scholarly journals Sexual segregation in a highly pagophilic and sexually dimorphic marine predator

2021 ◽  
Vol 1 ◽  
Author(s):  
Christophe Barbraud ◽  
Karine Delord ◽  
Akiko Kato ◽  
Paco Bustamante ◽  
Yves Cherel
Keyword(s):  
Sexual Segregation ◽  
Sexually Dimorphic ◽  
Marine Predator

scholarly journals Sexual segregation in a wide-ranging marine predator is a consequence of habitat selection

2015 ◽  
Vol 518 ◽  
pp. 1-12 ◽  
Author(s):  
IR Cleasby ◽  
ED Wakefield ◽  
TW Bodey ◽  
RD Davies ◽  
SC Patrick ◽  
...  
Keyword(s):  
Habitat Selection ◽  
Sexual Segregation ◽  
Marine Predator

Sexual segregation in bison: a test of multiple hypotheses

Behaviour ◽  
2005 ◽  
Vol 142 (7) ◽  
pp. 897-927 ◽  
Author(s):  
Eric W. Schaad ◽  
David S. Wiseman ◽  
Royce R. Huber ◽  
Michael S. Mooring ◽  
Dominic D. Reisig ◽  
...  
Keyword(s):  
Body Size ◽  
Predation Risk ◽  
Sexual Segregation ◽  
Bison Bison ◽  
Sexually Dimorphic ◽  
Activity Budgets ◽  
Single Sex ◽  
Multiple Hypotheses ◽  
Mixed Groups ◽  
Large Groups

AbstractSexual segregation, in which males and females form separate groups for most of the year, is common in sexually dimorphic ungulates. We tested multiple hypotheses to explain sexual segregation in bison (Bison bison) at National Bison Range, Montana and Fort Niobrara National Wildlife Refuge, Nebraska during June-August of 2002-2003. Fieldwork involved use of GPS to record space use by segregated groups, vegetation transects to measure forage availability, fecal analyses to document diet composition and quality, and behavioural observations to characterize activity budgets. During sexual segregation, males in bull groups used areas with greater per capita abundance of forage, higher proportion of weeds, and less nutritious grasses (as indicated by lower % fecal nitrogen) compared with females in cow or mixed groups. However, there was no difference between the sexes in activity budgets, predation risk factors, or distance to water. Single-sex bull groups were no more synchronized in activity than mixed groups. These results support the 'sexual dimorphism-body size hypothesis', which proposes that males segregate from females because their larger body size requires more abundant forage, while longer ruminal retention permits efficient use of lower-quality forage. The gastrocentric model, based on the digestive physiology and foraging requirements of dimorphic ungulates, supplies the most likely proximate mechanism for bison sexual segregation. Our results would also partly support the 'reproductive strategy-predation risk hypothesis' if females form large groups to reduce predation risk. The predictions of the 'activity budget hypothesis' were not supported for bison.

scholarly journals Thermal tolerance may cause sexual segregation in sexually dimorphic species living in hot environments

2015 ◽  
Vol 27 (3) ◽  
pp. 717-724 ◽  
Author(s):  
Juan C. Alonso ◽  
Iván Salgado ◽  
Carlos Palacín
Keyword(s):  
Thermal Tolerance ◽  
Sexual Segregation ◽  
Sexually Dimorphic ◽  
Hot Environments ◽  
Dimorphic Species

Sexual segregation in habitat use is smaller than expected in a highly dimorphic marine predator, the southern sea lion

2016 ◽  
Vol 554 ◽  
pp. 201-211 ◽  
Author(s):  
AMM Baylis ◽  
RA Orben ◽  
DP Costa ◽  
JPY Arnould ◽  
IJ Staniland
Keyword(s):  
Habitat Use ◽  
Sexual Segregation ◽  
Sea Lion ◽  
Marine Predator

scholarly journals Size dimorphism and sexual segregation in pheasants: tests of three competing hypotheses

