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1.
The majority of published accounts on scleractinian coral reproduction are from the tropical Pacific and Caribbean, with
very little information known about Red Sea species. This report examines variation in reproductive mode in 24 species of
hermatypic corals (belonging to seven families) in the Gulf of Eilat, Red Sea. Eighteen species are hermaphroditic broadcasters,
two are hermaphroditic brooders and three are gonochoric broadcasters. In the Pocilloporidae, the gonads project into the
body cavity, while in the other six families the gonads reside inside the mesenteries. The number of gonads per polyp in broadcasting
species follows family or genus lines. Fecundity (eggs per polyp) increases with polyp size. Brooding species usually exhibit
one or two gonads per polyp and each gonad contains only one to three oocytes. Oocyte size varies widely and does not relate
to mode of reproduction. The largest oocytes (diameter = 450 μm) occur in the brooding coral Alveopora daedalea and in broadcasting species of the genus Acropora (diameter = 420 μm). Gonad morphology and gonochorism versus hermaphroditism appear to be constrained phylogenetically at
the family or genus level. Lastly, this report compares the data presented for Red Sea scleractinian species with the data
available on scleractinian corals from other geographical regions.
Received: 2 February 1993 / Accepted: 9 March 1998 相似文献
2.
Reproductive characteristics of cirromorph octopuses, assigned to the species Opisthoteuthis grimaldii, were sampled as a commercial fishing by-catch on the Hebrides Slope, west of Scotland. A total of 254 specimens (99 female,
155 males), retrieved from bottom trawls fished at 750 to 1500 m depth, were examined. A maximum of 2097 eggs was counted
in a single female ovary (mean female body weight 1242.8 g), most of them <1 mm in length. At egg lengths over 1 mm, diminishing
numbers of eggs were present in 1 mm size categories up to a maximum of ≈10 mm. At body sizes >500 g (wet wt), and in every
female >750 g (max. female weight recorded in the sample was 2959 g), a succession of unattached eggs was present in the proximal
oviduct and a single, unattached mature egg occupied the tip of the distal oviduct. These females were assumed to be in spawning
condition and the characteristics of egg distribution in the reproductive tract to be consistent with sequential release of
individual eggs and continuous spawning throughout the growth period and lifespan of the mature octopus. In pre-spawning females
there was a positive relationship between estimated egg numbers and maximum egg size. After the onset of spawning there was
no significant further increase in estimated potential fecundity over the body-size range 500 to 3000 g. Follicular sheaths
remaining in the ovary after release of eggs into the proximal oviduct were counted and used to estimate the total number
of eggs released up to the time of capture. Follicular sheaths first appeared at 500 to 650 g body weight and increased steeply
in number to >1000 in females >1500 g. Two individuals were found with ovarian follicular sheaths but with no terminal egg
in the distal oviduct; these were assumed to have released their egg just before capture. Summation of the number of follicular
sheaths counted plus the number of eggs estimated as remaining attached in the ovisac, provided a revised estimate of total
potential fecundity and raised the estimate for any individual to a maximum of 3202 eggs (mean = 1396 eggs).
Received: 3 February 2000 / Accepted: 17 May 2000 相似文献
3.
The reproductive strategies of two gammaridean amphipod species, Gammarus wilkitzkii and Apherusa glacialis, that permanently inhabit the Arctic sea ice were investigated. G. wilkitzkii reaches sexual maturity at an age of 2 years and produces 128 ± 54 eggs fem.−1 yr−1. Mating takes place during fall and winter, and the development of the large eggs (0.60 to 0.80 mm diam.) lasts 6 to 7 months.
The sex ratio of G. wilkitzkii was dominated by males in a proportion of 1.5:1. In vivo studies showed that juveniles are released in batches from the brood
pouches of the females during April and May. A. glacialis reaches sexual maturity at the age of 1 year and produces 555 ± 151 eggs fem.−1 yr−1. The eggs are between 0.18 and 0.23 mm in diameter, and are the smallest known for gammaridean amphipods. Eggs are kept in
packages of two to eight in the brood pouches of females. The sex ratio of A. glacialis was dominated by females in a proportion of 3:1. The high fecundity of both amphipod species, the release of juveniles in
batches over a period of time, a high proportion of females (A. glacialis), and an elongated life-span with multiple spawnings (G. wilkitzkii) are discussed as possible adaptations to the specific and highly variable conditions under Arctic sea ice.
