Daytime surface swarms of the euphausiid Thysanoessa inermis off the west coast of Hokkaido,northern Japan

Biological characteristics of the daytime swarming of the euphausiid Thysanoessa inermis (Krøyer) were examined off the west coast of Hokkaido in the northeast Sea of Japan between 1982 and 1987. Swarms were composed exclusively of fully mature individuals; males possessed spermatophores at the ejaculatory ducts and females had attached spermatophores at the thelycum. Females predominated in most swarms, while males or nearly balanced swarms were infrequently encountered. Fully mature females occurred in the late swarming season, usually mid-April. Examination of stomachs indicated that feeding activity was low during the daytime surface swarming behavior. The body sizes of swarming T. inermis occurring around Yagishiri Island were significantly larger than those found simultaneously off the Shakotan Peninsula. This suggests that the euphausiid populations of the two areas are different.     

Play behavior and motor development in juvenile Belding’s ground squirrels (<Emphasis Type="Italic">Spermophilus beldingi</Emphasis>)

We evaluated the relationship between play behavior and motor development in juvenile Beldings ground squirrels (Spermophilus beldingi). We observed the social play behavior of juvenile S. beldingi during their primary play period and conducted motor skills tests at the beginning and end of the play period. We also placed different-sized boxes in juveniles natal areas during the play period and observed box climbing behavior to assess the difficulty of non-social play tasks undertaken by juveniles. Rates of social play were greater in heavy compared to light individuals, supporting the idea that juveniles must selectively allocate available energy among competing demands such as growth and play behavior. Juveniles played almost exclusively with littermates; however, they did not play at equal rates with all partners. Rather, they tended to have one preferred partner and to devote significantly less time to playing with each additional partner, indicating that stability and familiarity are important in social play interactions. Motor skill levels at the end of the play period were greater among juveniles who played with many compared to few partners, suggesting that exposure to a variety of play interactions helps facilitate motor development. Improvement in motor skills was greater among juveniles who played at high compared to low rates, had several compared to few male play partners, and engaged in several compared to few play bouts with male partners, suggesting that elements of play with male partners prominently influence motor development. The partner with whom males played at the highest rate tended to be male, and rates of social play were highest in male biased litters, raising the possibility that improvement in motor proficiency arising from play with males may be especially important for young males. The size of experimental boxes that juveniles climbed increased during the play period, supporting the idea that individuals choose play tasks that pose the greatest challenge.Communicated by T. Czeschlik     

Why insects swarm: testing the models for lek mating systems on swarming Empis borealis females

Summary Female dance-flies, Empis borealis L., gather to swarm, and males carrying nuptial gifts visit swarms for mating. Field observations and experiments were performed on this behaviorally sex-role reversed species to test models of lekking behavior. The key predictions were: (1) female preference model: male visiting rate and mating rate should increase with the number of females in swarm (swarm size), (2) hotspot model: male visiting rate should be independent of swarm size, and (3) hotshot model: swarm size should be positively correlated with the body size of the largest female in swarm. We found that male visiting rate and mating rate increased with swarm size, and that mating rate per female increased with swarm size. Males also mated more often in larger swarms than in smaller ones. Both males and females visited swarm sites even in the absence of other individuals. When females were successively removed from swarm sites more males than females on average arrived at these sites: 2.25 males per female. When no individuals were present at the swarm site, arriving males moved on to another site, whereas arriving females generally stayed. Larger experimental swarm-markers attracted both more males and more females and even more males when swarming females were present. There was no correlation between mean or median female size in swarms and the number of females in swarms. Thus, the female preference model and the hotspot model were corroborated, while other models were judged unlikely to explain swarming behavior in E. borealis. Correspondence to: B.G. Svensson     

Structure and function of Halice hesmonectes (Amphipoda: Pardaliscidae) swarms from hydrothermal vents in the eastern Pacific

