Paramecium sonneborni n. sp., a New Member of the Paramecium aurelia Species-Complex1

ABSTRACT. From an intermittent stream in College Station, Texas, a Paramecium was isolated that did not appear to belong to any recognized species. On the basis of nuclear and whole-body morphology, it can be assigned to the Paramecium aurelia species-complex, and it can be distinguished from other members of that complex on the basis of mating-type reactivity and isoenzyme patterns. These characteristics are felt sufficient to justify a new species assignment. The new species has been named Paramecium sonneborni n. sp. in honor of the late Dr. Tracy M. Sonneborn of Indiana University.     

The outcome of the invasion of Florida lakes by Daphnia lumholtzi

1. We examined 7–12 years of monthly to quarterly historical data from 15 lakes in FL, U.S.A. to determine the extent and outcome of invasion by the alien cladoceran Daphnia lumholtzi Sars. 2. The alien species was found in 10 of the 15 lakes, including Florida’s three largest lakes: Okeechobee, George and Apopka. All the surveyed lakes had resident populations of the smaller native species Daphnia ambigua Scourfield. 3. In most of the lakes, D. ambigua occurred seven to ninefold more often in plankton samples than D. lumholtzi, and at 10‐ to 100‐fold higher maximal densities. One exception was a small lake in central Florida (Lake Jesup), where D. lumholtzi attained high densities on several occasions in the 10 years of sampling. 4. In Lake Okeechobee, where data were of sufficient quality and quantity to perform statistical analyses, the results of canonical correlation analysis indicated that high densities of D. lumholtzi were correlated with lower concentrations of suspended solids, high algal biomass and higher temperature, whereas the opposite conditions were correlated with high densities of D. ambigua. 5. Based on the majority of data, D. lumholtzi has successfully invaded many lakes in Florida, yet it has not become a substantive component of the zooplankton. Additional research is needed to determine whether resources, fish predation or some other factor is responsible for this outcome of invasion.     

Structure of the “Peroxy-Y Base” from Liver tRNA<Superscript>Phe</Superscript>

WE wish to report that reconstituted sperm whale myoglobin prepared by the method of Breslow¹ (except that pH 2 was found sufficient to remove all the haem) (I) crystallizes² in a different habit from those prepared by the method of Rossi-Fanelli et al.³ (II) using haemin of Sigma lot 77B-0220 and our own ⁵⁷Fe photoporphyrin preparation and the native myoglobin (III). Although all three form type A³ monoclinic prisms, the best developed plane is [001] for II and III, it is [100] for I. There seems to be great interest in reconstituted haemoproteins^4,5, so it is important that crystallization habit may be a sensitive test for subtle changes in protein structures.     

Influence of Nitrogen Availability on Aminotransferases in Lemna minor L.

Protein contents and glutamate: glyoxylate, serine: glyoxylate,alanine: glyoxylate and glutamate: pyruvate aminotransferaseactivities per gram fresh weight declined sharply when Lemnaminor L., previously grown on nitrate medium, was starved ofnitrogen. Nitrogen replenishment after 5 d caused complete recoveryof these parameters with higher values in ammonium-fed thannitrate-fed plants 7 d after transfer of plants from nitrogen-freemedium. Glutamate: glyoxylate and alanine: glyoxylate aminotransferasespecific activities (based on total extracted protein) showedlittle change with nitrogen availability. Serine: glyoxylateaminotransferase increased slowly during nitrogen starvationand decreased following nitrogen replenishment whether withammonium or nitrate. After 1 d of nitrogen starvation the specificactivity of glutamate: pyruvate aminotransferase declined; itincreased following nitrogen replenishment and ammonium gaverise to agreater activity than nitrate. The results are discussed in relation to the differences instability of the various enzymes relative to the overall proteinturnover rate. Key words: Aminotransferases, Nitrogen source, Photorespiration     

The Mechanical Significance of Clasping Leaf Sheaths in Grasses: Evidence from Two Cultivars of Avena sativa

The elastic (Young's) modulus and flexural rigidity of internodeswith and without their clasping leaf sheaths were determinedfor culms from two cultivars (‘Astro’) and (‘Garry’)of Avena sativa L. Data indicate that early in the developmentof culms, leaf sheaths can have a higher elastic modulus thanthe internodes they envelope, and by virtue of their location,leaf sheaths contribute significantly to the flexural rigidity(hence, resistance to bending) of internodal segments. As culmsmature, the elastic modulus of leaf sheath and internodal tissuesreach parity. However, because of the acropetal pattern by whichnew internodes are produced by shoot apices, sheaths continueto provide mechanical support to distal internodes, particularlythe peduncle. Data for the two cultivars indicate that the elasticmodulus and flexural rigidity of culms can vary significantlywithin the species. Comparisons between the flexural rigidityof the two cultures and the resistance of stems to lodging indicatethat flexural rigidity is not significant to lodging. The engineeringprinciples relevant to the mechanical advantages conferred byclasping leaf sheaths are discussed within the context of grassshoot morphology. Biomechanics, leaf sheath, Avena, elastic modulus     

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.     

Hair of grazing cattle provides an integrated measure of the effects of site conditions and interannual weather variability on δ13C of temperate humid grassland

The carbon isotope composition (δ¹³C) of C3 ecosystems is sensitive to water availability, and provides important information for the assessment of terrestrial carbon (C) sink/source activity. Here, we report the effects of plant available soil water (PAW) on community ¹³C signatures of temperate humid grassland. The 5‐year study was conducted on pastures exhibiting a large range of PAW capacity that were located on two site types: peat and mineral soils. The data set included the centennial drought year 2003, and data from wet years (2000 and 2002). Seasonal variation of PAW was modeled using PAW capacity of each pasture, precipitation inputs and evapotranspiration estimates. Community ¹³C signatures were derived from the δ¹³C of vegetation and segments of tail switch hair of cattle grown while grazing pastures. Hair ¹³C signatures provided an assimilation‐weighted ¹³C signal that integrated both spatial (paddock‐scale) and temporal (grazing season) variation of ¹³C signatures on a pasture. The δ¹³C of hair and vegetation increased with decreasing modeled PAW in the same way on mineral and peat soils. But, at a given PAW, the δ¹³C of hair was 2.6‰ less negative than that of vegetation, reflecting the diet‐hair isotopic shift. Furthermore, the δ¹³C of hair and vegetation on peat soil pastures was 0.5‰ more negative than on pastures situated on mineral soil. This may have resulted from a ～10 ppm CO₂ enrichment of canopy air derived from ongoing peat mineralization. Community‐scale season‐mean ¹³C discrimination (Δ) exhibited a saturation‐type response towards season‐mean modeled PAW (r²=0.78), and ranged between 19.8‰ on soils with low PAW capacity during the drought year of 2003, and 21.4‰ on soils with high PAW capacity in a wet year. This indicated relatively small variation in season‐mean assimilation‐weighted p_i/p_a (0.68–0.75) between contrasting sites and years. However, this range is similar to that reported in other studies, which encompass the range from subtropical arid to humid temperate grassland. Furthermore, the tight relationship between season‐mean Δ and modeled mean PAW suggests that PAW may be used as proxy for Δ.