Search results for "Sexual selectio"

Sex roles and sex ratios in animals

2022

In species with separate sexes, females and males often differ in their morphology, physiology and behaviour. Such sex-specific traits are functionally linked to variation in reproductive competition, mate choice and parental care, which have all been linked to sex roles. At the 150th anniversary of Darwin's theory on sexual selection, the question of why patterns of sex roles vary within and across species remains a key topic in behavioural and evolutionary ecology. New theoretical, experimental and comparative evidence suggests that variation in the adult sex ratio (ASR) is a key driver of variation in sex roles. Here, we first define and discuss the historical emergence of the sex role c…

Sexual Selection Within the Female Genitalia in Lepidoptera

2015

The genitalia of male and female Lepidoptera are complex organs, composed of several structures that exhibit great diversity of shapes, sizes, and positions, suggesting that they have evolved in a relatively rapid and divergent way. In this chapter, we explore the selective pressures responsible for the evolution of genital morphology in the Lepidoptera , emphasizing the possible role of post-copulatory intersexual selection (PCIS) mechanisms (cryptic female choice and sexual conflict). Our exploration is in great extent speculative because knowledge on the functional morphology of genitalia in this group is limited. We start by describing the complexity and diversity of genitalia in Lepido…

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…

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…

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…

Honesty of agonistic signalling and effects of size and motivation asymmetry in contests

1999

Game theoretical models predict that the main function of fighting behaviour is to assess the relative fighting ability of opponents. The sequential assessment game has often been used to investigate contests, while honest signalling theory has received much less attention. With the wolf spider Hygrolycosa rubrofasciata we investigated whether male agonistic signalling can reveal honest information about fighting ability, and how size and motivation asymmetries affect male fighting behaviour. We also determined whether male–male competition affects the courtship behaviour of the males. We found that agonistic drumming activity is an honest indicator of male fighting ability, and that relati…

Intrasexual competition at work: Sex differences in the jealousy-evoking effect of rival characteristics in work settings

2010

Sex differences in jealousy-evoking rival characteristics in the relationship with a supervisor at work were examined in a community sample of 188 individuals from Argentina. Among men, the rivals’ social dominance and communal attributes evoked the most jealousy, followed by physical dominance. Among women, the rival’s communal attributes evoked the most jealousy, followed by social dominance and physical attractiveness. For men physical dominance of the rival and for women physical attractiveness of the rival evoked relatively more jealousy, especially among those high in intrasexual competition and confronted with a same-sex supervisor. When confronted with an opposite-sex supervisor, s…

Male coloration and species recognition in sympatric flycatchers

1994

Currently favoured views for explaining ornaments in males emphasize female preference such that females benefit from increased offspring production, good genes of the offspring, or the attractiveness of sons. Results from long-term studies in the pied flycatcher Ficedula hypoleuca suggest that factors associated with species recognition may also be important for male coloration. In sympatry the collared flycatcher F. albicollis is dominant in competition for nesting sites over the pied flycatcher. Bright pied flycatcher males resemble collared flycatcher males and suffer from interspecific interference, whereas dull and female-like males can acquire nesting sites close to those of the coll…