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1.
Seasonal variations in biochemical constituents during the reproductive cycle of the female dog cockle Glycymeris glycymeris 总被引:1,自引:0,他引:1
In an attempt to describe the biochemical events associated with the main stages of the annual and reproductive cycles of
the female dog cockle Glycymeris glycymeris L., we studied seasonal variations in the various stages of oocyte development of the ovaries, and the glycogen, total protein
and total lipid content of five body tissues – adductor muscle, foot, tunic coat, visceral mass and mantle. From November
1991 to November 1994, microscopic examination of the ovaries and measurement of the tissue concentrations of glycogen, total
proteins and total lipids in these five body tissues were made monthly on ten female dog cockles originating from the sea
area around Douarnenez (south Brittany, France). Morphological studies revealed that in the population investigated the annual
cycle is characterised by three major periods: a first period of vitellogenesis extending from February/March to April/May
and preceding a spawning in spring; a second period of vitellogenesis extending from May/June to September/October and leading
to either no spawning, a single autumnal spawning event, or to two spawning events in summer and autumn; and a third period
extending from October/November to February/March and characterised by a high level of oocyte lysis. In the muscular body
tissues of the dog cockle, i.e. the adductor muscles, the foot and the tunic coat (the muscular envelope containing the visceral
mass), the concentrations of glycogen, total proteins and total lipids underwent very similar variations during the annual
cycle. During each stage of vitellogenesis, a typical glycogen–protein–lipid sequence was observed in the muscular tissues
that was characterised firstly by a peak of glycogen concentration 2 to 3 mo before spawning, followed by a peak in total
proteins 1 mo before spawning, and finally by a peak in lipid content just before spawning. A similar glycogen–protein–lipid
sequence was also recorded in the first half of the winter period. However, these events were followed by general atresia
affecting all oocytes in the gonad. Maximum energetic value of biochemical constituents in females coincided with peaks in
lipid content in the visceral mass and mantle. These biochemical events occurred principally immediately before and at the
end of oocyte lysis (December/January). A drop in the total energetic value, affecting mainly the visceral mass and the mantle,
was recorded each year during the period January to March, coinciding with the period of shell growth in this species. Our
data clearly indicate that in female G. glycymeris all muscular tissues contribute to the storage of glycogen and proteins, and suggest that glycogen may be the source of energy
triggering vitellogenesis. Biochemical and microscopic observations revealed that oocyte development takes place during the
first half of winter, but that these oocytes undergo atresia in December/January. The metabolites produced from oocyte lysis
could contribute to somatic growth, which occurs in late winter.
Received: 3 March 1997 / Accepted: 23 July 1997 相似文献
2.
The annual epidemic spawning period of a Scottish population of Arenicola marina (L.) has been recorded over a period of 13 yr. This population spawns between mid-October and mid-November in a discrete
spawning event over a period of 4 to 5 d. Endocrine manipulation experiments showed that spawning is induced in females only
if sufficient titres of PMH (prostomial maturation hormone) are present in the prostomia. These levels are attained during
the 2 to 3 wk prior to the natural spawning date. The East Sands, St. Andrews population always spawns during periods of spring
tides regardless of tidal amplitude or whether they are full- or new-moon tides. Meteorological data, including sea-temperature
data were collected for each year, and correlation of the environmental data with spawning time was attempted. Correlation
of spawning times with weather patterns showed that mean daily air pressures were significantly higher during the spawning
period than from September to November as a whole. Evidence also suggests that a reduction in sea temperature is required
prior to spawning. A significant moderate negative correlation was found between May to July air temperatures and spawning
date, suggesting that higher May to July temperatures may induce early spawning. Daily rainfall and wind speed were also lower
during the spawning period, but not significantly so. These results indicate that air pressure (or changes therein) may act
as a final spawning cue, and the advantages of this are discussed in relation to fertilization success. A model of the interplay
between environmental parameters and the endocrine mechanisms controlling the induction of spawning is proposed. Higher than
average summer temperatures may advance gametogenesis to bring the population into a state of maturity (full-size oocytes,
well-developed sperm morulae), and may also advance spawning time. Once the population has completed gametogenesis, a drop
in sea temperature is then required to trigger an increase in endocrine titres within the prostomium, without which spawning
cannot be induced by prostomial injection. The population spawns on spring tides; however a lack of clement weather coinciding
with the spring tide will result in population-wide spawning being aborted, as in 1996. Clement weather (high pressure, low
rainfall and wind speed) in conjunction with spring tides permits spawning to proceed to completion.
