Spawning behavior ofChaetodon multicinctus (Chaetodontidae); pairs and intruders

Synopsis Spawning by the banded butterflyfish,Chaetodon multicinctus (Chaetodontidae) was observed on coral reefs off Kona, Hawaii. These fish occurred in male-female pairs during normal daytime activities, a behavior which is typical for the family. Courtship is also a paired male-female activity. During spawning, however, other individuals (males?) may intrude on the spawning pair. Spawning typically takes place at least a meter or two above the bottom. The spawning position consists of the male below and behind the female with his snout against the female's ventral flank or anal fin area. Intruding individuals may join in when the pair is in position and about to spawn. Intruders line-up against the male in the same position as he is against his female. Underwater photographs are included to illustrate these behaviors.     

鲢、鳙在天然条件下的摄食强度(Ⅱ)武汉东湖鲢、鳙周年摄食强度的研究

武汉东湖的鲢(Hypophthalmichthy molitrix)鳙(Aristichthys nobilis)在天然条件下摄食强度具季节性变化。摄食强度高峰处于夏季,低谷处于冬季。在实验条件下,按周年采样期间水温变化范围,测定鱼的肠管排空率。食物通过鱼肠管时间(Y_p—h)与水温(X_t—℃)的关系为: 鲢Y_p=270.63 X_t~(0.6408) 鳙Y_p=280.46 X_t~(0.6642) 根据修正后Bajkov公式(D=C (24.A)/n),估算鱼的日粮。鱼日粮(Y_D)与水温(X_t)关系为: 鲢Y_D=0.2683e~(0.1503X_t) 鳙Y_D=0.0075X_t~(2.2715) 计算鱼在天然条件下周年月粮及年粮。鲢、鳙对天然饵料年消耗量分别为18.924公斤及17.39公斤,饵料系数分别为18.02及13.38。     

Predicting variability in catch-per-effort in Atlantic cod, Gadus morhua, trap and gillnet fisheries

The relationships between catch rates and fish abundance, hydrographic conditions and fishing effort, for Atlantic cod caught by trapnets (fixed gear) and gillnets (non-fixed gear) in the northern Gulf of St Lawrence have been quantified. Daily changes in trap catch rates were accounted for by changes in salinity, currents and mean local cod densities in 1985 ( R ²= 0.78), and predicted 1986 trap catch rate changes (by 1985 model) were correlated significantly with those observed ( r = 0.60, P < 0.05). In contrast, the daily changes in 1985 gillnet catch rates were determined by currents, maximum (not mean) local cod densities, and fishing effort (negative) ( R ²= 0.68), while predicted 1986 gillnet catch rates (by 1985 model) were significantly correlated with those observed ( r = 0.35, P < 0.05). Seasonal catchability coefficients of the traps were similar in 1985 and 1986, but for gillnets this index was an order of magnitude higher in 1986 than in 1985.     

Amino acids as determinants of host preference for the xylem feeding leafhopper,Homalodisca coagulata (Homoptera: Cicadellidae)

Summary Homalodisca coagulata is a highly polyphagous xylem feeder with distinct seasonal patterns in it's selection of host plants. These patterns were examined in relation to the amino acid content of the xylem for four common host species; Lagerstroemia indica, Baccharis halimifolia, Prunus persica, and Prunus salicina. Xylem fluid was collected from each host species at times when numbers of feeding leafhoppers were both low and high. In each case, concentrations of amino acids were greatest when numbers were high. Similarly, comparisons between host species at given times showed that concentrations of amino acids were positively correlated with host selection. In a second study, amino acids of xylem were manipulated by budding scions of a non-preferred host (P. persica) on rootstocks of preferred (P. salinica) and non-preferred (P. persica) hosts. Morphology and phenology of the budded trees were similar to that of the scion species yet the xylem composition of amino acids was primarily dependent on the rootstock. Concentrations of amino acids and the preference of leafhoppers were roughly two-fold greater for scions of the preferred than the non-preferred rootstock. In both studies, amides (glutamine plus asparagine) were the amino acids most highly correlated with host selection. These compounds are the predominant amino acids in xylem fluid, have high nitrogen to carbon ratios, and account for a high percentage of the caloric value in xylem fluid. Many of the less abundant amino acids were positively correlated with host preference, but the correlations were less consistent and correlation coefficients were generally lower.Florida Agricultural Experiment Station Journal Series No. 9672     

