased from the shoot tip towards the base, cane heights in excess of 2 m are required for the attainment of top yields as the uppermost nodes with short and low-yielding laterals then can be eliminated by tipping.

Performance of Hazelnut Cultivars from Oregon in Northeastern Slovenia

Three cultivars and three selections from Oregon State University's (OSU) hazelnut (Corylus avellana) breeding program were investigated in a yield trial during the period 1997 to 2007 in northeastern Slovenia with the Italian ‘Tonda Gentile delle Langhe’ as the standard. All OSU genotypes had higher cumulative yield and yield efficiency than the standard, all exceeded the kernel percentage of 45%, and all had at least 76% good kernels. OSU 228.084 is promising due to good vegetative growth and the highest yields and yield efficiency. It set many catkins and had the highest percentage of marketable kernels. Its disadvantage could be early flowering and large yield reduction due to low temperatures in early spring. Cultivars/selections that were late flowering (‘Lewis’ and OSU 244.001) had longer durations of pistillate flower receptivity (‘Willamette’ and OSU 238.125) and had lower sensitivity to unfavorable weather conditions in early spring (‘Clark’) expressed the best climatic adaptation. Unmarketable nuts were mainly blanks and poorly filled nuts. ‘Clark’ is precocious early maturing, and well-suited to the kernel market. Due to its upright growth habit, ‘Clark’ could be planted more densely than others. ‘Lewis’ yielded well and had medium yield efficiency, and is suitable for in-shell and kernel markets. Excellent pellicle removal was observed in OSU 244.001 and OSU 238.125. All OSU cultivars and selections showed relatively low susceptibility to hazelnut weevil (Balaninus nucum).

Performance of Hazelnut Cultivars from Oregon in Northeastern Slovenia

Three cultivars and three selections from Oregon State University's (OSU) hazelnut (Corylus avellana) breeding program were investigated in a yield trial during the period 1997 to 2007 in northeastern Slovenia with the Italian ‘Tonda Gentile delle Langhe’ as the standard. All OSU genotypes had higher cumulative yield and yield efficiency than the standard, all exceeded the kernel percentage of 45%, and all had at least 76% good kernels. OSU 228.084 is promising due to good vegetative growth and the highest yields and yield efficiency. It set many catkins and had the highest percentage of marketable kernels. Its disadvantage could be early flowering and large yield reduction due to low temperatures in early spring. Cultivars/selections that were late flowering (‘Lewis’ and OSU 244.001) had longer durations of pistillate flower receptivity (‘Willamette’ and OSU 238.125) and had lower sensitivity to unfavorable weather conditions in early spring (‘Clark’) expressed the best climatic adaptation. Unmarketable nuts were mainly blanks and poorly filled nuts. ‘Clark’ is precocious early maturing, and well-suited to the kernel market. Due to its upright growth habit, ‘Clark’ could be planted more densely than others. ‘Lewis’ yielded well and had medium yield efficiency, and is suitable for in-shell and kernel markets. Excellent pellicle removal was observed in OSU 244.001 and OSU 238.125. All OSU cultivars and selections showed relatively low susceptibility to hazelnut weevil (Balaninus nucum).

Class II chitinase accumulated in the bark tissue involves with the cold hardiness of shoot stems in highbush blueberry ( Vaccinium corymbosum L.)

To understand the development of cold hardiness in highbush blueberry plants ( Vaccinium corymbosum L.), we investigated seasonal changes in the protein compositions of current-year and overwintered shoots. Electrophoresis using SDS-polyacrylamide gels indicated that the amounts of a few proteins increased in autumn, in association with an enhancement of cold hardiness. Of these proteins, 65- and 60-kDa proteins were confirmed to be dehydrins by western blotting. While the levels of most of the accumulated proteins decreased in April, a 27-kDa protein maintained its level in the overwintered stem during spring. The amino acid sequence deduced from a cDNA for this protein showed significant similarities with known chitinases. The stem segments from overwintered shoots sampled in July showed higher cold hardiness against sub-zero temperature than those from current-year shoots, and the bark tissue of overwintered shoots had higher cold resistance than that of current-year shoots. The 27-kDa protein (BC27) was mostly found in the bark tissue of stems. Appreciable accumulation of this protein in floral buds was not detected. The purified BC27 protein exerted a cryoprotective effect on protoplasts subjected to a freeze–thaw treatment. These results suggest that the stems of highbush blueberry develop a system of cold hardiness different from that of the buds and apices, and that the accumulation of chitinase is involved in tolerance to low temperature in winter or unseasonably low temperature in spring.

