Reproductive lability in pre-dispersal biology ofRhamnus alaternus L. (Rhamnaceae)

Summary Rhamnus alaternus L. is a dioecious, fleshy-fruited shrub, typical of Mediterranean vegetation, which has been recorded from the region since the tropical Tertiary. Reproductive biology of this species has been studied in Southern Italy over a period of 4 years with both field and laboratory experiments. In all the studied populations male plants predominate over the females, have a higher flower density and flower regularly every year while females are usually alternate-bearing. A strong negative association between fruit formation and vegetative growth has been found indicating that the presence of fruits on a branch reduces the growth of new shoots. This phenomenon, together with alternate-bearing, is evidence of a strong competition between vegetative growth and reproductive activity and indicates resource limitation. Flower morphology and quantity of pollen produced are typical of insect pollinated species, and flies of the Empididae and Muscidae were trapped bearing pollen at female plants but pollen is also dispersed by wind. Field experiments on pollination success showed that the exclusion of insects as pollen vectors produces a significant decrease in fruit development. Excess pollen provided by hand-pollination increases fruit set over open-pollination and reproductive success in the field is therefore pollen limited. The variability of sex expression, male fitness, fruit production, regrowth and pollination presented here suggests that these predispersal characteristics ofR. alaternus have been subject to evolutionary change since the tropical Tertiary climate was replaced by a Mediterranean one. This points to the possibility that reproductive, as well as morphological and physiological characteristics, may be equally selected for in extreme environments such as the Mediterranean.     

Energy allocation for reproduction in a marsupial arboreal folivore,the common ringtail possum (Pseudocheirus peregrinus)

This study examines the annual energetics of a small folivorous marsupial, Pseudocheirus peregrinus. Particular attention was given to the energy and time allocated to reproduction by the females. Daily energy expenditure was measured directly using the doubly labelled water technique. Energy transferred to the young via the milk was estimated from information on milk composition and production. There was no significant seasonal variation in the energy expenditure or water influx of males or females. The mean daily energy expenditure of a 1-kg non-lactating adult ringtail possum was 615 kJ day^–1 or 2.2 times standard metabolic rate. Females showed significant changes in daily energy expenditure according to their reproductive status. Without the burden of lactation the total annual energy expenditure of an adult female was estimated as 212.4 MJ kg^–1 year^–1. The total annual energy expenditure of a female rearing two young was 247.5 MJ kg^–1 year^–1, with the late stage of lactation constituting the most energetically expensive period accounting for 30% of the total yearly energy expenditure during 24% of the time. Total metabolisable energy allocation during reproduction (22 MJ kg) was similar to estimates available for other herbivores, although, the peak metabolisable energy allocation during lactation (759 kJ day^–1) was lower than values available for other herbivores. The total energy requirement for reproduction (metabolisable energy plus potential energy exported to young via milk) suggests that the ringtail possum also has a relatively low overall energy investment in reproduction. It is suggested that the lactational strategy of the ringtail possum has been selected in order to spread the energy demands of reproduction over time due to constraints on the rate of energy intake imposed by a leaf diet and/or to prolong the mother-young bond. The strategies a female ringtail possum may employ to achieve energy balance when faced with the energy demands of reproduction are discussed.     

Population structure and mycelial phenotypic variability of the ectomycorrhizal basidiomycete Laccaria bicolor (Maire) Orton

Mating type allele distribution and phenotypic variability were investigated in field populations of Laccaria bicolor. Sporophores associated with Norway spruce (Picea abies), colonized by natural sources of inoculum and growing in a seed orchard, were sampled to obtain dikaryotic strains and assay their phenotypic variability for traits important to the symbiosis. Basid-iospores were also collected for mating type analysis of different mycelia. Four sporophore mating types were identified containing seven A and five B factors. Out-breeding efficiency was estimated at 73.8% and the population was slightly inbred. Crosses with previously characterized L. bicolor strains from two nearby populations identified in total six sporophore mating types and ten A and nine B factors, for an estimated outbreeding efficiency (85.7%) similar to previous studies of more spatially disparate Laccaria spp. populations. Dikaryotic strains were tested for mycelial growth rate, as a measure of their competitive ability, on agar media containing a soluble (NaH₂PO₄), or an insoluble (CaHPO₄) phosphate source. Their ability to solubilize the latter was also tested to assess their relative capacity to access insoluble, inorganic phosphate. In most cases, significant variation was detected among strains from the same site for all variables. On three sites (VC4, VC5 and VC7), each determined previously to possess a uniform mycelial genotype, phenotypic variability was likely due to epigenetic variation among different strains of the same genotype. Possible evidence for dikaryon-monokaryon crosses was observed in vivo on one sample site (VC2) where adjacent mycelia shared two mating factors. The phenotypic variability of different mycelial genotypes reflected their genetic variability observed as mating type allele diversity and underlined the importance of basidiospore dispersal in introducing new genotypes into the population. The reproductive strategies of L. bicolor are discussed and compared to those of other basidiomycete species.     

