Androgen and glucocorticoid levels reflect seasonally occurring social challenges in male redfronted lemurs (Eulemur fulvus rufus)

Intense reproductive competition and social instability are assumed to increase concentrations of glucocorticoids and androgens in vertebrates, as a means of coping with these challenges. In seasonally breeding redfronted lemurs (Eulemur fulvus rufus), the mating and the birth season and the associated increased male competition are predicted to pose such reproductive challenges. In this paper, we investigate seasonal variation in hormone excretion in male redfronted lemurs, and examine whether this variation is associated with social or ecological factors. Although dominance status has been shown to affect individual stress levels across many taxa, we predicted no rank-related differences in glucocorticoids for redfronted lemurs because relatively equal costs are associated with both high and low rank positions (based on patterns of rank acquisition/maintenance and threats toward subordinates). Over a 14-month period, we collected behavioral data (1843 focal hours) and 617 fecal samples from 13 redfronted lemur males in Kirindy Forest/Madagascar. We found no general rank-related pattern of testosterone or glucocorticoid excretion in this species. Both hormones were excreted at significantly higher levels during the mating and the birth season, despite social stability during both periods. The elevated mating season levels may be explained by increased within-group reproductive competition during this time and are in line with previous studies of other seasonally reproducing primates. For the birth season increase, we propose that the predictable risk of infanticide in this highly seasonal species affects male gonadal and adrenal endocrine activity. We evaluate alternative social and ecological factors influencing the production of both hormone classes and conclude based on our preliminary investigations that none of them can account for the observed pattern.     

On the move around the clock: correlates and determinants of cathemeral activity in wild redfronted lemurs (<Emphasis Type="Italic">Eulemur fulvus rufus</Emphasis>)

Whether animals are active at night or during the day has profound consequences for many aspects of their behavioral ecology. Because of ecological and physiological trade-offs, most animals, including primates, are either strictly nocturnal or diurnal. However, a few primate species exhibit cathemeral activity, i.e., their activity is irregularly distributed throughout the 24-h cycle. Details and determinants of this unusual activity pattern are poorly understood because long-term 24-h observations are not feasible in the field. We therefore used small data loggers to record the activity of cathemeral redfronted lemurs (Eulemur fulvus rufus) from several neighboring groups quantitatively and continuously over a complete annual cycle in order to evaluate various proposed proximate and ultimate determinants of cathemeral activity. Activity data were examined for variation as a function of ambient temperature, time of day, lunar phase, and season. We found that cathemeral activity occurred year-round and that, on average, 3.5 times more activity occurred during the day. Total and diurnal activity increased during the long days of the austral summer. Nocturnal activity increased during the longer nights of the cool dry season. Irrespective of season, lunar phase had a significant effect on the distribution of activity across the 24-h cycle, with most nocturnal activity recorded during parts of the night with greatest brightness. These data indicate that light availability is the primary proximate determinant for the patterning of cathemeral activity. Several lines of evidence suggest that cathemerality in lemurs has evolved from nocturnal ancestors and that it represents a transitory state on the way to the diurnal niche.Communicated by F. Trillmich     

Seasonal variation in ejaculate traits of male red-winged blackbirds (Agelaius phoeniceus)

Many reproductive traits, including ejaculate characteristics, usually show remarkable seasonal variation, but the potential for such dynamics in sperm morphology has been overlooked. Several studies have revealed high within-male repeatability in sperm morphology, but samples have typically been collected within a few hours or days, and the consistency of sperm morphology over longer periods remains unexplored. Here, we tested whether ejaculate traits, including sperm morphology, sperm number, and sperm velocity, exhibit seasonal phenotypic plasticity in a long-lived seasonal breeder, the red-winged blackbird (Agelaius phoeniceus). We found absolute and/or relative flagellum length and sperm velocity to increase across the season, whereas sperm numbers within ejaculates declined. Sperm morphological traits were further positively associated with harem size or the total number of offspring that fledged in each male’s territory, suggesting that sperm morphology is likely to be linked to male reproductive quality. The underlying mechanisms of these patterns of seasonal variation remain unresolved, but we discuss our results in the context of dynamics of reproductive hormones, testicular structures and function, and reproductive behavior.     