Swiss Flint maize landraces—A rich pool of variability for early vigour in cool environments

Today's modern Dent × Flint maize ( Zea mays L. ssp. mays) hybrids have a high yield potential but often lack satisfying early vigour under typical low spring temperatures of temperate latitudes. Maize was introduced into Europe already in the 16th century and until the 1950s, landraces evolved and adapted well to various geographically restricted and climatically marginal regions in Europe. Therefore, the objective of this study was to assess representatives of the large pool of Swiss Flint maize landraces for their early vigour under cool conditions in the field. A set of 17 landrace accessions were tested for 2 years at sites on the Swiss plateau (450 and 550 m a.s.l.) and in the foothills of the Swiss Alps (830 and 870 m a.s.l.). Plant emergence (PE), emergence index (EI), the efficiency of the photosystem II ( F v/ F m), leaf greenness (SPAD) and plant dry weight at the three- and six-leaf stages (DW3 P, DW6 P) were measured. Compared to a modern European Dent × Flint reference hybrid of good early vigour (Magister), superior early growth was found for several accessions that originated in northern alpine valleys. Three of these landraces (176RV, 151RV and 055LV) combined their good early growth with good early establishment (PE) and seemed to break the usually observed negative association between PE and DW3 P or DW6 P, a prerequisite for high-yielding plant stands. Plant emergence and establishment were often markedly better for landrace accessions from the Southern Alps, mainly from Tessin region, but their growth performance was significantly lower at the three- and the six-leaf stages. We conclude that northern Swiss landrace accessions in particular show good potential for improving early vigour of maize in cool field environments and we propose that the fast, non-destructive early vigour scoring is an efficient tool for assessing differences in growth in the field during these early plant stages.

Cold tolerance and cold hardening strategy of the Japanese pine sawyer Monochamus alternatus (Coleoptera: Cerambycidae)

AbstractThe Japanese pine sawyer, Monochamus alternatus, is an important pine forest pest and vector transmitting the pine wilt nematode that causes pine wilt disease. Low temperatures in autumn, winter and spring often differentially affect mortality of M. alternatus larvae. In this paper, we mainly compared the differences of mortality and cold hardening of larvae from different seasons, based on supercooling point (SCP) and cumulative probability of individuals freezing (CPIF). The cold hardening of the larvae from autumn, winter and spring seasons were largely different. Correlations between mortality and CPIF of autumn and spring larvae were highest on day 1/4, and gradually decreased with prolonged exposure duration. This beetle's death mainly resulted from freezing in short exposure duration. However, the correlation between mortality and CPIF of winter larvae increased gradually with the prolonged exposure duration. Death did not mainly result from freezing in long exposure duration. Autumn larvae are more susceptible and adaptable than winter and spring larvae. Winter larvae have a slight freeze‐tolerance trend. Our research showed that M. alternatus came into complex cold‐hardening strategies under natural selection. Freeze avoidance is the primary strategy; with prolonged exposure duration to above SCP or < 0 °C, chill tolerance is more important; this is followed by freeze tolerance during harsh winters.

Tree-Ring Chronology as a Source of Information on Susceptibility of Sitka Spruce to Climatic Conditions of Pomerania (Northern Poland)

This paper presents results concerning climatic conditions affecting diameter growth of Sitka spruce introduced to Baltic Pomerania (Sławno Forest District). A relatively high homogeneity of tree-ring series permitted to construct on their basis the tree-ring chronology of Sitka spruce. A significant positive correlation was found between radial increments of Sitka spruce and air temperatures of winter and spring months (January-April) and a negative relationship between radial increments and temperature of May. This study also showed a distinctly positive correlation between diameter growth and precipitation in July and November of the previous year, and precipitation in February and in summer season (June-August) of the current year. During years with low precipitation in summer or low temperatures in winter and spring all trees produced narrow tree-rings. The proportion of air temperature and precipitation in variation of radial increment of Sitka spruce, expressed by the coefficient of multiple determination, was 52%.

