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Gonadal Cycle, Gametogenesis and Energy Allocation in Two Sympatric Mid Shelf Sea Stars with Contrasting Modes of Reproduction
Abstract
The goniasterid sea stars Anthenoides piercei and Tosia parva were collected 19 times over a 30-month period from a rhodolith substrate (90 m depth) in the northern Gulf of Mexico. Size frequency distributions of both sea stars indicated little evidence of annual recruitment. Cumulative population size distributions were unimodal and skewed towards larger body sizes, with a mean size of 57.3 g wet weight (R = 8.5 cm) in A. piercei and 6.1 g wet weight (R= 2.1 cm) in T. parva. Both species exhibited annual gonadal growth cycles. Anthenoides piercei produces small eggs (130 μm diameter) which are spawned during the fall and early winter and presumably develop into planktotrophic larvae. Tosia parva produces much larger lecithotrophic eggs (600 μm diameter) which are spawned during the summer months. It is unknown whether these lecithotrophic embryos are brooded as in the congener T. australis. An inverse relationship between the gonadal and pyloric cecal indices was apparent in both species during 1989. However, organ index reciprocity was less evident during the subsequent 16 months. The energetic composition of the mature ovaries of A. piercei (26.7 kJ˙g-1 dry weight) was lower than that of T. parva (31.1 kJ˙g-1 dry weight). This was attributable to higher lipid levels in the ovaries of T. parva than in A. piercei (54.7 vs. 25.9% dry weight). Nonetheless, the relative allocation of energy to the mature ovaries was similar in both species.
... The PCI values of the C. grenadensis females caught at 2000 -2200 m depth were four times higher than values recorded at 900 -1050 m. This high PCI recorded from individuals in the lower slope suggests that these females may be storing nutrients in the pyloric caeca in order to maintain a constant production of gametes in a food-limited environment (Benítez-Villalobos & Díaz-Martínez, 2010), allowing a constant transfer of energy from the pyloric caeca to the gonads (McClintock et al., 1995). In males, the gonad index (GI) values were significantly higher in summer and autumn, while lower (but nonsignificant) pyloric caeca index values were reported in summer, coinciding with other studies (McClintock et al., 1995). ...
... This high PCI recorded from individuals in the lower slope suggests that these females may be storing nutrients in the pyloric caeca in order to maintain a constant production of gametes in a food-limited environment (Benítez-Villalobos & Díaz-Martínez, 2010), allowing a constant transfer of energy from the pyloric caeca to the gonads (McClintock et al., 1995). In males, the gonad index (GI) values were significantly higher in summer and autumn, while lower (but nonsignificant) pyloric caeca index values were reported in summer, coinciding with other studies (McClintock et al., 1995). In females, the GI values were similar at all seasons. ...
... Thus, C. grenadensis follows a similar reproductive pattern to that described for many deep-sea echinoderms (e.g. Mcclintock et al., 1995;Ramirez-Llodra et al., 2002;Galley et al., 2008), which has been related to the low food availability at great depths (Mcclintock et al., 1995). The deep Mediterranean seafloor is particularly food-limited because of the overlying relatively oligotrophic waters Tyler, 2003;Zúñiga et al., 2009). ...
Ceramaster grenadensis
is one of the most abundant bathyal seastars in the north-western Mediterranean Sea and also presents a wide geographic distribution in the Atlantic Ocean. As with other species in this genus, little information is available on the biology and reproductive strategy of
C. grenadensis
. In this context, we describe for the first time the reproductive cycle of this species from bathyal depths in the north-western Mediterranean Sea. Specimens (N = 141) were collected seasonally from 194 benthic trawls (141 Otter Trawls and 53 Agassiz trawls) conducted during 10 cruises from October 2008 to April 2013. Open slope and canyon systems were sampled at depths between 900 and 2250 m. The population distribution of
C. grenadensis
showed a depth-related structure, with the smaller adult specimens and juveniles present at greater depths. Sex ratio was 2:1 females per male, constant among seasons and depths. Histological analyses of the gonads showed an asynchronous ovarian organization, with previtellogenic and vitellogenic oocytes throughout the year. These oogenesis patterns suggest a continuous reproduction. However, the Pyloric Caeca Index (PCI) decreased in summer while the Gonad Index (GI) increased in autumn in males, suggesting a higher spawning capacity in autumn. In both sexes, an increasing GI and PCI trend was observed with increasing depth.
