Sex ratio manipulation in response to maternal condition in pigeons: evidence for pre-ovulatory follicle selection

A number of recent reports have documented offspring sex ratio biases in birds. However, to date the potential mechanisms that have been put forward to explain the proximate basis for these deviations are entirely speculative. Using a captive population of domestic pigeons (Columba livia domestica), I tested the hypothesis that mothers in relatively poor physical condition should overproduce daughters by manipulating maternal body condition around the time of egg laying by continuous egg removal and differing feeding regimes. During treatment, females were fed a controlled quantity of food. This, combined with the high energetic costs of repeated egg production caused a significant reduction in maternal body weight. In contrast, during control when food was available ad libitum, maternal body weight did not decline, despite repeated egg production. No significant deviation from parity was evident in the sex ratio of either the first or second eggs during control, whereas during treatment a significant female bias was evident in not only the first egg, but also in the second egg. The absence of single-egg clutches, the rarity of infertile eggs and the lack of laying delays between eggs strongly suggests that the mechanism of sex ratio adjustment in pigeons occurs prior to ovulation. The highly skewed sex-distribution within the two-egg clutches and the unexpectedly large amount of variation in the yolk weight of eggs produced during treatment (but not control) are consistent with the expectations of pre-ovulatory selective resorption of wrong sex ovarian follicles.     

Genetic differentiation of populations of the planktonic copepod Labidocera aestiva

Planktonic populations of the calanoid copepod Labidocera aestiva show significant biochemical genetic heterogeneity along the Atlantic coast of the USA. In summer, 1981, copepods were collected by surface tows at Beaufort Inlet, North Carolina; Fort Pierce Inlet, Florida; and Vineyard Sound, Massachusetts. Genetic variation within each population and genetic differentiation among the three populations were studied by micro-acrylamide gel electrophoresis of six loci encoding four enzymes. All six enzyme loci were polymorphic when all populations were considered together, but the North Carolina population was monomorphic at two loci. High genetic variability was indicated by the following: (1) the number of alleles per locus averaged over all loci was 2.57±0.26 SD; (2) the average proportion of loci for which the frequency of the most common allele was not greater than 0.95 was 0.78±0.10; (3) the frequency of heterozygous individuals was 0.25±0.07. Genetic differentiation among population samples in the three regions was demonstrated in several ways: allele frequencies at one aminopeptidase-I locus, Lap-1, differed significantly among samples of the three populations, and there were unique alleles of high frequency at this locus in two population samples. Values of the statistic of genetic distance (D) averaged 0.20±0.08 for pairwise comparisons between all samples. Compared to expected heterozygosity if individuals across the entire range sampled mated at random, there were highly significant heterozygote deficiencies at five of the six loci. Genetic differentiation of populations of L. aestiva may result from (1) differential selection on populations in the three regions, or (2) restricted gene flow between the populations. Gene flow may be limited by geographic separation or differences in life history, such as seasonal presence in the plankton and diapause egg production.Contribution No. 5810 of Woods Hole Oceanographic Institution     

Geographical variation in morphological and electrophoretic characters in the holothurian Cucumaria curata

Both morphological and electrophoretic isozyme variation were examined in Cucumaria curata Cowles, 1907, a common intertidal holothurian of the West Coast of North America. This species has also been described under the name C. pseudocurata Deichmann, 1938. Thirteen populations were sampled. Spicule density, and shape, tentacle size and number of papillae at the male gonopore were determined. Five of the populations were examined for variability in 8 isozymes. Spicule densities varied between populations by more than an order of magnitude. The spicule shapes were the same for all populations although the ratios of the different types varied. No relationship was found between geographical location or habitat and any of the morphological characters. No polymorphisms or variation between populations were found in any of the 8 enzymes analyzed by electrophoresis. However, the morphological data indicate random differentiation between populations. The data indicate the existence of only a single species and thus the name C. pseudocurata should be considered a synonym of C. curata.Contribution No. 2 of the Bodega Marine Sciences Association and PACTREX Report No. 2.     

Fecundity of a euphasiid crustacean,Nematoscelis difficilis,in the North Pacific Ocean

The number, size, and carbon and nitrogen contents of eggs in the pouches of a euphausiid crustacean, Nematoscelis difficilis Hansen, were examined. A clear linear relationship exists between the number of eggs in the pouch and the body weight of the maternal euphausiid. The eggs are not spherical in shape, and the size of eggs is greater in larger egg masses. The carbon content of the egg masses (50.2%) is higher than that of the bodies (40.7%). The carbon: nitrogen ratio (C/N) is also higher in the egg masses than in the bodies of euphausiids. The carbon content of the eggs is equivalent to 28.4% of the body carbon, the nitrogen content to 19.2% of the body nitrogen.     

