Incubation behavior,brood patch formation and obligate brood reduction in Fiordland crested penguins

Summary The first-laid eggs of Eudyptes penguins are much smaller than second eggs, generally hatch later, and experience greater mortality, features that characterize a brood reduction system unlike that of any other avian group. Hypotheses that (1) first-egg mortality is incidental to aggressive behavior by nesting birds and (2) hatching asynchrony is created by preferential egg treatment during incubation were tested in a colony of Fiordland crested penguins (E. pachyrhynchus). Neither hypothesis was supported. Although first eggs experienced greater mortality than second eggs, losses were not associated with aggressive behavior or the degree of nest crowding. First eggs hatched later than second eggs and were found more often in the anterior (previously assumed inferior) nest position. However, that position was not thermally disadvantaged, nor were lower temperatures consistently recorded from the smaller eggs. Parental brood patches did not form until after the first egg was laid; this delay may be a causal factor in the evolution of the unique reversal in eudyptid egg dimorphism.     

Carotenoid-derived ornaments reflect parental quality in male and female yellow-eyed penguins (<Emphasis Type="Italic">Megadyptes antipodes</Emphasis>)

The handicap principle suggests that ornamental traits that function as honest signals in mate selection must be costly to be effective. We evaluated in the sexually monochromatic yellow-eyed penguin (Megadyptes antipodes) whether the carotenoid-derived plumage and eye coloration predicts parental quality and whether males and females within pairs mate assortatively in relation to these carotenoid-derived ornaments. In addition, we investigated whether age or body condition was related to the coloration of the ornamental traits. In yellow-eyed penguins, parental quality of males and females was predicted by eye and head plumage coloration. Even when we controlled for gender- and age-specific differences, eye and head plumage coloration reflected honestly parental quality. Males and females mated assortatively in relation to these ornamental traits. While age influenced coloration of both the eye and head plumage, body condition was related only to the saturation of plumage coloration. These results provide evidence that the carotenoid-derived ornaments in yellow-eyed penguins reflect the parental abilities of birds and, therefore, may be costly signals. Potentially, female and male yellow-eyed penguins could use eye and plumage coloration as an indirect cue in assessing age and quality of individual birds during mate choice. This is only the second study to examine plumage coloration in relation to sexual selection in penguins, while conspicuous ornamental traits in other species of penguin beg the question whether they also play a role in sexual selection.Electronic Supplementary Material Supplementary material is available in the online version of this article at Communicated by C.R. Brown     

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     

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.     

Inter-sexual differences in T-cell-mediated immunity of black-headed gull chicks (<Emphasis Type="Italic">Larus ridibundus</Emphasis>) depend on the hatching order

Hatching asynchrony in avian species leads to age and size differences between nestlings within a brood, handicapping last-hatched chicks in the sibling rivalry. Starvation due to this competitive disadvantage has been regarded as the primary cause of an increase in mortality with hatching order. However, for gulls it has also been suggested that disease is the cause of mortality for last-hatched chicks, possibly through reduced immunocompetence and thereby an enhanced susceptibility to infection. In addition, the male-biased mortality reported for several gull species may be related to a higher vulnerability to diseases in males compared to females. To determine the potential influence of the immune system on these mortality patterns, we investigated the T-cell-mediated immunity (CMI) of black-headed gull chicks in relation to hatching order and sex. We found a significant decrease in the CMI with hatching order. This result may be causally related to systematic changes in maternal yolk steroids and carotenoids within the laying sequence. For second-laid eggs, male CMI was significantly lower than female CMI. This is possibly linked to higher plasma levels of testosterone in male embryos which might have an immunosuppressive effect. If so, this effect is masked in eggs of either high (first egg) or low (last egg) quality. Chicks with low CMI showed enhanced mortality rates. Thus the differences in immune response are likely to contribute to the observed mortality patterns. However, hatching order significantly affected mortality independently of CMI, suggesting that competitive disadvantage due to hatching asynchrony is also important.Communicated by M. Webster     

Resource allocation varies with parental sex and brood size in the asynchronously hatching green-rumped parrotlet (<Emphasis Type="Italic">Forpus passerinus</Emphasis>)