Received: 21 June 1999 / Accepted: 25 January 2000 相似文献
3.
We studied the processes of gonadal maturation, spawning, fertilization and embryonic development of the giant jellyfish Nemopilema nomurai, which has been blooming in recent years in the Sea of Japan. Healthy medusae actively swimming offshore had immature gonads,
but damaged and ashore-drifted animals had relatively mature gonads. The animals maintained in a small net on the nearshore
to mimic the drifted condition showed induced gonadal maturation by the increase in oocyte diameter and darkness in the matrix.
A similar maturation process also occurred in isolated pieces of ovary incubated at the same temperature. Fully grown oocytes
that probably stopped at the prophase of the first meiosis reinitiated maturation divisions in response to light exposure,
and massive spawnings occurred 80–100 min after the exposure. The spawned oocytes were first released within the subgenital
sinus, then transported peripherally and finally shed into the gastrovascular cavity. Maturation and spawning in male gonads
were similar to those of females except that the male spawning occurred within 30 min after the light exposure and always
preceded the female spawning. Hence, it was suggested that fertilization might take place in the female gastrovascular cavity
by the sperm that came in from surrounding seawater by animals’ pumping activities after dawn. Having mechanical damages might
promote fertilization success of this species in the Sea of Japan. 相似文献
4.
This study reports the first multi-year observations on the reproductive patterns for an Antarctic predator/scavenger, Odontaster validus (Koehler 1912). Seastars were collected monthly from a shallow site (15–20 m depth) near the British Antarctic Survey (BAS) Rothera Research
Station (Adelaide Island, 67°34′S 68°08′W) from July 1997 to January 2001. Reproductive condition, oocyte size frequencies
and spermatogenesis were examined in at least ten seastars each month using histological and image analysis techniques. Gonad
indices (GI) and pyloric caeca indices (PI) were also examined in the same samples. Female and male GIs varied seasonally,
in parallel with a reduction in the proportion of large oocytes and mature sperm in the gonad in August to mid-October following
winter spawning. Despite there being remarkable consistency in the timing of spawning from year to year, differences in the
reproductive condition of individuals were apparent. Patterns in the digestive tissues also varied with season, peaking in
December and reaching a minimum in February in two of the three study years. This weaker annual pattern may partly reflect
the varied diet of this predator/scavenger species, which is not directly dependant on the timing and magnitude of the annual
phytoplankton bloom. Pooled oocyte size distributions and residual analysis suggested that oogenesis progressed over 18–24 months,
with the largest of the two size classes (maximum diameter = 183 μm) being spawned annually. This pattern of oocyte growth
and spawning was previously reported in the early 1960s for an O. validus population from McMurdo Sound, which lies south of Rothera by 10° latitude. The extremely catholic diet of this predator/scavenger
suggests the reproductive patterns of the seastar will be less susceptible to changes in food supply compared to polar suspension
feeders or deposit feeders.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
5.
