Reproductive effort,fecundity and energy allocation in two species of the genus Perinereis (Polychaeta: Nereididae)

Summary

The reproductive effort in terms of fecundity and energy allocation was studied in two species of semelparous polychaetes belonging to the genus Perinereis, living in the same environment, with different reproductive modalities. There is a great individual variability both in terms of reproductive effort and fecundity. Fecundity varied from 4080 to 15000 oocytes in P. rullieri and from 7000 to 26000 in P. cultrifera; no linear relationship was found between oocyte number and total jaw length utilised as size index. The energy content of germinal and somatic tissues was determined by Differential Scanning Calorimeter (DSC). The reproductive effort was calculated as RE = E_G/(E_G + E_S) where E_G is the total energy in germinal tissues and E_S is the total energy in somatic tissues. Reproductive effort is very high with mean values of 0.62 for P. rullieri and 0.79 for P. cultrifera. The different amounts of energy allocated in germinal tissues can be attributed to the different reproductive modalities—P. rullieri reproduces in the atokous phase whereas P. cultrifera has conserved epitoky in its life-cycle. The lack of correlation between reproductive effort and size index strongly suggests that reproductive allocation does not increase with age. In semelparous species the variability in fecundity and reproductive effort observed cannot be interpreted in terms of a trade-off between fecundity and survival as in iteroparous species. In fact, in semelparous an individual allocates all available resources to reproduction and then dies.     

Reproductive strategies of sub-Antarctic lithodid crabs vary with habitat depth

We present the first fecundity and egg size data for three species of lithodid crab from Antarctic waters south of the Polar Front, caught in the fisheries operating around the island of South Georgia. In all species, fecundity was observed to increase with body size, but reproductive allocation was found to differ significantly between species. The highest relative fecundity (eggs^−g body weight) and smallest egg size was found in Paralomis spinosissima, which is found in shallower waters, whereas the lowest relative fecundity values and largest eggs were recorded in the deeper living species, Neolithodes diomedeae. Evidence is presented that closely related sympatric species may employ quite different reproductive strategies that suit their depth distribution whilst indicating the overriding evolutionary adaptation of reproductive traits to temperature and food availability.     

The role of fecundity and reproductive effort in defining life‐history strategies of North American freshwater mussels

Selection is expected to optimize reproductive investment resulting in characteristic trade‐offs among traits such as brood size, offspring size, somatic maintenance, and lifespan; relative patterns of energy allocation to these functions are important in defining life‐history strategies. Freshwater mussels are a diverse and imperiled component of aquatic ecosystems, but little is known about their life‐history strategies, particularly patterns of fecundity and reproductive effort. Because mussels have an unusual life cycle in which larvae (glochidia) are obligate parasites on fishes, differences in host relationships are expected to influence patterns of reproductive output among species. I investigated fecundity and reproductive effort (RE) and their relationships to other life‐history traits for a taxonomically broad cross section of North American mussel diversity. Annual fecundity of North American mussel species spans nearly four orders of magnitude, ranging from < 2000 to 10 million, but most species have considerably lower fecundity than previous generalizations, which portrayed the group as having uniformly high fecundity (e.g. > 200000). Estimates of RE also were highly variable, ranging among species from 0.06 to 25.4%. Median fecundity and RE differed among phylogenetic groups, but patterns for these two traits differed in several ways. For example, the tribe Anodontini had relatively low median fecundity but had the highest RE of any group. Within and among species, body size was a strong predictor of fecundity and explained a high percentage of variation in fecundity among species. Fecundity showed little relationship to other life‐history traits including glochidial size, lifespan, brooding strategies, or host strategies. The only apparent trade‐off evident among these traits was the extraordinarily high fecundity of Leptodea, Margaritifera, and Truncilla, which may come at a cost of greatly reduced glochidial size; there was no relationship between fecundity and glochidial size for the remaining 61 species in the dataset. In contrast to fecundity, RE showed evidence of a strong trade‐off with lifespan, which was negatively related to RE. The raw number of glochidia produced may be determined primarily by physical and energetic constraints rather than selection for optimal output based on differences in host strategies or other traits. By integrating traits such as body size, glochidial size, and fecundity, RE appears more useful in defining mussel life‐history strategies. Combined with trade‐offs between other traits such as growth, lifespan, and age at maturity, differences in RE among species depict a broad continuum of divergent strategies ranging from strongly r‐selected species (e.g. tribe Anodontini and some Lampsilini) to K‐selected species (e.g. tribes Pleurobemini and Quadrulini; family Margaritiferidae). Future studies of reproductive effort in an environmental and life‐history context will be useful for understanding the explosive radiation of this group of animals in North America and will aid in the development of effective conservation strategies.     

