Interspecific variation in relative brain size is not correlated with intensity of sexual selection in waterfowl (Anseriformes)

2008 ◽  
Vol 56 (5) ◽  
pp. 311 ◽  
Author(s):  
P.-J. Guay ◽  
A. N. Iwaniuk
Keyword(s):  
Sexual Selection ◽  
Sexual Dimorphism ◽  
Sperm Competition ◽  
Brain Size ◽  
Interspecific Variation ◽  
Morphological Characters ◽  
Comparative Approach ◽  
Pair Bonds ◽  
Relative Brain Size

The role of sexual selection in shaping the brain is poorly understood. Although numerous studies have investigated the role of natural selection, relatively few have focussed on the role of sexual selection. Two important factors influencing the intensity of sexual selection are sperm competition and pair bonding and three different hypotheses have been proposed to explain how they could influence relative brain size. (1) The ‘extra-pair mating’ hypothesis predicts that sexual dimorphism in brain size will increase with sperm competition intensity. (2) The ‘Machiavellian intelligence’ hypothesis predicts that brain size will be larger in species with intense sperm competition. (3) The ‘relationship intelligence’ hypothesis predicts that species forming long-term pair bonds will have larger brains. We investigated sexual dimorphism in brain size and tested these three hypotheses in waterfowl by studying correlations between relative brain volume and three measures of sperm competition (testicular mass, phallus length and mating strategy) and pair-bond duration using the modern phylogenetic comparative approach. We found no evidence of sexual dimorphism in brain size in waterfowl after controlling for body mass and found no support for any of the three hypotheses. This suggests that brain size may not be sexually selected in waterfowl, despite evidence of sexual selection pressures on other morphological characters.

scholarly journals The evolution of sexual dimorphism in parasitic cuckoos: sexual selection or coevolution?

2007 ◽  
Vol 274 (1617) ◽  
pp. 1553-1560 ◽  
Author(s):  
O Krüger ◽  
N.B Davies ◽  
M.D Sorenson
Keyword(s):  
Sexual Selection ◽  
Sexual Dimorphism ◽  
Parental Care ◽  
Brood Parasitism ◽  
Selection Pressure ◽  
Life Histories ◽  
Exceptional Case ◽  
Evolutionary Pathways ◽  
Common Situation

Sexual dimorphism is ubiquitous in animals and can result from selection pressure on one or both sexes. Sexual selection has become the predominant explanation for the evolution of sexual dimorphism, with strong selection on size-related mating success in males being the most common situation. The cuckoos (family Cuculidae) provide an exceptional case in which both sexes of many species are freed from the burden of parental care but where coevolution between parasitic cuckoos and their hosts also results in intense selection. Here, we show that size and plumage differences between the sexes in parasitic cuckoos are more likely the result of coevolution than sexual selection. While both sexes changed in size as brood parasitism evolved, we find no evidence for selection on males to become larger. Rather, our analysis indicates stronger selection on parasitic females to become smaller, resulting in a shift from dimorphism with larger females in cuckoos with parental care to dimorphism with larger males in parasitic species. In addition, the evolution of brood parasitism was associated with more cryptic plumage in both sexes, but especially in females, a result that contrasts with the strong plumage dimorphism seen in some other parasitic birds. Examination of the three independent origins of brood parasitism suggests that different parasitic cuckoo lineages followed divergent evolutionary pathways to successful brood parasitism. These results argue for the powerful role of parasite–host coevolution in shaping cuckoo life histories in general and sexual dimorphism in particular.

scholarly journals Sexual size dimorphism and sexual selection in artiodactyls

2020 ◽  
Vol 31 (3) ◽  
pp. 792-797
Author(s):  
Marcelo H Cassini
Keyword(s):  
Sexual Selection ◽  
Sexual Dimorphism ◽  
Group Size ◽  
Sexual Size Dimorphism ◽  
Alternative Hypothesis ◽  
Mammalian Species ◽  
Generalized Least Squares ◽  
Size Dimorphism ◽  
Selection For

Abstract Sexual size dimorphism is biased toward males in most mammalian species. The most common explanation is precopulatory intramale sexual selection. Large males win fights and mate more frequently. In artiodactyls, previous tests of this hypothesis consisted of interspecific correlations of sexual dimorphism with group size as a surrogate for the intensity of sexual selection (Is). However, group size is not a proper measure of sexual selection for several reasons as is largely recognized in other mammalian taxa. I conducted an interspecific test on the role of sexual selection in the evolution of sexual dimorphism using the variance in genetic paternity as a proxy for the Is. I reviewed the literature and found 17 studies that allowed estimating Is= V/(W2), where V and W are the variance and mean number of offspring per male, respectively. A phylogenetic generalized least squares analysis indicated that dimorphism (Wm/Wf) showed a significant positive regression with the intensity of sexual selection but not group size (multiple r2= 0.40; F3,17= 12.78, P = 0.002). This result suggests that sexual selection may have played a role in the evolution of sexual size dimorphism in Artiodactyla. An alternative hypothesis based on natural selection is discussed.