... Among the Asteroidea, body compartments can be divided into three functional categories: the body wall, which is traditionally considered to serve a structural or protective function, the pyloric caeca, which are nutrient storage organs, and the gonads, the reproductive organs (Hyman 1955;Giese 1966). Both food availability and the biochemical and nutritional composition of the diet may have consequences in patterns of energy allocation to these body components (McClintock et al. 1990(McClintock et al. , 1995. For example, in high-latitude marine ecosystems, pronounced seasonal fluctuations occur in food availability (Clarke 1987;Almandoz et al. 2011) and in many cases individuals accumulate exceptionally large amounts of energy-rich lipids during spring (Pérez et al. 2008) and summer (McClintock and Pearse 1987) to be utilized during the winter. ...
Reproduction is a highly expensive process that during gonadal development requires an important supply of nutrients. The allocation of energy can vary throughout the reproductive cycle, between sexes and development modes. During research cruise aboard the RV Puerto Deseado in April 2016, we collected fifteen species of sea stars from the southernmost region of Argentina. The main purposes of the present study were threefold: first, to revise and report novel information on the reproductive strategies and energetic density (ED) of body components from the asteroids of the southwestern Atlantic Ocean including Burdwood Bank/ MPA Namuncurá; second, to compare the ED of these body components across species with contrasting reproductive strategies; third, to provide a tool to estimate the ED from dry mass of organs of the sea star species examined. Ovaries of Diplopteraster verrucosus (a brooder with a nidamental chamber) revealed a significantly greater ED than did the testes (29.81 ± 1.38 and 17.76 ± 1.59, respectively). In Glabraster antarctica (a broadcaster with yolky eggs and facultative planktotrophic larvae), the gonads had EDs of 25.78 ± 3.16 and 19.21 ± 0.52 (females and males, respectively). While in Peribolaster folliculatus (a broadcaster with eggs with low yolk content and inferred planktotrophic larvae) there was no significant difference in the ED values between sexes (females: 22.79 ± 1.10 and males: 20.46 ± 1.05). For the pyloric caeca, ED values did not reveal any difference between sexes, although in P. folliculatus, the ED was significantly higher than that for D. verrucosus and G. antarctica (25.90 ± 1.00, 23.03 ± 0.34, and 22.66 ± 0.65, respectively). The body wall had higher ED values in D. verrucosus and P. folliculatus than that for all the sea star species analyzed (46.48 ± 1.63, 51.17 ± 1.34, respectively). Higher ED values in the ovaries could be related to the nutrition of offspring, while differences found in the body wall may reflect the skeletal structure of this body component. This research provides basic information for understanding the differences on energetic allocation when contrasting development modes are considered.
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... The pyloric caeca of sea stars are dynamic storage-transfer organs that constantly process, accumulate and transfer nutrients to other organs (Lawrence, 1987;McClintock et al., 1995). Changes in weight of the pyloric caeca reflect complex processes of nutrient uptake, enzyme secretion and deposit of substances (Franz, 1986). ...
The sea star
Anasterias minuta
broods the embryos in the oral region; embryos then block the mouth and prevent the parent from taking up nutrients during the brooding period. Here, we analysed content of carbohydrates in different organs as well as in eggs, embryos and juveniles of
A. minuta
. We found that these biochemical components are used mainly by the pyloric caeca and the body wall as reserve substances to endure the periods of reduced consumption rates of non-brooding females and males and the long-term starvation of brooding females. The ability to translocate carbohydrates from females to embryos and juveniles observed in other species of sea stars was not confirmed.
... The pyloric caeca have both a digestive and a storage function. In many sea stars, the pyloric caeca show an inverse cycle to that of the gonads (Giese 1966, Crump 1971, Jangoux & Vloebergh 1973, Barker 1979, Barker & Nichols 1983, McClintock et al. 1995. We did not observe this pattern. ...
We assessed sex differences in reproductive investment of the brooding sea star Leptasterias polaris (in the northern Gulf of St. Lawrence, eastern Canada) by examining the biochemical composition and energetic content of the principal body components in 3 contrasting periods: just before spawning, after spawning and after brooding. The reproductive effort for a standard sea star with an underwater mass of 10 g (equivalent to 8.2 cm in radius) was similar for both sexes (15.1 kJ in males and 12.2 kJ in females). However, the sexes differed in how energy was allocated for reproduction. The energy loss due to gamete release was almost 4-fold greater for males (15.1 kJ) than females (4.1 M). The major reproductive expenditure in females came from maintenance costs during the prolonged brooding period (8.1 kJ). For the body wall and stomach, lipid, protein and energy contents were similar for males and females over the spawning and brooding periods. The ratio of males to females in the population was 1:1 in smaller size classes but was about 2:1 for individuals measuring > 11 cm in radius. This is possibly explained by slower somatic growth of females due to the repeated use of energetic reserves and lack of feeding during the 5 to 6 mo brooding period. The replenishment of body wall carbohydrates in males during the winter (not observed in females) suggests that males feed during this period.
