Morphological and physiological responses to increased salinity in marsh and dune ecotypes ofSporobolus virginicus (L.) Kunth

Summary Sporobolus virginicus (L.) Kunth is a halophytic grass native to tropical and warm temperate coasts throughout the world. A rhizomatous perennial with erect culms,S. virginicus occurs as two genetically distinct growth forms, which are designated by their characteristic habitats as marsh and dune. What accounts for the specific distribution and maintenance of two separate ecotypes ofS. virginicus is not known. The present study examined the effects of seawater salinity on several morphological and physiological responses of hydroponically cultivated marsh and dune plants to determine whether differential tolerance to substrate salinity might contribute to the observed pattern of habitation. Both marsh and dune form plants survived prolonged exposure to full-strength seawater and reproduced vegetatively via culms and rhizomes. Salinity-induced reductions in culm height, internode length, and leaf size led to a miniaturization of marsh and dune plants. Sodium ion levels were low (<1.0 mmol/g dry weight) in various organs of salinized plants irrespective of ecotype, and potassium ion content increased in all salt-challenged plants, as did quarternary ammonium compounds and proline. Significant differences, however, between marsh and dune plants with respect to the effects of salinity on resource allocation, flowering phenology, and protein composition suggested that external salt concentration has a role in determining ecotype distribution.     

Coexistence of Tetranychus urticae (Acarina: Tetranychidae) with different capacities for diapause: comparative life-history traits

Summary Individuals of the two-spotted spider mite, Tetranychus urticae Koch (Acarina: Tetranychidae), with and without a capacity for diapause, coexist in central Japan. Diapause appears to be adaptive because females in diapause suffered less mortality than non-diapausing individuals when frozen at –24°C for more than 4 h. However non-diapausing females showed good survival up to 4 h of freezing. Active non-diapausing mites survived on rose leaves in Kyoto (35°N) throughout the winters of 1988–1989 and 1989–1990. Cultures of mites with low (LD) and high (HD) diapause capacities at 18°C and 9L-15D photoperiod were successfully selected from the rose population and from a population on chrysanthemum in Nara (34.4°N). Their life-history traits at 15, 20, 25 and 30°C were characterized. HD and LD mites from both populations were of similar ages at first reproduction at 15–30° C. However, at temperatures 20° C, HD individuals produced more eggs than LD individuals, resulting in higher fecundity and intrinsic rate of natural increase. These traits allow HD individuals, which stop breeding between October and April, to increase faster in summer than LD individuals. This provides a mechanism, together with climatic fluctuations, in maintaining the coexistence of diapausing and non-diapausing T. urticae in Kyoto where winter conditions are rarely lethal to the non-diapausing individuals.     

Sex determination in cucumber (Cucumis sativus) as a model system for molecular biology

Floral biology and sex determination are reviewed in cucumber, one of the best studied monoecious plant systems. Sexual differentiation is controlled by genotypic and environmental factors. Sex conversion has been achieved by a variety of chemical treatments, some of which being extensively used for commercial purposes. Sex expression can be shifted in either direction: femaleness is promoted by ethylene, auxines and ethylene releasing compounds, while maleness is induced by gibberellins and chemicals counteracting ethylene action. Agrobacterium transformation affects, albeit rather nonspecifically, sex expression. An important collection of sex and floral mutants has been developed. The expression of sex genes has been shown to be under the control of modifier genes or the environment. Cloning strategies can take profit of the fact that sex conversion can be modulated alone or in combination by genetical, chemical and/or environmental parameters.     

The association between amount of red muscle and mobility in fishes: A statistical evaluation

Synopsis It is commonly accepted that more active fishes have a greater proportion of red muscle in their trunk musculature than do less active fishes. Further, the proportion of red muscle has been used to classify fish species into functional groups reflecting different activity patterns. Nevertheless, existing measures of both red muscle and mobility have several limitations, and the relationship between these parameters has never been evaluated quantitatively. Using data from the literature, we demonstrate a positive, statistical association between the proportion of red muscle in the caudal peduncle of marine fishes and a qualitative measure of mobility (categorization as sedentary vs. mobile based on natural-history accounts). Analyses of the frequency distribution of the proportion of red muscle also provide evidence for two subdistributions. However, this bimodality does not correspond with sedentary vs. mobile or sit-and-wait vs. active search dichotomies.     

