Morphological and quantitative changes in paternal brood‐pouch vasculature during embryonic development in two Syngnathus pipefishes

Vascular corrosion casts of Syngnathus floridae and Syngnathus fuscus brood pouches were examined by scanning electron microscopy. Morphological and quantitative data on the vasculature of the paternal brood pouch during each stage of embryonic development were investigated to explore potential changes during brooding, to consider interspecific differences and to provide structural evidence for previously reported functional roles of the brood pouch. The brood pouches of both species are highly vascularized structures with cup‐like arrangements of brood‐pouch vasculature developing around each embryo shortly after fertilization and breaking down before fry release. The density and size of paternally derived blood vessels in contact with the embryos were found to be consistent for S. fuscus once this structure was established early in development. On the contrary, these vasculature measurements varied with early S. floridae brood stages when the embryo still relied heavily on the yolk sac. Diameter measurements of S. fuscus brood‐pouch blood vessels were also comparatively smaller during these early developmental stages, suggesting that the structural stability and opportunity for greater transport via slower blood flow may contribute to greater paternal allocation. This is the first study to document changes in brood‐pouch vasculature during specific stages of embryonic development, to show regression of this vasculature before fry release and to provide morphological data for two syngnathid species for which information on brood‐pouch physiology is available.     

Trophic ecology of two congeneric pipefishes (Syngnathidae) of the lower York River,Virginia

Synopsis The northern pipefish, Syngnathus fuscus, and the dusky pipefish, S. floridae, co-exist in eelgrass beds in the lower York River. To compare the trophic ecology of both pipefishes, gut contents of 3488 northern pipefish, and 1422 dusky pipefish were examined and quantified by dry weight. Samples were taken with a dip net from May through November 1992. Syngnathus fuscus fed mainly on amphipods (Gammarus mucronatus, Amphithoe longimana, and Caprella penantis), and to a lesser degree on copepods, and isopods (Edotea spp. and Erichsonella attenuata). Syngnathus floridae fed mainly on grass shrimps (Palaemonetes pugio, P. vulgaris, and Palaemonetes eggs), and to a lesser degree on copepods, isopods, and mysids (Mysidopsis bigelowi). No seasonal trends were observed in the feeding habits of these pipefishes. Specimens of both species smaller than 100 mm TL fed mainly on copepods. Larger S. fuscus fed on amphipods, while larger S. floridae fed on grass shrimps. Schoener's diet overlap index revealed high consumption of the same prey type by both pipefish species only in July, but only for those specimens smaller than 110 mm TL. Food partitioning between both pipefish was associated with different snout sizes and shapes.     

Interspecific differences of parental polychlorinated biphenyl exposure on nutrient availability, egg production and brooding in two Syngnathus species

Parental nutrient contribution of two closely related, sympatric pipefish species was investigated following exposure to mid-range environmental concentrations of the polychlorinated biphenyl (PCB) mixture Aroclor 1254 (mean ± s . e . = 52·89 ± 2·12 μg l⁻¹). This study tested the hypothesis that differential nutrient supplementation during development predicts interspecific sensitivity to environmental stressors. Specifically, paternal PCB exposure was predicted to affect Syngnathus fuscus development because embryos depend on paternally derived nutrient sources in the brood pouch. Conversely, changes in Syngnathus floridae egg production were expected following maternal PCB treatment as a nurse-egg system generates the nutrient-rich pouch fluid. Lipid concentrations in adult blood plasma were significantly elevated following Aroclor 1254 treatment in S. floridae gravid females and post-brooding S. fuscus males ( P < 0·001) which suggested mobilization from body tissues in response to metabolic demands. Aroclor 1254 treatment also resulted in decreased protein concentrations in S. fuscus pouch fluid ( P < 0·05). These changes were not translated into significant exposure-related effects in the nutrient reserves of eggs and fry or fry size. Overall S. fuscus demonstrated a general sensitivity to disturbances from laboratory exposure conditions. Whereas a previous investigation of field-collected pipefishes showed comparable interspecific pouch fluid and fry nutrient concentrations and egg size, here, nutrient levels and egg diameter decreased in both laboratory-mated control and PCB-exposed S. fuscus . This study demonstrates the potential physiological effects of PCB exposure on parental nutrient allocation in syngnathids and the general sensitivity of S. fuscus to environmental disturbances.     