... Although much research effort has been focussed on the asterinids, reproductively divergent sister species have also been reported from the Poraniidae (Bosch 1989) and the Echinasteridae (Atwood 1973). The Goniasteridae, by contrast, has been the subject of few published studies, both in terms of reproductive mode and in terms of phylogeny (Birkeland et al. 1971;Lane and Hu 1994;McClintock et al. 1995;Mah 2005Mah , 2007. The majority of described goniasterids are found at shelf depth (>100 m), posing numerous practical challenges to the study of their reproduction and larval development. ...
The biscuit star Tosia australis Gray, 1840 is a well known component of the shallow rocky reef fauna of south-eastern Australia. The putative T. australis species complex was subjected to reproductive, morphometric and molecular analyses. Molecular analyses of the data from three markers (mitochondrial COI and 16S rRNA and the nuclear non-coding region ITS2) confirmed the presence of a cryptic species, the morphology of which does not agree with any of the existing nominal species. Two separate reproductive modes were observed within the complex and documented via scanning electron microscopy. T. neossia, sp. nov., described herein from south-eastern Australia, is shown to release gametes from gonopores on the actinal surface. Embryos develop first into non-feeding, non-swimming brachiolaria, and then into tripod brachiolaria before metamorphosis. No surface cilia are present at any point throughout development of T. neossia. T. australis sensu stricto is shown to release gametes from the abactinal surface. Embryos develop into non-feeding, swimming brachiolaria before metamorphosis. Whereas T. australis var. astrologorum is confirmed as synonymous with T. australis, the status of the putative Western Australian taxon T. nobilis remains unresolved.
... The biology of the tropical Atlantic Tosia parva is also poorly understood. Gonadal cycle, gametogenesis and energy allocation was described by McClintock et al. (1995). Tosia pan'a was among several echinoderm taxa that demonstrated significant chemical defences against different predators, but especially against different species offish (Bryan et al. 1997). ...
Morphology-based phylogenetic hypotheses developed for living and fossil goniasterid asteroids have provided several unique opportunities to study bathymetric and biogeographic shifts for an ecologically important group of prominent, megafaunal invertebrates. A cladistic analysis of 18 ingroup taxa employing 65 morphological characters resulted in a single most parsimonious tree. The tree supports assignment of the Atlantic Tosia parva (Perrier, 1881) and the Pacific Tosia queenslandensis Livingstone, 1932 to new, separate genera. The phylogenetic tree supports offshore to onshore bathymetric shifts between basal and derived taxa. The phylogeny is also consistent with historical events surrounding the separation of Antarctica from Australia and South Africa. Buterminaster Blake & Zinsmeister, 1988 from the Eocene La Meseta Formation, Antarctic Peninsula, was included in the phylogenetic analysis and is now supported as the only fossil species in the genus Pentagonaster Gray, 1840. Pentagonaster stibarus H. L. Clark, 1914 is separated from synonymy with P. dubeni Gray, 1847 and resurrected as a valid species. The new genus, Akelbaster, gen. nov., shows unusual new structures that resemble cribiform organs, although their function has not been determined. One specific ingroup lineage, including Tosia and Pentagonaster, attains a much larger adult size than those of its sister-taxa, suggesting that Cope’s rule may apply to asteroids within this clade. Pentagonaster and related genera are revised. Descriptions of four new genera and three new species are presented, including: Akelbaster novaecaledoniae, gen. nov., sp. nov., Ryukuaster onnae, gen. nov., sp. nov., Eknomiaster beccae, sp. nov., Pawsonaster parvus, gen. nov., comb. nov. and Anchitosia queenslandensis, gen. nov., comb. nov.