Environmental and phylogenetic correlates of Eulemur behavior and ecology (Primates: Lemuridae)

The extent of diversity within closely related taxa may be a function of their shared evolutionary history or of selective forces causing adaptive changes. Examining variation among taxa within a single genus may help to identify flexibility in trait variation because recently diverged populations are more likely living in the environment of adaptation. This study examines correlates of diversity in Eulemur, a genus that has a wide distribution in a variety of habitat types throughout Madagascar. Previously published data were gathered from 11 long-term studies of Eulemur populations. Variables were categorized into multiple datasets: (1) environmental characteristics, (2) social organization, and (3) ecology, which included subsets for ranging behavior, diet, and activity budget. Molecular phylogenies from the literature were used to create the fourth and final dataset, a dissimilarity matrix of evolutionary distance among the 12 species and subspecies. Principal components and cluster analyses were implemented to examine the overall ecological similarity among Eulemur populations and to determine which variables contribute most to the variation among taxa. Partial Mantel tests were conducted to test for correlations among the dataset matrices. The results suggest ecological flexibility for the genus, in particular, populations in similar environments displayed similar activity patterns. In contrast, social organization showed no relationship with environment but was correlated with phylogenetic distance among populations. While Eulemur seems to demonstrate some flexibility for ecological adaptations, characteristics related to group size and sex ratio more closely track phylogeny and thus may be less flexible.Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible to authorized users.     

Seasonal variation in the relationship between cellular immune response and badge size in male house sparrows (Passer domesticus)

The immunocompetence handicap hypothesis postulates that secondary sexual traits are honest signals of male quality because steroid hormones (such as corticosteroids and sex steroids), which are supposed to favor the development of secondary sexual traits, may also have immunosuppressive effects. Certain secondary sexual traits are not only used as mate choice signals but also play a role as badges of status. In the house sparrow (Passer domesticus), males have a bib of black feathers which is used both as a signal of social status in male-male interactions and by females when choosing a mate. We investigated the relationships between bib size and cellular immune response in male house sparrows during and outside the reproductive season. Males with large badges were found to have lower levels of immunocompetence, as assessed using a T-cell-mediated immunity assay, during the reproductive season, as predicted by the immunocompetence handicap hypothesis. Conversely, in November, the correlation between badge size and cellular immune response was positive, possibly reflecting the better access to trophic resources of large-badged dominant males in winter flocks. Received: 24 September 1998 / Received in revised form: 2 February 1999 / Accepted: 14 February 1999     

Seasonal variation in mineralization rates (C-N-P-Si) of mussel Mytilus edulis biodeposits

To determine seasonal variability in mineralization dynamics of mussel biodeposits, we applied a multiple-element approach measuring mineralization rates of carbon (C), nitrogen (N), phosphorus (P) and silicate (Si) during three periods (March, August and November). The results of this study showed that mineralization rates vary between seasons and between elements and that mineralization dynamics were influenced by both temperature and biodeposit nutrient composition. Mineralization rates were 3.2 ± 0.4 mmol C, 0.17 ± 0.04 mmol N, 0.06 ± 0.02 mmol P and 3.91 ± 3.75 mmol Si per gram biodeposit (DW) per day, which represented 24 % of the particulate organic C and 17 % of the particulate organic N in mussel biodeposits. Seasonal variability was largest for Si mineralization with 60–80-fold higher rates measured in March compared to August and November. This difference is most likely related to the difference in biodeposit nutrient composition. It was furthermore shown that the labile fraction of biodeposits became mineralized after, respectively, 18, 9 and 13 days during the experimental periods in March, August and November. This indicates that temperature enhances biodeposit decomposition with approximately 2–3 times faster turnover at a 10 °C temperature interval (Q ₁₀ ).     

