Life-history variation within a three-spined stickleback population in the Camargue

Among individuals of female three-spined sticklebacks Gasterosteus aculeatus from a population in the Camargue, southern France, studied in 12 successive years, adult L _T ranged from 31–64 mm, clutch size ranged from 33–660 eggs, and mean egg diameter per clutch ranged from 1.15–1.67 mm. Because the population was strictly annual, inter-annual variation corresponded to variation among generations having experienced different environmental conditions. Body mass varied significantly among years, suggesting an effect of varying environmental conditions. Gonad mass and clutch size increased with body mass, but mean egg diameter was not correlated to body mass. Body mass-adjusted gonad mass, interpreted as reproductive effort per clutch, did not vary significantly among years, suggesting that this trait was not influenced by environmental conditions. Body mass-adjusted clutch size and egg size varied significantly among years. Inter-annual variation in body length at breeding, clutch size and egg size was of the same order of magnitude as inter-population variation reported by other authors for this species. During the breeding season, reproductive effort and clutch size tended to increase. Egg size tended to decrease during the breeding season but this seasonal pattern varied among years. Observed life-history variation is discussed both in terms of its evolutionary significance and methodological implications in the study of life-history variation among populations.     

Reproductive activity of two dominant Antarctic copepod species, Metridia gerlachei and Ctenocalanus citer, in late autumn in the eastern Bellingshausen Sea

The main reproductive period of herbivorous Antarctic copepods is coupled to the phytoplankton bloom in spring, while omnivorous or carnivorous species apparently reproduce year round. However, our knowledge of the reproduction during autumn and winter is limited. Therefore this study during a cruise with RV "Polarstern" aimed to measure reproductive activity in two dominant copepod species, Metridia gerlachei and Ctenocalanus citer, in late autumn (April/May). For this purpose, gonad development stages were determined from both species, taken with Bongo net in the eastern Bellingshausen Sea (Antarctic Peninsula region), and related to the ambient feeding conditions represented as chlorophyll a concentration. In addition, experiments were conducted with M. gerlachei to study the influence of feeding and starvation on gonad development. Gonad maturity of M. gerlachei differed considerably between stations and decreased over time. The correlation of chlorophyll a and the proportion of mature females, though significant, was weak and highly variable. In experiments, the gonads of feeding females were in better condition than those of their starving counterparts, showing that reproductive activity in M. gerlachei was related to ambient feeding conditions. Mature females of C. citer were found at each station (17-67%). The gonad stage composition was rather similar at all stations, showing no clear temporal and spatial trend. In this species, the proportion of mature females was not related to the chlorophyll a concentration, indicating either that the ambient phytoplankton stock was sufficient to fuel maturation or that other food sources were used. Our study shows that both species are reproducing during the austral autumn, indicating that their reproduction is partially decoupled from the spring phytoplankton bloom.     

Clutch production in the darter Etheostoma lynceum and its implications for life-history study

We tested two hypotheses that describe previously untested assumptions about the appropriate stage(s) for use in determining clutch sizes in darters. Three sequential stages of clutch/ovarian development are recognized: mature oocyte/ovary, ripening oocytc/ovary, and ripe oocyte/ovary. Mean ratios of clutch size to female length (relative clutch size, RCS) were significantly smaller and variances of RCS were significantly greater in ripe females when compared to mature and ripening females. Correlation coefficients for the relationship between clutch size and standard length (S.L.) were significantly greater for mature and ripening females than for ripe females. Mean clutch size, adjusted for the S.L. covariate, was significantly greater in mature and ripening females than in ripe females. Thus, we conclude that counts of eggs from ripe females yield fecundity estimates that are lower and more variable than estimates from counts of oocytes from mature and ripening females collected at the same time. Based on this conclusion, we discuss methods for developing fecundity estimates in darters. Our results may be broadly applicable to other taxa of fishes with group-synchronous ovum development.     

