POLYMORPHISM IN THE ARCTIC SKUA STERCORARIUS PARASITICUS IN ICELAND

A survey of the frequency of the dark and light colour forms of the Arctic Skuas breeding in Iceland provided evidence of a south-north cline, the light form being more frequent in the north than in the south. In one area there were significantly more dark birds in 1971 than 30 years earlier, but in two other areas there was no evidence of a change in frequency. In northeast Iceland, where the light form is common, there was a statistical tendency towards unlike matings. It is suggested that the adaptive significance of the forms is to be sought in terms of facilitating departures from random mating, the genetic consequences of which are understood in general terms, although the ecological significance remains obscure.     

SCENT-MARKING, DOMINANCE AND FLEHMEN BEHAVIOR IN DOMESTIC RABBITS IN AN ARTIFICIAL LABORATORY TERRITORY

The olfactory exploratory and scent-marking behavior of domesticrabbits were observed in an artificial laboratory enclosure.The rabbits tended to mark certain objects more frequently thanothers with their chin gland secretion (chinning), apparentlyguided by visual characteristics; however, they preferred tosniff and chin objects which had been chinned previously overthose that had never been chinned. They chinned more frequentlywhen faecal pellets were present. Dominant male rabbits chinnedobjects more frequently, and subordinate male rabbits less frequently,in a freshly marked environment than in a clean one; similarlydominant males chinned more frequently and subordinates lessfrequently when urine from another rabbit was present. Rabbitspreferentially chinned urine and faecal pellets from other rabbitsover their own. The dominance relations of the rabbits were determined by analyzingthe behavior patterns correlated with chasing and fleeing. Oneof the most characteristic features of encounters between tworabbits was a complete sexual display. Long periods of sniffing of certain substances, usually urine,by the rabbits were analyzed and found to be basically similarto sniffing and flehmen patterns shown by cats. The data supportthe hypothesis that the whole flehmen pattern including lickingand headshaking is involved with transporting substances insolution to the vomeronasal organ. ^* Present Address: Laboratory of Neurophysiology, UCLA MentalRetardation Center, Los Angeles, California 90024.^** Present address: Laboratory of Animal Physiology, Kruislaan320, Amsterdam, The Netherlands.     

超甜玉米单倍体悬浮细胞系的建立及其生长特性

从超甜玉米的花药培养物中,筛选出28个具有高度胚胎发生能力的类型Ⅱ愈伤组织系,这种愈伤组织质地松散,易于分散,可以长期进行继代培养。将3个月龄的类Ⅱ愈伤组织接种在液体培养基中进行振荡培养,建立起分散程度很好的8个悬浮细胞系。实验结果说明,培养基中加入酪蛋白水解物(CH)和2-(N-吗啉代)乙基磺酸(MES)对悬浮细胞的生长是有利的。培养基的 pH 迅速下降吋,细胞的增殖十分缓慢,当培养基的 pH 值开始升高时,细胞的增殖也显著加快。利用滋养培养法,可以使悬浮细胞的愈伤组织形成率大大提高(比对照高11.8—19.7倍),并在低密度下达到较高的(41.3%)植板率。染色体计数表明,继代培养6个月之后,88.0%的悬浮细胞和95.2%的再生植株的染色体数保持着2n=x=10的单倍性水平。     

STABILITY AND INSTABILITY IN PLANT COMMUNITIES FOLLOWING FIRE

Tree species composition and density were monitored in closed oak-hickory forest and forest-prairie edge for a period of five years after a prescribed burn. In the closed forest, tree stem density declined markedly following the burn. Tree basal area and density decreased from 17.5 m²/ha and 630 trees/ha in the preburn sample to 12.0 m²/ha and 310 trees/ha five years later. In contrast, on the forest-prairie edge, tree basal area and density increased slightly during the same time period from 3.0 m²/ha and 117 trees/ha to 5.2 m²/ha and 172 trees/ha. Our data suggest that closed canopy forests in fire susceptible areas accumulate fuels to levels that encourage fires of sufficient intensity to destabilize forest systems and convert them to open forests or savannahs. Conversely, on the forest-prairie edge, amounts and patterns of fuel accumulation, and species response to burning, are such that fire can be considered to be a factor promoting stability.     

HETEROZYGOSITY AND DEVELOPMENTAL STABILITY UNDER INBREEDING AND CROSSBREEDING IN PINUS ATTENUATA

The relationship between stability of annual trunk growth and heterozygosity at 24 polymorphic isozyme loci was studied in 10-year-old trees of knobcone pine (Pinus attenuata Lemm.) that were the products of contrasting systems of mating, self-, and interpopulation cross-pollination. Heterozygosity and variability of trunk growth were strongly related only when inbreds and crossbreds were compared; the crossbreds showed greater residual variability on an absolute scale, and greater responsiveness to climate on both absolute and relative scales. Within the inbreds there was no evidence of a relationship between heterozygosity and variability. Within the crossbreds, only one trait, a measure of relative trunk growth rate, showed a relationship with heterozygosity, and indicated greater variability of the more heterozygous trees. These results, and others in the literature, suggest that the relationship of heterozygosity to homeostasis for fitness components is neither simple nor monotonic; it varies between scales of measurement, genetic backgrounds, and environments.