Seasonal and geographic variation in chlorophyll level of Elysia tuca (Ascoglossa: Opisthobranchia)

Elysia tuca Marcus were collected from the Florida Keys (USA) during 1978–1979, with the aim of clarifying the physiological significance of their kleptoplastids by studying variations in the chlorophyll content of the slugs. The chlorophyll levels in the field populations varied seasonally, with peak levels in autumn. Peak reproductive activity coincided with maximum chlorophyll levels, carbon fixation, and rate of macromolecular conversion of kleptoplastid (= symbiotic chloroplast) photosynthates. Changes in chlorophyll level are probably controlled by rate of feeding, which is in turn governed by such factors as algal density and climatic factors (light and temperature). Chlorophyll level and individual weight varied with location, with significant differences between sites in the Upper Keys and the Lower Keys. Environmental factors control benefits of kleptoplastid retention, and suggest that photosynthate yield is an important subsidy of reproductive output.     

Seasonal variation in some population parameters of Euchaeta species (copepoda: Calanoida)

Studies of the biology of oceanic copepods are few relative to those of coastal species. Females of the genus Euchaeta have spermatophores attached to the genital somite by the male and carry their broods of eggs attached to this somite, so defining the breeding season. Populations of E. norvegica in the fjordic environment of Loch Etive (collected between 1971 and 1974 and from 1978 to 1979), Scotland and in the marginal oceanic region of the Rockall Trough, northeastern Atlantic Ocean (collected between 1973 and 1976) and of a further eight species of Euchaeta in the Trough are examined. Seasonal changes in the incidence of egg masses and spermatophores attached to the females, sex ratio and population numbers are determined. Sampling errors in the estimation of these parameters are larger in the oceanic Rockall Trough. The Loch Etive populations of E. norvegica produce two generations per year with a proportion, variable between years, of the population producing a third generation. This species produces a single annual generation in the Rockall Trough as do E. acuta and E. pseudotonsa. Two generations per year are probably passed through by E. gracilis in the Trough while the large bathypelagic E. sarsi may produce a single generation in the autumn of every second year. The other bathypelagic species, E. barbata, E. scotti, E. abbreviata and E. longissima, breed continuously throughout the year and no estimate of their generation times is possible. Consequently, this approach to population analysis is useful where breeding is seasonal, but resolving generation time in bathypelagic crustaceans remains a problem.     

Sexual selection and variation in reproductive strategy in male yellow warblers (Dendroica petechia)

Summary Male yellow warblers (Dendroica petechia) exhibit extensive variation in the amount and conspicuousness of the sexually distinctive brown streaking on the breast. We investigated this intraspecific variation in degree of sexual dichromatism to see if male plumage rank (essentially the amount of brown streaking) is correlated with the amount of reproductive effort allocated to parental investment, as sexual selection theory would predict. As predicted, the average rate of feeding visits to the nest by males was negatively correlated with the plumage rank of the male in 1982 (Fig. 1) and 1983 (Fig. 2), and varied little between years or among study areas. Within one study area, the higher nest visit rate of dull (low plumage rank) males was correlated with higher nestling growth rates. But in the other two study areas, where bright (high plumage rank) males predominated, nestlings of bright males tended to have the highest growth rates despite minimal nest visit rates. Thus, overall there was no correlation between male plumage rank and nestling growth rate, a potential index of relative reproductive success, in either year (Figs. 3 and 4). This overall equal nest success likely helps to maintain the behavioral and plumage polymorphism. Since we could find no evidence that the high nestling growth rates of bright males were due to an adjustment of female parental effort to compensate for low male parental effort, there must be some other benefit of being bright which contributes to nest success. To address this, we used the relationship between parental feeding rates and nestling growth rates for each nest as an index of relative territory quality. This analysis suggests that bright males generally occupy the best territories available, possibly because they are more aggressive in obtaining and defending them than dull males. Dull males appear to be relegated to poorer territories, where an increase in male parental contribution would be necessary to achieve high nestling growth rates. We propose that different males are using alternative but evolutionarily stable reproductive strategies, in a way that is consistent with the predictions of sexual selection theory. Allocation of limited reproductive effort to parental investment decreases as sexual dichromatism increases, which probably reflects an increased investment in intermale competition for the best territories.     