Egg buoyancy variability in local populations of Atlantic cod (Gadus morhua)

Previous studies have found strong evidences for Atlantic cod (Gadus morhua) egg retention in fjords, which are caused by the combination of vertical salinity structure, estuarine circulation, and egg specific gravity, supporting small-scaled geographical differentiations of local populations. Here, we assess the variability in egg specific gravity for selected local populations of this species, that is, two fjord-spawning populations and one coastal-spawning population from Northern Norway (66–71°N/10–25°E). Eggs were naturally spawned by raised broodstocks (March to April 2009), and egg specific gravity was measured by a density-gradient column. The phenotype of egg specific gravity was similar among the three local populations. However, the associated variability was greater at the individual level than at the population level. The noted gradual decrease in specific gravity from gastrulation to hatching with an increase just before hatching could be a generic pattern in pelagic marine fish eggs. This study provides needed input to adequately understand and model fish egg dispersal.     

Potential latitudinal variation in egg size and number of a geographically widespread reef fish,revealed by common-environment experiments

Variation in maternal reproductive traits was examined in field and reared populations of a geographically widespread reef fish, Pomacentrus coelestis (Pomacentridae), drawn from three different latitudes in Japan. Size-specific clutch size and clutch weight of wild fish increased with increasing latitude. Conversely, latitudinal variation in egg size of wild fish was obscure in same-season comparisons, probably because of the temperature effect on egg size. Common-environment experiments conducted at three temperatures showed that egg size decreased with increasing temperature in all populations. In the experiments, egg size, clutch size and clutch weight differed among populations at all temperatures, showing clear latitudinal clines. Females from low latitude spawned larger eggs at every experimental temperature. Size-specific clutch size and weight were greater in females from high latitude. Thus, the northern fish had a larger reproductive output per spawning and a larger number of smaller eggs in a spawning. Such interpopualtion variation in this fish is likely to be partially genetically based, although environmental effects on the variation cannot be entirely ruled out. This study provides evidence of potential latitudinal variation in the egg size and number in a coastal fish, by common-environment experiments. The close correspondence between latitudes and these maternal reproductive traits may be a consequence of local adaptation.     

Relationship between egg features and maternal body size in the simultaneous hermaphrodite <Emphasis Type="Italic">Oxynoe olivacea</Emphasis> (Mollusca,Opisthobranchia, Sacoglossa)

This paper provides information on spawn morphology and egg features of the stenophagous planktotrophic Mediterranean sacoglossan Oxynoe olivacea. Smith and Fretwell’s hypothesis, predicting that individuals of the same population growing in the same environmental conditions and varying in size should spawn eggs of a constant size, was tested in a population of O. olivacea living in the Straits of Messina. To determine whether (a) spawn mass size, (b) total egg number per spawn, and (c) egg size were related to parent size of O. olivacea, 21 egg masses (seven egg masses deposited by seven different 20 mm animals, seven egg masses deposited by seven different 25 mm animals and seven egg masses by seven different 30 mm animals) were randomly chosen and examined. Results showed that both spawn mass width and number of eggs per spawn mass increased across O. olivacea body size and apart from the significant variation of the short capsule diameter, there was no consistent variation of egg features in O. olivacea. In conclusion the species allocates constant amounts of energy to individual embryos and thus supports the prediction designed by Smith and Fretwell.     

