Sperm quality, secondary sexual characters and parasitism in roach (Rutilus rutilus L.)

According to sperm competition models, a male spawning in a disfavoured role should have spermatozoa with higher velocity but shorter longevity compared with a male spawning in a favoured role. Moreover, immunosuppressive androgens are needed to produce both secondary sexual characters and sperm cells. The 'sperm protection' hypothesis suggests that the immunosuppressive action of androgens has evolved to protect haploid spermatozoa, which are antigenic, from autoimmune attacks. Therefore, a male with high sexual ornamentation may be more susceptible to diseases but may possess better quality ejaculate than his less ornamented rival. We studied sexual ornamentation (breeding tubercles), ejaculation quality (sperm concentration, longevity and spermatozoal velocity) and intensity of parasitism in the cyprinid, Rutilus rutilus . Sperm longevity and spermatozoal velocity were positively correlated. Males having elaborated sexual ornamentation had longer-lived sperm and more Myxobolus mülleri parasites in the liver compared with males with low ornamentation. However, no difference was found between males with different degrees of ornamentation with respect to sperm concentration, spermatozoal velocity or other parasites. Since the highly ornamented males had higher sperm longevity, the present results are partly consistent with the predictions of the sperm competition models and the 'sperm protection' hypothesis.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 81 , 111–117.     

Leaf litter decomposition and nutrient dynamics in a subtropical forest after typhoon disturbance

Decomposition of typhoon-generated and normal leaf litter and their release patterns for eight nutrient elements were investigated over 3 yr using the litterbag technique in a subtropical evergreen broad-leaved forest on Okinawa Island, Japan. Two common tree species, Castanopsis sieboldii and Schima wallichii, representative of the vegetation and differing in their foliar traits, were selected. The elements analyzed were N, P, K, Ca, Mg, Na, Al, Fe and Mn. Dry mass loss at the end of study varied in the order: typhoon green leaves > typhoon yellow leaves > normal leaves falling for both species. For the same litter type, Schima decomposed faster than Castanopsis. Dry mass remaining after 2 yr of decomposition was positively correlated with initial C:N and C:P ratios. There was a wide range in patterns of nutrient concentration, from a net accumulation to a rapid loss in decomposition. Leaf litter generated by typhoons decomposed more rapidly than did the normal litter, with rapid losses for N and P. Analysis of initial quality for the different litter types showed that the C:P ratios were extremely high (range 896 – 2467) but the P:N ratios were < 0.05 (range 0.02 – 0.04), indicating a likely P-limitation for this forest. On average 32% less N and 60% less P was retranslocated from the typhoon-generated green leaves than from the normal litter for the two species, Castanopsis and Schima. An estimated 2.13 g m^–2 yr^–1 more N and 0.07 g m^–2 yr^–1 more P was transferred to the soil as result of typhoon disturbances, which were as high as 52% of N and 74% of P inputted from leaf litter annually in a normal year. Typhoon-driven maintenance of rapid P cycling appears to be an important mechanism by which growth of this Okinawan subtropical forest is maintained.     

GRACILARIA EDULIS (RHODOPHYTA) AS A BIOLOGICAL INDICATOR OF PULSED NUTRIENTS IN OLIGOTROPHIC WATERS

The response of the marine macroalga Gracilaria edulis (Gmelin) Silva to nutrient pulses of varying magnitude was investigated to test its applicability as a marine bioindicator at two oligotrophic locations. After exposure to nutrient pulses, algal amino acid, tissue nitrogen, and chlorophyll a content were assessed relative to algae incubated under control conditions (no nutrient enrichment). The smallest nutrient pulse involved a nutrient enrichment experiment conducted within a coral atoll, whereas two larger pulses resulted from sewage discharge to a tropical coastal bay. After exposure to the smallest nutrient pulse (10 × ambient), only changes in macroalgal amino acid concentration and composition were detected (mainly as increases in citrulline). At 100 × ambient concentrations, increases in tissue % nitrogen of the macroalgae were detected, in addition to responses in amino acids. Macroalgae exposed to the highest nutrient pulse (1000 × ambient) responded with increased chlorophyll a , tissue nitrogen, and amino acids within the three day incubation period. In contrast to these algal responses, analytical water sampling techniques failed to detect elevated nutrients when nutrient pulses were not occurring. The responses of this algal bioindicator to variable nutrient pulses may provide a useful tool for investigating the source and geographical extent of nutrients entering oligotrophic coastal waters.     