Group histories and offspring sex ratios in ringtailed lemurs (Lemur catta)

Birth sex ratios were examined for ringtailed lemurs (Lemur catta) at the Duke University Primate Center. This population provides a long-term database of births under a variety of demographic and management conditions, including two semi-freeranging groups between which males transfer freely and females defend stable territorial boundaries. We examined three hypotheses usually considered in studies of primate sex ratio bias. The Trivers-Willard hypothesis predicts that dominant females produce males, local resource competition at the population level (LRC-population) predicts that the dispersing sex (males) will be overproduced in dense populations, and local resource competition among individuals (LRC-individual) predicts that dominant females overproduce the philopatric sex (females). We also examined a fourth hypothesis, local resource enhancement (LRE), which is usually subsumed under LRC-individual in studies of primate sex ratio evolution. LRE predicts that under certain conditions, females will produce the sex that provides later cooperative benefits, such as alliance support for within- or between-group competition. Our data provide support for LRE: females overproduce daughters given prospects of new group formation, either through group fission or threatened expulsion of young mothers. Behavioral data from Duke and also wild populations show that daughters serve mothers as important allies in this context and LRE effects also have been documented in other mammals that experience similar group histories. Nonsignificant trends in the data supported the LRC-population hypothesis, and we suggest that LRC interacts with LRE to explain offspring sex ratios in ringtailed lemurs. Received: 27 August 1999 / Received in revised form: 6 March 2000 / Accepted: 18 March 2000     

Female mate choice,male migration,and the threat of infanticide in ringtailed lemurs

Summary Paternity determination by DNA fingerprinting is reported for a long-term study group of semi-free-ranging ringtailed lemurs (Lemur catta), together with behavioral data collected independently. In 1985, fraternal twin males unfamiliar and unrelated to the resident ringtailed lemurs were introduced to the forest enclosure. Every mature resident male attacked the immigrants frequently across the next 5 months, whereas no female ever did. All observed estrous females showed sexual proceptivity toward the' immigrant males; three solicited copulation exclusively from them. Each female repelled sons, matrilineal brothers, and other resident males from attempting to copulate. Over a 5-year period, four of five females always reproduced with distantly related or unrelated males (Fig. 3). Despite low dominance status throughout the case study, an immigrant sired the off-spring of each female that was proceptive toward only the immigrants, demonstrating that female choice can override male dominance relations to determine reproductive success among male ringtailed lemurs. In the birth season following the 1985–1986 immigration, each of four females targeted one or two particular adult males for consistent attack across the period of infant dependency, beginning days after parturition. Paternity determinations, colony records, and subsequent study of two groups allowed 66 cases of this mode of maternal aggression to be documented. In each, the targeted male had not fathered the protected infant, and almost invariably, he was unrelated to the infant's mother. New mothers attacked every male that immigrated following their infants' conceptions and a few familiar males with whom they had not been seen to copulate during the previous breeding season. Recent attempts by immigrant males to kill infants confirmed the anti-infanticidal function of maternal targeting of males. All results were interpreted together to advance a prospective model of the mating system of ringtailed lemurs. Female avoidance of incest has led to the evolution of natal male dispersal. Subsequently, males should prefer to transfer into groups containing few and/or status-vulnerable males. We predict that, by killing others' infants, males simultaneously increase chances for success in females' next reproductive efforts and terminate current fathers' reproductive eligibility in a group. Basic hypotheses that await testing are that (a) raising an infant through weaning reduces a female's chances for reproductive success the following year and (b) males that demonstrate the capacity to promote the survival of infant offspring are most attractive to females as mates.     

