scholarly journals Temporal patterns in prey size between sexes in a raptor with extreme size dimorphism: testing the intersexual competition hypothesis using web-sourced photographs

2021 ◽  
Author(s):  
Connor T. Panter ◽  
arjun amar
Keyword(s):  
Sexual Dimorphism ◽  
Prey Size ◽  
Ingestion Rate ◽  
Size Dimorphism ◽  
Accipiter Nisus ◽  
Competition Hypothesis ◽  
Nestling Period ◽  
Dietary Niche ◽  
Reversed Sexual Dimorphism ◽  
Intersexual Competition

In most vertebrates, males are larger than females. For raptors, sexual size dimorphism is reversed, with females being larger. Reversed sexual dimorphism (RSD) in raptors is strongly linked to diet, with species feeding on the most agile prey, for example bird-eating raptors, showing the greatest size differences between the sexes. Hypotheses for reversed sexual dimorphism (RSD) include the ‘intersexual competition’ hypothesis, which proposes that RSD evolved to enable pairs to expand their dietary niche (taking a wider range of prey sizes) during the nestling period when both sexes occupy and hunt within the same territory, and thereby reduce competition between the sexes. If intersexual competition is responsible for the evolution of RSD, we predict that sex-related differences in prey size and dietary niche breadth will be particularly pronounced during the nestling period (cf. the non-nestling period). We explore this prediction in the highly dimorphic Eurasian Sparrowhawk (Accipiter nisus), which displays the largest degree of RSD of all raptors, using web-sourced photographs to identify diet throughout the entire year. We analysed 666 photographs of sparrowhawks on their prey over time. In contrast to our predictions, sex-specific prey sizes were most similar during the nestling period compared to any other time of the year. Both males and females reduced the size of their prey during the nestling period which may be a result of the ‘ingestion rate’ hypothesis, or a strategy employed to prevent hunting-related injuries during this critical period of the year.

Reversed sexual dimorphism in the beak of a finch

Ibis ◽  
2003 ◽  
Vol 145 (2) ◽  
pp. 341-343 ◽  
Author(s):  
Peter R. Grant ◽  
B. Rosemary Grant
Keyword(s):  
Sexual Dimorphism ◽  
Reversed Sexual Dimorphism

Sexual size dimorphism in the viviparous caecilian amphibian Geotrypetes seraphini seraphini (Gymnophiona: Dermophiidae) including an updated overview of sexual dimorphism in caecilian amphibians

2016 ◽  
Vol 37 (3) ◽  
pp. 291-299 ◽  
Author(s):  
Markus Maerker ◽  
Sandy Reinhard ◽  
Peter Pogoda ◽  
Alexander Kupfer
Keyword(s):  
Sexual Dimorphism ◽  
Body Length ◽  
Sexual Size Dimorphism ◽  
Molecular Ecology ◽  
Female Size ◽  
Sexually Dimorphic ◽  
Size Dimorphism ◽  
Mating System Evolution ◽  
Accurate Comparison ◽  
Widespread Phenomenon

Sexual size dimorphism (SSD) describing intersexual size differences of a given taxon is a widespread phenomenon in the animal kingdom. SSD plays a significant role in understanding life history and mating system evolution. The snakelike morphology of limbless caecilian amphibians lacking obvious secondary sexual characters (in contrast to frogs and salamanders) impedes an accurate comparison between sexes.Here, the phylogenetically derived teresomatan and viviparous caecilianGeotrypetes seraphini seraphiniwas analysed for patterns of sexual dimorphism. In terms of body size females were the larger sex, but when body length was adjusted male-biased intersexual differences in cloacal shape appeared. The larger female size is likely explained by fecundity selection as clutch size was positively correlated to female body length. Unexpectedly a cryptic, ontogeny related variation of the nuchal collars was found. An overview of SSD in caecilians including data for 27 species of nine out of ten existing families revealed a quite high number of taxa showing sexually dimorphic head size dimensions exclusively present among phylogenetically derived teresomatan caecilians. Still further research including insights into the behavioural ecology and molecular ecology of mating systems is warranted to better understand the evolution of sexual size dimorphism of caecilian amphibians.