Reproduction in the sea pen Pennatula phosphorea Linnaeus 1758 was investigated in a population located in southern Loch Linnhe, west Scotland. This was accomplished through
analysis of trends in oocyte size-frequency distribution and fecundity over a 12-month period. Pennatula phosphorea is dioecious and the study population exhibited a sex ratio of 1:1. Oogenesis in female P. phosphorea is characterised by the maintenance of a large pool of small oocytes throughout the year of which a small proportion (<30%)
mature synchronously and are broadcast-spawned during the summer months of July and/or August. Although spawning occurs annually,
the duration of oogenesis exceeds 12 months. Initial oocyte generation is best described as ‘quasi-continuous’ as it may be
suppressed during winter. The timing and periodicity of oogenesis and spawning may be related to seasonal environmental cues
and it is proposed that annual spawning constitutes a brief and synchronous event. Fecundity is high in P. phosphorea, typically up to 50 oocytes per polyp and 40,000 oocytes per colony in medium to large colonies. Although mean polyp fecundity
increased with colony size (axial rod length) there was no seasonal fluctuation in this measure of relative fecundity. Since
only a small proportion of oocytes present are spawned each year, the present study advises caution when making inferences
regarding the seasonal output of viable oocytes, especially on occasions where the definition of fecundity or the details
of the oogenic cycle of a species are unclear. Pennatula phosphorea produces large oocytes (>500 μm), indicative of the production of lecithotrophic larvae; this may confer certain advantages
with respect to larval longevity and survival. 相似文献
6.
Georgios Tsounis Sergio Rossi Maria Aranguren Josep-Maria Gili Wolf Arntz 《Marine Biology》2006,148(3):513-527
Red coral (Corallium rubrum, L. 1758) is an over-exploited Mediterranean gorgonian. The gonadal development cycle of this gorgonian is examined at the
Costa Brava (NW Mediterranean) taking into account for the first time colony size, depth and spatial horizontal variability.
This study compares the gonad development and fertility in two colony size classes (colonies <6-cm height, and >10-cm height,
both at 40–45-m depth), and two populations at different depths (16–18-m depth, and 40–45-m depth, both consisting of <6-cm
high colonies) in a 15-month period. The fertility of seven size classes (<2 cm to >12 cm high colonies, in 2 cm intervals)
was examined in the deep population, where large colonies were present. Furthermore, reproductive output was compared in 6
populations (distributed along more than 70-km coastline) one month before spawning (June). Red coral was found to be dioecious
and gonochoric with a sex ratio of 1:1, which differs from other NW Mediterranean populations. On the other hand, fertility
of different size classes indicates that small colonies of 2-cm height already produce gonads, which is in line with previous
studies. Female and male polyp fertility and sperm sac size increase significantly with colony size [sperm sac diameter: 476±144 μm
(mean±SD) and 305±150 μm in the >10-cm and <6-cm height colonies, respectively), whereas no significant effect on oocyte diameter
was found (oocyte diameter: 373.7±18.7 μm). Depth staggered spawning, that is, an earlier release of gonads in the shallow
populations, was observed in summer 2003, coinciding with the highest temperature gradient between shallow and deep water
during the study period. Colonies of <6-cm height were significantly less fertile than colonies >12 cm, thus the recommendation
of this study is that a minimum height should be incorporated into fishing regulations. The six studied populations at the
Costa Brava showed a comparable reproductive potential, which demonstrates little variability within the homogenous population
structure and range of size classes (due to overharvesting) found at the Costa Brava. The study of reproductive output is
an important tool for ecosystem management, and this work recommends basing specific exploitation laws for distinctive populations
on colony size, which is found to have a larger effect on reproductive potential than mesoscale variability.
An erratum to this article can be found at 相似文献
7.
B. Niehoff 《Marine Biology》2003,143(4):759-768
Gonad maturation processes were studied in Pseudocalanus spp. females from Georges Bank and Cape Cod Bay (northwest Atlantic) using a combination of morphological analysis and experiments. For light microscopy of the oocytes, females of different maturation stages were preserved immediately after capture. The maturation processes during the spawning cycle were described from observations of live females which were exposed to feeding and starvation at two temperatures, 8 and 15°C, for 12 days. The gonad morphology of these females was examined in 24 h intervals, and spawning events were recorded. Both light microscopy and whole animal observation revealed that oocytes during maturation change in shape and size, in the morphology of the nucleus, and in the appearance of the ooplasm. Due to these modifications of oocyte morphology and due to oocyte migration, the morphology of the gonads changed distinctly during a spawning cycle. Five oocyte development stages were identified by light microscopy and related to a macroscopic system of four gonad development stages, that can be applied to whole animals and allows the identification of females ready to spawn. The experiment showed that food and temperature had strong effects on gonad maturation processes. High proportions of mature females were found when food was available, whereas the proportion of immature females increased shortly after exposure to starvation. Compared to 15°C, gonad maturation at 8°C was prolonged and thus spawning frequency was lower. The final maturation processes at food saturated conditions were slower than the embryonic development, and no indication was found that mature oocytes are stored in the diverticula waiting to be released. The duration of the interspawning interval would thus be determined by the duration of final oocyte maturation which is dependent on both temperature and food supply.Communicated by O. Kinne, Oldendorf/Luhe 相似文献
8.