Energy content of spider eggs

Summary The energy content of spider eggs was determined on samples from 12 species representing 6 families. These values ranged from 26.32 to 29.00 joules per mg ash-free dry mass with a mean of 27.30±SE of 0.27. The higher values were found in those species that overwinter as developmental stages within the egg sac. Rates of energy expenditure of developing eggs and spiderlings within the egg sac were only 7 to 19% of those of emerged spiderlings. The energy conserved by this reduction in rate of metabolism may facilitate survival without feeding during the potentially long periods of aerial dispersal by ballooning, a characteristic activity of most newly emerged spiderlings. The variation in mass-specific energy content is less than variation in clutch size and individual egg size on an intra-and interspecific basis. There was no correlation between energy content per unit egg mass and size of the female parent, egg size, or clutch size. Further analysis indicated that no single measure such as clutch size accurately represents the proportional amount of energy invested in reproduction in these animals.     

Gonad growth in the sea urchin, Strongylocentrotus purpuratus (Stimpson) (echinodermata: Echinoidea) and the assumptions of gonad index methods

In central Oregon intertidal populations, the echinoid Strongylocentrotus purpuratus (Stimpson) first begins to produce mature gametes at a diameter of 25 mm during the second year of its life. All individuals above 40 mm in diameter have mature gametes during the mid-winter spawning season. Gonad size increases rapidly relative to body size until the animals are ≈45 mm in diameter and have a total dry weight of ≈ 15 g. The ratio of gonad to body size reaches its maximum in animals between 40 mm and 50 mm in diameter; thereafter the ratio drops slightly with increasing size. The curvilinear relation between gonad size and body size is not related to a relative difference in body proportions with size. Internal volume, height, and diameter increase linearly with size. Body proportions did not differ between the two populations studied. Differences between populations in the ratio of gonad to body size extend to all sizes in the populations and the direction but not the amount of the difference is consistent from year to year. These differences between habitats are probably related to food supply. The use of gonad ratio methods to normalize gonad size assumes that, within a given population, animals of different body size have the same ratio of gonad size to body size. This assumption is not correct for four species of sea urchins. Gonad index or ratio methods are useful for comparing animals of the same size through time within a population or from different habitats. Restriction of the size range of animals used and use of samples of sufficient size permit gonad ratios to be used to assess the capacity of different habitats to support gonad production in sea urchins and other animals.     

Maturity and gonad changes of Oreochromis (Nyasalapia) karongae raised in fish ponds in Malawi

The reproductive biology of pond-raised Oreochromis (Nyasalapia) karongae was investigated. Gonad histology and gonadosomatic indices (GSIs) indicated a potential for multiple spawning in a season. Several peaks of oocyte-size distribution and several maturation stages occurred in the same gonad. GSIs of 2.5% and 1.4% were recorded in female and male fish, respectively. Three stages of oocyte maturation (primary growth, formation of yolk vesicles, vitellogenesis) and three stages of sperm development (spermatogonia, spermatid, spermatozoa) were observed. With the exception of the final maturation stage, all development phases seemed to proceed satisfactorily. The final stage of maturation was attained at oocyte size of 2.70 ± 0.54 mm and was selectively impaired in some female fish by a lack of deposition of vitellogenin. This abnormal condition led to atrophic oocytes lacking yolk granules and vesicles. Sexual maturation was attained at a relatively large size of 16.0 cm (114 g) compared with other tilapia of the mossambicoid group (i.e. Oreochromis mossambicus and Oreochromis shiranus ). A combination of gravimetric and histological techniques was successful in charting gonad changes and calibrating external against internal gonad features.     

Body size versus gonad maturation form in under-yearling precocious males of the sea trout (Salmo trutta m. trutta L.)