Fecundity and spawning in a deep-water cirromorph octopus

 Reproductive characteristics of cirromorph octopuses, assigned to the species Opisthoteuthis grimaldii, were sampled as a commercial fishing by-catch on the Hebrides Slope, west of Scotland. A total of 254 specimens (99 female, 155 males), retrieved from bottom trawls fished at 750 to 1500 m depth, were examined. A maximum of 2097 eggs was counted in a single female ovary (mean female body weight 1242.8 g), most of them <1 mm in length. At egg lengths over 1 mm, diminishing numbers of eggs were present in 1 mm size categories up to a maximum of ≈10 mm. At body sizes >500 g (wet wt), and in every female >750 g (max. female weight recorded in the sample was 2959 g), a succession of unattached eggs was present in the proximal oviduct and a single, unattached mature egg occupied the tip of the distal oviduct. These females were assumed to be in spawning condition and the characteristics of egg distribution in the reproductive tract to be consistent with sequential release of individual eggs and continuous spawning throughout the growth period and lifespan of the mature octopus. In pre-spawning females there was a positive relationship between estimated egg numbers and maximum egg size. After the onset of spawning there was no significant further increase in estimated potential fecundity over the body-size range 500 to 3000 g. Follicular sheaths remaining in the ovary after release of eggs into the proximal oviduct were counted and used to estimate the total number of eggs released up to the time of capture. Follicular sheaths first appeared at 500 to 650 g body weight and increased steeply in number to >1000 in females >1500 g. Two individuals were found with ovarian follicular sheaths but with no terminal egg in the distal oviduct; these were assumed to have released their egg just before capture. Summation of the number of follicular sheaths counted plus the number of eggs estimated as remaining attached in the ovisac, provided a revised estimate of total potential fecundity and raised the estimate for any individual to a maximum of 3202 eggs (mean = 1396 eggs). Received: 3 February 2000 / Accepted: 17 May 2000     

Ovarian development and spawning in relation to the moult cycle in Northern krill, Meganyctiphanes norvegica (Crustacea: Euphausiacea), along a climatic gradient

Adaptive processes linked to reproduction were studied comparatively for three populations of Northern krill, Meganyctiphanes norvegica (M. Sars, 1857), sampled during winter and summer cruises in the Clyde Sea (W Scotland), the Kattegat (E Denmark), and the Ligurian Sea (NW Mediterranean). The aim was to investigate the functional relationship between egg production and moulting under contrasted climatic and environmental conditions. A staging system for female sexual development established for live krill was complemented by a histological study of the ovary at various developmental steps. During the reproductive season, all adult female krill were engaged in cyclical egg production. During experiments, female krill released one batch of mature oocytes in one or two spawning events. The ovary of postspawn female krill still contained developing oocytes for another egg batch. In the non-reproductive period, all female krill had a resting ovary. Ovarian structure and pattern of egg production were identical in the three populations, but seasonal timing of egg production was different. The model proposed for the Ligurian population of the annual cycle of ovarian development can be extended to the other two populations, taking into account the seasonal characteristics of each site. Random field samples were staged simultaneously for moult cycle and for sexual development. Moult stages and the seasonal variation of the intermoult period were studied for the Kattegat population using multi-year data and compared to data obtained during summer/winter cruises in the Clyde and the Ligurian Sea. At the three sites, intermoult period was shorter and temperature-dependent during the reproductive period, concurrent with the season of greatest food availability. During most of the year and the period of sexual rest, moulting activity was reduced. The relationship between spawning and the moult cycle was studied comparatively for the three populations. Eggs were released during the premoult phase of a “spawning moult cycle”, in one or two spawnings associated with apolysis and Moult Stage D1, respectively. Yolk accumulation for the next egg batch was completed during an alternating “vitellogenic moult cycle”. A model for the timing of cyclical egg production in relation to moulting, as proposed for the Kattegat, can be extended to the other populations, taking into account intermoult period variation with temperature. Temperature appeared to be the principal environmental factor controlling growth (through moulting) and egg production during the reproductive season, in connection with favourable trophic conditions. Received: 22 December 1997 / Accepted: 29 August 1998     

Influence of body size on the uptake,depuration, and bioaccumulation of polychlorinated biphenyl congeners by Baltic Sea blue mussels,Mytilus edulis