Ryo Yamada Keita Kodama Takashi Yamakawa Toshihiro Horiguchi Ichiro Aoki 《Marine Biology》2007,151(3):961-971
We investigated the growth and reproductive biology of the penaeid shrimp Trachysalambria curvirostris in Tokyo Bay, Japan, by monthly bottom-trawl surveys from May 2002 to December 2004. We also examined oogenesis in T. curvirostris by histological observation of the ovary. Females grew faster and attained a larger body size for age than males. The growth
rate was high in summer and low in winter and was likely to be associated with seasonal changes in water temperature. The
carapace length (CL) at which 50% of females contained vitellogenic oocytes was estimated to be 17.0 mm. The reproductive
season extended from May to October. Young-of-the-year appeared in October and could be traced across the months on CL histograms
to the following September or October, indicating a 1-year life cycle. This extended reproductive season, together with our
observation of asynchronous development of oocytes in the ovary, suggests that multiple spawning by individual females may
occur during the reproductive season. Postovulated oocytes were not found among the samples we collected during the daytime,
suggesting that final oocyte maturation and spawning occur at night. Cortical crypts in the cytoplasm of the oocyte, considered
to be a general feature of oogenesis in penaeid shrimps, were not found in T. curvirostris, even in oocytes undergoing germinal vesicle breakdown. This result implies that the cortical reaction after spawning of
T. curvirostris may be different from that of other penaeid shrimps. 相似文献
9.
The northern Pacific asteroid Asterias amurensis (Lütken) has been recently introduced to Tasmania and is now well-established in east and southeast Tasmania. This sea star
is conspicuous throughout the Derwent River estuary and is particularly abundant in the Hobart port area. Reproduction of
two populations of A. amurensis at Sullivans Cove and at Sandy Bay was investigated from August 1993 to October 1994 by gonadal histology and measurement
of the gonad index (GI). An intense period of vitellogenic and spermatogenic growth started in April, with the breeding condition
reached by June. In 1994, peak GI was recorded at Sullivans Cove in July and at Sandy Bay in August. Although these data indicated
that the Sullivans Cove population spawned before the Sandy Bay population, histological examination revealed that major spawning
activity occurred in both populations from July onwards. In the early part of the breeding season, gametogenesis proceeded
in parallel with spawning, with released gametes being replaced by continual gametogenesis. Maintenance of a higher GI during
the early part of the breeding season at Sandy Bay was due to prolonged gametogenic replacement at this site. Spawning continued
to October 1994, resulting in a sharp decline in the GI. The cyclic expansion and regression of the genital haemal sinus coincident
with germinal proliferation and growth, respectively, support the contention that haemal fluid provides nutrients for gametogenesis.
In Tasmania, A. amurensis experiences temperature and photoperiod regimes similar to those experienced by endemic populations of this species in the
north Pacific. Comparison of reproduction of A. amurensis in Japan and Tasmania at similar latitudes shows that gametogenesis of the northern and southern populations is 6 mo out
of phase. This phase shift provides evidence for photoperiodic regulation of gametogenesis in A. amurensis. The similar trend in sea-temperature regimes associated with the stages of gametogenesis in northern and southern populations
suggests that temperature also plays a modulatory role. Based on the periodicity of reproduction and the ontogeny of A. amurensis, the planktotrophic larvae of this species would be expected to be in the plankton for several months from the end of winter
through summer. Considering the highly fecund, dispersive life-history of A. amurensis, the southeast Tasmanian populations have considerable potential to serve as a seed source for establishment of new populations
of this asteroid elsewhere in Tasmania and in mainland Australia.