Reproductive systems in conifer seed orchards

Summary In order to quantify female and male fitness values of clones in a Pinus sylvestris L. seed orchard, multilocus-genotypes of parental clones were compared with those of open pollinated seeds in the bulked orchard crop. Female and male contributions to individual seeds were distinguished by observing enzyme gene loci active in both endosperm and embryo tissue. Seed probes from two successive flowering periods were surveyed. The female and male fitnesses of five parental clones measured relative to the population mean were derived. The contributions of four clones were found to be sexually asymmetric. One clone, for instance, made exclusively female contributions in one flowering period. Variations existed in fitness values between clones. Deviations in sex specificity occurred between flowering periods: one clone contributed asymmetrically in both periods, but in sexually reversed proportions. A method to comprehensively quantify and illustrate the observed phenomena is proposed.     

Stage-specific expression of three cell surface carbohydrate antigens during murine spermatogenesis detected with monoclonal antibodies

We have identified three germ cell surface carbohydrate antigens that exhibit a common, stage-specific pattern of expression during spermatogenesis in the mouse. IgM-class monoclonal antibodies designated "J1," "C6," and "A5" were absorbed by adult testis, but not by any adult somatic tissue tested. In indirect immunofluorescence assays using collagenase-dissociated prepuberal and adult testicular cells, these antibodies labeled the surfaces of early and late pachytene spermatocytes and round spermatids. Gonocytes from fetal and neonatal testes were not labeled. In paraffin sections of prepuberal and adult testes, sialidase treatment exposed antigens recognized by antibodies C6 and A5 on preleptotene, leptotene, and zygotene spermatocytes located near the perimeter of seminiferous tubules. The determinants recognized by antibodies J1, C6, and A5 were characterized partially using a sugar hapten inhibition assay. The binding of J1 to adult testicular cells was inhibited specifically by N-acetylglucosamine and the binding of both C6 and A5 was inhibited by N-acetyllactosamine. The glycoconjugates recognized by J1, C6, and A5 eluted from gel filtration columns with an apparent molecular weight greater than 1 X 10(6) and were sensitive to endo-beta-galactosidase (keratanase) treatment. The apparent high molecular weight of these glycoconjugates was confirmed by immunolabeling Western blots of testis extracts separated by SDS-polyacrylamide gel electrophoresis. The results suggest that polylactosamine (keratan) glycoconjugates of high molecular weight are associated with the plasma membranes of meiotic and haploid male germ cells. The effects of sialidase on antibody labeling patterns suggest that changes in cell surface sialylation accompany the transition of early meiotic germ cells to pachytene spermatocytes during spermatogenesis.     

Life history variation among female surfperches (Perciformes: Embiotocidae)

Synopsis Life history variation within the family Embiotocidae is extensive and involves differences in age of first reproduction, fecundity schedules, growth rates, longevity and size of young. Based on maximum reported body lengths, there are three distinct size groups among the family's 23 species. Small species do not exceed 215 mm TL, medium-size species attain 275 to 335 mm TL, and the large species attain 380 to 470 mm TL. The longevity oh surfperches varies from two to ten years, growth is indeterminate, and females of the medium-and large-size groups may delay first reproduction beyond age one. With one exception, all species show increasing length-specific fecundities. The life history characteristics of females differ among the three size groups. Relative to smaller species, the largest species have moderately high fecundity, delayed maturity and long life. Medium-size species have low fecundity, may delay maturity for 1 to 3 years and have intermediate life spans. Small species have generally higher, but variable, fecundity, do not delay maturity, and are short lived. Among the small North American species, the trend in fecundity varies inversely with environmental predictability. Fecundity is highest in the species which occupies highly seasonal freshwater environments. Coastal species produce moderately large broods and species which occupy stable deep water environments produce the smallest broods.     

Perception of residential crowding,classroom experiences,and student health

The present research is based on a typology of crowding experiences incorporating two main dimensions: neutral-personal thwartings and primary-secondary environments. The thwarting dimension concerns the degree to which crowding experiences are associated with spatial inconveniences, alone, or with spatial as well as social constraints. The environmental dimension relates to the type of setting in which crowding experiences occur. A major assumption of this typology is that crowding experiences involving social conflict will be more intense and disruptive to the individual than those in which interpersonal conflict is minimal. The reported study examined the relationship between college students' evaluations of the physical amenity, social climate, and crowdedness of their residential environments, on the one hand, and their sensitivity to crowding in a classroom situation, their academic performance, and the frequency of their visits to the campus health center, on the other. Results indicated that perceived residential crowding and negative perceptions of residential social climate were strongly associated with increased sensitivity to crowding in a classroom situation, impaired course performance, and visits to the student health center. The implications of these correlational findings for future field-experimental research are discussed.     

