Search results for "Sexual Dimorphism"

Much more than a clasp: Evolutionary pattern of amplexus diversity in anurans

2019

ABSTRACTThe evolution and diversification of animal reproductive modes have been pivotal questions in behavioral ecology. Amphibians present the highest diversity of reproductive modes among vertebrates, involving various behavioral, physiological and morphological traits. One of such features is the amplexus, the clasp or embrace of males on females during reproduction, which is almost universal to anurans. Hypotheses about the origin amplexus are limited and have not been thoroughly tested, nor had they taken into account evolutionary relationships in most comparative studies. However, these considerations are crucial to understand the evolution of reproductive modes. Here, using an evolu…

False dichotomies and human sexual size dimorphism: A comment of Dunsworth (2020)

2021

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…

Sexual dimorphism in primates: Where are we and where do we go from here?

1986

There are currently several debates taking place in palaeoanthropological circles in which the issue of sexual dimorphism is crucial. During the 60th Jubilee of the discovery of the TaungAustralopithecus skull, the authors concurred that much of the debate was due to differences in perception concerning dimorphism, and it was suggested that a study session dealing principally with sexual dimorphism in Primates should be organised with a view to determining what, if anything, could be observed in extant primates that might be utilised for determining the existence of dimorphism in fossil species. An advertisement was placed in the Journal of Human Evolution, calling for papers. Response was …

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…