Uncommon diversity in developmental mode and larval form in the genus <Emphasis Type="Italic">Macrophiothrix</Emphasis> (Echinodermata: Ophiuroidea)

Development mode in the ophiuroid genus Macrophiothrix includes an unusual diversity of planktonic larval forms and feeding types. The modes of development for seven congeners that coexist in coral reef habitats at Lizard Island, Australia were compared using larvae generated from crosses over several reproductive seasons from 1999 to 2003. Three species (Macrophiothrix koehleri Clark, Macrophiothrix longipeda Lamarck, Macrophiothrix lorioli Clark) develop from small eggs (<170 μm) into typical obligately feeding planktonic (planktotrophic) pluteus larvae with four larval arm pairs. The remaining four species develop from larger eggs (≥230 μm) into either facultatively-feeding or non-feeding (lecithotrophic) larval forms. The facultative planktotroph (Macrophiothrix rhabdota Clark) retains the ability to digest and benefit from food but does not require particulate food to complete metamorphosis. Among the lecithotrophic species, Macrophiothrix caenosa Hoggett retains the pluteus morphology with four pairs of larval arms, but is incapable of feeding, depending instead on maternal provisions for larval development. The remaining two lecithotrophs have simplified larval morphologies with only a single pair of full length (Macrophiothrix nereidina Lamarck) or highly reduced (Macrophiothrix belli Doderlein) larval arms and no functional mouth or gut. This genus includes the first example of facultative planktotrophy in ophiuroids, the first example in echinoderms of a complete pluteus morphology retained by a lecithotrophic larva, and three degrees of morphological simplification among lecithotrophic larval forms. Egg volume varies 20-fold among species and is related to variation in feeding mode, larval form, and development time, as predicted for the transition from planktotrophic to lecithotrophic development.     

Reproduction in five species of crinoids at Lizard Island,Great Barrier Reef

Reproduction in five species of crinoids [Himerometra bartschi (A. H. Clark), H. robustipinna (P. H. Carpenter), Cenometra bella (Hartlaub), Colobometra perspinosa (P. H. Carpenter), and Oligometra serripinna (P. H. Carpenter)] was studied at Lizard Island, Queensland, over 24 mo, from April 1981 to March 1983 (except for O. serripinna —June 1981 to March 1983). All five species of crinoids were dioecious, although a few instances of synchronous hermaphroditism were noted in H. bartschi, C. perspinosa, and O. serripinna. Gonad morphology and the sequence of developmental stages were similar in each species. Within individuals, gametogenesis was synchronous in gonads both along and between arms, except in some proximal and distal genital pinnules in which gonads never matured. Within a species, there was a degree of synchrony of gametogenesis in a sample, but the level of gametogenic activity varied considerably between years. A high level of continuous reproductive activity was observed in H. bartschi, H. robustipinna, Cenometra bella, and Colobometra perspinosa from about mid-summer to early/mid-winter, while O. serripinna probably had a bimodal reproductive cycle with peaks around February and June. There was a significant 1:1 male:female sex ratio in the populations sampled, and unsexable individuals were significantly smaller (as determined by maximum arm length) than either sexable males or females.     

Reproduction of sympatric populations ofHeliocidaris erythrogramma andH. tuberculata (Echinoidea) in New South Wales

Reproduction ofHeliocidaris erythrogramma (Valenciennes) andH. tuberculata (Lamarck) was compared through examination of oogenesis, spermatogenesis and monthly measurement of the gonad index. These species occur sympatrically in the Sydney region. Their reproduction was examined at two sites near Botany Bay, New South Wales, Australia, from February 1989 through January 1990.H. erythrogramma produces buoyant, 450µm-diam eggs and the sperm have a head region 10µm in length. By contrast,H. tuberculata produces negatively-buoyant, 95µm-diam eggs and the sperm have a head region 4µm in length. Histochemical examination of the gonads revealed that periodic acid Schiff-positive (PAS +) material stored in the nutritive phagocytes appears to support vitellogenesis in both species. InH. tuberculata this material is utilized in the formation of PAS + yolk oligolecithal eggs, whereas inH. erythrogramma the PAS + material appears to be converted to lipid yolk in macrolecithal eggs.H. erythrogramma had a seasonal reproductive pattern with a 3 mo summer spawning period, whereas both populations ofH. tuberculata had a 9 mo breeding period characterized by the continual presence of nutrient reserves and vitellogenic oocytes which rapidly replaced spawned ova. Spawning ceased only for 3 mo over the summer. Due to the 9 mo spawning ofH. tuberculata it is not clear what factors serve to cue reproduction in this species.     

