Energy For Egg Production Research Articles

Summer variability of reproductive pattern in the marine cladoceran Evadne nordmanni in Arctic waters

This paper analyses the spatial distribution and some aspects of the reproductive biology of the common marine cladoceran Evadne nordmanni in the southern Barents Sea. Samples were collected in summer seasons at four coastal sites off the Kola Peninsula. The numerical occurrence of E. nordmanni as a percentage of total mesozooplankton abundance ranged between 0.03 and 63%. Maximum population density was recorded in shallow water locations with high water temperature. Non-breeding females and juveniles dominated all study sites. Relative abundances of males, parthenogenetic females and gamogenetic females were low and never exceeded 10% of the total population density. Canonical Correspondence Analysis revealed significant influences of surface temperature and sampling depth on the distribution of E. nordmanni. Mean body length of gamogenetic females was higher than those of parthenogenetic females. Mean fecundity of parthenogenetic females was rather stable across the study locations (8.3 ± 0.1 late-stage embryos per female). The average size of late-stage embryos varied between 121 μm and 165 μm. Positive correlations between the average size of late-stage embryos/fecundity and female body length were found suggesting that larger females invest more energy in egg production. The species is well adapted to Arctic conditions in the southern Barents Sea. It is more likely that E. nordmanni reproduces intensively in late spring and continues into September.

Warm temperatures during cold season can negatively affect adult survival in an alpine bird.

Climate seasonality is a predominant constraint on the lifecycles of species in alpine and polar biomes. Assessing the response of these species to climate change thus requires taking into account seasonal constraints on populations. However, interactions between seasonality, weather fluctuations, and population parameters remain poorly explored as they require long‐term studies with high sampling frequency. This study investigated the influence of environmental covariates on the demography of a corvid species, the alpine chough Pyrrhocorax graculus, in the highly seasonal environment of the Mont Blanc region. In two steps, we estimated: (1) the seasonal survival of categories of individuals based on their age, sex, etc., (2) the effect of environmental covariates on seasonal survival. We hypothesized that the cold season—and more specifically, the end of the cold season (spring)—would be a critical period for individuals, and we expected that weather and individual covariates would influence survival variation during critical periods. We found that while spring was a critical season for adult female survival, it was not for males. This is likely because females are dominated by males at feeding sites during snowy seasons (winter and spring), and additionally must invest energy in egg production. When conditions were not favorable, which seemed to happen when the cold season was warmer than usual, females probably reached their physiological limits. Surprisingly, adult survival was higher at the beginning of the cold season than in summer, which may result from adaptation to harsh weather in alpine and polar vertebrates. This hypothesis could be confirmed by testing it with larger sets of populations. This first seasonal analysis of individual survival over the full life cycle in a sedentary alpine bird shows that including seasonality in demographic investigations is crucial to better understand the potential impacts of climate change on cold ecosystems.

Changes in Isotopic Niches across Stages of the Annual Cycle in the Arctic Tern (<i>Sterna paradisaea</i>)

Arctic Terns (Sterna paradisaea) are iconic seabirds of polar latitudes, whose successful reproduction is thought to depend on local food supplies near breeding colonies. We used stable isotopes of carbon and nitrogen in eggs, blood, and feathers of terns breeding in the Canadian High Arctic to compare their isotopic niche between life history stages and between two years. The isotopic niche of terns was smaller during incubation than during pre-breeding or winter. Over two breeding seasons, isotopic profiles of Arctic Terns suggested the high importance of local, exogenous nutrient supplies to form eggs (i.e., an income breeding strategy). Our results illustrate that using stable isotopes to assess the niche of a seabird population during critical periods of its annual cycle could be an essential tool in determining the influence that local forage conditions have on breeding decisions, especially for species that mostly rely on exogenous sources of nutrients and energy for egg production.