Sperm utilization and post-copulatory female-guarding in the Colorado potato beetle, Leptinotarsa decemlineata

Crosses between white and black color morphs of the Colorado potato beetle, Leptinotarsa decemlineata Say, used as genetic markers, showed that male beetles ride and guard females to achieve the three copulations required to fill the spermatheca. Multiple matings are necessary for the females to realize their full reproductive potential. Sperm mixing occurs in the spermatheca providing partial sperm precedence. The data support the competitive mate searching theory.

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Résumé Différentes combinaisons d'accouplements entre des mutants noirs et blancs du doryphore de la pomme de terre, Leptinotarsa decemlineata, servirent à étudier le comportement de guarde de la femelle par le mâle après un premier accouplement. Les résultats indiquent que le sperme de deux mâles accouplant la même femelle se mélange dans la spermathèque assurant ainsi un certain niveau de précédence du sperme du dernier mâle.La masse de sperme dans la spermathèque était inférieure à sa capacité chez les femelles ayant été accouplées une ou deux fois. Le doryphore mâle aurait donc avantage à demeurer sur la femelle après un premier accouplement afin d'obtenir le minimum de trois accouplements requis pour remplir la spermathèque avant que les autres mâles puissent accoupler cette femelle. Les autres mâles ont avantage à essayer de dérober cette femelle pour remplir eux mêmes la spermathèque ou tout au moins profiter d'une certaine précédence du sperme du dernier mâle pour fertiliser une partie des oeufs.Sans accouplements multiples, la femelle ne possède pas suffisamment de sperme pour féconder tous ses oeufs. II semble aussi que les accouplements répétés puissent augmenter sa fécondité.Les résultats supportent une stratégie reproductive de compétition plutôt qu'une simple maximisation du nombre d'accouplements.

     

Comparative bioenergetics of permanent and temporary pond populations of the freshwater clam,Musculium partumeium (Say)

The population energetics of a temporary and a permanent pond population of Musculium partumeium in Southwest Ohio were studied. In the permanent pond (surface area = 396 m², maximum depth = 0.7 m) the population was bivoltine and iteroparous whereas in the temporary pond (surface area = 1042 m², maximum depth = 0.9 m) the population was usually univoltine and semelparous.Growth and biomass were assessed as total organic carbon and total nitrogen to provide estimates of productivity and seasonal changes in C:N for each generation. Productivity (non-respired assimilation = growth + reproduction; N-R.A. = G + R) was 6939 mgC·m^–2·a^–1 (3858 and 3353 mgC·m^–2·a^–1 for each generation) and 1661 mgC·m^–2·a^–1 for the permanent and temporary pond populations respectively. The average standing crop biomass (B) was 606.8 mgC·m^–2 (357.5 and 249.3 mgC·m^–2 for each generation) and 231.9 mgC·m^–2 with overall productivity: biomass ratios of 11.4 and 7.2 for the permanent pond and temporary pond populations respectively.Respiration rates were converted to carbon equivalents (respired assimilation = R.A.) and used to evaluate the components of total assimilation (T.A. = R.A. + N-R.A.) and the efficiency of partitioning this energy to N-R.A. for G and R. When expressed as a percentage, the production efficiencies (100 × N-R.A.:T.A.) were 50.4 and 62%, and the reproductive efficiencies (100 × R:N-R.A.) were 26.4 and 18% for the permanent and temporary pond populations respectively. The reproductive efficiencies for populations of these viviparous clams are greater than those for most oviparous molluscs.The comparative information on the energetics of these populations does not completely fit any theoretical consideration of reproductive effort or life-history strategy. These data are discussed in relation to selection for population success in temporary ponds.Funded in part by grants to Albert J. Burky from the Ohio Biological Survey and the University of Dayton Research CouncilFunded in part by grants to Albert J. Burky from the Ohio Biological Survey and the University of Dayton Research Council     