Developmental types of shallow-water asteroids of McMurdo Sound,Antarctica

The mode of development was ascertained for 14 of the 16 species of sea stars known to occur in shallow waters of McMurdo Sound, Antarctica (77°51S; 166°40E). The species were collected between September 1984 and December 1985. Females of three species,Odontaster validus, O. meridionalis andPorania antarctica, spawn small to moderate eggs (0.17 to 0.55 mm), have a high fecundity, and produce feeding larvae. Females of an undescribedPorania species spawn a few eggs (150 to 310) that are 0.55 mm in diameter and develop into demersal non-feeding larvae. Females ofDiplasterias brucei andNotasterias armata produce a few (<300) large eggs (2.8 to 3.5 mm) and brood their young. Females of the remaining eight species have moderate fecundity and produce pelagic non-feeding larvae, as determined from egg type (buoyant, 0.54 to 1.28 mm diam) and direct observations of spawning and development. The high incidence (11 out of 14 species; 79%) of non-feeding development is consistent with predictions that environmental conditions in high-latitude regions are unfavorable for planktotrophic development. Nonetheless, most of the species surveyed (11 out of 14) had pelagic larvae, which contradicts inferences of unusual selection for benthic development in the Antarctic.     

Comparative fertilization biology of gymnolaemate bryozoans

Locations and oogenic stages of eggs at the time of sperm-egg fusion were determined for nine gymnolaemate species exhibiting different reproductive strategies with respect to site of embryonic development (e.g., water column, introvert, embryo sac, or ovicell) larval type, and zooid sexuality. Ovarian, coelomic, and recently spawned oocytes obtained from freshly collected colonies between 1988 and 1995 were stained with aceto-orcein and examined for the presence of a sperm nucleus. All nine species are shown to have a similar fertilization biology in which sperm fuse with eggs in or near ovaries and egg activation is delayed until eggs are spawned. In species such as the etenostomeAlcyonidium sp. and the cheilostomeElectra pilosa (Linnaeus, 1767), which produce marierons oocytes that are spawned into the water column and have cyphonautes larvae, sperm fuse with late growth stage ovarian oocytes after germinal vesicle breakdown (GVBD) at or near ovulation. In species that produce few oocytes, brood embryos, and release coronate larvae, sperm fuse with late growth stage ovarian primary oocytes before GVBD, as in the ctenostomeBowerbankia gracilis Leidy, 1855, or with very early growth stage ovarian primary oocytes, as in the cheilostomesCribrilina corbicula (O'Donoghue, 1923),Dendrobeania lichenoides (Robertson, 1900),Hippodiplosia insculpta (Hincks, 1882),Schizoporella serialis (Heller, 1867),T ricellaria gracilis (Smitt, 1867), andWatersipora arcuata Banta, 1969. Fertilization success was high in all nine species, with 83 to 100% of oocytes at an appropriate oogenic stage containing a sperm nucleus or early male pronucleus. Gymnolaemate bryozoans may maintain high levels of fertilization success by: (1) concentrating spawned sperm from the water column using colony feeding currents; (2) localizing sperm-egg encounters in or near the ovary, (3) using sperm when available by permitting sperm to fuse with early growth stage oocytes; and (4) selfing.     

Comparing biochemical changes and energetic costs in gastropods with different developmental modes: <Emphasis Type="Italic">Crepipatella dilatata</Emphasis> and <Emphasis Type="Italic">C. fecunda</Emphasis>

The Chilean gastropods Crepipatella dilatata and C. fecunda have different development modes: brooding and direct development in C. dilatata and brooding and planktotrophic development in C. fecunda. Unlike many other congeneric invertebrate species pairs, recent genetic evidence suggests that C. fecunda may have evolved from C. dilatata. To explore the changes involved in this unusual evolutionary path, this study examined the biochemical, energetic, and morphological characters during early development of both species. Mean egg size was slightly smaller for the direct-developing species C. dilatata, and initial energy content was lower—by about 27%—for eggs of that species. In both species, protein content in the eggs was the principal biochemical component. Although females of C. fecunda produce 180 times more eggs than C. dilatata, females of C. dilatata invest 20 times more energy in each of their offspring, through nurse eggs; their embryos have approximately eight times more energy at hatching and about 5 times more energy when they enter the benthos, despite a long planktonic feeding period in the larvae of C. fecunda. Evolutionary switching between modes of development in these species is reflected in shifts in maternal energy investment.     

