Foraging, oviposition sites and notes on the natural history of the harvestman Heteromitobates discolor (Opiliones, Gonyleptidae)

Abstract

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. Keywords: Parental care, maternal care, microhabitat choice, substrate choice, Laniatores, Goniosomatinae. SILVA, N.F.S., WILLEMART, R.H. Forrageamento, sítios de oviposic¸ã o e notas sobre a história natural do opilião Heteromitobates discolor (Opiliones, Gonyleptidae).http://dx.doi.org/10.1590/1676-06032015018614Resumo: A falta de dados de história natural por vezes dificulta estudos filogenéticos sobre a evoluc¸ão do comportamento. Nesse estudo nós fornecemos dados quantitativos de campo sobre forrageamento e sítios de oviposic¸ão 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 vegetac¸ão à noite, próximos à margem do rio e sem diferenc¸a 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. Palavras-chave: Cuidado parental, cuidado maternal, escolha de micro-habitat, escolha de substrato, Laniatores, Goniosomatinae.

A Neotropical armored harvestman (Arachnida, Opiliones) uses proprioception and vision for homing

“…We also found that females were more likely to return to their batches when they were displaced later in the day. This could be because they are nocturnal animals that move in and out of their shelter mainly later in the afternoon when it gets darker (Silva & Willemart, 2015). Unguarded eggs are also probably more vulnerable at night, as previously described in another Neotropical species (Chelini & Machado, 2012), and individuals displaced later in the day could have higher motivation to return (Goniosomatinae females do not leave their eggs/first instar immature unguarded to forage; Gnaspini, 1995).…”

“…We studied H. discolor females in a Neotropical forest, at the Parque Estadual da Serra do Mar, in the city of Ubatuba, state of São Paulo. Females of use granitic natural shelters by rivers as oviposition sites (Silva & Willemart, 2015), and we collected the data by four rivers that cross the highway Rio-Santos (SP-101): Corisco River (Casa da Farinha), River Cachoeira da Bacia, River Marimbondo (Cachoeira da Renata) and River Camburi (see Silva & Willemart, 2015).…”

“…For example, in species of Goniosomatinae, although females do not abandon their clutches to forage, heavy rain may cause them to look for shelter and leave the eggs unguarded (NFSS & GF Pagoti, personal observations, N = 3). Females may also leave following attacks by large predators such as marsupials or reduviid bugs (see Gnaspini, 1996;Silva & Willemart, 2015), or other disturbances (Gnaspini & Cavalheiro, 1998;Machado et al, 2000;Willemart & Gnaspini, 2004a). Despite the reason for displacement and distance, females of Goniosomatinae are still able to return to their clutches after minutes or hours (Ramires & Giaretta, 1994; RHW, G Machado, GF Pagoti & NFSS, personal observations), demonstrating consistent homing behaviour.…”

“…We studied the potential for homing in egg-guarding females of Heteromitobates discolor Soerensen 1884 (Goniosomatinae). Female H. discolor lay their eggs on large boulders along river banks (Silva & Willemart, 2015), and care for their eggs and first instar offspring for extended periods (e.g., 20-60 days in species of the same subfamily; . Removing guarding females greatly increases egg predation in other species of the subfamily (Machado & Oliveira, 2002;, thus, being able to utilize homing to relocate clutches after displacement could be a significant fitness-related behavior.…”

Predation on Hylodes phyllodes (Anura: Hylodidae) by the harvestman Heteromitobates discolor (Arachnida: Opiliones)

“…Heteromitobates discolor usually is nocturnal, spending the day hidden in rocky crevices near rocky streams. At night, individuals forage on rocks and in low vegetation; they stand upright with their bodies raised and leg pair number two extended to detect any possible prey (Silva and Willemart 2015).…”