When eggs hatch asynchronously, offspring arising from last-hatched eggs often exhibit a competitive disadvantage compared with their older, larger nestmates. Strong sibling competition might result in a pattern of resource allocation favoring larger nestlings, but active food allocation towards smaller offspring may compensate for the negative effects of asynchronous hatching. We examined patterns of resource allocation by green-rumped parrotlet parents to small and large broods under control and food-supplemented conditions. There was no difference between parents and among brood sizes in visit rate or number of feeds delivered, although females spent marginally more time in the nest than males. Both male and female parents preferentially fed offspring that had a higher begging effort than the remainder of the brood. Mean begging levels did not differ between small and large broods, but smaller offspring begged more than their older nestmates in large broods. Male parents fed small offspring less often in both brood sizes. Female parents fed offspring evenly in small broods, while in large broods they fed smaller offspring more frequently, with the exception of the very last hatched individual. These data suggest male parrotlets exhibit a feeding preference for larger offspring—possibly arising from the outcome of sibling competition—but that females practice active food allocation, particularly in larger brood sizes. These differential patterns of resource allocation between the sexes are consistent with other studies of parrots and may reflect some level of female compensation for the limitations imposed on smaller offspring by hatching asynchrony.     

In vitro reproduction of the turbellarian<Emphasis Type="Italic"> Urastoma cyprinae</Emphasis> isolated from<Emphasis Type="Italic"> Mytilus galloprovincialis</Emphasis>

Urastoma cyprinae is a species infecting the gills of several marine bivalves. Although there is some literature on this turbellarian, its life cycle remains unknown. In our work we have demonstrated that reproduction of U. cyprinae can be completed out of its host. More than 50% of turbellarians isolated from mussels (Mytilus galloprovincialis) secreted and cemented a cocoon to the well bottom during the first 72 h of incubation in seawater (34 salinity) at 14°C. Oviposition started at days 1–18 (average 4.8 days) and occurred in most cases inside the protective cocoon. Each Urastoma laid an average of 2.9 egg capsules (range 1–10) and 3.9 embryos were developed inside each egg capsule (range 1–11). Hatching started at days 20–43 (average 24 days). An average of 12.8 juvenile forms (range 1–64) escaped from the cocoon after hatching. The free-swimming juveniles showed a positive phototactic response and survived about a month after hatching. On the basis of our results, we propose a life cycle for U. cyprinae involving a sexual maturation parasitic period in the bivalve gills and a reproduction period including cocoon secretion, egg laying, and hatching that is entirely completed in the external environment.Communicated by S.A. Poulet, Roscoff     

Intraspecific brood parasitism as a conditional reproductive tactic in the treehopper<Emphasis Type="Italic"> Publilia concava</Emphasis>

In species exhibiting egg guarding as well as communal egg laying, females may adopt the strategy of laying eggs in the nests of conspecifics and leaving without providing care (termed intraspecific brood parasitism). This study is the first to describe such a behavior in the insect Publilia concava (Hemiptera: Membracidae) through field studies that followed 849 marked females across 1,828 brood associations. While brood parasitism increased the total number of eggs in a host brood, it did not reduce the overall hatching success of host broods. Solitary females exhibited a range of guarding durations while parasitic females rarely remained to guard eggs. Females exhibiting the parasitic tactic increased their lifetime number of clutches without decreasing the number of solitary clutches that they were able to initiate. Estimates of egg number for these individual broods revealed that females adopting the parasitic tactic (in addition to solitary breeding) had higher lifetime fecundity relative to females that did not parasitize. In females that exhibited both tactics (solitary and parasitic), the parasitic tactic yielded a higher rate of oviposition. The major component of oviposition rate was the time to find hosts and this time decreased with increasing host availability across 222 replicate groups. Females exhibited a shift toward the parasitic tactic when host broods were more abundant (i.e. in larger groups and later in the season). However, the time to find hosts increased as the frequency of the parasitic tactic increased, suggesting that this tactic may be maintained through negative frequency dependence. The results of this study suggest that brood parasitism may be the preferred tactic, as part of a conditional strategy, when hosts are readily available with solitary breeding being the preferred tactic when hosts are in short supply.     