Swarms of the pardaliscid amphipod Halice hesmonectes were sampled at low-temperature hydrothermal vents in the Venture Hydrothermal Fields of the East Pacific Rise. In excess of 3000 individuals were collected from a range of sites/habitats, and at two points in time (December 1991 and March 1994). The structure of swarms was described in terms of growth stages, the development of primary and secondary sex characteristics and the accumulation of nutritional reserves. The results demonstrated that swarms contained a wide range of growth stages, but that small juveniles and mature males and females were absent. Swarm structure was interpreted as an equilibrium dependent on the relative proportion of time spent by each growth stage in the swarm habitat. This equilibrium swarm structure was very similar at different sites and times. Swarms dominated by small juveniles occurred at the northern sites in December 1991 following a period of eruption and new venting in April 1991. Equilibrium swarm structure had become re-established at these sites by March 1994. The function of swarming was considered. The results indicated that swarming was not associated with reproductive activity. The available evidence, though not conclusive, suggested that swarms were associated with feeding. Received: 28 May 1999 / Accepted: 16 February 2000     

Diving of the sea snake Pelamis platurus in the Gulf of Panamá

The horizontal movement patterns of eleven yellow-bellied sea snakes [Pelamis platurus (Linnaeus)] were determined incidentally to acoustic tracking studies of their diving behavior in the Gulf of Panamá during 1983–1985. The average speed of the snakes was 1.9 km h^-1 (range 0.3 to 7.1 km). Movement direction is influenced by phasic northsouth tidal currents and secondarily affected by combinations of factors that affect local current velocity. The velocity of diving snakes did not always agree with that observed for the surface current. Drift rate was not correlated with average or maximum dive depth, however, snakes that surfaced to breathe one or more times during a period had greater average drift rates than those that did not surface. The role of such factors as feeding, predator avoidance, thermoregulation, orientation, and the avoidance of surface turbulence are considered in a discussion of the adaptive significance of diving for P. platurus. Diving in this species may enable it to avoid surface disturbance, facilitate relative position changes within the surface drift, and contribute to various aspects of its feeding behavior.     

Inbreeding-based bias in parental responsiveness to litters of oldfield mice

This study investigated variation in parental behavior in oldfield mice (Peromyscus polionotus). Specifically, I examined the possibility that parental behavior and probability of litter loss may differ depending on whether parents are related to one another and, therefore, whether offspring are inbred. When parents are related, they share more genes with their offspring and so may be predicted to invest more in inbred offspring if these offspring do not inherently have a greater risk of juvenile mortality. Survival of inbred pups did not differ from survival of outbred pups, and females tended to exhibit a preference, in the form of enhanced parental care, for inbred litters. Males did not display any consistent preferences. Inbred litters were left unattended more often during the immediate post-partum period than were outbred litters, but this inconsistent finding appeared to have a smaller effect than the overall improved maternal care provided to inbred litters. Females thus appeared to modulate their behavior to a greater degree than did males depending on characteristics of the litter. Patterns of litter loss indicated that complete death of litters was independent of litter inbreeding, whereas loss of selected pups in a litter occurred significantly more often when litters were inbred. Complete and partial loss of litters may be functionally different behaviors that are triggered by different cues. Received: 20 September 1996 / Accepted after revision: 28 April 1997     

Patchy distribution of zooplankton: Behavior,population assessment and sampling problems

Zooplankton and micronekton are often highly aggregated. Density in aggregations can reach 100 to more than 1000 times the average density of the population as estimated by net sampling. In order to assess true abundance of the animals and understand the significance of the aggregations, more information is needed on the behavior and population ecology of individual species and the species-specific attributes of discrete assemblages. We present information on patterns of intense aggregations of protozoans, platyhelminthes, scyphomedusae, copepods, mysids, and sergestids from our own observations. Characteristics behaviors of different species include feeding swarms of Noctiluca miliaris, behaviorally maintained swarms of planktonic flatworms, diel horizontal migration of Mastigias sp. swarms, three patterns of copepod swarms, bathymetric zonation of mysid schools, and seasonal migration and near bottom swarming of Sergia lucens. After the principles were demonstrated, we consider how to relate sampling, behavior, and population dynamics. We stress that the methodology is the result of the question, not the other way round. To tackle the problems associated with behavior in the open ocean, which we did not observe from the surface, it is necessary to sample in more than one way to extract data on differences in population-specific biology that alternative methods supply.     