scholarly journals Reversed sexual dimorphism and altered prey base: the effect on sooty owl (Tyto tenebricosa tenebricosa) diet

2011 ◽  
Vol 59 (5) ◽  
pp. 302 ◽  
Author(s):  
Rohan J. Bilney ◽  
John G. White ◽  
Raylene Cooke
Keyword(s):  
Sexual Dimorphism ◽  
Small Mammals ◽  
Prey Availability ◽  
Mammalian Species ◽  
Control Programs ◽  
European Settlement ◽  
Mammal Conservation ◽  
Reversed Sexual Dimorphism ◽  
Conservation Concern ◽  
And Function

The ecology and function of many Australian predators has likely been disrupted following major changes in prey base due to declines in distribution and abundance of small mammals following European settlement. This study investigated various aspects of the dietary ecology of sooty owls (Tyto tenebricosa tenebricosa), including sexual variation as they potentially exhibit the greatest degree of reversed sexual dimorphism of any owl species worldwide. Sooty owls are highly opportunistic predators of non-volant small mammals, consuming most species known to exist in the region, so their diet fluctuates seasonally and spatially due to varying prey availability, and is particularly influenced by the breeding cycles of prey. Significant intersexual dietary differences existed with female sooty owls predominantly consuming much larger prey items than males, with dietary overlap at 0.62. The current reliance on relatively few native mammalian species is of conservation concern, especially when mammal declines are unlikely to have ceased as many threatening processes still persist in the landscape. Sooty owl conservation appears inextricably linked with small mammal conservation. Conservation efforts should be focussed towards improving prey densities and prey habitat, primarily by implementing control programs for feral predators and preventing the loss of hollow-bearing trees throughout the landscape.

Interspecific variation in sexual dimorphism in brain size in Nearctic ground squirrels (Spermophilus spp.)

2001 ◽  
Vol 79 (5) ◽  
pp. 759-765 ◽  
Author(s):  
Andrew N Iwaniuk
Keyword(s):  
Sex Differences ◽  
Body Size ◽  
Sexual Dimorphism ◽  
Ground Squirrel ◽  
Mating Systems ◽  
Resource Competition ◽  
Brain Size ◽  
Ground Squirrels ◽  
Detailed Knowledge ◽  
Size Dimorphism

A possible relationship between sexual dimorphism in brain size and mating system was investigated in five ground squirrel species: Spermophilus lateralis, S. tridecemlineatus, S. richardsonii, S. columbianus, and S. parryii. Relative brain size was measured by determining the endocranial volume of 247 ground squirrel skulls and regressing these values against two measurements of body size: mass and length. Analyses of covariation in the brain size / body size relationship within the five species revealed that sexual brain-size dimorphism occurs in three of the five species: S. lateralis, S. richardsonii, and S. tridecemlineatus. Application of a reduced major axis regression model indicated, however, that only S. lateralis and S. richardsonii exhibit significant sexual brain-size dimorphism. These findings suggest that the degree of sexual brain-size dimorphism is not directly correlated with variation in mating systems. Spatial abilities may play a role in the evolution of sexual brain-size dimorphism in ground squirrels, but the spatial requirements of mating systems appear to be insufficient. The possibility of sex differences in cognition, resource competition, and other variables as contributory factors to the evolution of sexual brain-size dimorphism is offered, but detailed knowledge of sex differences in the behaviour of ground squirrels is required to provide a definitive answer.