Phosphorus metabolism and water uptake during final maturation of ovaries of teleosts with pelagic and demersal eggs

An earlier study showed large changes in ovarian phosphoprotein, a characteristic component of vertebrate yolk, during post-vitellogenic meiotic maturation (ripening) of ovaries of teleosts with pelagic eggs. Here, the study of four phosphorus-containing ovarian fractions is extended to other teleost families with pelagic eggs and to species with demersal eggs. Fishes were caught in the sea and lakes of western Scotland between 1982 and 1984. In the codGadus morhua, spratSprattus sprattus, dragonetCallionymus lyra, Norway poutTrisopterus esmarkii, saithePollachius virens, lingMolva molva and flounderPlatichthys flesus, all of which spawn pelagic eggs, the massive water influx during ripening which renders the eggs buoyant was accompanied by large changes in yolk phosphoprotein which were apparent as decrease or disappearance of protein phosphorus as conventionally determined. During ripening of the demersal eggs of the herringClupea harengus, both the water uptake and the decrease in protein phosphorus were less pronounced. In the three-spined sticklebackGasterosteus aculeatus, sea sticklebackSpinachia spinachia, sand gobyPomatoschistus minutus and perchPerca fluviatilis, little or no changes in water content or protein phosphorus both usually increased in species with pronounced water uptake and decreased in species with little or no water uptake. Lipid phosphorus showed little change in all species examined except herring, in which it increased. It is concluded that the characteristic changes in phosphoprotein and other phosphorus-containing fractions are most pronounced in species with pelagic eggs exhibiting massive water uptake on ripening, but are found to a lesser extent in species with demersal eggs in which considerable water uptake accompanies ripening.     

Some observations on spawning and fecundity in the luminescent fish Photoblepharon palpebratus

Spawning pairs of the fish Photoblepharon palpebratus (Boddaert), a bioluminescent shallow-water species from the Banda Islands, were observed in captivity for the first time. Both female individuals of the two pairs studied were slightly larger than the males, and possessed rounder tail-fin edges, criteria which can be used for sexing. Laboratory and field observations indicate that during several dark nights in April and May one female could produce a total of up to 1,000 sticky, transparent, 1.2-mm diameter, spherical, buoyant eggs, which after a brief planktonic phase of 5 to 10 h continue their development while adhering to a substrate. This short planktonic phase might explain why P. palpebratus only occurs around the Banda Islands, although similar habitats can be found elsewhere in the South Moluccan Sea. In addition to large ripe eggs, two size-classes of immature eggs were found in the ovaries. In the aquarium pairs of P. palpebratus tended to occupy a limited area but did not show aggressive territorial behaviour.     

Factors affecting buoyancy in the eggs of Bairdiella icistia (Pisces: Sciaenidae)

Several aspects of buoyancy were studied in the normally pelagic eggs of the sciaenid fish Bairdiella icistia (Jordan and Gilbert). Spawning fish acclimated to a low salinity (15‰) produced larger, more buoyant eggs which had a higher water content than eggs produced by fish living in ordinary sea water (33‰ S). Eggs fertilized in lower salinities were larger and more buoyant than eggs fertilized in higher salinities. The salinity of the medium during the first 5 to 7 min after fertilization had a lasting effect on egg buoyancy, but subsequent transfer to a different salinity also influenced buoyancy. Although egg buoyancy in this species can be influenced by the ambient salinity both before and after spawning, the capacity for adjusting buoyancy is limited, and eggs spawned in salinities lower than 30‰ would probably sink.     