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

Summary 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.     

THE COST OF MERISTEM LIMITATION IN POLYGONUM ARENASTRUM: NEGATIVE GENETIC CORRELATIONS BETWEEN FECUNDITY AND GROWTH

Growth and reproduction in higher plants depend on meristems, which have three developmental fates. A meristem can become reproductive, but doing so terminates its activity, it can differentiate vegetatively, or it can remain quiescent for extended periods. The first two fates are mutually exclusive, and only the second leads to the production of additional meristems for subsequent growth and reproduction. In Polygonum arenastrum (frequently referred to as P. aviculare in North American Floras), an annual species lacking quiescent meristems, a quantitative genetic analysis of inbred full-sibling families revealed genetic variation in the developmental pattern of axillary meristem commitment to vegetative growth versus reproduction. Developmental variation resulted in family differences in the age of first reproduction, in age-specific fecundity and growth, and in final plant size and reproductive output. Furthermore, there were strong negative genetic correlations between age-specific growth and fecundity. Early commitment of meristems to reproduction favors high early fecundity, but reduces the number of meristems available for vegetative differentiation, and leads to lowered growth rates and fecundity later in life, when meristems are limiting. Conversely, meristem commitment to vegetative growth early in life results in low early fecundity but high late fecundity and growth. Meristem limitation, like resource limitation, is a proximate mechanism that generates trade-offs between life history traits. Differences between meristem limitation and resource limitation are discussed. Meristem limitation leads automatically to a senescent life history because of the determinate fate of reproductive meristems. Developmental characters were also found to be genetically correlated with metamer characters (leaf size, internode length) and seed size in this selfing species. The pattern of correlation is suggestive of selection for particular suites of life history and morphological characters.     

Effect of resource gradient on age and size at maturity and their influence on early‐life fecundity in the predatory Asian lady beetle,Harmonia axyridis

Variation in food availability impacts the performance of insects in terms of their size and age to maturity and fecundity. Age at maturity determines how quickly individuals in a population can start to reproduce and how much they can reproduce. Results from studies on various insect species show that food availability influences the size and fecundity of adult females. It is predicted that under poor growth conditions, variation in size is low, but variation in age at maturity is considerable. This prediction was examined in a widely distributed lady beetle species, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), a predator of aphids and coccids. Using a food gradient from low to high aphid prey density, performance of females that were reared on excess food was recorded for pre‐reproductive duration, size at reproductive maturity, number of aphids consumed, and fecundity in the first 10 days of their reproductive period. Results suggested that female H. axyridis that were reared on surplus food when kept at low prey density (poor growth condition) took, on average, three times longer to attain maturity and produced, on average, 14 times fewer eggs than females that were also reared on surplus food, but kept at high prey density (good growth condition). Females performed best at a prey density of 30 aphids per female per 150 cm². Results suggested that the current food availability significantly influenced the age and size of females at maturity and their fecundity. Age and size at maturity of female lady beetles showed non‐linear responses to prey density as well as the occurrence of a minimum size of females, below which H. axyridis females fail to mature. The steep slope recorded at lower prey densities suggests relatively high variation in age at maturity but low variation in size.     

Reasons for success: Rapid evolution for desiccation resistance and life‐history changes in the polyphagous fly Anastrepha ludens

Species that exhibit broad ranges of distribution may successfully navigate environmental changes by modifying some of their life‐history traits. Environmental humidity imposes a critical stress that organisms may overcome by increasing their resistance to desiccation. We used experimental evolution to investigate adaptation to desiccation in the tephritid Anastrepha ludens, a species with high fecundity, late maturation, and long lifespan. We measured morphological, physiological, developmental as well as demographic changes involved in the adaptation to desiccation. Notwithstanding a low heritability (h² = 0.237), desiccation resistance evolved extremely rapidly and few negative trade‐offs were detected. Selected flies exhibited correlated increases in longevity, body size, the amount of body lipids, and bulk water content, and in the duration of the pupal stage. Females further delayed sexual maturation, decreased daily fecundity but retained high lifetime reproductive potential. No differences in male mating competitiveness were found. Selected and control lines differed in longevity but not in total female fecundity, demonstrating that A. ludens flies have the capability for fast adaptation to desiccation without loosing their reproductive capability. Thus, it seems that a rapid evolutionary response to desiccation in this polyphagous insect works as a buffer for environmental variation and reduces the strength of selection on reproductive traits.     