Changes in the surface morphology of the rabbit endometrium related to the estrous and progestational stages of the reproductive cycle

Summary Changes occurring on the surface of the uterine luminal epithelium of the rabbit during the estrous and progestational stages of the reproductive cycle were examined by scanning and transmission electron microscopy. The findings demonstrate that the uterine epithelium, or endometrium, contains two cell types: ciliated cells and nonciliated, microvillous cells. In estrous animals, ciliated cells, although not very numerous, were usually observed in small groups. However, at increasing intervals of time following mating, ciliated cells progressively disappeared from the endometrium until approximately eight to ten days post coitum, when they became scare. From several hours to four to five days following mating, extensive changes occurred on the surfaces of microvillous cells. When observed by TEM, these elements contained organelles typical of cells involved in the synthesis and secretion of glycoproteins. Furthermore, microvillous cells during this period displayed numerous apical protrusions of different sizes and shapes and containing material of varying electron density. Parallel SEM examinations of the same material confirmed the presence of these protrusions. Some of the protrusions appeared as spheroidal masses attached to the cytoplasm by means of a cytoplasmic strand. Other surface masses were clearly unattached to the cell surface and were distributed (1) on the surface of microvillous cells, (2) on the cilia of adjacent ciliated cells, and (3) on the surface of spermatozoa.Changes occurring on the luminal surface during the early postcoital period are interpreted as an expression of morphodynamic processes likely involving coupled secretion (exocytosis) and resorption (endocytosis) of luminal material. The observations presented here also demonstrate that between six and ten days post coitum, the rabbit endometrium contained increasing numbers of enlarged, nonciliated cells that probably arose by the fusion of smaller, microvillous elements.The work reported here was supported by C.N.R. contracts No. CT 760128809 and CT 77014239 (to P.M.) and NIH. Grant HD-04274 (to J.V.B.)     

Fish community structure in lakeshore lagoons on long point,lake Erie,Canada

Synopsis The interaction of fluctuating water level and the Long Point topography is discussed with regard to the formation of lake-shore lagoons and their subsequent invasion by fishes. The species composition of fish communities in these lagoons was determined by 12 collections from lagoons (23 m² to 25 ha) which yielded 33 fish species. The relationship of the number of fish species to lagoon area was lognormal; that is, with increasing lagoon area the number of species rose rapidly at first but soon decreased sharply, probably limited by the number of species capable of surviving in the habitat. The marked effect of area on species number in small lagoons is considered in the context of a hypothetical seasonal pattern of occasional invasion and continuous extinction.A sequence of reproductive guilds was found. In beach lagoons psammophils and lithophils were dominant. In a large vegetated lagoon in the interior phytophils and speleophils were dominant. This sequence was paralleled by an increase in the proportion of guarding and nesting species in the communities. The sequence was disrupted in the small interior lagoons where adaptations for survival were more important than reproductive strategy.     

Physiological responses of Uroleucon jaceae (L.) to seasonal changes in the quality of its host plant Centaurea jacea L.: multilevel control of adaptations to the life cycle of the host

Summary Exploiters of short-lived plants have evolved strategies in response to physiological changes that occur during the development of their hosts. The ability to adapt to host quality changes is necessary particularly if the mobility of an animal is poor or risk-constrained. In the plant-aphid system Centaurea jaceae-Uroleucon jaceae, the responses of the aphid to the seasonal changes in its host plant grown in poor and good quality soil were investigated. Coarse- and fine-tuned physiological reactions were observed in discrete aphid generations which were reared on plants grown either in a growth chamber or in a greenhouse. The number of ovarioles and developmental time depended on extrinsic factors (length of photoperiod) not directly related to plant quality. The reproductive investment of the aphids was also independent of their total dry weight. However, within the gonadal system high correlations were found at the embryonic level (e.g. the number of sclerotized embryos or the length of the oldest embryos per ovariole were highly correlated with gonadal dry weight). Aphids which were living on the 4-leaf stage of high-quality host plants showed a significantly higher investment in their gonads than aphids feeding on senescenting hosts. Factor analysis corroborated that aphids reared on poor-quality hosts revealed no grouping of variables measured, whereas those which were reared on high-quality plants showed clustering in respect of somatic (tibia length, dry weight of soma) and gonadal (number of sclerotized and unsclerotized embryos, length of the oldest embryos, ovariole number, gonad dry weight) factors. Three different levels of adaptive response to plant quality are distinguished: individual response to host quality, maternal influences on offspring and response to changes not specific to habitat (photoperiod). These different levels of regulation are thought to enable the aphids to adapt to a host of a given nutritional quality and anticipate deteriorating habitat quality simultaneously. It is concluded that physiological constraints in aphids are only revealed when aphids are exposed to severe nutritional stress for several generations.