Received: 29 December 1999 / Accepted: 8 March 2000 相似文献
4.
Using the number of segments of pleopod rami as a marker of instar number, the population structure (instar composition)
of the mesopelagic gammarid amphipod Cyphocaris challengeri was investigated by monthly samplings from May 1997 to April 1999 at a station off southwest Hokkaido, Japan. Laboratory-rearing
experiments were also conducted to establish the relationship between the number of segments of pleopod rami and instar number,
and to estimate the growth pattern of this gammarid based on the intermolt period and molt-increment data. Stratified sampling
in the field (0 to 200 and 200 to 400 m depth strata) showed this species occurred mainly at 200 to 400 m depth during the
day. Instar analysis indicated that C. challengeri has 12 instars in females and 11 instars in males. Based on observations of secondary sexual characters, Instars 1 to 6 were
designated juveniles (Instars 1 to 3 occurred in the marsupia of gravid females); in males, 7 to 9 were immature and 10 and
11 were mature, while in females 7 and 8 were immature and 9 to 12 were mature. Off southwest Hokkaido, Instar 4 (just released
from a female's marsupium) was found throughout the year, with a peak abundance occurring in April to July of each year. A
sequential development of Instar 4 to 9 (youngest adult instar) through the year was observed. Generation length (i.e. the
time required to grow from Instar 4 to 10) was estimated from a laboratory-obtained growth curve to be 216 to 584 d at the
in situ temperature range (2 to 5 °C), which is consistent with observations on field populations. Specimens older than Instar
9 were rare in the field and could not be used in laboratory-rearing experiments, so longevity could not be estimated. Eggs
were oval and measured 0.6 mm (large diameter). Brood size ranged from 20 to 65. Comparing the present results with those
of epipelagic hyperiid amphipods, the nearly identical growth rates together with the production of fewer but larger eggs
seen in C. challengeri appear to reflect to the typical life mode of deep-living pelagic crustaceans.
Received: 14 February 2000 / Accepted: 6 July 2000 相似文献
5.
Copepod resting eggs are abundant in the seabed of many bays and estuaries where they provide a potential source of recruits
for growth of planktonic populations. In the northeastern Gulf of Mexico the copepod Centropages hamatus (Lillejeborg) occurs in the water column only during the late fall, winter and early spring. The species produces subitaneous
and diapause eggs, and both egg types have been found in the seabed. We determined the longevity of these two egg types to
ascertain their potential for contributing to the growth of the planktonic population and for sustaining a persistent egg
bank. Eggs were collected from females and incubated in the laboratory under temperature and oxygen conditions chosen to simulate
field conditions. The diapause eggs were also exposed to sulfide. The total hatching success of subitaneous eggs in two experiments
declined from highs of 78 and 97% to zero after 60 and 90 d of exposure to anoxia. The total hatching success of diapause
eggs that were exposed to anoxia for 90 d however was typically greater than 80%. Some diapause eggs hatched after being incubated
under anoxia for 437 d. Diapause eggs survived longer at ambient field temperatures when incubated under anoxia (437 d) compared
to normoxia (118 d). Exposure to sulfide did not result in greater mortality of diapause eggs compared to anoxia alone. Diapause
eggs that were incubated at ambient field temperatures did not hatch when exposed to normoxia until the temperature dropped
to <20 °C. The results of this study suggest that C.␣hamatus sustain a short-term reserve of subitaneous eggs in the seabed that provides recruits for the current year's population.
The greater longevity of diapause eggs suggests that they sustain the seasonal reappearance of the species year after year
in the northeastern Gulf of Mexico. However, the contribution of diapause eggs of C. hamatus from the Gulf of Mexico to a persistent egg bank is questionable since hatching ceased after 437 d.
Received: 30 July 1997 / Accepted: 18 January 1998 相似文献
6.
