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931.
The benthic response to a plume front was studied in two areas of the northern Adriatic (Mediterranean Sea) differently influenced
by the Po River freshwater input. Sediment samples were collected in June 1996 and February 1997 from 12 stations. The adopted
sampling strategy was able to identify the front line in real time by satellite images and to locate sampling stations along
an inner–outer plume gradient in order to cover the benthic area beneath the river plume, where enhanced biological production
was expected, and open-sea sediments not directly influenced by freshwater inputs. Meiofaunal parameters were compared to
the physical conditions and to phytodetritus inputs, organic matter accumulation and bacterial secondary production. The sediments
of the Adriatic Sea were characterised by high concentrations of phytopigments (0.6 to 13.9 μg g−1 for chlorophyll a and 1.2 to 17.7 μg g−1 for phaeopigments) and biopolymeric organic carbon (0.15 to 3.02 mg g−1). The plume system extended for a large sector of the northern Adriatic. In the northern area, a large and highly dynamic
plume area was coupled with a sediment organic matter concentration significantly higher than in open-sea sediments. In the
southern sector, where the plume area and the front line did not change markedly during the year, plume–benthic coupling was
evident only in the sediments beneath the front, and corresponded to phaeopigment accumulation. Bacterial parameters and secondary
production were high and significantly higher in the frontal area than at open-sea stations. Meiofauna density (1342 to 8541
ind. 10 cm−2) did not change either by season or between areas and was significantly correlated with phaeopigments and bacterial secondary
production. Meiofauna displayed different responses to plume inputs in the two sampling areas. In the northern sector, meiofauna
density was coupled with organic matter distribution and displayed highest values beneath the plume. In the southern sector,
the densities of copepods, turbellarians and kinorhynchs displayed highest values under the front in summer, and the same
applied to total meiofauna density in winter. Juvenile decapods and copepod nauplii significantly increased their densities
in sediments beneath the front. Data presented in the present study suggest that plume inputs and frontal systems, enhancing
phytodetritus accumulation and benthic bacterial response, might influence density, composition and distribution of meiofaunal
assemblages. As river plumes are highly variable systems affecting the trophic characteristics of the sediments underneath,
their dynamics should be considered when analysing mesoscale spatial changes of meiofaunal assemblages.
Received: 30 November 1999 / Accepted: 24 May 2000 相似文献
932.
Maternal investment in rhesus macaques (Macaca mulatta): reproductive costs and consequences of raising sons 总被引:1,自引:0,他引:1
Maternal investment in offspring is expected to vary according to offspring sex when the reproductive success of the progeny
is a function of differential levels of parental expenditure. We conducted a longitudinal investigation of rhesus macaques
to determine whether variation in male progeny production, measured with both DNA fingerprinting and short tandem repeat marker
typing, could be traced back to patterns of maternal investment. Males weigh significantly more than females at birth, despite
an absence of sex differences in gestation length. Size dimorphism increases during infancy, with maternal rank associated
with son’s, but not daughter’s, weight at the end of the period of maternal investment. Son’s, but not daughter’s, weight
at 1 year of age is significantly correlated with adult weight, and male, but not female, weight accounts for a portion of
the variance in reproductive success. Variance in annual offspring output was three- to fourfold higher in males than in females.
We suggest that energetic costs of rearing sons could be buffered by fetal delivery of testosterone to the mother, which is
aromatized to estrogen and fosters fat accumulation during gestation. We conclude that maternal investment is only slightly
greater in sons than in daughters, with mothers endowing sons with extra resources because son, but not daughter, mass has
ramifications for offspring sirehood. However, male reproductive tactics supersede maternal investment patterns as fundamental
regulators of male fitness.
Received: 23 July 1999 / Received in revised form: 23 February 2000 / Accepted: 13 March 2000 相似文献
933.
Recent models of choosiness in mate choice have identified two particularly important factors: the potential reproductive
rate (PRR) of the choosing sex relative to that of the chosen sex, and the variation in quality of potential mates. This experimental
study tested how these factors affected choosiness in male and female sand gobies, Pomatoschistus minutus. We manipulated relative PRR by means of water temperature, and mate quality by means of body length. The choosing male or
female was offered a choice between two mates with either a small or a large difference in body length representing a small
or a large variation in mate quality. Choosiness was measured as (1) preference for the larger mate, and (2) as whether or
not spawning occurred with the smaller mate, while the larger mate was visible but screened off. We found that females preferred
large males, and that their level of choosiness was affected by variation in male quality, but not by their own relative PRR.
Males, on the other hand, seemed unselective in all treatments and were in general more likely than females to spawn with
their provided partner. This suggests that in the sand goby, variation in male mate quality has a greater influence than relative
PRR on facultative changes in female choosiness. However, a general difference in PRR between males and females may be one
important factor explaining the observed sex difference in choosiness.
