Poor Physiological Condition Research Articles

Microhabitat use and social structure in Linnet Carduelis cannabina and Corn Bunting Miliaria calandra at a winter roost in central Spain

Capsule Both species selected particular patches for roosting, and Linnets but not Corn Buntings showed a social structure with males occupying the preferred roosting positions. Aims To evaluate microhabitat preferences of Linnet and Corn Bunting within a winter communal roost, and to examine roost structure according to sex, age and body size. Methods We captured Linnets and Corn Buntings along a habitat gradient in a reed-bed in central Spain when they were coming to roost. Each bird was sexed, aged, and several body traits were measured. We also characterized the habitat patches where the birds were trapped and grouped patches according to their similarity. Results Three groups of patches were defined according to reed structure. Linnets preferred patches with low density of high and thick shoots, while Corn Buntings preferably used patches with intermediate values for these variables. Interspecific competition for preferred positions was not evident. Male Linnets were proportionately more abundant in the preferred patches, and individuals in lower body condition, independent of sex, age or body size, occupied the non-preferred patches. Male Corn Buntings were less abundant, bigger in size, and showed better condition than females, although differences in body size and condition were not apparent among patches within the roost. Conclusion Our results suggest that among-patch differences in structure and location within a reed-bed generate microhabitats that differ in quality for roosting passerines. This habitat heterogeneity in turn seems to be responsible for the social spatial structure observed in Linnets, in which females and individuals in poor physiological condition were displaced, possibly through competition, towards non-preferred positions. The relatively small body size of Linnets compared to Corn Buntings might explain Linnets' preference for patches that seem to provide more protection against harsh weather conditions.

Environmental and physiological conditions affecting Tetrahymena sp. infection in guppies, Poecilia reticulata Peters

Parasitic infections caused by Tetrahymena sp. constitute a serious problem in guppies, Poecilia reticulata. Tetrahymena was isolated from skin lesions of naturally infected guppies in a commercial aquaculture farm, cultured in vitro and used in subsequent experimental infections. In addition to guppies, angelfish, Pterophyllum scalare, platyfish, Xiphophorus maculates, and neontetra, Paracheirodon innesi, were susceptible, whereas tilapia (Oreochromis niloticus xO. aureus) was resistant. The ciliate had a high affinity for dead fish. Skin abrasion did not affect the infection, but fish with gas bubble disease exhibited a significantly higher infection than non-affected fish. Infection was significantly higher when fish were exposed to high levels of ammonia, high organic load and low water temperatures. Under shipment conditions, infection was significantly elevated. Full recovery was achieved at a low fish density. Results suggest that poor environmental and physiological conditions enhance infection with Tetrahymena sp.

Comparison of the cytotoxicity of the MEIC reference chemicals measured in protein free and in complete culture medium

In order to investigate if a protein free cytotoxicity assay could improve the prediction of human acute toxicity, the cytotoxicity of 40 MEIC reference chemicals was measured by the neutral red uptake inhibition after 24 h in protein free culture medium on rat hepatoma-derived Fa32 cells. The results were compared with the corresponding values obtained in complete culture medium, including 10% fetal calf serum. Potassium cyanide, arsenic trioxide, mercuric chloride, hexachlorophene and pentachlorophenol were much more cytotoxic in PF medium, as was the case to a lower extent for 16 other chemicals. The cytotoxicity of 8 chemicals was only changed to a limited extent when tested in PF medium, suggesting that serum proteins do not strongly interact with their cytotoxicity. Eleven other chemicals were less cytotoxic in PF medium, maybe because of too poor physiological conditions. Although a large number of differences in cytotoxicity were observed in function of the medium used for the assay, a good correlation was observed between both series of data ( r 2 = 0.946). The correlation between the cytotoxicity in PF medium and the human acute toxicity is lower ( r 2 = 0.647) than that in complete medium ( r 2 = 0.746). The results show that further research is necessary in order to improve the in vitro/in vivo correlations by introducing protein-dependent considerations.