PeerJ ◽  
2018 ◽  
Vol 6 ◽  
pp. e5674 ◽  
Author(s):  
Mark A. Whiteside ◽  
Jayden O. van Horik ◽  
Ellis J.G. Langley ◽  
Christine E. Beardsworth ◽  
Joah R. Madden
Keyword(s):  
Predation Risk ◽  
Activity Budget ◽  
Sexual Segregation ◽  
Sexually Dimorphic ◽  
Fine Scale ◽  
Size Dimorphism ◽  
Selection Hypothesis ◽  
Wide Range ◽  
In The Wild ◽  
Species Specific

Fine scale sexual segregation outside of the mating season is common in sexually dimorphic and polygamous species, particularly in ungulates. A number of hypotheses predict sexual segregation but these are often contradictory with no agreement as to a common cause, perhaps because they are species specific. We explicitly tested three of these hypotheses which are commonly linked by a dependence on sexual dimorphism for animals which exhibit fine-scale sexual segregation; the Predation Risk Hypothesis, the Forage Selection Hypothesis, and the Activity Budget Hypothesis, in a single system the pheasant, Phasianus colchicus; a large, sedentary bird that is predominantly terrestrial and therefore analogous to ungulates rather than many avian species which sexually segregate. Over four years we reared 2,400 individually tagged pheasants from one day old and after a period of 8–10 weeks we released them into the wild. We then followed the birds for 7 months, during the period that they sexually segregate, determined their fate and collected behavioural and morphological measures pertinent to the hypotheses. Pheasants are sexually dimorphic during the entire period that they sexually segregate in the wild; males are larger than females in both body size and gut measurements. However, this did not influence predation risk and predation rates (as predicted by the Predation Risk Hypothesis), diet choice (as predicted by the Forage Selection Hypothesis), or the amount of time spent foraging, resting or walking (as predicted by the Activity Budget Hypothesis). We conclude that adult sexual size dimorphism is not responsible for sexual segregation in the pheasant in the wild. Instead, we consider that segregation may be mediated by other, perhaps social, factors. We highlight the importance of studies on a wide range of taxa to help further the knowledge of sexual segregation.

Evolution of sexual segregation in mammalian herbivores: kangaroos as marsupial models

2006 ◽  
Vol 54 (3) ◽  
pp. 217 ◽  
Author(s):  
G. Coulson ◽  
A. M. MacFarlane ◽  
S. E. Parsons ◽  
J. Cutter
Keyword(s):  
Sexual Segregation ◽  
Sexually Dimorphic ◽  
Adult Males ◽  
Single Sex ◽  
Two Factors ◽  
Body Sizes ◽  
Preliminary Study ◽  
Western Victoria ◽  
Initial Results ◽  
North Western

Sexual segregation is best known in sexually dimorphic ungulates. Many hypotheses have been proposed to explain the evolution of sexual segregation in ungulates, but all are reducible to the influence of two factors: body size and sex-specific reproductive strategy. Definitive tests of these hypotheses are lacking in ungulates because these factors are confounded, all males being somewhat larger than females. Kangaroos represent a parallel radiation of terrestrial herbivores, but their populations are composed of a spectrum of adult body sizes, ranging from small males the same size as females to large males more than twice the size. We exploited this heteromorphism to assess the independent influences of size and sex in these ungulate analogues. We conducted a preliminary study of western grey kangaroos (Macropus fuliginosus) in north-western Victoria, Australia. Adult males predominately occupied grassland habitat, whereas females occurred mostly in lakebed, woodland and shrubland. Single-sex groups occurred more often than expected during the non-mating season. The diet of large males had the highest proportion of grass, and females had the least. These initial results indicate that both size and sex influence segregation in this species, confirming the worth of kangaroos as marsupial models for research into the evolution of sexual segregation.

reproductive biology of centrophorus cf. uyato from the cayman trench, jamaica

2005 ◽  
Vol 85 (5) ◽  
pp. 1185-1192 ◽  
Author(s):  
donna m. mclaughlin ◽  
john f. morrissey
Keyword(s):  
Reproductive Biology ◽  
Breeding Season ◽  
Mature Female ◽  
Sexual Segregation ◽  
Mature Male ◽  
Sexually Dimorphic ◽  
Total Length ◽  
Over Exploitation