The present study was designed to examine the influence of body size on the bioaccumulation of polychlorinated biphenyl (PCB) congeners by Baltic Sea blue mussels, Mytilus edulis L. This was done, firstly, by establishing the relationship (as a power function: PCB tissue conc = a tissue dry wt^b) between tissue concentration and body weight for seven PCB congeners (International Union of Pure and Applied Chemistry No. 52, 101, 105, 118, 138, 153, and 180) in field sampled mussels; and, secondly, by assessing the influence of body weight on the uptake clearance coefficients, the depuration rate coefficients and the calculated bioaccumulation factors (BAFs) of three ¹⁴C-labelled PCB congeners (IUPAC No. 31, 49, 153) in mechanistic kinetic experiments. Both the background tissue concentrations of PCB 138, PCB 153 and PCB 180 and the predicted BAF values in the kinetic experiments correlated negatively with body weight (b=-0.17 and-0.31, respectively). Of the two kinetic rate coefficients examined, only the uptake clearance rate showed weight dependency (b=-0.32, i.e. negative correlation with body weight), whereas depuration rates were unaffectd by body weight. Uptake clearance rates and BAFs adjusted for body weight increased with the octanol/water partition coefficient (K_ow) of the congener, whereas depuration rates dectreased with K_ow. These observations suggest that size-dependent bioaccumulation of hydrophobic organic contaminants (HOCs) in suspension-feeding bivalves is driven by size-related differences in uptake rate, although several other mechanisms may also affect bioaccumulation in natural mussel beds (e.g. sizerelated differences in lipid content, production, and contaminant exposure). From an ecotoxicological perspective size-dependent bioaccumulation implies not only that variability due to body size differences has to be dealt with in experimental designs, but also that several ecological factors such as size-specific predation and shifts in population structure may affect HOC cycling by dense populations of bivalve suspensionfeeders.     

Size at maturity,fecundity and reproductive potential of a protected population of the spiny lobster<Emphasis Type="Italic"> Palinurus elephas</Emphasis> (Fabricius, 1787) from the western Mediterranean

Protected lobster populations are expected to contribute to the replenishment of fished populations through increased egg production. We studied the reproductive biology and egg production potential of a population of the spiny lobster Palinurus elephas protected from fishing since 1990 in the Columbretes Islands Marine Reserve (western Mediterranean). An index of spawning potential was derived to compare egg production potential in the Reserve and in western Mediterranean exploited populations. Females' physiological maturity (ability to reproduce) and functional maturity (ability to mate and bear eggs) occurred at a carapace length (CL) of 76–77 mm. Males' physiological maturity occurred at a slightly larger size, 82.5 mm CL. In the Reserve, P. elephas' individual fecundity increases linearly with body size up to the females' maximum size, although maximum reproductive yield (eggs per body gram) was reached at intermediate sizes. Size-specific fecundity in the protected population was similar to that of lightly fished populations off Ireland and greater than that of western Mediterranean exploited populations. The female size class of 105–110 mm CL contributed most to egg production in the protected population and is well above the minimum landing size (MLS) for western Mediterranean fisheries. Newly mature females (below MLS) generate a very small fraction (1%) of the egg production from the Reserve. Given the pattern of exploitation in western Mediterranean fisheries, egg production potential depends more on the quantity than on the mean size and fecundity of the available females. The role of the greater availability of large males for mating in unfished populations is discussed in terms of the females' individual fecundity and mating success.     

Food and predators affect egg production in song sparrows

Although the possibility that food and predators may interact in limiting avian populations has long been recognized, there have been few attempts to test this experimentally in the field. We conducted a manipulative food addition experiment on the demography of Song Sparrows (Melospiza melodia) across sites that varied in predator abundance, near Victoria, British Columbia, Canada, over three consecutive breeding seasons. We previously showed that food and predators had interactive effects on annual reproductive success (young fledged per female). Here, we report the effects on egg production. Our results show that food limits the total number of eggs laid over the breeding season ("total egg production") and that interactive food and predator effects, including food effects on nest predation, determine how those eggs are "parceled out" into different nests. Food addition alone significantly affected total egg production, and there was no significant interannual variability in this result. At the same time, both food and predators affected the two determinants of total egg production: "clutch number" (total number of clutches laid) and average clutch size. Both clutch number and size were affected by a food x predator x year interaction. Clutch number was lower at low-predator locations because there was less nest predation and thus less renesting. Food addition also significantly reduced nest predation, but there was significant interannual variation in this effect. This interannual variation was responsible for the food x predator x year interactions because the larger the effect of food on nest predation in a given year, the smaller was the effect of food on clutch number; and the smaller the effect of food on clutch number, the larger was the effect of food on clutch size. Potential predator and year effects on total egg production were thus cancelled out by an inverse relationship between clutch number and clutch size. We suggest that combined food and predator effects on demography could be the norm in both birds and mammals.     