The chapter focuses on the possibility that an externally fertilizing organism's sexual selection is intense but approximately symmetrical across sexes. The result of sperm limitation leads to increased variation in the proportion of a female's eggs that are fertilized. Hence, the increased variation in female reproductive success relative to taxa with internal fertilization results in a selection for enhanced fertilization success for both males and females. As a consequence, sexual dimorphism in both primary and secondary sexual characteristics is reduced or absent. This hypothesis leads to the notion that anisogamy and copulation evolved because of sperm limitation rather than sperm competition. However, an adaptation, in this scenario, benefits both males and females. Males benefit because the average success of males increases, and males who are the best at copulation gain greatly. Females also benefit greatly because fertilization ceases to be a limiting factor, and choice becomes an option. The sperm-limitation hypothesis implies not that sperm competition is absent among broadcast spawners but that it has reduced importance and may be balanced by egg competition.
To assess sex differences in reproductive effort, we examined the biochemical composition and energetic content of the principal body components of the broadcast spawning sea star Asterias vulgaris in the Mingan Islands in the northern Gulf of St. Lawrence, eastern Canada. The body wall was the most stable body component, showing no variations in mass or in lipid and protein content (and total energetic content) between sexes or during spawning. Patterns in the gonads differed between sexes and with spawning. The lipid, protein and carbohydrate content of the ovary dropped during spawning, while only the protein content of the testis decreased significantly. Reproductive effort, expressed as loss of energy in the gonads during spawning for an individual weighing 10 g in underwater mass (8.2 cm in radius), was six times greater in females (49.5 kJ) than males (7.9 kJ). The energetic content of the pyloric caeca also decreased during spawning, by 17.7 kJ in females and 21.5 kJ in males, mainly due to a decrease in lipids. If this decrease is included as reproductive effort, it lessens the gender difference. The caecum decrease possibly represented expenditures due to formation of aggregations or the expulsion of gametes during spawning. Effectively, we observed aggregations during a massive spawning in this population. The sex ratio did not differ from 1:1 in all size classes sampled. This suggests that, unless males suffer higher mortality, females manage to allocate as much energy to somatic growth as males, possibly by feeding at higher rates to compensate for their higher reproductive effort. Stomach protein content tended to be higher in females than males and may indicate greater muscular development to facilitate digestion.
Production of the different body compartments during an annual reproductive cycle was measured in a population of Luidia senegalensis. In 1993, the maximal gonad indexes occurred in the fall (4.6 in males, 4.3 in females) preceding spawning. The pyloric caeca index peaked in the summer (July) at 7.7 and declined through early fall (September) as the gonad index increased. The following spring both caecal and gonadal indexes increased together and the pyloric caeca index reached a maximum value of 8.9 in June 1994. The higher caecal and gonadal indexes in 1994 suggests that environmental conditions, probably a greater food abundance, were more favorable than in 1993. The proximate composition of body compartments showed some similarities to that of the closely related five-armed starfish, Luidia clathrata. In both species concentrations of soluble protein and lipid were higher than carbohydrate when the pyloric caeca were largest. At the peak of the gonad index, the concentration of lipid and soluble protein in the gonads was higher in L. clathrata than in L. senegalensis. The annual increase in production in relation to body size was lower in L. senegalensis (8-fold increase in the pyloric caeca index, 4-fold in the gonad index) than in L. clathrata (10-fold increase in the pyloric caeca index, 13-fold in the gonad index).
Individuals and populations of Odontaster validus Koehler differed markedly among different habitats, as revealed in a study from October 1984 through January 1986 in McMurdo Sound, Antarctica. At McMurdo Station, individual sizes (wet weight) and population biomass (g wet wt m-2 and kJ m-2) decreased significantly with increasing depth. Individuals from shallow (10 to 20 m) habitats were in superior nutritional condition to those from deeper water (30 and 165 m), as shown by higher gonad and pyloric cecum indexes, and by higher lipid and energetic levels in the pyloric ceca. Moreover, gonadal output (reproductive output) was higher in shallow-water individuals. Higher levels of chlorophyll in the pyloric ceca and richer yellow to red coloration of the body wall in the shallow-water individuals indicate that they utilize the higher levels of primary production at shallow depths. At East Cape Armitage, where nearly permanent, thick, snow-covered ice most of the year resulted in very low levels of benthic primary production, the lowdensity sea stars were all very small and nutritionally similar to the deep-water individuals at McMurdo Station. At Cape Evans, where the generally snow-free sea-ice that broke up in mid-summer resulted in a luxurient benthic cover of diatoms and macroalgae, the sea stars were smaller than at McMurdo Station at comparable depths, but population densities were higher, resulting in 4 to 9 times greater biomass. Growth rates of sea stars fed in the laboratory were very low, especially compared to laboratory-reared temperate and tropical species; well-fed individuals need about 9 yr to reach 30 g wet weight, near the mean size of shallowwater individuals at McMurdo Station. No growth was detected in individuals caged at McMurdo Station for one year, suggesting even lower growth rates in the field. The stable size-frequency distributions at the different sites and depths throughout the year-long study suggest highly stable populations with low temporal variability in recruitment, migration and mortality. These data indicate that individuals and populations of O. validus quantitatively and qualitatively reflect the general level of productivity of a habitat. Differences noted in size, coloration, nutrition, and reproductive effort may be the result of long-term integration of local levels of primary production. These ubiquitous sea stars may serve as a biotic indicator of productivity in localized habitats around the continental shelf of Antarctica.
