Size-fecundity Relationship Research Articles

Stress promotes changes in resource allocation to growth and reproduction in a simultaneous hermaphrodite with indeterminate growth

In iteroparous animals, investment in growth is compromised by investment in reproduction, especially in species with indeterminate growth. Life-history theory predicts that growth should be favoured over reproduction, assuming size-related fecundity or survival. Hence, increase body condition represents an increase in reproductive potential. Simultaneous hermaphrodites should adjust their resource allocation to each sex function in response to current conditions but, recently, it has been suggested that, in hermaphrodites, gender allocation should be considered as a three-way trade-off, including the investment in somatic growth. Due to the higher costs involved, the female function is affected to a greater extent by environmentally stressful conditions rather than the male function. To examine this, we induced stress in the hermaphroditic earthworm Eisenia fetida (Savigny, 1826) and looked for changes in resource allocation in nonreproductive and reproductive individuals. Experimental stress was induced by using tweezers to elicit contractile escape movements. We predicted that stressed earthworms would preferentially allocate resources to growth. In nonreproductive individuals, however, stress had a negative effect on growth, although weight recovery was rapid once manipulation ceased, indicating the importance of body condition, as well as the existence of mechanisms of compensatory growth for growth trajectories in this earthworm species. The response of reproductive individuals was consistent with our expectation: (1) stressed worms maintained their growth rate at the expense of current reproduction and (2) stressed earthworms laid 25% fewer cocoons, which were 30% lighter than cocoons laid by control earthworms. The present results suggest that E. fetida regulates its reproductive effort and that future reproduction has more impact on its fitness than current reproduction. The trade-off between current and future reproduction should be taken into consideration in models of sex allocation in simultaneous hermaphrodites.

Size–fecundity relationships for Cancer pagurus and Necora puber in the Shetland Islands, Scotland: how is reproductive capacity facilitated?

Successful management of fishery resources is dependent on understanding the exploited species' reproductive potential, which, in turn, requires spatially relevant estimates of the size at maturity and the size–fecundity relationship. This information is used by fisheries managers to implement regional maturity-based legal landings sizes and seasonal fishery closures aimed at protecting the spawning stock and maintaining the reproductive output of the fished population at a sustainable level, despite exploitation. Crab fisheries in particular depend on such information, which is often limited, even in long-established fisheries. To address this issue, size–fecundity relationships were obtained for two commercially exploited crabs in waters around the Shetland Islands (60°N 01°W). These species were Cancer pagurus and Necora puber. A statistically significant positive size–fecundity relationship was found for C. pagurus which describes a mean reproduction potential ranging from ~0.78 million eggs in females of 129 mm carapace width (CW) to ~2.4 million eggs in females of 212 mm CW. The positive size–fecundity relationship found for N. puber was not statistically significant, but describes a mean reproduction potential ranging from ~0.16 million eggs in females of 56 mm CW to ~0.19 million eggs in females of 96 mm CW. Morphometric assessments of reproductive capacity in C. pagurus support the notion that positive size–fecundity relationships are attributable to the combined capacities of specific morphological features, each of which contributes to a female's spawning output ability. Statistically significant positive linear relationships were found between the natural logarithms of crab size (CW) and pleopod capacity, sperm plug mass, spermathecae capacity and gonad capacity. Respectively, these structures are crucial for successful egg attachment and incubation, sperm retention and protection, sperm storage and oogenesis.

Life History of the Southern Torrent Salamander (Rhyacotriton variegatus) in Coastal Northern California