Allocation of parental investment among individual offspring in the European beewolf Philanthus triangulum F. (Hymenoptera: Sphecidae)

Optimal allocation of parental resources is an important life history trait. However, it has been rarely investigated empirically. We tested aspects of optimal allocation theory in a digger wasp, the European beewolf. Investment allocation theory assumes (1) a trade‐off between investment per offspring and offspring number and (2) a convex relationship between investment per offspring and fitness returns. From mis relationship an optimum amount of investment per offspring can be derived and parents are predicted to provide each offspring with this optimum amount of investment. We used the number of bees in a brood cell as a measure of parental investment. Offspring fitness was quantified as both survival until emergence and success as adults. There is evidence for a trade‐off between current and future reproduction, suggesting that the first assumption is met. In contradiction to the second assumption, one mortality factor, parasitism, increased proportionally with the number of bees in a brood cell. However, overall mortality until emergence significantly decreased with the number of bees in a brood cell as assumed by the theory. The determination of the optimum amount of investment per offspring is complicated because the sexes possibly differ in their relationship between amount of investment and fitness. Individual males received considerably fewer bees (2.2 ± 0.8) than females (3.8 ± 0.5). Two independent estimates of the investment specific survival suggested that sons with two bees had the highest fitness returns per single bee and, consistent with the prediction, most sons were provisioned with two bees. For daughters, four bees is probably the optimum amount and most daughters were provisioned with this number. In both sexes the variation of investment per offspring was less than expected by a Poisson distribution with the same mean. These findings support the view that parental investment is allocated in a way that optimizes the trade‐off between offspring number and investment per offspring. However, variation contradicting the hypothesis still occurred. This might be explained either by adaptive variation in the amount of investment per offspring, constraints in the adjustment of the optimum amount of investment, or problems in measuring parental investment.     

Seed Dispersal of a High Quality Fruit by Specialized Frugivores: High Quality Dispersal?1

Dispersal quality, as estimated by the cumulative effects of dispersal, germination, seed predation, and seedling survival, was examined for Beilschmiedia pendula (Lauraceae) in Monteverde, Costa Rica. I determined the pattern of dispersal by finding seeds deposited by birds, protected the seeds from seed predators with cages to assess germination and seedling survival, and examined seed predation rates with marked seeds. Seed predation, germination, and seedling survival were compared between seeds naturally dispersed by birds and seeds placed at randomly located sites. Approximately 70 percent of seeds dispersed by birds (N= 244) were deposited <10 m from crown edges of fruiting B. pendula trees, although some seeds were dispersed at least 70 m away. Larger seeds were more likely to be dispersed under or close to the parent trees, and larger seeds produced larger seedlings. Seed size was not correlated directly with seedling survival, but larger seedlings at three months were most likely to survive one year. Seed predation by mammals and insects and seedling mortality due to fungal pathogens were concentrated beneath the crowns of parent trees. Seedlings and saplings were more abundant beneath fruiting B. pendula trees, but individuals farther away were taller on average. Thus, dispersal is beneficial for B. pendula, but such benefits appear most pronounced at a small spatial scale; seeds dispersed >30 m from the crown edges actually had a lower probability of survival than those dispersed 10–20 m. Only 10 percent of B. pendula. seeds received high‐quality dispersal in terms of landing in the zone with the highest per seed probability of seedling survival 10–20 m from parental crowns.     