Seasonal anorexia in the male red-sided garter snake,<Emphasis Type="Italic"> Thamnophis sirtalis parietalis</Emphasis>

Many animals show seasonal shifts in behaviors that coincide with breeding, migration, or hibernation. These behavioral shifts provide ideal opportunities to study the regulation of behavior. The red-sided garter snake (Thamnophis sirtalis parietalis) spends 8 months of the year inactive in underground hibernacula, 1 month breeding, and 3 months feeding to build up enough energy stores to survive the following winter. Although they emerge from 8 months of hibernation with severely depleted energy reserves, they do not feed until weeks later, after the breeding season. We tested the hypothesis that this lack of feeding during the breeding season is due to a shift in behavior rather than the distribution of food and potential mates. Male garter snakes were given a series of choices between pursuing a breeding or feeding opportunity. The proportion of tests in which males selected feeding over breeding gradually increased throughout the study period, reaching almost 100% in the final tests. Males also were given opportunities to feed and court at the beginning and end of the study. Males initially refused food and courted females, but when retested at the end of the study they fed and did not court females. Thus aphagia during the breeding season is due at least in part to an endogenous shift in behavior.Communicated by P. Weatherhead     

External secretion of tetrodotoxin from puffer fishes stimulated by electric shock

Four toxic species of puffers (Takifugu pardalis, T. poecilonotus, T. vermicularis and T. niphobles) secreted large amounts of tetrodotoxin into the surrounding water immediately after being stimulated by electric shock. The total amount of toxin secreted ranged from 2 000 to 50 000 MU depending upon the specimen. The amount of toxin secreted seemed to be related to the toxicity of individuals. Non-toxic specimens of T. rubripes did not secrete any toxin. The stimulation always caused inflation of puffers, and this is generally accepted as a repelling behavior of these species. The secreted tetrodotoxin may act as a repellent to predators.     

Scent-marking behavior in wild groups of common marmosets (Callithrix jacchus)

Scent-marking in mammals has been frequently related to within-group social and reproductive dominance and to defense of territory and resources. We studied the scent-marking behavior of five wild groups of common marmosets, Callithrix jacchus, during 5 months of the fruiting season in northeastern Brazil. Circumgenital marking was the most common type of marking. Marks were distributed throughout the home range and were deposited mainly during travel and intergroup encounters. Although marks were commonly deposited at gum trees, there was no evidence that the animals used scent marks to label fruiting trees or sleeping sites. Contrary to expectations, reproductively dominant females did not mark more than reproductively subordinate females. Moreover, during intergroup encounters, reproductively subordinate females displayed higher frequencies of scent-marking than the reproductively dominant females of their group. Our results suggest that scent-marking is not strictly tied to reproductive dominance or territorial (or resource) defense in common marmosets. Because marks provide information about individual identity and reproductive condition, scent marks could serve different functions when used by different individuals. The high frequency of marking by reproductively subordinate females during intergroup encounters suggests that scent-marking might be used to signal to individuals of neighboring groups. Our data highlight the importance of social and ecological variables in scent-marking behavior. Received: 26 October 1998 / Received in revised form: 20 May 1999 / Accepted: 30 May 1999     

Size and structure of a photographically identified population of manta rays <Emphasis Type="Italic">Manta alfredi</Emphasis> in southern Mozambique