Southern Torrent Salamanders (Rhyacotriton variegatus) range widely from north coastal Oregon to northern California but are a patchily distributed inhabitant of forested seeps and headwater springs. We collected bimonthly samples of this species from managed forest sites in the Mad River watershed, Humboldt County. Larvae were measured, marked, and released, but a limited number of transformed individuals were preserved for laboratory analyses. North coastal R. variegatus breeds annually and has an extended courtship and egg-laying period. Cloacal spermatophores were present in gravid females from February through June, and oviposition likely occurs spring through fall. A prolonged larval period (hatching to metamorphosis) lasts 2–2.5 yr; transformed females require another 1.5–2 yr until first breeding, and clutch size averages 7.5 eggs. Adult sizes, size at metamorphosis, and developmental times were comparable to north coastal Oregon R. variegatus, suggesting that a simple north-south, harsh-mild environmental cline does not influence developmental time for coastal populations. Unexpectedly, clutch size and size-fecundity relationships for the California population of R. variegatus were more similar to Rhyacotriton cascadae, an inland, northern species with longer larval periods and larger sizes at metamorphosis, than to R. variegatus in north coastal Oregon. Rhyacotriton variegatus has limited rates of population increase because of long generation times and low fecundities and could be highly sensitive to frequent disturbances that impact numbers.

The influence of population and forest structure on fruit production in mahogany (Swietenia macrophylla King) and their consequences for sustainable management

SUMMARY Like most other species, sustainable management of mahogany in natural forests ultimately relies on continued seed production by the population. Because larger trees produce more fruit, previous authors have emphasised the importance of retaining large trees. In this paper, we investigate levels of fruit production of mahogany in two ecologically distinct forests. Fecundity was related to tree size in some years, but this relationship was neither consistent nor strong. The contribution of any given size class to population-level fruit production depended on both its fecundity and its relative abundance and this differed between forests. The fecundity of small and medium-sized trees was also significantly different between forests and this was consistent with patterns of increased crown exposure caused by differences in forest structure. From a forest management perspective, these results suggest that size-fecundity relationships are insufficient to guide forest management prescriptions without als...

Lifetime fecundity and floral variation in Tuberaria guttata (Cistaceae), a Mediterranean annual

In Tuberaria guttata, petal length, ovule number, and seeds per capsule raised steeply with increasing plant size (respectively, in the ranges 6-11 mm, 40-100, and 20-80), while the number of stamens varied relatively little (14-20). All flowers set fruit, and the rates of embryo abortion were independent of plant size and low on average. Individual fecundities had a markedly right-skewed frequency distribution (in the ranges 1-20 capsules and 20-1500 seeds per plant), which issued not only from plant size and flower production being positively correlated, but also from per-flower ovule numbers being directly proportional to plant size. Correlated variation of plant and ovary sizes amplified among-plant inequalities regarding fecundity; allowed larger plants to set ca. 50% more seed than expected on the basis of flower number only; and caused the slope of the size-fecundity relationship to be considerably steeper (at the population level) than if ovule number was a fixed trait. Corolla, ovary and androecium plasticity in Tuberaria are discussed in terms of environmental effects and developmental constraints.

Padrão reprodutivo de Elachistocleis bicolor (Anura, Microhylidae) na Serra da Bodoquena, Mato Grosso do Sul, Brasil

The reproductive pattern of Elachistocleis bicolor (Guerin Meneville, 1838) was studied at Serra da Bodoquena, from October 2000 to September 2001. Reproduction occurred in the wet season (October to April) and was correlated to high continuous pluviometric precipitation. The species presents sexual size dimorphism, with females larger than males. The number of mature eggs per ovary was 620 ± 251 (n=39) and mature eggs measured 1.15 ± 0.30 mm (n=40). Elachistocleis bicolor presented significant relations between snout-vent length and number of mature eggs (n=39; r2=0.25; p=0.001), individual weight and number of mature eggs (n=41, r2=0.30; p=0.002), snout-vent length and ovarian weight (n=35; r2=0.47; p<0.01), and individual weight and ovarian weight (n=36; r2=0.55; p<0.01). Weight and volume are better to study size-fecundity relationships than snout-vent length. The females invested 22.7 ± 6.3 % (n=35) of their weights in reproduction and the variance associated to this variable was high, related to the reproductive mode of the species.

