scholarly journals Sexual Size Dimorphism and Bohemian Waxwings, Bombycilla garrulus

2009 ◽  
Vol 123 (2) ◽  
pp. 165
Author(s):  
Sarah M. Ludlow
Keyword(s):  
Parental Care ◽  
Sexual Size Dimorphism ◽  
Pectoral Muscle ◽  
Tarsus Length ◽  
Size Dimorphism ◽  
Monogamous Species ◽  
Socially Monogamous ◽  
Energetic Constraints ◽  
Males And Females ◽  
Selection For

Sexual size dimorphism is common among birds, with males generally being larger than females. Sexual size dimorphism is typically more extreme in polygynous species; socially monogamous males are typically only 5% larger than females. However, cryptic sexual size dimorphism has been found in some socially monogamous species. I used standard external measurements as well as two internal measurements (keel length and pectoral muscle mass) to determine whether, or to what extent, Bohemian Waxwings (Bombycilla garrulus) exhibit sexual size dimorphism. Males were only slightly larger than females in all of the characters measured except keel and tarsus length. Keel and tarsus length were 0.6% and 1% longer, respectively, in females than in males. The similar size exhibited by males and females may be related to the amount of parental care provided by males. Smaller body size in males may reflect a trade-off between selection for increased male size and energetic constraints imposed by parental care.

scholarly journals A Cautionary Tale: Cryptic Sexual Size Dimorphism in a Socially Monogamous Passerine

The Auk ◽  
2007 ◽  
Vol 124 (2) ◽  
pp. 515-525 ◽  
Author(s):  
Michael T. Murphy
Keyword(s):  
Muscle Mass ◽  
Body Mass ◽  
Sexual Size Dimorphism ◽  
Principal Component ◽  
Pectoral Muscle ◽  
Size Dimorphism ◽  
Monogamous Species ◽  
Socially Monogamous ◽  
Tyrannus Tyrannus ◽  
Wing Chord

AbstractAmong socially monogamous birds, standard metrics suggest that males are only ∼5% larger than females. An untested assumption is that, with the exception of reproductive systems, males and females are scaled mirror images of one another. I used external morphological and skeletal data, and information on muscle mass and organ size, to test this assumption in a population of breeding Eastern Kingbirds (Tyrannus tyrannus). Male and female Eastern Kingbirds exhibited no differences in body mass or standard measures of size, except in a longer (∼6%) wing chord and tail in males. However, keel length, a character rarely measured in the field, was 9.7% larger in males. In principal component analysis, overall body size (PC1) failed to differ between the sexes unless keel length was included. Analysis of 16 skeletal characters also showed that only the bones associated with flight were larger in males. However, the most significant differences between the sexes was that lean dry pectoral muscle mass (LDPMM) was nearly 30% greater in males, whereas the alimentary tract was 27.5% heavier in females. Females also carried more fat. In both sexes, LDPMM scaled in a positive allometric manner with body mass (i.e., slope > 1.0), but the significantly higher slope of males suggested especially strong selection for large muscle mass and, presumably, greater power generation during flight. Eastern Kingbirds thus exhibit pronounced cryptic sexual size dimorphism, but it is not clear whether natural or sexual selection is responsible. These data call for a broader perspective for measuring and a re-evaluation of sexual size dimorphism in other socially monogamous species.Un Llamado de Atención: Dimorfismo Críptico en el Tamaño en un Paserino Socialmente Monógamo

Reversed Sexual Size Dimorphism and Parental Care: Minimal Division of Labour in the Blue-Footed Booby

Behaviour ◽  
1995 ◽  
Vol 132 (7-8) ◽  
pp. 479-496 ◽  
Author(s):  
Hugh Drummond ◽  
Maria Guerra
Keyword(s):  
Parental Care ◽  
Sexual Size Dimorphism ◽  
Division Of Labour ◽  
Avian Species ◽  
Nest Defence ◽  
Adult Size ◽  
Size Dimorphism ◽  
Behavioural Observation ◽  
Males And Females ◽  
Reversed Sexual Size Dimorphism