Changes in male physiological condition during brooding activities in a natural population of a stream goby, <Emphasis Type="Italic">Rhinogobius</Emphasis> sp.

We investigated the change in physical condition of males during paternal care in a natural population of a stream goby Rhinogobius sp. LD. Hepatosomatic index (HSI) and Condition factor (K) of males guarding an egg mass were higher than those of non-breeding males. In the first brooding cycle, the HSI of males decreased with the progress of embryo development. Moreover, in the second brooding cycle, both the HSI and K decreased, suggesting that the energy reserves in the somatic tissue were used when the liver reserves were exhausted as a source of energy for paternal activities. After paternal care, males showed reduced K and were unable to recover HSI immediately. Comparisons of the physical condition between non-guarding males after the first brooding cycle and males guarding an early stage clutch in the second brooding cycle indicated that males which could recover HSI and K were able to have a second brooding cycle. This suggested that the physical condition determines participation in breeding activity and the number of brooding cycles, greatly influencing male reproductive success.     

Eel protection measures within the Manapouri hydro-electric power scheme,South Island,New Zealand

Variation in developmental rate from fertilization to swim-up, and body size at swim-up, may affect the growth and survival of young-of-the-year fish. Fish egg size (diameter) is often positively correlated to adult female size, but whether increased egg size equates to higher egg nutrient content and subsequently improved embryo/larval performance, remains unclear. Artificially fertilized northern pike eggs from individual females (total length 400–800 mm) were cultured under temperature controlled laboratory conditions to test the hypothesis that female body size positively influences egg size and the amount of specific nutrients (carbon, nitrogen, phosphorus, and fatty acids) allocated to eggs. We further hypothesized that greater egg nutrient content would positively influence egg survival, developmental rate, and the size of swim-up fry. These hypotheses were investigated in the context of two different northern pike spawning strategies (early season tributary vs. late season deep shoal spawning). Nutrients were allocated conservatively in northern pike eggs, showing very little variation in nutrient concentrations, but the total mass of all egg nutrients increased linearly with egg dry mass. Neither egg dry mass nor nutrient content (concentration or mass), were related to either egg diameter or female body size. The mass of individual egg nutrients was, however, strongly correlated with egg dry mass (r ² range 0.62 to 0.99 for individual nutrients) and positively related to the total length of swim-up fry (r ² = 0.58). The eggs of late spawning pike had significantly greater dry mass (average = 3.02 mg/egg) and developed more rapidly to swim-up (average = 17.89 days) than did those of early spawners (average = 2.28 mg/egg, 19.05 days). Our results indicate that egg quality may be best assessed by egg dry mass, which was correlated with greater nutrient mass and increased swim-up fry body length, as opposed to egg diameter or female body size which showed no correlation to egg nutrient composition and egg/larval performance. Guest editors: J. M. Farrell, C. Skov, M. Mingelbier, T. Margenau & J. E. Cooper International Pike Symposium: Merging Knowledge of Ecology, Biology, and Management for a Circumpolar Species     

Growth and uptake of mineral by embryos of the direct-developing frog Eleutherodactylus coqui

Embryos of the direct-developing frog Eleutherodactylus coqui take up small quantities of yolk and yolk mineral early in incubation but increase their uptake of yolk reserves at later stages of development. Growth and accumulation of calcium and magnesium by embryos also occur slowly at first and at a higher rate later. Accumulation of calcium and magnesium by embryos is largely a function of variation in size of embryos, but uptake of phosphorus is unrelated to size. Althrough patterns of growth and uptake of mineral by embryonic coquis resemble those for embryos of oviparous amniotes, embryonic coquis do not deplete the yolk of its nutrients to the same degree. Thus, residual yolk of coqui hatchlings contains a high percentage of the nutrient reserves originally present in the egg. This difference between embryonic coquis and embryos of oviparous amniotes may indicate that transfer of nutrients from yolk to embryo becomes limiting during the grwoth phase. Alternatively, some aspects of the neurologic system are so poorly developed at hatching that coqui may not be able to find prey effectively. A large nutrient reserve could sustain hatchling while the neurologic system continues to mature.     