A method is presented for estimating rates of individual growth and population mortality utilizing average individual size at two times during a year. The model assumes a constant rate of mortality, Brody-Bertalanffy growth, a stationary age distribution, and recruitment confined to one month each year. A hypothetical example is presented to show the interrelationships of the growth and mortality constants, size at recruitment, asymptotic size and average individual size. Three examples are presented using data from the literature: Flathead sole (Hippoglossoides elassodon), a sea urchin(Echinus esculentus), and the crown-of-thorns starfish(Acanthaster planci). The method appears to be a means of obtaining reasonable approximations of growth and mortality rates for a variety of organisms.
A photoperiod regime 6 mo out of phase between December 1978 and August 1980 resulted in gametogenesis, gonadal growth, and spawning in laboratory-maintained sea stars [Pisaster ochraceus (Brandt)] 6 mo out of phase with individuals in the field or laboratory on normal celestial photoperiods at Santa Cruz, California (USA). The seasonal fluctuation of pyloric cecum size also was shifted when the sea stars were held on the out-of-phase photoperiod regime. Phase shift of all these events was evident within 6 to 9 mo. Long daylengths (or short nightlengths) in spring and summer apparently synchronize or entrain the initiaion of gametogenesis and gonadal growth in fall.
The determination of the age of individual sea stars (Asterias rubens) by means of length measurements or identification of growth rings in the calcareous skeleton presents great difficulties. Age-determinations are, however, the prior condition to growth calculations. For the determination of growth parameters L00, K and t0 of the VON BERTALANFFY growth equation by means of the modal class progression analysis monthly dredging samples were taken in 12 profiles across the mouth of the Eckernförde Bay. Sea stars, which were exposed to lower temperatures during the first months after onset of growth, reach a larger asymptotic length than those exposed to higher temperatures. - By means of parallel diving observations to the dredging the mean biomass of Asterias in Kiel Bay was estimated to be about 32000 tons. Assuming a daily food uptake of 1 % of its own weight the sea star stock consumes about 120000 tons of food organisms per year. These data are discussed in context with biomass values of macrobenthos and cod in Kiel Bay. - The most striking finding, however, is the assumption of an intermediate phase, the "waiting stage", between the larval phase, serving propagation, and the growing stage, serving reproduction, in which tiny sea stars can remain for months waiting for a "free seat" in the ecological niche
Samples of three species of benthopectinid starfish were collected in a time-series from stations in the northern Rockall Trough. A detailed study was made of the reproductive biology of Benthopecten simplex (Perrier) from a fixed station at 2200 m. Studies of the gametogenic cycles of Pectinaster fllholi Perrier and Pontaster tenuispinus Düben & Koren from less regular and more scattered samplings are also presented.The oogenic cycles of the three species are similar. Growing oocytes line the ovary wall and come to lie in the lumen only when well developed. Accessory cells surrounding young oocytes become more numerous as the oocytes develop. Vitellogenesis begins when oocyte diameter reaches ≈ 250–300 μm and oocytes attain a maximum diameter of 950 μm in Benthopecten simplex, 850 μm in Pectinaster filholi, and 800 μm in Pontaster tenuispinus. Unspent oocytes are broken down by phagocytes and degenerate ovaries become filled with the breakdown products. Internal degeneration of large oocytes is not common.Size frequency data show a dominance of previtellogenic oocytes and a pattern of continuous growth of vitellogenic oocytes. There is no evidence of synchrony of growth between individuals and no suggestion of seasonal reproduction is evident from summated sample data.Spermatogenesis follows the pattern previously established for deep-sea asteroids. A mature male remains in a state of constant ripeness, ready to shed sperm at any chance encounter with a female releasing ripe eggs. There is no evidence of brooding in any of the species and from the large size and yolk content of the egg, we can infer direct lecithotrophic development demersally.