AbstractReversed sexual size dimorphism in avian species (females larger than males) may be an adaptive consequence of different roles of males and females in parental care. We examined the alleged division of labour in two-chick broods of the blue-footed booby, using behavioural observation and frequent weighing of chicks. In the first week of parental care, males and females fed broods at similar frequencies and provided similar masses of food, but females brooded more than males when broods were 5-10 d old. Subsequently, females provided a greater mass of food and frequency of feeds than males until chicks were at least 35 d old (mass) and 60 d old (frequency), while attending the brood for just as much time as males until chicks were at least 35 d old. Males and females did not differ in the tendency to feed (frequency and mass) the first-hatched chick differentially. In nearly all components of parental care examined here, and in other studies, the female's contribution is equal to or greater than the male's. Only in clutch attendance and nest defence does the male contribute more than the female, but his small size seems unlikely to enhance performance in these activities. Overall, small size appears potentially to limit male provisioning of the brood, and is unlikely to be an adaptation for division oflabour in parental care. This result casts doubt on the relevance of the division-of-labour hypothesis for adult size dimorphism.

scholarly journals Degree of anisogamy is unrelated to the intensity of sexual selection

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Judit Mokos ◽  
István Scheuring ◽  
András Liker ◽  
Robert P. Freckleton ◽  
Tamás Székely
Keyword(s):  
Sex Differences ◽  
Sexual Selection ◽  
Life History ◽  
Parental Care ◽  
Sex Roles ◽  
Sexual Size Dimorphism ◽  
Ecological Factors ◽  
Size Dimorphism ◽  
Wide Range ◽  
Males And Females

AbstractMales and females often display different behaviours and, in the context of reproduction, these behaviours are labelled sex roles. The Darwin–Bateman paradigm argues that the root of these differences is anisogamy (i.e., differences in size and/or function of gametes between the sexes) that leads to biased sexual selection, and sex differences in parental care and body size. This evolutionary cascade, however, is contentious since some of the underpinning assumptions have been questioned. Here we investigate the relationships between anisogamy, sexual size dimorphism, sex difference in parental care and intensity of sexual selection using phylogenetic comparative analyses of 64 species from a wide range of animal taxa. The results question the first step of the Darwin–Bateman paradigm, as the extent of anisogamy does not appear to predict the intensity of sexual selection. The only significant predictor of sexual selection is the relative inputs of males and females into the care of offspring. We propose that ecological factors, life-history and demography have more substantial impacts on contemporary sex roles than the differences of gametic investments between the sexes.

scholarly journals Bigger Males, Bigger Females? Pigeons’ Sexual Size Dimorphism

2020 ◽  
pp. 20-24
Author(s):  
P. M. Parés- Casanova ◽  
A. Kabir
Keyword(s):  
Body Weight ◽  
Body Size ◽  
Sexual Size Dimorphism ◽  
Wing Length ◽  
Rensch’S Rule ◽  
Size Dimorphism ◽  
Rensch's Rule ◽  
Neck Thickness ◽  
Males And Females ◽  
Domestic Pigeons

Sexual dimorphism, defined as phenotypic differences between males and females, is a common phenomenon in animals. In this line, Rensch’s rule states that sexual size dimorphism increases with increasing body size when the male is the larger sex and decreases with increasing average body size when the female is the larger sex. Domesticated animals offer excellent opportunities for testing predictions of functional explanations of Rensch’s theory. Pigeon breeds encounters many different functional purposes and selective constraints, which could influence strongly their morphology. The aim of this paper is to examine, for first time, Rensch’s rule among domestic pigeons. It was compiled a database of 12 quantitative traits (body weight, body height, beak thickness, beak length, neck length, neck thickness, wing length, rump width, tail length, tarsus length, tarsus thickness and middle toe length) for males and females of 11 different domestic pigeon breeds: Bangladesh Indigenous, Racing Homer, Turkish Tumbler, Indian Lotan, Kokah, Mookee, Indian Fantail, Bokhara Trumpeter, Bombai, Lahore and Hungarian Giant House; Rock Pigeon (Columba livia) was also considered as wild relative for comparative purposes. Comparative results between males and females showed that only body weight, wing length and neck thickness were consistent with Rensch’s rule. The rest of trait did not present correlations. Among domestic pigeons, there can appear different expressions of dimorphism according to each trait, so it must be considered that Rensch’s rule vary when considering other traits than body weight.

scholarly journals Sexual Size Dimorphism and Positive Assortative Mating in Alpine Choughs (Pyrrhocorax graculus)

The Auk ◽  
2001 ◽  
Vol 118 (2) ◽  
pp. 553-556 ◽  
Author(s):  
Anne Delestrade
Keyword(s):  
Sample Size ◽  
Assortative Mating ◽  
Body Condition ◽  
Sexual Size Dimorphism ◽  
Morphological Characters ◽  
Positive Trend ◽  
Tarsus Length ◽  
Size Dimorphism ◽  
Positive Assortative Mating ◽  
Larger Sample