Otolith size-at-hatch reveals embryonic oxygen consumption in the zebrafish, <Emphasis Type="Italic">Danio rerio</Emphasis>

Otoliths have frequently been used to reconstruct growth histories in larval, juvenile and adult fish. However, there is growing evidence that otolith growth is directly determined by metabolic intensity and, consequently, only indirectly related to somatic growth. By performing measurements of oxygen consumption rate and other early life-history traits on individual eggs of zebrafish (Danio rerio), we found that oxygen consumption explained residual variance in otolith size that is not accounted for by egg size. Total oxygen consumption during the embryonic stage explained 34% of the variance in sagitta size at hatch, whereas larval size at hatch (as a proxy for growth during the embryonic period) was not significantly correlated with sagitta size. This strongly suggests that otolith growth is directly related to metabolic rate, and yields a mechanism that may explain recent observations of a link between otolith size at hatch and viability in larval fish.     

Factors affecting the interval between clutches in the hermit crab <Emphasis Type="Italic">Pagurus nigrivittatus</Emphasis>

Interval between reproductive events is an important factor for iteroparous animals because it determines the number of clutches throughout life. This study examined whether female size, clutch size, shell size and prenuptial molting affected the clutch interval in the hermit crab Pagurus nigrivittatus. Precopulatory guarding pairs of P. nigrivittatus were sampled in the field and kept in the laboratory until the female extruded eggs. The clutch interval of each female was assessed as one of two types of relatively “short” and “long” intervals by checking whether the guarded female had eggs and/or egg cases from the preceding brood or not when the guarding pair was collected. The clutch interval was longer in females with prenuptial molting than those without molting and these females usually grew larger at the prenuptial molt. This suggests that female P. nigrivittatus with a long interval might allocate energy into growth at the expense of the number of clutches during the current reproductive season. The allocation to growth is theoretically predicted to decrease with female size. Gastropod shell size is also known to affect the reproductive activity in hermit crabs. However, female size did not significantly affect the clutch interval in P. nigrivittatus, and the effect of gastropod shell size on clutch interval was not consistent with previous empirical studies. These results may be caused by differences in the gastropod species of shell occupied by the females of P. nigrivittatus.     

Fitness consequences of sexual cannibalism in female<Emphasis Type="Italic"> Argiope bruennichi</Emphasis>

The evolution of sexual cannibalism as the most extreme form of nuptial feeding is still poorly understood. Although increasing evidence suggests that female aggressiveness is related to other aspects of foraging behaviour, it is not clear whether the nutritional value of a male is sufficient to provide an adaptive significance for sexual cannibalism. A widely cited though rarely tested explanation is based on a paternal investment model, and predicts that consumption of a male results in increased female fecundity. The available evidence is either correlational or restricted to species with relatively large and potentially nutritious males, and different studies have come to different conclusions. Here we present a test of the paternal investment hypothesis using the very cannibalistic and highly size-dimorphic spider Argiope bruennichi. After a preset schedule, we had females consume none, one or two males independent of the female's cannibalistic behaviour. Consumption of male bodies did not result in any detectable fitness benefit for the female: neither the number of clutches, nor clutch size or hatching success were affected by consumption of males. The frequency of cannibalism was around 80%, independent of the female mating status. We did not observe male complicity, but cannibalism was associated with prolonged copulation. This suggests a sexually selected benefit of cannibalism for males. We conclude that the paternal investment hypothesis does not explain the existence of sexual cannibalism in A. bruennichi and probably not in other spider species with a pronounced sexual size dimorphism.Communicated by L. Simmons     

Egg coloration in ring-billed gulls (<Emphasis Type="Italic">Larus delawarensis</Emphasis>): a test of the sexual signaling hypothesis

Although many avian eggs appear to be cryptically colored, many species also lay vibrant blue green eggs. This seemingly conspicuous coloration has puzzled biologists since Wallace, as natural selection should favor reduced egg visibility to minimize predation pressure. The sexual signaling hypothesis posits that blue green egg coloration serves as a signal of female quality and that males exert post-mating sexual selection on this trait by investing more in the nests of females laying more intensely blue green eggs. This hypothesis has received mixed support to date, and most previous studies have been conducted in cavity-nesting species where male evaluation of his partner’s egg coloration, relative to that of other females, may be somewhat limited. In this study, we test the sexual signaling hypothesis in colonially nesting ring-billed gulls (Larus delawarensis) where males have ample opportunity to assess their mate’s egg coloration relative to that of other females. We used correlational data and an experimental manipulation to test four assumptions and predictions of the sexual signaling hypothesis: (1) blue green pigmentation should be limiting to females; (2) extent of blue green egg coloration should relate to female quality; (3) extent of blue green egg coloration should relate to offspring quality; and (4) males should provide more care to clutches with higher blue green chroma. Our data provide little support for these predictions of the sexual signaling hypothesis in ring-billed gulls. In light of this and other empirical data, we encourage future studies to consider additional hypotheses for the evolution of blue green egg coloration.     