Annual reproductive and storage cycles of the asteroid Oreaster reticulatus (L.) were followed by organ index methods in populations from St. Croix in the U.S. Virgin Islands, and Carriacou and Union Island in the Grenadines. The periodicity of these cycles and their inverse relationship were similar among populations, but phase and amplitude varied. Gonad growth was activated in the spring (February to March) and progressed until spawning occurred in late summer or fall (July to October). The pyloric caeca increased in size during the quiescent phase of the gonad cycle (November to January), then decreased with increasing reproductive development to a minimum coincident with the spawning period. Reproductive development and spawning were more synchronous in the St. Croix populations than in those of the Grenadines. The inverse relationship between the storage and reproductive cycles indicated that gonadal development was subsidized by nutrient reserves previously accumulated in the pyloric caeca. Marked differences in storage and reproductive capacity among populations in the same geographic locality are attributed to differences in the quality and/or quantity of available food resources.
1.1. The biochemical and energetic compositions of the somatic body components of seven species of asteroids, one ophiuroid, and four echinoids from the northern Gulf of Mexico (30–95 m depth) were ascertained.2.2. Levels of ash were high (68.5–90.8% dry wt) in all body-wall tissues, with the exception of the asteroid Echinaster modestus (51.6% dry wt). Levels of ash were low in the pyloric cecae (nutrient storage organ) of asteroids (4.6–30.8% dry wt).3.3. Levels of lipid (8.1–34.5% dry wt), soluble protein (15.9–28.7% dry wt), and insoluble protein (18.1–48.6%, dry wt) were high in the pyloric cecae of all asteroids, but generally low in ophiuroid and echinoid body-wall tissues. High protein levels (28.5–44.5% dry wt) in the body-wall of the asteroids Echinaster modestus and Anthenoides pierceisuggest it may play a role in nutrient storage.4.4. All somatic tissues contained low levels of carbohydrate (0.2–1.4% dry wt).5.5. Levels of energy in pyloric cecal tissues (12.99–26.05 kJ/g dry wt) were 4–8 times higher than in echinoderm body-wall tissues (2.92–11.91 kJ/g dry wt).6.6. The biochemical and energetic compositions of echinoderms from the northern Gulf of Mexico are similar to those of species from other latitudes and depths.
In the field, Luidia clathrata are exposed to seasonal variations in temperature and salinity ranging from 12–31°C and 13–28‰ S. In the laboratory, righting ability and feeding rates decreased in individuals exposed to low temperature (17°C) for 30 days and showed little or no acclimation. Righting ability, feeding, total wet weight and pyloric caecal weight decreased in individuals exposed to low salinity (16‰). The latter two responses resulted from decreased food intake and an apparent increase in the metabolic cost of cell volume regulation. Although L. clathrata can acclimate partially to this low salinity, their condition deteriorated with chronic exposure. Changes in the levels and interactions of temperature, salinity and food had a greater influence on the responses of L. clathrata than changes in only one factor. Combinations of high or low temperatures and low salinity had a negative effect on righting, feeding and growth. The significant effects of combinations of environmental factors on organismal and physiological responses in the laboratory indicate their importance when interpreting the responses of individuals in the field.
Examination of the reproductive biology of three closely related sympatric astropectinid asteroidshas revealed two distinct reproductive strategies. In Plutonaster bifrons and Dytaster insignis the gonads are serially arranged and open at gonopores located at the tip of genital papillae found on the dorsal arm surface between the bases of the paxillae. The ovaries of these species produce numerous small (ca. 120/«n diameter) eggs which in Plutonaster bifrons appear to show a distinct synchrony of production. Initiation of gametogenesis occurs in June to August of each year with oocyte growthcontinuing until March with a spawn-out in the period March to early June. In specimens where spawningdoesnot occur, there would appear to be internal oocyte degeneration, or after spawning relict oocytesundergo phagocytosis. In males initiation of spermatogenesis may occur in August/September of eachyear but after this synchrony of sperm development is not evident. In Psilaster andromeda gonads are located at the base of the arms and each gonad opens at a single gonopore. A number of small (<300 /«n) oocytes are produced by each gonad. Some of these are phagocytosed and some undergo vitellogenesis and grow to a maximum size of 950 fim before being spawned. Unspent oocytes undergo internal degeneration. In neither females nor males is there any evidence of reproductive synchrony. From these egg sizes, fecundities and gametogenic strategies, we infer indirect planktotrophic development for Plutonaster bifrons, the transfer of a seasonal surface production to deep water providing a food source for developing larvae. The egg size and or close to the sea-bed, as there is no evidence of brooding in this species.
