Abundance of Lutzomyia ovallesi but not Lu. gomezi (Diptera: Psychodidae) correlated with cutaneous leishmaniasis incidence in north-central Venezuela

In north-central Venezuela Lutzomyia gomezi and Lu. ovallesi are the main endophilic/anthropophilic species of phlebotomine sandflies implicated as vectors of cutaneous leishmaniasis (CL). Lutzomyia ovallesi has been found infected with Leishmania braziliensis (1.2%) and less often with Le. mexicana (0.07%), while Le. braziliensis infections have also been found in Lu. gomezi (0.47%). We investigated population densities of these sandflies using two sampling methods with four series of collections between January 1991 and March 1995 at El Ingenio, Miranda State. All-night outdoor collections from a Shannon trap were correlated with indoor collections from CDC light–traps by linear regression, which proved to be statistically significant for both species. Estimated numbers of female sandflies per house per night were found to be proportional to monthly precipitation (i.e. rainfall), with a lag time of seven months for Lu. ovallesi and of six months for Lu. gomezi . Predominance of Lu. ovallesi over Lu. gomezi ( c. 10 :1 ) was observed throughout the year, with the number of infected females estimated as 0.043 ± 0.047 Lu. ovallesi and 0.0085 ± 0.0124 Lu. gomezi per CDC trap per house per night (ratio ∼ 5:1). The mean rate of new CL cases per house per year and sandfly abundance were correlated by linear regression, showing a statistically significant relationship for Lu. ovallesi but not for Lu. gomezi . The negative intercept indicated that, on average, the CDC trap density exceeds 800 Lu. ovallesi females/house/year before new CL cases occur at El Ingenio.     

Proline Accumulation as a Symptom of Drought Stress in Maize: A Tissue Differentiation Requirement

Ibarra-Caballero, J., Villanueva-Verduzco, C., Molina-Galan,J. and Sanchez-de-Jimenez, E. 1988. Proline accumulation asa symptom of drought stress in maize: a tissue differentiationrequirement.—J. exp. Bot. 39: 889–897. Seedlings and callus tissue of maize (Zea mays L.) were testedfor proline accumulation under drought stress. A variety froma tropical humid region, a semi-desertic variety and its improvedpopulation selected for drought stress resistance, were usedfor this study. Proline accumulation was found in green leaves of maize seedlingsunder drought stress; no correlation was found between prolineaccumulation in leaves and the variety or population tested.White tissue, callus and leaves of etiolated seedlings did notshow this response to drought stress, nor did green callus ordetached leaves (green or etiolated), even when stress causeda loss of water from leaves similar to that observed when wholeseedlings were drought-stressed. Addition of abscisic acid togreen or white tissue did not result in proline accumulation.The above data indicate that proline accumulation caused bydrought stress does not seem to be an indication of droughtstress resistance, but rather a symptom of it. For this accumulationto take place it seems that fully organized chloroplasts arerequired as well as the systemic development of the plant. Key words: Proline, maize, drought-stress     

A cladistic analysis of Nassauvia Comm. ex Juss. (Asteraceae, Mutisieae) and related genera

FREIRE, S. E., CRISCI, J. V. & KATINAS, L., 1993. A cladistic analysis of Nassauvia Comm. ex Juss. (Asteraceae, Mutisieae) and related genera. Nassauvia and the most closely related genera Calopappus and Triptilion from the southern Andes and Patagonia of South America, form a monophyletic group diagnosed by the following synapomorphies: cypsela trichomes single two-celled, cypsela testa with strengthened cells, pollen grains spheroidal to spheroidal-oblate, colpi membrane with sexine processes, pappus bristles two to six, and pappus deciduous. Furthermore, Nassauvia, Triptilion, and Calopappus form a group with two other Andean genera, Moscharia and Polyachyrus, diagnosed by occurrence of pseudocephalia and a reduction in the number of flowers to five, three or one. A cladistic analysis of the group was undertaken using 35 characters from morphology, anatomy, and palynology. The monophyletic terminal taxa were the 38 species of Nassauvia, the genus Triptilion, the monotypic genus Calopappus, the genus Polyachyrus, and the genus Moscharia. Character polarity was based on outgroup comparison using Cephalopappus. The analysis resulted in 223 equally parsimonious cladograms, each with 70 steps and a consistency index of 0.57. A successive weighting procedure was applied, resulting in 15 cladograms with a consistency index of 0.82. Results of the cladistic analysis support most of the current systematic classification of Nassauvia, with three exceptions: (1) Nassauvia (excluding Calopappus) is paraphyletic; (2) section Masligophorus appears to be a polyphyletic group (N. pygmaea does not cluster with the remaining species of the section); (3) section Panargyrum (without N. lagascae= section Caloptilium) appears to be a paraphyletic group. The capitula arranged in cymose conflorescences in Triptilion are regarded as a primitive condition which gave rise to all stages present in Nassauvia (conflorescence spicate, pseudocephalium, capitula solitary). The capitula arranged in pseudocephalia in Moscharia and Polyachyrus are regarded as a parallel development to the pseudocephalium found in Nassauvia. Nassauvia, subgenus Strongyloma appears as the most primitive taxon, with its spicate conflorescence, whereas section Masligophorus with its solitary capitulum is thought-derived. These results correspond well with cytological data where species of the subgenus Strongyloma have n= 11 and the species of section Masligophorus are tetraploids (n = 22).     