利用泽兰实蝇控制紫茎泽兰的生防策略研究

本文根据野外泽兰实蝇种群15个世代的调查资料,利用契贝谢夫正交多项式拟合了泽兰实蝇、紫茎泽兰的空间格局。阐明了泽兰实蝇空间格局的序列变化及紫茎泽兰空间格局的特点;揭示了泽兰实蝇空间格局的特点受当地主风及寄主紫茎泽兰空间格局特点的影响;并从最优控制系统的角度对泽兰实蝇-紫茎泽兰系统作了初步探讨。首次提出了最佳释放虫量指标为每条虫占有10条枝条。这些结果为多点释放及定点多次释放泽兰实蝇防治紫茎泽兰这一生防策略提供了理论基础。     

Seasonal changes in canopy structure in two mediterranean dune shrubs

Abstract. The annual cycle of canopy structure in two mediterranean shrubs in a pioneer zone of the mobile dune system in the Donana National Park, Scrophularia frutescens and Halimium halimifolium, has been analyzed. Destructive methods were used as well as a new non-destructive method, based on frequency analysis of organ distribution within the plant canopy. S. frutescens shows strong seasonal changes of photo-synthetic biomass, but little annual increment in dry weight. In H. halimifolium, seasonal changes are not as strongly differentiated as in S. frutescens, but a higher annual increment is shown. The canopy structure of both species and its temporal changes are compared with existingplant strategy models.     

How feeding performance and energy intake change with a small increase in the body size of the three-spined stickleback

Changes in the foraging behaviour due to variation in the body size of the three-spined stickleback Gasterosteus aculeatus were investigated. All sizes of fish had a high probability of attacking prey whenever encountered. The probability of eating the prey increased with the size of the fish, as the larger fish had larger jaws and a greater stomach capacity. Therefore, as fish increased in size there was an increase in the probability of successful prey capture. The level of satiation did not have an effect on the prey handling time, which is contrary to other studies and is probably a result of the large prey sizes. The physical size of the prey meant that the handling times were long regardless of the motivational level of the fish. The larger fish took in more energy and at a faster rate, although the time to reach satiation was similar for all fish sizes. The advantage that large fish appear to have in successfully gaining large prey is negated by their greater metabolic requirement. The changes in feeding performance induced by small increases in body size could have important consequences for intraspecific competition, habitat Use and risk of predation.     

EVOLUTIONARY LOSS OF LARVAL FEEDING: DEVELOPMENT,FORM AND FUNCTION IN A FACULTATIVELY FEEDING LARVA,BRISASTER LATIFRONS

Species with large eggs and nonfeeding larvae have evolved many times from ancestors with smaller eggs and feeding larvae in numerous groups of aquatic invertebrates and amphibians. This change in reproductive allocation and larval form is often accompanied by dramatic changes in development. Little is known of this transformation because the intermediate form (a facultatively feeding larva) is rare. Knowledge of facultatively feeding larvae may help explain the conditions under which nonfeeding larvae evolve. Two hypotheses concerning the evolutionary loss of larval feeding are as follows: (1) large eggs evolve before modifications in larval development, and (2) the intermediate form (facultatively feeding larva) is evolutionarily short-lived. I show that larvae of a heart urchin, Brisaster latifrons, are capable of feeding but do not require food to complete larval development. Food for larvae appears to have little effect on larval growth and development. The development, form, and suspension feeding mechanism of these larvae are similar to those of obligate-feeding larvae of other echinoids. Feeding rates of Brisaster larvae are similar to cooccurring, obligate-feeding echinoid larvae but are low relative to the large size of Brisaster larvae. The comparison shows that in Brisaster large egg size, independence from larval food, and relatively low feeding rate have evolved before the heterochronies and modified developmental mechanisms common in nonfeeding echinoid larvae. If it is general, the result suggests that hypotheses concerning the origin of nonfeeding larval development should be based on ecological factors that affect natural selection for large eggs, rather than on the evolution of heterochronies and developmental novelties in particular clades. I also discuss alternative hypotheses concerning the evolutionary persistence of facultative larval feeding as a reproductive strategy. These hypotheses could be tested against a phylogenetic hypothesis.     

