Sexual-Size Dimorphism: Influence of Mass and Mating Systems in the Most Dimorphic Mammals

Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. American Society of Mammalogists is collaborating with JSTOR to digitize, preserve and extend access to Journal of Mammalogy. I examined influence of body size and mating systems on sexual-size dimorphism by summarizing characteristics and testing for associations among the most dimorphic mammalian taxa-Macropodidae, Primates, Mustelidae, Pinnipedia, Elephantidae, Ruminantia. The most dimorphic taxa were seals in Otariidae. On average, males were three times larger than females, and all otariids displayed extensive dimorphism. Except for the Strepsirhini, most taxa had dimorphism ratios (mass of males:mass of females) between 1.2-1.8. Extent of dimorphism increased with body size but the effect was slight (power function between masses of males and females, 1.04-1.05) for most taxa. Phocid seals and macropodid marsupials had power functions of ca. 1.2. Mating systems were associated with size dimorphism in simian primates and ruminants. Monogamous simian primates were less dimorphic than simians that had polygynous mating systems. Ruminants with tending and harem mating systems were more dimorphic than those with territorial polygynous and monogamous mating systems. Polygyny and how it was conducted were associated with the extent of sexual size dimorphism. Most evolutionary biologists agree thatsexual selection is the source of sexual-size dimorphism in polygynous mammals (Charnov, 1992; Darwin, 1871; Ralls, 1977; Reiss, 1989). Whether males are the smaller sex, as in Hawaiian monk seals (Monachus schauinslandi), or the more common pattern of males larger than females (Ralls, 1977), hypotheses founded in sexual competition explain much about existing patterns of dimorphism (Alexander et al., 1979; Clutton-Brock et al.

Mating system, feeding type andex situconservation effort determine life expectancy in captive ruminants

“…In free-living mammal populations, the degree of male-biased adult mortality correlates positively to the degree of sexual size dimorphism [27]. Sex differences in adult longevity are more pronounced in polygynous (degree of sexual dimorphism correlates with degree of polygyny [28]) when compared with monogamous species [29]. Two results of our analysis support the theory that sexual dimorphism and mating system explain the pattern of sexual bias in adult LE of ungulates: (i) rLE in captive males of ruminant species with lower male reproductive investment (monogamous species) was higher compared to species with higher investment (polygynous species), and (ii) the difference between the rLE of females and males of monogamous species was significantly smaller than the difference between female and male rLE in polygynous species.…”

A phylogenetic approach to the study of sexual size dimorphism in Felidae and an assessment of Rensch´s rule.

“…En el caso de los félidos, nuestros resultados mostraron índices de dimorfismo sexual relativamente altos si se los compara con los de otros grupos de carní-voros como la familia Canidae. En estos últimos, los valores de SSD para masa corporal muestran una 1.17 (Bidau y Martínez, datos no publicados) en tanto que en los félidos de nuestra muestra, la media es de 1.41 lo que es comparable con otros grupos de mamíferos altamente dimórficos y poligínicos en donde el SSD varía principalmente entre 1.20 y 1.80 (Weckerly 1998). Una posible explicación de esta diferencia puede ser el hecho de que todos los cá-nidos son esencialmente monógamos (Kleiman 1977;Wittenberger y Tislon 1980) mientras que todos los félidos son poligínicos mostrando poliginia social o estrategia multi-macho (Isvaran y CluttonBrock 2007).…”

“…Otra familia de Carnivora que incluye numerosas especies y variados sistemas de apareamiento es Mustelidae. El grado de dimorfismo sexual es alto con una media= 1.31 aunque con gran variación interespecífica (CV= 22.61 para 23 especies) (Weckerly 1998). Sin embargo es importante notar que si bien existe una correlación significativa entre SSD y masa corporal de machos, la misma es negativa, es decir que se invierte la regla de Rensch (Moors 1980;Weckerly 1998).…”

“…Si bien es importante en una primera aproximación, el verificar la existencia de SSD en un grupo y describir su dirección y magnitud, lo esencial es detectar aquellos factores que pueden estar determinándolo y afectándolo (características ecológicas, geográficas y de historia vital) así como establecer de que forma el grado de SSD puede a su vez influir sobre características de los organismos. (Moors 1980;Leutenegger y Cheverud 1982;Weckerly 1998;Isaac 2005;Blanckenhorn et al 2006).…”

A model of sexual selection and female use of refuge in a coercive mating system

“…The proportion of females in patches 1 and 2 is represented by f 1 and f 2 , respectively, and the total number of females is given by N f . Patch 2 can be thought of as a refuge for females, where males are excluded because of high risk [20] or an inability to access this site owing to a larger size [21,22]. Figure 1 shows the distribution of males and females in each patch and the movement between patches.…”