Quantitative variation in ecological and hormonal variables correlates with spatial organization of pronghorn (Antilocapra americana) males

Whereas variation in pronghorn (Antilocapra americana) spatial organization is well documented, underlying ecological or physiological explanations are not well understood. This study quantitatively describes spacing systems of pronghorn males and correlates of their spatial organization. I collected behavioral data from two populations in South Dakota (Wind Cave) and Montana (Bar Diamond) to determine if males differed in space use, response to intruders, and behavior patterns indicative of area defense. I measured sex ratio and population density, and I examined characteristics of food resources, including forb species diversity, richness, coverage, biomass, and nitrogen content, and how they changed during the growing season. I also collected and analyzed fecal samples to determine if males differed in testosterone concentrations. Pronghorn males at Wind Cave were more territorial than males at Bar Diamond, although males at Bar Diamond became more territorial during the second year. The forb community at Wind Cave was more diverse, contained greater amounts of forbs later in summer, and had a higher nitrogen content later in summer. Population density was lower at Wind Cave, although density dropped at Bar Diamond during the second year, and sex ratios were skewed toward males at Bar Diamond. Finally, males at Wind Cave had higher testosterone concentrations than did Bar Diamond males, although differences were not statistically significant. With lower population density and higher forb abundance and quality, food resources were more economically defensible at Wind Cave, and males were more territorial there. Analyses using these and other pronghorn populations revealed that population density and sex ratio correlated weakly with spatial organization, whereas precipitation correlated most strongly, which suggests plant productivity has a powerful role in determining pronghorn territoriality. Received: 16 June 1999 / Received in revised form: 21 September 1999 / Accepted: 31 December 1999     

Geographic variation in social organization of Galápagos mockingbirds: ecological correlates of group territoriality and cooperative breeding

Summary To investigate ecological influences on cooperative social organization, I studied the four allopatric species of mockingbirds (Nesomimus spp.) endemic to the Galápagos archipelago on four islands. On three small, low and arid islands (Genovesa, Champion and Española), mockingbird territories filled all terrestrial habitat, mean group size varied from 4.5 to 14.2 adults, maximum group size ranged from seven to 24 birds, and 70–100% of groups contained more than two birds. San Cristóbal is larger and higher, and it supports a broader range of habitats. At one highland and two coastal sites on this island, mockingbirds did not hold territories in all available habitats, group size averaged 2.2 adults, only 25% of groups were larger than two, and none included more than three adults. Adults dispersed into vacant habitat to establish new territories only on San Cristóbal. Helping behavior has not yet been observed on San Cristóbal, but it occurs on the other three islands. These results support the hypothesis that social groups and cooperative breeding are maintained where limited availability of preferred habitat constrains dispersal. The mechanism relaxing habitat saturation on San Cristóbal, however, remains undetermined. Predation by introduced rats and cats may reduce survival and indirectly reduce group size; these predators are absent from Genovesa, Champion and Española. Differences in food supplies could also affect interand intra-island variation in population density. Variation in social organization among arid coastal sites on the four islands, and similarity between climatically different sites on San Cristóbal, suggest that climatic conditions are less important as determinants of dispersal and breeding. Skews in adult sex ratios also fail to account for inter-island variation in sociality. Although they live in a climatically variable environment, territorial behavior and the physical limits of suitable habitat have an overriding influence on cooperative social organization in Galápagos mockingbirds.     

Feeding over the 24-h cycle: dietary flexibility of cathemeral collared lemurs (<Emphasis Type="Italic">Eulemur collaris</Emphasis>)

Animals show specific morphological, physiological and behavioural adaptations to diurnal or nocturnal activity. Cathemeral species, i.e. animals with activities distributed over the 24-h period, have to compromise between these specific adaptations. The driving evolutionary forces and the proximate costs and benefits of cathemerality are still poorly understood. Our goal was to evaluate the role of predator avoidance, food availability and diet quality in shaping cathemeral activity of arboreal mammals using a lemur species as an example. For this, two groups of collared lemurs, Eulemur collaris, were studied for 14 months in the littoral forest of southeastern Madagascar. Data on feeding behaviour were collected during all-day and all-night follows by direct observation. A phenological transect containing 78 plant species was established and monitored every 2 weeks to evaluate food availability during the study period. Characteristics of food items and animal nutritional intake were determined via biochemical analyses. The ratio of diurnal to nocturnal feeding was used as response variable in the analyses. The effects of abiotic environmental variables were removed statistically before the analyses of the biotic variables. We found that diurnal feeding lasted longer during the hot–wet season (December–February), whereas nocturnal feeding peaked during the hot–dry and cool–wet seasons (March–August). Although the lemurs foraged mostly in lower forest strata during daylight and used emergent trees preferably at night, the variables which measured animal exposure to birds of prey failed to predict the variation of the ratio of diurnal/nocturnal feeding. Ripe fruit availability and fiber intake are the two variables which best predicted the annual variation of the lemur diurnality. The data indicate that feeding over the whole 24-h cycle is advantageous during lean periods when animals have a fibre-rich, low-quality diet.     

