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21.
In insect parasitoids, offspring fitness is strongly influenced by the adult females choice of host, particularly in ectoparasitoids that attack non-growing host stages. We quantified the fitness consequences of size-dependent host species selection in Dirhinus giffardii, a solitary ectoparasitoid of tephritid fruit fly pupae. We first showed a positive correlation between the size of emerged D. giffardii wasps and the size of their host fruit fly species (in order of decreasing size): Bactrocera latifrons, B. cucurbitae, B. dorsalis or Ceratitis capitata. We then manipulated individual wasps to show that the parasitoid preferred to attack the largest (B. latifrons) to the smallest (C. capitata) host species when provided with a choice, and laid a greater proportion of female eggs in B. latifrons than in C. capitata. There were no differences in developmental time or offspring survival between individuals reared from these two host species. Finally, we compared the foraging efficiency of large versus small wasps (reared from B. latifrons vs C. capitata) under two different laboratory conditions: high versus low host habitat quality, given that realized fecundity in parasitoids may be influenced by either egg-limited or time-limited factors. Under both conditions, large wasps parasitized more hosts than did small ones as a consequence of high searching efficiency in the host-poor habitat, and high capacity for adjusting egg maturation in response to host availability in the host-rich habitat. Considering the flexibility of body growth, the apparent lack of cost of achieving large body size in either development or survival, and the strong dependence of realized reproductive success on a females size, we argue that body size may be a key to understanding evolution of host species selection in ectoparasitoids. We also discuss constraints upon the evolution of size-dependent host species selection in parasitoids.Communicated by D. Gwynne 相似文献
22.
Fanie?PelletierEmail author Marco?Festa-Bianchet 《Behavioral ecology and sociobiology》2004,56(6):546-551
In sexually dimorphic ungulates, males generally spend less time foraging than females, possibly because of difference in body mass or because of the energetic requirements of lactation. The relationship between body size and foraging time has received little attention at the intra-specific level, because few studies have documented activity budgets for individuals of known size. Bighorn rams are a good model to explore how body mass affects foraging time, because they range in mass from 55 to 140 kg. We examined how the foraging time of bighorn rams varied according to individual characteristics. We observed rams in a marked population and constructed time budgets during the 3 months preceding the rut. We determined ram social rank based on agonistic encounters and collected fecal samples to count lungworm larvae. Time spent foraging was negatively correlated with body mass. After accounting for age differences, larger rams spent less time foraging and more time lying than smaller rams. Among rams aged 6–12 years, dominants spent less time feeding than subordinates, while fecal output of lungworm larvae was negatively correlated with foraging time for rams of all ages. Body mass accounts for much of the individual variation in foraging time, suggesting that sexual dimorphism is important in explaining differences in feeding time between males and females.Communicated by P. Heeb 相似文献
23.
Field studies demonstrate that natural populations of a group of water striders (Heteroptera: Gerridae) that share a common
mating system are characterized by weak assortative mating by size and by large sizes of mating males and females relative
to single individuals. This study presents an experimental assessment of the components of mating that may contribute to these
mating patterns. The effects of male and female body size on each of three components of mating were studied in three water
strider species in the laboratory. Large females of all three species mated more frequently, copulated for longer and were
guarded longer than small females. Large males mated more frequently than small males in all three species, and also guarded
females for longer in the two species where the average of mate guarding was long. However, we found an antagonistic effect
of male size on copulation duration: small males copulated for longer than large males in all three species. We show that
the combined effects of these size biases mimic the mating patterns found in the wild, e.g. weak and variable assortative
mating, and stronger and less variable size ratios of mating versus non-mating females relative to males. We suggest that
the antagonistic effects of male size on copulation and guarding duration may be a key source of interpopulational variation
in assortative mating and sexual selection on male size. Further, neither spatial or temporal covariation in size, nor mechanical
constraints, caused the assortative mating observed here in this group of water striders. Some combination of male and female
choice (either active or passive forms) of large mates and male-male exploitation competition for mates play potentially important
roles in producing population level assortative mating in water striders.
Received: 17 March 1995/Accepted after revision: 28 October 1995 相似文献
24.