Differences in reproductive strategies of morphs of the genus Echinaster (Echinodermata: Asteroidea) from the Eastern Gulf of Mexico

Two morphs of the asteroid genus Echinaster, E. Type 1 and E. Type 2, have reciprocal annual cycles of reproduction and nutrient storage. The pyloric caeca (storage organs) reach maximal size over winter then decrease with increasing gametogenic activity in the spring. E. Type 1 broadcasts buoyant eggs in late May to early June. E. Type 2 deposits benthic eggs in late April. Lecithotrophic larval development is similar in both morphs except that larvae of E. Type 1 undergo a brief planktonic phase. E. Type 1 reaches sexual maturity at a larger size, expends a lower reproductive effort but has a greater absolute reproductive output than E. Type 2. E. Type 2 produces fewer, larger eggs and has a greater parental investment per egg. In both morphs, females have much higher gonadal lipid levels than males and expend a higher reproductive effort in terms organic matter and energy. Reproductive effort, reproductive output, nutrient storage in the pyloric caeca and body size varied between populations and between years in each morph. Egg size and parental investment per egg were constant. Within-morph variability is attributed to differences in nutritional state. Differences in reproductive strategy support the hypothesis that the morphs are separate species.     

Buoyancy measurements and vertical distribution of eggs of sardine (<Emphasis Type="Italic">Sardina pilchardus</Emphasis>) and anchovy (<Emphasis Type="Italic">Engraulis encrasicolus</Emphasis>)

Measurements were made of the density and settling velocity of eggs of sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus), using a density-gradient column. These results were related to observed vertical distributions of eggs obtained from stratified vertical distribution sampling in the Bay of Biscay. Eggs of both species had slightly positive buoyancy in local seawater throughout most of their development until near hatching, when there was a marked increase in density and they became negatively buoyant. The settling velocity of anchovy eggs, which are shaped as prolate ellipsoids, was close to predictions for spherical particles of equivalent volume. An improved model was developed for prediction of the settling velocity of sardine eggs, which are spherical with a relatively large perivitelline volume; this incorporated permeability of the chorion and adjustment of the density of the perivitelline fluid to ambient seawater. Eggs of both species were located mostly in the top 20 m of the water column, in increasing abundance towards the surface. A sub-surface peak of egg abundance was sometimes observed at the pycnocline, particularly where this was pronounced and associated with a low-salinity surface layer. There was a progressive deepening of the depth distributions for successive stages of egg development. Results from this study can be applied for improved plankton sampling of sardine and anchovy eggs and in modelling studies of their vertical distribution.Communicated by J.P. Thorpe, Port Erin     

Lipid composition of eggs and adductor muscle in giant scallops (Placopecten magellanicus) from different habitats

Scallops (Placopecten magellanicus Gmelin) were collected during August 1989 from shallow water (10 m) and deep water (31 m) habitats at Sunnyside, Trinity Bay, Newfoundland, to compare the lipid composition of eggs and adductor muscle tissue. Less favorable food levels and lower temperature conditions associated with deeper water have previously been shown to produce slower growth and reduced fecundity in individuals from this habitat. Triacylglycerol reserves consistently accounted for 60% of the total lipids present in both groups. The total lipid content of the eggs and the composition of their triacylglycerol fatty acid pools were similar in shallow water and deep water scallops, indicating very little if any nutritional difference between the two groups. Relative to their counterparts from shallow water, individuals from deeper water contained higher proportions of docosahexaenoic acid [22:6(n-3)] in the egg phospholipids and higher levels of 24-methylenecholesterol (a phytosterol commonly found in diatoms) in the adductor muscle. Differences in fatty acid composition are interpreted as biochemical adjustments of cell membranes to increase membrane fluidity, thereby compensating for the lower temperatures prevailing at the greater depth.     

Mode of zooxanthella transmission does not affect zooxanthella diversity in acroporid corals

Two distinct modes of algal endosymbiont acquisition exist in corals, a direct transmission from the parental colony to the eggs and a larval or post-larval uptake from the environment. The former, maternal-transmission mode is expected to be a more closed system, while the latter is believed to be an open system. Here we test the hypothesis that the diversity of symbionts in closed systems is lower than that in open systems. We examine the identity and diversity of the algal endosymbionts (zooxanthellae) in 25 Montipora species sampled from Irian Jaya (Indonesia) and Magnetic Island (central Great Barrier Reef) and compare the results with those previously obtained from Acropora species, which belong to the same family. All Montipora colonies examined harbour clade C zooxanthellae, with two colonies harbouring both clade C and D zooxanthellae simultaneously. Two algal strains (named C· and D· in this study) present in Montipora have not been observed in Acropora, and may have co-evolved with Montipora. Symbiodinium C· shows approximately 5% sequence divergence from C strains observed in Acropora spp. and occurs in 76% of the colonies examined. Nevertheless, several other C strains commonly found in other corals occur in some of the Montipora colonies. Montipora species transmit their algal endosymbionts directly to the eggs, while Acropora species have to acquire zooxanthellae from the environment every generation. Contrary to our expectations, the diversity of zooxanthellae is similar for the two genera, indicating that the mode of symbiont transmission (i.e. maternal versus horizontal) does not affect symbiont diversity in acroporid corals.Communicated by M.S. Johnson, Crawley     

