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1.
In the present study 670 individuals of Gonatus onyx (Cephalopoda: Teuthoidea) were observed in Monterey Bay, California from a remotely operated vehicle. The vertical distribution
of this species was bimodal, with peaks at 400 and 800 m depth during the day and 300 and 500 m during the night. The bimodal
distribution reflects a life stage shift between younger, schooling juveniles living in shallower water and older, solitary
adults which live deeper. Ontogenetic changes in behavior associated with this life stage shift are reflected in the physiology
of the organisms as well. Both aerobic and anaerobic metabolism, as estimated using mitochondrial and glycolytic enzymes,
decline with increasing body mass, suggesting reduced locomotory capacity in deeper-living adults. Oxygen consumption rates
were also determined in relation to oxygen partial pressure. Oxygen consumption regulation was similar between juvenile and
adult squids. The critical oxygen partial pressures (29 to 30 mmHg) correspond precisely to the oxygen concentrations found
at the depth of maximal abundance for day and night populations of juveniles and adults, respectively. Behavioral and physiological
changes with ontogeny of G. onyx are believed to result from reduced visual predator/prey interactions in the light-limited deep sea.
Received: 7 February 1999 / Accepted: 26 January 2000 相似文献
2.
In many species of birds and mammals with a co-operative breeding and rearing system, offspring survival is positively related
to the number of helpers. In the New World callitrichine primates (marmosets and tamarins), adult males are considered as
particularly valuable helpers, and female reproductive success may depend strongly on the males' contribution to infant care.
We analysed the number of offspring (infants, juveniles) in groups of wild pygmy marmosets, Cebuella pygmaea (Callitrichinae, Cebidae, Primates), in relation to the number of adult males and to the number of adult and subadult group
members. In contrast to other callitrichines with a co-operative system of infant care, no relationship was found between
the number of adult males and the number of infants and offspring. However, there was a significant positive relationship
between the number of juveniles and the number of adult and subadult group members. The lack of a relationship between infant
and adult-male number is interpreted as resulting from the reduced importance of adult males as helpers in pygmy marmosets
in comparison to other callitrichines, probably due to the reduced costs of infant care. The relationship between the number
of juveniles and the number of adult and subadult group members is in accordance with increased offspring survival in larger
groups, as observed in other primates.
Received: 1 February 1999 / Received in revised form: 5 June 1999 / Accepted: 29 June 1999 相似文献
3.
Otolith microstructure and microchemistry were examined in juveniles of Australasian shortfinned eel, Anguilla australis, from Australia and New Zealand. Patterns in otolith increment widths were similar in these two stocks. A marked increase
in otolith increment width was found from age 138 to 198 d (mean ± SD: 164 ± 18.6 d) from Australia, 161 to 208 d (185 ± 17.3 d)
from the western coast of New Zealand and 161 to 211 d (187 ± 18.9 d) from the eastern coast. These changes coincided with
a drastic decrease in otolith Sr:Ca ratios, suggesting that metamorphosis began at these ages in each species. The duration
of metamorphosis estimated from otolith microstructure was the same in the different stocks, 17 to 41 d (mean ± SD: 27 ± 5.4 d).
Ages at recruitment were 186 to 239 d (mean ± SD: 208 ± 17.4 d) from Australia, 214 to 263 d (232 ± 19.8 d) from the western
coast of New Zealand and 208 to 266 d (237 ± 20.0 d) from the eastern coast. There was a significant difference in the age
between the Australian stock and the two stocks from New Zealand. No significant difference was found in the age between the
latter two stocks. The difference in the period for the recruitment between Australian and New Zealand stocks seems to reflect
their geographical separation.
Received: 1 March 1999 / Accepted: 19 July 1999 相似文献
4.