Effects of the winter Monsoon on the growth, mortality, and metabolism of adult oysters in Kinmen Island, Taiwan

The Pacific oyster, Crassostrea gigas, is cultivated intertidally in Kinmen Island by both a traditional way of growing oysters on the surface of stone blocks, nicknamed “rock oysters”, and a recently introduced and more efficient way of hanging them in clusters on horizontal nylon lines, i.e. “hanging oysters”. We investigated the growth and mortality of both types of oysters from late July to early December 2003, and measured condition index (CI) and rates of oxygen consumption and ammonium excretion for the hanging oyster. Growth of oyster shells stopped in early October for the hanging oysters and early December for the rock oysters. Mortality rates were higher for hanging oysters than rock oysters. Hanging oyster's O/N ratio and CI, determined by a home-made CI meter that measured the volume of oyster's inner shell cavity with high precision, decreased significantly in October. Hanging oysters were apparently in poor physiological condition during the winter Monsoon, which is characterized by cold and persistently strong wind. On Kinmen Island the monsoon season begins in late September and is accompanied by declining seawater temperature and high seston loads in oyster farms. Chlorophyll a concentrations and seston food quality decreased significantly in early October after the winter Monsoon began. The hanging oyster's poor acclimation to the local climate was probably caused by the import of its spat from southwest coast of Taiwan where it is warmer than Kinmen Island in fall and winter. We recommend that oyster growers collect spat locally or from areas of similar climate.

Mechanical passive and active models of the human basilar membrane

Simple three-dimensional passive and active models of the human basilar membrane were built, solved using the Finite Element Method and tested. In the active model an active mechanism connected with electromotility of outer hair cells was included. In the active model the active mechanism was incorporated in the form of additional, local pressure load. In the passive model the active mechanism was neglected. Hydrodynamic coupling between the cochlear partition and cochlear fluid was excluded in both models. Geometrical and physical parameters of the model were chosen to be adequate to those of humans in the best possible way. However, some of these parameters had to be estimated. The models were tested by calculation of typical curves known from cochlear measurements performed mostly on animals. For the passive model a linear input–output function and very small values of the basilar membrane velocities were obtained. This behaviour is to be expected for the passive model and for the basilar membrane in the poor physiological condition. For the active model the compressed input–output functions, tuning curves, isointensity curves and reasonable BM velocities were obtained. Possible inadequacies, which could explain the differences between numerical results and measurements were described.

Bathymetric shift in the distribution of Atlantic surfclams: response to warmer ocean temperature

Abstract Standard research vessel surveys during the 1980s and early 1990s demonstrated that Atlantic surfclams (Spisula solidissima solidissima) were common in the southern portion of their range (37–38°N) along the east coast of North America in the Delmarva region. Based on data from these surveys, the probability of capturing surfclams in shallow water (i.e. 20 m) tows of the Delmarva region was 75–85% in 1994 and 1997. In 1999 and 2002, this probability declined to 40–55%. The probability of capturing surfclams in survey tows from deeper waters (40–50 m) also declined, but this change was relatively small compared with that in shallower water. These changes were not the result of commercial clam fishing. Unusually warm water, which induces thermal stress in S. s. solidissima, was prevalent within the period from 1999 to 2002 over the Delmarva continental shelf during fall when annual bottom temperature was peaking. The combined effects of poor physiological condition and thermal stress likely resulted in mortality of Atlantic surfclams in shallow water habitats in the Delmarva region. This resulted in a shift in the bathymetric distribution of the population to deeper water. Between 1982 and 1997, most of the surfclams in the Delmarva region occurred at depths between 25 and 35 m, whereas in 1999 and 2002, most of the Delmarva population occurred at 35–40 m.

Effect of artificial and natural diets on energy allocation in Litopenaeus setiferus (Linnaeus, 1767) and Litopenaeus vannamei (Boone, 1931) early postlarvae

The amounts of energy channeled into growth ( P), maintenance ( R), excretion ( U) and exuviae ( E v) were quantified in six dietary treatments during early postlarval development in Litopenaeus setiferus and Litopenaeus vannamei reared at 28±1 °C and 35±1‰ salinity. The six diet combinations were: (1) freshly hatched Artemia nauplii, (2) freshly hatched Artemia nauplii supplemented with algae, (3) microparticulate commercial diet (MCD), (4) MCD supplemented with algae, (5) Artemia nauplii partially substituted (50%) by MCD and (6) Artemia nauplii partially substituted (50%) by MCD supplemented with algae. Oxygen consumption, ammonia excretion and dry weight were measured from postlarvae day 1 (PL 1) to PL 10 (1 to 10 days after metamorphosis). Energy distribution in both species was affected by diet with significantly higher proportion of energy allocated into production (1.49 J day −1 for L. setiferus and 1.77 J day −1 for L. vannamei) when animals were fed a mixed diet. The proportion of assimilated energy channeled into production ( P/As) was greater when both species were fed mixed diet and was lower when fed on MCD alone or MCD plus algae. On the contrary, the proportion of assimilated energy used in respiration ( R/A) was higher for both species when fed on MCD alone or MCD plus algae, with the lowest values in animals fed on the mixed diet. Low values of net growth efficiency ( K 2) were found in both species when the main food was MCD (alone or supplemented with algae), with the highest K 2 when animals were fed the mixed diet. Results show that divergences between these two species during early postlarval stages only appear when animals were in a poor physiological condition due to an inefficient diet. Artemia nauplii, partially substituted by MCD with a supplement of algae, integrated a high-quality diet for both species producing high net growth efficiency.