Comparing resource exploitation and allocation of two closely related aphid parasitoids sharing the same host

Species belonging to the same guild (i.e. sharing the same resources) can reduce the negative effects of resource competition through niche partitioning. Coexisting species may differ in their resource exploitation and in the associated allocation of nutrients, depending on their resource niche. Trade-offs in nutrient allocation, such as between reproduction and survival, or between early and late reproduction, are moderated by the abundance and distribution of resources. In this study we investigate differences in larval resource exploitation and adult reproductive strategy of two sympatric aphid parasitoids sharing a common host. The habitat specialist Aphidius rhopalosiphi and the generalist Aphidius avenae occur in cereal crops of Western Europe, where both species attack the major host resource: the grain aphid Sitobion avenae. For this purpose, we measured their acquisition of capital lipid resources, their age-specific fecundity and reproductive effort, their life span and their metabolic rate. We found that these species do not differ neither in larval lipid accumulation nor in the number of eggs at emergence and the timing of egg production, but diverge in other adult reproductive strategies. The rate of adult egg production was higher in A. rhopalosiphi than A. avenae, but at the expense of producing smaller eggs. Throughout adult life, reproductive effort was higher in A. avenae, perhaps facilitated by its higher metabolic rate than A. rhopalosiphi. The divergence between species in life history syndromes likely reflects their adaptations to their resource niche. A high egg production probably allows the specialist A. rhopalosiphi to exploit more S. avenae individuals in cereal crops, while the generalist A. avenae because of its variety of hosts, maximizes the investment per egg but at the expense of a lower lifespan. Our results suggest that differential resource allocation may be a more common pattern that promotes coexistence of species within a guild.     

The influence of environmental instability on the reproductive strategy of the critically endangered Acıgöl killifish (Aphanius transgrediens)

To investigate the variability in the reproductive tactics of Acıgöl killifish (Aphanius transgrediens), one of the most seriously threatened freshwater teleost species, this study compared its reproductive ecology in two contrasting habitats that differ substantially in terms of stability of environmental parameters, particularly salinity regime (stable vs. unstable). Fish were sampled monthly from October 2013 to September 2014 with the aim of testing whether the reproductive life-history response of fish to stable and unstable conditions differed. The reproductive effort (gonad weight) of both sexes did not differ significantly between the two habitats, but females in the unstable habitat had significantly lower fecundity and larger eggs. The relationship between fecundity and fish size was stronger in the stable habitat, whereas the relationship was quite variable and uncertain in the unstable habitat. Fish born in the unstable habitat reached their first maturity at a smaller size than those in the stable habitat. The gonado-somatic index and the duration of hydrated eggs showed that reproduction continued from February to May in both habitats; nonetheless, a second spawning event occurred during July and August in the unstable habitat, which included the reproductive contributions of YOY individuals and older generations. This study’s results suggest that A. transgrediens employs varying reproductive strategies against environmental instability in its restricted unique range. This may have further implications for the ways in which habitat-specific conservation methods are used.     

Variation in fecundity and other reproductive traits in freshwater mussels

1. Life histories of the highly diverse and endangered North American freshwater mussel fauna are poorly known. We investigated reproductive traits of eight riverine mussel species in Alabama and Mississippi, U.S.A.: Amblema plicata, Elliptio arca, Fusconaia cerina, Lampsilis ornata, Obliquaria reflexa, Pleurobema decisum, Quadrula asperata and Q. pustulosa, and compare our results with existing life history information for other species. 2. These eight species had reproductive traits characteristic of large, outcrossing populations: hermaphrodites were rare, we found no evidence of protandry, and sex ratios were even or slightly male‐biased. 3. Age at sexual maturity varied among species, ranging from <1 to 2 years for L. ornata to 3–9 years for Q. asperata. In all species, most mature females participated in reproduction and fertilisation success was high. 5. Fecundity was related positively to both length and age, but length was the best predictor. In six species, fecundity increased exponentially with increasing size; in two species the rate of increase in fecundity declined in larger animals. In four species, fecundity declined in older animals. These latter results indicate weak reproductive senescence; however, in all species, older individuals continued to produce large numbers of offspring. Mean annual fecundity differed widely among species ranging from 9647 to 325 709. Within‐species differences in fecundity were found among rivers and among populations within a river. 6. The wide variation in reproductive traits among species indicates the existence of widely divergent life history strategies in freshwater mussels.     