In situ egg production of the egg-carrying calanoid copepod Pseudodiaptomus marinus was investigated in Fukuyama Harbor, a eutrophic inlet of the Inland Sea of Japan, at 3- to 5-d intervals for a year. This
species reproduced throughout the year, and the adults showed a large abundance peak in June/July and a small peak in September/October.
Females usually outnumbered males, comprising 61.4% of the annual mean. The composition of ovigerous females varied from 7.9
to 100%, with an annual mean of 55.7%. Adult prosome length was consistently large throughout winter and spring, and decreased
with increasing temperature in summer and fall. Egg diameter varied from 98 to 121 μm, and was negatively correlated to temperature.
The seasonal variation in clutch size (range: 15.1 to 38.2 eggs) was bicyclical, with peaks in May and December. The egg production
rate of breeding females was low in January to March (mean: 2.3 eggs female−1 d−1), while it was constantly high from mid-May to early October (mean: 12.1 eggs female−1 d−1). The specific egg production rate for the breeding females was highly correlated to temperature; it increased linearly from
0.03 d−1 at 9 °C to 0.27 d−1 at 26 °C. Compared to other co-occurring copepods, the reproductive rate of P. marinus was lowest, which is one of the reasons why this species never dominates in this inlet.
Received: 11 November 1996 / Accepted: 7 December 1996 相似文献
7.
The European fanworm Sabella spallanzanii (Gmelin, 1791) was recently introduced to Port Phillip Bay and is now a conspicuous component of most benthic communities.
Reproduction of the worm was investigated in a population at Queenscliff over a 2 yr period (October 1995 to October 1997)
using gonadal histology. The worms are dioecious (sex ratio 1:1, n=250), and attained sexual maturity at ∼50 mm body length. Reproductive periodicity followed a distinct annual cycle, and
spawning proceeded through an extended autumn/winter period. Spawning was broadly synchronous between sexes, and coincided
with falling seawater temperatures and shorter day-lengths. The females were highly fecund, and >50 000 eggs were probably
shed from large females (>300 mm body length) during the annual spawning period. Breeding cycles of S. spallanzanii in Port Phillip Bay are ∼6 mo out of phase with endemic populations located at similar latitudes in the northern hemisphere.
The spread of S. spallanzanii within Port Phillip Bay has been monitored by divers on an annual basis since 1994. The most recent dive survey (1998) indicates
that S. spallanzanii has extended its range through out the entire 2000 km2 embayment, and has invaded most subtidal habitats. Quantitative estimates of S. spallanzanii abundances were highest on pier pylons (12.5 individuals m−2, 0.5 to 7 m depths). On sediments, estimates were highest at shallow sites (0.3 m−2, 7 m depth), but numbers declined significantly with depth (0.1 m−2, 17 to 22 m depth). Mean worm lengths and biomass were, by contrast, significantly higher at intermediate depths (12 to 17 m)
than in shallower (7 m) or deeper (22 m) locations. S. spallanzanii demonstrates a clear preference for growth in sheltered, nutrient-enriched waters, so it may not spread from Port Phillip
Bay into the adjacent oceanic waters of Bass Strait; however, in view of S. spallanzanii's current high abundance, fecundity and extended spawning periodicity, there is a high risk of future range expansions, mediated
by shipping, into other temperate-water ports.
Received: 17 November 1998 / Accepted: 6 January 2000 相似文献
8.
The reproductive biology of the alfonsino Beryx splendens was studied by histological examinations, gonadosomatic index and macroscopic scales of maturation of a large sample of gonads.
Alfonsino is a gonochoric species. The size-frequency distribution of the sex ratio was bimodal and considered to be due to
size dimorphism. In New Caledonia, the breeding period of this species occurs during the southern summer, with a peak in December
to January. The spawning stage is attained at a minimum fork length of 28 cm for females and 33 cm for males. The size at
which 50% of the population attain sexual maturity (FL50) is 33.2 cm for females and 34.5 cm for males. Maximum potential fecundity is estimated to lie between 270 000 to 675 000
eggs for fish between 34 and 40 cm in fork length. It was possible to differentiate vegetative zones, in which juvenile alfonsino
grow until they reach maturity, from reproductive zones (fishing grounds) which are inhabited by mature individuals. The larvae
and juveniles could be carried from the reproductive zone to the vegetative zone by currents in an oceanic eddy system.