Otolith microstructure and microchemistry were examined in juveniles of American (Anguilla rostrata) and European (A. anguilla) eels. Otolith increment width markedly increased from age 132 to 191 d (156 ± 18.9 d; mean ± SD) in A. rostrata and 163 to 235 d (198 ± 27.4 d; mean ± SD) in A. anguilla, both of which were coincident with drastic decreases in otolith Sr:Ca ratios, suggesting that metamorphosis from leptocephalus
to glass eel began at those ages in each species. The duration of metamorphosis was estimated to be 18 to 52 d from otolith
microstructure, for both species studied. Ages at recruitment were 171 to 252 d (206 ± 22.3 d; mean ± SD) in A. rostrata and 220 to 281 d (249 ± 22.6 d; mean ± SD) in A. anguilla. In these two species, positive linear relationships were found in ages between the beginning of metamorphosis and recruitment,
suggesting that early metamorphosing larvae recruited at younger ages. Duration of the leptocephalus stage to recruitment
in A. anguilla was about 40 d longer than that in A. rostrata. The geographical segregation between the two species in the Atlantic Ocean seems to be involved in the differences in the
duration of the leptocephalus stage (age at metamorphosis).
Received: 8 November 1999 / Accepted: 8 May 2000 相似文献
5.
Importance of food quantity to structural growth rate and neutral lipid reserves accumulated in Calanus finmarchicus 总被引:1,自引:0,他引:1
Growth and developmental rates were determined for copepodids of Calanus finmarchicus (Gunnerus) from experimental seawater mesocosms in a western Norwegian fjord. The instantaneous growth rates (g) from copepodid stage I (CI) to adult ranged from 0.08 to 0.10 d−1. Daily per capita mortality rate of the cohorts was as low as 0.012 d−1 (1.2% d−1). At local increasing temperatures (5.1 to 8.3 °C), development was equiproportional, and the cumulative median development
time from egg to CV was approximately 65 d. CV moulted to males and females, and egg production was initiated. Enhancement
of food resources by nutrient addition caused a 23.4% increase in growth rates from CI to adult. Additionally, copepodid stages
showed a generally larger body size, carbon and nitrogen content and total storage lipid content (wax esters + triacylglycerols)
in response to enhanced resources. Our data support an elsewhere proposed exponential-growth hypothesis; growth of the structural
compartments and store lipids (mostly wax esters) was exponential during the copepodid stages. However, a sigmoidal pattern
of growth best described growth of adult stages if reared at high resources, and depot lipid accumulation in late CVs and
adults at high resources. Body nitrogen growth increased exponentially, however, no significant changes in nitrogen specific
growth rates were found between individuals from low and high resources. CV and adults seem to have reached near-maximal weights
at high resources, whereas structural weight continued to increase at low resources. Despite the differences in structural
growth dynamics, cohort development was similar until the end of CV. During the onset of sexual differentiation, the male:female
ratio and the adult:CV ratio were highest at high food resources, suggesting that the time used for the final moult depends
on the feeding history of the copepods in relation to food quality and quantity. It appears that relatively small changes
in food availability strongly influence the biochemical composition of C. finmarchicus copepodids.
Received: 28 May 1999 / Accepted: 10 February 2000 相似文献
6.
Experiments were conducted to determine the effect of four algal diets (Corallina spp., Gelidium pristoides, Ulva rigida and an equal volume mixture of these seaweeds) on growth and reproduction of the South African gastropod Turbo sarmaticus Linnaeus, 1758. The best growth rate of juveniles (up to 13.8 mm shell length and 34.26 g wet body weight increase in 12
months), reproductive fitness of mature specimens (gonad index up to 33%) and energy reserves (up to 4.76 mg glycogen/100 mg
foot tissue) were achieved when T. sarmaticus was fed U. rigida or a mixed diet. In addition, the gonad index of individuals fed these diets was almost twice that of similar-sized field
specimens. Juveniles fed Corallina spp. only, grew very little (only 2.4 mm shell length and 4.23 g wet body weight increase in 12 months). The reproductive
fitness of adults fed on such a diet was also poor (gonad index <4.5%) and energy reserves were low (<3.5 mg glycogen/100 mg
foot tissue). Along the southeastern coast of South Africa, T. sarmaticus has a distinct reproductive cycle with gametogenesis occurring from March/April until August/September, whilst maturity (gonad
index = 15%) was maintained until December, after which spawning occurred until March.
Received: 6 July 1998 / Accepted: 8 March 1999 相似文献
7.