Physiological Insights from Cellular and Network Models of the Stomatogastric Nervous System of Lobsters and Crabs

SYNOPSIS. The stomatogastric nervous system of decapod crustaceansis an ideal system for the study of the processes underlyingthe generation of rhythmic movements by the nervous system.In this chapter we review recent work that uses mathematicalanalyses and computer simulations to understand: 1) the roleof individual currents in controlling the activity of neurons,and 2) the effects of electrical coupling on the activity ofneuronal oscillators. The aim of this review is to highlight,for the physiologist, what these studies have taught us aboutthe organization and function of single cell and multicellularneuronal oscillators.     

Cybrids and tetrad sterility for developing true potato seed hybrids

Potato cybrids result from the fusion between cytoplasm and nuclear gene donors. Such genetic materials are an alternative means to broaden the breeding pool by non‐sexual gene transfer. Tetrad pollen sterility provides also another source of male sterility with some potential for true potato seed breeding. The objective of this research was to investigate cybrid‐derived offspring for both agronomic and reproductive characteristics in two contrasting Peruvian locations, and to examine new exotic germplasm for tetrad sterility, with the aim of broadening the breeding pool available at the Centro Internacional de la Papa (CIP). The cybrids were derived from fusions between Y‐245.7, a clone with tetrad sterility, and Atzimba. These cybrids were crossed with selected male parents from the CIP breeding population, and their hybrid offspring were tested in La Molina (coastal desert) and Huancayo (cool highlands). In addition, other clones with tetrad sterility were also crossed with selected testers to determine their breeding value. There were significant differences for tuber yield, style length, and berry number among the hybrid offspring, and the genotype by environment interaction was significant for tuber yield and berry number. The top 25% highest yielding cybrid‐derived offspring across both locations showed the same tuber yield although they were significantly different for some of the reproductive characteristics. With the exception of one cybrid, the others did not exhibit segregation for tetrad sterility in their hybrid offspring, which were male fertile. However, the offspring derived from crosses between other sources of tetrad sterility and the same testers all showed tetrad sterility, and some of them had outstanding tuber yield at La Molina. The lack of segregation for tetrad sterility in these new crosses suggests that the non‐cybrid, male sterile, female parents are triplex or quadriplex for the Tr nuclear locus, which interacts with a sensitive cytoplasm (e.g. Trs from S. verrucosum or S. stoloniferum) to produce tetrad sterility in potato.     

Scanning electron microscopy of glochidia and juveniles of the freshwater mussel,Hyriopsis myersiana

Summary

The ultrastructure of early stages of the mussel, Hyriopsis (Limnoscapha) myersiana (Lea, 1856), was observed by scanning electron microscopy from the glochidial period until the onset of the juvenile stage 10 days later. Further observations were performed for an additional 13 days to assess juvenile development. Glochidia extracted from the brood chambers have a hookless, semi-oval and equivalve calcareous shell with numerous pores in the internal surface, pits in the external surface and cuticular spines in the ventral region. Keratin fibers with a random arrangement in the cuticle of the glochidial shell were also detected. The appearance of the foot within 10 days of in vitro glochidial culture was considered the main feature of metamorphosis to the juvenile stage. Another change during the following 13 days was the formation of a new periostracum exhibiting growth lines under the old glochidial shell. This development occurs mainly in the anterior region and is followed by hardening of the periostracum matrix by calcium deposition. Periostracum growth gradually became apparent in the lateral and posterior regions at the end of this period. The retraction of spines and the alteration of the external surface of the old shell are also described. It is speculated that transcuticular filaments identified in the juvenile stage may have sensory or metabolic exchange functions. The prominent foot, gradually covered by long dense cilia, shows rhythmical movements which suggest a role in feeding. Similarly, cilia present in the mantle may also be involved in the capture of food, while microvilli may facilitate absorption of dissolved materials. Longer cilia, sparsely distributed in the mantle, may function as chemo- or tactile sensors.