THE ROLE OF PERIPHYTON IN PHOSPHORUS RETENTION IN SHALLOW FRESHWATER AQUATIC SYSTEMS

Eutrophication caused by phosphorus (P) leads to water quality problems in aquatic systems, particularly freshwaters, worldwide. Processing of nutrients in shallow habitats removes P from water naturally and periphyton influences P removal from the water column in flowing waters and wetlands. Periphyton plays several roles in removing P from the water column, including P uptake and deposition, filtering particulate P from the water, and attenuating flow, which decreases advective transport of particulate and dissolved P from sediments. Furthermore, periphyton photosynthesis locally increases pH by up to 1 unit, which can lead to increased precipitation of calcium phosphate, concurrent deposition of carbonate-phosphate complexes, and long-term burial of P. Actively photosynthesizing periphyton can cause super-saturated O₂ concentrations near the sediment surface encouraging deposition of metal phosphates. However, anoxia associated with periphyton respiration at night may offset this effect. Linking the small-scale functional role of periphyton to ecosystem-level P retention will require more detailed studies in a variety of ecosystems or large mesocosms. A case study from the Everglades illustrates the importance of considering the role of periphyton in P removal from wetlands. In general, periphyton tends to increase P retention and deposition. In pilot-scale constructed periphyton-dominated wetlands in South Florida, about half of the inflowing total P was removed.     

Photosynthetic Performance and Pigment Composition of Leaves from two Tropical Species is Determined by Light Quality

Abstract: A suitable light quantity and quality is essential for optimal photosynthetic metabolism. Using combinations of three lamp types, the impact of the quality of artificial light conditions on the photosynthetic apparatus of leaves developed in growth chambers was analysed. The VIALOX‐Planta lamps are quite poor outside the green to orange (520 ‐ 620 nm) wavelength range, while the HQI‐BT lamps present a more uniform spectral intensity between 425 and 650 nm (blue to red). The halogen lamps are particularly rich in the red and far red range of the electromagnetic spectra. The lamps also differ in the red: far red ratio, which were 3.07 (VIALOX), 2.06 (HQI‐BT) and 1.12 (halogen). Clear positive effects were detected in most of the photosynthetic parameters in relation to light quality, both at stomatal and mesophyll levels. Despite some species‐dependent sensitivity to blue and red/far red wavelengths, observed among the studied parameters, the best photosynthetic performances of the test plants (Packyrhizus ahipa and Piatã, a hybrid of Coffea dewevrei×Coffea arabica) were obtained almost always with the reinforcement of blue (HQI‐BT lamps), red and far red (halogen lamps) wavelengths and with a red: far red ratio closer to that observed in nature. This suggests the involvement of more than one photoreceptor family in photosynthetic performance. Under such light conditions, increases in net photosynthesis and stomatal conductance were observed and, despite the moderate effects on photosynthetic capacity, strong effects were observed in the capture and transfer of light energy in the antennae pigments, photochemical efficiency of photosystem II and electron transport. This was related to the striking quantitative and qualitative impacts observed on total chlorophylls and carotenoids, which reached, in some cases, increases of 100 and 200 %, respectively. Among carotenoids, increases as high as 9‐fold for α‐carotene were observed (P. ahipa), with chlorophyll (a/b), total (chlorophyll/carotenoid) and carotene (α/β) ratios also strongly affected. This would have affected the structure and stability of photosynthetic membranes which, in turn, affected photosynthetic‐related processes (e.g., antennae pigments, photosystem II and electron transport efficiencies). This was particularly clear in the HQI + halogen treatment. The results unequivocally show that light quality could remain a clear limiting factor for leaf/plant development under artificial light conditions, which could be overcome using more than one lamp type, with complementary emission spectra.     