Life history and settlement preferences of the edible jellyfish Catostylus mosaicus (Scyphozoa: Rhizostomeae) 总被引:5,自引:0,他引:5
K. A. Pitt 《Marine Biology》2000,136(2):269-279
The life history and settlement preferences of larvae of Catostylus mosaicus (Scyphozoa: Rhizostomeae) (Quoy and Gaimard, 1824) were investigated in New South Wales, Australia, over a 2 mo period beginning
in November 1998. The life history consisted of an alternation between a sexual, medusoid stage and an asexual, polypoid stage,
and was similar to that described for other rhizostomes. Planula larvae were brooded by the adults. Approximately 4 d after
collection, larvae settled on a variety of substrata including wood, sandstone, shell, seagrass and glass, and metamorphosed
into four-tentacled polyps. The number of tentacles increased and polyps strobilated when they had between 12 and 20 tentacles.
Strobilation occurred within 15 d of settlement, but only polyps that settled on the concave surfaces of the shells strobilated.
Both monodisk and polydisk strobilation was observed. Ephyrae were raised for one month and were observed developing oral
arms. Polyps reproduced asexually via the formation of podocysts, by production of buds, and by partial fission.
Received: 30 April 1999 / Accepted: 27 August 1999 相似文献
8.
Y. Shrivastava G. G. Mahambre C. T. Achuthankutty B. Fernandes S. C. Goswami M. Madhupratap 《Marine Biology》1999,135(4):663-670
The cladoceran Diaphanosoma celebensis Stingelin is reported on for the first time from Indian waters (Mandovi estuary, Goa). Amictic females were maintained in
the laboratory (temperature 24 ± 1 °C and salinity 17 psu) for three successive generations in order to follow the parthenogenetic
reproductive behaviour, growth, survival and neonate production. The mean life span and body length of adult females in the
three generations showed some variations and ranged from 9 to 12.5 d and 842 to 932 μm, respectively. The mean length of the
neonates produced also varied (283 to 446 μm) in the three generations. Cladoceran preference for three phytoplankton food
sources, i.e. Isochrysis galbana (Parke), Chaetoceros calcitrans (Paulsen) and Tetraselmis gracilis (Kylin), was determined. Growth was faster in the initial stage with all three diets but slowed down in later life. Increased
food concentrations resulted in higher neonate production but reduced the life span of females. However, long-term feeding
experiments revealed that the percentage survival was high with I. galbana and low with C. calcitrans.
Received: 23 June 1999 / Accepted: 20 September 1999 相似文献
9.
Previous studies have shown that large numbers of ciliated and nonciliated epithelial cells (diam.: 6 to 15 μm) are released
by adult sea scallops, Placopecten magellanicus (Gmelin), during summer months in Newfoundland when water temperatures are at a maximum and gonads are well developed. Such
exfoliation of cells could be a response to stresses associated with elevated water temperatures and/or spawning activity.
In the present study an electronic particle counter/sizer was used to further investigate the factors that influence exfoliation
of epithelial cells by juvenile and adult scallops throughout the year. We observed release of epithelial cells from juveniles,
and from adults collected in months when gametogenic activity was minimal, indicating that exfoliation does not occur as a
result of reproductive activity alone. SEM analysis revealed little difference in surface characteristics of the gills, mantle
and gonad between scallops that had released cells and those that had not, suggesting that exfoliation of small numbers of
cells may be a consequence of cellular turnover and normal physiological function. Adult scallops were monitored in a second
experiment to determine the effects of raising water temperatures from 8.5 to 14.7 and to 21.0 °C on the frequency (proportion)
and rate of cellular exfoliation. Only at the highest experimental temperature (21.0 °C) were exfoliation rates significantly
higher than rates recorded at 8.5 or 14.7 °C. SEM analyses revealed some damage to gill, mantle and gonad tissues when scallops
were exposed to 14.7 and then to 21.0 °C for a total of 8 d.
Received: 21 August 1996 / Accepted: 13 September 1996 相似文献
10.
The biochemical composition of vegetative cells and resting spores of Chaetoceros pseudocurvisetus Mangin was compared in cultures under various nutrient and light conditions. The cellular content of major nucleotides such
as AMP, ADP, ATP and UTP decreased in the order: vegetative cells, nutrient-starved (vegetative) cells and resting spores,
indicating that the general metabolism of resting spores is relatively inactive. ADP-glucose was only abundant in nutrient-starved
vegetative cells, suggesting metabolic imbalance in these cells. The chl a–specific fluorescence yield of vegetative cells grown under all culture conditions was low, but very high in resting spores.
