Sexual size dimorphism in bighorn sheep (<i>Ovis canadensis</i>): effects of population density

In species with sexual size dimorphism, the offspring of the larger sex usually have greater energy requirements and may lead to greater fitness costs for parents. The effects of offspring sex on maternal longevity, however, have only been tested in humans. Human studies produced mixed results and considerable debate mainly owing to the difficulty of distinguishing the effects of sexual dimorphism from sociocultural factors. To advance this debate, we examined how the relative number of sons influenced maternal longevity in four species of free-living ungulates (Soay sheep Ovis aries ; bighorn sheep, Ovis canadensis ; red deer, Cervus elaphus ; mountain goat, Oreamnos americanus ), with high male-biased sexual size dimorphism but without complicating sociocultural variables. We found no evidence for a higher cumulative cost of sons than of daughters on maternal longevity. For a given number of offspring, most females with many sons in all four populations lived longer than females with few sons. The higher cost of sons over daughters on maternal lifespan reported by some human studies may be the exception rather than the rule in long-lived iteroparous species.

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Sexual size dimorphism in bighorn sheep (Ovis canadensis): effects of population density

Canadian Journal of Zoology ◽

10.1139/z01-128 ◽

2001 ◽

Vol 79 (9) ◽

pp. 1661-1670 ◽

Cited By ~ 31

Author(s):

Mylène LeBlanc ◽

Marco Festa-Bianchet ◽

Jon T Jorgenson

Keyword(s):

Population Density ◽

Body Mass ◽

Phenotypic Expression ◽

Mass Gain ◽

Bighorn Sheep ◽

Ovis Canadensis ◽

The Body ◽

Young Males ◽

Negative Effect ◽

Female Body Mass

Sexual dimorphism is an important characteristic of many mammals, but little is known about how environmental variables may affect its phenotypic expression. The relationships between population size, body mass, seasonal mass changes, and sexual mass dimorphism were investigated using 22 years of data on individually marked bighorn sheep (Ovis canadensis) on Ram Mountain, Alberta. The number of adult ewes was artificially maintained low from 1972 to 1981 and then allowed to increase. The body mass of males from 0 to 7 years of age was negatively affected by population density. Female body mass was negatively affected by population density up to 2 years of age. As the number of ewes increased, sexual mass dimorphism of sheep aged 27 years declined. Population density had a negative effect on seasonal mass changes of young males and females. Density also had a weak but significant positive effect on yearly mass gain of 2-year-old females, suggesting compensatory growth. Females appear to compensate for resource shortages early in life, while males show a lifelong negative effect. We suggest that these sexual differences are due to the greater flexibility of resource allocation to growth or reproduction by females than by males.

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Maternal Inheritance and Rapid Evolution of Sexual Size Dimorphism: Passive Effects or Active Strategies?

The American Naturalist ◽

10.2307/3473064 ◽

2005 ◽

Vol 166 (4) ◽

pp. S17 ◽

Cited By ~ 1

Author(s):

Badyaev

Keyword(s):

Sexual Size Dimorphism ◽

Maternal Inheritance ◽

Rapid Evolution ◽

Size Dimorphism

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Geographic Variation in Body Size and Sexual Size Dimorphism of a Seed-Feeding Beetle

The American Naturalist ◽

10.2307/4541100 ◽

2007 ◽

Vol 170 (3) ◽

pp. 358

Author(s):

Stillwell ◽

Morse ◽

Fox

Keyword(s):

Body Size ◽

Geographic Variation ◽

Sexual Size Dimorphism ◽

Size Dimorphism

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Morphology and diet of two sympatric colubrid snakes, Chironius flavolineatus and Chironius quadricarinatus (Serpentes: Colubridae)

Amphibia-Reptilia ◽

10.1163/156853808784125027 ◽

2008 ◽

Vol 29 (2) ◽

pp. 149-160 ◽

Cited By ~ 15

Author(s):