Energy expenditure for egg production in arthropod ectoparasites: the effect of host species

We studied the energy cost of egg production in two flea species (Parapulex chephrenis and Xenopsylla ramesis) feeding on principal (Acomys cahirinus and Meriones crassus, respectively) and auxiliary (M. crassus and A. cahirinus, respectively) rodent hosts. We predicted that fleas feeding on principal as compared with auxiliary hosts will (a) expend less energy for egg production; (b) produce larger eggs and (c) live longer after oviposition. Both fleas produced more eggs and spent less energy per egg when exploiting principal hosts. Parapulex chephrenis produced larger eggs after exploiting auxiliary hosts, while the opposite was true for X. ramesis. After oviposition, P. chephrenis fed on the auxiliary hosts survived for a shorter time than those fed on the principal hosts, while in X. ramesis the survival time did not differ among hosts. Our results suggested that one of the proximate causes for lower reproductive performance and subsequent lower abundance of fleas on auxiliary hosts is the higher energy cost of egg production. However, in some species, lower offspring number may be compensated to some extent by their size, although this compensation may also compromise their future reproduction via decreased survival. In addition, the reproductive strategy of exploitation of low profitable (i.e. auxiliary) hosts may differ between flea species.

The size and shape of shells used by hermit crabs: A multivariate analysis of Clibanarius erythropus

Shell attributes such as weight and shape affect the reproduction, growth, predator avoidance and behaviour of several hermit crab species. Although the importance of these attributes has been extensively investigated, it is still difficult to assess the relative role of size and shape. Multivariate techniques allow concise and efficient quantitative analysis of these multidimensional properties, and this paper aims to understand their role in determining patterns of hermit crab shell use. To this end, a multivariate approach based on a combination of size-unconstrained (shape) PCA and RDA ordination was used to model the biometrics of southern Mediterranean Clibanarius erythropus populations and their shells. Patterns of shell utilization and morphological gradients demonstrate that size is more important than shape, probably due to the limited availability of empty shells in the environment. The shape (e.g. the degree of shell elongation) and weight of inhabited shells vary considerably in both female and male crabs. However, these variations are clearly accounted for by crab biometrics in males only. On the basis of statistical evidence and findings from past studies, it is hypothesized that larger males of adequate size and strength have access to the larger, heavier and relatively more available shells of the globose Osilinus turbinatus, which cannot be used by average-sized males or by females investing energy in egg production. This greater availability allows larger males to select more suitable shapes.

Intersexual niche segregation in Cepero’s Ground-hopper, Tetrix ceperoi

Sexual differences in habitat preferences have been reported from a variety of animal taxa. However, the ultimate causes for this intersexual niche segregation remain poorly understood. It has been suggested that sexual dimorphism is a consequence of dimorphic niches based upon different reproductive costs and activities of the sexes. Here we provide evidence from field data to examine this hypothesis by studying the behavioral background of niche segregation in Tetrix ceperoi. Our data revealed distinct sexual differences in the substrates on which the insects perched and in the solar radiation of these locations. Males were found at brighter locations and more often on bare ground than females. Incorporation of behavioral data in our analysis showed that patches of bare ground were mainly utilized during mating behavior, in which males invested more time than females. In contrast, females spent more time resting and feeding in the vegetation. Intersexual differences in the proportion of autotomized individuals indicate that males might suffer higher predation risks. These patterns support the dimorphic niches hypothesis, which suggests that differential habitat utilization is caused by differences in the life history strategies of males and females, since males should accept a higher predation risk due to the benefits of multiple matings. Females should invest more time in gaining nutrients and energy for egg production and survival, whereas males should spend more time with searching for mates. We suggest that behavioral covariates should more often be implemented in ecological analyses, since these might have a strong explanatory power.

Phenotypic Plasticity in the Reproductive Behavior of Female Sand Tilefish, Malacanthus plumieri

Female sand tilefish (Malacanthus plumieri) inhabiting a deep channel in the fringing reef at Glover's Atoll, Belize (channel females) spawned planktonic eggs more frequently than those occupying the shallow sand-rubble slopes adjacent to patch coral reefs inside the atoll lagoon (reef-slope females). We tested five non-exclusive hypotheses to explain habitat differences in female spawning frequency. We found no evidence that spawning frequency variation was a consequence of differences in food availability, variation in male fertility, or the intensity of predation on spawned eggs. On reef slopes, barracuda stalked tilefish near their benthic burrows, whereas these piscivores attacked channel tilefish by diving suddenly from higher in the water column. Differences in the hunting behavior of barracuda suggested that the behavior of tilefish females might be influenced by temporal variation in predation risk (risk allocation hypothesis). Consistent with this hypothesis, reef-slope females had a much higher frequency of retreats to burrows in response to barracuda, spent more time burrowing and ventured less far from these refugia in response to a simulated predatory threat. As predicted by the risk allocation hypothesis, reef-slope females also had lower and more variable frequencies of foraging bites, and shorter and more variable travel distances to forage than channel females. Estimated mortality from predation was over nine times higher in channel tilefish. Consistent with the hypothesis that investment in current vs. future reproduction is influenced by rates of adult mortality (mortality risk hypothesis), channel females invested more supplemental energy in egg production whereas reef-slope females invested more in growth. Our results indicate that behavioral and life-history traits of female tilefish show phenotypic plasticity depending upon the nature and intensity of localized predation risk.

