Ultrastructure and function of long and short sperm in Cicadidae (Hemiptera)

The cicada, Graptopsaltria nigrofuscata, produces two distinct sizes of sperm, as determined by either nuclear volume of early spermatids or nuclear length of mature sperm. Between both sperm, there is no difference in location of the acrosome and flagellum during spermiogenesis. The acrosome is covered by an anteacrosomal bleb, which is inserted in a common mass, spermatodesm, derived from cyst cells. Both kinds of sperm linked to the spermatodesm form sperm bundles, respectively. During copulation, the sperm bundles are transported from the vesicula seminalis of the male to the bursa copulatrix of the female. Morphometric analyses of the nuclear length revealed that the two kinds of sperm reach the bursa copulatrix in the same condition as that found in the vesicula seminalis. Once transferred inside the latter, the sperm bundles disintegrated to individual sperm within a few hours, and the tail components, such as the axoneme and mitochondrial derivatives, become separated from each other over time. The tail completely splits from the sperm nucleus 24 h after copulation. Fertile sperm accumulate in the spermatheca, the final storage organ, where only long sperm survived for any length of time. Fertilized eggs examined by vital staining contain only sperm with long nuclei.     

Motion: the long and short of it

Several authors have proposed that motion is analyzed by two separate processes: short-range and long-range. We claim that the differences between short-range and long-range motion phenomena are a direct consequence of the stimuli used in the two paradigms and are not evidence for the existence of two qualitatively different motion processes. We propose that a single style of motion analysis, similar to the well known Reichardt and Marr-Ullman motion detectors, underlies all motion phenomena. Although there are different detectors of this type specialized for different visual attributes (namely first-order and second-order stimuli), they all share the same mode of operation. We review the studies of second-order motion stimuli to show that they share the basic phenomena observed for first-order stimuli. The similarity across stimulus types suggests, not parallel streams of motion extraction, one short-range and passive and the other long-range and intelligent, but a concatenation of a common mode of initial motion extraction followed by a general inference process.     

Cognitive screening test: short and long version

Three versions of the Cognitive Screening Test (CST), varying in length from seven to 20 items, are compared using the original data. The shortest version, the CST-7, is not inferior to the longer CST-14 and CST-20. Various psychometric properties are compared. According to the Mokken nonparametric IRT scaling technique, all three CST versions can be considered unidimensional. The Mokken scaling indices H and rho hardly differ in the three versions of the CST. The alpha indices from Classical Test Theory are also very comparable, as is the very good sensitivity and specificity (around 95%). Age and gender have no significant effect on the classification success of the CST-7. Cross-validation of the promising properties of this very short screening instrument is recommended.     

A note on the evaluation of similarity (homology) of short sequences with long sequences

Monte Carlo data on the comparison of a short sequence with a long one are developed in a manner to quantify the occurrence of gaps.     

Phloem: the long and the short of it

The structure of phloem sieve-element-companion-cell complexes reflects a duality of function: to conduct photoassimilates throughout the plant, and to exchange solutes between the phloem and surrounding tissues. The conceptual integration of these long- and short-distance functions requires the abandonment of a long-cherished concept in phloem physicochemistry, that source-sink turgor differentials control flow. The manifest inability of decentralized organisms such as plants to control phloem translocation centrally disqualifies such differentials as control variables; besides, the phloem is maximally efficient if the pressure differentials are small. Testing this hypothesis and whether turgor differentials are small will require a significant recommitment to studying the quantitative anatomy of phloem.     

Olfactory memory: the long and short of it

It has been proposed that memory for odors does not have a short-term (or working) memory system. The distinction between short- and long- term memory in other sensory modalities has been generally supported by three main lines of evidence: capacity differences between the proposed systems, evidence of differential coding, and differential memory losses in neuropsychological patients. The present paper examines these issues in an effort to establish a similar distinction for the memory of olfactory stimuli. Each of these lines of evidence is examined in relation to the literature on olfactory memory. Based on this examination, it seems that there is at least preliminary support from each of these lines of evidence to advocate a distinction between a long- and short-term memory for olfactory stimuli. Emphasis is placed upon the qualitative similarity of olfactory memory to other memory systems. This similarity is further highlighted through an examination of the literature pertinent to serial position effects in memory for olfactory stimuli.      

Stereocilia: the long and the short of it

Mutations in whirlin, a putative PDZ scaffold protein, have recently been shown to cause deafness and short cochlear hair cell stereocilia in whirler mice and recessive deafness (DFNB31) in humans. Through its PDZ domains, whirlin might organize a group of proteins into a functional complex required for stereocilia elongation. Identifying these protein partners will advance our understanding of the development of stereocilia and their function as mechanosensory organelles indispensable for normal hearing.     

Mechanism of long slender (LS) to short stumpy (SS) transformation in the African trypanosomes

The transformation of the long slender to the short stumpy stages of the African trypanosomes is an essential part of the trypanosome life cycle. Four possible mechanisms which could control this event have been investigated. It has been shown that (a) the dividing long slender to non-dividing short stumpy transition is not a programmed event in the trypanosome life cycle; nor (b) would it appear to be initiated by some form of cell to cell contact inhibition of growth. In addition, evidence is presented which would suggest that (c) the transition is not started by the depletion of a critical growth nutrient from the environment during the growth of the trypanosomes. The last possibility (d) considered is that during trypanosome growth, a growth inhibitor-short stumpy inducer accumulates in the trypanosomes' environment. Evidence is presented which shows that plasma from infected animals can inhibit the incorporation of thymidine by the trypanosomes. These data are consistent with the suggestion of an exogenous growth inhibitor accumulating during the infection.     

The long and short of siRNAs

A recent work identifies a distinct class of siRNAs derived from transgenes and endogenous retroelements in plants (Hamilton et al., 2002). This class has slower electrophoretic mobility than previously characterized siRNAs and may play an important role in transgene-induced systemic silencing and in methylation of endogenous retroelement DNA.     

The long and short of it

It can take twice as long to get a PhD in biomedical sciences in the US as it does in other countries such as the UK and Australia. Are US PhDs worth more, or are there advantages to a speedier system?