The study was aimed at analysing body size in relation to form of gonad maturation (amount of mature germ cells) in 329 under-yearling sea trout males. The fish, aged 7 months, were caught in late October-early November in 3 streams located in north-western Poland. Each stream supported fish belonging to a different sib group. Standard histological techniques and a computer image analysis programme were used to detect the class of gonad maturation and percentage of the gonad area occupied by tubules with active spermatogenesis. Gonad maturation forms were distinguished based on the latter criteria. Gonads with developing germ cells occupying less than 90% of gonad area were classified as incomplete forms of gonad maturation, others as complete maturation forms. In each sib-groups analysed, even the smallest individual were already precocious, their gonads being incompletely mature. The smallest maturing male measured 7.1 cm in length. The average size of an incompletely maturing individual was slightly smaller than that of the completely mature one but the difference lacked statistical significance (P > 0.05). The sib-group of smaller fish contained less precocious, and the gonads of the more precocious were incompletely mature, compared to the sib-group of larger fish (P < 0.001). It seems that the incomplete form of gonad maturation (defected maturation) occurs at a smaller critical fish size than the complete gonad maturation form. Incomplete maturation is more frequent smaller individuals and possibly in among slow-growing groups of fish.     

Gonad development and size‐at‐maturity of silver therapon Leiopotherapon plumbeus (Kner 1864; Teleostei:Terapontidae) in tropical volcanic lakes in south Luzon,Philippines

Gonad development of the silver therapon Leiopotherapon plumbeus in two volcanic crater  lake  habitats (Sampaloc Lake, Taal Lake) in south Luzon, Philippines was examined during the annual reproductive cycle. The minimum body size‐at‐maturity of fish in these two lake habitats was also compared. Four gonad development stages were characterized as basis for the classification of ovarian (immature, maturing, mature, spawned) and testicular maturation (immature, maturing, mature) phases. The occurrence of all development stages in individual gonads suggest an asynchronous development whereby advanced stages are recruited continuously from a pool of younger stage germ cells to result in elevated female and male GSI throughout the annual cycle due to active gonadogenesis. Together with the increasing occurrence of advanced stage oocytes and spermatozoa from March until October, the elevated GSI of fish may indicate peak gonadal growth during the onset of the dry season (December–January) for eventual spawning from the beginning (May–June) until the end of the wet season (October–November). In both lake habitats, male fish were smaller than females but, regardless of sex, the minimum size‐at‐maturity of fish in Sampaloc Lake was significantly smaller than fish in Taal Lake. Overall, asynchronous development during oogenesis and spermatogenesis allows for year‐round reproduction of silver therapon, with elevated gonad growth in the dry season in preparation for spawning during the wet season. Compared with fish in Taal Lake, a smaller size‐at‐maturity of fish in Sampaloc Lake may be a response of the wild fishery stock to long‐term high fishing mortality and degradation of the lake habitat.     

The effect of feeding frequency on consumption of food,absorption efficiency,and gonad production in the sea urchin Lytechinus variegatus

The frequency of feeding in the field is variable in sea urchins, ranging from nearly continuous to diel or intermittent. It is essential to know the effect of feeding interval on physiological and metabolic processes to understand the basis for production. Lytechinus variegatus (50 mm horizontal diameter) were collected in January 1999 and held in closed-circuit aquaria at 25 degrees C and 35 per thousand salinity. After 9 days without food, individuals were fed one of three treatments: food available ad libitum, food available for 1 day every 2 days or food available for 1 day every 4 days for 28 days. The rate of food consumption per day of all individuals was high the first week of feeding. It then decreased to a lower, constant rate in those fed ad libitum but remained high in those fed one day every 2 or 4 days. The total amount eaten was directly related to frequency of feeding. The apparent dry matter digestibility (absorption efficiency) did not vary with frequency of feeding. As the total amount of energy absorbed was directly related to the frequency of feeding, the increase in the rate of food consumption does not compensate for a decrease in frequency of feeding. Gonad production efficiency was directly related to frequency of feeding. Gonad gross production (assimilation) efficiencies were 8.4, 3.9 and 3.4% for individuals fed every day, or fed one day every 2 and 4 days, respectively. The corresponding gonad net assimilation efficiencies were 12.5, 5.5, and 4.8%. A decrease in frequency of food availability results in use of a greater proportion of the food consumed for maintenance and less for gonad production.     

