Bateman-Trivers in the 21st Century: sexual selection in a North American pitviper

Abstract

Assessment of sexual selection in organisms with cryptic life histories is challenging, although accurate parentage assignments using genotypic markers, combined with behavioural observations and a method to account for open population bias, allow for robust estimation of metrics. In the present study, we employed 22 tetranucleotide microsatellite DNA loci to interpret mating and reproductive success in a population of Copperhead (Viperidae, Agkistrodon contortrix) in Connecticut, USA. We sampled DNA from 114 adults (56 males, 58 females) and 137 neonates from known mothers to quantify Bateman gradients (βss), as well as sex-specific opportunities for selection (I) and sexual selection (Is). We also estimated selection on male size [snout-to-vent length (SVL)], a trait important for successful combat and subsequent copulations. Estimates of male I and Is differed significantly from those of females when estimated with four different methods and only males had a significant Bateman gradient. As predicted, male reproductive success was positively correlated with increasing SVL. These results contrast with those derived in another study investigating the same population but based solely on observational data and without correction for open population bias. We thus argue that molecular approaches to quantifying reproductive success and strength of sexual selection provide more accurate results than do behavioural observations alone.

Male mating success in a North American pitviper: influence of body size, testosterone, and spatial metrics

“…Our research group (Levine et al . , ) conducted a parallel study on male fitness in A. contortrix from the population discussed herein, but analyzed mating success per Arnold & Duvall () using 22 microsatellite markers to assign the parentage of fathers (all mothers were known) and the methods outlined in Mobley & Jones () for open populations. Unlike the results of this study, Levine et al .…”

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

“…The effect of SVL on AMS and ARS for males and females was present regardless of the data set analyzed (i.e., complete vs. SVLfiltered). Larger SVLs have previously been shown in male snakes to correlate with greater AMS (Shine et al, 2000) and ARS (Levine et al, 2015) due to larger males having a competitive advantage over smaller males for gaining priority-of-access to females (Duvall & Schuett, 1997;Madsen & Shine, 1993. While male-male combat for priority-of-access to females has not been observed in wild BTS, it has been observed in captivity .…”

“…We predicted an influence of SVL on AMS and ARS because SVL is a trait correlated with AMS (Shine et al, ) and ARS in other snakes (Levine et al, ). Male snakes with larger SVLs have a competitive advantage over smaller males in combat for gaining priority‐of‐access to females (Duvall & Schuett, ; Madsen & Shine, , ), and such “combat dances” have been observed among male BTS in a laboratory setting (Greene & Mason, ).…”

Putative Pair-Bonding inAgkistrodon contortrix(Copperhead)

“…Females in this population were highly dispersed during the mating season (Smith et al 2009), and multiple paternity has been documented, with evidence of more than1 sire found in 45% of litters tested (Levine et al 2015). As a result, smaller males may realize greater reproductive success by forming short-term pair-bonds with unaccompanied females once located rather than by searching for additional females for which they may have to directly compete with larger males (Schuett 1997).…”

“…1 C.F. Smith and G.W Schuett siring more offspring (Levine et al 2015). Therefore, smaller males are not as likely to sire offspring under conditions where they must compete with larger males for access to females.…”