Received: 18 October 1996 / Accepted: 22 October 1996 相似文献
10.
Confirmation of serial spawning in the chokka squid Loligo vulgaris reynaudii off the coast of South Africa 总被引:1,自引:0,他引:1
Ovary maturation and spawning in the chokka squid Loligo vulgaris reynaudii were investigated by collecting squid from across their distributional range on the southeastern coast of South Africa between
1992 and 1993. Based on histological examination of the ovarian tissue and the separation of multiple modes in oocyte size-frequency
distribution, ovary development was characterised by eight distinct stages. Our study confirms serial spawning in L. v. reynaudii.
Received: 9 October 1998 / Accepted: 22 April 1999 相似文献
11.
The reproductive cycle of the large brooding seastar Leptasterias polaris Müller and Troschel was examined over an 18-month period in the St. Lawrence Estuary, Québec, Canada. There is a distinct annual cycle with spawning over several months in the autumn. The female has an unusual cycle in that the ovary only slightly decreases in size during spawning, and the size structure of the oocyte population is remarkably stable throughout the year. The major annual change observed in the oocyte population is the development of a small number of 600-to 800- oocytes prior to spawning and their loss during spawning. This stability, combined with the lack of evidence of phagocytosis, suggests that oocyte development takes place over many years. By contrast, the developmental cycle of the testis is similar to that of most echinoderms. The large reservoir of oocytes probably guarantees a steady annual recruitment, and brooding during the winter probably minimizes metabolic costs for the female and ensures the release of the juveniles when conditions are favourable in the spring and summer. 相似文献
12.
The sabellid polychaete Sabellastarte spectabilis (Grube 1878) was collected at approximately monthly intervals from January 2002 to December 2003 from intertidal and subtidal
reefs near the Hawaii Institute of Marine Biology in Kane’ohe Bay, Hawaii, USA (21°N, 157°W). Gametogenesis and spawning periodicity
were investigated using histological techniques and induction of spawning trials. Worms were characterized into four discrete
reproductive stages based on histological evidence: (1) No evidence of reproductive activity in the coelom (sex cannot be
determined), (2) Only coelomocytes present in the coelom (sex cannot be determined), (3) Some gametes present in the coelom
(sex can be determined) and (4) Coelom densely packed with gametes (sex can be determined). The small hermaphroditic portion
of the population was not used in this study. Stage 4 worms were present over an extended period of time (females, March–December
and males, March–November) indicating a potentially broad reproductive season. No correlation between day length and maturation
stages in S. spectabilis was detected. However, the statistical model Y = ([394.26 × X] − [7.793 × X
2]) − 4960.781 where Y the % frequency of Stage 4 worms and X the mean monthly water temperature explained 44% of the variation between water temperature and % frequency of Stage 4 worms.
Maturation appeared to coincide with water temperatures of 24–25°C (March–September) after which there is a reduction in the
% frequency of stage 4 individuals. Induction of spawning trials conducted between May and January showed the month of October
with a significantly higher percent success than any other month investigated. According to all available information (e.g.,
natural spawning in water tables, histological data, induction of spawning trials, correlation of maturation stages with observed
changes in average monthly water temperature.), there is an apparent peak in reproductive activity (spawning) within a broad
maturational season, which may be influenced by water temperature. 相似文献
13.
The spawning patterns of two penaeid prawns, Metapenaeus endeavouri (Schmitt) and M. ensis (De Haan), were examined from data collected at 45 stations between March 1986 and March 1992. An index of population fecundity
based on the abundance, proportion and fecundity of sexually mature females was used as a measure of spawning output of the
prawn stock. The population fecundity index for M. ensis was higher than that for M. endeavouri. The monthly population fecundity index for M. endeavouri varied markedly among years, while that for M. ensis was consistent among years. Spawning of M. endeavouri occurred year-round, while that of M. ensis was concentrated mainly in spring (September to November). For M. endeavouri, a minor spawning, derived from a relatively small number of summer spawners, occurred in the 20 to 30 m offshore waters
in summer. In early summer (after May), the major spawning group consisted of large females from the winter-spawning cohort,
and the spawning area shifted to depths of 30 to 60 m. In winter (July), the major spawning, derived from the winter-spawning
cohort, occurred at depths of 20 to 40 m. For M. ensis, the major spawning, derived from the spring-spawning cohort, was observed in depths <50 m and was concentrated particularly
in inshore waters (<20 m) in spring. In autumn, the spawning output was mainly from the autumn-spawning cohort, which comprised
but a small number of individuals. In winter, the major spawning group again consisted of the large females from the spring-spawning
cohort, and spawning increased in the oceanic waters (>50 m). These results suggest that mature female M. endeavouri and M. ensis move offshore (>40 m) by May and July, respectively, and return to shallow waters (<35 m) in July and November, respectively.