Seasonal variation in settlement and spiculation of sponge larvae

A settlement study, based in the Hauraki Gulf, Auckland, New Zealand, has revealed 3 different seasonal reproductive patterns among Demospongiae. Species which settled on our substrates can be divided into summer settlers, winter settlers, or all-year-round settlers. The composition of these groups is given, and the affinities and habitats of the constituent species are commented on. Variation in aspects of the spicule complement have been observed and discussed for three species: Mycale macilenta, Microciona coccinea and Ectyomyxilla kerguelensis.     

Seasonal variation in the properties of muscle mitochondria from the tropical scallop Euvola (Pecten) ziczac

In scallops, gametogenesis leads to considerable transfer of energetic reserves from the adductor muscle to the gonads. During an annual cycle, the scallops are exposed to changes in temperature and food availability. As these changes may affect muscle metabolic capacities, we examined whether the properties of the mitochondria in the phasic adductor muscle were modified during the annual cycle of the scallop Euvola (Pecten) ziczac (L. 1758). During our study, temperature and chlorophyll a levels generally showed an inverse relationship: high temperatures and low chlorophyll a levels occurred from mid-April to early June. Lower temperatures and higher chlorophyll a levels were found from January to late March and from mid-June to mid-September. Throughout the annual cycle, the substrate preferences and the pH sensitivity of the isolated muscle mitochondria changed little, whereas the maximal oxidative capacities and respiratory control ratios (RCR) varied considerably. Consistently, the maximal capacities for substrate oxidation were 30 to 80% lower in mitochondria isolated in May than at other times in the year. The RCR values of mitochondrial oxidation of glutamate, glutamine and succinate varied throughout the year with lower values characterizing the mitochondria from scallops harvested in May and in certain cases in August. In May, adductor muscles had lower protein levels than at other times. These data suggest that the requirements of gametogenesis, coupled with␣the high temperatures and low food availability occurring during April and May, led to a mobilization of muscle proteins which concomitantly decreased the oxidative capacity of isolated mitochondria. Received: 29 November 1996 / Accepted: 5 December 1996     

Seasonal variation in the balance between physiological mechanisms of feeding and digestion in Mytilus edulis (Bivalvia: Mollusca)

Seasonal variations in the balance between physiological mechanisms of feeding and digestion are considered among 45 to 57 mm shell length Mytilus edulis L. from southwest England. Mussels had been acclimated to standardised conditions of food availability in March, June and October, 1981. Results indicate that despite showing a negative relationship (P<0.001) with the efficiency of ¹⁵N absorption, coincident alterations of both ingestion rate (0.17 to 0.54 mg total Phaeodactylum tricornutum h^-1) and organic gut content (1.00 to 1.80 mg) represent significant mechanisms effecting the seasonal regulation of nutrient acquisition. Concurrent changes in absorption efficiency alone clearly exerted a relatively minor influence upon seasonal rates of absorption. Associated gut residence times of ¹⁵N-labelled material varied between 4 and 10 h. Furthermore, despite the ensuing deleterious effects, together with increased gut contents, absorption efficiencies among mussels that had been starved throughout acclimation were consistently maintained equivalent to those among individuals feeding normally. Such constancy was at least partially achieved by an increased residence time of material within diverticulae, relative to the digestive system as a whole. Finally, comparison of isotopic absorption efficiencies with those recorded for total organics and organic nitrogen has demonstrated differences of as much as 30% between gross and net uptake due, we suggest, to excretion of metabolically derived material within the alimentary canal.     

