José G. Palacios-Vargas

Effects of fire and agricultural practices on neotropical ant communities

Fire is extensively used in agricultural management in Mexico. There is little information on the effects of those practices on the abundance and diversity of animals that live within these forest soils. We studied the effect of slashing, burning and land use in a tropical deciduous forest on ant communities in the State of Jalisco, Mexico. The original vegetation (tropical deciduous forest) was modified into a corn field. Sampling was carried out in five stages: before slashing, after slashing, after burning, after seeding and after harvest. We found that very severe fires greatly reduced ant diversity. The most important effect of fire was the reduction of ant density, and the change of species composition and trophic guilds. These changes are relevant in the recycling process of energy in the ecosystem.

fine-structure of spermatogenesis and mature spermatozoa in cryptocellus-boneti bolivar y pieltain, 1941 (arachnida, ricinulei)

The testes of Cryptocellus boneti are composed of a germinal and a secretory part. Epithelial cells of the latter are capable of phagocytosing mature spermatozoa besides secreting a proteinaceous secretory product delivered into the lumen of the testes. The germinal part comprises somatic cells surrounding cysts of germ cells. Mature spermatozoa are roundish cells. Their central cytoplasm is ensheathed by two electron-dense intracellular plates. An elongated nucleus and an axoneme of the usual 9 × 2 + 2 pattern are rolled up within the cell. An acrosomal complex comprising a small acrosomal vacuole and an acrosomal filament is present. Early spermatogenesis reveals that eight electron-dense plates are derived from Golgi vesicles and are distributed to the spermatids during meiotic divisions. Elongation of spermatids occurs during chromatin condensation. The nucleus is paralleled by the axonemal tubules which are attached via a specialized centriolar region to the anterior curved acrosomal vacuole.

FIRST ULTRASTRUCTURAL OBSERVATIONS ON THE TARSAL PORE ORGAN OF PSEUDOCELLUS PEARSEI AND P. BONETI (ARACHNIDA, RICINULEI)

Abstract Due to their relative rareness and restricted distribution, little is known about the ultrastructure of ricinuleids. In particular, sense organs have not been the subject of electron microscopic research until now. Ricinuleids use their forelegs to explore their surroundings with tentative movements. The distal tarsomeres of legs I and II of two cavernicolous Mexican species, Pseudocellus pearsei from the Yucatán Peninsula and Pseudocellus boneti from Guerrero, were examined in this study with light microscopy, scanning (SEM) and transmission electron microscopy (TEM). A conspicuous feature of the distal tarsomeres of legs I and II is a single circular opening that extends as a deep tube-like pit into the tarsus. This pore organ is lacking in the 6-legged larvae. Comparable organs are present in Araneae, Scorpiones, Amblypygi and Anactinotrichida. The tarsal organs of the mentioned groups possess several types of sensilla (olfactory, thermo- and hygrosensitive and mechanosensitve). The pore organ is located in the distal third of the dorsal half of the tarsus. In longitudinal sections it shows a long oval shape. In cross sections it is nearly circular. The pore organ contains a large number of long, slightly curved setae. These setae are localized on the bottom and the lower two thirds of the wall of the pit and project into the lumen. The upper third of the wall is free of setae and shows folds which extend parallel to the opening. All setae inside the pit seem to be of the same type. In sections they show a complex inner structure and likely represent chemoreceptive wall pore single-walled (wp-sw) sensilla. This indicates a possible olfactory function. The pore organ is underlain by numerous gland cells which represent characteristics of unicellular “class I” gland cells.

Two New Species of Deuterosminthurus (Bourletiellidae), Epiphytic Collembola from the Neotropical Region with a Key for the American Species

Two new species of Deuterosminthurus are described and illustrated. One is found in dry forest canopy at Chamela, Jalisco, Mexico, and the other is associated with sugarcane at La Habana, Cuba. A key for identification of the American species is included.

The pedipalp of Pseudocellus pearsei (Ricinulei, Arachnida) - ultrastructure of a multifunctional organ.