Behavioral diversification in a young species flock of pupfish (<Emphasis Type="Italic">Cyprionodon</Emphasis> spp.): shoaling and aggressive behavior

Increasing empirical and theoretical evidence supports the idea that sympatric speciation is operating, for example, in species flocks comprising several closely related fish species within one lake. Divergent natural selection (promoting spatial and food niche partitioning) and sexual selection (assortative mating) have been identified as key selection factors in intralacustric adaptive radiations. However, the evolution of social behaviors accompanying such adaptive radiations is less well understood. Using a phylogenetically young species flock of pupfish (Cyprinodon spp.) as a model, we examined differences among six sympatric species and compared their shoaling, aggressive, and territorial behaviors with that of a sister species (C. artifrons). Despite an estimated age of the species flock of less than 8,000 years, pronounced behavioral differentiation was found. C. simus, the smallest species in the flock, shoaled more than the other species and was less aggressive and less territorial than C. beltrani. F₁-hybrids between C. simus males and C. beltrani females showed an intermediate expression of shoaling and aggressive behavior. Niche partitioning among the members of this species flock appears to be accompanied by rapid divergent evolution of social behaviors. We discuss the potential role of phenotypic plasticity and within-species variation of social behaviors for such rapid behavioral diversifications in sympatric speciation processes.     

Egg production by the subtropical copepod Undinula vulgaris

Egg production by Undinula vulgaris, collected off Kaneohe Bay, Hawaii, was measured under field and laboratory conditions on 16 occasions from June to December 1991. In situ rates ranged from 0 to 15.7 eggs female^-1 d^-1, with a mean of 6.4 eggs female^-1 d^-1, 2.1% female body carbon d^-1. Maximum in situ production was 53 eggs female^-1 d^-1, 17.2% C d^-1. Average egg production (Y, eggs female^-1 d^-1) was related to the concentration of particulate carbon (X, g C l^-1) by the Ivlev function, Y=13.9[1-e^{-0.0097 (x-10)}], with R ²=0.96. Individuals with the same feeding history produced more eggs at lower temperatures in the laboratory. Egg production was not significantly correlated with dry weight, and no noticeable temporal trend was found. Despite the elevated habitat temperatures (26 to 27°C) of this subtropical copepod, maximum fecundity of U. vulgaris was comparable to, but average rates were lower than, egg production rates of similarly-sized, temperate and borcal species of the genus Calanus. Our results caution against broad extrapolations of the temperature-growth relationship for temperate coastal copepods to species from poorly studied, oligotrophic regions of the oceans.Contribution No. 3257 from the School of Ocean and Earth Science and Technology, University of Hawaii at Manoa, Honolulu, Hawaii 96822, USA     

Vital staining of Patiria miniata larvae

Larvae and unfertilized eggs of the California sea star Patiria miniata (Brandt) were exposed to 3 stains: Nile Blue Sulfate, Neutral Red and Rhodamine B. Concentration of the stains was 5 or 10 ppm, and length of exposure 5, 10 or 20 min. None of the stains were toxic, and Nile Blue Sulfate was found to be the best tested for retention of stain over long periods of time. This method is suggested for studies of development, growth, survival and dispersal of sea-star larvae in the plankton and in laboratory studies.Contribution No. 38, Pacific Marine Station, Dillon Beach, California, USA.     