Comparisons of size at maturity and fecundity of two Scottish populations of the European lobster, Homarus gammarus

Sampling of Homarus gammarus on commercial boats and regular visits to local ports were carried out during 1999–2001 for the Firth of Forth and Hebrides fisheries. Biological data on size, sex, morphometric measurements and egg samples were collected. Size at the onset of sexual maturity (SOM), fecundity and egg development were compared between populations. Techniques that require transformed (Logarithm base e) or untransformed morphometric data, were applied to the data. Lobsters from the Firth of Forth had smaller SOM ( ♂=80 mm carapace length (CL) and ♀=79 mm CL) than those from the Hebrides ( ♂=98 and ♀=110 mm CL). Fecundity ( x ̄ =8154 eggs) for the Firth of Forth was lower than for the Hebrides ( x ̄ =14 238 eggs). ANCOVA showed no significant differences in the size–fecundity relationship between locations ( F 1,1=2.62, P>0.05) for lobsters with eggs in which the eye spot index (ESI) was between 0.29 and 0.54, using CL and ESI as co-variates. The reliability of the methods and the resulting estimates are discussed.

Maturity, fecundity and reproductive potential of the European lobster (Homarus gammarus) in Ireland

Fecundity and size at maturity of the European lobster Homarus gammarus (Crustacea: Decapoda) was estimated in four coastal regions of Ireland. Egg size increased with carapace length (CL) (egg size=0·9939×ln (CL)−3·0809). The size–fecundity relationship for all coasts combined was (fecundity=0·0044×CL3·1554). Physiological maturity was assessed using ovary colour, ovary factor, ova size, abdomen width/CL ratio, cement gland activity and moult status as criteria. Size at 50% maturity varied from 92·5 to 96 mm depending on region. The size–maturity relationship for all coasts combined was (Maturity= 1/(1+exp(14·595−0·15598×CL))). Over 60% of lobsters in the commercial landings were under the size at 50% maturity. Relative reproductive potential (RRP) of different size-classes was calculated from the size–fecundity and size–maturity models and the numbers by length in the landings. The modal RRP size-class was 98–100 mm. The commercial landings were dominated by the 86–92 mm size-classes.

Size-fecundity relationships in the land snail Helix aspersa: preliminary results on a form outside the norm

Summary Reproductive traits of the land snail Helix aspersa Müller were investigated under artificial conditions in a breeding population of a giant subspecies from North Africa, namely Helix aspersa maxima. The results were compared with data obtained from experiments conducted under the same experimental with the common form Helix aspersa aspersa from (1) a population from the same snail farm, which shares with Helix aspersa maxima the same environment since several generations and (2) a set of wild populations from habitats spanning environmental heterogeneity of the species range. The significantly higher egg production in Helix aspersa maxima was explained by the clutch number per snail rather than by clutch size. Moreover, an uncommon high egg weight (41.4–44.6 mg) was observed in maxima when compared with that of Helix aspersa aspersa from previous studies (28–33 mg). However, reproductive differences between the two subspecies can largely be explained by size-effects and, as a consequence, relative allocation trade-offs among components of current reproduction did not greatly differ among populations.

Spruce budworm (Lepidoptera: Tortricidae) field fecundity: new insights into its estimation and use

Relationships between female spruce budworm, Choristoneura fumiferana (Clem.), pupal width and live weight, with realized field fecundity were determined in cages on branches of black spruce, Picea mariana (Mill.) B.S.P., in northern Maine. These are the first such determinations made on individual spruce budworms under field conditions. Fecundity varied from maximum levels similar to previously published findings in laboratory studies, to zero, independent of pupal size. Results suggest that previous laboratory studies of the pupal size–fecundity relationship have overestimated actual egg laying under field conditions, and therefore reduced the accuracy of some population studies.

Architectural Constraints on Flower Number in a Photoperiodic Annual

Plant fecundity is typically correlated with size (e.g. biomass); however, in plants whose reproduction is meristem-limited, there should be a stronger relationship between fecundity and architecture (the number and arrangement of subunits, or modules, composing a plant). In a reciprocal common garden experiment, I measured the effects of latitude-dependent flowering date on fecundity, biomass, and architecture in a photoperiodic annual (Perilla frutescens) to test the hypothesis that branch number limits flower production. If it does, the relationship between architecture and fecundity should remain constant across environments, even if the size-fecundity relationship varies. I planted Perilla seedlings from populations at 39°15'N and 33°05'N into a common garden at each latitude. Plants within a garden flowered on the same day, two weeks earlier in the south than in the north. Within a garden, size and flower number were positively correlated, but the slope of the relationship differed between gardens: plants of a given size made more flowers in the south than in the north. By contrast, the relationship between architecture and flower number was constant both within and between gardens. These data suggest that in meristem-limited plants, architecture is better than biomass at predicting fecundity across environments. Considering architecture, in addition to plant size, should enhance our understanding of environmental effects on plants whose reproduction is potentially meristem-limited.

