Male Snakes Allocate Time and Energy according to Individual Energetic Status: Body Condition, Steroid Hormones, and Reproductive Behavior in Timber Rattlesnakes,Crotalus horridus

Abstract

Life-history theory predicts that organisms will hedge current reproductive investment against potential costs in terms of survivorship and future fecundity. However, little is known regarding the endocrine mechanisms underlying bet-hedging strategies in free-ranging male vertebrates. We examined the relationships among individual energetic status, steroid hormones, mate search, and reproductive behavior in free-ranging male timber rattlesnakes. Snakes were monitored over four active seasons in order to test two hypotheses: (1) males adjust the amount of time and energy allocated toward reproduction according to the level of individual energy stores, and (2) observed condition-dependent reproductive allocation is associated with circulating concentrations of steroid hormones (testosterone and corticosterone) thought to regulate reproductive behaviors in vertebrates. A positive relationship between body condition and testosterone was observed in both the field and the laboratory. Male mate search effort was positively correlated with both body condition and testosterone. Body condition and testosterone concentrations were negatively related to time allocated toward foraging during the breeding season. A strong effect of year was observed in the analysis of testosterone and search effort, suggesting that multiple environmental factors impact hormone production and reproductive investment. Corticosterone was not related to any measured variable. Therefore, our results did not indicate a clear role of corticosterone in mediating observed relationships between energetic status and behavior. Observed relationships are consistent with the hypothesis that males allocate time and energy toward reproduction according to individual energetic status and that testosterone plays a role in mediating the trade-off between current reproductive investment and residual reproductive value.

Stress Ecology of the Pacific Rattlesnakes (Crotalus Oreganus and Crotalus Helleri)

“…Contrasting relationships between CORT and testosterone are also observed in different populations of the garter snake Thamnophis sirtalis (Moore, Lemaster & Mason 2000;Moore et al 2000). We found no relationship between testosterone and treatment or CORT levels, which is supported by many other studies on rattlesnakes (Taylor, DeNardo & Jennings 2004;Lind et al 2010;Holding et al 2014a;Lind & Beaupre 2015) and other reptiles (Cree, Amey & Whittier 2000;. Our study was conducted shortly after the active breeding season for C. oreganus (Lind et al 2010), which is likely similar for northern populations of C. helleri.…”

“…Baseline CORT was negatively correlated with testosterone in male Timber Rattlesnakes (Crotalus horridus) (Lutterschmidt et al 2009), but acute stressed CORT led to increased testosterone. In a different population of the same species, no relationship between CORT and testosterone was observed (Lind & Beaupre 2015). Contrasting relationships between CORT and testosterone are also observed in different populations of the garter snake Thamnophis sirtalis (Moore, Lemaster & Mason 2000;Moore et al 2000).…”

Genomic pedigree reconstruction identifies predictors of mating and reproductive success in an invasive vertebrate

“…For example, larger male BTS gain access to females by being successful in confrontations with smaller males (Greene & Mason, ). Sufficient energy reserves also permit mate searching by males (Lind & Beaupré, ) and allow more time for mate searching in that competing activities such as foraging are less mandatory (Beaupré, ). Although the energetic status of male snakes often influences their ability to mate [e.g., Red‐Sided Garter Snake (Shine & Mason, ), Timber Rattlesnake (Lind & Beaupré, )], the relationship between BCI and male reproductive success remains somewhat nebulous (Shine & Mason, ).…”

“…Differently, females with larger SVLs may appear more attractive to males (Blouin-Demers, Gibbs, & Weatherhead, 2005), resulting in greater AMS, and their larger body cavities may correlate with an increased capacity to produce eggs (Blouin-Demers et al, 2005;Brown & Shine, 2007). We expected body condition to be influential for AMS and ARS in that underweight individuals in either sex may lack sufficient energy reserves to search for mates (Lind & Beaupré, 2015), engage in mating and mating-related activities [e.g., male combat (Shine et al, 2000)], and/or produce offspring (Aubret, Bonnet, Shine, & Lourdais, 2002).…”

To forage, mate, or thermoregulate: Influence of resource manipulation on male rattlesnake behavior

“…Condition‐dependent reproductive investment is believed to be a trade‐off between current and future reproductive success. For example, Lind and Beaupre () studied male timber rattlesnakes ( Crotalus horridus ) across four active seasons and found individuals with higher energy stores invested greater effort into mate searching, whereas those with lower body condition spent more time foraging during the breeding season. Continuing studies such as ours over multiple active seasons should reveal more apparent effects on life history, as was documented for food‐supplemented female rattlesnakes that had an overall much higher incidence of reproduction than unfed females (Taylor et al., ).…”