The ratios of the cellular contents of diadinoxanthin to chl a and of diatoxanthin to chl a were higher in resting spores and nutrient-starved vegetative cells than in nutrient-replete vegetative cells. The diadinoxanthin–diatoxanthin
xanthophyll cycle was active in resting spores; the xanthophyll cycle was synchronized with a 14 h light:10 h dark photoperiod.
Also, the ratios of cellular content of diadinoxanthin and diatoxanthin to cellular content of chl a in resting spores were relatively high in high irradiance, and decreased gradually in conditions of darkness over long culture
periods. Under conditions of strong light and high temperature, most resting spores survived more than 40 d while nutrient-starved
vegetative cells died within 33 d. These results suggest that resting spore formation is a strategy for enhancing protection
and lowering metabolic rate for survival. These physiological changes accompanying spore formation enable resting spores not
only to overwinter but also to “oversummer” in the coastal euphotic layer.
Received: 23 March 1999 / Accepted: 11 August 1999 相似文献
11.
Halogenated metabolites in two marine polychaetes and their planktotrophic and lecithotrophic larvae
This study investigated the occurrence and ontogenetic changes of halogenated secondary metabolites in planktotrophic and
lecithotrophic larvae and adults of two common, infaunal polychaetes, Streblospio benedicti (Spionidae) and Capitella sp. I (Capitellidae), with different life-history traits. S. benedicti contains at least 11 chlorinated and brominated hydrocarbons (alkyl halides) while Capitella sp. I contains 3 brominated aromatic compounds. These halogenated metabolites are potential defense compounds benefiting
both larvae and adults. We hypothesized that: (1) planktotrophic larvae contain halogenated metabolites because they are not
protected by adult defenses, (2) quantitative and qualitative variation of planktotrophic larval halogenated metabolites parallels
that of adults, and (3) brooded lecithotrophic larvae initiate the production of halogenated metabolites only after metamorphosis.
To address these hypotheses, volatile halogenated compounds from polychaete extracts were separated using capillary gas chromatography
and identified and quantified using mass spectrometry with selected ion monitoring. All four life stages (pre- and post-release
larvae, new recruits, adults) of both S. benedicti and Capitella sp. I contained the halogenated metabolites previously identified from adults. This is the first report of halocompounds
identified and quantified in polychaete larvae. Allocation of potential defense compounds to offspring varied as a function
of species, feeding type and developmental stage. Pre-release larvae of S. benedicti with planktotrophic development contained the lowest concentration of total halogenated metabolites (1.75 ± 0.65 ng mm−3), post-release and new recruits contained intermediate concentrations (8.29 ± 1.72 and 4.73 ± 2.63 ng mm−3, respectively), and planktotrophic adults contained significantly greater amounts (28.9 ± 9.7 ng mm−3). This pattern of increasing concentrations with increasing stage of development suggests synthesis of metabolites during
development. Lecithotrophic S. benedicti post-release larvae contained the greatest concentrations of halometabolites (71.1 ± 10.6 ng mm−3) of all S. benedicti life stages and developmental types examined, while the amount was significantly lower in new recruits (34.0 ± 15.4 ng mm−3). This pattern is consistent with a previously proposed hypothesis suggesting a strategy of reducing potential autotoxicity
during developmental transitions. Pre-release lecithotrophic larvae of Capitella sp. I contained the highest concentration of total halogenated metabolites (1150 ± 681 ng mm−3), whereas the adults contained significantly lower total amounts (126 ± 68 ng mm−3). All concentrations of these haloaromatics are above those known to deter predation in previously conducted laboratory and
field trials. As a means of conferring higher larval survivorship, lecithotrophic females of both species examined may be
expending more energy on chemical defenses than their planktotrophic counterparts by supplying their lecithotrophic embryos
with more of these compounds, their precursors, or with energy for their synthesis. This strategy appears common among marine
lecithotrophic larval forms.
Received: 14 July 1999 / Accepted: 20 January 2000 相似文献
12.