Male seahorses (genus Hippocampus) provide all post-fertilization parental care, yet despite high levels of paternal investment, these species have long been
thought to have conventional sex roles, with female mate choice and male–male competition. Recent studies of the pot-bellied
seahorse (Hippocampus abdominalis) have shown that sex-role reversal occurs in high-density female-biased populations, indicating that male mating preferences
may lead to sexual selection on females in this species. Egg size, egg number, and offspring size all correlate positively
with female body size in Hippocampus, and by choosing large mating partners, male seahorses may increase their reproductive success. While male brood size is
also positively correlated with body size, small H. abdominalis males can carry exceptionally large broods, suggesting that the fecundity benefits of female preference for large partners
may be limited. We investigated the importance of body size in reproductive decisions of H. abdominalis, presenting focal individuals of both sexes with potential mating partners of different sizes. Mating preferences were quantified
in terms of time spent courting each potential partner. Male seahorses were highly active throughout the mate-choice trials
and showed a clear behavioral preference for large partners, while females showed significantly lower levels of activity and
equivocal mating preferences. The strong male preferences for large females demonstrated here suggest that sexual selection
may act strongly on female body size in wild populations of H. abdominalis, consistent with predictions on the importance of female body size for reproductive output in this species.
An erratum to this article can be found at 相似文献
25.
P. Neuhaus 《Behavioral ecology and sociobiology》2000,48(1):75-83
I studied reproductive costs in the female Columbian ground squirrel (Spermophilus columbianus) using individually marked animals. I compared weight changes during the active season and over winter, and mortality for
females that did and did not wean young. Females raising young were heavier at emergence in that spring than unsuccessful
ones. Females that did not raise young gained more weight during summer, were heavier than successful females at the time
of entry into hibernation, and were heavier emerging from hibernation the following spring. Over-winter mortality was higher
for females that reared young compared to reproductively unsuccessful females. A food supplementation experiment showed that
energy-rich food can accelerate individuals’ weight gain. Interactions between litter size, birth weight, weight at emergence
from the natal burrow, survival of young to yearling age, and maternal fitness were also studied. Litter sizes were experimentally
manipulated to evaluate how females cope with costs of rearing one additional young. Birth weight of juveniles was positively
correlated with survival to emergence from the natal burrow and with survival to yearling age. Partial litter loss was higher
in experimentally enlarged litters than in either experimentally decreased or control litters. Total litter loss, survival
of adult females or the probability of weaning young the following year were not affected by the litter size manipulation.
Females appear to adjust the size of their litter before birth, and to some extent during lactation, to their ability to wean
young.
Received: 20 January 2000 / Received in revised form: 12 March 2000 / Accepted: 18 March 2000 相似文献
26.
Archaeological and paleontological datasets are used in conservation to add time-depth to ecology. In central Texas, several
top carnivores including prehistoric Native American hunters have been extirpated or have had their historic ranges restricted,
which has resulted in pest-level white-tailed deer (Odocoileus virginianus texana) populations in some areas. Differences in body size of deer between prehistory and modernity are expected, given that a
lack of predation likely has increased intraspecific competition for forage among deer, resulting in smaller body size today.
In fact, modern deer from settings without harvest pressure are significantly smaller than those from harvested areas and
from prehistoric deer. From a natural history perspective, this research highlights potential evolutionary causes and effects
of top-predator removal on deer populations and related components of biological communities in central Texas. 相似文献
27.
Changes in serum concentrations of polychlorinated biphenyls (PCBs), hydroxylated PCB metabolites and pentachlorophenol during pregnancy 总被引:2,自引:0,他引:2
We studied pregnancy-related changes in serum concentrations of five polychlorinated biphenyls (PCBs, CB 118, CB 138, CB 153, CB 156, CB 180), three hydroxylated PCB metabolites (4-OH-CB107, 4-OH-CB146, 4-OH-CB187), and pentachlorophenol (PCP). Median serum lipid content increased 2-fold between early (weeks 9-13) and late pregnancy (weeks 35-36) (N = 10), whereas median PCB levels in serum lipids decreased 20-46%, suggesting a dilution of PCB concentrations in serum lipids. Nevertheless, strong positive intra-individual correlations (Spearman’s r = 0.61-0.99) were seen for PCBs during the whole study period. Thus, if samples have been collected within the same relative narrow time window during pregnancy, PCB results from one single sampling occasion can be used in assessment of relative differences in body burdens during the whole pregnancy period. Concentrations of OH-PCBs in blood serum tended to decline as pregnancy progressed, although among some women the concentrations increased at the end of pregnancy. Positive intra-individual correlations (r = 0.66-0.99) between OH-PCB concentrations were observed during the first and second trimester, whereas correlations with third trimester concentrations were more diverging (r = −0.70-0.85). No decline in PCP concentrations was observed during pregnancy and no significant correlations were found between concentrations at different sampling periods. Our results suggest that for both OH-PCBs and PCP, sampling has to be more specifically timed depending on the time period during pregnancy that is of interest. The differences in patterns of intra- and inter-individual variability of the studied compounds may be due to a combination of factors, including lipid solubility, persistence of the compounds, distribution in blood, metabolic formation, and pregnancy-related changes in body composition and physiological processes. 相似文献
28.