Sixty-seven specimens of the common North Atlantic asteroid, Asterias vulgaris, were collected at seasonal intervals over a 2-year period and their testes observed with both light and electron microscopy. In the germinal epithelium, a predictable series of interactions between versatile somatic cells and germinal cells is repeated annually in relation to sequential events in spermatogenesis. For example, massive proliferation and differentiation of spermatogenic cells depend on the elaboration of thousands of spermatogenic columns, which are distinct cellular subdivisions of the germinal epithelium. Each fully developed column is composed of at least one somatic cell surrounded by ≈ 400 germinal cells. Such columns form only after intensive spermatogonial mitosis begins in the germinal epithelium. Single annual periods of spermatogenic proliferation and differentiation are initiated from 1 to 3 months out of phase in different individuals and overlap incompletely. Therefore, it is possible to observe testes that are entirely in the proliferative phase, entirely in the differentiative phase, or in both phases simultaneously. Detailed ultrastructural observations and preliminary autoradiographic data demonstrate that columns maintain their height for a variable period of time as germinal cells are generated near their bases, pass along their lengths, and differentiate near their tips; therefore, simultaneous proliferation and differentiation of more than one generation of germinal cells occur in the same column. Finally, formation of primary spermatocytes ceases basally, (terminating proliferation), and remaining columns degrade completely as germinal cells composing them differentiate or are phagocytized (terminating differentiation and spermatogenesis); resulting spermatozoa ultimately accumulate in the expandable lumen. It is proposed that spermatogenic columns provide the structural basis for organization of the microenvironment of small groups of spermatogenic cells (≈ 400 at a time) during proliferation and differentiation. Preliminary evidence from A. vulgaris and other species also suggests that somatic cells are temporally pluripotent and are variously involved in the formation, structure, and activities of columns, in extensive phagocytosis, and probably in contributing intrinsic (e.g., 1-methyl adenine and steroids) and mediating extrinsic (e.g., gamete shedding substance and nutrients) microenvironmental factors influential during spermatogenesis in asteroids. The prodigious spermatogenic capabilities of asteroids apparently depend on the generation of spermatogenic columns, on the progressive interaction of germinal and somatic cells before, during, and after columns form, and on the predictable effects of microenvironmental factors received and interpreted at the structural level of the spermatogenic column.
Thirteen species of antarctic asteroids were collected in McMurdo Sound during the austral spring and summer of 1984–1985 and 1985–1986. Variability in the energetic composition of the body wall, pyloric cecum, and gonad was directly related to differences in levels of protein, carbohydrate, lipid and ash in these tissue types. Reproductive output was generally similar between males and females when expressed in gravimetric units. When considered in energy units, females generally had greater reproductive output than males. Reproductive output values of antarctic asteroids were similar to published values for temperate, tropical, and subpolar species. In a given year, the majority of antarctic asteroids have the greatest energy resources in the body wall, a tissue representing a long-term energy investment. Lesser amounts of energy are devoted to annual nutrient storage (pyloric ceca) and reproduction (gonads).
A method of estimating the length of the exponential growth phase is developed by solving a difference equation derived from the regression of growth increments on the initial sizes. This method facilitates quick assessments of the juvenile lifespan of animals, e.g. the coral-reef asteroid Culcita novaeguineae, which grow exponentially with very low growth rates. The juvenile life span of C. novaeguineae was estimated to be about 2 years from metamorphosis to transformation into the pin-cushion form.