scholarly journals Sex allocation and investment into pre- and post-copulatory traits in simultaneous hermaphrodites: the role of polyandry and local sperm competition

2013 ◽  
Vol 368 (1613) ◽  
pp. 20120052 ◽  
Author(s):  
Lukas Schärer ◽  
Ido Pen
Keyword(s):  
Sexual Selection ◽  
Sperm Competition ◽  
Sex Allocation ◽  
Optimal Allocation ◽  
Recent Theory ◽  
Detailed Knowledge ◽  
Female Reproduction ◽  
Sexually Selected Traits ◽  
Simultaneous Hermaphrodites

Sex allocation theory predicts the optimal allocation to male and female reproduction in sexual organisms. In animals, most work on sex allocation has focused on species with separate sexes and our understanding of simultaneous hermaphrodites is patchier. Recent theory predicts that sex allocation in simultaneous hermaphrodites should strongly be affected by post-copulatory sexual selection, while the role of pre-copulatory sexual selection is much less clear. Here, we review sex allocation and sexual selection theory for simultaneous hermaphrodites, and identify several strong and potentially unwarranted assumptions. We then present a model that treats allocation to sexually selected traits as components of sex allocation and explore patterns of allocation when some of these assumptions are relaxed. For example, when investment into a male sexually selected trait leads to skews in sperm competition, causing local sperm competition, this is expected to lead to a reduced allocation to sperm production. We conclude that understanding the evolution of sex allocation in simultaneous hermaphrodites requires detailed knowledge of the different sexual selection processes and their relative importance. However, little is currently known quantitatively about sexual selection in simultaneous hermaphrodites, about what the underlying traits are, and about what drives and constrains their evolution. Future work should therefore aim at quantifying sexual selection and identifying the underlying traits along the pre- to post-copulatory axis.

scholarly journals Selection on sperm morphology under relaxed sperm competition in a wild passerine bird

2008 ◽  
Vol 5 (1) ◽  
pp. 58-61 ◽  
Author(s):  
Sara Calhim ◽  
Helene M Lampe ◽  
Tore Slagsvold ◽  
Tim R Birkhead
Keyword(s):  
Sexual Selection ◽  
Sperm Competition ◽  
Sperm Morphology ◽  
Reproductive Traits ◽  
Female Preference ◽  
Passerine Bird ◽  
High Heritability ◽  
Individual Consistency ◽  
Sperm Size

Theories regarding the role of sexual selection on the evolution of sperm traits are based on an association between pre-copulatory (e.g. female preference) and post-copulatory (e.g. ejaculate quality) male reproductive traits. In tests of these hypotheses, sperm morphology has rarely been used, despite its high heritability and intra-individual consistency. We found evidence of selection for longer sperm through positive phenotypic associations between sperm size and the two major female preference traits in the pied flycatcher, Ficedula hypoleuca . Our results support the sexually selected sperm hypothesis in a species under low sperm competition and demonstrate that natural and pre-copulatory sexual selection forces should not be overlooked in studies of intraspecific sperm morphology evolution.

scholarly journals Brain size evolution in pipefishes and seahorses: the role of feeding ecology, life history and sexual selection

2016 ◽  
Vol 30 (1) ◽  
pp. 150-160 ◽  
Author(s):  
M. Tsuboi ◽  
A. C. O. Lim ◽  
B. L. Ooi ◽  
M. Y. Yip ◽  
V. C. Chong ◽  
...  
Keyword(s):  
Sexual Selection ◽  
Life History ◽  
Feeding Ecology ◽  
Brain Size ◽  
Size Evolution

scholarly journals Sexual dimorphism in the South American water snake Helicops polylepis (Serpentes: Dipsadidae)

2021 ◽  
Vol 20 (1) ◽  
pp. 15-25
Author(s):  
Isla Carol Marialva Camargo ◽  
Jackeline Cristina Palma Veras ◽  
Síria Ribeiro ◽  
Ricardo A. Kawashita-Ribeiro ◽  
Rafael de Fraga ◽  
...  
Keyword(s):  
Sexual Selection ◽  
Sexual Dimorphism ◽  
Prey Availability ◽  
Morphological Characters ◽  
Offspring Size ◽  
Female Size ◽  
South American ◽  
The South ◽  
Water Snake ◽  
Fecundity Selection

Sexual selection, fecundity selection and ecological divergence have been the main explanations proposed for the origin and maintenance of sexual dimorphism. In this study we provide evidence of sexual dimorphism in the South American aquatic snake Helicops polylepis, which is mainly determined by body and head sizes. Males have longer tails and more subcaudal scales, and females have larger body and head and more ventral scales. The sexual dimorphism observed in different morphological characters of H. polylepis occurs in other species of xenodontine snakes and is interpreted as a consequence of sexual selection pressures. Data on growth rates associated with prey availability and female size-related offspring size are necessary to refine our analyzes and test specific hypotheses about the ecological and evolutionary bases of sexual dimorphism in H. polylepis.