Received: 26 April 1996 / Accepted: 20 September 1996 相似文献
9.
Population dynamics and production of the egg-carrying calanoid copepod Pseudodiaptomus marinus were studied for a year in Fukuyama Harbor, a eutrophic inlet of the Inland Sea of Japan. This species was perennial, with
a large numerical peak in June and small peaks in September/October and November/December. During the study period, at least
11 generations could be detected. For each generation, the stage-specific survival from egg to Copepodite Stage (C) V was
determined; it was very high during early life stages (egg to NIII), and gradually decreased beyond. On average, 94% of eggs
recruited into NIII, which is strongly contrasted with very high (>ca. 90%) mortality during the corresponding stages for
free-spawning copepods, i.e. Acartia omorii, Centropages abdominalis and Paracalans sp. This demonstrates that the egg-carrying strategy has a great advantage to reduce mortality in egg stage. The biomass
of this species showed marked seasonal variations largely in parallel with numerical abundance. The instantaneous somatic
growth rate increased linearly with temperature. The population production rate was estimated as the sum of somatic growth
of larval stages and egg production of adult females; the annual integration was 51.0 mg C m−3 yr−1 or 0.38 g C m−2 yr−1.
Received: 11 November 1996 / Accepted: 7 December 1996 相似文献
10.
The aim of the present study was to use samples, collected by trawling throughout the year along the lower west coast of
Australia, to determine the reproductive biology, size and age compositions, and growth rate of Urolophus lobatus, a member of a speciose elasmobranch family (Urolophidae) for which there was previously only a small amount of such data.
U. lobatus copulates about 3 months prior to the time when females ovulate, which implies that sperm is stored in the oviducal gland
of the female in the intervening period. Gestation lasts for 10 months, which is relatively long for a species that does not
grow to a large size. This feature is reflected in the fact that the mean disc width at parturition (105 mm) is equivalent
to as much as 44% and 52% of the asymptotic disc widths of the females and males of this species, respectively. The trends
exhibited by the marginal increments on vertebral centra demonstrated that each of the translucent zones in these centra is
laid down annually and that their numbers can thus be used to age this species. Maturity was attained by about 70% of females
and 50% of males at the end of the 4th and 3rd years after conception, respectively, or at just over 3 and 2 years after birth,
respectively. Females and males typically first reach maturity at ˜200 and ∼160 mm, respectively, and attained maximal disc
widths of 277 and 237 mm, respectively. Females reached maximum ages of 15 years from conception and 14 years from birth,
with the corresponding values for males being 13 and 12 years, respectively. Since such a large amount of growth occurs during
gestation, von Bertalanffy growth curves were constructed using the date of conception, that is, the fertilisation date, as
age 0, as is usually the case with teleosts, as well as employing the birth date as age 0, as is typically the case with elasmobranchs.
The growth curves drawn through the points for the disc width-at-age of the older female and male fish gave a slightly better
fit when using, as age 0, the parturition date rather than the conception date. However, the asymptotic disc widths derived
for females and males using the conception date, that is, 241.3 and 202.9 mm, were each still only 7.6 mm less than those
derived using the birth date. Moreover, the fit of the line drawn through the points for the disc width-at-age of fish during
gestation was better using the conception date as age 0 than would be achieved by a backwards extrapolation of the growth
curve using the birth date as age 0.
Received: 6 January 2000 / Accepted: 17 June 2000 相似文献
11.