Seasonal variation in total and soluble tissue nitrogen of Pleurophycus gardneri (Phaeophyceae: Laminariales) in relation to environmental nitrate

Seasonal variations in tissue nitrogen (ethanol soluble nitrate and ninhydrin positive substances, as well as total nitrogen) of different thallus parts of Pleurophycus gardneri Setchell and Saunders were monitored simultaneously with ambient seawater nitrate from 1982 until 1984 in Bamfield, Vancouver Island, British Columbia, Canada. A trend of low, nearly zero levels in ambient nitrate typical for the area in late spring and early summer normally contrasts with average nitrate concentrations of 10 mol NO₃ ^- l^-1 in late fall and winter. Total nitrogen content was greater in the perennial thallus parts, stipe and holdfast than in the annual blade and peaked in fall and early winter. The longitudinal thallus distribution of nitrate revealed a distinct and significant concentration of nitrate in the haptera reaching at maximum 8% nitrate-N of the internal total nitrogen. Internal nitrate concentration ranged from 20 to 5 000 times the ambient nitrate concentration in the midrib, and from 40 to 3 100 times in the wing, while the range was greatest with 400 to 14 000 times in the haptera. P. gardneri contained at most about 7 mol NO₃ ^- g fresh wt^-1 in the blade, which corresponds to about 6% of total tissue nitrogen. Ninhydrin positive substances comprised the major portion of the soluble N pool in P. gardneri and showed a pronounced seasonality. Concentrations of ninhydrin positive substances ranged from 20 to 800 g N g fresh wt^-1 in the midrib and in the wing. In the stipe, ninhydrin positive substances varied from 180 to 2 200 g N g fresh wt^-1, and from 250 to 1 200 g N g fresh wt^-1 in the haptera. Evidence is given that (1) the perennial parts, stipe and haptera of P. gardneri contain the majority of nitrogen products independent of season and ontogenetic stage; (2) ninhydrin positive substances are the most abundant internal nitrogen constituents; (3) the low N values in the blade in summer suggest a nitrogen limited growth; and (4) nitrate may not be the predominant external nitrogen source.     

Adolescent social environment shapes sexual and aggressive behaviour of adult male zebra finches (Taeniopygia guttata)

Adolescence is the pivotal transitional phase during which animals become sexually and socially mature and acquire the skills to cope with a variety of environmental challenges on their own. We investigated in a bird species, the zebra finch, how the social environment experienced during this period influences their behaviour in a sexual context. Zebra finches were kept in pairs (male–female or male–male) or larger mixed-sex groups (three males and three females) during adolescence and the long-term consequences were studied on courtship behaviour, aggressiveness and attractiveness in 42 males. To investigate the stability of the observed effects over time, all behavioural tests were repeated approximately 4 months after the initial recordings. Males that grew up with a single female showed the most intense courtship and highest aggressiveness and were most attractive to females, while group-reared males had the lowest courtship and aggressiveness and were the least attractive. The observed differences in courtship and aggressiveness were stable, while the differences in attractiveness disappeared over time. These findings are very similar to earlier studies on guinea pigs, indicating that the observed effects represent a general phenomenon, not restricted to mammals with a similar function and presumably also similar underlying mechanisms.     

Seasonal variation and diversity of rotifers in Ehoma lake, Nigeria

The zooplankton and physicochemistry of Ehoma lake were studied from March 2005 to August 2006 in order to evaluate seasonal trend in species composition and abundance in relation to water quality. Forty two (42) species of rotifers dominated by Keratella tropica tropica were encountered. Species richness declined by nearly 50% from dry season values during the rainy season. Species richness was higher in the littoral zone during the dry season, the reverse was the case during the rainy season. Species abundance followed similar trend as species richness. Abundance was closely associated with dissolved oxygen, biological oxygen demand and width of the lake and these in turn varied significantly between seasons. Shannon-Weaver diversity varied from 2.2 to 3.8 bit ind(-1) and significantly between seasons (p<0.05). Anuraeopsis navicula navicula and Euchlanis dilatata dilatata Ehrenbreg were the only species gained during the flood periods.