Egg size and laying order in relation to offspring sex in the extreme sexually size dimorphic brown songlark,<Emphasis Type="Italic"> Cinclorhamphus cruralis</Emphasis>

In some bird species, mothers can advantage the offspring of one sex either by elevating them in the laying order to promote earlier hatching or by allocating greater resources to eggs of the preferred sex. In size dimorphic species, the predictions as to which sex should benefit most from such pre-laying adjustments are ambiguous. The smaller sex would benefit from an initial size advantage to help compensate for the faster growth rate of the larger sex. However, an early advantage to offspring of the larger sex might have a greater effect on their lifetime reproductive success than an equivalent advantage to offspring of the smaller sex. We investigated these hypotheses in the polygynous brown songlark, Cinclorhamphus cruralis, which is one of the most sexually size dimorphic birds known. We conducted within-clutch comparisons and found that females hatched from larger eggs and were initially heavier (but not structurally larger) than their brothers. This may afford females an early competitive advantage, as egg volume remained correlated with chick mass until at least 5 days of age. Similarly, we found that hatch order was still positively associated with nestling mass and size when the brood was 10 days of age, but there was no clear relationship between offspring sex and hatching order. During this study, food was plentiful and there were few obvious cases of nestling starvation. When food is limited, we suggest that the greater nutrient reserves of female hatchlings could not only help compensate for their slower growth, but could also give them a survival advantage over their brothers early in the nestling period. Consequently, egg size dimorphism may be an adaptation that facilitates an early shift in brood sex-ratio towards cheaper daughters in conditions of low food availability.     

Diet of the Humboldt penguin (<Emphasis Type="Italic">Spheniscus humboldti</Emphasis>) in northern and southern Chile

The diet of the Humboldt penguin (Spheniscus humboldti) was examined and compared in two colonies in Chile. Field work was conducted on Pan de Azúcar Island in northern Chile in the breeding season 1998/1999 and on the Puñihuil Islands in southern Chile over two successive breeding seasons during 1997/1998 and 1998/1999. Penguin diet was studied by stomach-pumping birds and analysed by species composition, size and mass of prey. Fish were the dominant prey item at both sites, the contribution of cephalopods and crustaceans varying between sites. The fish prey consisted predominantly of school fish, but there were clear latitudinal differences in fish prey taken. Penguins in the northern colony consumed primarily garfish (Scomberesox saurus), while birds at the southern colony of Puñihuil fed primarily on anchovy (Engraulis ringens), Araucanian herring (Strangomera bentincki) and silverside (Odontesthes regia). The results showed significant differences in terms of numbers of fish taken between the two breeding seasons at Puñihuil. In 1997/1998 penguins consumed almost exclusively anchovy, while they fed primarily on silversides in the successive year. Almost all prey, except stomatopods, were characterised as being pelagic species that occur in relatively inshore water, consistent with the foraging behaviour of Humboldt penguins. The dependence of Humboldt penguins on commercially exploited, schooling prey species makes the species particularly susceptible to changes in prey stocks, due to non-sustainable fisheries management.Communicated by O. Kinne, Oldendorf/Luhe     

Lipid and protein utilisation during early development of yellowtail kingfish (<Emphasis Type="Italic">Seriola lalandi</Emphasis>)