The relationship between transpiration and nutrient uptake in wheat changes under elevated atmospheric CO2

The impact of elevated [CO₂] (e[CO₂]) on crops often includes a decrease in their nutrient concentrations where reduced transpiration‐driven mass flow of nutrients has been suggested to play a role. We used two independent approaches, a free‐air CO₂ enrichment (FACE) experiment in the South Eastern wheat belt of Australia and a simulation study employing the agricultural production systems simulator (APSIM), to show that transpiration (mm) and nutrient uptake (g m^?2) of nitrogen (N), potassium (K), sulfur (S), calcium (Ca), magnesium (Mg) and manganese (Mn) in wheat are correlated under e[CO₂], but that nutrient uptake per unit water transpired is higher under e[CO₂] than under ambient [CO₂] (a[CO₂]). This result suggests that transpiration‐driven mass flow of nutrients contributes to decreases in nutrient concentrations under e[CO₂], but cannot solely explain the overall decline.     

Respiratory morphology of the Abedus herberti Hidalgo egg chorion (Hemiptera: Belostomatidae)

Although giant water bugs (Hemiptera: Belostomatidae) are large, aquatic insects known for their obligate paternal egg brooding behaviors, little research has focused on the structure of their eggs. The respiratory requirements of developing embryos likely created selection for brooding, so a thorough understanding of the respiratory morphology of belostomatid eggs could help explain how brooding behaviors facilitate embryonic gas exchange. This study used scanning electron microscopy to document the respiratory microstructure of the eggs of Abedus herberti, a back brooding giant water bug. The exochorion is similar to that of other belostomatids in texture and organization except that the respiratory region is confined to the uppermost quarter of the egg. This is the area exposed to the atmosphere by encumbered males. A plastron network made up of densely packed vertical projections demarcates the boundary between the respiratory and nonrespiratory regions of the chorion. The internal chorion is composed of alternate air‐filled and denser layers that likely facilitate the movement of oxygen from the aeropyles at the top of the eggs to the developing embryonic tissues. J. Morphol., 2011. © 2011 Wiley‐Liss, Inc.     

Diurnal periodicity in Daphnia reproduction

The diurnal periodicity of reproduction in a reservoir population of Daphnia galeata Sars was tested by two methods (egg age distribution analyses and direct observation of hatching). No significant diurnal synchronization of reproduction in the natural cladoceran population was found. A conspicuous shortage of older embryonic stages was parallely revealed by analyses of diurnal changes of egg age distribution. Suggested selective feeding of fish on gravid females of Daphnia brooding embryos with black eye pigmentation is discussed.     

POLYGYNANDRY IN THE DUSKY PIPEFISH SYNGNATHUS FLORIDAE REVEALED BY MICROSATELLITE DNA MARKERS

In the dusky pipefish Syngnathus floridae, like other species in the family Syngnathidae, ‘pregnant’ males provide all post-zygotic care. Male pregnancy has interesting implications for sexual selection theory and the evolution of mating systems. Here, we employ microsatellite markers to describe the genetic mating system of S. floridae, compare the outcome with a previous report of genetic polyandry for the Gulf pipefish S. scovelli, and consider possible associations between the mating system and degree of sexual dimorphism in these species. Twenty-two pregnant male dusky pipefish from one locale in the northern Gulf of Mexico were analyzed genetically, together with subsamples of 42 embryos from each male's brood pouch. Adult females also were assayed. The genotypes observed in these samples document that cuckoldry by males did not occur; males often receive eggs from multiple females during the course of a pregnancy (six males had one mate each, 13 had two mates, and three had three mates); embryos from different females are segregated spatially within a male's brood pouch; and a female's clutch of eggs often is divided among more than one male. Thus, the genetic mating system of the dusky pipefish is best described as polygynandrous. The genetic results for S. floridae and S. scovelli are consistent with a simple model of sexual selection which predicts that for sex role-reversed organisms, species with greater degrees of sexual dimorphism are more highly polyandrous.     