Short-term temporal variation in population structure of two harpacticoid copepods,Zausodes arenicolus and Paradactylopodia brevicornis

Aspects of the population biology of two harpacticoid copepod species [Zausodes arenicolus Wilson and Paradactylopodia brevicornis (Claus)] living in Tampa Bay, Florida, USA, were studied on time scales of hours to days during November 1983. Fluctuations in population agestructure, adult sex-ratio, and proportion of ovigerous females were determined for these two species in a control plot and in an experimental plot defaunated by raking. For both species, immigrants into the defaunated plot differed significantly from conspecifics in the control plot in all characteristics examined. The disturbed plot contained a larger proportion of young juveniles of both species compared to the unmanipulated site after 4 h but not after 8 h. In Z. arenicolus, adult males returned to the experimental plot more quickly than adult females. For both species, rapid and significant changes in population age-structure, adult sex-ratio, and the proportion of adult females with eggs occurred within the control plot. It is suggested that this variation was too large and occurred too rapidly to be accounted for solely by in situ processes in the absence of large-scale immigration and/or emigration of individuals. Potential implications of these results for population studies of harpacticoid copepods and other benthic invertebrates are discussed.     

Subitaneous, diapause, and delayed-hatching eggs of planktonic copepods from the northern Gulf of Mexico: morphology and hatching success

Experiments were conducted to examine the morphology and hatching success of eggs, either spawned by freshly caught planktonic copepods or recovered from bottom sediments in the northern Gulf of Mexico. Collections were made between August 1992 and September 1995. Eggs of nine species were described and these differed in their diameter, color and surface attributes. Three types of eggs were distinguished: subitaneous, diapause, and delayed-hatching. Three species, Labidocera aestiva Wheeler, Acartia tonsa Dana, and Centropages velificatus (Oliveira) produced only subitaneous eggs. Hatching success varied greatly among these species. Two species, Labidocera mirabilis Fleminger and Centropages hamatus (Lilljeborg) produced diapause eggs and subitaneous eggs. The length of the refractory phase of the diapause eggs differed greatly both within and between these two species. A third type of dormant egg, delayed-hatching, was recognized in Labidocera scotti Giesbrecht and Pontella meadi Wheeler. The existence of delayed-hatching eggs may be an adaptive response of subtropical species to less seasonal fluctuation. Based upon morphological characteristics of the eggs and rearing of nauplii to an identifiable stage, benthic dormant eggs of eight species of calanoid copepods were also identified. Received: 9 September 1996 / Accepted: 1 October 1996     

Overwintering strategies of dominant calanoid copepods in the German Bight, southern North Sea

Abundance, stage composition and reproductive parameters (egg production, egg viability, proportion of spawning females) of the four copepod species Acartia clausi, Centropages hamatus, C. typicus and Temora longicornis were measured at the long term sampling station Helgoland Roads (German Bight, southern North Sea) from September 2003 to May 2004 to study their overwintering strategies. A. clausi was overwintering as females with arrested reproduction from November to January. T. longicornis, which is known to produce resting eggs in the North Sea, had a pelagic population with all developmental stages present during winter and reproductive rates closely related to food concentrations. Although their females produced eggs in response to ambient food conditions, both C. hamatus and C. typicus were rare in the pelagic. The C. hamatus population returned in May, probably from resting eggs, whereas C. typicus depended on advection. The Centropages species seemed to be less adapted to pelagic life in winter than A. clausi and T. longicornis. Sporadic occurrence of large numbers of nauplii and young copepodids of A. clausi and Centropages spp. pointed to different overwintering strategies or more successful survival in adjacent regions and advection of them into the waters around Helgoland island. While A. clausi was decoupled from environmental conditions in late autumn and winter, the other species were able to respond to variations in the food environment. Thus, egg production of T. longicornis increased during an unusual autumn diatom bloom.     

Nitrogen and phosphorus turnover in some benthic marine invertebrates: implications for the use of C:N ratios to assess food quality

The present study was designed to measure the relative turnover of nitrogen and phosphorus during a standard period of metabolism among several co-occurring species of benthic invertebrates: chitons (Poneroplax albida Blainville 1825); albalones (Haliotis roei Gray, 1826); gastropods [Turbo (ninella) torquatus Gmelin, 1791]; ascidians [Herdmania momus (Savigny)]; and sponges (Aplysina sp. and Iotrochata baculifera Ridley, 1884). Five of the six species (collected at Wreck Rock, Western Australia in 1985) exhibited a high turnover of phosphorus (P) relative to nitrogen (N). In contrast to N, P turnover was related to the concentration of P in body tissues. A relatively high demand for P in the diet is required to support the observed rapid turnover of P with respect to N. This observation suggests that the evaluation of potential foods would be better accomplished by the measurement of the C:P or the N:P ratio, rather than the commonly used C:N ratio.