COMPARISON BETWEEN Trachypithecus auratus AND Trachypithecus cristatus BRAIN SIZE IN INDONESIA

Zoo Indonesia ◽  
2020 ◽  
Vol 29 (1) ◽  
Author(s):  
Endah Dwijayanti ◽  
Anang Setiawan Achmadi ◽  
Maharadatunkamsi Maharadatunkamsi ◽  
Nanang Supriatna
Keyword(s):  
External Factor ◽  
Brain Size ◽  
Morphological Characters ◽  
Clinal Variation ◽  
Brain Volumes ◽  
Trachypithecus Auratus ◽  
Relative Brain Size ◽  
Taxonomic Studies ◽  
Trachypithecus Cristatus ◽  
The Brain

Taxonomic studies on Trachypithecus species in Indonesia define that this genus separated into two species that are Trachypithecus auratus and Trachypithecus cristatus with Trachypithecus auratus auratus as a subspecies. To determine relative brain size differences between species of the genus Trachypithecus in Indonesia and to examine clinal variation, a study related to brain size and morphological characters that affect the brain size is carried out. This study analyzes the brain volume between both species and examines its relationship with morphometric measurement and variables such as sex, age, and specimen location. Brain volumes were calculated from braincase volumes using 0.5 mm silica gel as mini beads. This study reveals that there are significant differences in relative brain size inter-species, sex, age and interaction among variable. Overall, T. auratus have a bigger brain size than T. cristatus, and the brain size of males are larger than females. The older individual tends to have similar brain size with younger ones. The different relative brain size on age level influenced by GSL size. Allometric body size affects the size of the brain directly. Also, there is a clinal trend in relative brain size. Trachypithecus auratus brain size is increasing from West Java to Lombok island. Further study is needed to understand the influence of external factor such as ecological and social factors on brain size in Trachypithecus.

scholarly journals A Review of Effects of Environment on Brain Size in Insects

Insects ◽  
2021 ◽  
Vol 12 (5) ◽  
pp. 461
Author(s):  
Thomas Carle
Keyword(s):  
Body Size ◽  
Social Behaviour ◽  
Brain Size ◽  
Social Brain ◽  
Encephalization Quotient ◽  
The Social ◽  
Relative Brain Size ◽  
The Relationship ◽  
Development And Evolution

Brain size fascinates society as well as researchers since it is a measure often associated with intelligence and was used to define species with high “intellectual capabilities”. In general, brain size is correlated with body size. However, there are disparities in terms of relative brain size between species that may be explained by several factors such as the complexity of social behaviour, the ‘social brain hypothesis’, or learning and memory capabilities. These disparities are used to classify species according to an ‘encephalization quotient’. However, environment also has an important role on the development and evolution of brain size. In this review, I summarise the recent studies looking at the effects of environment on brain size in insects, and introduce the idea that the role of environment might be mediated through the relationship between olfaction and vision. I also discussed this idea with studies that contradict this way of thinking.

scholarly journals Morphological distinction and sexual dimorphism in divergent clades of Neurergus kaiseri (Amphibia: Salamandridae)

2018 ◽  
Vol 32 ◽  
pp. 5-17
Author(s):  
Hadi Khoshnamvand ◽  
Mansoureh Malekian ◽  
Yazdan Keivany
Keyword(s):  
Sexual Selection ◽  
Body Size ◽  
Sexual Dimorphism ◽  
Principle Component Analysis ◽  
Morphological Differentiation ◽  
Taxonomic Revision ◽  
Morphological Characters ◽  
Head Width ◽  
Morphological Distinction ◽  
Ecological Differences

Morphological differentiation and sexual dimorphism in the two genetically distinct clades (Northern and Southern clades) of the Lorestan newt, Neurergus kaiseri, was evaluated for 72 live specimens, using five body- and nine head-related characters and eight calculated ratios. Principle component analysis of morphological characters confirmed that the Lorestan newt populations are well separated into two distinct groups, suggesting that a taxonomic revision in N. kaiseri may be required because of significant molecular, morphological and ecological differences between these clades. Sexual dimorphism in N. kaiseri includes body size and shape. Females were clearly larger than males in most body- and head-related variables and males had relatively greater head width and eye length. Sexual dimorphism in this species may be linked to sexual selection and ecological differences between sexes. However, many aspects of the ecology and reproductive biology of this species remain unknown.

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