The size and structure of a photographically identified population of reef manta ray, Manta alfredi, were examined at aggregation sites over a four-year period in southern Mozambique. The use and standardisation of photo-ID techniques was examined as a minimally-intrusive means to study this species. Using these techniques, we report on the size, structure and seasonality of this population of M. alfredi. In total, 449 individuals were identified during this time period, 40.5% of which were re-sighted on at least one occasion. The longest period between re-sighting events was 1,252 days. During the study period, annual population size estimates for M. alfredi ranged from 149 to 454 individuals. The superpopulation size estimate for the entire study period was 802 individuals, the first reported for M. alfredi at a monitored aggregation site. A highly significant sex bias was evident with a female:male ratio of 3.55:1. The majority of rays (89.9% males; 49.7% females) were considered mature, with most individuals between 3.0 and 4.9 m in disc width. Manta alfredi were observed at the study sites in each month of the calendar year. The maximum number of individual rays seen per dive was 30. Large numbers of rays (20 + per dive) were seen in the months of November, December and January, which coincide with the breeding season. Natural markings were unique to individuals and did not change substantially with time, which provided further support for their use in the identification of individual M. alfredi over multiple years. Multiple re-sightings of individual M. alfredi suggest that many individuals in this population exhibit site fidelity to the examined aggregation sites. As target subsistence fishing for M. alfredi exists along the Mozambican coastline, management efforts to monitor and prevent overexploitation at these critical habitats should be a priority.     

Hydrography and distribution dynamics of larval and juvenile fishes in the coastal waters of the Tanshui River estuary,Taiwan, with reference to estuarine larval transport

Distribution dynamics of fish larvae and juveniles in the coastal waters of the Tanshui River, Taiwan was studied fortnightly using surface horizontal tows with a larval net in daytime during the period from early April through early June 1991. Environmental factors, including water temperature, salinity, dissolved oxygen, pH, transparency and depth at sampling stations, were also monitored. A total of 10737 fish eggs and 1387 individuals, representing 43 families and 93 species, was collected during five cruises from 12 stations in the coastal waters. Most fish were estuarine-dependent marine species. Liza macrolepis, Ambassis gymnocephalus, Terapon jarbua, Mullidae and Gobiidae were the most dominant, making up 64.7% of the total catch. Early life stages, including egg, preflexion, flexion and postflexion larvae were abundant in surface samples. However, yolk-sac larvae were absent in the surface water, probably due to an ontogenetic behavioral shift as a consequence of a change in specific weight during early development. The species composition of fish larvae and juveniles was related to the microhabitats found in the coastal waters. The physico-chemical conditions, along with ontogenetic behavior, played an important role in larval fish distribution in the coastal waters.     

Lunar rhythms of vertical migrations coded in otolith microstructure of North Atlantic lanternfishes,genus Hygophum (Myctophidae)

Otoliths of five Hygophum species were examined by means of light and scanning electron microscopy. In otoliths of four species (H. benoiti, H. macrochir, H. reinhardtii and H. taaningi) a strong cyclic pattern of the incremental structure was observed. In the fifth species (H. hygomii) such a pattern did not exist. An analysis of archival data on mesopelagic collections suggested three types of Hygophum spp. migratory behavior in relation to the lunar cycle which corresponded with the otolith microstructure. In H. hygomii only limited influence of moon phase on the uppermost range of night-vertical migration toward the surface was observed. The abundant nighttime occurrence of this species moved from the 0 to 50 m into the 50 to 100 m depth strata at full moon. In H. benoiti, a great part of the population, mainly juveniles, showed a tendency toward cessation of the vertical migrations during the first and fourth quarters of the lunar cycle. H. macrochir and H. taaningi had the strongest correlation of behavior with the lunar cycle. Both species showed arrested vertical migrations at the new moon phase, staying at day depths during the night, i. e., below 400 m. Thus, sequences of clear growth increments in otoliths represented a fast-growth period associated with the night migration to the warm surface layers, while bands without easily distinguishable incremental structure were interpreted as a period of slow growth in deep, cold waters due to limitation of the upward migration range occurring approximately at new moon.     