Reproductive cycles in oregon populations of the echlnoid, Strongylocentrotvs purpuratus (Stimpson). I. Annual gonad growth and ovarian gametogenic cycles

Four annual reproductive cycles were followed in the echinoid, Strongylocentrotus purpuratus (Stimpson), at three places on the central Oregon coast near 44°45′N lat., where intermittent upwelling depresses coastal sea temperatures from June through September. Monthly measurements were made of the gonad index of samples of 30 urchins and the relative frequency of five stages in oogenesis were determined from sectioned ovaries from these samples.Individuals in these populations are synchronous in their annual cycle of gonad growth, oogenesis, and spawning, the latter taking place between late December and March. The population usually undergoes one major, complete spawning within a period of 30 days. When large reserves of stored nutrients are present, ova continue to mature over a longer period and may be present in quantity from December into April. Gonad weight does not change significantly from March through June. From July through November the gonad undergoes its annual growth at a mean instantaneous relative growth rate of ≈ 1 % per day. Gonad growth is not significantly correlated with sea temperature. Variable temperatures resulting from upwelling do not result in erratic fluctuations in the reproductive cycle, probably because of the annual change in feeding rate, the seasonal shift in energy utilization, and the constancy of the amount of food assimilated during gonad growth. Gonad size and annual growth rates may differ significantly between years and locations, indicating that both are influenced by local environmental factors, probably food availability and degree of wave action.The frequency of oogonial clusters is least in mid-winter, increases after spawning, reaches an annual maximum in June and declines in the fall. Primary oocyte growth is very slow until October, when it increases abruptly, and some oocytes become ova as early as late October. When stored nutrients are low, many oocytes do not complete growth by January, and are not spawned until May. Prolongation of the spawning period delays the increase in frequency of oogonial clusters in the following new cycle. The timing of the annual increase in oogonial cluster frequency and of the onset of rapid oocyte growth did not otherwise vary between places and years. In these populations, entrainment or synchronization of the reproductive cycle to seasonal environmental events probably occurs at the beginning of one or all of these critical annual events: oogonial proliferation, annual gonad growth and rapid oocyte growth.     

Diapause in the life cycle of Calanoides carinatus (Kroyer), (Copepoda, Calanoida)

The distribution and stage composition of Calanoidescarinatus (Kroyer) are described together with changes in protein and lipid content, respiration rate and gonad development in copepodite stages IV and V (CV) and adults in the Northern Benguela current (17°S, 23°S and 25°S).During active upwelling the population consisted of two parts: the surface part over the shelf was represented by all development stages, while the deep part offshore was dominated (90–95%) by diapausal CVs. In the surface CVs the surplus assimilated energy was allocated to structural growth and maturation or to synthesis of reserve lipids. CVs with large oil sacs and high lipid content descended into deeper layers and formed diapausal stock; they were characterized by a dramatic decrease of respiration rate. Increase of gonad size in association with decrease of oil sac volume in diapausal CV suggests that reserve lipids were expended not only for respiration but also for gonad development. The moulting of dispausal CVs into adults took place in deep water.These results are discussed in relation to the life cycle of the C. carinatus population and the factors causing the formation and termination of the diapausal phase.     

Reproductive cycle and reproductive output of the sea urchin Loxechinus albus (Echinodermata: Echinoidea) from Beagle Channel, Tierra del Fuego, Argentina

Reproductive cycle, frequency and duration of spawning, energetic content of gonads, and reproductive output of the common green sea urchin Loxechinus albus were analyzed in the Beagle Channel (Tierra del Fuego) between May 2004 and May 2005. Gonad indices (GI, percentages of gonad mass in total body mass) were significantly higher in March, April, July, and August than in November and May, thus showing a negative correlation with the photoperiod. Highest GI values of mature individuals were observed in August, and spawning occurred from September to December. In females, the mass-specific energy content of gonads (ECG) was highest in spawned gonads and lowest in mature ones, while in males ECG values were higher in immature stage and lower in premature and mature stages. High ECG values can be explained by the abundance of nutritive phagocytes. Both ECG and total gonad energy content (TECG) were higher in females than in males. Mean reproductive output was 7.28% for females and 6.15% for males (expressed as the difference between mean GI of mature and spawned gonads) and 25.02 kJ for females and 19.26 kJ for males (expressed as the difference between mean TECG of mature and spawned gonads).     