EFFECT OF LIGHT QUALITY AND INTENSITY ON GLYCEROL CONTENT IN DUNALIELLA TERTIOLECTA (CHLOROPHYCEAE) AND THE RELATIONSHIP TO CELL GROWTH/OSMOREGULATION1

Dunaliella tertiolecta Butcher was grown at two intensities (33, 150μEin · m^?2· s^?1) of blue light and white light at 0.25, 0.50 and 1.00 M NaCl. Growth rates were used as an indication of the relative osmoregulatory ability of cells in the various treatments. There was no significant effect on growth rate due to various NaCl molarities. No significant difference in growth rate was found between blue- and white-light cultures at the high intensity, the average growth constant being 2.07 divisions/day. However, at the low intensity illumination, blue light produced a significant increase in growth rate; 1.42 vs. 0.93 divisions/day for blue light and white light grown cells respectively. The average glycerol content of exponentially dividing cells grown at 0.25, 0.50 and 1.00 M NaCl was 0.12, 0.41 and 1.12 mg/10⁸ cells, respectively, as measured by gas chromatography. The intracellular glycerol content was significantly reduced by blue light at both light intensities and at each NaCl molarity. However, high light intensity reduced cellular glycerol content more than the reduction effected by blue light. Glycerol accumulated in the medium throughout culture growth. Intracellular glycerol content also increased with cellular aging reaching 2.72 mg/10⁸ cells in stationary phase, low intensity 1.00 M NaCl cultures. A negative correlation between glycerol content and growth rate was found. Total inhibition of glycerol production could not be obtained by treatment with blue light. However, this negative correlation possibly indicates that D. tertiolecta expends energy producing an excess amount of glycerol over that required for osmoregulation, leading to a reduction in the growth rate for the organism.     

Landscape structure affects food quality of sika deer (<Emphasis Type="Italic">Cervus nippon</Emphasis>) evidenced by fecal nitrogen levels

Evaluating the quality of wildlife habitat is essential for understanding and predicting population dynamics in heterogeneous environments. We used fecal nitrogen levels as an indicator of habitat quality of sika deer (Cervus nippon) and explored important landscape elements influencing nitrogen levels, taking deer density into account. We established 92 plots differing in deer density and landscape structure on the Boso Peninsula, central Japan, and collected fecal samples along a 1-km transect at each plot. The regression models involving two independent variables, i.e., deer density and the length of forest edge within an area of 100 or 200 m from the transect, were selected based on the Akaike’s Information Criterion (AIC). Levels of fecal nitrogen were positively correlated with the length of the forest edge and negatively correlated with population density of deer. The area of 100 or 200 m from the transect most likely reflected the behavioral scale of the deer. Coverage of palatable understory vegetation increased with proximity to forest edge and decreased with deer density. Variability in the level of fecal nitrogen could thus be explained by food availability in the landscape. These results suggest that landscape alterations increase the carrying capacity of sika deer and thereby increase impacts upon the ecosystem.     

Horizontal and vertical distribution of saproxylic beetles (Col., Buprestidae, Cerambycidae, Scolytinae) across sections of forest edges

Abstract:  We evaluated the preferred home ranges of three saproxylic beetle taxa along transects from the open field into the forest interior, and from the forest floor up to the canopy. By means of trap sets on metal scaffolds, vertical and horizontal strata were sampled across two types of forest edges: soft-edge ecotones with a gradual transition from the field into the forest and hard edges with an abrupt transition. The forest edges consisted of different strata such as herbaceous fringe, shrub belt, unmanaged forest and managed forest. The thermophilic buprestids were mainly caught in the open land (herbaceous fringe and agricultural land) and in the upper forest mantle. In general, the cerambycids were most abundant in the open land and the lower forest mantle, but a few species favoured the forest interior. The bark beetles (Scolytinae) were equally distributed in all habitats. These distribution patterns of the taxa were observed in terms of both species numbers and abundances. Each species with at least five collected specimens was assigned to one of the three habitat types: open land, forest mantle and forest interior. Of 74 ranked species, only 16% were prevalent in the forest interior and are thus considered to be true forest species. The other 84% of the species were attributed to open land or the forest mantle and are, therefore, forest edge species. Soft forest edges generally supported a higher species richness than hard edges, particularly as regards Cerambycidae and Scolytinae. In terms of Shannon diversity, soft edges tended to be more diverse in buprestids and cerambycids. Overall, the forest interior showed the least species richness and diversity. Therefore, for the conservation of saproxylic beetles, not only the amount and quality of dead wood is important, but also the presence and design of forest boundary structures.