The monthly reproduction patterns of both species in the “effective spawning” area showed that the major spawning season for
M. endeavouri is August to October and that for M. ensis is September to December.
Received: 19 February 1999 / Accepted: 18 June 2000 相似文献
14.
Reproductive biology in two species of deep-sea squids 总被引:2,自引:0,他引:2
Deep-sea squids, Moroteuthis ingens and Gonatus antarcticus, were collected in the slope waters off the Falkland Islands and their reproductive systems preserved and investigated onshore.
Changes in oocyte length-frequencies at maturation and spawning, and their fecundity were studied. These squids, as well as
many other species, are characterised by a synchronous oocyte growth and ovulation. Oviducts are not used for ripe egg accumulation
and consequently the universal scale of Lipinski (1979) cannot be applied to assign female maturity. M. ingens spawns near the bottom; its fecundity is 168–297 thousand eggs. Maximum egg size is 1.8–2.7 mm. G. antarcticus spawns midwater; its fecundity is 10–25 thousand eggs. Egg size is 3.2–3.3 mm. In M. ingens spawning takes place in the austral autumn and winter, in G. antarcticus—in austral winter. Our data and the literature data show that the so-called “synchronous ovulation” probably occurs in all
deepwater squids. This pattern is very rare among fish, but is quite common among benthic octopods that brood their egg masses. 相似文献
15.
Host sea anemones are ecologically important as they provide habitat for obligate symbiotic anemonefish in many areas of the
Indo-Pacific. Despite their importance, no information is available on their gametogenic cycles. This study aimed to address
this lack of knowledge by determining the gametogenic cycles of Entacmaea quadricolor. Gonad samples were taken from January 2003 to February 2005 at North Solitary Island, Solitary Islands Marine Park, Australia
using a specially developed non-lethal field biopsy sampling technique. Sampling was done 17 times during the study period,
with 15–20 individuals being sampled on each occasion. Samples were examined prior to fixation, and then histologically sectioned
to determine the reproductive activity of each individual. Female anemones were significantly more abundant than males, and
had asynchronous oocyte development both within and among individuals. Male anemones showed a single annual cycle of spermary
growth, development and spawning. Data from the 26-month study indicated that spawning occurred in the austral summer and
autumn between January and April, which coincided with the observed spawning periods that have previously been documented
for this species in outdoor flow-through seawater tanks at the study location. The biopsy sampling technique used during this
study provides an opportunity to gain a more thorough understanding of the gametogenic cycles and sexual pattern of host sea
anemones throughout their distribution. 相似文献
16.
Growth and reproduction were compared among six geographically and genetically distinct intertidal populations of the annual,
semelparous, dorid nudibranch Adalaria proxima (Alder & Hancock) to evaluate variation in fitness-related traits. The six populations spanned the geographic range in the
northern British Isles: NE England (Cowling Scar), E Scotland (Kinkell Braes), NW Scotland (Loch Eriboll), W Scotland (Cuan
Ferry), Northern Ireland (Portaferry), and N Wales (Menai Bridge). Nudibranchs from five sites were collected in July to August
1992 as post-metamorphic juveniles and were laboratory-reared under the same conditions of ambient temperature and photoperiod
for up to 10 months and the completion of spawning. Individuals from the sixth site were added to the experiment in December
1992. Growth was monitored every 2 weeks, and reproductive performance was expressed as a weight-adjusted dimensionless index
(ΣRI) of each individual's spawnings summed over the reproductive period. In general, larger nudibranchs produced larger first
spawn masses and more total spawn than did smaller nudibranchs, but these size-related trends were observed only in some populations.