The adaptive significance of behavioural ontogeny in some. centrarchid fishes

Synopsis Studies on the ontogeny of behaviour in fish have seldom considered the adaptive significance of the order of appearance of the behaviours. Results of laboratory studies and field observations on the ontogeny of feeding, predator-avoidance, and agonistic behaviour in largemouth bass, Micropterus salmoides, rock bass, Ambloplites rupestris, and pumpkinseed, Lepomis gibbosus, young indicate that the order of appearance of the various behavioural systems enhances the survival of the young. In the laboratory, all species spend significantly more time feeding during the first weeks of free-swimming than the later weeks. During a corresponding period in the field the young are either occupying an offshore area low in predators (rock bass, pumpkinseed) or are being guarded by a parent (largemouth bass); thus the risk of predation is low. When the young are in a predator-rich environment (inshore) both the predator-avoidance response and agonistic behaviour are well developed. Agonistic behaviour is the last to appear and may serve to disperse the young. Dispersal may relate to the feeding mode of the various species and may also reduce the probability of predation. It is apparent that the sequential onsets of the behavioural systems are in concert with ecological events and selective pressures confronting centarchid young.     

Social and reproductive behavior of three mouthbrooding cardinalfishes,Apogon doederleini,A. niger and A. notatus

Synopsis Social and reproductive behavior of three paternal mouthbrooding cardinalfishes (Apogonidae) were investigated in the shallow marine waters of Shirahama, Japan. The solitary species Apogon doederleini and A. niger bred in transient pairs, in which a male and female associated for only a few hours of each afternoon on less than 5 successive days. The prespawning behavior was the same as the courtship display on days prior to spawning. After spawning, egg-incubating males were usually left alone. The gregarious species Apogon notatus formed territorial lasting pairs, which resided at given sites from dawn to dusk on each day during a period of a month or more. After spawning, the egg-incubating male either continued to stay with his mate in the territory, or left it to enter into an aggregation. In the latter case, the female continued to reside in the territory, pairing with a new male whom she brought from an aggregation. It is suggested that in paternal apogonids the prolonged pair bond and territoriality should have developed only in gregarious species as secondary adaptation for reproductive success: to avoid conspecific interference during spawning.     

Time-budgeting and foraging strategy of the stoplight parrotfish Sparisoma viride Bonnaterre,in Jamaica

Quantitative data on the ways in which the different phases of the stoplight parrotfish (Sparisomaviride Bonnaterre) distribute their time among various activities in different habitats are presented. Individuals spent from 84–97% of their diurnal time swimming, feeding, and hovering. Additionally, large adults spent a significant amount of time sheltering among crevices. Phase-related differences in these activities are statistically significant, as are differences in duration and rates of change of the activities. Large individuals spent more time swimming, while small individuals spent more time hovering. In addition, large individuals performed longer bouts of activity and switched activities less frequently than small individuals. Adult males and females spent approximately equal proportions of time in each of the activity states. Stochastic analyses of behavioural sequences show second order Markov chain dependencies, suggesting that preceding activity states affect subsequent behaviour. Possible relationships between behavioural sequencing and the species foraging strategy are discussed, and it is suggested that the sequence of behavioural activities can provide an estimation of the distribution of food resources in the environment.     

Reproductive strategies of the orang-utan: New data and a reconsideration of existing sociosexual models

Recent field data indicate that MacKinnon’s model of the orang-utan’s sexual and agonistic activity needs to be revised. In this model, male reproductive activity is concentrated in an extended phase of subadulthood and in early adulthood. According to this model, the role of older adult males is primarily that of range guardian, and in that role they would ensure that the offspring they had generated earlier would have safe access to food resources. This study presents cases suggesting that subadult males, even though sexually active, may have low reproductive success. In previous studies adult males were shown to display less sexual initiative than subadult males. In this study an adult male was at times involved infrequent mating activity in response to proceptive activity of females in the course of consortship. This adult male proved to be a successful breeder, thus refuting the hypothesis of adult male sterility. The female is most likely to conceive through cooperative mating in lengthy consortships with the dominant resident adult male. We hypothesize that the extended subadult phase represents a submissive strategy, allowing subadult males to remain in the home range of adult males but with minimal reproductive success.