Search results for "SELE"
showing 10 items of 4721 documents
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…
THE EFFECT OF ALTERNATIVE PREY ON THE DYNAMICS OF IMPERFECT BATESIAN AND MÜLLERIAN MIMICRIES
2004
Both Batesian and Müllerian mimicries are considered classical evidence of natural selection where predation pressure has, at times, created a striking similarity between unrelated prey species. Batesian mimicry, in which palatable mimics resemble unpalatable aposematic species, is parasitic and only beneficial to the mimics. By contrast, in classical Müllerian mimicry the cost of predators' avoidance learning is shared between similar unpalatable co-mimics, and therefore mimicry benefits all parties. Recent studies using mathematical modeling have questioned the dynamics of Müllerian mimicry, suggesting that fitness benefits should be calculated in a way similar to Batesian mimicry; that i…
Evolutionary processes in the emergence and recent spread of the syphilis agent, Treponema pallidum
2022
Abstract The incidence of syphilis has risen worldwide in the last decade in spite of being an easily treated infection. The causative agent of this sexually transmitted disease is the bacterium Treponema pallidum subspecies pallidum (TPA), very closely related to subsp. pertenue (TPE) and endemicum (TEN), responsible for the human treponematoses yaws and bejel, respectively. Although much focus has been placed on the question of the spatial and temporary origins of TPA, the processes driving the evolution and epidemiological spread of TPA since its divergence from TPE and TEN are not well understood. Here, we investigate the effects of recombination and selection as forces of genetic diver…
Synthesis of sialyl-Tn antigen. Regioselective sialylation of a galactosamine threonine conjugate unblocked in the carbohydrate portion
1994
Abstract Regioselective and stereocontrolled formation of the sialyl-Tn antigen conjugate 6 was achieved by reacting the NeuNAc-2-xanthate 2 with the GalNAc threonine acceptor 5 bearing three hydroxy groups. Complete deprotection afforded the sialyl-Tn antigen structure 11 .