Received: 17 April 2000 / Revised: 24 June 2000 / Accepted: 17 July 2000 相似文献
934.
In the meerkat (Suricata suricatta), a cooperative mongoose, pups follow potential feeders while the group is foraging and emit incessant calls when soliciting
food from them. In contrast to a ’stationary’ brood of chicks, in which nestlings are fed at a fixed location, meerkat pups
are ’mobile’ and become spread out. The question arises whether meerkat pups that experience different constraints to those
facing chicks have evolved similar begging strategies. This paper describes the vocalisations that meerkat pups emit in the
context of begging and investigates the influence of these calls on food allocation by older group members and on the behaviour
of littermates. Meerkat pups use two types of calls when soliciting food from a potential feeder. The most common is a ’repeat’
call, which pups emit continuously when following an older forager over several hours a day. In addition, when a potential
feeder finds a prey item, the pups next to it emit a bout of calls with increased calling rate, amplitude and fundamental
frequency, termed ’high-pitched’ calls. Observations, together with playback experiments, showed that more prey was allocated
to pups that called longer and more intensely. The pup closest to a feeder was almost always fed. The probability of emitting
high-pitched calls did not depend on the time since a pup had received food, and the change from repeat to high-pitched calls
occurred suddenly. The main function of the high-pitched call, therefore, does not appear to be to signal a pup’s hunger state.
More likely, the two calls, in the context of begging, may be an adaptation to energetic constraints in a mobile feeding system.
Pups, which are dispersed during foraging, may emit repeat calls over long periods to prevent potential feeders from eating
all the prey themselves. At the moment a potential feeder finds prey, pups may give the more intense high-pitched calls to
direct feeders to bring the food item to them and not to a littermate. Therefore, unlike the stationary feeding system where
chicks emit one type of begging call when the feeder approaches the nest, meerkats, with a mobile feeding system, have evolved
two discrete types of vocalisations in the context of begging.
Received: 22 November 1999 / Revised: 1 July 2000 / Accepted: 17 July 2000 相似文献
935.
Experimental evidence of a testosterone-induced shift from paternal to mating behaviour in a facultatively polygynous songbird 总被引:5,自引:2,他引:3
Previous studies have suggested that testosterone (T) profiles of male birds reflect a trade-off between mate attraction behaviours
(requiring high T levels) and parental care activities (requiring low T levels). In this study, we experimentally elevated
T levels of monogamous males in the facultatively polygynous European starling (Sturnus vulgaris), and compared mate attraction and paternal behaviour of T-treated males with those of controls (C-males). T-males significantly
reduced their participation in incubation and fed nestlings significantly less often than C-males. Females paired to T-treated
males did not compensate for their mate’s lower paternal effort. The observed reduction in a male’s investment in incubating
the eggs was accompanied by an increased investment in typical female-attracting behaviours: T-males spent a significantly
higher proportion of their time singing to attract additional females. They also occupied more additional nestboxes than C-males,
although the differences just failed to be significant, and carried significantly more green nesting materials into an additional
nestbox (a behaviour previously shown to serve a courtship function). T-males also behaved significantly more aggressively
than C-males. During the nestling period, the frequency of mate-attracting behaviours by T-treated and control males no longer
differed significantly. Despite the reduced paternal effort by T-males and the lack of compensation behaviour by females,
hatching and breeding success did not differ significantly between T- and C-pairs.
Received: 7 February 2000 / Revised: 10 August 2000 / Accepted: 3 September 2000 相似文献
936.
Male willow warblers have song repertoires which vary in complexity along several dimensions. We examined whether female choice,
as measured by date of pairing, was based on these song characteristics in 4 different years. Pairing date was negatively
correlated with song repertoire size in 1 year, and with song versatility in another year, but there was no consistent effect
of any song characteristic on pairing throughout the years or in the pooled sample. The variable that best explained how soon
a male pairs is male arrival date (only males that had settled territories before the first female arrived were considered
in the analysis). This correlation is consistently significant in all years. This is most parsimoniously interpreted as females
choosing some habitat characteristic in the same way that males do. A small percentage of males (8.3%) attracted and paired
with a second female. The likelihood of becoming polygynous was not explained by any measured song characteristic, but it
was related to arrival date: early males were more likely to pair with two females. Males with large repertoires fledged more
young in their primary nests, and there was a trend for the offspring of these males to have a greater probability of being
recruited into the population. In conclusion, the results show that in most years there is no sexual selection by female preference
on song characteristics, although the data on reproductive success is consistent with the idea of repertoire size being an
indicator of male quality.
Received: 4 June 1999 / Received in revised form: 1 December 1999 / Accepted: 31 December 1999 相似文献
937.