Comparative oocyte morphology and fecundity of five characid species from São Francisco River basin,Brazil

The morphology of vitellogenic oocytes and the batch fecundity of five tropical forage species belonging to the family Characidae, were studied in 104 late‐maturing ovaries. Significant morphological differences between vitellogenic oocytes and ovarian follicles were found. The lowest batch fecundity values were recorded in Hemigrammus marginatus (480 ± 163) and Orthospinus franciscensis (1701 ± 562), which were the smaller species in terms of total length, body weight and oocyte diameter. The highest batch fecundity value was observed in Tetragonopterus chalceus (8384 ± 3944) having the highest GSI and oocyte diameter. Batch fecundity and gonad weight was highly correlated followed by body weight and total length. Relative fecundity was estimated per unit total length, body weight and gonad weight. The wide variation in fecundity observed between the specimens and the species analysed is possibly related to the multiple spawning reproductive strategy of these fishes. Since T. chalceus have higher values of batch and relative fecundity, it is concluded that this species has a higher reproductive potential than the other forage species studied.     

Context-dependent effects of parental effort on malaria infection in a wild bird population, and their role in reproductive trade-offs

Although trade-offs between reproductive effort and other fitness components are frequently documented in wild populations, the underlying physiological mechanisms remain poorly understood. Parasitism has been suggested to mediate reproductive trade-offs, yet only a limited number of parasite taxa have been studied, and reproductive effort-induced changes in parasitism are rarely linked to trade-offs observed in the same population. We conducted a brood size manipulation experiment in blue tits (Cyanistes caeruleus) infected with malaria (Plasmodium) parasites, and used quantitative PCR to measure changes in parasitaemia. In one of two years investigated, parasitaemia increased as a result of brood enlargement, and was also positively associated with two other indicators of reproductive effort: clutch size and single parenthood. These associations between both experimental and naturally varying reproductive effort and parasitaemia suggest that immune control of chronic malaria infections can be compromised when parents are working hard. Brood size manipulation significantly affected the number of independent offspring produced, which was maximised when brood size was unchanged. Moreover, when parents were infected with one of two common Plasmodium species, the shape of this trade-off curve was more pronounced, suggesting that parasitic infection may exacerbate the trade-off between quantity and quality of offspring. Although the involvement of parasites in survival costs of reproduction has received much attention, these results suggest their role in other commonly documented reproductive trade-offs, such as that between number and quality of offspring, warrants further study.     

Female fecundity traits in wild populations of African annual fish: the role of the aridity gradient

The evolution of life history is shaped by life expectancy. Life‐history traits coevolve, and optimal states for particular traits are constrained by trade‐offs with other life‐history traits. Life histories contrast among species, but may also diverge intraspecifically, at the level of populations. We studied the evolution of female reproductive allocation strategy, using natural populations of two sympatric species of African annual fishes, Nothobranchius furzeri and Nothobranchius orthonotus. These species inhabit pools in the Mozambican savanna that are formed in the rainy season and persist for only 2–10 months. Using 207 female N. furzeri from 11 populations and 243 female N. orthonotus from 14 populations, we tested the effects of genetic background (intraspecific lineage) and life expectancy (position on the aridity gradient determining maximum duration of their temporary habitat) on female fecundity traits. First, we found that variation in female body mass was small within populations, but varied considerably among populations. Second, we found that fecundity was largely defined by female body mass and that females spawned most of their eggs in the morning. Third, we found that the trade‐off between egg size and egg number varied among lineages of N. furzeri and this outcome has been confirmed by data from two separate years. Overall, we demonstrate that local conditions were important determinants for Nothobranchius growth and fecundity and that eggs size in arid region was less limited by female fecundity than in humid region.     

Reproductive allometry does not explain the temperature-size rule in water striders (Aquarius remigis)