Reproductive biology of the common shrimp Crangon crangon (Decapoda: Crangonidae) in the central Irish Sea

Aspects of the reproductive biology of the common shrimp Crangon crangon (L.) were studied in Port Erin Bay, Isle of Man, Irish Sea. Size at sexual maturity was determined from the proportions of ovigerous females and of females with maturing ovaries. The size at which 50% of females are mature is estimated (±95% confidence intervals) as 12.5±0.48 mm carapace length. Based on the proportions of ovigerous females and of mature females, the main breeding season was from January to June. Mean ovarian dry weights indicated two broods (winter and summer), with females bearing winter broods (WB) having higher gonad indices than those with summer broods (SB). WB females with non-eyed eggs and with eyed eggs differed in the regression of ovarian dry weight on carapace length, indicating preparation for laying a second brood. In both broods the moult stages of berried females were related to egg stage. Moulting will occur following the release of the brood. During embryonic development, mean egg length and egg volume were larger in all stages, and the mean dry weight of individual eggs of all stages heavier, in WB than in SB; there was no difference in egg number, however. Consequently, reproductive investment, the proportion of female weight devoted to egg production, was 67% higher in WB (0.20±0.04) than in SB (0.12±0.03). There is a significant effect of egg volume on brood weight, but not on egg number. In both broods, egg number was a negatively allometric function of female body size in non-eyed eggs and an isometric function of female body size in eyed eggs. Brood mortality during incubation was higher in SB (17%) than WB (10%). Differences in the reproductive variables and investment between the two broods of C. crangon are discussed in the light of reproductive strategies and life history.Communicated by J.P. Thorpe, Port Erin     

Born to lose. I. Measures of tissue loss and regeneration by the brittlestar Microphiopholis gracillima (Echinodermata: Ophiuroidea)

To measure amounts of tissue lost in natural populations of the burrowing amphiurid ophiuroid Microphiopholis gracillima (Stimpson), individuals were collected from subtidal mud flats in North Inlet, South Carolina, USA, at monthly intervals between February 1985–February 1987 and December 1989–November 1990. Between 20 and 70% of all individuals were regenerating the disc, and 85% of the 2045 arms examined had regeneration scars; >50% had one scar and some arms had up to 4 scars. Fewer individuals were regenerating discs in warmer months, but there was no seasonality in arm-loss frequency. To quantify rates of arm regeneration in the field, individuals which had 1, 2, or 3 arms removed were placed in mud-filled cores in the field in late July and November 1988 and in March and May 1989, and recovered after periods of about one month. Another set of cores was held in a running seawater laboratory during the May 1989 experiment. No regeneration occurred during the cooler times of year (November and March), and rates of regeneration were slower in May (total: 0.13 mg/d; tissue: 0.03 mg/d) than July (total: 0.17 mg/d; tissue: 0.05 mg/d). These rates indicate complete replacement of lost tissue in 100 to 120 d during the growth season. Within experiments, per arm regeneration rates were similar regardless of the number of arms removed. This finding is complicated by small sample size, high variability and low statistical power, but in general individuals which lost 2 or 3 arms regenerated proportionally more tissue than individuals which lost 1 arm. Individuals held in the laboratory regenerated the same amount of tissue but 30% less skeleton than individuals in the field. Sublethal tissue loss is common in this population, and M. gracillima is capable of regenerating at least 50% (each arm=17% of total body weight x 3) of its standing crop in a single growing season. Burrowing brittlestars probably constitute a significant renewable energy source for higher trophic levels in areas where they occur in dense populations.     

Factors affecting the spawning period of sardine in two highly oligotrophic Seas

Ovarian histology and weight dynamics of reproductive and somatic tissues were used to investigate seasonality of spawning and factors affecting reproductive period in two E Mediterranean sardine, Sardina pilchardus, populations (central Aegean and Ionian Seas), between September 1999 and May 2001. Despite similarities in the general spawning pattern of the two populations, i.e. protracted spawning season during the colder months of the year, reproductive period in the Ionian was shorter and lagged behind the Aegean by 2–3 months. In both Seas, reproductive period was influenced by body size as smaller females tended to have both shorter and delayed spawning season. Whereas hepatosomatic index (HSI) was consistently higher in reproductively active females during the whole spawning period, seasonality of spawning did not match variations of HSI. In both Seas fluctuations of HSI matched the spring burst of primary productivity and were followed by fluctuations in somatic condition and mesenteric fat by a 2 months’ lag. Somatic condition and reproductive activity displayed inverse seasonal patterns, implying that egg production in sardine basically relies on visceral and muscular fat deposits, accumulated during the summer growing season. Reliance of egg production on past energetic reserves suggests that sardine is a capital breeder, which is a rather efficient strategy in such oligotrophic habitats as the E Mediterranean, where winter spawning is accompanied by a particular decline in adult preying fields.     

