Effect of food concentration on digestion and vacuole passage time in the heterotrichous marine ciliateFibrea salina

Vacuole passage time (VPT) and digestion time (DT) in the heterotrichous marine ciliateFabrea salina (Henneguy) (from cultures) were measured in 1986 under different food concentrations, using epifluorescence microscopy, and employing fluorescent particles andRhodomonas lens as tracers. Both VPT and DT were unaffected by food concentrations ranging form 0 to 10⁶ cells ml^?1 and can be treated as constants (120.0 and 71.2 min, respectively). Vacuole life expectancy may be related to the ingestion-rate-determining need forde novo membrane synthesis and “old” vacuole membrane recycling which feeds new endocytotic vacuole production. Both processes are enzyme-controlled, which would explain the observations of other investigators that at least in certain ciliates digestion time is responsive to changes in temperature.     

Escalating fights for rank-order position between male swordtails (Xiphophorus helleri): Effects of prior rank-order experience and information transfer

Summary A previous hypothesis which we originally based on standardized mirror tests was examined. It stated that subordinate males from socially stabilized groups, when confronted with a strange male of similar fighting ability, tend to take the offensive; in contrast, dominant males tend to wait and see and to increase their aggressiveness only as far as necessary to counter the aggressive actions of the opponent. 30 highly escalating fights between well matched opponents, either with different or with the same prior rank-order experience, were recorded on video tape and then analysed in detail. Rank-order experience affected neither the escalation level nor the outcome of the fights. However, in the first nonescalated stage of the fights all measures of unilateral aggressive actions were higher in the omega than in the alpha males. This is contrary to expectations based on the theory of social conditioning; nor can it yet be explained by game-theory models. We then discuss why it should pay subordinates to be more offensive and to show higher levels of unilateral aggression than dominants. Some current aspects of game theory are supported by our data: (1) Threat display is a poor predictor of attack and fleeing, and simply informs the opponent that the threatening individual will probably just stay and avoid further escalations. (2) Relative fighting ability is demonstrated during highly-escalated fighting by delivering Fin Grips, the most effective and costly attack pattern. The high energetic costs of Fin Grips can be compensated by reducing the rate of Biting. (3) Probably, the combatants did not transfer information about their intentions, i.e. they concealed their intentions as to what they were going to do next. Contrary to the predictions of game theory, winners and losers showed some differences in Pecking early in the nonescalated stage of the fights, the prospective losers exhibiting more Pecking than the winners.This study was supported by grants from the Deutsche Forschungsgemeinschaft     

Diel vertical migration and feeding patterns of Mysis mixta (Crustacea,Mysidacea) in the Baltic Sea

The extent of the nocturnal vertical migration of Mysis mixta Lilljeborg varied between early July and late October (of 1985 and 1986) in a coastal area of the Baltic Sea. Migration was more restricted in early July and late October. Seasonal changes in surface light levels and transparency were sufficient to explain the observed differences. Mysids avoided light levels above 10^-4 lux throughout the study period. Smaller juveniles migrated higher up than larger juveniles and adults. A two-layered distribution with part of the population close to the bottom was observed at night. Zooplankton were more abundant in water layers above the main concentration of mysids. M. mixta fed on phytoplankton, detritus, copepods, cladocerans, rotifers and tintinnids. Diel changes in gut fluorescence indicated a higher intake of phytoplankton at night, but levels were low compared to primarily herbivorous zooplankton. Comparisons of stomach contents of mysids caught at the bottom in the evening and in the water column at night showed a higher ingestion of zooplankton at night and of detritus during the day. Mysids caught at the bottom at night had an intermediate diet. Copepods and cladocerans constituted between 90 and 100% of ingested material by weight in all mysid groups.     

Elemental concentrations of hydrothermal vent organisms from the Galápagos Rift

Concentrations of 40 elements were determined in tissues and whole bodies of mussels (Bathymodiolus thermophilus) and/or whole bodies of limpets (Neomphalus fretterae) collected from the submarine thermal springs on the Galápagos Rift in 1977. Concentrations of Ag, As, Fe, Mn, Mo, Se, Sr, and Zn were comparable or elevated relative to those of intertidal mollusks, which have been utilized as indicators of anthropogenic trace-metal contamination. Both species contained concentrations of some elements (e.g. Ag, As, Fe, Mn, Mo, Se, Zn) which corresponded with the elevated levels of those elements discharged from hydrothermal vents. Many elements were most enriched in the gills and digestive glands of the mussels. Iron:manganese ratios of those tissues were similar to ratios of pelagic and transitional sediments, indicating that metal-rich suspended particulates had been absorbed onto mucous membranes. Comparisons with other benthopelagic organisms were precluded, since the present data represent essentially the only trace-element analyses of deep-sea macroinvertebrates.     