Most ectotherms follow the temperature-size rule meaning that individuals growing up under cool conditions are larger as adults than those growing up in warm conditions. This pattern is difficult to explain because growth is usually slower in the cold meaning it takes longer to reach a larger adult size. One potential explanation for this pattern is that the typical increase in fecundity with body size is steeper in cool environments than it is in warm environments. As such, the relative gain in fecundity for being larger in the cold would compensate for the extra time it takes to grow to that size. We present the first empirical test of this model using the water strider Aquarius remigis. Individuals were reared at either 20° or 25°C with subsampling at each instar to estimate growth trajectories. At adult eclosion, half were switched to the alternate temperature and all females isolated, mated, and reproductive output measured for 3 weeks. We found that A. remigis does follow the temperature-size rule but that fecundity was highly plastic with respect to laying temperature such that the slightly greater fecundity of those reared at 20°C was due to their larger size. Overall, those laying at 25°C were more fecund and showed a positive relationship between body size and fecundity. Those laying at 20°C did not show a significant relationship between size and fecundity. As such, the reproductive allometry shows a pattern reverse to what would be needed for a larger size in the cold to be adaptive in this species. Although A. remigis follows the temperature-size rule over this temperature range, this is likely due to a constraint on growth and development rather than being adaptive plasticity.     

Reproductive cycle,sexual maturity and longevity of Odontophrynus americanus (Anura: Odontophrynidae) in South Brazil

Studies on the reproductive biology and age of amphibians provide primary information about the life history and population demographic parameters of species. Here, we describe the reproductive cycle, size–fecundity relationships, reproductive effort, sexual dimorphism and sexual maturity of Odontophrynus americanus, the flood frog, from South Brazil. A total of 96 individuals were analysed. The reproductive cycles of males and females were described through morphoanatomical analysis of testis and ovary. Age at onset of sexual maturity and estimated longevity were determined by skeletochronology. Individuals of O. americanus presented a potentially continuous reproductive cycle with a peak of reproductive activity in the warmer months. Females presented a higher reproductive investment than males. Sexual maturity was reached at around one year of age for both sexes while longevity differed between the sexes, with females living up to six years and males up to ten years. No evidence of sexual size dimorphism was found. This study is among the few that have assessed age at sexual maturity and longevity in a Neotropical anuran. Basic aspects of life history are of paramount importance because they allow comparisons and test of hypotheses to be made, which can help to build generalizations about the evolutionary meaning of ecological strategies.     

Reproduction Strategy of the Deep-sea Hermit Crabs Pagurus alatus and Pagurus excavatus of the Central-Western Mediterranean Sea

Some aspects of the reproductive biology of two hermit crabs Pagurus alatus (Fabricius, 1775) and P. excavatus (Herbst, 1791) were studied. Specimens were collected monthly from April 2000 to March 2001 on the continental shelf and the upper-middle slope off the Southwestern coasts of Sardinia, in the central-western Mediterranean Sea. Crab size (minimum and maximum shield length) was 1.7 and 9.5 mm for 1150 females of P. alatus; 4.0 and 10.4 mm for 347 females of P. excavatus, respectively. Females of P. alatus with ripe ovaries were only found in February-April and ovigerous females were observed throughout the year except in March, with the highest incidence in summer. Females of P. excavatus with fully developed ovaries were collected during all months of the year reaching a peak from April to June. Ovigerous females of P. excavatus occurred throughout the year and the main spawning period occurred in March and April. Fecundity of both species was calculated to assess seasonal variation of reproductive intensity and was positively correlated with the size of the individuals. Monthly fecundity did not reveal significant differences in P. alatus ovigerous females, whereas P. excavatus exhibited significant differences in monthly fecundity depending on the time of year. Difference in fecundity among P. alatus and P. excavatus can be related to the size of the ovigerous females and species of hermit crab, but their different reproductive strategies suggest that they are specifically related to different environmental conditions.     

Reproductive traits of riverine shrimps may explain the impact of altered flow conditions

1. The response of a species to environmental disturbance is largely mediated by its life history traits that have evolved within a particular habitat template. Altered flow seasonality, as a direct consequence of river regulation, is a major environmental disturbance and has been implicated in the redistribution of a range of riverine organisms. An understanding of the reasons for species‐specific responses, however, has proved elusive. 2. Here, we investigated the reproduction of three riverine shrimp species (Paratya australiensis, Caridina mccullochi and Macrobrachium australiense) that show contrasting patterns in distribution and abundance in regulated Australian rivers. 3. In all three species, breeding females were largest, and fecundity was greatest early in the breeding season (November–December). Fecundity and egg size subsequently declined, with lower investment (overall and per offspring) perhaps indicating that conditions for larvae were more favourable later in the breeding season (a time normally characterised by low flow, warm water and high productivity). 4. Interspecific differences in absolute values of reproductive traits were, however, striking. Paratya australiensis has typically ‘opportunistic’ traits (small body size, small eggs and high fecundity), whereas M. australiense has more ‘equilibrium’ traits (larger body size, larger eggs and moderate fecundity). Caridina mccullochi is intermediate, having neither high fecundity nor large size, and has limited swimming ability when young. This species is now absent from at least one heavily regulated river in south‐eastern Australia, and we hypothesise that its life history may explain this absence. 5. Studies involving aspects of life history, such as reproductive traits, are likely to improve our understanding of a range of organisms and assist in the management of disturbed or altered environments.     