The Prediction of Human Acute Systemic Toxicity by the EDIT/MEIC In Vitro Test Battery: The Importance of Protein Binding and of Partitioning into Lipids

The aim of the two studies presented in this paper was to further improve the predictability of the original Multicentre Evaluation of In Vitro Cytotoxicity (MEIC) in vitro test battery for acute systemic toxicity. In the first study, whether a protein-free cytotoxicity assay could improve the prediction of human acute systemic toxicity was investigated. The cytotoxicity of 39 MEIC reference chemicals was measured by the neutral red uptake inhibition test after 30 minutes in phosphate-buffered saline (PBS), with hepatoma-derived Fa32 cells. The results were compared with the corresponding values obtained in complete culture medium, including 10% fetal calf serum. Mercuric chloride and hexachlorophene were much more cytotoxic in PBS, as was the case, to a lesser extent, for seven other chemicals. Potassium cyanide and eight other chemicals were less cytotoxic in PBS than in complete culture medium, probably because of poor physiological conditions. The correlation between the cytotoxicity measured in PBS and human acute toxicity was rather low, but became of the same order as for other assays, when mercuric chloride and hexachlorophene were withdrawn from the comparison. In the second study, modelling of human lethal blood concentrations by using the results of the three cell line tests of the original MEIC test battery were complemented by logP (octanol-water partition coefficient) values. The introduction of logP into the modelling did not improve the correlations, but some improvement of both R(2) and Q(2) was obtained by expanding the logP values with logP(2) values. The highest R(2) (0.84) and Q(2) (0.80) values were obtained for a model in which both experimental and calculated (ambiguous) logP values were used. When only experimental logP values were used, the corresponding values were 0.80 and 0.78. These two studies showed that including protein binding and the partition of chemicals in the MEIC in vitro test battery is important, in order to improve the predictability of the results obtained.

Inbreeding and building up small populations of stingless bees (Hymenoptera, Apidae)

A study of the viability of small populations of Hymenoptera is a matter of importance to gain a better zoological, ethological, genetical and ecological knowledge of these insects, and for conservation purposes, mainly because of the consequences to the survival of colonies of many species of bees, wasps, and ants. Based on the Whiting (1943) principle, Kerr & Vencovski (1982) presented a hypothesis that states that viable populations of stingless bees (Meliponini) should have at least 40 colonies to survive. This number was later extended to 44 colonies by Kerr (1985). This would be necessary to avoid any substantial amount of homozygosis in the pair of chromosomic sexual loci, by keeping at least six different sexual gene alleles in a reproductive population. In most cases this would prevent the production of useless diploid males. However, several facts weigh against considering this as a general rule. From 1990 to 2001, 287 colony divisions were made, starting with 28 foundation colonies, in the inbreeding and population experiments with the Meliponini reported here. These experiments constitute the most extensive and longest scientific research ever made with Meliponini bees. In ten different experiments presented here, seven species (one with two subspecies) of Meliponini bees were inbred in five localities inside their wide-reaching native habitats, and in two localities far away from these habitats. This was done for several years. On the whole, the number of colonies increased and the loss of colonies over the years was small. In two of these experiments, although these populations were far (1,000 km and 1,200 km) from their native habitat, their foundation colonies were multiplied successfuly. It was possible to build up seven strong and three expanding medium populations, starting with one, two, three or even five colonies. However, in six other cases examined here, the Whiting (1943) principle and the hypothesis of Kerr & Vencovski (1982) and Kerr (1985), possibly hold up. In two other cases, the results are still unclear. Outside native habitats, most inbreeding experiments failed, possibly because of conditions that cause ecological stress. Although much more data are still needed, a new working hypothesis on the molecular level was presented to explain the results of the experiments described here. In the absence of any considerable stress, and in the eventuality of a good nutritive situation, even individual bees that are homozygous in the pair of chromosomic sexual locus would produce a sufficient amount of a sex determining substance. Therefore, the female genes of all the diploid individuals of a colony, both homozygous and heterozygous, would be activated. However, situations of considerable stress would cause a poor physiological and nutritive condition. This, together with homozygosis in the pair of chromosomic sexual locus, would lead to a smaller production of the sex determining substance. When this happens in the diploid homozygous individuals of a colony, in relation to sex, only male genes are activated. As a result, all such homozygous diploid bees of the colony become useless males. However, when there is a heterozygous situation in the chromosomic sexual locus of all bees of a colony, all diploid individuals would produce a high amount of the sex determining substance. Consequently, all diploid individuals of such a colony would become females (queens and workers). Stresses, including ecological stress, as well as the nutritive condition and the genetic situation in the chromosomic sexual loci, will have a key influence in the life and behavior of the Meliponini, including sex determination. In relation to genetic factors, hybrid vigour may often cause a greater production of biological substances. This may be due to the presence of a greater number of copies of allelic genes when there is heterozygosis. This is a hypothesis requiring further research. However, in the experiments presented here, this hypothesis seems to apply well to the production of a sex determining substance in bees (Apoidea) and other Hymenoptera.