Occurrence and characteristics of unusual protistan symbionts from surgeonfishes (Acanthuridae) of the Great Barrier Reef,Australia

The occurrence of unusual symbiotic microorganisms was examined in the intestines of a range of fish from the Great Barrier Reef, Australia. The fish taxa examined included 26 species of the family Acanthuridae, as well as representatives of phylogenetically related and herbivorous taxa. The microorganisms, referred to as protists, were only found in herbivorous and detritivorous members of the Acanthuridae. Protists were not found in planktivorous acanthurids, nor in any members of the families Kyphosidae, Pomacentridae, Scaridae, Zanclidae, Siganidae and Bleniidae we examined. In addition, protists were absent from the herbivorous acanthurids A. xanthopterus and A. nigricans. A range of protist forms, characterized by differences in size (8 to 417 m), shape and mode of cell division (daughter-cell production and binary fission), was observed. The occurrence of these forms appeared to be correlated with host feedingecology. Large forms (>100 m) of the protists were only found in acanthurids which fed over hard-reef substrata. Smaller forms were found in sand-grazing and detritivorous species. One of the protist forms appears identical to protists previously reported from Red Sea acanthurids.     

Payoff asymmetries in contests among male brown-headed cowbirds

Summary Morphometric analyses and behavioral observations of a marked population of brood parasitic brown-headed cowbirds (Molothrus ater) revealed several male attributes correlated with dominance. Males that won larger percentages of the contests in which they were involved tended to be older and larger than other males. Dominant males arrived earlier on the breeding grounds and became engaged in more contests than subordinate males. If a female was present during a contest among males, the male which she was accompanying (her consort, and mate in most cases) was more likely to win the contest than were any of his opponents. Multiple regression analyses were performed to determine any significant partial effects of these attributes on male dominance. Age and involvement in more contests exerted significant partial effects in some analyses, but only the presence of a female consort did so consistently. I suggest that the female is a resource of greater value to the male with whom she is consorting than to other males. Her value is greater in terms of present and future benefits because he has already expended some or all of the effort necessary to establish a pair bond. He will have to expend less future effort to remain her mate than would another male to become her mate. Her presence during contests induces him to persist (or escalate) and to dominate his male opponents.     

Spacing of leks in relation to female home ranges,habitat requirements and male attractiveness in the great snipe (Gallinago media)

Summary In an attempt to examine three main hypotheses on the evolution of leks, data on female home ranges, distance between leks and male site fidelity in the great snipe (Gallinago media) were obtained. In a 30 × 40 km area in central Sweden, the locations of 12 leks were identified. Six were within the study area (7 × 11 km) in which probably all leks were known. In the study area, nearest neighbor distances between leks were longer than the predicted drawing area (diameter of female home ranges plus the detection range of leks). Furthermore, in only 1 of 13 radio-tracked females did the estimated home range enclose many leks. These data do not fit the prediction from the hotspot hypothesis on the dispersion of leks, namely, that the distance between leks should be less than the drawing area and hence an average female home range should enclose more than one lek. The observed distance between leks was about the same as predicted by the female preference hypothesis. This hypothesis also predicts females visit mainly one lek; however, we found they sometimes visit two and nest close to a third. We propose that males may first settle according to hotspot rules, but females will resettle according to preferences for certain males and/or larger leks. In this way some hotspot leks are abandoned, and the distance between leks is increased as males become more tightly clumped. However, when all males and females have settled, the leks still existing would be on hotspots. In the female preference hypothesis, males are assumed to aggregate on leks because females prefer clustered males as they can be more easily compared than if they are dispersed. Alternatively, in the attractiveness hypothesis, it is suggested that females prefer certain males, and hence unattractive males surround the attractive are forced to join leks in order to come close to females. Our data on male site fidelity support the attractiveness hypothesis because successful and dominant males return to the same lek and territory, both within and between years, whereas unsuccessful males move to other leks. Attractiveness of certain males may explain why according to hotspot rules in this species males are more clumped than expected. Offprint requests to: J. Höglund