Robin’s egg blue: does egg color influence male parental care?

A recent hypothesis suggests that birds’ blue-green egg colors may be a sexually selected signal of female (and potentially nestling) quality that males use to make parental investment decisions. While there is some empirical support for this idea, both theory and observations question its validity. To test this hypothesis experimentally, we examined the influence of egg color on male American robin Turdus migratorius behavior by replacing natural clutches with four artificial eggs that were all either pale or vividly colored, close to the extremes in natural egg coloration. At the end of the incubation period, three unrelated nestlings were fostered into each experimental nest, and parental provisioning behavior was monitored when nestlings were 3, 6, and 9 days old. Male provisioning rate for 3-day-old nestlings was significantly higher in the vivid egg treatment compared to both the pale egg treatment and untreated controls, but there was no effect of egg color on paternal behavior at the older nestling stages. Male feeding rate at unmanipulated nests was only weakly positively related to natural egg color (chroma) when nestlings were 3 days old. These results suggest that blue-green egg color may act as a post-mating signal of female quality or investment in this species, but our findings do not exclude the possibility that egg color pigmentation also serves other adaptive functions.     

The effect of reproductive condition on the foraging behavior of female hoary bats,Lasiurus cinereus

Summary Female mammals experience larg changes in time and energy budgets associated with reproduction and these may influence the foraging strategies of individuals. I studied the changes in foraging behavior associated with reproduction in female hoary bats, Lasiurus cinereus. As lactation progressed, individuals departed to forage earlier in the evening and spent more time foraging per night and less time roosting with their young. Foraging time increased by at least 73% between early lactation and fledging and then declined as the young became independent. Females with two young foraged for longer than did those with one and females with pre- and postfledging young foraged in different habitats. The changes in foraging time suggest that foraging activity of female L. cinereus is constrained and individuals act as time minimizers, adjusting their foraging behavior to meet current energy demand. Predation risk is unlikely to constrain the behavior of these bats. However, maximizing energy intake throughout lactation may not be the optimal strategy because storing excess energy increases flight cost and may reduce foraging efficiency. The need to keep newborn young warm may also influence foraging time. Such constraints, causing changes in foraging activity, may alter the availability of habitats and prey and must be considered when modelling foraging strategies. In addition, changes in flight time may significantly alter the energy budgets of bats in different stages of reproduction.     

Induction of swarming ofNereis succinea

Nereis succinea (Frey and Leuckart, 1847), collected in 1987 from the Weser estuary, FRG, was exposed to different temperatures in the laboratory. Metamorphosis to heteronereid stages, as well as swarming at a minimum temperature of 12°C, was induced by raising temperatures around the time of the new moon. Lunar periodicity was illustrated under natural temperature-programs, and at 16°C. An abrupt increase in temperature caused swarming to occur at different times of the lunar cycle.     

Bird song as a signal of aggressive intent

A central question in animal communication research concerns the reliability of animal signals. The question is particularly relevant to aggressive communication, where there often may be advantages to signaling an exaggerated likelihood of attack. We tested whether aggressive signals are indeed reliable signals of attack in song sparrows (Melospiza melodia). We elicited aggressive signaling using a 1-min playback on a male’s territory, recorded the behavior of the male for 5 min, and then gave him the opportunity to attack a taxidermic mount of a song sparrow associated with further playback. Twenty subjects attacked the mount and 75 did not. Distance to the speaker was a significant predictor of attack for both the initial recording period and the 1 min before attack. For the initial recording period, none of the measures of singing behavior that we made was a significant predictor of attack, including song-type matching, type-switching frequency, and song rate. For the 1-min period immediately before attack, only the number of low amplitude “soft songs” was a significant predictor of attack. Although most aggressive signals contained little information on attack likelihood, as some models suggest should be the case, the unreliability of these signals was not caused by convergence of individuals on a single signaling strategy, as those models argue should occur.     

