Variance in offspring sex ratio and maternal allocation in a highly invasive mammal

This study was conducted at the Savannah River Site (SRS), a 78,000 ha U.S. Department of Energy facility located in Aiken, Barnwell, and Allendale counties, South Carolina, USA. We sampled from live-trapped (and consequently released for other studies, e.g., neonate survival [Chinn et al. 2021]) and humanely-euthanized according to established protocols (A2015 12-017) wild pigs throughout the year between March 2017 and July 2019. We collected fetal data, tissue for genetic analysis, and morphological measurements from females >27 kg to quantify litter and maternal attributes (n = 160). We weighed and measured each female dorsally from snout to base of tail. We calculated a standardized body condition index (subsequently referred to as maternal condition) for each individual as mass/length (LaBocha et al., 2014). We measured extraneous fat reserves, a quantitative measurement of maternal nutritional condition, from culled females and used it as a proxy for local resource availability. We assessed age by tooth eruption and replacement patterns (Matschke, 1967; Mayer, 2002), and individuals were classified into 3 age classes: juvenile (between 6 months and 1 year), yearling (1-1.5 years), and adults (≥ 1.5 years old). If present, fetuses were removed, weighed and measured in a straight-line from crown to rump (CRL). Fetuses ≥36 days old were sufficiently developed to visually determine sex. We quantified the ancestry of wild pigs following methods described in Smyser et al. (2020). We centered and z-transformed continuous variables to a mean of 0 and a standard deviation of 1 to allow for standardized comparison for all analyses. We censored individuals from analyses if they did not have all variables measured (i.e., removed a female from analysis if she was missing rump fat data).