Search results for "Systematics"

2021

Because of its parasitic habits, reproduction costs of the common cuckoo (Cuculus canorus) are mostly spent in pre-laying activities. Female costs are limited to searching host nests and laying eggs, whereas, males spend time in performing intense vocal displays, possibly with territorial purpose. This last aspect, together with a sexual plumage dimorphism, points to both intra- and inter-sexual selections operating within this species. One element triggering sexual selection is a differential fitness accrued by different phenotypes. Before analyzing possible sexual selection mechanisms operating in cuckoos, it is therefore necessary to verify whether there is a variability among male secon…

Bill colour and immunocompetence in the European blackbird

2003

The level of expression of secondary sexual characters has been suggested to signal male ability to resist parasitic infestations. To test this idea, several studies have examined the link between sexual signals and immunocompetence in birds. However, most of them have used only a single aspect of immune response to evaluate immunocompetence. We investigated the relation between bill colour and immunocompetence in captive male European blackbirds, Turdus merula, during the breeding season by assessing both cell-mediated and humoral components of the immune system. The blackbird is a sexually dimorphic species with bill colour varying from yellow to orange in males. Humoral immunity was asse…

Forceps size and immune function in the earwig Forficula auricularia L.

2007

Females of many species select their mates on the basis of the size or intensity of sexual ornaments, and it has been suggested that these provide reliable signals of a male’s ability to resist parasites and pathogens. European earwigs, Forficula auricularia, are sexually dimorphic in forceps shape and length. Male forceps are used as weapons in male contests for access to females, but recent findings suggest that females also choose males on the basis of their forceps length. In the present study, we tested the hypotheses that in the European earwig, F. auricularia, the size of forceps is correlated with immune function and that immune function differs between the sexes. We found that enca…

Sex-specific patterns of antagonistic and mutualistic biotic interactions in dioecious and gynodioecious plants

2013

a b s t r a c t A major transition in flowering plants has been the evolution of separate sexes from hermaphroditism via gynodioecy which is considered to be the most important route. Biotic interactions, both antagonist and mutualistic, have been proposed to influence this transition which is generally accompanied by the evolution of sexual dimorphism in secondary sexual traits. While some researchers have studied sex- specific patterns in herbivory and pollination, less attention has been paid to pathogens/parasites and a limited number of studies have revised sex-specific patterns in mycorrhizal symbiosis. In this article, we explore sex-specific interactions in dioecious and gynodioecio…

Quantification of sexual dimorphism in Asellus aquaticus (Crustacea: Isopoda) using outline approaches

2002

A marked sexual dimorphism is often observed in arthropods species in which males perform precopulatory mate guarding. It is generally thought to reflect the influence of sexual selection. Until now, sexual dimorphisms associated with mate guarding have mainly been qualitatively described. However, assessing the effects of sexual selection on sexual dimorphims requires a preliminary quantitative assessment of differences in morphology between sexes. Using Fourier analyses, we tested if morphological dimorphisms could be quantitatively assessed in the isopod Asellus aquaticus. In addition, we checked whether sexual dimorphism in shape was exclusively related to mate guarding through consider…

Why are male rotifers dwarf?

2011

Sperm competition and small size advantage for males of the golden orb-web spider Nephila edulis

2000

Sexual selection, through female choice and/or male‐male competition, has influenced the nature and direction of sexual size dimorphism in numerous species. However, few studies have examined the influence of sperm competition on size dimorphism. The orb-web spider Nephila edulis has a polygamous mating system and extreme size dimorphism. Additionally, the frequency distribution of male body size is extremely skewed with most males being small and few large. The duration of copulation, male size and sexual cannibalism have been identified as the significant factors determining patterns of sperm precedence in spiders. In double mating trials, females were assigned to three treatments: either…

Redescription of the rare European harvestman Dicranopalpus brevipes Marcellino, 1970, based on first records from Sardinia (Arachnida: Opiliones)

2020

New records of the small, enigmatic harvestman Dicranopalpus brevipes are presented, the male is redescribed and the female is described for the first time. The species originates from Sicily, while the novel findings are from Sardinia, where it may have been introduced by man. Paedomorphic modifications such as reduced sexual dimorphism in colouration and pedipalpal morphology, regression of genital structures and shortening of the legs, appear to result from its ground-dwelling habits induced by xeric climatic conditions. Avoiding the dry and hot season, D. brevipes matures in autumn and winter and has completed its lifecycle in April. Additional information on phenology, ecology, distrib…

Behavioral roles of the sexually dimorphic structures in the male harvestman, Phalangium opilio (Opiliones, Phalangiidae)

2006

Abstract: In various animal species, male sexual dimorphic characters may be used during intrasexual contests as ornaments to attract females, or to hold them before, during, or after copulation. In the well-known harvestman, Phalangium opilio L., 1758, the behavioral functions of these male sexually dimorphic structures have never been studied in detail. Therefore, in addition to a morphometric study, 21 male contests and 43 sexual interactions were analyzed. Our observations revealed that during contests, the male cheliceral horns form a surface by which the contestants use to push each other face-to-face while rapidly tapping their long pedipalps against the pedipalps of the opponent, oc…

Mimicry between unequally defended prey can be parasitic: evidence for quasi-Batesian mimicry

2010

The nature of signal mimicry between defended prey (known as Mullerian mimicry) is controversial. Some authors assert that it is always mutualistic and beneficial, whilst others speculate that less well defended prey may be parasitic and degrade the protection of their better defended co-mimics (quasi-Batesian mimicry). Using great tits (Parus major) as predators of artificial prey, we show that mimicry between unequally defended co-mimics is not mutualistic, and can be parasitic and quasi-Batesian. We presented a fixed abundance of a highly defended model and a moderately defended dimorphic (mimic and distinct non-mimetic) species, and varied the relative frequency of the two forms of the …