Infection of wild fishes by the parasitic copepod Caligus elongatus on the south east coast of Norway

Natural Caligus elongatus Nordmann infections of wild coastal fishes on the Norwegian south east coast were monitored at various times of the year from 2002 to 2004. The prevalence for all coastal fish (n = 4427) pooled was 15%, and there were great differences between fish species and seasons. Lumpfish Cyclopterus lumpus L. spawners were the most infected fish, with a prevalence of 61% and a median intensity of 4 lice fish(-1), whereas gadids had a mean prevalence of 19% and a median infection of 1 to 2 lice fish(-1). Sea trout Salmo trutta L. and herring Clupea harengus L. carried C. elongatus at prevalence values of 29 and 21%, respectively. The results were compared with infection data for immature North Sea lumpfish. Lumpfish spawners caught on the coast in March to April had fewer lice than North Sea lumpfish in July. Spawners carried mostly adult lice, as did coastal fish hosts in May to June. The low development rates of lice at low spring temperatures and new genetic data suggest that the May to June adult lice could not have been offspring of the March to April lice, indicating transfer of adult lice to coastal fish. Most coastal fish species appeared to acquire new C. elongatus infections between May to June and September. The relatively high numbers of chalimii on North Sea lumpfish suggest that offshore fish sustain an oceanic population of this louse species.

Maize Populations as Sources of Favorable Alleles to Improve Cold‐Tolerant Hybrids

Low spring temperatures are one of the main limiting factors for maize (Zea mays L.) growth along the European Atlantic coast. Several breeding programs have been performed to obtain cold‐tolerant maize genotypes, but the few cold‐tolerant inbreds and hybrids available need further improvements for cold tolerance and agronomic performance. The objective of this study was to identify cold‐tolerant maize populations with favorable alleles to improve cold tolerance and agronomic performance in early sowing of two cold‐tolerant hybrids. The parental inbred lines of two cold‐tolerant hybrids were crossed to nine cold‐tolerant populations. Tests were performed in a cold chamber and in the field for 2 yr at two locations. The populations Rojo de Tolosa and Puenteareas were the most promising sources of new favorable alleles for transferring cold tolerance to the hybrids EP80 × F7 and EP80 × Z78007, respectively. The populations Puenteareas and Silver King were the most outstanding donors to improve the agronomic performance of EP80 × F7 and EP80 × Z78007, respectively. Some improved versions of the cold‐tolerant inbred parents could be developed from crosses between F7 or Z78007 and Puenteareas; alternatively, Rojo de Tolosa or Silver King could be used as donors of favorable alleles, but the simultaneous improvement of yield and cold tolerance is not straightforward.

NORTHWARD EXTENSION OF GEOGRAPHIC RANGE OF THE SEA URCHIN HEMICENTROTUS PULCHERRIMUS IN HOKKAIDO, JAPAN

Abstract In the early 1990s, the geographic range of the sea urchin Hemicentrotus pulcherrimus from the Sea of Japan increased from off southwestern Hokkaido to off northern Hokkaido. This was caused by episodic recruitment in 1989, 1990, and 1991. These recruitments coincided with high water temperature during the larval periods (March to May). In 1993, H. pulcherrimus, at a density of 2.4 individuals/m2 derived from those three year classes, was found at a depth of 2–3 m in Tomari, where it had not been found in 1989. In Oshoro Bay, this sea urchin appeared dramatically in 1990, reached a peak density of 5.3 individuals/m2 in 1992, consisting mainly of 1989- and 1990-y classes. The high-density level of >2 individuals/m2 continued until 1998. Afterwards, no marked recruitment was found, corresponding to low water temperature in spring, and the density decreased markedly to 0.1 individuals/m2 in 2005. High water temperature in the 1990s is more likely to be responsible for the reproductive success of H. ...