Effects of shell utilization on reproductive patterns in tropical hermit crabs

Dittoral and sublittoral hermit crabs (Coenobita clypeatus, Clibanarius tricolor, Calcinus dibicen, Petrochirus diogenes, Paguristes grayi, Pagurus miamensis, Paguristes tortugae, Paguristes cadenati and Pagurus sp.) were studied on Lighthouse Atoll, Belize. The Clibanarius tricolor population differed markedly in mean clutch size from congeneric populations at temperate latitudes and from conspecific populations in the Florida Keys. These differences can be attributed primarily to variation in shell utilization pattern, overlap with competitors, and breeding season. Regression analyses indicate that shell weight but not internal shell volume affects the clutch size of C. tricolor in Belize, probably due to selection for optimum volume resulting in the use of broken and encrusted shells with high weight: volume ratios. Both egg size and clutch size differed significantly among egg developmental stages in C. tricolor, Calcinus tibicen, and Pagurus miamensis.     

Brood size and chemical composition of Pareuchaeta norvegica (Crustacea: Copepoda) in Loch Etive,Scotland

Brood size and chemical composition (carbon, nitrogen, and ash) of Pareuchaeta norvegica in Loch Etive, Scotland have been determined. From 23 to 37 eggs were found in each egg mass (mean=30 eggs). The eggs are oval; the mean size of the longer axis is 438 m. Variation in egg mass (as dry weight) is related to increase in dry weight of the maternal body. an increase of 1 mg in maternal body dry weight produces an increase of 0.03 mg dry weight in the egg mass. Carbon content increases with increasing body dry weight both in pre-spawning and spent females, but nitrogen content decreases with increasing body weight. Thus, the carbon:nitrogen ratio increases with increasing body dry weight. The carbon content of an egg mass ranges from 61.4 to 65.3%, and nitrogen content from 9.6 to 13.2% of the total dry weight. Some examples of partitioning of chemical components of the maternal body into the egg mass are also described.     

Annual population development and production by small copepods in Disko Bay,western Greenland

The population of small copepod species (approximately <1 mm) were investigated during an annual cycle in Disko Bay, western Greenland. The small species considered were Acartia longiremis, Pseudocalanus spp., Oithona spp., Oncaea spp., Microsetella spp., and Microcalanus spp. Most of the small species were present in the surface waters year round and numerically dominated the community, and in biomass from late summer and throughout winter. Oithona spp. was numerically the main contributor, while Pseudocalanus spp. dominated in terms of biomass. In the uppermost 50 m, maximum abundance, biomass and secondary production were observed in late September after the phytoplankton production practically had terminated and the winter initiated. The free spawning Acartia longiremis showed a strong seasonal fluctuation in biomass and egg production, in contrast to the egg carrying species Pseudocalanus spp. and Oithona spp. These had a long spawning season and maintained a more stable biomass year round. Secondary production was estimated by three different ways: (1) based on the obtained specific egg production rates, (2) a temperature dependent equation, and (3) a multilinear regression taking temperature, body weight and chlorophyll into consideration. The contribution of the small species was insignificant when compared to the large Calanus species during the spring- and post-bloom. However, during late summer and winter, where Calanus had left the upper water strata for hibernation, the small species played a crucial role in the pelagic carbon cycling.     

Population structure and energetics of the shallow-water antarctic sea star Odontaster validus in contrasting habitats

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.     

Prelaying maternal condition modifies the association between egg mass and T cell-mediated immunity in kestrels

Theoretical models of parental care predict differential allocation in relation to the expected fitness of the offspring. As birds must allocate all the resources required for embryonic development in self-contained packages, maternal egg allocation takes a central role in avian life histories. It is predicted that mothers can influence offspring performance by varying the size or composition of their eggs. In this context, T cell-mediated immune response has been revealed as a valuable tool to evaluate fledgling fitness. However, little is known about its relationships to egg mass. I describe a negative association between egg mass and cellular immune response in Eurasian kestrel nestlings (Falco tinnunculus) throughout 3 years. To explore how environmental conditions could mediate this relationship, I experimentally supplied food to females before egg formation in the third study year. I found that this relationship turned to positive in food-supplied females without any effect on egg size. This result shows that environmental conditions before egg formation mediate the relationship between egg mass and future immune response of the nestlings. I suggest that females may be constrained in improving the future immune response of their offspring due to resource allocation trade-offs determined by their pre-laying condition.