Phenotypic Plasticity of Size--Fecundity Relationships in Arabidopsis Thaliana

1 The patterns of above ground allocation of meristems and resources are primary components of plant life history strategies, and are reflected in fecundity allocation, i.e. the observed relationship between plant size and fecundity. Phenotypic plasticity in fecundity allocation was investigated in the annual Arabidopsis thaliana. Individuals of each of three genotypes were grown under light, nutrient and pot volume gradients. Plant size (above ground vegetative mass excluding seeds) and fecundity (number of seeds) were measured for each individual at complete senescence. 2 In all combinations of three genotypes and three environmental factors, fecundity increased significantly with increasing plant size (P < 0.001). This increase was expressed through linear, quadratic, cubic and exponential relationships. Analyses of covariance with transformed data indicated that size-fecundity relationships were variable both between factors for individual genotypes and between genotypes within environmental factors. Hence not only size and fecundity, but also the relationship between size and fecundity can display phenotypic plasticity in this species. 3 Under light limitation some plants remained vegetative throughout their life span and it was therefore possible to identify a minimum size necessary to initiate production of reproductive meristems. However, some individuals of the same genotypes under nutrient limitation flowered and set seed although they were below this size limit. Hence, the minimum size for reproduction may also show phenotypic plasticity in A. thaliana. The observed variability in minimum size for reproduction and in fecundity allocation was not due to variation in developmental stage since all plants were harvested after fully completing their development. 4 Phenotypic plasticity in fecundity allocation and minimum size for reproduction implies that plants of the same size, in different environments, may not have the same fecundity, even if they are the same genotype. This plasticity has important implications in the interpretation of fitness estimates and in comparisons of life histories in plants.

Interactions between size and temperature influence fecundity and longevity of a tortricid moth, Zeiraphera canadensis.

Females of Zeiraphera canadensis Mut. & Free., the spruce bud moth, were reared in the laboratory at constant and alternating temperatures, and in an outdoor insectary, to (1) determine the effects of temperature, age and size on several reproductive parameters and, (2) to test the hypothesis that body size-temperature interactions influence longevity and realized fecundity. Egg maturation was linearly related to age and large moths developed eggs at a higher rate than small ones. Mcan lifetime oviposition rate reached a maximum and remained stable at temperatures ≥20° C while the mean lifetime rate of egg maturation increased linearly with temperature, indicating that higher temperatures adversely affect oviposition. The production of nonviable eggs increased with age but also with temperature, suggesting high temperature (≥25° C) reduces egg quality and/or hinders fertilization. The realized fecundity and longevity of females reared under an alternating temperature regime (mean 20° C) was significantly less than that of females reared at constant 20° C. Similar realized fecundity, longevity and mean lifetime oviposition rates for females reared at temperatures alternating between 10 and 25° C (mean 20° C) and those at constant 25° C reflected the inability of females to recover from elevated diurnal temperatures. Longevity was positively related to female body size at constant 15 and 20° C but the relationships were negative for moths exposed to diurnal temperatures equal to or exceeding 25° C. Due to the reduced longevity of large moths at high temperatures, linear regressions between size and realized fecundity were only significant at constant temperatures ≤20° C. At higher temperatures, the size-fecundity relationship became curvilinear as a result of the diminished reproductive output of large individuals. Reduced fecundity and longevity of large females at high temperatures may have been due to elevated internal temperatures of large-bodied moths. Large females in a controlled-environment chamber maintained at 25° C developed an internal temperature excess (i.e. temperature above ambient) of nearly 2° C while small-bodied females exceeded ambient by only 0.3° C. However, when held at 20° C, the temperature excess of large-bodied moths was much less than 1° C and small-bodied females did not differ from ambient. Such interactions between temperature and body size suggest that there should be stabilizing selection toward moderate-sized individuals and may explain the absence of size-related effects on fecundity and longevity previously reported for several other lepidopterans.