Climatic effects on arrival and laying dates in a long‐distance migrant, the Collared Flycatcher Ficedula albicollis

Long‐distance migrants may respond to climate change in breeding, wintering or staging area by changing their phenology. The geographical variation in such responses (e.g. coastal vs. continental Europe) and the relative importance of climate at different spatial scales remain unclear. Here we analysed variation in first arrival dates (FADs) and laying dates of the Collared Flycatcher Ficedula albicollis in a central European population, from 1973 to 2002. The North Atlantic Oscillation (NAO) index correlated weakly with local temperature during the laying period. Decreasing spring temperatures until 1980 were associated with a trend towards later laying. The rate of warming (0.2 °C per year) and laying advancement (0.4 days per year) since 1980 are amongst the highest values reported elsewhere. This long‐term trend in laying date was largely explained by the change in climatic factors. The negative effect of local spring temperature on laying was relatively stronger than that of NAO. The number of clutches initiated on a particular day was marginally affected by the temperature 3 days prior to laying and the response of females to daily variation in temperature did not change over years. Correspondence between the average population‐level and the individual‐level responses of laying date to climate variation suggests that the advancement of laying was due to phenotypic plasticity. Despite warmer springs and advanced laying, FADs did not change over years and were not correlated with local spring temperature. Marginal evidence suggests later departure from wintering grounds and faster migration across staging areas in warmer conditions. Advancement of arrival was probably constrained by low local temperatures in early spring just before arrival that have not changed over years. The interval between first arrival and laying has declined since 1980 (0.5 days per year), but the increasing temperature during that period may have kept the food supply approximately unchanged.

The introduction of the European bitterling (Rhodeus amarus) to west and central Europe

AbstractThe European bitterling is considered to be a native species over much of its present range in Europe. A dramatic decline in its abundance from 1960 to 1980 in west and central Europe, attributed to aquatic pollution, led to the establishment of stringent national and international regulations for protection of the species. Here, we review the evidence that until AD 1100 the bitterling was restricted to the Ponto‐Caspian and Aegean regions (south‐eastern Europe and adjacent regions of Asia Minor) and only expanded into its present range during the 19th century. The earliest records of bitterling in west and central Europe are from regions where carp cultivation was common and the bitterling appears to have spread into this region in association with the gradual expansion of carp cultivation. After an initial period of expansion, between approximately 1150 and 1560 in regions with carp cultivation, the species virtually disappeared from Europe during the coldest period of the Little Ice Age. Bitterling reappeared at the end of the 18th century, initially in historical centres of carp cultivation, and was again abundant and widespread in Europe by around 1850. Its reappearance appears to have been through expansion of refuge populations as well as new invasions. The decline in abundance of bitterling during the period 1960–80 in west and central Europe appears not only to have been caused by pollution, as is generally believed, but may also be correlated with low spring temperatures. From approximately 1980 onwards the European bitterling once again expanded its distribution in many parts of Europe, particularly in eastern Europe. This recent expansion may be due to a combination of factors, including a rise in ambient temperature coupled with an increase in anthropogenic dispersal and changes to aquatic habitats favourable to bitterling. Thus, the bitterling, which is legally protected in Europe at a national and international level as an endangered indigenous species, is actually an invasive species and a parasite of freshwater mussels. Its current expansion in distribution could pose a hazard to freshwater mussel populations in regions where they are already threatened.

Genetic analysis and gene mapping of cold-induced seedling chlorosis in rice

We found that the seedlings of indica rice cultivar Dular showed chlorosis but the seedlings of japonica rice cultivar Lemont remained green under natural low temperature in early spring. Using an F2 population of Lemont Dular, we found that the difference of cold tolerance at seedling stage between Dular and Lemont is controlled by a single major gene, with the chlorosis allele being recessive. We named the gene cisc(t). With the help of SSR markers, cisc(t) was mapped in a 5.5 cM interval between SSR markers RM257 and RM242 on chromosome 9.