This paper considers the adaptive significance of two different reproductive methods in two co-occurring, competing sea stars. The smaller (3 to 8 g mean wet weight) Leptasterias hexactis broods relatively few, large young in the winter, while the large (300 to 650 g mean wet weight) Pisaster ochraceus broadcasts relatively many, small eggs each spring. L. hexactis matures at a small size (2 g wet weight) in about 2 years, and P. ochraceus matures at a larger size (70 to 90 g wet weight) in about 5 years (Menge, 1974). As in many broadcasting asteroids, gonad and storage organ indices of P. ochraceus are inversely related over time, and maximum storage-organ index correlates with the summer feeding maximum (Mauzey, 1966). In contrast, both organ indices of L. hexactis and feeding increase and are positively correlated until early autumn, when feeding activity begins to decline. At this time the male gonad index continues to rise, and the storage-organ index drops. In contrast, both organ indices of females rise. Spawning occurs from November to January. Thereafter storage-organ indices decline in females, presumably because females draw upon energy reserves while brooding; storage-organ indices rise in males, presumably because males do not brood and can feed if food is available. The primary cause for the differences between annual reproductive cycles of P. ochraceus and L. hexactis is suggested to be patterns of food availability for the released young (planktonic food for the broadcasted young of P. ochraceus and benthic prey for the brooded young of L. hexactis. Estimates of pre-maturity survival and post-maturity longevity indicate that the probability of survival per individual of young P. ochraceus is vastly lower than that of L. hexactis. However, once mature, P. ochraceus has a much longer expected lifespan. Brooding is suggested to be a coadaptive consequence of competition-induced small size. Assuming planktonic mortality rates in this environment are roughly constant across broadcasting species, I suggest that a small broadcasting species could not produce enough offspring in its expected lifespan to replace itself. This hypothesis is partly supported by some simple simulations. Broadcasting is suggested to permit rapid location and utilization of spatially and temporally unpredictable, but highly desirable, resources by allowing rapid and widespread dispersal. Brooders presumably cannot disperse rapidly and must rely on more reliable, but perhaps less desirable, resources. Factors affecting reproductive patterns in marine invertebrates include (1) food availability for both adults and offspring, (2) planktonic mortality rates, (3) interactions between species and latitudinal changes in these factors, and (4) various physical factors. This paper suggests that competition and predation can have an important effect on the evolution of reproductive methods, a possibility heretofore largely ignored. Although several similar examples of co-occurring species' pairs which differ in reproductive method and size are available, the role of adult interactions is unknown in these examples.
1.1. Egg diameters (mm) of the spatangoid echinoids Abatus shackletoni, Abatus nimrodi and the asteroids Notasterias armata, Diplasterias brucei, and Perknaster fuscus antarcticus were 1.28, 1.97, 3.54, 2.80 and 1.20, respectively. A. shackletoni, A. nimrodi, N. armata and D. brucei, brood their embryos to a juvenile stage; P. fuscus antarcticus apparently is a broadcast spawner with pelagic lecithotrophic larvae.2.2. Eggs were composed primarily of protein (33–53%) and lipid (36–59%). Juveniles had higher levels of insoluble protein and ash due to the formation of structural and skeletal material.3.3. There was little decrease in the amount of energy from egg to juvenile during development. This supports the hypothesis that large egg size in marine invertebrates with lecithotrophic development is more important in producing a large juvenile than in the provision of a large amount of energy for development.4.4. Comparisons of reproductive output and reproduotive effort in echinoderms with lecithotrophic development reveal a high degree of interspecific variability.5.5. This variability is related to the differential allocation of energy to somatic and gametic tissues based on differences in functional morphologies.6.6. Variable reproductive efforts in species with lecithotrophic development confound comparisons with species with planktotrophic development and make tests of energetic hypotheses for alternate life-history stategies in marine invertebrates difficult.
It is suggested that local animal species diversity is related to the number of predators in the system and their efficiency in preventing single species from monopolizing some important, limiting, requisite. In the marine rocky intertidal this requisite usually is space. Where predators capable of preventing monopolies are missing, or are experimentally removed, the systems become less diverse. On a local scale, no relationship between latitude (10⚬ to 49⚬ N.) and diversity was found. On a geographic scale, an increased stability of annual production may lead to an increased capacity for systems to support higher-level carnivores. Hence tropical, or other, ecosystems are more diverse, and are characterized by disproportionately more carnivores.
The energetic echinoderm. Pages 47-68 in
- J M Lawrence
Lawrence, J. M. 1985. The energetic echinoderm. Pages 47-68 in B. F. Keegan and B. D. S. O'Conner,
eds. Echinodermata. A. A. Balkema Press, Rotterdam. 651 p.
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Reproduction of Antarctic benthic marine invertebrates: tempos, modes, and timing
BULLETIN OFMARINE SCIENCE. VOL. 57. NO.2.1995
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J. B. McClintock and I. Bosch. 1991. Reproduction of Antarctic benthic marine invertebrates:
tempos, modes, and timing. Amer. ZooI. 3]: 65-80.