A. L. Moran 《Marine Biology》1997,128(1):107-114
An understanding of spawning and larval development can be fundamental to interpreting the abundance, distribution, and population
structure of marine invertebrate taxa. Tegula funebralis (A. Adams, 1855), the black turban snail, has been the focus of numerous ecological studies on the Pacific coast of North
America. To date, there are only conflicting and anecdotal reports of spawning, and there is no information on larval or juvenile
development for this conspicuous and abundant species. On 19 September 1995, two individuals of T. funebralis were observed free-spawning gametes into seawater in tanks at the Oregon Institute of Marine Biology. Embryos and larvae
were subsequently reared to metamorphosis and beyond. Development was pelagic and similar to development described for other
trochids, and larvae were observed not to feed at any stage. Larvae began to metamorphose at 5.7 to 6.7 d and settled at 260
μm shell length. Juveniles grew ≃ 10 μm in shell length per day and appeared to feed on detritus. Juveniles lacked some adult
diagnostic shell characters, including two columellar nodes and a closed umbilicus. In the field, small (<3 mm) juveniles
occurred in the adult habitat on all sampling dates between October and March. Small juveniles were found only under rocks
and were most abundant under rocks partially buried in coarse sand, suggesting that juveniles may utilize a specific microhabitat
within the adult T. funebralis habitat.
Received: 7 October 1996 / Accepted: 17 October 1996 相似文献
13.
Zooplankton responses to hypoxia: behavioral patterns and survival of three species of calanoid copepods 总被引:2,自引:0,他引:2
Seasonally recurrent and persistent hypoxic events in semi-enclosed coastal waters are characterized by bottom-water dissolved
oxygen (d.o.) concentrations of < 2.0 ml l−1. Shifts in the distribution patterns of zooplankters in association with these events have been documented, but the mechanisms
responsible for these shifts have not been investigated. This study assessed interspecific differences in responses to hypoxia
by several species of calanoid copepods common off Turkey Point, Florida, USA: Labidocera aestiva (Wheeler) (a summer/fall species), Acartia tonsa (Dana) (a ubiquitous year-round species), and Centropages hamatus (Lilljeborg) (a winter/spring species). Under conditions of moderate to severe hypoxia 24-h survival experiments were conducted
for adults and nauplii of these species from August 1994 to October 1995. Experiments on adults used a flow-through system
to maintain constant d.o. concentrations. Adults of A. tonsa showed no decline in survival with d.o. as low as 1.0 ml l−1, sharp declines in survival at d.o. = 0.9 to 0.6 ml l−1, and 100% mortality with d.o. = 0.5 ml l−1. Adults of L. aestiva and C. hamatus were more sensitive to oxygen depletion: both species experienced significant decreases in survival for d.o. = 1.0 ml l−1. Nauplii of L. aestiva and A. tonsa showed no significant mortality with d.o. = 1.1 to 1.5 ml␣l−1 and d.o. = 0.24 to 0.5 ml l−1, respectively. In addition, experiments investigating behavioral avoidance of moderate to severe hypoxia were carried out
for adults of all three species. None of the three species effectively avoided either severely hypoxic (d.o. < 0.5 ml l−1) or moderately hypoxic (d.o. ≈ 1.0 ml l−1) bottom layers in stratified columns. These results suggest that in␣nearshore areas where development of zones of d.o. < 1.0 ml
l−1 may be sudden, widespread, or unpredictable, patterns of reduced copepod abundance in bottom waters may be due primarily
to mortality rather than avoidance.
Received: 31 August 1996 / Accepted: 24 September 1996 相似文献
14.
Profiles of diarrhetic shellfish poisoning (DSP) toxins produced throughout the growth cycle and the cell cycle of the toxigenic
marine dinoflagellate Prorocentrum lima were studied in triplicate unialgal batch cultures. Cells were pre-conditioned at 18 ± 1 °C, under a photon flux density
(PFD) of 90 ± 5 μmol m−2 s−1 on a 14 h light:10 h dark photoperiod. In exponential growth phase, cultures were synchronized in darkness for 17 d. After
dark synchronization, cultures were transferred back to the original photoperiod regime. Cells were harvested for DSP toxin
analysis by LC-MS (liquid chromatography with mass spectrometry), and double-stranded (nuclear) DNA was quantified by flow
cytometry. The cell populations became asynchronous within approximately 3 d after transition from darkness to the 14 h light:10 h
dark photoperiod. This may be due to the prolonged division cycle (5 to 7 d) that is not tightly phased by the photoperiod.