Otavio Augusto Vuolo Marques ◽

Ronaldo Fernandes ◽

Roberta Richard Pinto

Keyword(s):

Foraging Behaviour ◽

Sexual Size Dimorphism ◽

Sympatric Species ◽

Colour Pattern ◽

Ontogenetic Variation ◽

Brazilian Cerrado ◽

Size Dimorphism ◽

Snake Species ◽

Dietary Ecology ◽

Arboreal Habit

Abstract The morphometry and diet of two sympatric species of Chironius (C. flavolineatus and C. quadricarinatus) from Brazilian Cerrado are described. The two snake species differ in external morphology, as Chironius flavolineatus was the largest species (body, tail and eyes) whereas C. quadricarinatus the heaviest. Each species also showed marked sexual size dimorphism. In terms of dietary ecology, both species feed exclusively on frogs with a heavy preference for hylids and may have tendency to eat small items, as noticed in other colubrine species. These two snake species showed a brownish colour pattern and exhibited no ontogenetic variation, suggesting that juveniles and adults use similar substrates. Chironius flavolineatus and C. quadricarinatus present a semi-arboreal habit, with active foraging behaviour, feeding in the ground most of time. Chironius flavolineatus uses higher vegetation for resting and, based on morphological results, seems to be more arboreal than C. quadricarinatus.

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Latitudinal clines in sexual selection, sexual size dimorphism, and sex‐specific genetic dispersal during a poleward range expansion

Journal of Animal Ecology ◽

10.1111/1365-2656.13488 ◽

2021 ◽

Author(s):

Rachael Y. Dudaniec ◽

Alexander R. Carey ◽

Erik I. Svensson ◽

Bengt Hansson ◽

Chuan Ji Yong ◽

...

Keyword(s):

Sexual Selection ◽

Range Expansion ◽

Sexual Size Dimorphism ◽

Size Dimorphism ◽

Latitudinal Clines

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A uni- and multivariate analysis approach to reveal sexual size dimorphism in Iranian populations of Hypera postica (Coleoptera: Curculionidae)

Biologia ◽

10.1515/biolog-2015-0137 ◽

2015 ◽

Vol 70 (9) ◽

pp. 1228-1233 ◽

Cited By ~ 3

Author(s):

Ehsan Sanaei ◽

Marjan Seiedy ◽

Farzaneh Momtazi

Keyword(s):

Body Size ◽

Sexual Size Dimorphism ◽

Egg Laying ◽

Morphological Divergence ◽

High Fecundity ◽

Hypera Postica ◽

Size Dimorphism ◽

Female Body Size ◽

Divergence Pattern ◽

Iranian Populations

Abstract Body size dimorphism between genders is a commonly observed phenomenon in insects, usually manifested in larger female body size. Sexual Size Dimorphism (SSD) varies from species to species, the degree and direction influenced by certain evolutionary pressures. Intraspecific variation in SSD may also occur between populations. The Hypera postica (Gyllenhal, 1813) is a well-known alfalfa plant pest that shows a degree of morphological divergence in its populations. The female alfalfa weevils are very fecund and have a larger body size compared to males. To improve our knowledge on magnitude and direction of SSD in alfalfa weevil, we studied 200 specimens of H. postica from four Iranian populations (Karaj1, Karaj2, Tuyserkan and Jovein). 10 morphological variables from three external anatomic parts (pronotum, elytra and rostrum) and 45 ratio characters were statistically analyzed in order to determine the amount of SSD in Iranian populations. In addition we investigated for morphological divergence pattern in mentioned populations. The results of this study show that a low degree of morphological divergence occurs in Iranian populations. Measured variables indicate that the SSD pattern of H. postica is compatible with the Rensch’s rule, and is related to high fecundity of females and a lack of strong sexual selection. Also it is mentioned that the larger rostrum in females may correspond to its unique role in egg laying.

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