The evolution of sexual dimorphism in the lizard Anolis polylepis (Iguania): evidence from intraspecific variation in foraging behavior and diet

1996 ◽  
Vol 74 (7) ◽  
pp. 1238-1245 ◽  
Author(s):  
Gad Perry
Keyword(s):  
Sexual Selection ◽  
Sexual Dimorphism ◽  
Feeding Behavior ◽  
Rain Forest ◽  
Sexual Size Dimorphism ◽  
Costa Rican ◽  
Agonistic Interactions ◽  
Size Dimorphism ◽  
Food Items ◽  
Competing Hypotheses

Two main explanations, intraspecific niche divergence and sexual selection, have been proposed to explain the origin of sexual size dimorphism. To test these competing hypotheses I studied the ecology, feeding behavior, and diet of the lizard Anolis polylepis in a Costa Rican rain forest. Male A. polylepis were significantly larger and heavier than females but ate smaller food items and had lower stomach volumes, despite possessing longer and wider heads. Males were more sedentary than females or juveniles, chose higher perches, and were more likely to be involved in agonistic interactions. Diets of males, females, and juveniles were also significantly different taxonomically. These data are consistent with the sexual selection origin theory but not with an ecological one. Thus, observed dietary differences probably evolved once dimorphism had been attained through sexual selection.

scholarly journals A new miniature Pristella (Actinopterygii: Characiformes: Characidae) with reversed sexual dimorphism from the rio Tocantins and rio São Francisco basins, Brazil

2021 ◽  
pp. 339-348
Author(s):  
F.C.T. Lima ◽  
R.A. Caires ◽  
C.C. Conde-Saldaña ◽  
J.M. Mirande ◽  
F.R. Carvalho
Keyword(s):  
Phylogenetic Analysis ◽  
New Species ◽  
Sexual Dimorphism ◽  
Color Pattern ◽  
Bony Fishes ◽  
Reversed Sexual Dimorphism ◽  
A New Species

A new species of the genus Pristella Eigenmann, 1908 (Pristella crinogi sp. nov.) is described from the middle rio Tocantins and middle rio São Francisco basins, Brazil. The new species can be diagnosed from its two congeners, Pristella ariporo Conde-Saldaña, Albornoz-Garzón, García-Melo, Villa-Navarro, Mirande, and Lima, 2019 and Pristella maxillaris (Ulrey, 1894), by a combination of color pattern and teeth morphology characters. A phylogenetic analysis of the genus recovered P. crinogi as the sister taxa of P. ariporo. Pristella crinogi, along with P. ariporo, are the first characiform fishes, and one of the first bony fishes, to be reported as presenting a reversed sexual dimorphism, with females presenting a more developed color pattern than males. Comments on the miniaturization of the species, as well as remarks on the biogeography of the genus Pristella, are presented.

scholarly journals A Comparative Study of the Canine Tooth as a Tool in Gender Determination in Nigerian Population

2019 ◽  
Vol 26 (2) ◽  
Author(s):  
Peter O Otuaga ◽  
Lilian Ebite Chris-Ozoko ◽  
Oghenetega Lynda Sakpoba ◽  
John Chukwuma Oyem
Keyword(s):  
Sexual Dimorphism ◽  
Sex Determination ◽  
Canine Tooth ◽  
Maxillary Canine ◽  
Male And Female ◽  
Study Results ◽  
Significant Difference ◽  
Nigerian Population ◽  
Reversed Sexual Dimorphism ◽  
Dental Evidence

Dental evidence has been demonstrated as a major forensic tool for the identification of individuals and sex determination. The objective of the research was to determine sex in Delta Ibo ethnic group of Nigeria using the mandibular and maxillary canine teeth. Materials and methods. The study comprised 201 (100 males and 101 females) subjects of Delta Ibo ethnicity at the age of 17 – 25 years. The mesiodistal crown width and intercanine distance of both the maxillary and mandibular canines were measured intraorally using a pair of dividers and a ruler. Unpaired T-test at a probability value of p<0.05 was used to ascertain the mean significant differences between the male and female canine indices.   Results. Study results showed a statistically significant difference between male and female mandibular and maxillary canine mesiodistal width. This implied a sexual and reversed sexual dimorphism in the studied population.        Conclusions. The study confirmed that the canines of Delta Ibos exhibit sexual dimorphism like other populations and the maxillary canine indices give the most accurate prediction in sex determination.

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