The pelagic yellowtail kingfish Seriola lalandi has become a target species for aquaculture in Asia and Australasia. Australasian production is reliant on larviculture from eggs of captive brood stock; however, knowledge regarding the nutritional requirements of larvae of this species is still scarce, particularly in relation to lipids. As a first step in establishing these requirements, eggs and larvae from captive S. lalandi brood stock were examined for differences in total protein, total lipid and lipid classes between individual spawning events, over the spawning season, and during larval development from fertilisation to 15 days post hatch. Results indicate that total protein egg⁻¹ varied significantly between individual spawning events within a season, but neither total lipid nor total protein egg⁻¹ varied significantly across the spawning season. Brood stock egg lipids were made up of approximately 60% phospholipid, 25% wax and/or sterol esters (WE), 15% triacylglycerol (TAG), and small amounts of sterols and free fatty acids. During the early larval period, both WE and TAG were utilised concurrently for energy. The larvae experienced very high mortality around 5–7 days post hatch, which coincided with very low levels of all neutral lipid classes. Although many other factors may also influence larval mortality, these results indicate that lipid provisioning may be an important factor in larval survival during the critical period around first-feeding in this species. Examination of ratios of TAG:ST, often used as a condition index in fish larvae, suggested that some of the larvae were suffering from starvation. However, as egg-derived WE appears to provide a significant source of energy during the early larval period in S. lalandi, it is suggested that WE should be included in any index of larval nutritional state.     

Sex-specific costs of hatching last: an experimental study on herring gulls (<Emphasis Type="Italic">Larus argentatus</Emphasis>)

An organism’s pattern of development can have important long-term fitness effects. In species where the sexes differ in size or other phenotypic traits, they may also have different optimal developmental rates. This influences both parental sex allocation strategies and susceptibility of the sexes to early developmental conditions. However, sex differences in developmental rate and vulnerability to environment during the embryonic period are not well understood. In birds, sibling competition and hatching asynchrony may select for accelerated embryonic development of the last offspring in order to reduce their competitive disadvantage after hatching. They may advance their hatching in response to vocal stimuli by the older siblings. It is, however, unclear whether this flexibility in developmental rates is sex specific. In this study, we experimentally manipulated between-embryo contact and tested whether this affected the pre-natal developmental rate and post-hatching performance of male and female offspring from last-laid eggs in the herring gull. Post-hatching performance was measured both in competitive and non-competitive situations. Among young incubated in isolation, males hatched faster than females, but both sexes fledged in similar, relatively good condition. Among young incubated with normal between-embryo contact, hatching time did not differ between sexes, but males fledged in poorer condition than females, regardless of whether they were reared singly or in a brood. These results suggest that male and female offspring differ in their ability to mitigate the costs of hatching asynchrony.     

Influence of environmental factors and female size on reproductive output in an invasive temperate marine gastropod <Emphasis Type="Italic">Rapana</Emphasis><Emphasis Type="Italic">venosa</Emphasis> (Muricidae)

Life history and reproductive strategies influence population dynamics at the inter- and intra-specific level. Environmental conditions suitable for gonad development and spawning, the reproductive range, may be a smaller portion of the broader species distribution. The only known breeding population of veined rapa whelks (Rapana venosa) in North America is in Chesapeake Bay, USA. There is considerable interest in the potential reproductive range of this non-indigenous species given the rapa whelk’s negative impacts on commercial shellfish species in both its native and introduced ranges. Weight-specific reproductive output is described for wild caught Chesapeake Bay rapa whelks maintained in flow-through mesocosms for 2 years. Measured reproductive output within and between egg capsule deposition seasons (years) in relation to water temperature, salinity, daylength, and female size is used to describe the rapa whelk’s reproductive range. Egg capsule production is influenced by seasonal and absolute water temperatures as well as seasonal daylength cycles. Egg capsule deposition by Chesapeake Bay rapa whelks begins at water temperatures of approximately 18°C and continues for 11–15 weeks. Forty to 70% of female whelks deposited egg capsules in most weeks during this season, producing 150–200 egg capsules female⁻¹ week⁻¹. Water temperatures >28°C caused reduced egg capsule production relative to temperatures of 20–25°C. Egg capsule production was positively related to seasonal changes in daylength, and two peaks of egg capsule deposition were observed in the 2001 and 2002 deposition seasons. The combination of declining daylength and higher water temperatures in late summer was associated with the cessation of egg capsule deposition. A lower average weight specific reproductive output in 130–145 mm SL rapa whelks (average 12 ± 1%) than in 90–106 mm SL rapa whelks (average 22 ± 1% of body weight) may reflect a life history that balances the physiological costs of maintaining a large body mass with the production of many planktonic larvae from multiple clutches of egg capsules per breeding season over a 10–15-year lifespan. Estimates of the cumulative day-degree requirements corresponding to the annual initiation of egg capsule deposition were 238 and 236 for 2001 and 2002, respectively. Reproductive output and day-degree requirements for Chesapeake Bay rapa whelks were similar to values calculated from previous studies of native muricids (Eupleura caudata and Urosalpinx cinerea). A latitudinal range of 30–41° (N and S) is predicted as the realized reproductive range for rapa whelk populations on the basis of the day-degree requirements for native whelks and reproductively active invasive rapa whelk populations. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Yolk testosterone organizes behavior and male plumage coloration in house sparrows (<Emphasis Type="Italic">Passer domesticus</Emphasis>)