J. H. M. Kouwenberg H. I. Browman J. A. Runge J. J. Cullen R. F. Davis J.-F. St-Pierre 《Marine Biology》1999,134(2):285-293
The copepod Calanus finmarchicus Gunnerus is a key component of the planktonic food web in the Gulf of St. Lawrence, Canada. In this region, productivity-determining
biophysical interactions occur in the upper 0 to 30 m of the water column. The eggs and nauplii of C. finmarchicus are found in this layer. Measurements of the diffuse attenuation coefficients for solar ultraviolet-B radiation (280 to 320 nm,
UV-B) at various locations in this region indicated maximum 10% depths (the depth to which 10% of the surface energy penetrates)
of 3 to 4 m at a wavelength of 310 nm. This represents a significant percentage of the summer mixed-layer water column: organisms
residing in this layer are exposed to UV-B radiation. Laboratory experiments using a Xenon-arc-lamp based solar simulator
revealed that C. finmarchicus embryos exposed to UV-B exhibited high wavelength-dependent mortality. The strongest effects occurred under exposures to
wavelengths below 312 nm. A significant percentage of nauplii hatched from eggs exposed to these wavelengths exhibited malformations
indicative of errors in pattern formation during embryogenesis. At the shorter wavelengths (<305 nm), UV-B-induced mortality
was strongly dependent on cumulative exposure. The biological weighting function (BWF) derived for UV-B-induced mortality
in C. finmarchicus eggs is similar to that reported for naked DNA. This suggests that the UV-B-induced mortality effect on C. finmarchicus embryos is a direct result of DNA damage. There was no evidence of a detrimental effect of ultraviolet-A radiation (320 to
400 nm). Calculations based upon the BWF indicate that, under current noon surface irradiance, 50% of C. finmarchicus eggs located at or very near (within 10 cm) the ocean surface will be dead after 2.5 h of exposure. Under solar spectral
irradiance simulating a 20% decrease in ozone layer thickness, this time drops to 2.2 h. These are first-order estimates based
upon irradiance taken at a time of day during which the values would be maximal. Nonetheless, they illustrate the relative
changes in UV-B effects that will result from ozone layer depletions expected over the coming decades. It is also important
to point out that variability in cloud cover, water quality, and vertical distribution and displacement within the mixed layer,
can all have a greater effect on the flux of UV-B radiation to which C. finmarchicus eggs are exposed than will ozone layer depletion at these latitudes.
Received: 2 March 1998 / Accepted: 18 December 1998 相似文献
12.
Two species of seed-eating true bugs, Neacoryphus bicrucis (Heteroptera: Lygaeidae) and Margus obscurator (Heteroptera: Coreidae) co-occur on ragwort, Senecio tomentosus, in southern Georgia, USA. Males of both species sometimes engage in chases and protracted grappling with females that flee
initial mountings. Sometimes genital coupling occurs while the wriggling female is restrained in the male's grasp. Chases,
grappling, and mounting attempts are misdirected toward heterospecific females, heterospecific males, or conspecific males.
In a laboratory study, confinement of mated N. bicrucis females with either conspecific or heterospecific males reduced fecundity by approximately one-half relative to mated females
confined only with other females. Perhaps as a consequence of this, N. bicrucis females frequently leave areas of high host plant density, where they prefer to oviposit, when males are abundant. The abundance
of each species is positively correlated with host plant density but the two species rarely occur together on the same plants.
This may be an effect of heterospecific courtship which induces the flight of N. bicrucis more than the flight of M. obscurator. The laboratory results suggest that copulations following chases and grappling represent sexual harassment, not a mechanism
of active female choice for a vigorous mate. As sexual harassment imposes high fitness costs that favor abandonment of host
plants, it may, when misdirected, incidentally limit habitat use by ecologically similar species.
Received: 3 October 1998 / Received in revised form: 21 January 1999 / Accepted: 14 February 1999 相似文献
13.