Reduced Feather Growth Rates of Two Common Birds Inhabiting Central Amazonian Forest Fragments

Abstract: Forest fragmentation may negatively affect populations typically found within continuous forest tracts. Some effects, such as absence from small fragments, are obvious, but other effects may be subtle and easily overlooked. We evaluated the hypothesis that forest birds dwelling in fragments, where microclimatic conditions have been shown to be hotter and drier than in continuous forest, may be in poorer physiological condition than those in the forest interior. We studied two bird species, the Wedge‐billed Woodcreeper ( Glyphorynchus spirurus) and the White‐crowned Manakin ( Pipra pipra), common to the fragmented landscape north of Manaus, Brazil. We analyzed feather growth rates in Pipra and Glyphorynchus captured in 1‐, 10‐, and 100‐ha forest fragments and continuous forest. Mean daily feather growth rates of the outer right rectrix of birds captured in fragments were significantly slower than feather growth rates of birds captured in continuous forest. Based on recapture data, Wedge‐billed Woodcreepers probably grew their feathers in sites where they were first captured. White‐crowned Manakins, however, were highly mobile and were recaptured rarely. Although we cannot conclusively show that fragmentation caused birds to be in poorer physiological condition, the data indicate that birds in poorer physiological condition were more likely to be captured in fragments than in continuous forest. Thus, our data suggest that forest fragmentation may have subtle but important effects on species that are relatively common after landscape alteration.

Consequences of Dominance-Mediated Habitat Segregation in American Redstarts During the Nonbreeding Season

AbstractSeveral species of migratory songbirds exhibit a distinct form of habitat segregation while on their Neotropical wintering grounds in which males and females occupy different habitat types. In the American Redstart (Setophaga ruticilla), that sexual habitat segregation is a result of behavioral dominance of older males. In that study, we examined whether such dominance behavior and the resulting differential habitat segregation has consequences for the condition or survival of excluded individuals. We quantified the physical condition and survival of redstarts (both males and females) occupying two habitat types that differed in the proportion of males and females present in Jamaica. Both sexes of redstarts occupying female-biased habitat lost significantly more mass over-winter and had lower annual survival and longevity compared to individuals in male-biased habitat. These results suggest that nonbreeding habitats differed in suitability, with the least suitable habitat being occupied predominately by females. Because most female redstarts are forced to over-winter in these kinds of habitats, they may often be in poor physiological condition prior to departing on spring migration for the breeding grounds. This in turn may influence dynamics of the breeding period by determining their condition and perhaps reproductive success. Furthermore, because winter habitat segregation appears to lower female survivorship, it may also limit the number and availability of breeding females. These results implicate events that occur during the nonbreeding period as playing a critical role in the annual dynamics of this migratory species.