FECAL METHANOGENS AND VERTEBRATE EVOLUTION

It has been assumed that the feeding habits of vertebrates predispose the variety of intestinal differentiations and the composition of the microbial biota living in their intestinal tracts. Consequently, the presence of methanogenic bacteria in the various differentiations of the large intestine and the foregut of herbivorous vertebrates had been attributed primarily to the existence of anaerobic habitats and the availability of carbon dioxide and hydrogen originating from the fermentative microbial digestion of plant-based diets. However, Australian ratites, many murids, and several New World primates lack methanogens, despite their intestinal differentiations and their vegetarian feeding habits. Crocodiles, giant snakes, aardvarks, and ant-eaters on the other hand release significant amounts of methane. A determination of methane emissions by 253 vertebrate species confirmed that competence for intestinal methanogenic bacteria is shared by related species and higher taxa, irrespective of different feeding habits. In “methanogenic” branches of the evolutionary tree, a variety of differentiations of the large intestine evolved and, in some cases, differentiations of the foregut. In contrast, the lack of competence for methanogens in chiropterans/insectivores and carnivores apparently has precluded the evolution of specialized fermenting differentiations of the digestive tract. Our observations reveal that the presence of intestinal methanogenic bacteria is under phylogenetic rather than dietary control: competence for intestinal methanogenic bacteria is a plesiomorphic (primitive-shared) character among reptiles, birds, and mammals. This competence for methanogenic bacteria has been crucial for the evolution of the amniotes.     

Antixenotic resistance of subterranean clover cotyledons to redlegged earth mite, Halotydeus destructor

The short-term response of redlegged earth mite, Halotydeus destructor (Tucker) (Acarina: Penthaleidae) to cotyledons of different varieties of subterranean clover (Trifolium subterraneum subsp. subterraneum L.) was assessed by means of paired choice tests, and no-choice tests. H. destructor had lower numbers and fed less on detached cotyledons of resistant than susceptible varieties, yielding a correlation between the numbers of mites and feeding damage to the cotyledons during a three hour test period. For a number of resistant and susceptible varieties, there was a negative correlation between cotyledon deterrence in the three hour choice test and feeding damage to seedling after a two week period. Since the response of the mites to different subclover varieties occurred within three hours, it is concluded that the resistance is based on antixenosis.No evidence was obtained for antifeedant activity in organic solvent extracts from the variety DGI007 (resistant) in comparison with those from the variety Dalkeith (susceptible). Water soluble compounds from DGI007 cotyledons were preferred by mites, in feeding tests in terms of numbers, over those from Dalkeith (susceptible). Squeezed sap from the cotyledons of both varieties showed the same effects on mites as 5% glucose and were more phagostimulatory than water extracts. Mechanically damaged cotyledons of Dalkeith and DGI007 attracted more mites than the undamaged counterparts. The toughness of cotyledons in 17 varieties of T. subterraneum subsp. subterraneum was measured with a manual penetrometer. Results showed a negative correlation between toughness values and mite feeding damage scores (r²=0.752) for all varieties except S3615D (resistant). This implies a likely involvement of epidermal toughness as a contributor in the antixenotic resistance of these varieties. Other mechanisms may be involved in the resistance of S3615D.