Relationship between oocyte morphology and reproductive strategy in loricariid catfishes of the Paraná River, Brazil

Relationships between ovarian structure, oocyte structure/development, and parental care/life history strategies of six loricariid catfishes common in the upper Paraná River, Brazil were examined with analysis of catch data, relative gonad weight, histology, and microscopy. Three life history strategies were observed. Loricariichthys platymetopon , Loricariichthys sp. And Loricaria sp. produce several small clutches of large eggs over a protracted spawning period. Males of these species guard their eggs and larvae, which are transported as a mass on the ventral surface of the male's body. Hypostomus ternetzi and Megalancistrus aculeatus produce the largest mature eggs and the smallest clutches relative to adult mass. The spawning periods of these species are short, and males guard their broods in excavations. Rhinelepis aspera has high fecundity, high relative mass of mature gonads (both sexes), small mature eggs, and broadcast spawning with no parental care. This species migrates to spawn over firm substrates in channel areas during a contracted period. Mature oocytes of external bearers had the thickest zona radiata, followed by the egg scatterer, and cavity nesters. The thickness of the zona radiata probably is an adaptation to protect the developing egg from injury from abrasion. The zona granulosa appeared to be associated with production of secretions responsible for egg adhesion, and this layer was thickest in mature oocytes of the cavity nesting species, followed by the external bearers. All six species have wide distributions in the Paraná River, tributaries, floodplain lagoons, and the Itaipu Reservoir, but brood guarders tended to be most common in lentic habitats.     

Pollen dispersion, pollen viability and pistil receptivity in Leymus chinensis

BACKGROUND AND AIMS: Leymus chinensis is an economically and ecologically important grass that is widely distributed across eastern areas of the Eurasian steppe. A major problem facing its propagation by man is its low sexual reproductivity. The causes of low fecundity are uncertain, largely because many aspects of the reproductive biology of this species remained unknown or incomplete. This study aims to address some of these issues. METHODS: Pollen dispersion, pollen viability, pollen longevity and pistil receptivity were studied in a representative, natural population of L. chinensis growing in Inner Mongolia. KEY RESULTS: Flowering of L. chinensis occurred at the end of June and lasted for 5 d. Pollination peaked between 1600 h and 1700 h, and about 56.1 % of the total pollen grains were released at this time. Pollen density was highest towards the middle of flowering spikes and lowest at the bottom over the 5 d measurement period. Pollen viability (62.4 %) assessed using TTC was more accurate than using IKI (85.6 %); 50 % of pollen arriving on stigmas germinated. Pollen remained viable for only 3 h and the pollen : ovule ratio was 79 333 : 1. Pistil receptivity lasted for only 3 h and, overall, 86.7 % of pistils were pollinated. Within the spike, the relative fecundity of different positions was middle > lower > upper throughout the period of pollination; daily variation of fecundity was similar to that of the pollen flow. The spikes that opened on the day of highest pollen density exhibited the highest fecundity (36.0 %). No seeds were produced by self-pollination. CONCLUSIONS: The data suggest that low pollen viability, short pollen longevity and short pistil receptivity all appear to contribute to the low seed production typical of this important forage crop.     

Copulation reduces male but not female longevity in Saltella sphondylli (Diptera: Sepsidae)

Mating more than once is extremely costly for females in many species, making the near ubiquity of polyandry difficult to understand. However, evidence of mating costs for males is much rarer. We investigated the effects of copulation on longevity of male and female flies (Saltella sphondylli). We also scrutinized potential fecundity and fertility benefits to females with differing mating history. Copulation per se was found to decrease the longevity of males but not that of females. However, when females were allowed to lay eggs, females that mated died earlier than virgin females, indicating costs of egg production and/or oviposition. Thus, although longevity costs of copulation are higher for males, reproduction is nevertheless costly for females. We also found no differences in fecundity or fertility relative to female mating history. Results suggest that polyandry may be driven by minor costs rather than by major benefits in this species.     