B. A. Kerrigan 《Marine Biology》1997,127(3):395-402
The effects of food availability, female size, and social interactions on the quality of Pomacentrus amboinensis larvae at hatching were examined using two field-based experiments. In Experiment 1, food availability and female size significantly
influenced size, eye diameter and levels of yolk reserves of larvae at hatching. Small females (47 to 52 mm standard length,
SL) whose diets were not supplemented, produced the longest larvae (3.0 ± 0.01 mm total length, TL) with the least yolk reserves
(50.1 ± 1.04 μm2). Irrespective of female size, those that received additional food produced larvae with the largest yolk-sacs (large females:
87.60 ± 1.53 μm2; small females: 80.14 ± 1.24 μm2). In Experiment 2, interactions with conspecifics had a greater affect on the somatic development of larvae at hatching than
food availability. Increased social interactions resulted in larvae that were ⋍3% longer, with 2% greater head depth, than
larvae from females that spawned in isolation on the experimental reefs. Fed females produced larvae with ⋍20% more yolk than
larvae from females whose diets were not supplemented. All three factors (food availability, female size, and intensity of
social interactions) tested within these experiments vary spatially and temporally among reefs. There is the potential, therefore,
for larvae at the onset of the planktonic stage to vary in quality, level of development, and probability of survival.
Received: 12 August 1996 / Accepted: 26 August 1996 相似文献
14.
M. Thiel 《Marine Biology》1998,132(2):209-221
The suspension-feeding amphipod Dyopedos monacanthus (Metzger, 1875) is a common epibenthic amphipod that lives on self-constructed “mud whips” (built from filamentous algae,
detritus and sediment particles) in estuaries of the northern North Atlantic Ocean. The population biology of D. monacanthus at a shallow subtidal site in the Damariscotta River Estuary (Maine, USA) was examined between July 1995 and July 1997. The
resident population at the study site was dominated by adult females during most months of the year. High percentages of subadults
were found in late summer/early fall. Often, between 10 and 20% of the adult females were paired with males, and the percentage
of ovigerous females varied between 40 and 100%, indicating continuous reproduction. The percentage of parental females varied
between 40 and 80% during most months, but dropped to levels below 20% during summer/early fall. The average size of amphipods
on their own mud whips was ∼4 mm during the summer/early fall, after which it increased continuously to >7.0 mm in March or
April, and then dropped again. In March and April, the average number of eggs and juveniles female−1 was ∼100 eggs and 55 juveniles, while during the summer/early fall the average number of eggs female−1 was <20 and that of juveniles female−1 was <10. Many juveniles grew to large sizes (>1.4 mm) on their mothers' whips in winter/early spring but not in the summer/fall.
The average number of amphipods at the study site was low in late summer/early fall (<50 individuals m−2), increased steadily during the winter, and reached peak densities of >3000 individuals m−2 in April 1996 (>1600 individuals m−2 in May 1997), after which densities decreased again. The decrease of the D.␣monacanthus population at the study site coincided with a strong increase of amphipods found pelagic in the water column. This behavioural
shift occurred when temperatures increased and benthic predators became more abundant and active on shallow soft-bottoms,
suggesting that D. monacanthus at the study site is strongly affected by predation. The effects are direct (by predation on amphipods) and indirect (by
reducing duration of extended parental care and enhancing pelagic movements). Both extended parental care and pelagic movements
are important behavioural traits of D.␣monacanthus (and other marine amphipods), and significantly affect its population dynamics.
Received: 18 January 1998 / Accepted: 27 May 1998 相似文献
15.
A multi-factorial experiment on heart rate variations in the intertidal crab Pachygrapsus marmoratus
A multi-factorial experiment was designed to investigate the effect of the following factors on the cardiac activity of the
intertidal crab Pachygrapsus marmoratus: respiratory medium (air, water), temperature (four levels, 10, 17.5, 25, 32.5 °C), season (winter, summer) and body size
(two levels, carapace ≤21 mm and carapace >21 mm). The results showed that the heart rate of P. marmoratus increased linearly with temperature and decreased when the specimens were exposed to air rather than water. Moreover, the
heart rate values in summer were lower than those in winter at the corresponding temperature and body size. The summer heart
rate–temperature regression line was laterally (to the right) shifted with respect to the winter line, suggesting a seasonal
acclimation. Body size affected heart rate only at the acclimation temperature (17.5 °C), while no significant effect was
detected at lower or higher temperatures. During the reproductive season a separate experiment was carried out to assess the
effect of sex and reproductive status on heart rate. No significant difference was found among mean values of males, berried
females and females without eggs. The results of the present study confirm the high physiological plasticity of this species,
suggesting that P. marmoratus is a truly amphibious crab, able to deal with both water- and air-breathing during its activity.