Vertebrate eggs contain maternal steroid hormones in their yolks; and in avian species the concentration of these steroids vary within and among clutches. The organizational actions of these variable doses of maternal steroids in the avian egg, analogous to those regulating the development of sexually dimorphic traits, are little explored. In this study, we examined the organizational effects of yolk testosterone in the house sparrow, Passer domesticus, a sexually dichromatic passerine bird in which males are characterized by the presence of a throat patch or badge of black feathers that varies in size among males. We injected a physiological dose of testosterone or vehicle into eggs in the field, removed nestlings, and hand-raised them in the laboratory. At 5 months of age, we investigated treatment effects on plumage and behavior. Males that hatched from testosterone-injected eggs developed a larger badge than males that hatched from vehicle-injected (control) eggs. However, testosterone did not induce the expression of a badge in females. In staged dyadic encounters, both males and females hatched from testosterone-injected eggs were more successful at obtaining and defending a food source than individuals of the same sex hatched from control eggs. The results suggest that variable concentrations of maternal testosterone in the eggs of the house sparrow organize the expression of a plumage trait in males and behavior in both sexes.Communicated by J. Graves     

Limited population structure in Northern and Spotted Wolffishes (<Emphasis Type="Italic">Anarhichas denticulatus</Emphasis> and <Emphasis Type="Italic">A. minor</Emphasis>) despite low apparent dispersal potential

Northern and Spotted Wolffishes (Anarhichas denticulatus and A. minor) are demersal marine fishes listed as “threatened” in Canadian waters. Both species have unusually large benthic eggs and large size at hatch, which should reduce passive dispersal. We examined population differentiation with microsatellite and AFLP loci across the ranges of both species in the North Atlantic Ocean. Although significant population structure was documented, differentiation was less than expected based on knowledge of life history characteristics. Significant differentiation was found in Northern Wolffish between the Barents Sea and other samples based on both microsatellite and AFLP data. In contrast, population structure in the Spotted Wolffish was notably weaker, particularly with microsatellites. Both species were characterized by low genetic diversity for marine fishes and had significantly lower genetic diversity than the congeneric Atlantic Wolffish. This finding was consistent with the conservation status of these three species and suggests potential vulnerability to over-exploitation in Northern and Spotted Wolffishes.     

The effect of egg versus seston quality on hatching success,naupliar metabolism and survival of <Emphasis Type="Italic">Calanus finmarchicus</Emphasis> in mesocosms dominated by <Emphasis Type="Italic">Phaeocystis</Emphasis> and diatoms

We studied the effect of a developing Skeletonema marinoi/Phaeocystis spp. bloom on Calanus finmarchicus hatching success, early naupliar survival and metabolism. Our focus was (1) on the development of reproductive rates during a bloom initiation, peak and decline in relation to the production of potentially toxic algal metabolites and (2) on the proportional importance of female nutrition versus naupliar food environment for the production of viable nauplii. Despite polyunsaturated aldehyde (PUA) production by both S. marinoi and Phaeocystis sp., we did not observe any harmful effects on hatching success or naupliar survival and condition in any stages of the short-term (<1 week) algal bloom. Hatching success appeared to be controlled by egg lipid composition, while the beneficial effect of a high food concentration was reflected in naupliar RNA:DNA ratio, protein content and total production of viable nauplii. The egg lipids reflected seston lipids, indicating that the egg fatty acid composition was not modified by the females. Our results suggest that unselective feeding and/or retention of specific lipids can induce qualitative food limitation, although recruitment during the S. marinoi/Phaeocystis sp. bloom was high.