The patterns of energy partitioning to spawnings varied significantly among populations, from allocations of a large number
of eggs to few spawn masses (Loch Eriboll) to production of many small spawnings over a long spawning period (Portaferry).
There was no relationship between maximum body size and the amount of spawn produced after the first spawning, nor to the
length of the spawning period or the number of spawn produced. Both Menai Bridge and Kinkell Braes had low mean population
ΣRI, reflecting a very poor reproductive performance, given their large maximum (pre-spawning) body sizes. By contrast, the Loch
Eriboll, Cuan Ferry, and Portaferry populations all displayed high mean population ΣRI, albeit as a result of differing combinations of numbers and sizes of spawn masses and duration of the spawning period. This
high variance of reproductive allocation among populations, and previous evidence of relatively stable among-population differences
in allozyme frequencies, adult color, and embryo characteristics suggest very restricted larval transport of lecithotrophic
larvae of A. proxima.
Received: 10 December 1998 / Accepted: 23 March 2000 相似文献
17.
Reproduction in the widely distributed tropical sea urchin Echinometra mathaei (de Blainville) was examined in three Kenyan reef lagoons that differed in substrate cover and E. mathaei population density. Histological examination of the gonads and gonad index measurements for 3 years showed a seasonal reproductive cycle with gametogenesis commencing in July, when temperature and light are at their lowest, and spawning commencing in December and peaking in February to May, when temperature and light reach their annual maxima. Monthly gonad indices correlated significantly with seawater temperature and light intensity. Male urchins had mature gametes for a longer period (8 months) than females (6 months), possibly an adaptive strategy that increases the probability of fertilization. Lunar periodicity was not observed, as male and female gonads were full of gametes on all days of the lunar cycle during the period of spawning. The peak in spawning activity coincides with the peak in phytoplankton abundance, which could ensure high food availability for the planktonic larvae. Gonad weights were significantly higher relative to urchin weight at the reef having the largest mean sizes and lowest population of urchins, indicating availability of food resources for growth and reproduction. E. mathaei at the reef with the highest density had the smallest urchins and high relative gonad sizes, indicative of a tradeoff between growth and reproduction when food is limited.Communicated by O. Kinne, Oldendorf/Luhe 相似文献
18.
CLAUS WEDEKIND GUILLAUME EVANNO TAMÁS SZÉKELY MANUEL POMPINI OLIVIER DARBELLAY JOACHIM GUTHRUF 《Conservation biology》2013,27(1):229-234
In some fishes, water chemistry or temperature affects sex determination or creates sex‐specific selection pressures. The resulting population sex ratios are hard to predict from laboratory studies if the environmental triggers interact with other factors, whereas in field studies, singular observations of unusual sex ratios may be particularly prone to selective reporting. Long‐term monitoring largely avoids these problems. We studied a population of grayling (Thymallus thymallus) in Lake Thun, Switzerland, that has been monitored since 1948. Samples of spawning fish have been caught about 3 times/week around spawning season, and water temperature at the spawning site has been continuously recorded since 1970. We used scale samples collected in different years to determine the average age of spawners (for life‐stage specific analyses) and to identify the cohort born in 2003 (an extraordinarily warm year). Recent tissue samples were genotyped on microsatellite markers to test for genetic bottlenecks in the past and to estimate the genetically effective population size (Ne). Operational sex ratios changed from approximately 65% males before 1993 to approximately 85% males from 1993 to 2011. Sex ratios correlated with the water temperatures the fish experienced in their first year of life. Sex ratios were best explained by the average temperature juvenile fish experienced during their first summer. Grayling abundance is declining, but we found no evidence of a strong genetic bottleneck that would explain the apparent lack of evolutionary response to the unequal sex ratio. Results of other studies show no evidence of endocrine disruptors in the study area. Our findings suggest temperature affects population sex ratio and thereby contributes to population decline. Persistencia de Proporción de Sexos Desigual en una Población de Tímalos (Salmonidae) y el Posible Papel del Incremento de la Temperatura 相似文献
19.