Postural Shifts During Egg‐Brooding and Their Impact on Egg Water Balance in Children’s Pythons (Antaresia childreni)

Parental care typically consists of distinct behavioral components that are balanced to address the multiple needs of offspring. Female pythons exhibit post‐oviposition parental care in which they coil around their parchment‐shelled eggs throughout incubation (40–80 d). Subtle postural shifts during egg‐brooding facilitate embryonic gas exchange but may entail hydric costs to the clutch. This study used a simple behavioral model to (1) further quantify the costs and benefits of specific parental behaviors to developing offspring and (2) determine the influence that developmental stage and relative clutch mass have on parental behavior. Although previous research has demonstrated that egg‐brooding as a whole reduces clutch water loss, we hypothesized that egg‐brooding female pythons specifically adopt a tightly coiled posture to conserve embryonic water, but must make postural adjustments to enhance gas exchange between the clutch and nest environments at the cost of increased clutch water loss. We measured rates of water loss in brooding Children’s pythons (Antaresia childreni) and their respective clutches (i.e., brooding units) and monitored changes in brooding posture. We conducted serial trials to elucidate the effect of developmental stage on postural adjustments and water loss. Results demonstrated that the proportion of time females spent in a tightly coiled posture was inversely related to mean water loss from the brooding unit. Analyses indicated that slight adjustments in posture led to bursts in brooding unit water loss. Indeed, brooding unit water loss during postural adjustments was significantly higher than during tight coiling. These findings imply that python egg‐brooding provides an adjustable diffusive barrier that leads to discontinuous gas exchange, which minimizes clutch water loss. Because females with larger relative clutch masses spent more time tightly coiled, egg‐brooding female pythons may use a ‘water first’ strategy in which they intentionally conserve clutch water at the cost of reduced embryonic respiratory gas exchange.     

Embryonic and larval development of brown trout, Salmo trutta L.: exposure to aluminium, copper, lead or zinc in soft, acid water

Freshly fertilized ova, eyed ova and yolk-sac fry of brown trout, Salmo trutta L., were exposed to each of four trace metals (aluminium: 6000 nmol l^?1; copper: 80 nmol l^?1; lead: 50 nmol l^?1; zinc: 300 nmol l^?1) while held in flowing artificial soft-water media maintained at pH 4.5 or 5.6 and [Ca] 20 or 200 μmol l^?1. In continuous exposure from fertilization, survival of ova was severely affected at pH 4.5 and [Ca] 20 μmol l^?1, regardless of the presence of Cu, Pb or Zn; Al reduced embryonic mortality and improved hatching success. High ambient [Ca] at pH 4.5 increased egg survival. At ‘swim-up’, surviving fry exposed to Al or Pb had lower whole body Ca, Na and K content, irrespective of pH or ambient [Ca]. Cu reduced whole body Ca and K content at pH 5.6 and [Ca] 200 μmol^?1, and whole body Ca, Na and K content in the other media. Zn reduced whole body mineral content at pH 5.6 and [Ca] 20 μmol l^?1. Whole body Mg content was reduced by all trace metals at pH 5.6 and [Ca] 20 μmol l^?1, and by Cu at pH 5.6 and [Ca] 200 μmol l^?1. Al and Cu impaired skeletal calcification at pH 5.6 at both ambient [Ca]; Pb only at [Ca] 20 μmol I^?1. Zn enhanced calcification at pH 4.5 and [Ca] 200 μmol l^?1. In the absence of trace metals, low pH reduced body Ca, Na, K content and skeletal calcification at [Ca] 200 μmol l^?1. The uptake of Ca, Na and K, measured at regular intervals from hatching was impaired to the same extent by all treatments at pH 4.5, irrespective of ambient [Ca] or trace metal presence. At pH 5.6, irrespective of ambient [Ca], Al, Cu and Pb impaired Ca and K uptake. The rate of Na uptake was reduced by Al and Cu. Al-treated yolk-sac fry, exposed to low ambient [Ca] from 200–300° days post-hatch, suffered high mortalities regardless of pH. Ca, Na and K uptake was impaired by all treatments at pH 4.5, and by Al and Cu at pH 5.6 in a similar exposure period. The development of the early stages of brown trout in the presence of trace metals is discussed in relation to recruitment failure in areas of soft, acid water.     

Can structural enrichment reduce predation mortality and increase recaptures of hatchery-reared Atlantic salmon Salmo salar L. fry released into the wild?