Impact of changing soil moisture distribution on net ecosystem productivity of a boreal aspen forest during and following drought

The interannual and seasonal variability of gross ecosystem photosynthesis (P), ecosystem respiration (R) and evapotranspiration (E), and their relationships to environmental factors were used to explain changes in net ecosystem productivity (F NEP) at the onset of, during, and following a 3-year-long (2001–2003) drought in a mature boreal aspen stand in central Saskatchewan, Canada. The forest was a moderate carbon (C) sink over its entire 11-year data record (F NEP = 153 � 99 g C m � 2 year � 1 ), including the peak drought years of 2002 and 2003. In 2001, the depletion of water near the soil surface likely reduced heterotrophic soil respiration while water remaining deep in the root zone maintained P above the pre-drought mean, resulting in above-average F NEP. In 2002 and 2003, the forest remained a C sink even though P was below average because R was also below average—a likely consequence of the influence of low soil water content in deep and shallow soil layers on both autotrophic and heterotrophic respiration. In 2004, the recharge of soil water in shallow soil layers allowed R to recover to its pre-drought values, whereas low spring temperatures, the slow recharge of soil water in deep soil layers in spring, late leaf emergence and diminished leaf area index combined to suppress P and produce the lowest annual F NEP of the 11-year record (4 g C m � 2 year � 1 ). The low F NEP and P were mirrored in the lowest stem growth and LAI values of the 11-year record. In 2005, a warm wet year, both the annual values and seasonal variations of F NEP, P and R returned to those of pre-drought years; the partial recovery of LAI to pre-drought values suggests that aspen P was able to adjust to this restriction on C assimilation. Growing season average dry surface conductance (gsv), the Priestley–Taylor coefficient (a) and light use efficiency (LUE) reached their lowest values in 2003 and became similar to predrought years in 2004–2005. Water use efficiency (WUE) was highest in 2003 and remained above average in 2004 and 2005. At the ecosystem scale, the above-average gains made in C sequestration in the first year of the drought were significantly offset by belowaverage stand F NEP in the final 2 years of the drought, and in the year following the drought. # 2006 Elsevier B.V. All rights reserved.

Seasonal course of translocation, storage and remobilization of 13C pulse‐labeled photoassimilate in naturally growing Larix gmelinii saplings

Autocorrelation--correlation of tree-ring parameters such as ring width, density and isotope ratios to the environmental conditions of the previous year(s)--is associated with the use of previous photoassimilate for current year's tree ring formation. To clarify the seasonal course of carbon allocation patterns among needles, branches, stem and roots, we pulse-labeled 10 Larix gmelinii growing in a continuous permafrost zone with 13CO2. Photoassimilate incorporated in June was allocated mainly to above-ground parts, indicating active above-ground growth in spring. Very little was allocated to below-ground parts (2.6-7.9%), probably because root growth is inhibited by low soil temperatures in spring. Conversely, a higher proportion of July and August photoassimilate was allocated to below-ground parts (32-44 and 12-24%, respectively). About half the carbon in new needles was derived from stored material. The starch pool in non-needle parts, which can be used for xylem formation, drew approx. 43% of its carbon from the previous year's photoassimilate, indicating that carbon storage is a key mechanism behind autocorrelation in (isotope) dendroclimatology.

Impacts of the introduced basswood thrips ( Thrips calcaratus Uzel) on forest health in the Great Lakes region