Received: 5 January 1999 / Accepted: 7 July 1999 相似文献
16.
Bioluminescence spectra of shallow and deep-sea gelatinous zooplankton: ctenophores, medusae and siphonophores 总被引:3,自引:0,他引:3
We have examined the variability and potential adaptive significance of the wavelengths of light produced by gelatinous zooplankton.
Bioluminescence spectra were measured from 100 species of planktonic cnidarians and ctenophores collected between 1 and 3500 m
depth. Species averages of maximal wavelengths for all groups ranged from 440 to 506 nm. Ctenophores (41 species) had characteristically
longer wavelengths than medusae (34 species), and the wavelengths from siphonophores (25 species) had a bimodal distribution
across species. Four species each produced two different wavelengths of light, and in the siphonophore Abylopsistetragona these differences were associated with specific body regions. Light from deep-dwelling species had significantly shorter
wavelengths than light from shallow species in both ctenophores (p = 0.010) and medusae (p = 0.009). Although light production in these organisms was limited to the blue-green wavelengths, it appears that within
this range, colors are well-adapted to the particular environment which the species inhabit.
Received: 27 April 1998 / Accepted: 27 October 1998 相似文献
17.
P. J. Krug 《Marine Biology》1998,132(3):483-494
A San Diego population of the opisthobranch mollusc Alderia modesta (Lovén, 1844) exhibits poecilogony, the presence of two development modes within a single species. In spring, half of the
adults spawned masses containing ∼300 eggs with a mean diameter of 68 μm. After 3 d, these egg masses hatched planktotrophic
veligers with a maximum shell dimension of 116 μm. The remaining adults spawned masses containing ∼30 eggs with a mean diameter
of 105 μm. These egg masses hatched after 5 to 6 d, releasing lecithotrophic larvae with a maximum shell dimension of 186 μm.
About 1% of field-collected adults produced mixed clutches containing a continuum of larval sizes, spanning the size extremes
of planktotrophy and lecithotrophy and hatching larvae with a mean maximum shell dimension of 152 μm. Adults producing planktotrophic
and lecithotrophic larvae were interfertile, and no hybrid breakdown was observed through the F3 generation. When starved,
adults which previously produced only lecithotrophic larvae switched to producing planktotrophic larvae or mixed clutches
with both planktotrophic and lecithotrophic larvae. Sequence-polymorphisms from a portion of the mitochondrial cytochrome
c oxidase I gene support the conclusion that the two reproductive morphs represent a single species. Most of the lecithotrophic
larvae and a small percentage of the larvae from mixed clutches were metamorphically competent within 3 d of hatching. A. modesta is the only molluscan species as yet known to have both planktotrophic and pelagic lecithotrophic development within a single
natural population.
Received: 14 August 1997 / Accepted: 11 April 1998 相似文献
18.
J. H. M. Kouwenberg H. I. Browman J. J. Cullen R. F. Davis J.-F. St-Pierre J. A. Runge 《Marine Biology》1999,134(2):269-284
In the Gulf of St. Lawrence, Canada, productivity-determining biophysical interactions occur in the upper 0 to 30 m of the
water column. The eggs and larvae of several commercially important marine invertebrates and fishes (e.g. Gadus morhua L.) are found in this layer. Measurements of the diffuse attenuation coefficients for ultraviolet-B radiation (280 to 320 nm,
UV-B) at various locations in this geographic region indicated maximum 10% depths (the depth to which 10% of the surface energy
penetrates at a given wavelength) of 3 to 4 m at a wavelength of 310 nm. This represents a significant percentage of the summer
mixed-layer water column: organisms residing in this layer are exposed to UV-B radiation. Laboratory experiments using a Xenon-arc-lamp
based solar simulator revealed that cod embryos exposed to UV-B exhibited high wavelength-dependent mortality. The strongest
effects occurred under exposures to wavelengths below 312 nm. This susceptibility was also dependent upon developmental stage;
mortality was particularly high during gastrulation. At the shorter wavelengths (<305 nm) UV-B-induced mortality was strongly
dose-dependent, and not significantly influenced by dose-rate. The biological weighting function (BWF) derived for UV-B-induced
mortality in cod eggs is similar to that reported for naked DNA – suggesting that the mortality is a direct result of DNA
damage. There was no evidence of a detrimental effect of ultraviolet-A radiation (320 to 400 nm). Calculations based upon
the BWF indicate that, under current noon surface irradiance, 50% of cod eggs located at or very near (within 10 cm) the ocean
surface will be dead after 42 h of exposure. Under solar spectral irradiance simulating a 20% decrease in ozone layer thickness,
this time drops to 32 h. These are first-order estimates based upon surface irradiance taken at a time of day during which
the values would be maximal. Nonetheless, they illustrate the relative changes in UV-B impacts that will result from ozone
layer depletions expected over the coming decades. It is also important to point out that variability in cloud cover, water
quality, and vertical distribution and displacement of cod eggs and larvae within the mixed layer, can all have a greater
effect on the flux of UV-B radiation to which fish eggs are exposed than will ozone layer depletion at these latitudes.
