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Ezzine O.,National Water Research Institute | Ezzine O.,Tunis el Manar University | Branco M.,University of Lisbon | Villemant C.,French National Center for Scientific Research | And 3 more authors.
Annals of Forest Science | Year: 2015

Key message: During outbreak, a discrepancy between larval performance and the main host used for egg laying was found in Orgyia trigotephras. It results mostly from intraspecific competition, but reduced egg mortality on the less suitable host plant may play a secondary role. Context: Host range of polyphagous herbivores often comprises plants of low nutritional quality, which may however provide other benefits to the animal. Understanding the effect of host plants use on insect fitness and its population dynamics are central questions in insect-plant ecology. O. trigotephras Boisduval is a polyphagous Mediterranean defoliator. During outbreaks, larvae are frequently found on two unrelated host species, Pistacia lentiscus L. and Quercus coccifera L. Aim: The aim of this study was to clarify the effect of population density on host use and the effects of host tree on insect performance. Methods: The realized fecundity and egg mortality were measured during 3 years showing different population levels of the defoliator. Larval performance on the two host species was analyzed. Results: Larvae fed on Q. coccifera had faster development, lower mortality, higher female/male ratio, and higher fecundity than larvae fed on P. lentiscus. Yet, at high population densities, under high intraspecific competition, P. lentiscus was the most used for egg laying. During outbreak, higher levels of parasitism by Aprostocetus sp. and predation by Coccidiphila rungsella Nel and Brusseaux were found on eggs laid on Q. coccifera compared to those laid on P. lentiscus. Conclusions: The results indicate a discrepancy between host use and larvae performance, possibly ruled by resources exploitation and intraspecific competition. The reduced egg predation on P. lentiscus during outbreaks might also provide an indirect benefit to the insect. © 2015, INRA and Springer-Verlag France.

Kotrba M.,SNSB Zoologische Staatssammlung Munich ZSM | Huber J.,TU Munich | Feijen H.R.,Naturalis Biodiversity Center
Organisms Diversity and Evolution | Year: 2014

The present study investigates the coevolution of a particular male genital process and the female spermathecal ducts in a clade of stalk-eyed flies (Diptera, Diopsidae) and debates the underlying evolutionary mechanisms. The fine morphology and interaction of the male and female genitalic structures are reconstructed from serial sections of mating pairs in one of the species. It is found that the male genital process traverses the common spermathecal duct to enter the base of one of the separate spermathecal ducts during the mating. Spermatozoa and accessory secretions are not transferred through the male genital process but can be discharged only from the male gonopore near its base. A detailed morphometric study reveals low intraspecific variation and hypoallometry of the male genital process. Across 17 species studied comparatively, the lengths of the male genital process and the female common and separate spermathecal ducts are highly variable. The length of the male genital process is correlated significantly with that of the female common spermathecal duct, but not with that of the separate spermathecal ducts. Based on the combined evidence it is concluded that the male genital process and the female common spermathecal duct have coevolved, and that sexual selection by cryptic female choice constitutes a possible and parsimonious explanation for their coevolution. Alternative or additional explanations in terms of sexually antagonistic coevolution cannot be ruled out conclusively, but are not supported by the available evidence. © 2013 Gesellschaft für Biologische Systematik.

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