Captive-reared fish often have poor survival in the wild and may fail to boost threatened populations. Enrichment during the nursery period can in some circumstances generate a broader behavioural repertoire than conventional hatchery production. Yet, we do not know if enrichment promotes survival after release into the wild. We conducted a field experiment during three field seasons using age 0+ year Atlantic salmon Salmo salar to investigate if enrichment during rearing, in the form of structural complexity (shelters), reduced immediate (within 2 days after release) predation mortality by piscine predators (brown trout Salmo trutta) and if such rearing environments improved long-term (2–3 months after release) post-release survival. In addition, we investigated if predation mortality of released fry was size-selective. S. salar fry were reared in a structurally enriched environment or in a conventional rearing environment and given otolith marks using alizarin during the egg stage to distinguish between enriched and conventionally-reared fry. The outcome from the field experiments showed that structural enrichment did not consistently reduce immediate predation mortality and it did not improve, or had a negative effect on, the recapture rate of fry from the river 2–3 months after release. The data also showed that enriched rearing tended to reduce growth. Additionally, we found that S. trutta predators fed on small individuals of the released fry. Overall, the data suggest that structural enrichment alone is not sufficient to improve long-term survival of hatchery-reared fish after release and that other factors might affect post-release survival.     

Brooding in Psolus patagonicus (Echinodermata: Holothuroidea) from Argentina, SW Atlantic Ocean

The mode, season, and time of brooding, egg diameter, egg number per brood, and the characteristics of newly released juveniles of Psolus patagonicus were investigated off Mar del Plata, Buenos Aires, Argentina, between October 1999 and February 2001. Individuals were attached to the Patagonian scallop, Zygochlamys patagonica. Spawning occurs between February and March. The mean egg diameter, 887 ± 26 μm, is the highest reported for the family Psolidae. Eggs are brooded under the mother’s sole until they develop into crawling juveniles within 7 months. The largest embryos reached a length of 1,941 ± 228 μm in September. During the brooding period (February–September) the number of brooded embryos decreased while their size increased. Our study confirms brooding behaviour in female P. patagonicus.     

Distribution of lipids from the yolk to the tissues during development of the water python (<Emphasis Type="Italic">Liasis fuscus</Emphasis>)

Energy metabolism during embryonic development of snakes differs in several respects from the patterns displayed by other reptiles. There are, however, no previous reports describing the main energy source for development, the yolk lipids, in snake eggs. There is also no information on the distribution of yolk fatty acids to the tissues during snake development. In eggs of the water python (Liasis fuscus), we report that triacylglycerol, phospholipid, cholesteryl ester and free cholesterol, respectively, form 70.3%, 14.1%, 5.7% and 2.1% of the total lipid. The main polyunsaturate of the yolk lipid classes is 18:2n-6. The yolk phospholipid contains 20:4n-6 and 22:6n-3 at 13.0% and 3.6% (w/w), respectively. Approximately 10% and 30% of the initial egg lipids are respectively recovered in the residual yolk and the fat body of the hatchling. A major function of yolk lipid is, therefore, to provision the neonate with large energy reserves. The proportion of 22:6n-3 in brain phospholipid of the hatchling is 11.1% (w/w): this represents only 0.24% of the amount of 22:6n-3 originally present in the egg. This also contrasts with values for free-living avian species where the proportion of DHA in neonatal brain phospholipid is 16–19%. In the liver of the newly hatched python, triacylglycerol, phospholipid and cholesteryl ester, respectively, form 68.2%, 7.7% and 14.3% of total lipid. This contrasts with embryos of birds where cholesteryl ester forms up to 80% of total liver lipid and suggests that the mechanism of lipid transfer in the water python embryo differs in some respects from the avian situation.Abbreviations ARA arachidonic acid - DHA docosahexaenoic acidCommunicated by G. Heldmaier     

Behavioural temperature preference in a brooding male pipefish Syngnathus typhle

In the broad‐nosed pipefish Syngnathus typhle, brooding males positioned themselves significantly more often towards the warmer part (18° C) of an aquarium, whereas females were indifferent in this respect. This behavioural temperature preference may increase male brooding rate and indirectly influence patterns of mating competition.     