Received: 2 March 1998 / Accepted: 18 December 1998 相似文献
19.
Kathleen E. Hunt Thomas P. Hahn John C. Wingfield 《Behavioral ecology and sociobiology》1999,45(5):360-369
In males of socially monogamous birds, plasma testosterone (T) typically declines to low levels during the parental phase.
Studies on multiple-brooded species indicate that high T may be incompatible with high-quality paternal care. The length of
the breeding season may affect the costs and benefits of high T and its effect on paternal care. We studied the effect of
experimentally elevated T on paternal care in a single-brooded species with a short breeding season, the Lapland longspur
(Calcarius lapponicus). We monitored T levels and parental behavior in 16 males with subcutaneous T implants, 14 males with empty implants, and
14 unimplanted males. We videotaped nests when nestlings were 2–3 days old and again at 4–5 days. T males with 2- to 3-day-old
young visited nests and fed young less often than control males, and the mates of the T males compensated with elevated visits
and feedings. However, when nestlings were 4–5 days old, T males visited their nests at normal rates – though feeding movements
remained below normal – and T females visited and fed at normal rates. Nestling mass and nest success were similar in both
groups. Overall, high T suppresses paternal care in Lapland longspur males. The partial improvement of paternal care when
nestlings are older, despite high T, may be related to the short 6-week breeding season of this arctic species, and the consequently
reduced benefits of sexual behavior late in the breeding season.
Received: 2 February 1998 / Accepted after revision: 2 November 1998 相似文献
20.
Several aspects of the biology of Bathypolypus sponsalis were studied from 297 individuals (115 males, 180 females and 2 indeterminates) caught in a depth range of 200–800 m depth
in the western Mediterranean Sea. The paper presents data on sizes (length-weight relationships, size-frequency distributions)
and reproduction (sex ratio, maturation, condition), and also analyses of the diet of B. sponsalis from samples taken throughout the year. Length-weight relationships showed that females are heavier than males at the same
mantle length. Although mature individuals were found all year round, the maximum number occurred in spring and summer. Sexual
maturation data revealed that males mature at smaller sizes than females. The gonadosomatic index increased with maturity
in both sexes; the increase was gradual in males, but abrupt in females. The digestive gland index was used as a condition
index and showed a differential behaviour with maturity; it increased gradually in females, but decreased in males. Like other
octopus species, B. sponsalis appears to be an opportunistic predator, feeding on a great variety of preys. Stomach content analysis yielded a total of
19 different prey items belonging to four major groups (Crustacea, Mollusca, Ophiuroidea and Osteichthya). The first three
groups were the more frequent preys, since crustaceans, molluscs and ophiuroids appeared in 76%, 49% and 30% of the stomachs,
respectively. Decapoda Reptantia (among crustaceans) and cephalopods and bivalves (among molluscs) constituted the more abundant
prey items. While the Decapoda Reptantia group was significantly more abundant in stomach contents of females, gastropods
were taken more frequently by males. These differences in diet could reveal females as a more active predators than males.
Received: 5 March 2000 / Accepted: 7 November 2000 相似文献