A local influence approach applied to binary data from a psychiatric study

Recently, a lot of concern has been raised about assumptions needed in order to fit statistical models to incomplete multivariate and longitudinal data. In response, research efforts are being devoted to the development of tools that assess the sensitivity of such models to often strong but always, at least in part, unverifiable assumptions. Many efforts have been devoted to longitudinal data, primarily in the selection model context, although some researchers have expressed interest in the pattern-mixture setting as well. A promising tool, proposed by Verbeke et al. (2001, Biometrics 57, 43-50), is based on local influence (Cook, 1986, Journal of the Royal Statistical Society, Series B 48, 133-169). These authors considered the Diggle and Kenward (1994, Applied Statistics 43, 49-93) model, which is based on a selection model, integrating a linear mixed model for continuous outcomes with logistic regression for dropout. In this article, we show that a similar idea can be developed for multivariate and longitudinal binary data, subject to nonmonotone missingness. We focus on the model proposed by Baker, Rosenberger, and DerSimonian (1992, Statistics in Medicine 11, 643-657). The original model is first extended to allow for (possibly continuous) covariates, whereafter a local influence strategy is developed to support the model-building process. The model is able to deal with nonmonotone missingness but has some limitations as well, stemming from the conditional nature of the model parameters. Some analytical insight is provided into the behavior of the local influence graphs.     

Comparative population growth and life table demography of the rotifer Asplanchna girodi at different prey (Brachionus calyciflorus and Brachionus havanaensis) (Rotifera) densities

Population growth and life table demography of the predatory rotifer A. girodi using spineless Brachionus calyciflorus and spined Brachionus havanaensis as prey at densities of 1, 2, 4 and 8 ind. ml^–1 at 25°C were studied. Regardless of the prey species, the population of A. girodi increased with increasing availability of Brachionus in the medium. At any given prey density, A. girodi fed B. calyciflorus showed consistently better growth than when fed B. havanaensis. The maximum population densities of A. girodi varied from 0.28 to 1.8 ind. ml^–1 depending on the prey species and the density. The rate of population increase observed in population growth studies varied from 0.17 to 0.43 day^–1 when fed B. calyciflorus and 0.09 to 0.27 day^–1 when fed B. havanaensis. Male population of A. girodi was closely related to female density. The lowest average lifespan was observed for A. girodi when fed B. havanaensis at 1 ind. ml^–1, while the converse was the case when fed B. calyciflorus at comparable prey concentration. Net reproductive rates varied from 16 to 26 offspring female^–1 lifespan^–1 depending on the prey species and concentration. Generation time of A. girodi decreased with increasing food concentrations for both the prey species. The rates of population increase obtained from life table demography were lower for A. girodi when fed B. havanaensis than when fed B. calyciflorus.     

Reproductive Biology of the Smooth Dogfish, Mustelus canis, in the Northwest Atlantic Ocean

Shark populations tend to be highly vulnerable to overexploitation due to low fecundity and slow growth rates. Recent fishing pressure on the smooth dogfish in the northwest Atlantic has created a necessity for more information about their basic biology. Length and age at maturity, fecundity, and reproductive season were estimated. Total length at 50% maturity was 102cm for females, and 86cm for males. The majority of females were mature at age 4 or 5, and all males were mature at 2 or 3 years of age. Females had an 11–12 month gestation with parturition occurring in May, ovulation occurring between May and July likely in late May and early June, and mating occurring between May and September. Fecundity ranged between 3 and 18 pups per litter, and was positively related to length and age, with a mean of 9.53 pups per litter. Sperm was found in the terminal zone of the oviducal gland of females throughout the year.     

Reproductive Parameters and Maternal Investment in Mandrills (Mandrillus sphinx)