Hollow formation in eucalypts from temperate forests in southeastern Australia

We examined factors associated with the occurrence of tree hollows in four eucalypt species from temperate forest in southeastern New South Wales and East Gippsland. A total of 1 256 standing trees and 328 felled trees was examined. The proportion of trees containing hollows with small entrances (2-5 cm) was significantly negatively associated with dbh, while the proportion of trees containing hollows with medium (5-10 cm) and large (>10 cm) entrances was positively associated with dbh. There was a significant, but weak, relationship between hollow depth and minimum entrance width that was improved with the addition to the model of the variables branch diameter and branch health. Trees of all sizes and ages contained hollows, although larger and older trees had a higher probability of doing so. For two tree species (Brown Barrel or Cuttail Eucalyptus fastigata and Messmate E. obliqua), the probability of live trees containing hollows remained below 0.5 for stems less than 180 years of age. Un logged forest supported, on average, 22.0 hollowbearing trees per ha ? 18.5% of which were dead trees. For all values of dbh, trees were more likely to contain hollows if either dead or in poor physiological condition, indicating the potential for hollow development to be accelerated in eucalypts by killing or injuring suitably-sized trees.

Feather mites, pectoral muscle condition, wing length and plumage coloration of passerines

I compared the feather mite (Acari, Proctophyllodidae) loads of moulting birds with features of the new plumage that they were growing. I examined 21 samples, each sample containing individuals of the same species, sex and age class (juvenile, yearling or adult). I used nine species: wren, Troglodytes troglodytes; dunnock, Prunella modularis; robin, Erithacus rubecula; blue tit, Parus caeruleus; great tit, P. major; chaffinch, Fringilla coelebs; greenfinch, Carduelis chloris; linnet, C. cannabina; and yellowhammer, Emberiza citrinella. As previously reported for the house finch, Carpodacus mexicanus, birds with more feather mites grew duller plumage and relatively shorter wings than less infested individuals of the same sex and age class. They also had lower protein reserves judged by the shape of their pectoral muscle. Mite load was usually a better predictor of coloration than pectoral muscle score, but the opposite was true for changes in wing length. In contrast to house finches, birds whose plumage was dull before moult had higher mite loads while moulting. Even if feather mites do not cause dull plumage or short wings, they appear to be a good indicator of birds in poor physiological condition.

Luminescence variations in cucumber (Cucumis sativus L.) leaves derived from different regeneration systems

Plants obtained from in vitro culture can show increased susceptibility to environmental stress conditions. In the process of their adaptation to natural conditions it requires monitoring of their physiological state. The methods used to check this phenomenon should estimate quickly and exactly the tolerance to suboptimal environmental factors. Such requirements are satisfied by the methods of measuring chlorophyll luminescence in vivo, e.g. fluorescence induction and delayed luminescence. The objects of our studies were cucumber plants regenerated from cultures of callus and embryogenic cell suspension, as well as the plants obtained from seeds. The plants derived from in vitro cultures displayed a poor physiological condition at the early phase of adaptation characterised by higher susceptibility both to stress caused by increased density of the light flux and low temperature (4 °C) in comparison with the plants obtained from seeds.

The influence of multiple environmental stressors on susceptibility to parasites: An experimental determination with oysters

A large ‐scale field experiment was used to test whether exposure to a suite of potential environmental factors (flow speed, temperature, salinity, and low dissolved oxygen) influences the level of parasitic infection of the oyster Crassostrea virginica. The parasite was the protozoan Perkinsus marinus, which has decimated populations of oysters in estuaries of North America. The environmental factors were considered stressors because they influence the physiological condition of either the host or parasite. Between December 1994 and July 1995, flow speed, temperature, salinity, dissolved oxygen concentration (DO), Perkinsus infection, and mortality of oysters were monitored across 24 experimental oyster reefs in the Neuse River estuary, North Carolina. Eight reef treatments were created consisting of an orthogonal combination of three factors: water depth (3 m vs. 6 m deep), reef height (2 m vs. 1 m tall), and position on reef (base vs. crest). Principal component analysis revealed that there was clear separation of environmental factors among reefs and that a majority of the variation (96.2%) among treatments could be explained by two principal component axes (PCs): one (24.3% of variation explained) was formed by flow and the other (71.9% of variation explained) by temperature, salinity, and DO. Oysters with the highest proportion of individuals infected (prevalence), highest intensity of infection, and highest mortality were located at the base of reefs, where flow speeds and food quality were lowest and sedimentation rates highest. However, there was no significant effect of hydrographic conditions on Perkinsus infection or mortality of oysters, despite large differences in mean salinity, DO, and exposure to hypoxia ‐anoxia. Temperature did not vary among treatments. Correlation of disease responses (infection prevalence and intensity, and mortality) with the first two PCs showed that these response variables were significantly (and negatively) correlated with flow only. Oysters in low flow were hypothesized to have the greatest susceptibility to Perkinsus infection because of their poor physiological condition. The restoration of oyster reefs increases reef height and thus flow speeds (by elevating oysters higher above the boundary and by actively influencing flow), thereby reducing the negative effects of disease by restoring reef morphology to its natural size.