Random mating by size in the simultaneously hermaphroditic land snail Arianta arbustorum: experiments and an explanation

It has been proposed that size-assortative mating should occur in simultaneous hermaphrodites with reciprocal fertilization and size-related fecundity because all individuals invest substantially in mating. Mating patterns were recorded in two species of simultaneously hermaphroditic land snails. In a natural population of Helix pomatia, snails showed a slight (but non-significant) tendency towards sizeassortative mating, whereas mating in a population of Arianta arbustorum was random with respect to size. Laboratory experiments were conducted to test (1) whether individuals of A. arbustorum discriminate between mating partners of different size, and (2) whether a large shell might be of advantage during courtship to increase mating success. In mate-choice tests with individuals of different shell size, pairs formed randomly with respect to size. Courtship was neither hindered nor prolonged in pairs with large size differences. In the second experiment, a large snail was placed close to two courting conspecifics (both smaller). The larger snail interfered with the courting snails, but in general did not displace one of them. Courtship progressed to copulation only if one of the three snails ceased to court; this was independent of the size of that individual. Thus, a large shell did not increase mating success. It is suggested that time-constraints of locomotory activity and high costs of searching for a mate can explain the prevalence of random mating patterns in simultaneously hermaphroditic land snails.

Ovarian Cyclicity and Fecundity in Boreal Common Frogs Rana temporaria L. Along a Climatic Gradient

Hypotheses that the patterns of energy storage, ovarian development and fecundity change along a climatic gradient were tested. Data from adult female common frogs Rana temporaria L. were collected in three study areas from mixed boreal lowland forest to alpine heath. There were no consistent altitudinal trends in body length or weight. Age, however, increased with altitude. During the feeding season, the rate of primary deposition of energy in the fat bodies was higher in mid-altitude than in lowland females. Relative ovary weight increased faster in alpine heath and mid-altitude frogs than in lowland frogs. There were no indications of an ovarian resting period. Rather, with increased altitude the oocytes for next year's reproduction tended to have entered the vitellogenic growth phase even before oviposition; possibly this was an adaptation to a short feeding season. Body length and fecundity were exponentially related in the lowland and the mid-altitude study areas. The relationship between body weight and fecundity appeared to be linear in at least the lowland population. Fecundity per gram body mass increased with age. Although differences between study areas were found, there was no consistent altitudinal trend in either absolute or size-relative fecundity. Fecundity varied between years as well as between populations. A negative correlation between relative liver weight and fecundity indicated a high cost to reproduction. Nevertheless, skipping years of reproduction, a phenomenon suggested to occur primarily in resource-poor environments, was rare.

Claudicuma Platense Roccatagliata, 1981 (Cumacea): A New Reproductive Pattern

An intertidal population of Claudicuma platense, a cumacean that inhabits the Rio de la Plata bottom, was sampled for 15 months. This species produces 3 generations per yearoverwintering, spring, and summer-instead of 2, as reported for other temperate shallow-water cumaceans. The spring and summer generations develop over a shorter period (about 2 and 3 months, respectively) than the overwintering generation (about 7 months). Lower abundances were observed in late winter (mean minimum abundance = 133 individuals m-2) when the population consisted mainly of adults, the survivors of the overwintering generation, whereas higher abundances occurred in early summer and early autumn (mean maximum abundances = 4,003 and 2,090 individuals m-2, respectively) when the population was composed primarily of mancas and juveniles. Claudicuma platense was also collected in the subtidal zone near the coast, where the temporal pattern of variations in abundance is apparently similar to that of the intertidal zone. Both the size of marsupial females and the fecundity decrease from overwintering, to spring, to summer generations. Each generation exhibits a linear, but different, female size-fecundity relationship. Hence, other factors, besides female size, influence the fecundity of C. platense.