We report on 14 years of reproductive data for semifree-ranging mandrills (Mandrillus sphinx) in Gabon, and we explore relationships between female rank, age and parity, and reproductive strategies. Most births (61% of 132) occurred during the wet season in Gabon, between January and March. Female rank and parity were unrelated to the timing of parturition. Gestation lengths average 175 days (SE = ±1 day; N = 61) and were similar irrespective of female rank, parity, or sex of offspring. Birth sex ratio did not differ significantly from unity (52% male), and was unrelated to maternal rank or parity. Stillbirths and neonatal mortality tended to be more common among lower-ranking females than among either mid-ranking or dominant females. Median age at first birth is 4.71 years, at a median body mass of 7.6 kg, ca 5 years before females attain their adult body mass (median 12 kg). Age at first reproduction is significantly correlated with dominance rank, with dominant females giving birth on average 1.3 years earlier than lower-ranking females do. Interbirth intervals (IBI) average 405 days (range 184–1159 days, N = 103), and are independent of the sex of the offspring. Infant death within 6 months shortened IBI to 305 days. Increasing age and parity are also associated with short IBI, as is higher rank. Maternal rank and parity appear to influence reproductive success in female mandrills, but there is no apparent differential maternal investment by sex.     

Reproductive Biology of Southwestern Atlantic Wreckfish, Polyprion americanus (Teleostei: Polyprionidae)

We report on the reproductive biology of southwestern Atlantic wreckfish. Females mature first at 77.9cm total length (TL) (10.4 years) and all are mature by 90cm TL (15.2 years). Males mature first at 74.9cm (9 years) and all are mature by 80cm TL (10.9 years). The wreckfish is a gonochoristic multiple spawner and the gonadal cycle is synchronized at the population level. Spawning occurs from late July to early October along the continental slope (<300m). Ovarian fecundity varies from 3 to 11.9 million (135–311 oocytes×g^–1) and increases exponentially with length. Spawning at western boundary current systems, maintained by homing of adults, is a basic requirement for self-sustaining populations of this species.     

Impact of cysteine proteinase inhibition in midgut fluid and oral secretion on fecundity and pollen consumption of western corn rootworm (Diabrotica virgifera virgifera)

Cysteine proteinases predominate in the midgut fluid (MF) and oral secretion (OS) of adult western corn rootworm (WCR) based on their mild acidic pH optima (pH 6.0), enhanced activities after treatment with thiol reducing agents, and inhibition by selective cysteine proteinase inhibitors (PIs). Four cysteine PIs including E-64, calpeptin, calpain inhibitor II, and leupeptin (also a serine PI) strongly inhibited azocaseinolytic activity in a dose-dependent manner in both the MF and OS. The most significant effect on adult female WCR of cysteine PI consumption with corn pollen was the reduction in fecundity, but female survival was not apparently affected. Mean fresh weights for all PI-fed females were also lower than control groups. All PI-fed groups [E-64, calpain inhibitor I (Cal I) and leupeptin] had a significantly lower daily egg production than respective corn pollen-fed controls. E-64 was more potent than leupeptin and Cal I on inhibiting fecundity, which correlates with their relative anti-proteinase potency in vitro. E-64, Cal I, and leupeptin at 1.5-2 nmol/beetle/day reduced fecundity down to 25-45% of control values. Reduced egg production by PI-fed beetles results from a combination of the direct inhibition of protein digestion and a post-ingestive negative feedback mechanism, which reduces food intake. The supplement of ten essential amino acids into the E-64-treated pollen enhanced up to 3.7-fold the number of eggs laid compared to the E-64-fed group without these amino acids, suggesting that egg production is dependent on the supply of essential amino acids from corn pollen proteolysis.     

Habitat Preference, Reproduction and Diet of the Earthworm Eel, Chendol keelini (Teleostei: Chaudhuriidae)

The ecology of the earthworm eel, Chendol keelini, was studied in the field over a period of nine months. In addition this information was supplemented by aquarium observations. The species was most abundant in pools where it was associated with leaf litter and mats of fine tree roots along the banks. It fed on benthic invertebrates, especially chironomid and ephemeropteran larvae. C. keelini is sexually dimorphic; adult males develop a headhump and grow to a larger size than females. Reproduction was seasonal; the reproductive phase coincided with the wet season and lasted for several months. Fecundity was around 40 eggs per clutch. The eggs were spherical, between 1.2 and 1.5mm in diameter, and possessed a pair of long filaments for adhesion to the substrate. Females probably spawned more than once during the breeding season. The length frequency distributions and juvenile growth suggest that C. keelini is a short-lived species that matures during the first year with few individuals surviving to the second breeding season.