Ricinulei possess movable, slender pedipalps with small chelae. When ricinuleids walk, they occasionally touch the soil surface with the tips of their pedipalps. This behavior is similar to the exploration movements they perform with their elongated second legs. We studied the distal areas of the pedipalps of the cavernicolous Mexican species Pseudocellus pearsei with scanning and transmission electron microscopy. Five different surface structures are characteristic for the pedipalps: (1) slender sigmoidal setae with smooth shafts resembling gustatory terminal pore single-walled (tp-sw) sensilla; (2) conspicuous long, mechanoreceptive slit sensilla; (3) a single, short, clubbed seta inside a deep pit representing a no pore single walled (np-sw) sensillum; (4) a single pore organ containing one olfactory wall pore single-walled (wp-sw) sensillum; and (5) gustatory terminal pore sensilla in the fingers of the pedipalp chela. Additionally, the pedipalps bear sensilla which also occur on the other appendages. With this sensory equipment, the pedipalps are highly effective multimodal short range sensory organs which complement the long range sensory function of the second legs. In order to present the complete sensory equipment of all appendages of the investigated Pseudocellus a comparative overview is provided.

Importance and evolution of sexual dimorphism in different families of Collembola (Hexapoda)

A bibliographic revision of sexual dimorphism in different families of Collembola was performed in order to determine the most common patterns in each group. We list several examples of the sexual dimorphism in different families of Collembola, which illustrate from some of the smallest differences between males and females to major differences between both sexes in some families. We show different cases of sexual dimorphism in Spinactaletes, Sminthurides, and the remarkable morphology of Guthriella muskegis. It seems that most of the cases of strong sexual dimorphism are related to aquatic habitats or behaviour still not fully understood. Species belonging to primarily aquatic families (fresh water or marine water) have the most evolved morphology, where males have clasping antennae to attach the females in order to avoid loosing them with the movement of the water.

Biological activity of the mite Sancassania sp. (Acari: Acaridae) from bat guano associated with the pathogenic fungus Histoplasma capsulatum

Mites and the mammal pathogenic fungus Histoplasma capsulatum are the major components of bat guano microbiota. Interactions between mites and H. capsulatum were evaluated under laboratory conditions. Acarid mites, mainly Sancassania sp., were the most abundant microarthropod in the sampled guano of the Mexican bat Tadarida brasiliensis mexicana and, based on its morphology, Sancassania sp. was similar to the cosmopolitan species Sancassania sphaerogaster. The mycophagous and vectoring activities of this mite were tested for H. capsulatum and two other fungal species, Sporothrix schenckii (pathogenic) and Aspergillus sclerotiorum (non-pathogenic). S. ca. sphaerogaster was able to reproduce in H. capsulatum and S. schenckii colonies, multiplying in great numbers under controlled fungal mycelial-phase culture conditions. H. capsulatum colonies were completely destroyed after 14 days of in vitro interaction with mites. In contrast, S. ca. sphaerogaster did not reproduce in A. sclerotiorum cultures. S. ca. sphaerogaster was found vectoring H. capsulatum, but not the two other fungal species studied.

A new species of Troglobius (Collembola, Paronellidae) from Brazil

The genus Troglobius was described originally from caves of Madagascar. The only species known is the type species T. coprophagus Palacios-Vargas & Wilson, 1990. Now we have found a new species of this genus in Brazil. Cave Collembola from Brazil are very poorly known. PalaciosVargas (1989)reported four new records from Brazil. Species reported from Brazilian caves are: Acherontides leo Palacios-Vargas & Gnaspini-Neto, 1992(Hypogastruridae); Troglolaphysa aelleni and T. hauseri both of Yoshii (1988) (Paronellidae); Cyphoderus sp. (Cyphoderidae) and recently Mesaphorura iowensis and M. yosiii (recorded by Palacios and Diaz in press). Information about the families of collembola associated to bat guano deposits was given by Gnaspini-Netto (1989a, b).Agood compilation on the cave fauna from Brazil was done by Trajano and Sanchez (1994)who cited about 160different taxa including seven families of Collembola.

Three New Species of Nahuanura (Collembola: Neanuridae) from México

Three new species of Nahuanura, an endemic genus of Collembola from Mexico, are described and illustrated. A key for the identification of the four know speices is included.

Redescription of the Male of Coenaletes caribaeus (Collembola: Coenaletidae) Associated with Hermit Crabs (Decapoda: Coenobitidae)

Abstract The male of Coenaletes caribaeus is described and illustrated. It is recorded for the first time from Mexico, with specimens from hermit crabs Coenobita clypeatus, from beaches in Quintana Roo. Drawings and scanning electron microscope pictures are included.