Aggression and resource sharing among foundresses in the social wasp Polistes dominulus: testing transactional theories of conflict 总被引:3,自引:0,他引:3
Tug-of-war models of within-group conflict predict that the frequency of conflict will be positively related to the degree
of reproductive sharing within the group; in contrast, a negative relationship supports transactional models, in which reproductive
payments among group members limit the degree of within-group selfishness. We tested predictions of the tug-of-war and transactional
models by examining cofoundress interactions during the founding (preworker) phase of colony development in 30 naturally nesting
colonies of the paper wasp Polistes dominulus. We found that the mean rate of foundress aggression and the mean probability of food sharing were significantly negatively
associated, which supports the prediction of the transactional, not the tug-of-war model. Further, cofoundress aggression
significantly increased over the founding phase (independently of temperature), while the fraction of aggression initiated
by the dominant (alpha) foundress significantly decreased over this period. We show that both of these results are predicted
by the transactional model of within-group conflict. Interestingly, the alpha’s rate of aggression was significantly positively
temperature dependent, while the beta’s was not. This indicates that the alpha’s aggression level may often be near her physiological
maximum, while the beta’s aggression is limi- ted by other factors, contradicting the prediction of the tug-of-war model.
Moreover, the alpha’s aggression was significantly positively temperature dependent only in the second half of the founding
period, as predicted by the transactional model since this is when there is least reproductive sharing. Finally, our results
indicate that the alpha’s level of aggression depends on the resources controlled by the beta.
Received: 18 January 2000 / Revised: 19 June 2000 / Accepted: 24 June 2000 相似文献
938.
Life history costs of olfactory status signalling in mice 总被引:4,自引:0,他引:4
L. M. Gosling S. C. Roberts E. A. Thornton M. J. Andrew 《Behavioral ecology and sociobiology》2000,48(4):328-332
Large body size confers a competitive advantage in animal contests but does not always determine the outcome. Here we explore
the trade-off between short-term achievement of high social status and longer-term life history costs in animals which vary
in competitive ability. Using laboratory mice, Mus musculus, as a model system, we show that small competitors can initially maintain dominance over larger males by increasing investment
in olfactory status signalling (scent-marking), but only at the cost of reduced growth rate and body size. As a result they
become more vulnerable to dominance reversals later in life. Our results also provide the first empirical information about
life history costs of olfactory status signals.
Received: 15 December 1999 / Revised: 6 June 2000 / Accepted: 24 June 2000 相似文献
939.
We present a hitherto unknown prey perception strategy in bats: Myotis nattereri (Vespertilionidae, Chiroptera) is able to perceive prey by echolocation within a few centimeters of echo-cluttering vegetation,
by using frequency-modulated search signals of very large bandwidth (up to 135 kHz). We describe the species’ search behavior
and echolocation repertoire from the field and from experiments in a flight tent. In the field, bats varied signal parameters
in relation to their distance from vegetation and usually flew close to vegetation. In the flight tent, M. nattereri detected and localized prey by echolocation alone as close as 5 cm from vegetation. Apparently, the bats were able to tolerate
some overlap between prey and clutter echoes. Passive prey cues (vision, olfaction, prey-generated sounds) were not used in
prey perception. The bats selected prey by size. The animals performed aerial catches and produced approach sequences typical
for aerial hawking bats, but were able to do so within a few centimeters of the substrate. M. nattereri thus has access to silent, suspended prey very close to vegetation (e.g., spiders, and caterpillars on threads).
Received: 29 September 1999 / Received in revised form: 12 February 2000 / Accepted: 12 February 2000 相似文献
940.
Abstract: Counts of the number of animal carcasses arriving at Malabo market, Bioko Island, Equatorial Guinea, were made during two, 8-month study periods in 1991 and 1996. Comparisons of the availability and abundance of individual species between years showed that more species and more carcasses appeared in 1996 than in 1991. In biomass terms, the increase was significantly less, only 12.5%, when compared with almost 60% more carcasses entering the market in 1996. A larger number of carcasses of the smaller-bodied species (i.e., rodents and the blue duiker [ Cephalophus monticola ] ) were recorded in 1996 than in 1991. Although an additional four species of birds and one squirrel were recorded in 1996, these were less important in terms of their contribution to biomass or carcass numbers. Concurrently, there was a dramatic reduction in the larger-bodied species, Ogilby's duiker ( C. ogilbyi ) and seven diurnal primates. We examined these changes, especially the drop in the number of larger animals. We considered the possible following explanations: (1) the number of hunters dropped either because of enforced legislation or scarcity of larger prey; (2) a shift in the use of hunting techniques occurred ( from shotguns to snares); or (3) consumer demand for primate and duiker meat dropped, which increased demand for smaller game. Our results suggest that the situation in Bioko may be alarmingly close to a catastrophe in which primate populations of international conservation significance are being hunted to dangerously low numbers. Although there is still a need for surveys of actual densities of prey populations throughout the island, working with the human population on Bioko to find alternatives to bushmeat is an urgent priority. 相似文献