Unlike other planktonic Prorocentrum spp., cytokinesis in P. lima occurred early in the dark and ceased by “midnight”. Cellular levels of the four principal DSP toxins, okadaic acid (OA),
OA C8-diol-ester (OA-D8), dinophysistoxin-1 (DTX1) and dinophysistoxin-4 (DTX4), ranged from 0.37 to 6.6, 0.02 to 1.5, 0.04
to 2.6, and 1.8 to 7.8 fmol cell−1, respectively. No toxin production was evident during the extended period of dark synchronization nor during the initial
period when NH4 was consumed as the major nitrogen source. Soon after the cells were returned to the 14 h light:10 h dark cycle and they
began to take up NO3, cellular levels of all four toxins gradually increased. This increase in DSP toxins usually occurred in the light, marked
by a rise in DTX4 levels that preceded an increase in the cellular concentration of OA and DTX1 (delayed by 3 to 6 h). Thus,
DTX4 synthesis is initiated in the G1 phase of the cell cycle and persists into S phase (“morning” of the photoperiod), whereas
OA and DTX1 production occurs later during S and G2 phases (“afternoon”). No toxin production was measured during cytokinesis,
which happened early in the dark. The evidence indicates that toxin synthesis is restricted to the light period and is coupled
to cell cycle events.
Received: 3 September 1998 / Accepted: 30 March 1999 相似文献
15.
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
16.
Adult talitrid amphipods often display a nocturnal activity pattern, which has been shown in a number of cases to be partly
controlled by an endogenous rhythm of circadian period. Juvenile talitrids have been little studied in the past, but evidence
from field studies indicates that they may display a different diel pattern of locomotor activity from that of adults. This
study presents evidence from the field in south–central Chile that juvenile Orchestoidea tuberculata Nicolet show crepuscular activity peaks, contrasting with the nocturnal peaks shown by adult conspecifics. Under constant
conditions in the laboratory, both juveniles and adults exhibit endogenous rhythms of circadian periodicity. However, the
phasing of activity differs in juveniles and adults, corresponding to the differences observed in the field. It is suggested
that differing phasing of peak locomotor activity may be a mechanism to reduce contact between juvenile and adult talitrids.
Experimental evidence indicates a significant negative influence on survival of juveniles in the presence of adult conspecifics
by intraspecific predation. Other factors influencing the timing of surface activity are also discussed.
Received: 3 August 1999 / Accepted: 26 May 2000 相似文献
17.
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
18.
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
19.
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
20.
The effects of two fixed photoperiodic regimes on the rate of somatic growth and segment proliferation in the semelparous
polychaete Nereis (Neanthes) virens Sars has been investigated. The two photoperiods (16 h light:8 h dark and 8 h light:16 h dark, hereafter LD 16:8 and LD 8:16)
were close to the extremes experienced naturally by N. (N.) virens in the course of a year. The experiments were carried out during the ambient winter and all worms (including four-setiger
larvae raised out of season) showed elevated feeding, growth and enhanced segment-proliferation rates when reared under LD
16:8, compared to worms reared under LD 8:16. The rate of replacement of lost segments after caudal ablation was also higher
under LD 16:8. The number of segments present when the segment proliferation rate had fallen to zero was higher in individuals
grown from birth under LD 16:8 compared to those grown under LD 8:16. Feeding activity showed a degree of spontaneous recovery
under LD 8:16 from January onwards, but remained lower than under LD 16:8. This difference continued into the following spring,
and was not attributable to differences in sexual maturity. We conclude that the rate of feeding in N. (N.) virens and other indicators of somatic growth rate such as rates of caudal regeneration and segment proliferation are directly influenced
by the photoperiod, but that the seasonal cycle of growth also includes a circa-annual component modifying the response to
static photoperiods according to the time of year.
Received: 20 October 1998 / Accepted: 4 February 1999 相似文献