A population of Tapes rhomboides (Pennant) in the Bay of St. Malo, France, was studied for one and a half years (July 1984–October 1985) to determine spawning frequency and fecundity under natural conditions, using the techniques of qualitative histological staging, condition index calculation and quantitative stereology. Spawning took place twice a year, in late May and in July/September. There was an extended winter resting period. Gonad development and oocyte production were positively correlated with female body size. The annual fecundity in a 40 mm clam was about 5x105. Stereological techniques provided accurate information on oocyte dynamics within a gonad and the relationship with atretic processes. Each oocyte generation from the onset of the cycle to the winter resting stage was spawned eventually if conditions were suitable, or the oocytes were resorbed. Atresia of oocytes was seen throughout the reproductive period, but especially after the spring spawning and at the end of the summer. 相似文献
20.
In many vertebrates, environmental factors influence gamete differentiation and growth of the mature gonad through alteration
of sex steroid production or action; however, it is unclear how gamete differentiation and gonadal growth are regulated in
echinoids. The purpose of this study was to examine the influence of dietary administration of estradiol (E2), progesterone
(P4), testosterone (T) and finasteride (F, a 5α-reductase inhibitor) on the ovaries and testes of mature Lytechinus variegatus (Lamarck) during gonadal growth. Echinoids were fed a formulated diet supplemented with steroids or steroids in combination
with finasteride for 36 d. The effects of dietary administration of steroids on L. variegatus were both steroid- and sex-specific. The mean ovary index was 54% greater in individuals fed E2 than from individuals fed
the control (C) diet (10.0 ± 1.1 vs 6.5 ± 0.7, respectively; P < 0.05). Individuals fed E2, P4, E2/P4, and P4 in combination with F had significantly smaller oocytes (P < 0.005) than individuals fed C. The volume fraction occupied by nutritive phagocytes in ovarian tubules from individuals
fed E2/P4 or P4 were significantly larger than the volume fraction occupied by nutritive phagocytes from individuals fed C,
indicating that E2 and 5α-reduced progestins may promote nutrient allocation to nutritive phagocytes. Although oocytes from
the individuals fed T alone were significantly smaller than those fed T in combination with F, oocytes from individuals in
both treatments were significantly larger compared to oocytes from individuals fed C. These data suggest that upon removal
of 5α-reduced androgens, T is able to promote an increase in oocyte diameters. In contrast, the mean testis index was 56%
greater in individuals fed P4 than in individuals fed C (8.9 ± 0.6 vs 5.7 ± 0.9, respectively; P < 0.05); the testis index did not increase in individuals fed P4/F, suggesting that 5α-reduced progestins stimulate testicular
growth. Testes growth in the presence of 5α-reduced progestins was accomplished by significant increases in the volume fraction
occupied by nutritive phagocytes and by a significant reduction in the volume fraction occupied by spermatogenic columns in
testicular tubules. These data further indicate that 5α-reduced progestins (or 5α-reduced androgens) may inhibit spermatogenic
column formation. In conclusion, E2 stimulated ovarian growth but inhibited oocyte growth, whereas T had no affect on ovarian
growth but promoted oocyte growth in L. variegatus. We hypothesize that the E2 (or E2 metabolites) and/or 5α-reduced androgens in combination with T regulate oocyte growth
in the echinoid L. variegatus. In addition, 5α-reduced progestins promoted nutrient accumulation in nutritive phagocytes within the ovaries and the testes.
Furthermore, 5α-reduced progestins stimulated growth of the testes and inhibited spermatogenic column formation, suggesting
that 5α-reduced progestins regulate nutrient accumulation into nutritive phagocytes and spermatogenic column formation in
L. variegatus. The differences in estrogen effects between echinoids and asteroids may be related to differences in gonad morphology and,
ultimately, the differences in cellular signalling pathways (paracrine vs endocrine).
Received: 22 May 1999 / Accepted: 24 May 2000 相似文献