High Parasite Load in House Finches (Carpodacus mexicanus) is Correlated with Reduced Expression of a Sexually Selected Trait

Independent of age or geographic variation, males of many species of birds exhibit dramatic variation in the expression of elaborate secondary sexual characters. "Good genes" models of sexual selection propose that males with relatively low resistance to parasites suffer high parasite loads that inhibit their ability to express these characters fully. In turn, variation in such characters may reliably indicate male quality and may be used by females to choose males. This is the first study to monitor (via mark-recapture) the long-term effects of parasites on color and growth of plumage in individual birds. Specifically, we used house finches, Carpodacus mexicanus, a sexually dimorphic species in which females are known to prefer more brightly plumaged males for mating, to test the hypothesis that high parasite load in males is correlated with poor physiological condition and reduced development of male secondary sex characters. Our results clearly demonstrate that both ectoparasitic feather mite (Proctophyllodes sp.) infestations and endoparasitic avian pox viral infections during molt are correlated with poor physiological condition and reduced development of bright male plumage during the same molt period, thus supporting good genes models.

Prey choice of Tengmalm's owls (Aegolius funereus funereus): preference for substandard individuals?

Errington proposed that predators mainly kill substandard prey, because dominant individuals force subordinate ones into poor habitats, where the predation risk is higher. We studied the prey choice of breeding male Tengmalm's owls (Aegolius funereus funereus) in 1992, when vole densities crashed. We trapped small mammals in the main habitat types in 21 owl territories, and simultaneously identified prey items cached by the same owls in their nest boxes. The main prey of owls in western Finland are the common vole (Microtus epiroticus), field vole (M. agrestis), bank vole (Clethrionomys glareolus), and common shrew (Sorex araneus). Common voles were the preferred prey of owls, followed by field voles, bank voles, and common shrews. Prey captured by owls tended to be lighter and smaller than those available in the field. This tendency was significant for field voles and common shrews. Field voles, common voles, and female common shrews captured by owls tended to have more internal fat than those available in the field. This tendency was significant for male field voles and female common shrews. Owls appeared to choose small individuals of some, but not all, prey species, and that these prey items were not in poor physiological condition.

Photosynthetic Carbon Assimilation and Allocation by Surface and Deep Phytoplankton in Colpoys Bay (Western Georgian Bay)

We used reciprocal shift experiments to test the hypothesis that surface (i.e., epilimnetic) and deep (i.e., metalimnetic) phytoplankton from thermally stratified Colpoys Bay (Georgian Bay) would differ in their photosynthetic and biosynthetic patterns. A deep chlorophyll maximum existed in the metalimnion during the first half of the stratified season. Surface phytoplankton always had higher light-saturated rates of photosynthesis [Formula: see text] and photoadaptation parameters (Ik) than did deep phytoplankton, but most of the difference was due to the proximate effect of temperature on [Formula: see text], and not to true photoadaptation. Neither sensitivity to photoinhibition (limited) nor light-utilization efficiency (α) varied between surface and deep populations. Depth-related differences in photosynthate allocation to protein, total lipid, neutral lipid, and phospholipid were significant according to ANOVA but were nonetheless small compared with other sources of variation. Photosynthetic rates were generally low, while allocation to polysaccharide and neutral lipid was large, suggesting a relatively poor physiological condition of the phytoplankton. Short-term dynamics (days to weeks) of water masses in Colpoys Bay, and probably many other nearshore Great Lakes locations, appear sufficient to preclude strong vertical differentiation of phytoplankton physiology.

