Lifetime selection on a hypoallometric size trait in the spotted hyena

Abstract

Size-related traits are common targets of natural selection, yet there is a relative paucity of data on selection among mammals, particularly from studies measuring lifetime reproductive success (LRS). We present the first phenotypic selection analysis using LRS on size-related traits in a large terrestrial carnivore, the spotted hyena, which displays a rare pattern of female-biased sexual size dimorphism (SSD). Using path analysis, we investigate the operation of selection to address hypotheses proposed to explain SSD in spotted hyenas. Ideal size measures are elusive, and allometric variation often obfuscates interpretation of size proxies. We adopt a novel approach integrating two common methods of assessing size, and demonstrate lifetime selection on sizerelated traits that scale hypoallometrically with overall body size. Our data support selection on hypoallometric traits in hyenas, but not on traits exhibiting isometric or hyperallometric scaling relationships, or on commonly used measures of overall body size. Our results represent the first estimate of lifetime selection on a large carnivore, and suggest a possible route for maintenance of female-biased SSD in spotted hyenas. Finally, our results highlight the importance of choosing appropriate measures when estimating animal body size, and suggest caution in interpreting selection on size-related traits as selection on size itself.

Society, demography and genetic structure in the spotted hyena

“…(1996); Hofer & East (1993c, 1996, 2003); Watts et al. ( 2009) ; Swanson et al. (2011); (4) Holekamp et al.…”

“…the upper 95% CI = 0.0006 < 0.976). Presumably the degree of skew observed among Talek females is due largely to variation in lifespan among the adult females (also see Swanson et al. 2011).…”

Ejaculate quality in spotted hyenas: intraspecific variation in relation to life-history traits

“…We used absolute testes size, rather than relative testes size, because body mass in spotted hyenas can fluctuate greatly over short periods of time and thus does not necessarily reflect overall body size accurately (Swanson et al 2011). To test for relationships between ejaculate quality and age, tenure, and social rank, we used similar linear models, after square-root transforming social rank and tenure.…”

Brains, brawn and sociality: a hyaena's tale

“…2). Life span is a major determinant of fitness in this species (Swanson, Dworkin, & Holekamp, 2011), and highly gregarious females have longer life spans than others (Shaw, 2012). We also found significant positive relationships between sociability and reproductive success in low-ranking, but not high-ranking, female hyaenas (see Supplementary Material), suggesting that hyaenas, like monkeys, can use social strategies to offset costs of low rank.…”