Reproductive ecology of the intertidal sea anemones Anthopleura xanthogrammica (Brandt) and A. elegantissima (Brandt): Body size,habitat, and sexual reproduction

Anthopleura xanthogrammica (Brandt) and A. elegantissima (Brandt) were collected monthly (1974–1976) from a variety of intertidal habitats in Washington State. Histological preparations were used to examine oocyte maturation, testis maturation, gonad number, and gonad volume. Maturation was examined over two years and both species were found to build gonad during the winter, spring, and summer followed by spawning in the late summer and autumn. Gonad volume and gonad number increase with individual size after a certain minimum size has been reached. Gonad volume as a function of body size does not change with habitat although the size structure of the population may change substantially.     

Zooplankton growth rates: diel egg production in the copepods Oithona, Euterpina and Corycaeus from tropical waters

Clear diel periodicity in the timing of egg laying was observedin the tropical cyclopoid cope-pods Oithona plumifera, Oithonanana, Oithona simplex and Corycaeus amazomcus, and the harpacti-coidEuterpina acutifrons in waters surrounding Jamaica, West Indies.Individual females incubated under ambient food conditions formultiple clutches displayed remarkable constancy in their clutchdurations (= egg or embryonic development time). All speciesexhibited clutch durations of 20–23 h and cycle durations(= sum of clutch and inter-clutch durations) of 24 h, exceptfor the offshore species O.plumifera where the clutch durationwas 36 h and the cycle duration 48 or 72 h. Egg laying appearedto be synchronized by photoperiod, occurring around dawn formost species. In order to avoid biases, diel periodicity mustbe accounted for in estimates of egg production rates, and futureefforts should concentrate on the responses of clutch size andinterclutch durations to natural food climates.     

The autecology of the chub, Squalius cephalus (L.), of the River Lugg and the Afon Llynfi

(1) The pattern of absolute atid relative gonad growth during the life-span and the seasonal gotiad cycle were determined from monthly samples of chub taken from two tributaries of the Herefordshire Wye. (2) A marked change in the pattern of absolute gonad growth was thought to indicate the attainment of sexual maturity. This was found to occur synchronously with corresponding changes in the pattern of body growth described previously and was in agreement with the age at which a seasonal gonad cycle was detectable. (3) Sexual maturity was attained during the eighth year of life (7+) in female chub and in males from the Afon Llynfi, but most males from the River Lugg matured a year earlier. (4) The chub gonads continued to increase in relative size after the attainment of sexual maturity. This was more evident in female chub. (5) Seasonal changes in the gonad condition and weight were followed. Gonad maturation occurred during spring and the gonad mass increased rapidly just prior to spawning. (6) Spawning occurred during June.     

The effect of feeding or starvation on resource allocation to body components during the reproductive cycle of the sea urchin Sphaerechinus granularis (Lamarck)

To determine the effects of feeding or starvation on resource allocation to body components during the reproductive cycle of Sphaerechinus granularis, sea urchins were placed in laboratory tanks and either fed ad libitum or starved during two different periods of their biological cycle, i.e. the mature stage and the recovery stage. The urchin growth was monitored over the whole experimental period, the gonad, gut, lantern indices and organic matter levels of different organs were determined at the end of the experiment. During the mature stage sea urchins in good nutritional conditions did not increase in size, but allotted energy to gonad production and stored reserves in body wall. Limiting food stopped the gonadal growth without complete regression. During the recovery period food allowed somatic growth, i.e. test growth and the storage of reserves in gonad somatic cells. This somatic production did not occur under food-limited conditions and the resources allotted for survival and maintenance were taken from different body components.     