Function of the mating plug in Drosophila hibisci Bock

The mating plug in Drosophila hibisci Bock is a firm, gelatinous structure that forms within the female’s uterus during copulation. Two non-mutually exclusive hypotheses for the function of the plug were evaluated. The plug may serve as a nutritional gift that females digest, using the constituents for somatic maintenance or to provision eggs as they mature within the ovaries. Alternatively, the plug may act as a chastity enforcement device by preventing subsequent copulations, and thereby reducing sperm competition. Plug size did not decrease within females over a period of 2 days, and dietary treatment in females did not affect plug size. The extent of ovarian provisioning was also not related to plug size. These results weaken the nutritional gift hypothesis. In contrast, the probability of a second copulation increased sharply with an experimental decrease in plug size. Moreover, females with plugs experimentally reduced in size were courted significantly more and mated significantly faster than females with larger plugs. These results support the chastity enforcement hypothesis. The plug retains the ejaculate and concentrates sperm at the anterior end of the uterus near the apertures of the sperm storage organs. The presence of the plug thus probably facilitates the movement of sperm into storage by retaining sperm at the anterior end of the uterus near the apertures of the sperm storage organs, which may be especially important for D. hibisci, in which sperm length is nearly twofold greater than ventral receptacle length. Matings with newly eclosed virgin females were significantly shorter than with older virgins, and copulations with the younger virgins ended more often without any sperm having yet entered into storage. The effectiveness of the plug in safeguarding a male’s ejaculate may have favoured the evolution of shortened copula durations with young virgins. One fitness advantage of shortened copula duration could be time liberated for the pursuit of further mating opportunities. Received: 12 May 2000 / Revised: 22 September 2000 / Accepted: 15 October 2000     

Autecology of Fucus distichus ssp. distichus (Phaeophyceae: Fucales) in Nova Scotia,Canada

The autecology of Fucus distichus L. ssp. distichus was investigated at several sites on the Atlantic coast of Nova Scotia, Canada, throughout a 2-year period. This species is confined to high-littoral rock pools at exposed sites, where there appears to be little competition from other organisms. Water temperature, salinity, dissolved oxygen, and hydrogen-ion concentrations underwent both considerable seasonal and short-term variation. Pools with extremes of salinity did not contain F. distichus ssp. distichus. Receptacles are formed during winter, and by late spring they are cast. Sporelings were first visible during September; their development was slow, and these plants did not become reproductive until the second year. During the period February to May, rapid growth of new fronds occurred; an increase in both length and bulk of the plants resulted from this growth. Fronds of mature plants continued to elongate slowly throughout the summer and the early autumn with the formation of receptacles in winter. Plants were frequently damaged, which resulted in regeneration of new fronds from the wounded surface.Issued as NRCC No. 14510     

Consequences of communal gall occupation and a test for kin discrimination in the aphid Tamalia coweni (Cockerell) (Homoptera: Aphididae)

This study investigated the consequences of communal gall induction on individual and group fitness in the aphid Tamaliacoweni. The possibilities that kin discrimination and foundress density are factors favoring communal gall occupation were examined. Clonally produced aphid foundresses were collected to create two treatments: clonal groups and groups of less closely related individuals. These were confined on suitable host plant tissue to compare their respective propensities towards communal behavior. There were no significant differences in the frequencies of communal gall occupation; therefore, active kin discrimination by T.coweni foundresses apparently does not play a role in their communal behavior, within the context of this experiment. In a second experiment, aphid foundress density on the host plant was manipulated in three treatments and was correlated with the frequency of communal gall occupation. Individual fitness was inversely related to the mean number of foundresses per gall. These results suggest that communal gall occupation does not necessarily represent mutual cooperation but may instead be the outcome of competition for limited gall sites on the host plant. However, natural selection at the clonal level may favor communal gall occupation under the conditions of resource limitation and high within-group relatedness. Received: 26 September 1997 / Accepted after revision: 28 March 1998