František Vožeh Antonín Doněk Jan Cendelín Ivana Korelusová Jan Vrba 《The Environmentalist》2007,27(4):501-504
The effect of long-term exposure to high frequency electromagnetic field (HF EMF) on some somatic and neural characteristics
was studied in neurodefective Lurcher mutant (+/Lc) and normal wild type mice (+/+). Both newborn and young adult (3 months)
animals derived from two strains (C3H, B6CBA) were exposed to HF EMF (870 MHz) from 1st to 21st day or from 91st to 120th
day respectively. In animals of both groups and controls we observed the development of body weight. Moreover, in the HF EMF
exposed adult B6CBA animals we studied spatial learning ability, motor functions and the CNS excitability. To investigate
specific energy absorption rate (SAR) in experimental animals we have done the basic 3D calculations of the electromagnetic
energy distribution in the simplified model of the mouse. The HF EMF exposed animals exhibited mild differences of body weight
between them and unexposed controls. The long-term exposure to HF EMF did not significantly influence the ability to learn
in the Morris water maze. However, significant lower swimming speed was found in the irradiated +/Lc as well as lower motor
activity of +/+ in the open field when compared to controls. No significant differences were found between HF EMF irradiated
animals and controls in examination of the CNS excitability and motor functions. 相似文献
29.
Insect larvae increase in size with several orders of magnitude throughout development making them more conspicuous to visually
hunting predators. This change in predation pressure is likely to impose selection on larval anti-predator behaviour and since
the risk of detection is likely to decrease in darkness, the night may offer safer foraging opportunities to large individuals.
However, forsaking day foraging reduces development rate and could be extra costly if prey are subjected to seasonal time
stress. Here we test if size-dependent risk and time constraints on feeding affect the foraging–predation risk trade-off expressed
by the use of the diurnal–nocturnal period. We exposed larvae of one seasonal and one non-seasonal butterfly to different
levels of seasonal time stress and time for diurnal–nocturnal feeding by rearing them in two photoperiods. In both species,
diurnal foraging ceased at large sizes while nocturnal foraging remained constant or increased, thus larvae showed ontogenetic
shifts in behaviour. Short night lengths forced small individuals to take higher risks and forage more during daytime, postponing
the shift to strict night foraging to later on in development. In the non-seasonal species, seasonal time stress had a small
effect on development and the diurnal–nocturnal foraging mode. In contrast, in the seasonal species, time for pupation and
the timing of the foraging shift were strongly affected. We argue that a large part of the observed variation in larval diurnal–nocturnal
activity and resulting growth rates is explained by changes in the cost/benefit ratio of foraging mediated by size-dependent
predation and time stress. 相似文献
30.
Although assortative mating is widespread among long-lived monogamous birds, the underlying mechanisms still remain unclear
in many species. In this study, we analysed assortative mating by age and body mass in the common tern Sterna hirundo with special regard to mate choice decisions of newly paired birds. To assess whether assortative mating by age is an active
decision involving either homotypic or directional preferences or rather a passive process due to restricted availability
of potential mates, we analysed the influence of age-dependent arrival date and cohort size. Furthermore, we looked for direct
benefits in terms of reproductive success. Common terns mated assortatively by age and arrival date but not by body mass at
arrival. Assortative mating by age was age dependent and was detected mainly in younger birds, whereas birds older than 8 years
rather re-paired with younger ones. The availability of same-aged mates was restricted by cohort size and arrival date. We
found no general evidence for better reproductive performance of same-aged pairs. Instead, relative reproductive success was
related to own age and the relative age of mate: It should be advantageous for any bird to acquire an old mate; hence, assortative
mating by age seems to be beneficial only for old terns but not for young ones. Age-assortative mating in common terns occurred
by both passive and active processes, which are not mutually exclusive. Our results do not indicate a homotypic but a directional
preference and support the theory that high-quality (older/experienced) individuals tend to mate assortatively if same-aged
mates are available, which leaves low-quality (young/inexperienced) individuals to mate among themselves. 相似文献