Sexual variation in assimilation efficiency: its link to phenotype and potential role in sexual dimorphism

Abstract

Sex-specific variation in morphology (sexual dimorphism) is a prevalent phenomenon among animals, and both dietary intake and resource allocation strategies influence sexually dimorphic traits (e.g., body size or composition). However, we investigated whether assimilation efficiency (AE), an intermediate step between dietary intake and allocation, can also vary between the sexes. Specifically, we tested whether sex-based differences in AE can explain variation in phenotypic traits. We measured morphometric characteristics (i.e., body length, mass, condition, and musculature) and AE of total energy, crude protein, and crude fat in post-reproductive adult Children's pythons (which exhibit a limited female-biased sexual size dimorphism) fed both low and high dietary intakes. Meal size was negatively related to AE of energy. Notably, male snakes absorbed crude protein more efficiently and increased epaxial (dorsal) musculature faster than females, which demonstrates a link between AE and phenotype. However, females grew in body length faster but did not absorb any nutrient more efficiently than males. Although our results do not provide a direct link between AE and sexual size dimorphism, they demonstrate that sexual variation in nutrient absorption exists and can contribute to other types of sex-based differences in phenotype (i.e., sexual dimorphism in growth of musculature). Hence, testing the broader applicability of AE's role in sexually dimorphic traits among other species is warranted.

Sex-specific nutrient use and preferential allocation of resources to a sexually selected trait in Hyalella amphipods

“…Regardless, the patterns of assimilation that we observed clearly indicate that assimilatory responses to P availability are dependent upon the age and sex of an organism. Together, these results point to the potentially important role of physiological processes in driving the allocation of resources to traits (Olijnyk and Nelson, 2013;Stahlschmidt et al, 2011), which is generally thought to be controlled by acquisition (Robinson and Beckerman, 2013).…”

“…The pattern observed in late-stage juvenile males may be due to the interaction between acquisition and assimilation. In particular, the increased acquisition observed under LP may induce a decrease in assimilation, resulting from a decrease in gut passage time caused by constant feeding (Navarro and Winter, 1982;Stahlschmidt et al, 2011). Given that juveniles have a shorter gut length than adults, it is possible that increases in acquisition may influence juvenile assimilation to a different degree from that in adults.…”

Morphological and Physiological Changes during Reproduction and Their Relationships to Reproductive Performance in a Capital Breeder

“…On one hand, pythons are long-lived and can reproduce annually (Madsen and Shine 1999), suggesting relatively limited effects of each reproductive event. On the other hand, pythons are capital breeders that heavily allocate their body reserves into the production of large clutches (one-third or more of maternal body mass) and care to the eggs (brooding), and more than one-quarter of their adult life can be spent in an aphagic reproductive state (reviewed in Stahlschmidt and DeNardo 2011). Such traits could result in considerable physiological costs.…”

Neither male gonadal androgens nor female reproductive costs drive development of sexual size dimorphism in lizards

“…West et al, 2001). The degree of SSD, then, should largely reflect sexual differences in energy acquisition [or potentially also energy assimilation (Stahlschmidt et al, 2011)] or energy allocation to reproduction (e.g. Cox, 2006).…”