Time of Breeding in Relation to Food Availability of Female Great Blue Herons (Ardea herodias)

-I examined the hypotheses that Great Blue Herons (Ardea herodias) began breeding in spring shortly after acquiring enough food to make eggs, or so that chicks were in nests when food was most plentiful. Egg laying began about nine days after a female's daily food intake crossed an estimated energy threshold of 1,715 kJ/day. In contrast, the peak in availability of food energy to adults occurred at least 26 days before the peak food demands of their chicks. The estimated food energy intake by adults increased gradually in March and April with increasing duration of low tides and the inshore movement of fishes. Adult food energy intake reached a peak in May when shiner seaperch (Cymatogaster agreggata) were most abundant, and diminished through June and July. Received 9 January 1992, accepted 11 April 1993. LACK (1954) POSTULATED that natural selection favors adults whose nestlings are present when food is most available to the parents. This hypothesis predicts that early and late nesters should fare less well than those nesting on the average date. Several studies have supported Lack's (1954) hypothesis (see review by Perrins and Birkhead 1983), but early clutches in other species are often the most productive (e.g. Cave 1968, Davies and Lundberg 1985, but see Noordwijk et al. 1981). Alternatively, Perrins (1965, 1970) proposed that food shortages during egg laying prevent most females from breeding as early as Lack predicted so that young would be in the nest after the parents' food supplies had peaked. Several studies suggest that females breed when food becomes plentiful (Drent and Daan 1980, Daan et al. 1988), but it is not clear whether most young are in nests when food is increasing or decreasing in abundance (see Daan et al. 1988). Tests of Lack's (1954) and Perrins' (1965, 1970) hypotheses have been hampered by methodological problems. Most studies have used the abundance of food at foraging sites as an index of food availability to the parents rather than measuring food availability itself (see definitions in Daan et al. 1988). Moreover, these hypotheses assume that food is in short supply to the egg-laying female (Perrins 1965, 1970) or adults with nestlings (Lack 1954), although many studies have found that breeding birds are not short of food (see reviews by Martin 1987, Linden and M0ller 1989). A suitable species in which to compare timing of breeding is one in which both food availability and prey consumption can be measured directly. The Great Blue Heron is a suitable species because: (1) it eats fish whose populations can be sampled with beach-seine nets; and (2) its rate of consumption of fish can be estimated (Simpson 1984, Bayer 1985). The aim of my paper is to relate the seasonal availability of food energy to heron time of breeding. First, I estimate the relative availability of prey energy to adult herons at three points in time-when they have eggs, small chicks and large chicks. I then examine whether critical food shortages occur by comparing estimates of food energy consumption on the foraging grounds by breeding adults with those of an average-sized brood of heron chicks in the nest. Next, I evaluate the hypotheses that: (1) females begin to lay eggs after a threshold of available energy for egg production has been passed (Perrins 1965, 1970); and (2) chicks are in the nest when food for adults is most plentiful (Lack 1954). STUDY AREA AND METHODS Fieldwork.-I studied a colony of 85 to 100 pairs of herons from 21 March to 24 September 1987, and 21 February to 18 August 1988 on Sidney Island (48?40'N, 123?20'W), about 4 km east of the town of Sidney and 23 km ENE of Victoria, British Columbia. Sidney Island is mostly covered in second-growth Douglas fir (Pseudotsuga menziesii). The herons nested in red alder (Alnus rubra) trees. Littoral drift has created a lagoon (ca. 100 ha) in which most herons fed each day. The first part of the lagoon exposed by falling tides is a salt-marsh community dominated by Salicornia virginica and Distichlis spicata. Herons used this marsh as a

Efficiency of utilization of energy for egg production in feed-restricted single comb White Leghorn hens