Is body size a good indicator of fecundity in the genus Thaumetopoea? A story told by two intrageneric Mediterranean forest defoliators

1. Body size correlates with several factors such as reproductive fitness, environmental changes, the quality and quantity of food during critical development stages, and the feeding season. For the Palearctic moths of the genus Thaumetopoea (Lepidoptera; Notodontidae), the larval development is crucial and differs between species according to their feeding season; larvae of the pine processionary moth Thaumetopoea pityocampa (Denis & Schiffermüller 1775) feed during winter while larvae of its congeneric cedar processionary moth Thaumetopoea bonjeani (Powell 1922) develop during summer in North Africa.
2. This discrepancy in lifecycles leads to different reproductive traits such as egg batch length, number of eggs per batch, eggs protection mechanisms and female body size.
3. According to Darwin's fecundity advantage hypothesis (1871), female body size should have a positive influence on reproductive fitness, since larger females supposedly have higher fecundity. The universal allometric scaling phenomenon rule proposed by Rensch (1950) predicts that the degree of sexual size dimorphism tends to decrease with the increase of female body size.
4. Here, two morphometrical parameters that is, body size and scale size, estimated from body measurements of individuals of both species, feeding on the same host Atlantic cedar Cedrus atlantica (Manetti & Carrière 1855) (Pinales; Pinaceae) in Algeria were proposed. The aim was to find out traits that might rule the competition for food and space, in particularly fecundity and body size.
5. Results of the present study highlight a female-biased sexual size dimorphism in both species. The positive correlation between female body size and fecundity shown in this study weakly supports Darwin's hypothesis. Finally, the intrageneric test performed leads to conclude that Rensch's rule does not hold in the considered species.

     

Reproductive potential of four freshwater prawn species in the Amazon region

The bioecology of freshwater prawns can be understood by studying their reproductive biology. Thus, the aim of this paper was to determine and compare the reproductive potential of four freshwater caridean prawns collected in the Amazon region. For two years, we captured females of Macrobrachium brasiliense, Palaemon carteri, Pseudopalaemon chryseus and Euryrhynchus amazoniensis from inland streams in the municipality of Itacoatiara (AM). At the laboratory, we measured the biometric variables total length, carapace length, abdomen length and total weight, and recorded the number of eggs (NE) by direct counting. There was a significant difference for all variables between the species. The females of M. brasiliense were the most abundant and had the largest sizes and NE. However, the fecundity index shows that P. carteri has the highest reproductive potential of the four species. Despite the differences in size and weight, all the species showed low fecundity, which is a characteristic of continental palemonidean K strategist prawns.     

Egg number–egg size: an important trade-off in parasite life history strategies

Parasites produce from just a few to many eggs of variable size, but our understanding of the factors driving variation in these two life history traits at the intraspecific level is still very fragmentary. This study evaluates the importance of performing multilevel analyses on egg number and egg size, while characterising parasite life history strategies. A total of 120 ovigerous females of Octopicola superba (Copepoda: Octopicolidae) (one sample (n = 30) per season) were characterised with respect to different body dimensions (total length; genital somite length) and measures of reproductive effort (fecundity; mean egg diameter; total reproductive effort; mean egg sac length). While endoparasites are suggested to follow both an r- and K-strategy simultaneously, the evidence found in this and other studies suggests that environmental conditions force ectoparasites into one of the two alternatives. The positive and negative skewness of the distributions of fecundity and mean egg diameter, respectively, suggest that O. superba is mainly a K-strategist (i.e. produces a relatively small number of large, well provisioned eggs). Significant sample differences were recorded concomitantly for all body dimensions and measures of reproductive effort, while a general linear model detected a significant influence of season*parasite total length in both egg number and size. This evidence suggests adaptive phenotypic plasticity in body dimensions and size-mediated changes in egg production. Seasonal changes in partitioning of resources between egg number and size resulted in significant differences in egg sac length but not in total reproductive effort. Evidence for a trade-off between egg number and size was found while controlling for a potential confounding effect of parasite total length. However, this trade-off became apparent only at high fecundity levels, suggesting a state of physiological exhaustion.