Insect, disease, tree condition, weather, and soil data were sampled from 22 northern hardwood forest sites containing American basswood, Tilia americana L., in Michigan, Wisconsin, and Minnesota from 1998 to 2000. Basswood dieback increased by 10% during this period. Insect abundance on basswood foliage was dominated by Thysanoptera, of which the introduced basswood thrips, Thrips calcaratus Uzel, accounted for over 95% of total catch. There was little evidence of pathogens or abiotic stress factors having pronounced effects on basswood. Weak associations between basswood dieback and T. calcaratus abundance suggest that it is an important component of basswood decline in the Great Lakes region, but that other factors are also involved. The native predator, Leptothrips mali (Fitch), is highly synchronized with the native basswood thrips, Neohydatothrips tiliae (Hood), with both species emerging in late spring and persisting into August. The two introduced herbivores, T. calcaratus and Taeniothrips inconsequens (Uzel), peak in late spring before becoming almost totally absent by August. Numbers of adult T. calcaratus in early May can be used to predict subsequent numbers of larvae. T. calcaratus abundance was more variable among sites than among trees within a site. This indicates that future investigations will benefit most by increasing the number of study sites rather than more intensively surveying fewer sites. A significant year-by-site interaction was observed for both adult and larval T. calcaratus. Adult populations were inversely associated with organic matter, calcium, nitrate, ammonium, soil pH, summer precipitation, April minimum temperature, April precipitation, and basswood live crown ratio. They were directly associated with low winter temperature and basswood crown light exposure. Larval T. calcaratus were inversely associated with soil potassium, precipitation, basswood live crown ratio, and basswood crown position. They were directly associated with low winter and spring temperatures, basswood light exposure, and winter snowfall. Interpretation of these relationships must be tempered, however, by the presence of autocorrelations among many of these variables. This study shows that basswood is declining throughout the Great Lakes region, and T. calcaratus, along with other contributing factors, are related to this phenomenon.

Growing season changes in Fennoscandia and Kola peninsula during the period 1982 to 1999 - Implications for reindeer husbandry (In Norwegian with Summary in English)

Growing season changes in Fennoscandia and Kola peninsula during the period 1982 to 1999 - Implications for reindeer husbandry (In Norwegian with Summary in English)

Analysis and modelling of water and near water temperatures in flooded rice ( Oryza sativa L.)

The knowledge of micrometeorological conditions in flooded rice fields is crucial for better modelling the behaviour of the crop in mid and high latitudes, where the thermal mitigation provided by water layer is significant against the climatic risk of low temperatures in spring and early summer. Two micrometeorological models (a mechanistic and an empirical one) for the simulation of thermal profile related to water and near water temperatures were calibrated and validated with data gauged in some rice fields located near Milano, Italy. The mechanistic model is based on the solution of the equation of the surface energy balance; the empirical one is funded on Gaussian filters. Both the models need as input data only daily values of maximum and minimum temperatures and therefore are suitable for agroecological operational purposes. The results show that the models could improve the performances of crop simulation models physically based, currently used for crop growth, development and production analysis. In fact, the comparison between measured and simulated temperature values indicates that both the presented models are able to reproduce the effect of water on temperature (average RRMSE = 14% for the mechanistic model and 7% for the empirical one; modelling efficiency always positive).

Why egg-caring males of Isaza (Gymnogobius isaza, Gobiidae) refuse additional females: preliminary field observations

Like many other gobies, males of the Isaza goby, Gymnogobius isaza endemic to Lake Biwa, Japan, conduct parental care of eggs at nests, and females are likely to choose mates while visiting nests. The reproductive strategy should induce polygyny, but Isaza males never accept additional females in one breeding cycle. Sampling data of broods indicated that the egg mass areas were much smaller than the nest sizes, suggesting that nest size is not the limiting factor in obtaining further eggs from additional females. The brood size greatly decreased as the duration of care progressed. Few individuals including caring males ate eggs, and heterospecific egg predators were rarely observed. Sixty percent of egg masses at the middle stages of egg development were infected with aquatic fungi, some being covered with a fungus mat that drastically reduced survivorship. Infected egg masses contained more eggs than non-infected ones at the same stage, indicating that large egg masses are prone to be frequently destroyed by fungi. It is likely that the activity of parental males is lowered during the long care periods at low water temperature in early spring. Such lowered activity of caring males might be responsible for infections in large broods that would have needed more care. We propose the hypothesis that male rejection of additional females may be related to optimal brood size, which will be less susceptible to fungus infection and produce more hatching young than otherwise. This hypothesis will explain not only male avoidance of additional females but also some unique reproductive behaviors of this fish such as some females’ spawning of a portion of of the mature eggs in one nest.