the taxonomy of the genus centrophorus (squaliformes: squalidae) is currently in a great deal of uncertainty. the characteristics of the species subject to the present study most closely resemble those of centrophorus uyato, hence the use of centrophorus cf. uyato, though the species in question may be a species of centrophorus that has not been described previously. specimens were obtained via vertical and horizontal longline at depths of 250–913 m. the reproductive biology of 51 female and 8 male centrophorus cf. uyato were examined. this species is sexually dimorphic, with females attaining a larger size than males. the smallest mature male was 81.2 cm total length whereas the smallest mature female was 91.5 cm total length. females are aplacentally viviparous, with the pups acquiring nutrition via large external yolk sacs, and there was a maximum of two pups per litter. oocytes continued to develop throughout gestation. most females carrying developing embryos had two large (>3.3 cm), equally developed ovarian oocytes, which leads us to believe that they ovulate soon after parturition. this species seems to exhibit complete sexual segregation during the non-breeding season, with mature males absent from the study site during summer months. centrophorus cf. uyato may have one of the lowest fecundities among sharks, giving birth to a maximum of two pups every three years. all species in genus centrophorus have small litters (<6) making them vulnerable to over-exploitation.

Androgen-induced plasticity at a “vocal” neuromuscular synapse

1994 ◽  
Vol 52 ◽  
pp. 32-33
Author(s):  
Darcy B. Kelley ◽  
Martha L. Tobias ◽  
Mark Ellisman
Keyword(s):  
Xenopus Laevis ◽  
Motor Neurons ◽  
Sexual Differentiation ◽  
Molecular Basis ◽  
Neuromuscular Synapse ◽  
Sexually Dimorphic ◽  
Intracellular Protein ◽  
Developmental Program ◽  
Androgen Action ◽  
Clawed Frog

Brain and muscle are sexually differentiated tissues in which masculinization is controlled by the secretion of androgens from the testes. Sensitivity to androgen is conferred by the expression of an intracellular protein, the androgen receptor. A central problem of sexual differentiation is thus to understand the cellular and molecular basis of androgen action. We do not understand how hormone occupancy of a receptor translates into an alteration in the developmental program of the target cell. Our studies on sexual differentiation of brain and muscle in Xenopus laevis are designed to explore the molecular basis of androgen induced sexual differentiation by examining how this hormone controls the masculinization of brain and muscle targets.Our approach to this problem has focused on a highly androgen sensitive, sexually dimorphic neuromuscular system: laryngeal muscles and motor neurons of the clawed frog, Xenopus laevis. We have been studying sex differences at a synapse, the laryngeal neuromuscular junction, which mediates sexually dimorphic vocal behavior in Xenopus laevis frogs.

The Relationship of Digit Ratio (2D:4D) and Gender-Role Orientation in Four National Samples

2007 ◽  
Vol 28 (2) ◽  
pp. 78-87 ◽  
Author(s):  
Stefan J. Troche ◽  
Nina Weber ◽  
Karina Hennigs ◽  
Carl-René Andresen ◽  
Thomas H. Rammsayer
Keyword(s):  
Gender Role ◽  
Sex Role ◽  
Role Orientation ◽  
Sexually Dimorphic ◽  
Gender Role Orientation ◽  
Left Hand ◽  
Fourth Finger ◽  
And Gender ◽  
Relationship Of ◽  
The Relationship

Abstract. The ratio of second to fourth finger length (2D:4D ratio) is sexually dimorphic with women having higher 2D:4D ratio than men. Recent studies on the relationship between 2D:4D ratio and gender-role orientation yielded rather inconsistent results. The present study examines the moderating influence of nationality on the relationship between 2D:4D ratio and gender-role orientation, as assessed with the Bem Sex-Role Inventory, as a possible explanation for these inconsistencies. Participants were 176 female and 171 male university students from Germany, Italy, Spain, and Sweden ranging in age from 19 to 32 years. Left-hand 2D:4D ratio was significantly lower in men than in women across all nationalities. Right-hand 2D:4D ratio differed only between Swedish males and females indicating that nationality might effectively moderate the sexual dimorphism of 2D:4D ratio. In none of the examined nationalities was a reliable relationship between 2D:4D ratio and gender-role orientation obtained. Thus, the assumption of nationality-related between-population differences does not seem to account for the inconsistent results on the relationship between 2D:4D ratio and gender-role orientation.

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