Abstract
Megabunus diadema (Fabricius, 1779) is an Atlantic and European harvestman species characterized by a discontinuous distribution from Scandinavia to the Iberian Peninsula. With very few male individuals ever observed in the field until now, the biological uniqueness of the species lies in its reproduction mode, hitherto regarded as asexual, facultative parthenogenesis. Based on a large sample of 741 sexed individuals, the study indicates a sex ratio much higher than what was formerly known, equal to 65.58% of males. Locally varying from 0 to 100% (median 75.5% of males), the sex ratio depends indeed on the altitude and the phenological cycle: the proportion of males decreases with increasing altitude and increases gradually during the spring to reach a plateau in summer. By describing populations locally dominated by male individuals and providing new information on the spatial and temporal patterns of tertiary sex ratio, we question the currently admitted reproduction mode of the species which could be normally sexual, at least locally, rather than asexual. A distribution map of the species on the northern slope of the Pyrenees is provided for the first time. Our study also complements the distribution for the southern slopes of the Pyrenees and the rest of the Iberian Peninsula published recently by Merino-Sainz et al. (2013).
Highlights
Described for the first time under the binominal name Phalangium diadema by Fabricius (1779), the nomenclature of the species was complicated with its subsequent description under two different species names: Meade (1855) recognized a different species from British and Irish individuals under the name of Megabunus insignis while Simon (1881) described Megabunus grouvellei from an individual from Hautes-Pyrénées
A distribution map of the species on the northern slope of the Pyrenees is provided for the first time, with mostly new records from all the french Pyrenees
Our work provides new and original information on the variability of the tertiary sex ratio of this species whose notable originality lies in its reproduction mode: considered until now as facultative parthenogenesis, with very few male individuals observed in the nature, our study
Summary
Described for the first time under the binominal name Phalangium diadema by Fabricius (1779), the nomenclature of the species was complicated with its subsequent description under two different species names: Meade (1855) recognized a different species from British and Irish individuals under the name of Megabunus insignis while Simon (1881) described Megabunus grouvellei from an individual from Hautes-Pyrénées (cirque of Troumouse). Megabunus diadema (Fabricius, 1779) is an unmistakable species, identified from its crown of spines on the ocularium (D’Amico, 2015), both in the male and in the female, at any age. Observed both in coastal environment and in mountain woodland, this species astonishes by its eurytopy: in Iceland for example, the species is found near the sea (where individuals are mostly observed on wet cliffs) and further inland (where they are found mostly on mosses and debris) (Agnarsson, 1998); it is rather a woodland species (in particular mountain woodlands but not exclusively), where the species is found on the ground, on rocks or tree trunks (Curtis & Morton 1974). Its distribution in Spain has been updated by Merino-Sáinz et al (2013) who stated the species might even reach Portugal
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