δ18O‐derived incubation temperatures of oviraptorosaur eggs

In order to determine the incubation temperature of eggs laid by non‐avian dinosaurs, we analysed the oxygen isotope compositions of both eggshell carbonate (δ¹⁸O_c) and embryo bone phosphate (δ¹⁸O_p) from seven oviraptorosaur eggs with preserved in ovo embryo bones. These eggs come from the Upper Cretaceous Nanxiong Formation of Jiangxi Province, China. Oviraptorosaur theropods were selected because of their known brooding behaviour as evidenced by preserved adult specimens fossilized in brooding posture on their clutch. Incubation temperature of these embryos was estimated based on the following considerations: eggshell δ¹⁸O_c value reflects the oxygen isotope composition of egg water fluid; embryo bones precipitate from the same egg fluid; and oxygen isotope fractionation between phosphate and water is controlled by the egg temperature. A time‐dependent model predicting the δ¹⁸O_p evolution of the embryo skeleton during incubation as a function of egg temperature was built, and measured δ¹⁸O_c and δ¹⁸O_p values used as boundary conditions. According to the model outputs, oviraptorosaurs incubated their eggs within a 35–40°C range, similar to extant birds and compatible with the known active brooding behaviour of these theropod dinosaurs. Provided that both eggshell and embryo bones preserved their original oxygen isotope compositions, this method could be extended to investigate some reproductive traits of other extinct groups of oviparous amniotes.     

NUTRITIONAL STUDIES OF THE SUBMERGED MARINE ANGIOSPERM THALASSIA TESTUDINUM I. GROWTH RESPONSES OF AXENIC SEEDLINGS TO NITROGEN ENRICHMENT

Algae- and bacteria-free seedling cultures of the seagrass Thalassia testudinwn Banks ex König were utilized to evaluate effects of nutrient enrichment on growth and chemical composition. Seedlings cultured in media based on both synthetic seawater and NH-15 medium amended with inorganic nitrogen (NH₄⁺) and organic nitrogen (glutamine, glutamate, urea and yeast extract) exhibited no growth enhancement relative to controls in the growth parameters measured. General decreases in green leaf areas and leaf widths after one month coupled with relatively high C:N ratios after 3 months in culture suggest utilization and depletion of stored reserves with little or no assimilation of exogenous nutrients. These observations coupled with previous results in non-axenic seedling cultures indicate microbial associations may play a critical role in the nutrient physiology of this species.     

Biomass production and nutrient accumulation in <Emphasis Type="Italic">Sparganium emersum</Emphasis> Rehm. after sediment treatment with mineral and organic fertilisers in three mesocosm experiments

The response of the aquatic plant Sparganium emersum to different sediment nutrient levels was studied in three mesocosm experiments. The aim was to assess plant growth parameters and nutrient accumulation in the plant tissue under conditions relevant for habitats with sediments affected by anthropogenic nutrient enrichment. The experimental treatments were produced by fertilisation of the rooting medium (washed river sand) with differing doses of either NPK mineral fertiliser or digested sludge from solid pig slurry waste. Growth inhibition by high nutrient levels was not observed in any treatment (highest nutrient concentrations in the sediment with mineral fertiliser: N 250 mg kg⁻¹, P 50 mg kg⁻¹; organic fertiliser: N 6300 mg kg⁻¹, P 1800 mg kg⁻¹), which confirms the tolerance of S. emersum to high nutrient loads. The sediment nutrient concentration was best reflected in shoot dry mass. Nutrient contents in plant tissues were similar for most nutrient concentrations in the rooting media; only N increased significantly with N levels in the sediment in belowground parts. Nutrient standing stocks in plants, however, generally corresponded to the nutrient supply, and reached highest values (max. N 3.7 g m⁻², P 1.2 g m⁻²) in the richest treatments with organic fertiliser. The capability of S. emersum to use nutrients from high sediment concentrations and in organically polluted environments recommends this species for use in water quality management including tertiary wastewater treatment.     

Evidence of paternal nutrient provisioning to embryos in broad-nosed pipefish Syngnathus typhle

In two experiments, radioactively labelled nutrients (either (3)H-labelled amino-acid mixture or (14)C-labelled glucose) were tube-fed to brooding male Syngnathus typhle. Both nutrients were taken up by the males and radioactivity generally increased in the brood pouch tissue with time. Furthermore, a low but significant increase of (3)H-labelled amino acids in embryos was found over the experimental interval (48 h), whereas in the (14)C-glucose experiment the radioactivity was taken up by the embryos but did not increase over the experimental time (320 min). Uptake of radioisotopes per embryo did not differ with embryo size. A higher uptake mg(-1) tissue of both (3)H-labelled amino acids and (14)C-labelled glucose was found in smaller embryos, possibly due to a higher relative metabolic rate or to a higher surface-area-to-volume ratio compared to larger embryos. Uptake in embryos was not influenced by male size, embryonic developmental advancement or position in the brood pouch. It is concluded that brooding males provide amino acids, and probably also glucose, to the developing embryos in the brood pouch.