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 Why female birds of prey are larger than males

2020 ◽  
Vol 129 (3) ◽  
pp. 532-542
Author(s):  
Jonny Schoenjahn ◽  
Chris R Pavey ◽  
Gimme H Walter
Keyword(s):  
Sexual Size Dimorphism ◽  
A Priori ◽  
Nest Defence ◽  
Birds Of Prey ◽  
Causal Process ◽  
Size Dimorphism ◽  
Substantial Body ◽  
Key Factor ◽  
Reversed Sexual Size Dimorphism ◽  
Passionate Debate

Abstract The causes of the reversed sexual size dimorphism (RSD; females larger than males) in birds of prey are subject to a centuries-old, passionate debate. A crucial difficulty is to distinguish whether the postulated benefits derive from the proposed causal process(es) or are incidental. After reviewing the existing literature, we present a methodology that overcomes this difficulty and renders unnecessary any speculative a priori distinctions between evolved function and incidental effects. We can thus justify the following novel version of the well-known nest defence hypothesis as the most likely to explain the phenomenon in all birds of prey that show RSD: if the female predominates in actively defending the eggs and young against predators, then she is the heavier sex, and her relatively greater body mass is adaptive. That is, heavier females are favoured (independently of males) by natural selection. The attractiveness of this hypothesis is that it has the potential to explain the phenomenon in all raptors exhibiting RSD, can deal with the exceptional cases in this group, explains the direction of the dimorphism, focuses on a key factor in the reproductive success of most raptors, is parsimonious, i.e. does not require supporting hypotheses, and is supported by a substantial body of evidence.

Reversed sexual size dimorphism and parental care in the Red-footed Booby Sula sula

Ibis ◽  
2005 ◽  
Vol 147 (2) ◽  
pp. 307-315 ◽  
Author(s):  
HERVE LORMEE ◽  
CHRISTOPHE BARBRAUD ◽  
OLIVIER CHASTEL
Keyword(s):  
Parental Care ◽  
Sexual Size Dimorphism ◽  
Size Dimorphism ◽  
Reversed Sexual Size Dimorphism

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 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.

Reproductive isolation and sex-role reversal in two sympatric sand-dwelling wolf spiders of the genus Allocosa

2008 ◽  
Vol 86 (7) ◽  
pp. 648-658 ◽  
Author(s):  
A. Aisenberg ◽  
F. G. Costa
Keyword(s):  
Reproductive Isolation ◽  
Sexual Size Dimorphism ◽  
Sex Role ◽  
Wolf Spider ◽  
Coastal Dunes ◽  
Pitfall Trap ◽  
Role Reversal ◽  
Adult Size ◽  
Wolf Spiders ◽  
Size Dimorphism

Allocosa brasiliensis (Petrunkevitch, 1910) is a nocturnal wolf spider inhabitant of coastal dunes. Pitfall-trap data suggested the occurrence of two sympatric and synchronic morphs, with differences in adult size and abdominal design (minor and major morphs). Previous studies performed with the major morph of A. brasiliensis, postulated courtship-role and sexual size dimorphism reversal for this spider. In the present study, we compare data on development and morphology and test reproductive isolation between morphs of A. brasiliensis, with the hypotheses that the two morphs are reproductively isolated and both show courtship-role reversal. As had been reported for the major morph of A. brasiliensis, the minor-morph females approached the burrows of minor-morph males, entered, initiated courtship, and after copulation, males closed their burrows with female cooperation from the inside. Females did not court or copulate with males belonging to the other morph and, in two cases, major-morph females cannibalised minor-morph males. Morphometrical and developmental data showed differences between morphs. The occurrence of copulation only between individuals of the same morph confirm reproductive isolation, supporting the occurrence of two species. Morphological and behavioural data are consistent with courtship-role-reversal hypotheses for the minor morph, constituting the second report in spiders of this atypical behaviour.

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 Reversed sexual size dimorphism: body size patterns in sexes of lesser kestrels (Falco naumanni) in the Ikh Nart Nature Reserve, Mongolia

2019 ◽  
Vol 12 (3) ◽  
pp. 363-368 ◽  
Author(s):  
Onolragchaa Ganbold ◽  
Richard P. Reading ◽  
Ganchimeg J. Wingard ◽  
Woon Kee Paek ◽  
Purevsuren Tsolmonjav ◽  
...  
Keyword(s):  
Body Size ◽  
Sexual Size Dimorphism ◽  
Nature Reserve ◽  
Size Dimorphism ◽  
Falco Naumanni ◽  
Reversed Sexual Size Dimorphism

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.

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