Morphology of the arthrodial membrane gland in a Neotropical harvester (Arachnida: Opiliones)

We describe a gland in the arthrodial membrane of the coxa-trochanter articulation in the fourth pair of legs in the Neotropical harvester Mischonyx squalidus Bertkau, 1880. Externally the glandular area has a rough appearance with pores on its surface, with folds of the arthrodial membrane. Internally, its secretory cells have spherical secretory vesicles, smooth endoplasmic reticulum, mitochondria and ducts that exit from the cells and cross the arthrodial membrane. Histochemical tests indicate the presence of proteins and neutral glycoproteins. The function of the gland might be to produce lubricating products that allow better movement of the coxa-trochanter region.

Protein components of the arthrodial membrane gland in a Neotropical Harvestman (Arachnida, Opiliones)

The content of arthrodial membrane glands in arthropods has seldom been studied. Here, we have analyzed the proteins of the arthrodial membrane gland of the trochanter–coxa articulation of the fourth pair of legs in the harvestman Mischonyx cuspidatus via reverse-phase high-performance liquid chromatography (RP-HPLC), polyacrylamide gel electrophoresis (PAGE), and nanoscale liquid chromatography coupled to mass spectrometry (nLC-MS/MS) analysis. Most of the fractions studied are hydrophobic, being proteins with molecular weights of ∼28, 62, and ∼198 kDa. These proteins seem to be homologous to proteins involved in product secretion, cytoskeleton, protein binding, cellular metabolism, and antimicrobial action among others. Lubricant function is also possible based on the literature. We were able to identify 147 proteins in the inner region, 91 proteins from the outer dorsal region, and 36 proteins from the outer ventral region. Some proteins are present only in one of these regions and some are shared by one or more regions. Our work provides, to the best of our knowledge, the first proteome characterization of the content of an arthrodial membrane gland in arachnids. Dataset Identifier: ftp://massive.ucsd.edu/MSV000087195/.

Water locomotion and survival under water in a riparian harvestman (Opiliones, Arachnida).

Animals that live by rivers may benefit from being able to cross them, but behavioral adaptations are needed. Additionally, being able to remain submerged is also important if the animal moves under water. Here we asked whether the harvestman Heteromitobates discolor (Opiliones), that lives by rivers, (a) can propel itself across the water surface, (b) moves onto the water if disturbed and (c) can survive for long periods when submerged. Heteromitobates discolor exhibited two gaits on water, whereas a strictly terrestrial species was not able to propel itself. When experimentally submitted to simulated predator attack on a rock on the river, H. discolor walked onto the water, while a strictly terrestrial species did not. Finally, it was able to survive for 6 h under water, presumably due to the conspicuous air film that formed around its body, which was also observed in a strictly terrestrial species. Altogether, these observations suggest that the aquatic environment is not a barrier for regular activity and can be used as an extension of the terrestrial environment for H. discolor.

Foraging, oviposition sites and notes on the natural history of the harvestman Heteromitobates discolor (Opiliones, Gonyleptidae) / Forrageamento, sítios de oviposição e notas sobre a história natural do opilião Heteromitobates discolor (Opiliones, Gonyleptidae)

The lack of data on the natural history often hampers phylogenetic studies on the evolution of behavior. Herein we provide quantitative field data on foraging and oviposition sites of a Neotropical harvestman belonging to a subfamily with a published phylogeny, Goniosomatinae. Heteromitobates discolor rests during the day on granitic boulders on rivers, laying eggs in sheltered and darker areas. The female guard the eggs and aggressively respond to approaching conspecific females. In the absence of the female, ants, conspecifics and reduviids may predate the eggs. Egg-guarding females are known not to leave the clutch, but males and non-guarding females may leave the granitic boulders and forage on the vegetation at night, close to the river margins and with no difference in the sites explored between males and females. The general features described in H. discolor are similar to what has been reported for other species in this subfamily, suggesting an evolutionary conservatism within the group.

A falta de dados de história natural por vezes dificulta estudos filogenéticos sobre a evolução do comportamento. Nesse estudo nós fornecemos dados quantitativos de campo sobre forrageamento e sítios de oviposição de um opilião Neotropical pertencente a uma subfamília com uma filogenia publicada, Goniosomatinae. Heteromitobates discolor passa o dia em rochedos graníticos em rios, onde deposita os ovos em áreas abrigadas e escuras. A fêmea cuida dos ovos e responde agressivamente a fêmeas co-específicas que se aproximam. Na ausência de fêmeas, formigas, co-específicos e percevejos reduvídeos podem predar os ovos. Fêmeas que guardam ovos não deixam as desovas, mas machos e fêmeas sem ovos deixam os rochedos graníticos e forrageiam sobre a vegetação è noite, próximos è margem do rio e sem diferença nos sítios explorados entre os machos e as fêmeas. As características gerais descritas em H. discolor são similares ao que tem sido reportado para outras espécies nesta subfamília, sugerindo um conservadorismo evolutivo dentro do grupo.