Physiological activities of late-gestation rat fetuses in vitro

A novel method for the in vitro maintenance of rat fetuses was used to study their physiological properties. Rat fetuses together with the uterus were isolated from anesthetized pregnant rats of 14.5–21.5 days gestation, placed in a chamber, perfused through a cannula inserted into the uterine artery with a physiological solution, and decerebrated. In this condition, it was possible to maintain heartbeats of rat fetuses for 24 h. The in vitro fetuses showed various spontaneous body movements including those that resembled respiration. Various body movements were also observed when mechanical or electrical stimulation was applied to the skin. These body movements were abolished by application of general anesthetics. It was shown that reflex-like electrical activities were retained in spinal cords isolated from fetuses which had been maintained in vitro for 10 h. These results show that in vitro rat fetuses retain abilities to generate various body movements that are presumably mediated by the electrical activities of the central nervous system. The presence of various neural activities, some of which are known to be particularly susceptible to poor physiological conditions, suggests that the condition of the in vitro fetuses is good and that the method may be applied to various studies on late-gestation mammalian fetuses.

Secondary Sex Ratios and Egg Sequence in Herring Gulls

Variation in the secondary (hatching) sex ratio has been documented for many bird species. Significant deviations from the 1:1 ratio have led to theoretical speculation about adaptive facultative manipulation of the sex ratio (Trivers and Willard 1973). Seasonal changes in the nestling sex ratio of the Common Grackle (Quiscalus quiscula; Howe 1977) and the Redwinged Blackbird (Agelaius phoeniceus; Fiala 1981) and the biased production of male Zebra Finches (Poephila guttata; Burley 1981) by females mated with highquality males provide some support to the TriversWillard hypothesis. Recently, Ankney (1982) found that in newly hatched Lesser Snow Geese (Chen caerulescens) the first two eggs of 4-egg clutches produced more males (64%) than females and the last two eggs produced more females (72%) than males. Similarly, Ryder (1983) reported in Ring-billed Gulls (Larus delawarensis) the first-laid eggs of 3-egg clutches hatched predominantly more males (66%) than females and the second-laid eggs hatched more females (61 %) than males. This phenomenon suggested a facultative manipulation of the sex produced, although the adaptive significance is unexplained. Weatherhead (1985) examined the occurrence of a sex-sequence relationship in the Red-winged Blackbird after Fiala's (1981) documentation that the last-laid egg of this species produced significantly more females than males. Although Weatherhead (1985) found a sex-sequence relationship, the pattern was not consistent among different clutch sizes. Stimulated by these studies, we examined the secondary sex ratio in relation to laying sequence in newly hatched Herring Gull (L. argentatus) chicks on Granite Island (48?43'N, 88?29'W) in Black Bay, northern Lake Superior (see Ryder 1976 for a description of the colony). During the 1983-1986 nesting seasons, newly constructed Herring Gull nest sites were marked numerically with spray paint and the nests checked daily for the presence of new eggs. Each egg in a clutch was marked in sequence laid by placing dots of nail enamel on the blunt end of the egg (1 dot = first egg laid, 2 dots = second, 3 dots = third). The latest date we arrived at Granite Island was 11 May in 1983. We thus used 11 May as the standard date to compare the progress of Herring Gull egg laying in the three nesting seasons (1984 data were not available). Close to the expected time of hatching, nests were checked twice daily for signs of pipping eggs. Chicks hatched from 3-egg clutches were collected and their sex determined by gonadal inspection. We used only those clutches from which all eggs hatched and where the position of each chick in the sequence laid was known for statistical analyses. We compared clutch sizes using ANOVA and Scheffe a posteriori tests. The sex-ratio data were analyzed using Chi-square and G-tests (Sokal and Rohlf 1981). Significance was accepted at P < 0.05. Upon our arrival at Granite Island each year, laying in several nests had already commenced. The difference in the proportions of initiated and completed clutches by 11 May each year (Fig. 1) indicates that Herring Gulls breeding in 1983 did so later in the season than those nesting in 1985 and 1986. The proportion of nests with 3 eggs was much lower in 1983 than in the other years (Table 1). This low 3-egg clutch-size frequency was manifested in the significantly lower average clutch size for 1983 (F = 5.02, P < 0.05). The secondary sex ratio favored females in 1983 and 1985 and males in 1984 and 1986 (Table 2). The deviation from a 1:1 sex ratio, however, was not significant in any of these years. The G-statistic also indicated no significant relationship between sex and sequence for any year. Similar results were obtained from the combined data. Our results suggest that the allocation of sex chromosomes by the heterogametic female Herring Gull is a random process. A late season, lower average clutch size and hatch of 12% more females than males occurred in 1983. Although it was tempting, at first, to invoke the predictions of the Trivers-Willard (1973) hypothesis, whereby the later-starting females may have been in relatively poor physiological condition