Abstract The degree of sexual size dimorphism in a number of different morphological characters was examined in a social corvid, the Alpine Chough, using measurements taken on 178 males and 144 females. A small amount of size dimorphism appeared in all morphological characters, and weight was the most dimorphic character. To identify if Alpine Choughs mate assortatively, measurements of mates were compared in 76 pairs. A positive assortative mating was found on tarsus length, and a small positive trend is suggested between body condition of partners, but that needs to be confirmed with a larger sample size.

Sex-biased parental-care allocation in three tern species (Laridae, Aves)

1995 ◽  
Vol 73 (8) ◽  
pp. 1461-1467 ◽  
Author(s):  
Mauro Fasola ◽  
Nicola Saino
Keyword(s):  
Parental Care ◽  
Agonistic Behavior ◽  
Sexual Size Dimorphism ◽  
Reproductive Effort ◽  
Seabird Species ◽  
Theoretical Predictions ◽  
Males And Females ◽  
Sandwich Tern ◽  
Parental Expenditure ◽  
Care Allocation

We studied parental-care allocation by males and females in three tern species. Female Common Terns (Sterna hirundo) and Little Terns (S. albifrons) performed more incubation and brooding than males, whereas in the Sandwich Tern (S. sandvicensis) the sexes shared these duties equally. In all three species, agonistic behaviors were performed equally by females and males. Prey types brought by males and females of each species were similar, but males tended to bring larger prey and had higher delivery rates than females. Information on parental-care allocation by female and male seabirds of various species, 5 gulls, 6 terns, and 1 skimmer, indicates that females perform most of the incubation and brooding in both gulls and terns, whereas males perform most territory attendance and agonistic behavior (gulls) and more prey provisioning (terns). These patterns are qualitatively consistent with the explanation that the differences between gulls and terns in sex-biased parental care are related to the fact that gulls exhibit sexual size dimorphism but terns do not. Contrary to theoretical predictions that in monogamous birds, females contribute more reproductive effort than males, in all the seabird species studied so far the total parental expenditure by males seems to equal or outweigh that by females.

Is parental care behavior in Belostoma species an evolutionary cause for their common sexual size dimorphism pattern?

2011 ◽  
Vol 15 (2) ◽  
pp. 155-161 ◽  
Author(s):  
Mónica Sandra IGLESIAS ◽  
Francisco Antonio CRESPO ◽  
Alejandra del Carmen VALVERDE
Keyword(s):  
Parental Care ◽  
Sexual Size Dimorphism ◽  
Size Dimorphism ◽  
Care Behavior

Size-Dependent Selective Mechanisms on Males and Females and the Evolution of Sexual Size Dimorphism in Frogs

2014 ◽  
Vol 184 (6) ◽  
pp. 727-740 ◽  
Author(s):  
Renato C. Nali ◽  
Kelly R. Zamudio ◽  
Célio F. B. Haddad ◽  
Cynthia P. A. Prado
Keyword(s):  
Sexual Size Dimorphism ◽  
Size Dimorphism ◽  
Size Dependent ◽  
Males And Females

Egg size, prey size, and sexual size dimorphism in digger wasps (Hymenoptera: Sphecidae)

1985 ◽  
Vol 63 (9) ◽  
pp. 2187-2193 ◽  
Author(s):  
Kevin M. O'Neill
Keyword(s):  
Body Size ◽  
Selection Pressure ◽  
Sexual Size Dimorphism ◽  
Species Selection ◽  
Male Size ◽  
Size Dimorphism ◽  
Female Body Size ◽  
Mean Size ◽  
Males And Females ◽  
Apparent Association

Female digger wasps invest substantially in each of their offspring, laying relatively few, large eggs and providing the young with the insect prey on which they depend for food. In a study of six species in the genera Philanthus, Bembecinus, and Bembix, it was found that within each species, there is a positive correlation between female body size and both the size of their ovarial eggs and the size of the prey they provision. In five of the six species, females were larger than males on average. It is suggested that the apparent association between body size and certain aspects of parental investment by females may provide the directional selection pressure that results in the evolution of sexual size dimorphism in digger wasps. In one species, males and females have the same mean size, probably because, in this species, selection pressure on male size is similar to that on females.

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.

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