Sexual Differences in Contemporary Selection Acting on Size in the Hermit Crab Clibanarius digueti

The hermit crab Clibanarius digueti shows strong sexual dimorphism with respect to size, with almost no overlap between adult males and females. Both sexes gain in fitness-related parameters with increasing body size. Courting males average 35% heavier than noncourting males; males in the largest-size classes, which make up less than 1% of the total male population, accounted for 12% of the reproductive activity during the study. Female mating success apparently is not affected by body size, since breeding frequencies did not vary with size. In addition, courting pairs are formed non-assortatively, indicating that males are not choosing females on the basis of size. Females did show an increase in clutch size with body size, as do virtually all ectotherms, but the rate of increase is among the lowest recorded for decapod crustaceans. If female fecundity in C. digueti increased isometrically with body size, as is typical in decapod crustaceans, then female fitness would actually increase more rapidly than male fitness with body size. This modest size-related fecundity gain in females is unexplained (possibly resulting from increased shell limitations on larger crabs), but it leads to the conclusion that selection for large size is stronger in males than in females, a necessary condition for sexual differences in selection to have a role in sexual size dimorphism.

Breeding phenology, variation in reproductive effort and offspring size in a tropical population of the woodlouse Porcellionides pruinosus.

Most species of woodlice in temperate habitats have discrete breeding seasons. It is hypothesised that breeding synchronises with favourable environmental conditions to maximise offspring growth and survivorship (Willows 1984). We measured the breeding phenology of a species introduced to a tropical environment, primarily to consider the assumption that life histories in the tropics will differ fundamentally from those in temperate habitats. In addition to breeding phenology we considered variation in reproductive effort between individual females and the division of this effort between the size and number of young.A continuous breeding phenology was observed in a synanthropic population of Porcellionides pruinosus within the tropics. Reproductive effort varied between months, showed a weak relationship with female size and was independent of female fecundity. Female sizefecundity relationships varied between samples and when the proportion of reproductive females was high size-fecundity slopes were steeper than at other times. Mean offspring size varied between months and there was a wide range in offspring size within broods. Offspring size was not related to female body mass, reproductive effort or fecundity; consequently brood mass increased linearly with an increase in fecundity. Increased reproductive effort goes into more rather than larger offspring.We propose that the continuous breeding in this population was the result of the constant presence of an environmental cue to reproduction evolved in temperate habitats. Continuous breeding is not necessarily equivocal to high individual reproductive success even though overall population growth may be rapid. However, variation in reproductive effort suggests that individuals respond to current environmental conditions on short time scales.

Size at onset of maturity and size-dependent reproductive output of female and male spiny lobsters Jasus edwardsii (Hutton) (Decapoda, Palinuridae) in northern New Zealand

50% of female spiny lobsters Jasus edwardsii (Hutton) from a marine reserve in north-east New Zealand had ovigerous setae or were carrying external eggs at 87.5 mm carapace length (CL). The proportion of mature follicles in the testes indicated that most males were physically mature at 85 mm CL. Female reproductive output, as measured by size-fecundity relationships, increased with CL from the onset of physical maturity as described by a power function [fecundity = 0.169· CL 3.0091]. In contrast, only males ≥ 140 mm CL were observed courting females in the field although smaller mature males were abundant. Field observations and a laboratory experiment in which males < 140 CL were either exposed to or isolated from males > 140 mm CL suggested that aggressive behaviour prior to and during the mating period prevents smaller mature males from courting females. Female choice, if it operates, may only apply to males > 140 mm CL which have the opportunity to both court and be rejected. Male size at onset of mating may affect female fecundity and male growth rates.

Growth, Reproduction and Population Dynamics

The relationship between individual resource use and fitness is fundamental to an understanding of population dynamics.It has been demonstrated that,in theory,reproductive thresholds have destabilizing effects on population dynamics.We review the published size-fecundity schedules and demonstrate a fundamental difference between plants and animal.Most animal schedules have large,significant thresholds for reproduction,but few plant species exhibit size-fecundity relationships that have negative intercepts.This leads to the prediction that plant populations will generally have stable dynamics whereas animal populations will display the full repertoire of dynamical behaviour