SummaryEgg production and body mass changes were measured in six groups, each containing 10 single comb White Leghorn (SCWL) hens, in which each group received decreasing amounts of dry matter (D.M.) in decrements of 10%. Group 1 received 101·2 g D.M./day (100%), an amount normally offered these hens, whereas group 6 received 52·8 g D.M./day (50%). Egg production remained relatively high but body mass declined rapidly in the feed-restricted groups when compared with group 1 in the first 4 weeks (period I); in the second 4 weeks (period II), egg production declined to a great extent but body mass remained constant. Egg production and egg mass were significantly lower in period II than in period I in the feed-restricted birds. In period I egg production did not decrease significantly until the hens were restricted in feed by 30%; in period II this occurred at 20% feed restriction. Energy of eggs produced as a fraction of metabolizable energy intake (MEI) tended to increase in the feed-restricted groups when compared with group I in period I, but decreased significantly at the 40% and 50% group in period II. Maintenance energy requirements for the hens were 569·2 kJ/kg0·75per day and the efficiency of utilization of energy for egg production was 88·2% in period I; these values were 551·6 kJ/kg0·75per day and 74·0%, respectively, in period II. Energy yielded from the catabolism of body tissue per gram body mass loss was 23·08 kJ.It was concluded that the hens initially maintained near-normal egg production at the expense of body energy reserves and then at the expense of egg mass. The efficiency of utilization of energy for egg production was higher when the energy source was mainly from body energy reserves than from MEI (88·2% v. 74·0%). The level of feed restriction and its length of imposition, the body energy reserves of the hen and the source of energy for egg production can explain many of the different responses reported in feed-restricted laying hens. In addition, reduction of 20 to 30 % feed intake in laying hens had little effect on egg production for a short period (4 weeks) during which time the hens mobilized body energy reserves. If these hens were to be sold, then this would add an additional option to this enterprise; that is, reduce feed cost at the expense of body mass prior to the sale of the hens.

Effects of Unilateral Eyestalk Ablation on Moulting, Growth, Reproduction and Energy Budget of Macrobrachium nobilii

Unilateral eyestalk ablation in juvenile Macrobrachium nobilii advanced the onset of sexual maturity by 88 days. During a 330.day experiment, ablated prawns undertook nine moults as adults, carried seven clutches and produced an average of 6,935 eggs. Nonablated prawns undertook four moults as adults, carried three clutches and produced only 2,042 eggs. Ablated female prawns allocated more energy for egg production than did nonablated females (0.98 J egg-1 and 0.72 J egg-1, respectively); this was accomplished by an improvement of food conversion efficiency in ablated females.

Effects of feeding regime on energy allocation to reproduction in the silkwormBombyx mori

Pattern of energy allocation for reproduction was studied as a function of feeding regimes in the silkwormBombyx mori. The larvae were restricted to feed for 6, 12, 18 or 24 h (ad libitum). Restriction of feeding duration resulted in slow growth and extended larval duration. Consumption, assimilation, conversion and metabolism and their rates showed steady increase with the increase in the feeding duration. On pupation, energy allocation for egg production was studied by dissecting the pupa and estimating the reproductive and body tissues separately during the entire pupal period. Length and biomass of ovary steadily increased with increasing feeding duration as well as with increasing age of pupa. During egg development, the tissue protein was transferred to the ovary. This type of conversion was more in those fedad libitum than in those restricted to feed for shorter durations. Tissue fat and ovarian fat decreased as a function of age of pupa, indicating that fat served as the main source of energy for pupal metabolism.Bombyx mori restricted to feed for 6 h duration allocated 55% pupal energy for reproduction while those fedad libitum allocated about 67% of the pupal energy for reproduction. However, they allocated about 15–19% of assimilated energy for egg production in all the feeding regimes.

Geschlechtsspezifische Unterschiede beim Nahrungserwerb des Fichtenkreuzschnabels (Loxia curvirostra)

By recording the rate of glancing (i. e. looking up), the number of seeds taken by a crossbill per unit time from a larch cone (Larix X eurolepis) was evaluated. Female crossbills took more seeds per unit time from the cones than males do. Because of similar bill (and body) sizes the sexual difference could be explained in the following ways: a) during the breeding season the females need more energy for egg production than males do for spermatogenesis; b) females are more vigilant than males.