The relationship of gonad and egg size to weight and age in the European and Chinese races of the common carp Cyprinus carpio L.

Gonad development was studied in young carp of the European and Chinese (big-belly) races. The effects of age and body weight on gonad and egg size were partitioned and the following findings were made: (i) Gonad weight was correlated, in both males and females, with body weight, but proportional gonad weight, i.e. the ratio gonad weight divided by body weight, was independent of body weight, (ii) Proportional gonad weight had reached its maximum value in one year old males, but it more than doubled in two year old females, (iii) Egg size of two year old females was more than twice the size of eggs of one year old females, (iv) The European and Chinese races of carp differed in several aspects of gonad development. In particular, the Chinese matured earlier and their relative gonad sizes were considerably larger, (v) Genetic variation in gonad development was also found within the European race, where faster rate of development is dominant over slower rate. The evolutionary implications of the above differences were discussed.     

Variable host quality, life-history invariants, and the reproductive strategy of a parasitoid wasp that produces single sex clutches

The parasitic wasp Achrysocharoides zwoelferi (Hymenoptera, Eulophidae) produces clutches consisting of only one sex. Moreover,male clutch size is invariably one while female clutches arein the range one to four. We designed field experiments todetermine the effect of host quality on clutch composition.We found that solitary male and solitary female clutches werereared from the same size mines, and that larger mines tendedto produce gregarious female clutches. A higher proportionof male clutches were placed in older hosts, despite theirlarge size. Variation in body size, both between and withinclutches, was measured in order to test the predictions of models that take into account the constraint that clutch size is aninteger trait, something of potential importance when absoluteclutch size is low. Our data supported several predictionsof these models, including the trade-off-invariant rule foroptimal offspring size developed by Charnov and Downhower.However, while most invertebrate clutch size models assume equal resource share among members of the same clutch, we found anincrease in inequality in larger clutches.     

Reproductive success and foraging of the crab spider Misumena vatia

Summary Reproductive success and growth rate data were collected for individually marked crab spiders Misumena vatia (Clerck) in 1980, 1981, and 1982. All measures of reproductive success were found to be quite variable between individuals within years, but did not differ between years. Reproductive effort (mass of clutch/prereproductive mass of female) was the least variable measurement and was not correlated with female weight at reproduction. Clutch weight and number of eggs per clutch were highly correlated with female reproductive weight. Egg weight was not correlated with the number of eggs per clutch. Hatching success did not vary with clutch size and averaged 94.5%. Growth rates of spiders were highly variable, indicating large variation in feeding rate. In 1981 and 1982, approximately 20% of female spiders were unable to capture enough prey to grow and reproduce. Primary prey species differed in weight and in their contribution to spider egg production. Spiders attacked a larger percentage of bumblebees but captured a larger percentage of honeybees. There was no simple relationship between diet choice and reproductive success. Spiders which selected suboptimal umbels to forage on some or all of the time, however, had significantly lower reproductive success than spiders choosing the best umbels.     

Starvation tolerance, development time and egg production of Calanoides carinatus in the Southern Benguela Current

The intermittent nature of phytoplankton blooms in the extremesouth of the Benguela Current may be an important factor limitingthe zooplankton population. Calanoides carinatus, a dominantzooplankton species, was studied in the laboratory to measureits tolerance to starvation, development time and rate of eggproduction. The species was found to have a large food reservein the form of a lipid sac which gives it a high tolerance tostarvation. Starvation tolerance depends on age, temperatureand feeding during development but once mature, feeding doesnot increase the tolerance. Development time depends on temperatureand feeding and is of the order of 25 days at average temperaturesin the area (13–15C). Egg production is rapid (–70eggs per female per day) when food is abundant and ceases immediatelyfood is removed. Overall the species shows considerable toleranceof a patchy food regime but nevertheless is probably controlledto some degree by the intermittent food supply, especially duringthe juvenile stages.